Tuesday, July 25, 2017

Gambler AG mods, beginners RC discus launched glider (DLG)

The Gambler AG is a great plane. Elsewhere on this blog is information about its construction. I've used the model a lot. On flat fields, its discus launch or off a bungee, but it's also fun to slope soar it. For towing, it needed a tow hook, so here's a picture of the one I made for it:

The tow hook is reinforced internally as shown here. Also, as I mentioned in previous posts, I got rid of the rudder pushrod. Here, through the foam guide, you can see the diamond hook of the new rudder control rod, where it attaches to the pull string of the return spring arrangement:

The elevator servo has stayed firmly placed over time, simply being glued down. I guess that loads on the rudder servo are greater, because in contrast, the rudder servo tended to move. I've also had to replace it twice. Fed up with trying to re-stick replacement rudder servos, I decided to make a mount for it, and this is what it looks like:

The servo screws are tightened using a cranked star screwdriver (which is a flash way of describing "one wot I bent!"). The rudder servo mount has been a major improvement. Apart from making it easier to replace servos, it has also improved rudder control finesse and centering. Will it stay put over the long term? Time will tell...

Repairing Elapor Foam, WLToys Sky King F959

These days there are some cheap but great small models about. Especially amazing value is this Sky King 75cm span electric glider, which comes complete with 2.4 GHz transmitter. I flew it in a heavy wind and it caught a gust and spiralled in. The nose dented. When I got home, I boiled the kettle for a cup of tea and used the hot water to dunk the crushed side of the nose in. The foam on that side expands and "repairs" the injury.

Here it was before the repair:

And here is the repaired nose:

Monday, August 10, 2015

Kyosho Swing v. Great Planes Fling RC Gliders HLG

My first RC glider was the Great Planes FLING and I battered it properly. Superb fun, even the crashing! It's still airworthy, but now rather heavier than when new (it's all that fibreglass repair patching!) I like to think of it as having a "slightly higher wing loading" for more speed and better penetration on windy days or the slope.

Soon after, I noticed that Kyosho made a glider of similar size and shape called SWING. It seems to be less well known. I bought one but have yet to assemble a fly it. It seems better quality and lighter than the Fling.

It made me wonder: which came first, and is one a "copy of" or "inspired by" the other?

Here is instruction manual of the Great Planes Fling, and the manual for the Kyosho Swing.

These are a good read, but I found the copyright notices on them interesting: the Swing manual is (c) 2003, whereas the Fling is (c) 2004. This would seem to indicate that the Swing came first and the Fling about a year later.

I think the reasons for the Fling's success compared to the Swing are:

  • Great Planes had the foresight to include a high start bungee towline in the Fling package
  • Colour of the covering: rich and memorable mauve on the Fling, but bland transparent on the Swing
  • For these models, Great Planes' marketing, in Europe at least, is much stronger than Kyosho's

I'll post some pictures of my models later.

Friday, September 19, 2014

Tiny Gliders: 8" HLG

Kevin Mosley designed a great 8 inch span chuck glider a few years back called LET'S ROLL. It was for the Tiny Gliders postal league. I built one -not quite to plan - and on the very first full throw it flew away, out of sight, caught in a growing thermal. Months later, a lady from a farm 3 miles away found it and called me (one should always write a mobile number on the model!) The wing and fuselage was still fine, so I rebuilt the tail feathers. Here, years later, are a couple of videos of the re-built, well-travelled glider in flight. Calm evening in early autumn, a fine way to de-stress:
These videos were taken on my Nexus 4 mobile phone. I chucked the glider up, held my phone up and filmed. A very tricky exercise, but the results were ok. However, the launch and transition could not be captured.
Finally, video of a 12" hand launched glider of my own design:

After a time away from chucking gliders, my arm is now sore! It's good exercise.

Monday, September 8, 2014

Pull Spring Servo linkage for DLG type glider rudder

My Gambler discus launched glider had a rattling rudder pushrod in the carbon boom. Also, it didn't move that smoothly. So, I decided to convert it to a pull-spring rudder. The first thing was to cut the old pushrod at the pod end, and tack some strong thread on it with CA glue. Pulling the pushrod out from the tail end allowed me to thread string through the boom with no fuss at all. I'm using BCY archery serving, which seems really strong, light and abrasion resistant. This is the thread emerging from the end and you can see where I tacked it to the old pushrod. 
The spring is simply really thin wire, sorry not sure the diameter, bent into a U shape with one leg off at an angle. (The torque is determined by the length of the spring and the thickness of the wire. I just guessed). So when you place the U on a table, one of the legs is flat to the table and the other one sticks up. I then carefully pushed each leg into the rudder near the horn and boom exit. Now, three things are important here. First, it's crucial to have the rudder horn on the other side of the plane from the throwing peg. That was already the case for me, so all good. Second, you need to think carefully about which orientation the spring goes, so that the servo and string are pulling in the right direction. Third, you should really have the bevelled edges of the rudder and fin exposed in order to push the spring legs in. However, the bevel side was on the other side, and I didn't want to remove the strong 3M Blenderm hinge tape. So, I went for it as it was. Here I've pushed one leg in, and am pushing the other in, feeding a drop of CA in as I push:
This is it pushed home. So to recap, one leg into the fin, the other into the rudder. 
Then tie off the string to the horn, a little drop of CA to secure the knot and I put a small piece of cloth tape over the spring - probably not really necessary:
Same thing at the other end. I kept a bit of wire leading to the servo, in order to have some adjustment for finding throw centre. 
It works really well. Much smoother and a tad daresay lighter than the pushrod arrangement. And happily, the rattle of the rods in the boom has gone! No issues (e.g. buzzing) due to the servo arm being under tension. That must mean I got the spring tension about right. So far, it's been very reliable. 

Thursday, February 20, 2014

P30 Rubber Power: A Beginner's Guide (all you need to know to get going!)

My modified Roger Dodger P30, after recovery from a tree. Twin fins had broken off, but otherwise unscathed
I haven’t flown a P30 in ages and intend to change that this summer. As a prelude, here are some things I've learned about it.

Rules and Designs

The P30 rubber class originated in the USA in the 1970s. It was intended to provide a simple entry point into rubber power for novices, yet a challenge for expert “rubber fanciers”. Specifying a ready made plastic propeller meant that carving one was not required, a daunting task for newcomers. The combination of a 10g rubber motor [1], 40g model weight [2] and 30” maxima for projected span [3] and overall length presented a brainteaser that experienced aeromodellers would relish. Clearly, those rules were good, as here we are nearly 40 years later and P30 competitions continue to be well attended in many countries.

Model designs vary from simple traditional stick and tissue construction, to complex forms using carbon fibre and mylar covering. Rolled sheet balsa fuselage construction is common and once mastered is a quick way to build. Motors are typically 4 or 6 strand, or 3mm or 2mm rubber, wound to something in the range of 600-1700 (yikes!) turns. It is wise to balance the prop and take steps within the rules [4] to ensure it spins smoothly and disengages cleanly to freewheel.

This is a Roger Dodger built to the plan, with a single fin
My modified version has twin fins and a slightly altered rear fuselage
Here you can see what I did to modify the rear end

Flight Patterns

Anyone who has built a simple stick rubber model and flown it with a neutral trim will know that it has a tendency to turn left under power. The left turn is mainly from the model’s reaction to motor/propellor torque. For P30 and many outdoor rubber classes, turning to the left on climb is generally considered a no-no because it is not very stable and does not launch as high as climbing right. In a left turning power climb, trimming to the left with thrust adjustment, rudder trim and using high powers, can all lead to dangerous left spirals. Most P30 flyers trim their models to turn right on the climb. In a right climb, the motor/propeller torque constantly rolls the model the the left, lifting the inside (right) wing to encourage a spiral climb (rather than a dive!) to the right. On the glide, the freewheeling propeller acts like a front fin that makes the model glide right. Consequently, a right-right pattern is common. However, some flyers trim for a right-left pattern.
Another factor to think about is whether the fin is above or below the fuselage, because the spiralling airflow behind the prop causes rolling forces, both under power and during the glide as the prop freewheels. A study [5] showed that having the fin under the fuselage rather than on top imparts a strong right trim under power, diminishing rapidly as the power decreases and then turning into a strong left trim during the glide phase.  

I would suggest only trying right-left where the model designer specifies it, the fin is underneath the fuselage and/or the model has a strong natural tendency to fly left when test gliding. I’ve never tried right-left with a P30 though, because it sounds like a difficult trim to achieve and many experienced flyers insist that right-right is best.

Trimming and Flying

As ever, trimming starts at home. With the rubber motor in position, CG should be as indicated in the plan, but if you do not know the CG position, then 50-60% from the LE is as good a place as any to start. Ensure flying surfaces are flat and warp free, or whatever trim tabs, wash in, wash out, stab tilt, etc, as are described on the plan are present and correct. It may be useful to input a tad of down thrust and right side thrust to the prop from the get go while you are still at home. This may be done by shimming the nose block, or adjusting screws if there are any.

Before setting out to the flying field, you will need a winding stooge, blast tube, stuffing stick (for loading the motor) [6], winder, a selection of pre-weighed prepared motors, various shims and tabs, a smorgasbord of stuff for running repairs including glue and tape, blue tack for weighting, rubber lube (castor oil, silicone paste, soap, glycerine, etc), optionally, a camera, pole and streamer and something to carry it all in. You will also need a bag of patience, to help you wait for a dry relatively calm day for test flying!

Then out to long grass to test glide with good old trimming-style throws from the shoulder. Some people advocate test gliding without the prop, but with a weight instead to give the same CG. That may be useful to help understand the model’s character, but many others test glide with the prop in freewheel position. After all, that is how it is going to glide in practice. Do not alter CG at this stage, but adjust wing or stab incidence to achieve a good stable glide with no stall or dive. Most models seem to have some decalage, not 0-0.  If you can, then test glide from a few feet up to get more airtime. When the model flies in wide circles to the right, you are ready to move on to the next stage - power. However, at this stage, some flyers are looking for a left glide circle, as noted above.

Start with about 150 turns. Watch how the model behaves under power and adjust thrust line accordingly. Add down thrust for power hangs, right thrust to keep it turning right, noting that right thrust can sometimes cure stalls. If right thrust is getting large, you may employ a fin tab for a bit of right, but use that rudder trim sparingly. Increase the number of turns, until you are happy at high-ish power and then you could try a new motor for a full power test. It’s not a great idea to try a full power flight for the first time during competition - something bad and unexpected may happen! How do you know what is full power? A common way is to test wind a similar motor to destruction and then take some high percentage (e.g.~90%) of that to be a practical “full” power. Another is to use a torque meter. Build experience and know what rubber feels like before it blows!

Try out different motor strand combinations to figure out what works best for your model. Does it perform better with a punchy powerful climb, or does a longer dribble of power yield more flight duration? The advantage of the former (typically a 6 strand motor) is more height, and the latter (usually a 4 strand) is a longer power run and possibly easier trimming as the difference between power and glide phase is less stark.

In essence, trimming is about finding a compromise between all the variables that gives the best results. Sounds simple, but there are quite a few variables:
  • Decalage
  • CG
  • Thrustline
  • Power profile (motor construction and winding)
  • Trim tabs, flying surface warps and stab tilt
There is more than one way to skin a cat, and there are many different approaches to finding this compromise. My suggestion is to be logical, organised and try to change only one variable at a time, otherwise it is easy to get lost.

Enjoy and Look After your P30 Model

If you are intending to compete at meets, then practice in a variety of weather conditions so that you know how best to handle them when the day comes. That said, there is nothing wrong with being a fair weather flyer and competing only in postal events.

Use a DT and set it to a sensible time on every flight, especially on a thermic day. I have watched my P30 fly away with the DT set to 2mins - because that turned out to be way too long for the size of the field I was in! Write your phone number on the model. The most effective DTs are arrangements that detach the wing and have a line from the wingtip to the rear of the fuselage. Pop up stab and pop up wing are common.
A DT is very important, as P30s fly away easily. This is a button timer for my pop up stab DT
Store your model in a protective box. Try to avoid the flying surfaces warping during storage, for example, by banding them to something flat.

P30s are immensely satisfying and fun to build and fly. Now I cannot wait to get out there and fly mine again!


[1] Same as F1G (Coupe d’hiver). The 10g weight includes lubricant.
[2] Measured without rubber motor.
[3] Projected span is the measurement from one tip of the built model wing to the other tip. It is not as measured flat on the plan e.g. adding the lengths of each panel.
[4] BMFA Rules: “Only a commercial plastic propeller with a maximum diameter of 9.5 inches may be used. The hub may be modified to fit the shaft and for freewheeling purposes but not for folding. Plastic may be removed from the surface of one blade for balancing purposes only. The diameter, pitch and blade shape may not be altered.”
[5] Andrew Longhurst, Free Flight Quarterly, Issue 39, April 2011, pp.14-15.
[6] The first three of these can be easily self constructed.

Monday, December 23, 2013

Phoenix Kicks: HLG Tales from Arizona & Chuck Glider Launching Advice

Russ H, a reader in Phoenix sent me a batch of photos of his gliders. For the first time, he had a go at flying for duration and this is the story. Here's a photo of his Fleet. The 6" ones are Whipper Whizzes, there's a Plain Sailor on the left, the big one is a Bowers 20" Old Timer and on the right a Harry Johnson 14" (plans for which I think you can get from Unsure about the model between the Old Timer and the 14", but I guess it's around 8".

Here is a top view of Russ's Plain Sailor.
For the first time, he had a go at duration flights. Russ said: 

"...Well I finally got out to the park about a week ago to try out the big gliders, It was breezy and I was nervous, which, hurt me on my first attempts with the Plain Sailor and the 14" because I didn't throw them (high enough) hard enough into the wind causing the Plain Sailor to get picked up and tossed backwards but as it tried to right itself it came down on the right wing (on the little concrete walking path of all places) causing it to break. So that was that. Then the 14" I did the same stupid thing but the 14" is so light that when it got swept up and back it turned itself around and glided quite a ways, when it landed, the nose kinda dug into the grass and it flipped over breaking off the rudder. So that was that. Fixed both of them and they're ready to go again."

But that didn't put him off, see further below. (I'm glad he took these photos before he chucked!) 

Then Russ tried launching the 20" Old Timer, and he said:

"After my first two failed attempts, something popped into my head about throwing to the right of the wind. So I tried that but with a harder throw and a baseball type throw, which I didn't do on the first two, But I let it go and it went up and turned to the right then started circling left and landed nicely. That gave me confidence so I started throwing harder and harder. The plane went up coming back over my head upside down and as it got to altitude it right itself and flew beautifully into its left turn. I started getting 20' 25' 30' second flights. Then got one that was 46' seconds causing me to [get rather excited. Ed note: some colourful language edited there!]. Then I almost caught a thermal, As it got to altitude and started its turn it got lifted up as it came back towards me, I realized what it was but it was to late by the time it landed for me to catch it again. I was able to watch where it went because there was a hawk riding it for 10 minutes or so (I'll never get that lucky on finding one again) but it was going towards houses and trees so I didn't chase it."

The strong black and orange colouring would certainly make it stand out against the sky, but I do hope the paint is not too heavy. Weight is the ENEMY!

Some of my comments in reply to his exploits:

"Ha Ha! I know what you've just been through! The thrill of hitting lift never goes away.

When you go again, choose a relatively calm dry day to practice. Plain Sailor isn't really an outdoor duration focussed model. (It's for a single sheet of balsa three-event indoor contest: longest straight glide, spot landing and duration).

The following instructions are for right handed baseball [Javelin] style throwers. Reverse for a left hander. Using gentle glides from the shoulder, trim for a left turn, with a slightly “stally” glide. I usually "breathe and bend" - put your mouth close to stab or rudder and breathe out on it, then gently bend the balsa surface and hold it for a few seconds while it "sets". As you trim, try ever so slightly harder throws levelish from the shoulder and as you release the plane launch with a slight left bank on wings. Try to get it to do full left circles a few feet off the ground like that. Adjust the size of the circle - depends on model span and weather - with rudder and use stab up to keep it floaty and stally. On many models most of the turn comes from stab "tilt" which will be described on the plan, so you won't need much rudder if any for those types. Trimming it for a slightly stally glide *initially* is protection so that when you try full power throws, you don't get a straight up and down "crunchie"! Full power throws are to the right of the wind with a slight right bank. It takes practice to know the angles. I tend to pick a spot in the sky/clouds at 30-45deg angle to horizontal and aim for that. 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. A thing of beauty when it does that consistently.

Yes, birds, not just hawks, are great indicators of lift, as are fluffy seeds in summer and even the hairs on your legs! Pros use a streamer on a pole up wind of your launch point - a few yards of old video cassette tape works well on top of a cheap collapsible fishing rod."

Here is another photo of some of Russ's Fleet. 

It is really fabulous to hear from people around the world who are discovering the magic of chuck gliders! If my blog has been interesting or useful for folks, then I feel very pleased. Russ, thanks for sharing!

Some of the best things in life are free (or don't cost much)...