Chuck Glider's Model Aircraft Jotter

Kids Gliders

2011-08-07T16:15:00.000-07:00

My kids needed to build gliders for a school design project. Basically, it was indoor, longest glide. So, we quickly hashed a couple up and my son glued up his first ever built up wing. After the project, we later repurposed the bigger glider for towing, and we all enjoyed launching it (see above).

Here are the gliders. The larger is 24" span and the smaller is 15" (5 panels of 1/16"x3"x3"). It had a 1/8" balsa pod and a bamboo skewer boom. As you can probably guess, the larger one is inspired by John Barker's Lulu classic but with a balsa pod and carbon tube boom.

The uncovered wing came out at 6.3g, which is not bad!

Details of the wing brace. Central spar is 1/16" hard balsa and the brace is a hard wood veneer.

The "plan" was simply 2cm sq paper. He did a great job of gluing it all up. We used evo stick waterproof glue. Alas, the smaller glider was broken in class - but at least that was after it had won its competition! The larger one was not launched correctly by the teaching assistant so was unable to display its performance. Next, we'll try it on a bungee!

Footy Sailboat Model Yacht Build Log: Part 1

2010-10-17T15:00:00.000-07:00

I'm off on a slight excursion into model yachts. They have a lot in common with gliders, at least, they have a wing above the water and another one below it! So here's my first ever effort at an RC model boat. I've chosen a Footy class model, as they're so cute. Well, Chuck's following a plan you say? Er, not quite. I'm following a few plans and no plan! Hull is based on Mario Stiller's Papaya III (his beautifully drawn plans are available on the Footy class website).
Template placed on to 3mm Depron foam.
Cutting Depron is so easy. In fact, it's so easy, that it's easy to make a mistake!
Pinning up the bulkhead. I'm using wider side pieces, and also decided to widen the transom edges. The reason for this is not really strength, but waterproofing. Larger glue areas must be more waterproof.
All the hull parts ready for assembly. That foam strip is not part of the hull, but just a test piece for paint - this one (Japlac) did not dissolve the foam.

Sides joined to transom, bulkhead and stem piece. I'm using UHU Por, becaause I love the stuff. And the tea!

At this stage, it weighs a mere 7.5g.

Now the bottom of the hull, trimmed and sanded smooth. Much quicker to assemble than a plane, methinks.

Close up of the stem piece. This will have a nose piece glued on it later.
Side view of the hull.
Dry fitting the roughly carved nose piece. This will be added at the end and carved to shape and size.
View from the transom (stern end).
Another view of the hull.
Plan view of the hull.

Close up of the bulkhead. The keel will fit on to this.

Front view.

Rudder taking shape. I glued an aluminium tube on to a 5mm balsa piece. Glued that onto the transom. The carbon fibre rod is glued to the balsa rudder (1/16" hard). Two teflon washers at each end of the bearing. Used epoxy for all these ruddery bits.

Next, some painting, keel making, rudder pushrod, mast tubes, sheeting, decking and sails!

Multiplex EasyStar Review: Part 3, New Battery, windy day

2010-09-10T14:39:00.000-07:00

I charged up one of these:

It's an NiMH battery pack, bought from Vapextech via eBay (a nice price and speedy delivery, by the way). The pack has 8 cells of 2/3A size, 9.6V, 1500mAh, ~210g and most importantly, just the right size to fit in the cockpit. EasyStar's weight has now gone up to 600g, and CoG is where it says in the manual, or perhaps a mm forward of that. (Just as a reminder, the old NiMH pack was 7xAAA cells, 8.4V, 800mAh, ~100g. AUW was 525g and she needed ballast).

So, today, the wind was 15mph, gusting to 25mph. But I didn't let a little thing like that put me off! Went flying... half expecting to return with a broken plane...

Well, what a difference the new battery made. Despite the 75g weight increase, she has a frightening amout of power. I daren't push the throttle stick all the way open... Great fun in the wind, but I was careful to quit while ahead. There was a bit of nose bruising from a low level stall on the first launch - because the trim setting was wrong for the first flight with the new battery - but nothing serious. Thereafter, the wind itself was not the main problem because she could motor upwind comfortably enough. The real challenge was the gustiness, blowing her all about the place. I'll be back on a calmer day, but already, she's been a blast. None of my other power models would have handled this kind of weather as well as she did. Trying to control low level power fly-bys in the gusty wind was a larf and a harf :)

Who needs a brushless and LiPo? That would be too scary for me!

Multiplex EasyStar Review: Part 2, Assembly and Maiden Flights

2010-09-02T16:35:00.000-07:00

She has loads of character, graceful lines and means business!

In this Part 2 of my Multiplex EasyStar review, I'll trot through the assembly procedure and first flights.

Assembling the Multiplex EasyStar

It's been commented on by others that it's odd for a beginner's model to start off with soldering. I agree, but the motor needs leads.

Heatshrink tubing makes a neat job, even if I do say so myself. Note the black and red ink dots, which I marked once I'd hooked up the ESC and battery and figured out the correct polarity for electric connection and prop rotation. This is a brushed motor of course.

The motor and ESC being laid out. This is RC equipment from my old GWS SlowStick model, so I don't want to mess around with new cables and such. As I've said on this blog before, I'm not a real fan of CA glue. It has its uses, but is nasty stuff in my view. The instruction manual calls for CA glue and kicker. Yuck! I gave the motor mounting area a spray of kicker and put the glue on the motor parts before assembly. The smell of kicker makes me feel a little sick, so I decided not to use it again on this build. I'd rather wait for the CA to cure "au naturelle". I also used UHU Por in some places - which is really superb, foam-safe contact adhesive.

Since I'm going to leave awhile to let the glue set, I taped and banded up the fuselage sides. Here's the top view.

And here's the rear part of the fuselage banded and taped for setting. Masking tape is great - I love the stuff.

The receiver is fixed to the fuselage floor with velcro. If I had more wire slack, I'd move it forward, but it'll do for now.

The battery pushed forward completely to get the right CoG. I also needed to add 30g of ballast, because the battery is a lightweight NiMH job - 7xAAA cells, 800 mAh, ~110g. I'll upgrade it later.

Sorry for the blurred image. However, you should be able to see the canopy latching system above.

The servos are positioned in cutouts on each side of the fuselage. My servos are a bit smaller than the mountings, so I bodged some balsa support structure balsa. This will be covered up with stickers from the decal sheet later, so my aim was to be functional rather than pretty.

I've read in many places that the rudder authority is not great. Now, that rudder does look piddly to me. So, I decided to slot the edge and insert a small acetate tab, just to increase the size of the thing. "Acetate" is a flashy way of saying "packaging from my daughter's toy". Call me crazy, but I do save big bits of clear plastic from toy blister packs for model material. The stuff comes in handy all over the place.

Rudder horn fitted. The plastic tubing was CA'd in position in ready-made grooves on the fuselage sides. I set rudder throw to 10mm each way, as indicated in the manual.

A better view of the acetate rudder tab. I found it worthwhile to flex the rudder and elevator back and forth to loosen up the foam hinge. What an interesting way to create a hinge. It seems quite robust too.

The elevator horn is underneath the plane. The wire pushrods are gripped by the grub screw, which has a neat allen key head. You can adjust centering conveniently from here.

The prop had to be turned into pusher mode. Epoxy was used here as per instructions (minor thing, but it would have been preferable to have some sort of collet or removable clamp arrangement instead of gluing it to the prop shaft). In the background, you can see a wing root with a hole in it for taking the main spar, also a plastic - or possibly fibreglass? - tube.

This is the other wing, with the spar in it. I decided to glue the spar into one wing, simply because it means less faffing around when assembling in the field.

A photo of both wings and the spar. They fit together like jigsaw puzzle pieces. The foam has enough "give" in it to allow a "wiggle and push" fit.

Here are the wings being fitted together in the field. I have to say that it's a very clever and convenient wing joining mechanism.

All in all, assembling the EasyStar and kitting her with RC equipment was simple, helped by the manual being very clear with lots of pictures. She weighed in at 525g AUW with CoG as indicated in the manual, or possibly one or two mm behind it. Because of the small 7xAAA battery, she was over 100g lighter than the AUW indicated in the manual (680g with 6xAA pack).

Maiden Flight

This is a tale of "third time lucky".

I chose a great day for the maiden flight. Very light wind (6-8mph) and sunny. After checks, I turned up the throttle and threw her. The prop slipped forward off the spinner and freewheeled. I pushed forward to achieve a nose down attitude and then eased up to avoid a bad crash. I re-pressed the prop back in and tried again, but it slipped forward again. So, I came up with an inelegant field fix using a rubber band:
This was enough to hold the prop in place for the evening, so that I could fly.

Initially, she didn't fly straight, went into a turn and I was unable to straighten out from it! I was puzzled. Despite the acetate tab, perhaps the rudder authority was still insufficient? Lack of response to rudder input was especially apparent when flying downwind and trying to turn back upwind. The end result was a number of tip first landings. Thank goodness she's a tough plane! I adjusted rudder trim, she flew straighter, but turns were still a problem, unable to roll out of a turn once established. Pathetically, I managed to encourage her to climb using S turns upwind. That worked to allow a flight of 2-3 mins, with about a few seconds spent gliding and a reasonable landing. But by then, the puny battery was weak. So, I resorted to chucking her by hand. To my surprise, she had a fairly decent glide and good response with power off, especially to elevator inputs. Clearly, I had to try more rudder deflection.

First mods

So, overnight, I moved the control horn link position as close to the fin as it would go, in order to tease out max throw of the rudder (12mm instead of 10mm). Also, to fix the prop, I wound and CA'd a thread on to the prop spinner shaft to prevent it slipping forward:

Both changes had an immediate impact. The next day with a re-charged battery, she flew much better. There was a bit more power too - it could be that this battery needed a couple of discharges to liven it up, since it has being lying around for a while and/or the rubber band field fix had been added noticeable friction the previous day. Whatever the reason, I managed a flight of 7-8min, but still felt a lack of rudder control. Encouragingly, I enjoyed a few attempts at thermal soaring with the motor off and did a loop with no problem at all.

Next Mod: a Bigger and Better Rudder

That night, I decided to cut the fin at the rudder line and make a full length balsa rudder.

First, ruler and pen to mark off the cut line.

Using a scalpel, I cut along the line, leaving a tad of excess foam to allow me to bevel both sides of the fin into a V, again using a scalpel and finishing with a sanding block.

From medium 3/32" balsa, I cut a new full length rudder. The photo above shows the slot for taking the rudder horn. I decided to reinforce this by sticking a 1/32" cheek on the other side from the horn, cross grain, using waterproof wood glue. This would create a stiff, strong rudder.

I fashioned two hinges from roughened mylar. This kind of width was what I reckoned to be enough to create a smooth, easy to move hinge. I cut slits in the rudder to accommodate the hinges.

Before gluing in the hinges, I gave it two coats of sanding sealer and coloured two black stripes with permanent marker pen. The hinges were glued in with CA, and the horn with 5 min epoxy.

This is a view from the other side, showing the 1/32" balsa cross-grain reinforcing cheek.

Then, I cut slots in the fin (right on the apex of the V bevel) and CA'd in the hinges. Rigged up the wire pushrods.
It seemed to be better to put the grub screw underneath the horn, because this would reduce the bend on the pushrods and plastic housings. I made a tiny hole in the elevator hinge, to enable the allen key to reach the grub screw.
I adjusted the horn linkage position to give good throw, 12mm each way - using a steel ruler to measure it.

So, here we have it, the new full length, larger area rudder. It is light, stiff and moves smoothly, centreing well.

The following day, I flew her again, in a slightly stronger wind (9-10mph, with a few gusts). I used the same 800mAh battery, recharged overnight. The first flight was 10mins long with about 20% being thermal soaring. The second flight was about 3 mins, again borrowing climb from thermals. I packed up after that and at that stage, the battery still had a bit more oomph left in it. With more rudder, she was transformed. Quite enjoyable - I can now turn properly and roll easily back out of established turns! She flew a few loops and chandelles and we tried a half loop to inverted, which was a bit heart-thumping. It was fun to turn the motor off and soar. In the limited time I had that day, I thought she soared well, indicating lift clearly. She made one lovely climb in a thermal ending high up slightly downwind. I used the moter to get back upwind.

After initial teething troubles, she has ended up providing fresh excitement. I think she is just what I was after. I'm a little perplexed as to why Multiplex cannot give her a larger rudder, because it seems crystal clear to me that she needs one. They could also elimate the soldering step, but I suppose that allows users to choose their preferred motor connectors.

Also, she looks great from virtually all angles. I just love those upturned wing tips, curvy tail feathers and pusher prop.

And isn't that a gorgeous profile to look at in the sky? Love that torpedo shaped fuselage.

In summary, the Multiplex EasyStar is a convenient, stylish, neat and entertaining model. I'm hoping for many memorable flights in the future.

Multiplex EasyStar Review: Part 1

2010-09-02T15:12:00.000-07:00

A few weeks ago, I found myself feeling a bit fed up with my GWS SlowStick - pictured. Not because of the plane - I'd recommend it to anyone, it has a loyal following for a reason. No, it was the realisation that I prefer to fly it with the engine off! I would climb up, switch off that buzzing prop and then fly about looking for lift. I'm a glider junkie, it's true. Plus, in a bit of wind, she didn't have the oomph to make much headway with the stock brushed motor.

So, it was time for a change. I could upgrade to LiPo and brushless, but that wouldn't solve the constant "I want to glide and thermal" desire in my bones. I wanted to take the battery and radio gear off the SlowStick and re-use it quickly on something else. So, what to do? The Multiplex EasyStar ought to be suitable, because it:

looks like a glider, so should soar reasonably well with the motor off!

has a great reputation as an ideal newbie's plane, also pre-fabricated

comes with a brushed motor and is 3 Ch

can be upgraded, and modified for aerial photography

should handle a bit of wind better than the SlowStick (including better penetration)

has loads of resources and info about it on the internet

Eagerly, I ordered one online from rcmodelcentre.co.uk. When the box arrived, I was like a kid opening it up. However, to my horror it had been bashed in transit and the photos below show what I saw.

Oh ,those beautiful wings, so crushed and crumpled!

Thankfully, Mike at rcmodelcentre.co.uk was very good about it and sent a replacement very quickly. The pack included the wings, fin, stab, fuselage, canopy- all in Elapor foam (not regular foam like Depron, but Multiplex's stuff), pushrod wires, plastic tubing of various diameters, a main spar tube, horns and other small parts, a bit of velcro, motor, prop, spinner, a decal sheet and some thorough, well illustrated instructions.

So, EasyStar is the name, but just how easy was she going to be to build and fly? In Part 2 of this Review, I'll tell you the rest of the story.

FREE MODEL GLIDER PLAN: QUEEN BEE 8" Tiny glider

2010-07-28T15:26:00.000-07:00

This is a conventional pod and boom design with V dihedral. A notable feature is the use of natural carbon fibre for the boom. Natural carbon fibre? Yes, I mean kebab skewers! These can be bought for peanuts (satay sauce?) from a supermarket or online for less than 2 pence each. Search through a pack and you may find a decent number that are straight, stiff and suitable for building with. Any hard outer skin on the cane should be positioned underneath the boom. The wonky ones can be used for, you guessed it, kebabs! Of course, if you cannot find real bamboo, please do feel free to substitute with carbon fibre instead.

For ease of construction, the wing has a straight high point. In the normal HLG manner, after the wing has been shaped, finished and cut, the ends are bevelled and glued into the correct V dihedral setting. A matching V is sanded carefully into the fuselage top - I make a tool for that using a coffee stirrer, balsa and Al-ox paper. Use epoxy for the dihedral joint and wing-fuselage junction. After the wing has set on the fuselage, you can cyano thread to the LE. It may act as a turbulator, but even if not, it protects the LE. I could not detect a change in performance after adding it. That said, if you leave the LE bare with no thread and it receives a bang or dent, then you can sponge it out with a tiny bit of water. It is really up to you.

The QUEEN BEE plan shows the original dayglow yellow and black stripe colour scheme. Finish in the same way as DOGEAR in the previous blogpost.

For some previous notes about flying this model click here. My "still air times" (as described in the DOGEAR blogpost) for QUEEN BEE were in the range ~28-30s.

FREE MODEL GLIDER PLAN: DOGEAR 6" Tiny glider

2010-07-28T15:13:00.000-07:00

This is DOGEAR, a development of DOGCHEW (see previous blog post, again, just click and save the plan). DOGEAR differs mainly in the wing design. The planform is elliptical at the front with a basswood leading edge (or use lime wood which is also genus Tilia). Trailing edge is mostly straight with single taper near the tips. The wing is also thicker, 2.5mm (~5%) compared with the 1.6mm of DOGCHEW. By feel, I carefully sand a small "Phillips entry" under the LE, but the rest of the underside is flat. It is a typical HLG aerofoil. The wing is assembled as a straightforward three panel structure using epoxy at the breaks - the tips are raised by 15mm from the flat centre.

The three panel wing and the fact that dogs appear to find my models "tasty" were the reasons for the name DOGEAR.

Fuselage is laminated using pva (e.g. Titebond II). The thin glue layer increases stiffness and strength a great deal. A lighter way is to use spots of cyano. Alternatively, forget about the laminating completely and use hard 1/8 balsa instead. Please do feel free to experiment with nose length. In other words, cut it shorter if you wish. The size shown on the plan seemed work well in calmish conditions. I use epoxy for the wing fuselage joint and throw tab. Fin and stab should be sanded as thin as you dare, so that you can breathe and bend for trim.

My finish is the traditional 2 coats of thinned down sanding sealer with very fine Al-ox paper between coats. I finish the wing with sanding sealer before it is cut into three panels and the stab and fin before they are glued to the fuselage. A splash of dayglow colouring helps enormously for visibility. Apply Al-ox paper grips on the fuselage sides. In the photo below, you can see some inked stripes that also help to see the plane against the sky (er, I mean clouds, cos that's wot we av ere most in England).
By my reckoning, DOGEAR will stay up for about 5s longer than DOGCHEW in "still" air; by that I mean in very calm conditions outdoors early morning or late evening. I recorded consistent times of ~22-24s for DOGEAR in such conditions (I am sure a lighter version would do better).

FREE MODEL GLIDER PLAN: DOGCHEW 6" Tiny glider

2010-07-27T14:46:00.001-07:00

The Small Flying Arts site has changed dramatically. I think they are in the process of transferring all the plans and articles over to the newly designed site. However, the plan and build notes for my DOGCHEW design are currently unavailable there. So I thought I'd publish them here. In future blogposts, I'll also publish some other tiny glider plans. Click and save the plan below. The build notes, which I wrote in 2006, are shown in full below the plan.

Build notes for DOGCHEW 6" glider

These notes accompany the plan for a simple 6" span free flight HLG. Small gliders do not have much momentum so tend not to break easily. Another advantage is that they can float on a whisper of lift. You get maximum fun with minimum fuss!

Now this is the first 6" glider of mine to fly over 30 seconds. When I was testing the prototype in a local park, there was nothing for me to do but laugh while I watched a "friendly" Dobermann Pinscher pick it up tenderly with its jaws, manouvre it about and then crunch it, very gently. I said to the dog-owner: "Well, I guess it looks a bit like a stick." He replied, "You’ll be needing a bit of glue then. A pity, cos it flew really well." I thought "yeah FLEW." At least the dog seemed to enjoy the flavour of dope on balsa. I spent the lonely walk home carefully spying the ground for other deeds by my new best mate Dobie….

That is why this design is called DOGCHEW. Its best flight so far is about 63 seconds and still air time around 18 seconds. In the 2006 Tiny Gliders postal contest (see http://www.windandwavemodels.com), average flight time was about 32 seconds.

It is a straightforward build. The plan is to scale, so you may find it easiest to use a photocopier or scanner to enlarge or reduce it in accordance with the fuselage dimensions.

Instead of laminating the fuse with PVA, you can use spots of CA – this is lighter. Alternatively, forget about the laminating completely and use hard 1/8 balsa instead. The wing is made in the usual HLG way. Make a template from the plan. Use it to cut out the whole wing planform, sand in the airfoil with the high point as per the dotted line and apply 2 coats of sanding sealer. Then cut the wing in half, sand the dihedral angle at the root chord and glue together with epoxy. Sand a “v” in the fuse for a wing seat and use epoxy here and for the throw tab. Fin and stab should be sanded as thin as you dare, so that you can breathe and bend for trim. (The prototype had trim tabs, but these were dropped in the final design because they were easy to break). Apply sandpaper or similar for grips on the side of the fuselage.

Feel free to play around with the length of the nose – e.g. chop it shorter if you like. The length shown on the plan seems to work well in calm conditions. Also, you may find it beneficial to sand a bit of washout under the starboard wing tip TE.

Using gentle glides from the shoulder, trim for a left turn, with a slightly “stally” glide. Full power throws are to the right of the wind with a slight right bank. As with most HLGs, avoid throwing with less than full power! Add left rudder if it stalls in the glide, but not too much otherwise it will spiral dive. When properly trimmed, it should transition at the top quickly and start turning nice flat left circles.

Thermal in peace….. :)

Berkshire, U.K., 2006

Silly Putty Timer DT (Dethermalizer)

2010-01-08T10:00:00.000-08:00

The silly putty timer has been around for well over a decade in free flight aeroplane model making.

Over the last few months, Tony Mathews, free flighter extraordinaire, has been experimenting with micro versions of the timer. He has come up with a timer that is amazingly small - 1/8" x 0.7" (3 x 18 mm) - and light at about 0.3g.

Here is a photo of his excellent Stinger 8" CLG with a micro silly putty timer installed. It operates an aluminium drinks can foil DT. Notice that the foil is on the inside of the circle turn, causing a steep downward spiral. When I saw that, my initial reaction was more "Death Trip!" than De-Thermaliser! Encouragingly, he reports that small gliders like this suffer no damage on DT deployed landings.

Tony has put together an absolutely superb pictorial build guide here. You must look at it. I've made some timers according to his plan and found them to be quick and easy to build. Cutting aluminium tube with a scalpel is fun! You need to roll the blade over the tubing to make one cutting groove around the circumference and perpendicular to the axis. As you continue to roll, it then pings off at air pistol speed, so one trick is to thread some wire or string through the aluminium tubing before cutting it, to catch the piece.

I have some ideas to try to improve the consistency of the timer, which is not as good as a commercial viscous button timer. If I find success I will report it.

Here is more background on silly putty timers. Useful sources of information include articles by Peter Michel (on Ramon Albon's great free flight site) and Pensacola free flighters. Thayer Syme's super page and diagrams dating back to 1996 are here. Martin Gregorie has posted some useful and detailed information here.

Drag explained for model aeroplanes

2009-10-17T14:27:00.000-07:00

This is my attempt to provide a simple explanation of drag for the model builder.

DRAG is the force that resists the forward motion of an object through the air. For model aircraft, there are essentially two types of drag (refer to Figure 1 which is a plot of Drag force against air speed, v):

1. PARASITE DRAG is the resisting force that is due to the shape, roughness and form of the aeroplane. As the model moves through the air, the flow is disrupted by the shape and texture of the model. Its magnitude is given by the expression shown in Figure 1 (red, think of A as a constant). Parasite drag increases as the plane speeds up. Think of it as "High speed drag".

2. INDUCED DRAG is simply the drag force caused by the circular flow of air around the tips of the wing, that is, the vortex. An alternative name is "vortex drag". To get an idea of what it "looks" like, just search on wake turbulence or wing vortex in Google Image Search. Notice also the dependency with the lift force squared, L^2. That is why it is also known as "drag due to lift". So, the induced drag also increases with lift, for example with increasing angle of attack. Its magnitude is given by the expression shown in Figure 1 above (black, think of B as a constant). Since it is inversely proportional to v^2 it means that as the model speeds up, the induced drag decreases. Conversely, as the plane slows down, induced drag increases. Think of it as "Slow speed drag".

The total drag is the sum of the parasite drag and the induced drag (see blue curve in Figure 1 and Equation (1)).

Note for readers who like a bit of mathematics: Equation (2) is the "drag polar". To understand where it comes from you would need to look at an aerodynamics book (see References). The full expression for Equation (1) is Equation (6). You can easily derive Equation (6) by substituting equations (3) and (4) into (2) and recalling the relationship between aspect ratio (AR), span (b) and area (S). Equation (5) is the usual expression for dynamic pressure (q).

So much for the theory...

What does this mean for model aircraft performance and design?

1. It is generally desirable to reduce drag. Lower drag means a flatter glide (see the discussion of glide angle in a previous blog post here). In other words a higher L/D, which is a key performance indicator. Modern open class gliders can achieve L/D of 60 or better. In contrast, the Wright Flyer of 1903 had L/D of 5.7.

2. Mathematically, Equation (1) means that the total drag is a minimum at the air speed where the parasite drag equals the induced drag. That is the air speed where the best L/D is achieved. So if one of these drag contributors (parasite or induced) is low at that speed, then the total drag will be two times that low number. While that's a good thing, the plane's behaviour may suffer at one or other extreme of speed.

3. Take for example a small span pylon racer model. It has a small cross section area, smooth, clean, polished surfaces and therefore low parasite drag. Due to its high wing loading, it will have a high induced drag (this will be explained further below). Since it is fast, it will generally fly on the right hand side of the drag-speed curve shown in Figure 1. The good news is that parasite drag is lowish for this model, so it will perform fine under normal operating conditions; it is not impaired by the high induced drag.

4. For slow flyers for example, thermalling gliders and free flight rubber planes, induced drag is much more important. At low air speeds, parasite drag does not have any appreciable influence - this is the left hand side of Figure 1.

5. For many types of aircraft however, both parasite drag and induced drag should be minimised, for instance hand launched gliders and catapult launched gliders. These travel quite fast on release, so low parasite drag means a higher launch. After the transition to glide, they fly slowly, so low induced drag is required for a flatter glide. Another example is the RC glider. It needs to glide well at slow speed in order to climb in thermals. Then after the climb, it needs to be able to glide at shallow angle to cover lots of ground with little loss of height, in order to catch the next thermal. Induced drag is very important for free flight models too, including rubber power.

Reducing Induced Drag and Parasite Drag

6. The wing is the biggest contributor to both induced drag and parasite drag. So concentrate on the wing before the fuselage and tail feathers!

7. The biggest factor for reducing induced drag is the span loading W/b. This comes from Equation (6), noting that L~W, and see also previous blog. It is not as simple as just increasing AR for reasons explained in that blog post. (The over-emphasis sometimes placed on increasing AR to reduce induced drag probably arises from the dimensionless expression in Equation (2) above).

8. That means keep her light and make her span as big as allowed!

9. Another factor to reduce induced drag is wing planform design (elliptical and similar shapes are good). Non-planar surfaces can also reduce induced drag compared to a same span planar wing. For example, winglets, polyhedral configurations and span-wise camber. Some efficiencies can also be gained from multi-surfaces (e.g. boxplanes), but there is obviously a parasite drag and weight penalty.

10. For reducing parasite drag the biggest factors are the apparent cross section area and the wetted area (the area of the plane that is in contact with the air). Keeping the fuselage as narrow and small as possible is a good start. Sharp corners and junctions between wing and fuselage could be smoothed or "filleted" to reduce the drag. Surface roughness also plays a part (but its not as simple as smoother the better: sometimes a rough surface can keep air flow attached to the wing - "turbulators" are a PhD study on their own!).

11. Note that adding weighty fairings and cowlings in an effort to reduce parasite drag could be counter productive because it may increase induced drag! Fairings and such like may help the high speed flight, but could ruin the low speed glide.

CONCLUSION

I hope this blog has helped you to understand drag. Think about what your plane will be doing most of the time. Flying fast or flying slow? What kind of drag would be most relevant to your model? Having decided that, work to reduce the predominant source of drag. However, concentrate on the wing first. As ever, weight is a major factor especially for induced drag.

REFERENCES

1. Anderson J D (2005) Introduction to Flight, McGraw Hill, 5th edition

2. Simons M (1999) Model Aircraft Aerodynamics, Special Interest Model Books, 4th edition

3. Kroo I (2001) Drag due to lift: Concepts for prediction and reduction, Ann. Rev. Fluid. Mech 33:587-617

Queen Bee 8" HLG: A simple hand launched glider

2009-09-26T16:11:00.000-07:00

Nothing in aeromodelling gives me more pleasure than flying the humble chuckie. Lately, I've been messing around with RC: gliders and electric planes. They're fun, but for some reason, the enjoyment can wear off. I always come back to the chuck glider. Photos here of a simple model that I enjoyed flying yesterday and today, in the light wind and sunny blue sky of September.

Best flight was a 66s today, but alas, that was not one I'd declared for the tinygliders postal competition

I guess it's obvious why she's called QUEEN BEE. She has a bamboo fuselage and simple wings.

Another thing. Chucking gliders is great exercise. I can tell that it has been a while since I did some throwing, because my body really feels it - especially the bicep and shoulder!

Yesterday, I lost WEE BO WEEVIL. It went OOS at ~210s. The DT had triggered - I could see the elastic hanging, but the wing failed to pop up.... :( All the more upsetting because the DT worked perfectly for maxes earlier that day.

Albert Hatfull: The Senator, Junior 60 and much, much more!

2009-08-18T14:51:00.000-07:00

Albert Edward Hatfull ought to be more famous.

At free flight events in the UK (and around the world) you are likely to see a SENATOR rubber model soar up into the sky for yet another flight over 3 minutes. I never tire of watching the SENATOR. It may well be the most successful rubber model that has ever been sold in kit form (by Keil Kraft). To demonstrate what I mean, here is a great video of a SENATOR being trimmed on a short motor run by US modeller Almico123:

Isn't that superb?!

Many RC afficianados will know and love the Junior 60 design. Originally a free flight "gasser", you'll still see Junior 60s being used by radio control clubs as "workhorses" and camera platforms. It is charming and possesses a functional attractiveness that is difficult to explain to non-modellers. See this fabulous article on an electric conversion by Barry Slater.

The plans for these iconic designs are as beautiful as the models themselves. The SENATOR and JUNIOR 60 were just two of the many models designed by Albert Edward Hatfull. The plans were drawn by him while he was engaged by Keil Kraft as a young man.

Albert was born in 1926 in London. His family had a strong engineering and sea-faring tradition. However, he was into aeroplanes and from the age of 9 he cut his teeth on Megow and Guillow's kits. By all accounts he was a colourful character with a great sense of humour. He was fond of New Orleans jazz, followed the US model aircraft scene (Korda et al) and played the piano. He attended Tottenham Technical College, studied maths and draughtsmanship and developed an interest in aerodynamics. Sadly in 1942 at the tender age of 16, he contracted polio from a local swimming pool. This was a time when vaccination was not yet available. The disease restricted his hand mobility, but the wonderful thing is that he did not let it stop him from being creative.

Soon after the polio infection, the youthful designer created his first model for Keil Kraft. As it was wartime, he named it the INVADER glider and it became a best-seller. Before the age of 20, the JUNIOR 60 was created, quite literally "while the V2s were falling on London". Despite the polio, he built a career as a proficient draughtsman. Engineering drawings and later patent work at the Science Library provided a living, but model aircraft were his passion. He designed dozens of planes, including the SENATOR in ca. 1950 and the SKYSCRAPER around the same time. The two models are very similar, the main difference being an undercambered fuselage on the SKYSCRAPER. Albert was clearly interested in aerofoil shaped "lifting" fuselage profiles. Interestingly, he did not report any difference in the performance of the SENATOR as compared to the SKYSCRAPER and the former became much better known, widely flown.

Apart from gliders (e.g. SOARER series) and rubber power jobs, he also designed many Jetex models. Of the jet designs, his personal favourite was the De Havilland VENOM. Many of his plans were published in the aeromodelling press. He even designed Keil Kraft's triangular trade mark logo!

After Keil Kraft, he did some design work for Worcraft models (Dewsbury) and Elite models (Manchester). These included the Worcraft SCARAB - with lovely elliptical wing profiles and the Elite ELF, which like the SKYSCRAPER, sported a beautiful aerofoil shaped "lifting" fuselage profile. Ill health forced him into retirement in 1984 and he passed away in 2007.

I hope this blog post helps to make Albert E. Hatfull's name as famous as his models. Aeromodellers will not forget him!

(I hope to continue researching and will endeavour to expand this blog post accordingly. For example, I wonder if someone has a good list of all his models - if you do, please email me!).

References

1. Harry Payling (2007), Obituary of Albert Edward Hatfull, New Clarion SAM 1066 newsletter, November 2007, p.20-21.

2. Bill Morley (1996), SAM meets Albert, SAM 35 Yearbook 9 , p.2-7.

3. Andrew Longhurst (1995), Rubber Column No.149, SAM Speaks No.155 June 1995, p.3, 5-6.

Mad Scorpio RC glider and Things to do

2009-07-14T15:38:00.000-07:00

This is megatastic, a Scorpio rocket glider with RC! :)

I've got many projects that are sitting around to be completed. So much to do, so little time. Work, family and other aspects of life always seem to take higher priority. Here's a potted list:

Scorpio 19.25" FF Rapier rocket powered glider, a superb design by Steve Bage. Lovely kit from Shorty's Basement to build. Cool video here.

Pearl 1.49m R/E radio control discus launched glider. ARF from South Coast Sailplanes, but kitting it out with radio gear will take some concerted effort and time.

Sovereign, 2m RC glider. Full kit to build from Mountain Models The photo below shows a fabulous example by hangerdude from the RC Groups forum. Isn't that a mouth-watering picture?

Dingbat vintage HLG from plans, which I've been meaning to build for years.

AND Lots of flying to do - CLGs, HLGs, DLGs, rubber, RC electric, RC gliders...

Wee Bo Weevil: 12" Catapult Launched Glider CLG

2009-07-14T12:20:00.000-07:00

The original Texas Bo' Weevil hand launched glider HLG by Don Chancey was published in American Aircraft Modeler in 1972. It was a 17" span all wood design of traditional layout and very steady, reliable performance.

I thought it would be fun to miniaturise, modernise and catapultise it!

So, here's a 12" span scaled down version, with carbon fibre boom and pop-up wing DT operated by a button timer. Natty rainbow colours anyone?

Side view showing the wing down. To give you a sense of scale, the button timer on the nose is 15mm diameter.

I call it the Wee Bo Weevil.

Another view of the DT system, with wing in the up position.

All up weight including nose ballast is 13.5g. It launches and flys pleasingly well, but is not as super-performing as a "clean" and modern 12" design, a la the experts such as Lee Hines, Tony Matthews, et al.

Fun though, and it's great to watch dog walkers in the park looking puzzled as it DTs down.

FREE MODEL GLIDER PLAN! Tiny glider, 8 inch Catapult Launched Glider (CLG)

2009-02-15T16:30:00.000-08:00

If you downloaded this plan before 28 February 2009, please discard that copy and use this version instead - some important details were either wrong or missing Sorry!

As you can see from earlier blog posts, I've been playing with Charlie Sotich's simple 8" CLG. Necessity really, after the original 1/32 thin wings - as per his plan - shredded on launch.

So here is my "re-mix" of his design. Main changes are conventional HLG style wing, three panel instead of V-dihedral, a slightly longer nose and some mods for a stronger wing fuselage joint.

Sotich named many of his designs [SOMETHING] DIP. For example, his famous 48" glider was called LIL DIP. Since this 8 incher is intended for the Tiny Gliders postal event, I called it the TINY DIP, but I don't know whether he ever made a design with that name.

I hope you enjoy the plan - drawn with a smile on my face and a bit of tongue in cheek. An easy build, lots of fun, pretty in the air and satisfying performance (right click on the plan and select Save Image As). Try a 3/16" rubber loop for the catty. You can use kevlar tow instead of CF. Fix to the model's balsa sides with CA glue. Note the washout on both tips and the washin triangular wedge on the left wing only. There is a slight incidence (decalage) in the design. I visualise it as the bottom of the fuselage being horizontal, and the top line of the fuselage a slope, taller at the front. The closer you get to 0-0, the straighter and higher the launch, but stability decreases. Too much decalage, then the climb becomes a height-sapping spiral (or worse, gets loopy).

Photo below of the TINY DIP glider (4.1g ready to fly).

Source of Vintage (Old Timer) Plans and Articles

2009-02-08T16:53:00.000-08:00

There's an excellent new source of information on "vintage" model gliders and free flight aircraft. The POPULAR SCIENCE magazine series has been digitized and is now available on the internet via Google Book Search.

Screen shot of an article by Frank Zaic on the THERMAL HUNTER rubber model is shown left. It also includes building instructions, tips and drawings.

I had a look through some issues for articles and this is just a selection of the gems that I found:

New Thermal Hunter Plane Model, Frank Zaic, August 1936, p60
International Contest Flyer, Frank Zaic, June 1940, p150
Model Fuselage Building, Edwin T Hamilton, July 1931, p110
Give your model the right propeller, Edwin T Hamilton, July 1930 p96
From ten parts you can build twenty model planes, Edwin T Hamilton, August 1931, p72
Model-Airplane Short Cuts, Frank Zaic, September 1941, p170
Test Flying Model Airplanes, Frank Zaic, June 1942, p196
Gas Models and Towline Gliders, Frank Zaic, September 1942, p.HW230
Novel Inventions aid Model-Plane Champions [no author indicated] November 1939, p67
The modern 300 incher, Zaic, Aug 1942, p.HW174
Hints that will help you build airplane models, Edwin T Hamilton, January 1931, p116
Miss Science (gas model), Frank Zaic, September 1939, p142

Happy reading!

Tiny Gliders Postal 2009

2009-02-05T10:12:00.000-08:00

Alexandre Cruz has created a fabulous blog for the Tiny Gliders postal event this year. Please do enjoy building some 6" and 8" gliders and fly in it. It's a lot of fun and easy to join in! It would make a great club event too, or activity for the kids. There's no excuse....

Left, a photo of my 6" DOGEAR hlg.

Thanks Alexandre!

P-51D Mustang - Completed model

2009-01-27T08:46:00.001-08:00

Here she is, complete with pilot. One thing I learn from this is to never, I repeat, NEVER, use domestic tissue again. Japanese is so much better. This stuff shrinks in weird ways, is not easy to apply and the finish is lousy.

I love the lines of that wacky Dick Baxter prop - which is pretty much as per plan. I used a yoghurt pot rather than a coffee cup.

Weight without rubber was 8.8g. Prop on its own weighed 1.8g. Here is a photo of two prop centre shafts. The top is a ramp type of freewheel clutch, the bottom has a Garami-style latch. They're both smooth, but the ramp is more compact so I used it because of the spinner. Spinner was made out of tissue pva'd to paper. Cut out a semi-circle and made a cone out of that.

Power is one 1/8" loop. So far, I've only given her ~150 turns. Stab adjustment was required, but no ballast at all (thus far). All indications are that she's a good flyer! Need a good day to try her out properly.

A very enjoyable build.

Free Flight Postals

2009-01-10T16:27:00.000-08:00

Postal events allow competition without the formality of a meet. Each modeller sends in scores by a certain deadline, usually a series of times. Many are run on an honour basis - and I certainly don't know anyone who'd cheat by sending in false times - what's the point? In any case, weather conditions are not the same for everyone. So in my view, postals should not be thought of as "real" competitions.

Click here for a super list of some free flight postals. I was sad to see that the 2008 Tiny Gliders Postal had few entries because it is one of my favourites. The plus side is that Alexandre Cruz did a great job of keeping it going and there is good reason to anticipate that it will be bigger and better in 2009! If I find out the new website for it, I'll post it here.

Finally, how on earth did this patent get granted by the US Patent Office in 1975? There's no way it was novel or inventive at that time!

Catapult launched glider: Sotich 8" CLG

2008-12-30T01:02:00.000-08:00

This is a catapult glider design by Charlie Sotich. It's a quick n easy build and flies reasonably well. The plan is available from the Aeromaniacs site here (click on the pdf symbol next to Catapult!).

This one took me just over half an hour to make and came in at 2.7g including nose weight. Not bad for an 8" span model. She flew right off the board with an in built left turn. First flight was a promising 36s in cold weather, 8mph wind.

Alas, after about a dozen flights, I pulled the elastic back too enthusastically and shredded the right wing - the curse of small CLGs! I'm oddly pleased because it was the wood that failed, not the glue joint.

Great fun while she lasted.

All was not lost, as I decided re-utilise the fuselage for another, different, wing and see what I could learn from that

So here she is the next day with a conventional 3 panel wing made out of 1/8 balsa. Also now sporting carbon fibre tow on the sides to keep the fuselage stiff. Weight has gone up to 4.2g, but she still flies well. Polyhedral is 1 3/8" under each tip. Too much, because she Dutch wobbles in flight, but at least showed no tendency to spiral in.

Here's a photo of the underside. You can see the Al-foil tape that I've used to reinforce the wing-fuselage joint. So far, no more shredding!

I think the original is prettier. The modified version seems more consistent. Best flight today was just under 45 s in winter conditions, with no flights under 30 s.

Rapier Rocket Car / Test Rig

2008-12-23T13:04:00.000-08:00

Just got my sticky mitts on some Rapier rockets. I've always wanted to make a rocket-powered glider. Another project for next year...

I've never used these rockets before, so I built a test rig for my son. OK, it's a car, but the spoiler counts as a wing! Inserted a stick-like fuse into the hole at the rear, lit it and then watched it fizzle out. Left it for a while, then tried again. Eventually, it ignited and whizzed off leaving a satisfying trail of smoke. I must get an electric igniter. It has a hot tip: insert in the hole to start the rocket.

Model Glider Plans

2008-12-02T15:20:00.001-08:00

If you're looking for really interesting A/2 glider plans, then the January 2007 issue of New Clarion is a great resource. It contains fabulous information on a number of, shall we say, "nostalgic" glider designs. A/2 gliders are basically the big ones - usually between 60 and 79 inch span (~ 2m). SAM 1066 is a UK based chapter of the Society of Antique Modellers - well worth a visit and their membership is free!

Converting a free flight glider to radio control RC

Free Flight gliders could be useful starting points for an RC conversion - to make a really high performance radio control glider. To flesh this out, here's an example of enlarging a Keil Kraft Soarer and converting it to RC (discussed on the RC Groups forum) :

And here's a super example of an RC conversion of the Lulu (50" free flight glider, discussed on the SFA forum, by my friend Eagleone):

I would suggest that neither the Soarer nor the Lulu is in the same league as the big A/2 gliders. Indeed, I daresay that converting one of those "biggy" free flight A/2 designs to RC would create a very high performance radio control sailplane.

If only I had the time to try it....

A Story about Pre-Flight Checks

2008-11-17T14:25:00.000-08:00

Had to take a break from building the P-51D - birthdays, family stuff and such. In the meantime, here's a little tale.

When flying radio control, I try to be diligent about pre-flight checks. However, a month or so ago, I came a cropper while flying the STARLITE (see photos).

Picture this: after changing the prop and replacing the battery with a more powerful plant, she was flying beautifully, save for a noisy (definitely broken) rudder servo. I replaced the servo, and while testing on the dining room table, was delighted that the rudder operated as quietly as the elevator. Charged her up and excitedly, went off to the field. Did my checks and launched from a throw. She climbed a bit then - spiral dived to the ground! I checked rudder centre trim setting, it seemed ok, so I launched again.

Painfully, she spiraled in once more, this time losing a leg and a suffering a bit of minor damage to the fuselage.

What to do? I checked alignment of all surfaces. Nothing except an ever so slight warp on the rudder. Surely the spiralling could not be from that? With the plane pointing ahead of me, I waggled the stick.

Then I saw it. The rudder was moving in the wrong sense! I had done my checks the first time with the plane pointing towards me (and without engaging my brain!). It took 5 seconds to reverse the new servo from the TX switch, after which she flew beautifully (although now with one leg - fine practice for holding off on landings!).

When I first heard the story of the pilot who chucked his radio control glider off a ridge, only to realise he hadn't turned the receiver on and then watched it fly off into the distance out of sight, I used to wonder "how could that happen?". Now I understand! For me, repairs were cheap and easy but I hope the valuable lessons learned last forever:

- Always take care over pre-flight checks. Do them PROPERLY, especially when excited about the flight.

- Never assume that a replacement servo operates in the same direction as the previous one. Check it!

P-51D Mustang - Fuselage and tissue covering

2008-10-29T15:40:00.000-07:00

For some strange reason, I chose to use normal domestic tissue instead of the usual (and better) Japanse Esaki. This was white stuff from the local newsagent shop, pre-shrunk with water. This is my first effort at colouring tissue. Here, I'm using some very old art charcoal that's been lying around at home for over 15 years! You can also use coloured chalk. Loads of colours and tints are possible.

Simply rub it on, then wipe about in circles with a soft tissue until it's evenly shaded. I did both sides. In the photo, a strip of the original white tissue is on the left and a gey coloured piece for the wing is on the right.

I am not an expert builder, but I enjoy it and do take pride in my work. Below, fuselage sides going down. I'm building both at the same time (this is NOT the same thing as the second one over the first!). Don't bother with cling film between them - you can separate with a razor blade afterwards.

Assembling box fuselages can be tricky and fiddly. Cardboard formers - lightly tacked in place with CA glue - are tremendously helpful. Generally, I use woodwork PVA for all balsa joints and avoid CA except for the places where it's really advantageous, like for the formers here. The photo below is just before the sides were "cracked" to bring the back ends together.

Another view of the fuselage assembly and card formers. They are from a pizza box.

Here are the wings glued up and setting at the correct dihedral angle. This newsagents shop tissue is nowhere near as easy to work with as Japanese Esaki. It does make a change to use a material with a different texture though. The grey colour is just what I wanted - simulating the metal of the full-size. I will have to lightly dope it, to fix the charcoal in the tissue. Note the slightly graded colouring on the fuselage side - the top is grey while the bottom is white. I wouldn't have the patience to build proper scale models, and chapeau to folks who do. Sports-scale is good fun though - it's like a nod and a wink to the original full-size shape.

P-51D Mustang - Sport Scale Rubber Model

2008-10-23T16:35:00.000-07:00

The P-51D Mustang is a very popular model aeroplane subject - and for good reason. The sight and sound of one in flight is just as iconic and neck-tingling as the Spitfire. The P-51D is recognisable by its teardrop bubble canopy, fin gusset (although not every D model has one) and distinctive "kink" in the wing LE near the root.

www.mustangsmustangs.com is a superb resource for information on these amazing planes. They served in air forces all over the world.

For some time, I've been wanting to build Dick Baxter's 14.5" sport scale rubber power design, plans for which are available at SFA. You can see the relationship of this design to his Akro model. It's a fairly simple to build rubber model that can be flown outdoors or with care indoors. All you really need are some 1/16" square spars, a bit of 1/16 sheet and a 1/8 square spar. Clearly, he has tried to avoid tricky building and curves while at the same time, creating a fair impression of the full-size plane. It seems like a well thought out design.

I started off with the canopy. This is the first time I've ever tried to hot-stretch canopies out of discarded packaging plastic. It's great fun!

Airframe is fairly easy to build, though a bit fiddly. Here are the wings.

More pictures to follow.

Starlite 36" Radio Control

2008-10-15T14:14:00.000-07:00

Site Changes
Frequent visitors will note the slight change of style to this blog and the new title. I wanted to broaden the coverage and more accurately reflect my aeromodelling activities.

Flying the STARLITE
After giving up on the 150mAh 9.6V NiMH battery and replacing it with a 400mAh 7.4V LiPo, the performance was transformed. She climbs better and keeps going much longer (25min).

These photos were taken by my 6 year old son. I'm quite proud of him and them. Evocative lighting, dew on the morning grass in the one above. Since the photos, I've added shiny aluminium foil windows to the cabin and day-glow orange stripes under the wing (directly beneath the black top wing stripes). Both are to assist visibility in flight. More pictures later perhaps.

Starlite, by Sig / Herr Engineering

2008-09-28T14:04:00.000-07:00

So I've been dabbling with the "dark side" again. Yes, radio control, but at least it is a balsa and tissue model - 36" span and very "free flight like". I won't say any more, just show you some pictures instead.

It's a lovely, beautifully laser-cut kit available from Sig/Herr direct. Exceptional value for money, especially wood bag and plan.

Do you remember your first ever model plane?

2008-09-22T18:37:00.001-07:00

I do. I get the feeling that many (if not all) aeromodellers do too. Yes, the memories are hazy. I wonder how many of them in later years decide to build their first model again? For me it was a small 24" tow glider called the CROFTER by Ian Barrett published in Aeromodeller in 1973.

I built it during an after school club run by my teacher. Recently, I located and bought the plan for it. How weird to see it again? It's like that feeling of going back to your old school after many years - everything seems smaller and simpler than it did as a child.

I also remember the frustrations at the time, because no one explained how to trim and fly it properly. It is a simple design with Jedelsky style balsa sheet wings and 6mm balsa fuselage. Should I build (again) it or leave it for my son to cut his teeth on? Actually, it would be fun to strap it to a rocket motor! Now that's an interesting idea....

Andy Crisp's World of Free Flight Model Aircraft

2008-09-22T18:16:00.000-07:00

If you've ever met Andy Crisp, you would know that infectious enthusiasm which he has for free flight. What a character! Now Andy has just published a new book. It's one of those instant download e-books and is available at the bargain price of £2.99 from http://www.instant-books.org/

I've bought it and the transaction was smooth. I received the book in a 47 page long pdf file. The book includes many plans and notes of gliders, hlg, clg, dlg, power and rubber. It's really great to see this book - it is not only a record of some of Andy's fabulous models but also a really encouraging e-book project from Instant Books.

I wish you every success!

Video of discus launched glider DT

2008-09-10T14:16:00.000-07:00

I've not been able to fly Lipzoid much (or blog for that matter). Here's a quick view of how the glider's dethermaliser operates. In the video below, the DT timer triggers at about 3 seconds in. It brings the glider down, but could be improved (and I have some thoughts on how to do that). The second video is a rare event captured on camera. Watch out for the kite flyer near the end and sorry for the dark skies!

Model aircraft building board heals itself!

2008-09-10T13:24:00.000-07:00

I started to build a model aeroplane on the building board (see the May 2008 post below). The plane is a 1m electric job. I have to say that this is the best building board I've ever used. It holds the pins with just the right grip and "feel". However, stupid me, for using thick brass thumb tacks (or as we call 'em "drawing pins") to pin the plan down. The next photo below shows what happened to the balsa block underneath:

As you can see, the thumb tacks left significant holes and dents while the proper modelling pins (pink ones in the top photo) left negligible fine holes. However, after a quick wipe with a wet rag, the balsa healed itself "organically" in just a few minutes:

Wow, that's cool! As you can see the drawing pin holes closed up a lot and the dents have gone. completely The modelling pin holes were not an issue anyway, but even they have virtually disappeared.

I won't be using drawing pins again - I've found some finer map pins for holding plans down. Proper modelling pins are well worth buying. These are Czech ones, from Flitehook.

Who says wood is dead when it can still heal itself like that?

Building Boards

2008-05-12T15:07:00.001-07:00

My building board is knackered (for those not familiar with English slang, just read "unuseable"). A good building board is an essential piece of kit for the free flighter. The requirements are simple, it must be:

flat
easy to pin and grip pins well
big enough for your needs - long wings, bigger board

Some people are lucky enough to find a suitable fibreboard, blockboard, soft timber board or other ready made sheet in their local DIY shop or hardware store. I searched all over and could not find anything suitable. So I decided to make my own and here is the build sequence. It did not take long and cost me less than £10.

I used hard 15mm balsa planks, 4" wide mounted on a flat chipboard backing (an old bookshelf).

The planks and the chipboard were evenly coated with contact adhesive.

After 10 minutes, the planks were glued down to the chipboard. In addition to the contact adhesive under each plank, PVA glue was used between the edges of each plank. The excess PVA was wiped off with a clean damp rag.

The whole thing was weighted down overnight while the glues set.

Here is the finished board, trimmed and sanded flat. It takes pins well with good grip.

Now, what shall I build on it....?

Model gliders - all Chuck Gliders - Old and New

2008-04-13T07:29:00.001-07:00

Here is a photo of 4 hand launched model gliders. In a way, they represent many decades of aeromodelling between them. Anti-clockwise from the top right:

20" span vintage HLG by Bowers from the 1930s. This is the oldest polyhedral design HLG that I'm aware of. This one has a drinks can aluminium side flap dethermaliser (DT). Build information is shown elsewhere in this blog. Since then, I've maxed it (>60s) a number of times.

14" span vintage HLG from a range of books entitled Newnes Pictorial Knowledge. This seems to be from the 1940s and is a good basic all balsa design. I found it in a SAM35 year book.

8" span HLG based closely on Kevin Moseley's excellent LET'S ROLL design (bamboo "kebab skewer" fuselage instead of carbon fibre and dihedral angles are slightly different). This one flew out of sight on its maiden flight (literally the first hard throw). It was found months later many miles away - always write a mobile phone number on your model! When I picked it up the wing was fine and it still flew, but the tail needed replacing.

36" span tip launched glider LIPZOID. Its design and build is shown in this blog below. It follows the recent discus launch developments and I suppose represents the modern era of chuck gliders.

DLG Plan: Part 6, Finishing the glider

2008-04-11T17:49:00.000-07:00

This photo of the finished glider - LIPZOID - was taken just before its maiden flight. See the video in Part 5 below.

Parts for the left side of the fuselage. From the left: 1/16" ply, 3/32 balsa (the hole is for the DT viscous button timer - I modify the basic cheepo buttons available from Flitehook for £1.50) and 1/16" balsa. Edges were sanded so that the surfaces blend together smoothly.

After the front of the fuse is finished, I cut out the wood boom block (pine) and measure out and cut the rear of the fuse.

I ca'd a bit of thin clear plastic to reinforce the rear of the fuselage, as this will come into contact with the spruce block when the boom is up. This was then trimmed and cleaned up.

This is the pine boom block ready for gluing with ca. Then it was glassed with the cloth running round the 5mm carbon fibre tube.

Ready for drilling. It was quick and easy to drill the pine boom block first. Glued one 1/16" ply cheek and when dry, marked and drilled it. Then did the same for the other ply cheek.

Wing being glued to fuselage. I simply sanded the top of the fuselage flat to mate with the wing underside. However, because of the upsweep under the LE, I also made a small wedge shaped balsa piece to match the space between LE and fuselage.

This is a close up of the wedge under the LE.

Close up of the finished boom block socket.

Glass cloth was applied to wing joints - two 2" squares, one over the LE and the other over the TE, plus a strip top and bottom. Lightly tacked with a spray glue, ready for resin to be sparingly brushed on. In addition, the left wing was given extra reinforcement in the form of oval patches in the middle of the joint on both surfaces (not shown in this picture). The centre wing-fuselage joint was also reinforced in a similar manner.

Detail of rear of fuselage. The gf cloth reinforcement is visible as is the nylon hing bolt. I used two transparent hair bands around the boom (Lark's Head knot) looped over a bamboo peg in the middle of the wing. The yellow band is thinner pole elastic for the timer.

Detail of the boom arrangement. Pink band is 1.6mm pole elastic, tied (Surgeon's knot) to the thinner yellow elastic. The yellow is tied to nylon fishing line with a small loop tied to the end. The loop is hooked over the timer arm. Coaxing it to operate reliably (one turn of the arm should take about 1 minute) is good fun and surprisingly easy. Under the wing the pink elastic is tied to a steel pin head and run round two cocktail stick pegs. Also, you can just see the adjusting screw for decalage.

Glider with boom in the up position. Just numbers (BMFA and mobile) to apply. The finished model without ballast was 83 g, a bit heavier than I would have liked. I definitely overdid the glassing, especially on the tail. On the other hand, it's pretty strong and I reckon it will need to be because it's going to get a good bashing!

I enjoyed this design and build process. It is always amazing to see one's model fly. LIPZOID seems to be fairly stable with hardly any trimming effort so far. My tip launching was not very consistent, but thankfully, the model recovered from most of the scary attitudes. There was one very heavy landing, but just a minimal repair to the right wing was needed (I knew that was going to happen because there was a natural softer spot in the wood there). I'm now waiting for good weather to have a decent trimming session. I'd like to try increasing the decalage and perhaps moving the CoG more forward. It's at 50% at the moment.

DLG Plan: Part 5, Sneak preview Video!

2008-04-09T15:17:00.000-07:00

I will continue the build posts, but in the meantime, here's a sneak preview of the glider LIPZOID in flight today on its maiden outing. It dived off the top of the launch, but stabilised nicely in a wide right turn. Lee Hines commented on a forum somewhere that CoG at 45-50% and a fair amount of decalage works well for him. From the brief flying that I've done so far, I'd agree with that. LIPZOID is not trimmed yet as I only had a bit of time to fly today. The sky was beautiful, but it was getting dark.

DLG Plan: Part 4, Wing breaks and fuselage

2008-03-26T18:12:00.001-07:00

Photo left is just a reminder of where I had reached at the end of Part 3 in this build. The wing high point is just visible as a dotted line and both wing and fin have denser wood LE reinforcement.

After cutting at the breaks and sanding, the photo right shows what the aerofoil looked like. The walnut LE shows up nicely. The TE is thicker than I would normally finish a HLG. However, I'm nervous about strength and kept the TE at just over 1mm thick to provide some surface area for the glue and to preserve some rigidity in the wing. Quite close to AG03.

Photo left is the wing drying. Glue is Araldite Precision slow setting epoxy. It's all standard HLG building so far. 109 mm under each tip (the convenient height of a tomato tin!) .

While the wing was setting, I glassed up some 1/32" (0.8mm) marine ply using medium glass cloth and two part epoxy. This will make the wing break reinforcing braces - it's cunningly sized to fit exactly within a tenon saw cut. I may also use it for the boom hinge plates (or 1/64 ply - haven't decided yet). Poly bag below and above, then weighted down with books overnight while it set. This is the first non-standard HLG bit.

A closeup of what the glassed ply looked like when dry. Probably too much resin this time. However, job done and it's much stronger and not significantly heavier than without the glass fibre.

Also while the wing was setting, I cut out the fuselage parts. Very simple: 6mm square spruce, a carefully selected coffee stirrer (thanks Starbucks!), and 1/4" (6mm) balsa 18mm wide. Glue these together with PVA and rubber bands, with the spruce butting against the coffee stirrer.

Then apply 1/32" (0.8mm) ply cheeks to reinforce the central part. This was standard marine ply, not the glassed stuff. Again, glue with PVA. The ply cheeks also act as the locator for the carbon fibre boom.

After cleaning up the glassed ply, and sawing the wing along the high point line from the underside with a tenon saw, test fit the glassed ply wing break reinforcer. Mark with a pen above and below the wing and trim.

Cut off the excess and lightly sand up the glassed ply brace. This is what it looks like - a sort of chevron. When happy, I glued it in place with Araldite Precision .

This is what the underside looks like after the glassed ply brace has been glued into the saw cut.

I hope it's strong. So far, this is easy and relaxing building. But will it fly, or is it destined to crash into the ground with a sickening crunch?....

DLG Plan: Part 3, More work on wings & feathers

2008-03-24T16:08:00.000-07:00

For aerofoil section, I am trying to follow the AG03 by Mark Drela. He developed it for the Apogee RC hand launched glider. Unsurprisingly, it is remarkably like conventional HLG aerofoils. Walnut works well with plane and sandpaper - I would use it again.

The high point was marked with a fine felt tip pen dotted line. It is 28 mm from the front of the LE running parallel and then curving to the wingtip centre line. Use the wing tip template to draw it.

The sanded fully shaped wing weighs 40.8g. I've kept the TE at >1mm for strength.

The stab was given very little work. Just rounded off the LE and sanded the rearmost ~ 1" of the top in a taper to the TE (but not too thin, because I want to preserve some strength). A thin strip of bass wood was glued and rubber banded to the LE of the fin, wrapping it a little around the bottom edge.

Photo left is a close-up of the bass wood LE of the fin, after the bands had been removed and a bit of cleaning up with sandpaper.

Next, wing breaks, or shall I start the fuselage instead?

DLG Plan: Part 2, Cutting out the flying surfaces

2008-03-23T19:01:00.001-07:00

At long last, I had a chance to put scalpel to balsa today and cut out the wing, stab and fin. Wing is from 1/4" (6 mm, ~ 6.5 lb/ft3), stab and fin from 1/16" (1.6 mm, ~ 8 lb/ft3). The first step was to print ellipses of the right size on to thick paper and cut them out to use as templates. In keeping with the design objectives, I will not be sanding the stab and fin to aerofoil sections, but will round the leading edges and lightly taper the trailing edges.

In the photo, hardwood strip has been glued to the leading edge of the wing with waterproof PVA. I use rubber bands and masking tape to clamp it while the glue sets. Normally, I would use spruce or bass wood for LE reinforcement, but this time I used walnut D strip simply because it was there and it was long enough - I used one piece for the whole LE. The walnut bends well using steam from a kettle and the dark colour makes a nice contrast to the balsa. Should be strong too.

Thanks Stevie B for the encouragement!

DLG Plan: Part 1, Design thoughts

2008-03-10T17:31:00.000-07:00

"The time has come," the Walrus said, "to build a DLG:
Of wings - and fins - and carbon booms -

Of glass fibre - and pins -

And why the sky is bubbling -
And whether pigs have wings."

It is time for me to build such a pig. First question, shall I use an established plan or kit, like Spin Up, Round-A-Bout, Dynamo Hum, Turn Up, or other? Erm....No. Why? Because I wanna make my own! I enjoy designing. I cannot do better than the established designs. No, my objectives are different. I see this as a learning experience. I'm not going to ignore the exisiting designs. I'd like to create a free flight tip-launched glider that has the following attributes:

Simple design

Quick and easy to build

Pleasant looking

So, ladies and gentlemen, I present to you LIPZOID, well, a back-of-an-envelope sketch of it.

DESIGN THOUGHTS

The original Monster DLG by Tetsuo Itoh in 2004 had 8 panel wings. Phew! At that time, it was the fashion in conventional "javelin" style launching HLGs to have multi panel polyhedral wings (5 or more panels). A few months ago, Tim Batiuk smashed the US HLG record with his 4 panel design, Turn Up. His plan is freely available at Kurt Krempetz' excellent AMA Glider website. If I was sensible, I'd make a Turn Up (er, affectionately, "Turnip"). It has a 4.5" root chord, four wing panels and is not my own design! Maybe later.

I have 4" wide 6mm balsa in stock and want to try to make a three panel free flight DLG. 4x36 worked on Dynamo Hum, Twirly Bird and the Monster was close to that size. Three panels works for the Gambler RC DLG. Most F3K designs are simple dihedral (though of course, they have aileron servos!). There is long history in 3 panel wings in Free Flight, such as the iconic, super-performing Keil Kraft Senator rubber model, many F1A glider designs and quite a few conventional HLGs. So why not a FF DLG in 4x36 three panel? The wing can be glued up in one session and the wing root fuselage joint is a simple butt joint (no need to sand a v in the fuselage). So time can be spent instead on that lovely glass fibre cloth stuff. Fewer joints means lighter weight too.

For a bit of style, and because capriciously, I'd like to call the model LIPZOID, I decided to utilise ellipses for all flying surface planforms. My excuse is that ellipse planforms have a long history in free flight, especially in HLGs. They are also easy to print on a pc! None of this fancy drawing package nonsense, no. I use old-fashioned PowerPoint. I'll use ply biscuit(s?) and GF cloth on wings, no CF tow. It must have bass wood or spruce on LEs (thread may be ok on the tail feathers). Fuselage from 6mm balsa reinforced with GF, spruce or bass and ply, aiming for light weight and simplicity. Probably a nylon bolt for the boom pivot. Button timer and probably 2 different thicknesses of fishing pole elastic to hold the boom yet create appropriate tension on the timer arm. No throwing peg - just sandpaper top and bottom - just like Mr Batiuk.

Will it fly? Who knows? But I'm gonna enjoy finding out!

Chuck Glider discus launches Gambler AG

2008-02-18T17:46:00.000-08:00

This is not a free flight glider. I've been dabbling with the "dark side" and my chosen weapon is the Gambler AG from Wright Brothers RC.

Why am I dabbling in the dark side (aka radio control)? Well, there is method in Chuck Glider's madness. The main reason for playing with RC is to learn about discus launching - what it feels like and how bad launches go!

The latest thing in free flight chuck gliders is the discus method of launching, also called tip launching. This is a field of aeromodelling where free flighters have learned from our radio control cousins (not the other way round, as is usually the case ;) ).

The Gambler is a fine model and I've thoroughly enjoyed flinging it about to play with low level thermals. Best flight so far is nearly 3 minutes (in wintery conditions). I have not flown it in good thermic conditions yet and am looking forward to that!

The next stage would be to build a free flight DLG! So watch this space....

Polish Aircraft - Superb Scale Subjects

2008-02-14T16:25:00.001-08:00

I've been a fan of Polish planes ever since I watched a full-size Ogar (SZD-45) taking off at an airfield. This is a motor glider designed in the 1970s and is simply hypnotic to watch. No wonder they issued a stamp picturing it (left).

After I had the fortune to fly in other Polish gliders, such as the SZD Junior and Puchacz, I was hooked. They were well made and handled superbly. The SZD-55 is to my mind one of the most beautiful gliders ever.

Now here is a fabulous Polish movie, probably from the early to mid 1960s. It seems to be about wave soaring in the mountains. You need to put the sound on, because the music (Moon River) adds to the effect. Watch out for the footage of an SZD-22 Mucha Standard glider, a model sailplane (at 3:50 minutes in), the Mucha Std being aerotowed by a Gawron (4:40 to 6:30) and the super streamlined SZD-24 Foka glider (8:25).

The Polish aviation industry has a track record of coming up with amazing, ground-breaking and eye-catching designs. PZL means "state aviation works" and no doubt, early on the industry was heavily state funded. After SOLIDARITY and the rise of capitalism, it seems that some of the aviation industry was bought by the European aviation giant EADS. I have never fully understood how the industry is structured and organised. Currently, there seem to be at least two glider manufacturers - PZL Swidnik (who make the PW5 and PW6) and SZD Allstar PZL Sp. z.o.o. (who have a long history in sailplane manufacture).

In the early 1930s, arguably the best fighter plane in the world was the PZL P.11 (photo right). It had these amazing parasol, gull wings. It is not difficult to see why it is a subject for scale modellers, though perhaps not common enough. At that time, the pace of aeroplane development especially in Germany, was very fast and the performance of the P.11 was soon surpassed.

The PZL 101 Gawron was designed in the late 1950s/early 1960s for agricultural and other civilian uses. (Photo left; the tug plane in the video above is one of these). I have not seen a free flight model of it, but it would make a fine subject with those wing tip plates and slightly swept back wings.

The PZL 104 Wilga (left and below) is a fairly common subject for RC models - both scale and semi-scale. With its slightly quirky but cute looks and short take off run, it would make a great rubber or electric free flight model. It makes a good glider tug, full-size and I suppose, as a model.

The PZL 130 Orlik (below) is a very small, ~10m span, 2 seater, highly versatile training plane. It is used by many air forces and the Polish Air Force display team.

The wing planform and the proportions are fabulous (see the three-view below). This would make a lovely model plane.

Unsurprisingly, Poland has produced some fine pilots and aeromodellers too.

Chuck Glider from one 1/16" balsa sheet: Part 5, FREE PLAN!

2008-02-02T16:25:00.000-08:00

The final plan for PLAIN SAILOR is below. Right click to save it.

Flying the prototype revealed a weak point at the fin to fuselage joint. This is because the main strength at that point comes from one side of the fuselage, that is, 5mm of 1/16" balsa!

So, I cut the fuselage at the stab and trimmed the fin down, as it was too big. After re-attaching the tail feathers, the glider was much better behaved. I guess the moment arm of the prototype was too long. Compared to the prototype, the overall length (not including ballast) of Plain Sailor is 18".

Unfortunately, I do not have an indoor venue to fly in, but outdoors in the calm evening air I was getting flights of 25 to 30s. I'm sure that could be improved on with more work on the launch and transition trimming. However, this model was not designed purely for duration, but also for the other "tasks" that make up the one-sheet indoor competition, including longest glide and spot landings.

I used a small pea of blu tack on the left wing and a teeny bit of left rudder to get it flying conventional right - left. Take those trims off and it will go straight and level, since there is no stab tilt.

To make it suitable for outdoor, I would suggest gluing a thread on the LE with CA, increasing the dihedral to 2" under each tip and finishing it with 2 coats of sanding sealer with very fine sandpaper in between them. With its light wing loading it could easily fly away in thermal lift. Higher launches would require a decalage setting closer to 0-0, but as has been discussed before, that can introduce inconsistency in way the glider recovers at the top of the launch.

If you build this simple glider, please let me know how you get on.

Vintage "Old Timer" Chuck Glider

2008-01-27T12:59:00.000-08:00

I've finished and flown the Bowers glider (see photo left). It ended up at 30g flying weight, which is not amazingly light, but not heavy either. The main aim was achieved though, which was to improve over the Wallerstein 22" that I built too heavy at 50g (see earlier blog, Wallerstein was the "wing donor").

Flying at dusk in cool, still air, I was getting "still air times" of 36 to 42s. I may be able to improve the launch by moving the decalage closer to 0-0 for a more direct up line, but it's working consistently at the moment so I'll leave it alone. CoG ended up at about 60%.

In the air it looks "retro-fabulous" and floats around flatly. In the park a bloke and his son wanted to know where to get one! I explained it was self-built from a 1930s design, but did give them a closer look, explained how the DT works, and let the son have a little chuck.

I reckon it could fly away, so I fitted a simple DT flap (shown in the other two photos). This type of DT is typically made with aluminium foil from a drinks can, but I find balsa easier to work with and keep flat to the fuselage. The orange paint on the inside is an aid to see the DT operate. I use 3M Blenderm(TM) tape for the hinge, a little "fingernail" from a drinking straw to push the flap out and a balsa triangle stop to keep the flap perpendicular to the fuselage side. The airflow does the rest. There is negligible weight penalty with such a DT as the timer and parts add up to little over 1g and it is all in the nose.

There is a small increase in profile drag of course, but that will mainly affect the high speed launch, which is one of the biggest variables in any case! After testing, the flap was cut down to about 2" in length, which was found to be enough to turn the glide from the left hand circle into a straight line, while just about avoiding a dangerous "lawn dart" dive.

That's one problem with drag flaps - too big and the plane can spiral dive hard to the right and die an ugly death on crash landing. If the flap is too small, it willl not bring the glider down from a thermal and it goes OOS.

Personally, I think it is important that the flap turns the glide into a straight line, not a turn to the right, so that the plane exits the thermal.

It's all in the lap of the thermal gods!

Vintage "Old Timer" HLG plans: build pictures

2008-01-23T16:06:00.000-08:00

I think this vintage Bowers 20" HLG is going to be quite an eye-catching chuck glider. Here are a couple of build photos.

Left, the wing has been decorated, orange silk applied to the outer break joints as indicated on the plan, and the wing to fuselage joint is glued, aligned and setting.

Right, is a picture earlier in the build. The fuselage has been roughed out, the wing centre joint glued up and drying.

Plans for Vintage HLG or "Old Timer" Chuck Glider

2008-01-21T13:43:00.000-08:00

This photo is of a hand launched glider designed in the 1930s by Syd Wallerstein. It qualifies as "Vintage" according to SAM rules. While pretty, the fuselage is heavy pine and so it flies like an overweight hippo. My best flight with it is 55s, which is pretty poor for a 22" span glider. This "fat boy" weighs in at around 50g. The streamer on the nose is an experimental dropping ribbon DT (which actually worked fairly well).

I'm going to re-use the wings on another vintage glider. The chosen design is also from the 1930s and is by Peter Bowers. I guess he is the same aviator who according to Wikipedia went on to work for Boeing and design the Fly Baby homebuilt aeroplane.

I have no idea how the Bowers 20" HLG will fly, but it is an attractive build for various reasons. First, it is the earliest polyhedral HLG that I'm aware of. Second, it seems to be the very early work of Bowers as a young man (possibly while a teenager) before he went on to become such an accomplished pilot and aeroplane designer. Third, the use of silk on the wing joints is interesting and I have a bit of orange silk knocking around.

The tail moment looks a bit short by modern standards and consequently, the tail feathers have a comparatively large area. It should be fun.

Wings of the Wallerstein cut off, reshaped and then sliced into sections, ready for joining into a Bowers wing. One of the advantages of cutting a wing is that you are able to see the aerofoil cross section. In this case, it was clear that more sanding work was required. You may be able to see that I've avoided the high point line.

Peck Polymers takes over Sting

2008-01-20T05:04:00.000-08:00

Last month, Sting Aero, was snapped up by Peck Polymers in the USA. Sting Aero was a business run by Len Surtees in Australia (photo, left). It was acquired by Peck Polymers/A2Z Corp in an impressively quick transaction.

I suspect that Len did not make the decision to sell lightly. Tim G of Peck clarified: "Sting Aero Product will become a product line that we sell through our Peck Polymers online store in addition to selling through other dealers". (When you click on the link above, click on "FF Gliders" on the left to see the range).

Peck Polymers should be a great home for Len's product range, which includes the following superb, successful English designs (and I would say design classics):

- BUTTERFLY, by Mick Page (photo, right)

- 2KAN, by Mark Benns

Both are UK Nationals winners. Butterfly kits started shipping soon after the acquistion and other kits are ready or nearly prepared to be offered for sale. The range also includes Len's STING HLGs (various spans and past Australian Nationals winner) and the more recent SPIN UP range of DLGs, by Mark Benns which are all established winners.

Tom Norell of Peck Polymers has confirmed that they will also take over running the annual Heave Ho postal contest. This is a popular, informal worldwide competition originally started by Kevin Brown some years ago. Tom also said:

"We here at A2Z Corp./Peck Polymers hope to continue Len's tradition of high quality competition kits and accessories. If you need something that is not listed yet or have any suggestions feel free to email me directly here at the plant. tomn@peck-polymers.com"

Chuck Glider wishes you all the best of luck!

Chuck Glider from one 1/16" balsa sheet: Part 4, Trimming

2008-01-15T17:08:00.001-08:00

Here are a few views and a video (below) of the finished plane. See Part 5 as well, for further developments.

I think it looks neat, so thanks to the wife for choosing this wing profile!

I've decided to call it PLAIN SAILOR because the build was easy, it seems to have produced a decent performance and exactly as designed.

A view from underneath.

With the balance at 63%, I did some glides from the shoulder. I was pleasantly surprised that it needed no trimming at all. It flew straight and level in a good, floaty glide. No elevator or rudder, washout, washin etc required at all at this stage.

This one flew right off the board!

Here is a video of a test glide from the shoulder. It was blustery 20 mph winds today, but I managed to gently glide it a few times during lulls. Indoors, in the living room, it is very stable and floats serenely with a nice flat glide (I can tell because it hits the curtain high up on the other side of the room). Now I need to find an indoor venue to trim and fly it properly. For example, perhaps the stab or fin could be reduced in area.

If you make PLAIN SAILOR - see the FREE plan in part 5 (Feb 08) of this series of blogposts, and build guide below - please let me know how you get on.

Chuck Glider from one 1/16" balsa sheet: Part 3, Building

2008-01-15T13:22:00.000-08:00

I've been building at night and it has been murky and overcast lately, so apologies for the dark pictures. Here we go step-by-step:

Photo 1. After looking at the grain, deciding which side will be the wing and fuselage, make the first cut dividing the sheet into 17" and 19" pieces. (NB. the final version requires an 18" piece for the fuselage, not 19" - see Part 5 of this series of blogs).

Photo 2. Marking out the fuselage. Cut a 22 mm strip from the 19" piece and then mark 4 mm at each edge.

Photo 3. Here are the fuselage sides, fin and stab cut out of the 19" piece. The back of the right hand fuselage side is trimmed to accommodate the fin. See photo 4. When deciding which piece should be which, ensure that any natural bow in each side opposes the other. This helps to prevent a banana fuselage! (But don't worry if you get a bend, as it can be steamed out easily over a boiling kettle).

Photo 4. Note sharper taper over last few mm of fuselage. Glue the fin in place and then the fuselage sides together. Use PVA and spread it out thinly on both faces.

Photo 5. Place a steel ruler and weights over the whole fuselage and fin assembly while PVA dries.

Photo 6. Shaping the wing. First, round off corners and the LE. For the slope, I felt that sanding the top surface from 33% as originally planned may compromise strength. I decided to taper from 50% of chord. Take care with the razor plane! The blue masking tape prevents errors with the sanding block.

Photo 7. Sanding wing break joints. The sanding block face is kept vertical, and the tip is placed as shown to get the right slope. The middle panel joints are sanded while it is flat on the board. With care, it is easy to get a good joint with such a thin wing.

Photo 8. Wing glued up. Middle panel weighted and tips have light weights (balsa off cuts) just to keep it all lined up. I used Araldite Rapid epoxy, spread evenly on both joint surfaces, but thinly.

Photo 9. Here are all the parts ready for assembly. I made a throw tab - it adds strength to the wing-fuselage joint and would be useful for duration tasks. The long thin piece is the nose skid.

Photo 10. Use CA to glue on the skid, and rubber bands to hold it while it dries. Looks like the nose will be quite strong, so I would be able to taper it later for a better appearance.

Photo 11. Thin the stab. You should be able to see translucent light through it near the TE.

Photo 12. Sand the fin thin as well.

Photo 13. All aligned and glued up. Rubber cutting mats are great for this. Use a set square to ensure that everything is square, especially the fin is perpendicular to the stab (while the stab is flat on the mat).

Photo 14. Check tip heights before the glue dries!

Photo 15. Shape the nose. The skid ensures some strength.

Photo 16. Glue and shape the throw tab - note grain direction. Not easy to see at this angle, but the skid overlaps the sharp end of the tab by ~ 5 mm.

Photo 17. Add blue tack to balance at about 1 1/8" in front of the TE, that is about 63%. Total weight came out at 10.4 g.

All done, lovely!

Chuck Glider from one 1/16" balsa sheet: Part 2, PLAN

2008-01-12T14:12:00.000-08:00

As I said, I could not decide on the wing planform. So, I asked my wife to choose one out of D, E, F and K. She went for E. Why? Because it looked the best. Good enough reason for me! I suppose E requires the least amount of work too, which is in keeping with the Design Objectives.

FREE PLAN!

I sketched out a quick plan for the prototype (left). PLEASE NOTE: this is for the prototype - the final plan is in Part 5 of this series of blogs (in Feb 08). You can download by right clicking and then saving. Each square represents an inch.

DESIGN DETAILS

1. All dimensions are inches except for the close-up of the fuselage cut lines, which is in mm.

2. Longish nose for less overall weight. Some indoor gliders have really long noses.

3. Nose skid for hard landings.

4. Wing aerofoil: flat underneath, sand the LE to an elliptical profile, top and bottom parallel for about 33% and then sand a taper on top to as sharp as I dare at the TE. (Most lift force from a wing comes from its angle of attack, not its aerofoil shape. Here, I'm just trying to improve on the "flat plate". Perhaps Prototype 2 will have undercamber...)

5. The TE of wing tips, stab and fin should be really thin so that trim can be "breathed and bent" into the balsa. (This is the typical HLG way to warp flying surfaces for trimming).

6. Build it straight (no stab tilt, wing offset, skew, etc). It should fly straight and level! Turn can be induced with blue-tack on one wingtip, a bit of rudder and wing warping.

7. Laminated fuselage. Two pieces of 1/16" balsa stuck together. The glue must be PVA, because the adhesive line will provide some flexible strenth. Hopefully, it won't weigh too much. The taper in the fuselage, wing on top and stab underneath means that there is some built in decalage, but it is very close to 0-0.

8. Longish moment arm (distance between aerodynamic centres of wing and stab), for stability.

9. Try to keep the back end light. This means sanding down the stab and fin so that they are quite thin, a tapered fuselage with a sharper taper over the last inch or so and using glue sparingly.

10. I have guestimated the amount of polyhedral and the areas of fin and stab.

I'll build her and post photos as I go. I'm hoping that the weight without ballast will be under 14g (ideally, the flying weight with ballast should be under that). That would make the wing loading about:

0.5 / (46 / 144) = 1.6 oz/ft^2

That's lighter than a typical outdoor HLG, but heavier than an indoor duration HLG (which are ridiculously light). Have to think of a name....

Chuck glider from one 1/16" balsa sheet: Part 1, Aims

2008-01-12T05:58:00.000-08:00

There is an interesting thread on the Small Flying Arts forum, started by Allan Wright (the designer of the Gambler AG radio control discus launched glider DLG). It is all about designing and making a chuck glider out of one balsa sheet of dimensions 3 x 36 x 1/16". You are allowed to use glue and clay for ballast, but nothing else. The glider is to be flown indoors on various tasks. E.g. longest glide, duration, spot landings, etc.

Very interesting challenge. I thought it would be fun to go through the design process and share it on this blog.

DESIGN OBJECTIVES

I decided that the main aims are:

1. A good glide. So this means maximum span and minimum weight (which is the same as min wing loading and max AR - see earlier blogs on L/D)

2. Stability

3. Trimmable for straight flight AND a turn. This is different to the usual HLG objective, which is a thermalling circle (usually a left turn for a right handed thrower))

4. Reasonably robust (for the spot landing) but not a "tank". This means that the extremely light weight Indoor HLG designs are out of the question

5. Simple design and easy to build - suitable for a beginner

MATERIALS

There is a huge variation in balsa. My 1/16" sheets vary from 9g (very light and flexible) to about 20g (hard and stiff). I'm going to make the first prototype from mid weight stuff. After playing with my sheets and waving them around (which I must admit was fun) , I decided to go for a 17 x 3 inch wing.

PLANFORMS

I did the sketch above on the train while commuting. Squared paper allows you to estimate wing area.

Planform A is the whole rectangular sheet: big area, 51 in^2 and AR of 5.7

Planform G is sort of elliptical: area is 43 in^2 and AR of 6.7

The others are somewhere in between

Planform A would have the most lift and drag, G the least. The shape also affects the strength of the wing, especially at the tips. I have probably decided that the design will be a 3 panel polyhedral (two breaks). This allows easy gluing to the fuselage and since each panel is small, more stiffness and strength. Lighter tips are better.

At the moment, my favourites are D, E, F and K. Hmm....need to think about this....

Angle of Incidence and Decalage in HLG

2007-12-27T03:39:00.000-08:00

This is one of the real secrets of HLG flying. A stubborn glider that does not launch well can often be transformed into a fine performer by changing the angle of incidence of the stab or the wing. The photo (left) is DOGEAR, a 6 inch span hand launched glider that I designed and built. It did not launch well until I replaced the stab and now it's great. Its first ever timed flight was 38 seconds.

Why and how?

Angle of Incidence is the angle between the wing's surface and the fuselage axis. (Usually for polyhedral wing models, you can place a ruler flat with the underside of the wing near the root chord to get an idea of the incidence).

Decalage, geometrically and simply speaking, is the angle between the wing's surface and the stab's surface. If you were to use a ruler under the wing and another ruler under the stab as described above, then it is the angle between the rulers. See the diagram here.

0-0 (said "zero-zero") is when the two surfaces (or rulers in the example above) are parallel.

Some HLG modellers swear that 0-0 is the best setting. On the other hand, many others (including me) say that a HLG should have a small decalage. When I say small, I mean small. For example, if the stab has zero angle of incidence, then the wing should have just a few degrees positive, e.g. the LE of the wing is 1-2 mm higher than the TE. What I can say is that the vast majority of HLG pilots say that "large" decalage is bad. Now, bear in mind that it is not easy to measure AOI accurately even with rulers and "large" is really a referring to a small measurement.

How to recognise large decalage?

Usually, you see a loopy launch. Instead of the plane arrowing up in a straight-ish launch, it loops round and may even execute a full loop frighteningly close to the ground. In addition, such a model may balance well-forward of the ~2/3 rule: generally, for traditional HLGs the Centre of Gravity is at around 66% of the root chord (i.e. closer to the TE than the LE). To compensate for the large decalage, the CoG of such a model may be at 40% or less. Too far forward.

Your throwing energy is converted into a pretty but dangerous low level aerobatic manouvre, not into height!

How to recognise small decalage?

Straight up and straight down! It goes up like a rocket and down like an arrow. Sadly, there is little or no glide bit in between. Hopefully, it will not land with a sickening crunch. You may see quite a lot of "up" elevator bent into the stab to compensate.

If you have a HLG that does not launch well, try altering the decalage. Yes, that may mean removing the stab, sanding and/or planing the rear of the fuselage and fitting a new one, but it is well worth it. For a pod and boom model with tip up wing or tipping boom, you can insert a set screw or thin shim that for fine adjustments.

There is nothing like seeing your glider rocket up and flip over beautifully into a stable soaring pattern high in the air.

Free Plan! Indoor Fun Glider: Man-o-Straw

2007-12-08T19:32:00.001-08:00

Fancy something to chuck around the house during winter? Need a quick glider fix? Man-o-Straw takes just a few minutes to build out of paper and straw. It's just a bit of fun. However, on another level, you can use it for prototyping larger models. Since it can be made quickly, the design provides a convenient way to explore aerodynamics and to experiment. You can try out wing planforms, mess around with dihedral, polyhedral and wing tips. Most importantly you can experiment with tail moment length, rudder and stabliser sizing. And the kids love it (including the adult ones)! Just click on the plan to download the .jpg file:

Get a Load of this! Glide Angle, Wing Loading & Span Loading

2007-09-29T10:36:00.000-07:00

You wanna fly model planes, so why bother with all this glide angle and loading mumbo jumbo? Well, because it is helpful and, as Mr Spock famously said, "fascinating". Glide angle is a fundamental concept. Wing Loading and Span Loading are important design considerations that affect the model's performance. In this post, I will explain the terminology and try to describe what it means. There is some maths, but don't let that put you off!

GLIDE ANGLE

Figure 1. Showing a plane in steady glide and how the lift force and drag force relate to the glide angle.

L is the lift force generated by the wing.

D is the drag force experienced by the model.

W is the model's flying weight.

h is the height above ground.

x is the distance travelled.

Glide Angle or L/D (pronounced "ell over dee") is an indicator of a glider's performance. From the geometry of the forces acting on a glider in steady flight, you can see that the glide angle relates directly to the ratio of the lift force over the drag force, regardless of the weight of the plane. The maths is set out in Figure 1 (above). High lift and low drag means a flatter (more horizontal) glide. The plane flies forwards, not down like a brick!

WING LOADING & SPAN LOADING

Wing Loading is simply the weight of the plane divided by the wing area. Span Loading comes in two "flavours". The first is the weight of the plane divided by the span. The second is the weight of the plane divided by the span squared. Unfortunately, both are referred to as "span loading". For convenience, I will call these Span Loading v.1 and Span Loading v.2 respectively.

Referring to Figure 2 (below):

Wing Loading or WL = W / S
Span Loading v.1 = W / b
Span Loading v.2 = W / b^2

Figure 2. Showing the important areas for Wing Loading and Span Loading

where:

W is the flying weight of the model.

S is the area of the wing (in blue in Figure 2).

b is the span, and S = ab, where a is the mean chord of the wing. The red area in Figure 2 above is b^2.

Qualitatively speaking, lower Wing Loading means that the model:

climbs better, both under power and when gliding: it has a "floatier" glide
flies slower with respect to the air
requires a shorter take off and landing for rise off ground models
is more prone to being bumped around by turbulence

Lower Span Loading v.1 means:

less drag at lower flying speeds, that is less "induced drag

Lower Span Loading v.2 means:

better glide performance, that is, a flatter more horizontal glide angle

Taken all together, the above indicates that a light weight plane with big span would be ideal. Just consider a typical full-size soaring glider (or 'sailplane' for readers in the USA). For example, the famous and beautiful Duo Discus. I've flown one of these and it was absolutely lovely. In these glass ships, when you push the stick forward, the plane just whooshes forwards (not downwards!).

Note that you can also reduce the Wing Loading (WL) of a given design by increasing the wing area while trying to keep the weight increase to a minimum. However, if you do this by increasing the wing chord alone while keeping the span the same this may not result in a flatter glide. Hopefully, these intricacies will become clearer after you've read the rest of this post.

LEARNING FROM MATHEMATICS!

I suggest that there are three equations worth considering, playing with and understanding. This is quite rewarding and helps to develop a feel for some basics of aerodynamics generally. They are:

Or, when limited by my keyboard:

L = q S CL ......(1)

Di = q S CDi ......(2)

CDi = (CL^2)/(pi AR E) .....(3)

where:

L is the lift force. For a decent model in a steady glide it is essentially equal to the weight.

q is 1/2(rho v^2), also called the "dynamic pressure". Rho is the air density, v is the airspeed.

CL is the coefficient of lift (which depends on angle of attack of the wing).

S is the area of the wing (see above).

Di is the induced drag force. The total drag is this plus the drag from other sources (skin friction and form drag). At lower speeds, the induced drag dominates.

CDi is the induced drag coefficient.

pi is its usual 3.14...

AR is the aspect ratio, that is the span over chord: AR = b/a = b^2/S.

E is a factor relating to the efficiency of the wing. It depends on the design and shape of the wing, 1 for perfect shape, otherwise less than 1, 0.7 is typical for a rectangular planform.

Eeek! What does all this mean?

First, there are some basic ideas contained in these three relationships.

The lift force depends directly on the wing area. Bigger wing, more lift. When the plane goes faster, the lift increases as the square of the airspeed. That's why jet airliners look as if they have smallish wings in relation to the size of the whole plane. Lift from the wing is greater at sea level than in the mountains, where density is lower. So your model may not fly well if you move to a flying location at a different altitude. The drag increases if you decrease the aspect ratio while keeping all else the same (which goes part of the way in explaining why increasing chord to reduce Wing Loading as discussed above, may not lead to a flatter glide).

Substituting (1) and (2) into (3) gives the induced drag:

Di = L^2 / (q pi E S AR) = (L/b)^2 / (q pi E)

This tells you that the induced drag depends on the quantity L/b squared. As mentioned above, in a steady glide, L is essentially the weight of the plane, W, so L/b is the same as Span Loading v.1. A small increase in Span Loading v.1 increases the induced drag significantly because of the squared relationship.

Dividing both sides by L gives the very important Di/L ratio (often referred to the other way round as L/Di):

Di/L = (L/b^2) / (q pi E)

From the geometry of the forces acting on a gliding aircraft, it is a measure of the glide angle (please see Figure 1 to see why). The above relationship shows that Span Loading v.2 is a key determinant of the glide angle (again using the relationship that L ~ W in a steady glide). The smaller Span Loading v.2, the flatter (more horizontal) the glide angle. Also, the more efficient the wing design (E gets closer to 1.0) and the flatter the glide angle.

Another thing to note from the above equations is that Span Loading v.2 = W/b^2 is just the same as WL/AR (just divide top and bottom by wing area S). This explains the point that I made above that reducing the Wing Loading by increasing the chord alone and not the span, may not flatten the glide because although the Wing Loading reduces, the AR decreases as well. We can now see that it will not flatten the glide unless the ratio WL/AR decreases overall.

CONCLUSION

Summing up, if you want to improve the Glide Angle of your model, then concentrate on reducing Span Loading v.2 and on improving the wing's design and efficiency (airfoil, planform, etc). In free flight, good models also tend to have low Wing Loading, at least for calm conditions.

I hope this gives a flavour of how powerful this stuff can be!

Top Tips for Free Flight model making

2007-09-25T14:54:00.000-07:00

Free Flight Aeromodelling is not new by any stretch of the imagination. One of the most celebrated models of the 19th Century was this rubber power job by the amazing Alphonse Penaud called the Planophore or Planaphore, c.a. 1871:
All the modern aspects are there. This was about 20 years before Otto Lilienthal's daring gliding exploits and those of Percy Pilcher. Both aviators died as a result of plane crashes. The Wright brothers began to solve the control problems in the first few years of the 20th Century.

With so much development over a great deal of time, you'd think we may have learned something by now!

Here are five things that may help you to improve your free flight aeromodelling skills:

1. Build light. This means that within the relevant rules, the model should be as light weight as possible. If a model is built so tough that it is crash resistant it will be too heavy to perform really well. Generally glue is heavy. Choose materials wisely. Balsa is amazing in terms of the strength to weight ratio, but there is a great variation between planks as well. I had a balsa board that was as dense as spruce. I've not been able to utilise it in a model plane.

2. Stability is really important. It's no use having the flattest glide ever, if the plane spiral dives to earth whenever it hits a bit of turbulence. Learn about stability. Try to adjust or re-design planes that are not stable.

3. Learn to "pick good air". Get a mylar streamer or a 10 ft piece of old audio tape and attach it to the top of a tall pole. Stand it upwind of your launch point. Watch it carefully and work out what it does as the air changes. It will move around to show the wind strength and direction. Importantly, you may be able to feel cool air when the streamer points downwards and warm air when it points upwards. Thermals are often marked by a rise in temperature, a drop in the wind strength and a change in wind direction. It takes a lot of practice to learn to launch your model into lift.

4. Do try to minimise drag of the plane. However do not increase weight to do so. Putting it simply, at low flying speeds, one type of drag dominates while at high speeds, another type of drag is more important. The low speed one is due to the disturbance created by the model, mainly the wing and is called induced drag or vortex drag. The high speed one is to do with the form or profile of the plane, and its skin friction. Read up on drag and design accordingly.

5. Keep excellent records, notes, plans and sketches. For example, your model's flying weights and "still air" times (taken for flights in the early morning or late evening on calm days) are invaluable resources later. Design ideas can come out of the blue, so it may be a good idea to have a pocket book to jot them down in.

To close this post, here is a photo and some info about a century old, patented, rubber powered canard, by T.W.K Clarke that I snapped from the London Science Museum. I guess it was around 50 inches in wing span. Those years would have been exciting times for aeroplane lovers...

FREE CHUCK GLIDER PLAN!

2007-07-30T14:32:00.001-07:00

"Jellybean" 18" Hand Launched Glider - "HLG" model glider or "Chuck Glider"

I enjoyed designing and flying this model glider. The name "Jellybean" comes from the appearance while it is flying. From underneath, the tissue is backlit by the sky and the colours reminded me of jellybean sweets. Use it as a second model, or decent beginner's competition HLG. It can be fairly competitive - I've 1 minute maxed with it quite a few times and thankfully, it has not yet flown away!

No DT, but one could be fitted (e.g. side or top flap made from an aluminium drinks tripped by a button timer).

I haven't figured out how to make and attach a .pdf file, but hopefully, you should be able to copy and save the above .jpg file on to your computer and use some image manipulation software to enlarge it.

If you try this model, I hope you enjoy it as much as I have.

The photo below shows some of my other designs:

Dogchew 6" span HLG (for plan and build notes click here )

Oompah 16" span HLG

P30 - Ideal for Improvers

2007-06-27T17:23:00.001-07:00

Did you enjoy building and flying your first rubber powered model? Are you hungry for more? A P30 class model may be the perfect answer. This class is a few decades old and is very popular. It suits the developing modeller and also provides a real challenge for experienced fliers. The rules vary slightly country to country, but in essence are:

1. Wingspan and overall length each less than 30 inches.

2. Plastic commercially available non-folding prop less than 9.5 inches in diameter.

3. Rubber to be enclosed within the fuselage.

4. Rubber including lubricant to weigh less than 10g.

5. Model without rubber to weigh 40g or more.

These things can fly! Two minute maxes are not difficult to achieve. Flyaways are common, so you need a good dethermaliser. The minimum DT is the pop up stab - see the photo at the bottom. While these are ok, they may be insufficient to bring the plane down from a strong thermal. More drastic DT is the pop off wing. The wing tip is connected with a line to the rear end of the fuselage. When the DT releases, the wing comes off. The fuselage hangs down and the wing spirals around as the plane descends.

These are photos of my first P30. It is based on the Roger Dodger design, but I could not help modifying it in various ways.

The photos also show a simple design for a "stooge". This is basically an anchor point to hold the plane while you wind the rubber with a mechanical winder. It is also advisable to use a "blast tube". Mine took 5 minutes to make out of a piece of 20mm plastic piping that I had lying around.

Below is a brief video of the model at the top of the power climb. It flew OOS on that occasion, but was later recovered (thank Hung I wrote the phone number on it!) That happened because I set too long a time period on the DT. Doh!

Free Flight models can fly OUT OF SIGHT!

2007-06-25T06:53:00.000-07:00

Flights that go OOS (out of sight) create mixed feelings. In competition, they can mark the end of your flying day. In recreation, they are a little upsetting, but in an odd way satisfying. After all, the model has performed very well to stay in lift for so long. There is a theory among aeromodellers that the thermal God, known as "Hung", takes only the best models away. This is so that good people can play with them in the afterlife :)

Here are some tips:

1. WRITE YOUR MOBILE NUMBER CLEARLY ON THE FUSELAGE AND WING

It is worth it! Two of my models have flown OOS in the last year. One, an 8" span HLG, was found months later a few miles away in the woods by an old lady out walking her dog. The other, a P-30 rubber plane, was found about a week later in front of a house. It must have been on the roof for a while, because the prop was still stuck up there. In both cases, the finder rang the mobile number and the models were back in the air after just a little repair work.

2. ALWAYS GIVE THE FINDER A LITTLE GIFT

Chocolate is good, wine for adults is ok too.

3. FIT A DETHERMALISER.... OR BUILD LOTS OF MODELS!

DT's are a subject in themselves. Examples are:

Pop up flaps (side or top)
Dropping weight
Dropping streamer
Pop up stab
Pop up wing
Pop up tailboom, also called "broken back"
Pop off wing

However, even if you have one, it does not mean that it will bring your plane down safely. Things can go wrong. For example, the DT may not be powerful enough to make the model descend out of strong thermals. Or the DT may fail to operate. Some people just don't bother with DTs, but instead just make lots of models. If you are into competition, I think you need to learn how to make and fit DTs and use them consistently.

Make your own Propeller

2007-06-24T00:29:00.000-07:00

Why?

Why bother with carving a propeller when you can buy a plastic one cheaply? Surely a balsa prop would break easier than a plastic one, I hear you say. Perhaps that is true, but I was surprised by the robustness and lightness of my first self-made prop. Less weight spinning around means easier trimming, not to mention a lighter model.

How?

I followed the inspirational instructions provided by Dannysoar here. I did not have a block, so laminated bits of 6mm balsa that were lying around with PVA glue. One piece was a "dog" because it was so heavy. It is almost as dense as spruce and I could not find any use for it in my models. So I used that piece as the topmost sheet, that is, to be the front or the leading edge of the prop. Also, I was careful about aligning the grain of each sheet so that one piece was not running opposite. This prevents "snagging" during the carving. I sawed the block into triangles, marked and glued it (photo above) this time with epoxy. Then started carving with a normal craft scalpel. Balsa cuts easily and it was really quick.

The photo on the right shows the initial carving. Basically, you carry on, try to keep it even, then shape the tips. Every now and then, put a piece of wire through the hole and check the balance of the prop. Remove material from the heavier side. Carefully glue some tubing in the hole, check balance, sand and smooth it off. You will need some form of free-wheeling device. I used a simple Z bend clutch - called a Garami. This prop was for my Cloud Tramp. It flies much better than it did with the plastic prop.

The photos below and on the left show details of the Garami freewheel clutch and the finished prop installed on my Cloud Tramp. As a final job, I superglued thin cotton thread to the LE for protection. So I've found a use for that heavy balsa after all! Even though this laminated prop had lots of glue in it and the heavy bit of balsa, it was still 20% lighter than the plastic prop. Wood is a difficult material to beat...

It is a very satisfying thing to do and much easier than I expected. Since the pitch of the wooden prop is higher, the duration of the power run is longer.

I think it also looks prettier.

Trees

2007-06-23T11:08:00.000-07:00

Trees attract balsa. Even if there is only one tree around, you can guarantee that your model will end up in its highest branches. Here are some tips for recovering your work from the clutches of a "balsa magnet" otherwise known as a "tree":

Don't fly where there are trees!

It is not worth risking your life to get it down, even if did take a long time to build. This means: do not try to climb the tree

Watch the model carefully. Binoculars are useful. Note where the model landed - not just which tree, but where in the tree

For lower level stuff, use a 6m telescopic fishing pole. In England, these are called a "whip". Buy from eBay or online for just a few pounds. Put some white tape at the end, so you can see the tip. Use it gently, or you may put a hole in the wing!

For higher level stuff, use the ball and line method. This involves looping strong fishing line over the correct branch, taking hold of both ends and shaking until the model falls out. To get the line up there, attach a weight to it. A heavy-ish ball the size of a tennis ball is good, because you need to be able to throw it accurately. Throw it as close as you dare to the model over the branch that it is snagged on. The fishing line should be heavy duty (at least 10kg (approx. 20lb) strength). Attaching the line with loads of plastic parcel tape to a tennis ball can work fine. I used it to get a plane down from the tree in the photos here..

The plane was stuck just next to the ball that you can see here. It was at about 10m high. This is a lovely oak tree. However, we got down eventually, with no harm to tree or any person. I'm afraid, a ball was left behind, but it did fall out later.

Jargon Busting!

2007-02-23T10:25:00.000-08:00

Ah, Jargon! Love it or hate it, there is a lot of it. Some is really important to know. For example, bits and pieces of information that relate to "trimming", that is, getting the best performance out of your model. Other terminology is more esoteric, and arguably, not necessary for you to enjoy the sport of Free Flight (and it is officially a "sport" in the UK). I'm not proposing to explain all of the jargon. Instead, I'll list a whole raft of it now. Later, I'll explain some of the important terms, or at least give you a link to more information. So, in no particular order, here's a list:

Lift
Drag
Best L/D
Min Sink
Polar
Centre of Gravity
Centre of Pressure and Aerodynamic Centre
Angle of Attack
Angle of Incidence
Dihedral
Decalage (sometimes called Longitudinal Dihedral) - great diagram here
Moment Balance
Stab Up, Stab Down
Stab Tilt
Stab Twist
Stall
Sideslip
Dutch Roll
Wash Out
Wash In
Tip Weight
Wing Offset
Wing Planform
Aspect Ratio
Wing Area
Wing Loading
Chord and Mean Aerodynamic Chord (MAC)
Aerofoil section
Camber
Thickness
Winglet
Dethermaliser, or DT, or Dethermalizer
Span Loading (two flavours)

Watch out for "those that prowl in them thar Parks!"

2007-02-20T15:04:00.000-08:00

Because, this is what can happen to your model aeroplane!

Cloud Tramp

2007-02-19T14:47:00.000-08:00

My Cloud Tramp. This 22" span classic is one of the rubber models that I would recommend for a beginner (see previous blogs). It is fairly easy to build. Powered by six strands of 3/32" rubber (three loops), it climbs beautifully especially in lift. This gives a motor run of about 50 s. Best flight so far is around 90 s. It's OK under power, but the glide is not as flat as a decent hand launched glider.

And here is a photo earlier in the build of the fuselage, undercarriage legs and stabiliser:

Getting Started

2007-01-26T11:38:00.000-08:00

Sorry for the delay since the last blog – I’ve been travelling. Here are some specific recommendations for beginners on what to read, good first models, where to obtain plans, and other things that you need to get started.

Reading Material

- Gliders especially HLG:

Flying Hand Launch Gliders by John Kaufmann, 2006 edition

This is a classic read, for any modeller, but is really useful for hand or catapult launch glider flyers. It can be bought from the National Free Flight Society at the reasonable price of US$13.

An introduction to HLG, superb how to build and fly tips and a nice selection of plans are available from Mike Chapman's wonderful site called F4Bscale.

- Free flight generally:

SmallFlyingArts has great tips, articles, and the best free flight discussion forum on the web with a truly massive wealth of knowledge to look over.

- For seriously addicted free flighters:

British Model Flying Association Free Flight Forum reports, published annually.

Freeflight Quarterly, a magazine on free flight matters, technical and historical, published - you guessed it - quarterly.

Good First Models

I believe that building from plans provides the best experience for a budding free flighter. Following the guidelines on my last blog, here are some recommendations for satisfying, easy to build and not too big first models:

Gliders:

Dogchew, 6” span – plan and building notes available here.

Simple 10 or WAM 10, both 10" span, by Heman Lee and Emile Carles respectively - plan available from the Free Plans page of the Aeromaniacs site.

Baby Jazz, 13” span by Andrew Hewitt - plan available from Mike Chapman's F4Bscale site.

As you will see, each of these has only one or two wing joints, which makes them simpler to construct. I wouldn’t recommend a bigger glider for a first model. For why, please see my last blog.

Rubber Power:

Recommending plans for beginners is easy:

Cloud Tramp: I would suggest that this is now a free flight design classic, with many fliers worldwide. The original article and plan are available from The Plan Page (click on "Special Things"). The Cloud Tramp model also has a dedicated website for its afficianados.

The Squirrel is a very well-thought out design. Involves tissue as well as balsa, yet is easy to make and ideal for beginners. A very light design that flies well indoors and outdoors.

Also worth mentioning are the Dart and Gyminie Cricket available cheaply via the Educational Kits page of the BMFA. In addition, the AMA Cub (also known as the Delta Dart). Kits can be purchased very cheaply form the webstore of the AMA.

Sources of Plans

In addition to the websites mentioned under Good First Models above, the best recommendation I have is to take your time to go through this excellent collection of links to free of charge free flight plans compiled by DB Design Bureau.

There are lots of other sources of plans where payment is required, and prices are usually low. Please respect copyright, read notices where provided and in particular, do not deal commercially in plans without the copyright owner's consent.

Tools and Stuff

I regard the following as essential tools, bits and pieces for the first model:

A source for balsa wood – not difficult to find over the internet. As you get more experienced, you will need to be more selective about the quality of the wood you use. In the UK, I recommend Flitehook, Blackburn Models and FreeFlightSupplies.

Flat smooth cutting surface. E.g. fibre board, and old large kitchen chopping board or a plate of glass.

Squared paper or one of those rubbery cutting boards that has squares ruled on it. This is useful when you assemble your model, because it makes aligning the parts so much easier by truing things up by eye to the squares.

Card, pencil and scissors – all needed to mark out and cut templates (e.g. of the wing profile from the plan).

Craft knife or scalpel.

Sand paper of various grades (best to wrap and pin it to a block of wood).

Glues – Epoxy, PVA white wood glue and Superglue. Each has its uses. Try them all and learn about their relative advantages and disadvantages.

Ruler and square. For marking out and aligning parts. Plastic school/office types are fine, but you will need a metal one for cutting lines.

Sanding sealer, non-shrinking dope or a spray varnish for a lightweight finish to the wood.

Your First Model

2006-12-20T09:58:00.000-08:00

Choosing your first model is important. Go for one that's too tricky and you could easily get put off the whole "aeromodelling thing". On the other hand, the model needs to have enough potential for performance to keep you interested and challenged.

If you have a reasonable ability to throw, the best starting point for a fledgling free flight modeller is the hand launched glider or "HLG". In this category, the aim is to keep your model up as long as possible. Usually, maximum points are scored for a flight of 60 seconds (a "max").

It took me a few months to achieve that magic first ever max. I remember it well - Although it was a pleasant evening, it was not the perfect day for flying - which would be a day with light wind and hot sunshine. I did it first with a 17" glider and then a few minutes later with a 12" span glider. Since then, I've done it with gliders as small as 8" and 6" span. A great warm feeling all over....

In competitions, you normally get a number of launches e.g. 6 or 9. Also, in many competitions, your flight will not be counted if you land within 10 seconds, provided the next flight is over 10 seconds!

HLG is a great starting point to learn about trimming (the art of getting your model to fly really well). I would recommend a smaller span glider initially, because such models:

have less momentum so are not so easily broken by the inevitable "handshake" with the ground

are quicker to build.

Both these count towards more fun for less expended time and effort!

If you are doubtful about your throwing arm, then the alternative recommendations for a first model are catapult launch glider ("CLG") or a simple rubber-powered model. (There is also Discus Launched Glider - which is thrown in a discus spinning style, rather than the common javelin style like HLG. At this time, DLG is an relatively new area of exciting development in free flight aeromodelling. However, I would not recommend it for a first model, mainly because: the model needs to be very well designed and built to withstand the high forces and strains put on it during launch, launching consistently is difficult and trimming a DLG is trickier than a traditional HLG).

Next: recommended reading and sources for model aircraft plans....

Why Free Flight Aeromodelling? (My first Blog!)

2006-12-07T02:11:00.000-08:00

This is a unique moment in Chuck Glider's aero life. Blogging about a childhood passion!

Before answering the "why" question, it may be useful to deal with a "what": What is free flight aeromodelling? Is it an anorexic waif skydiving from a high altitude? No. It's thinking about, designing, making, flying, caring for and enjoying flying model aircraft that have no direct control from the ground. Yes, all those things. It covers:

gliders: launched by hand, catapult, bungy or towline;
propeller-driven planes - which are in essence motor gliders launched by rubber-power, electric power or internal combustion engine;
jet and rocket powered planes;
oddballs - like ornithopters, helicopters and autogyros.

So WHY?

Because it's fun. It's absorbing. Building the beastie is enjoyable. Why is it that Humans have always had a fascination with flying? If you enjoy watching a bird of prey circle around and dive on its victim, then you're likely to love this pastime. Gadget-freaks can go wild. If you don't like gadgets, that's OK as well - there is much joy in minimalistic models. You get a fantastic buzz to see your creation fly, and a bigger one when it flies high and well. It's not just a visual stimulation - there is something organic and natural about it (at least gliders and rubber-powered models - the gas-guzzlers and jets are not the same). It can also be competitive, which adds yet another buzz.