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Friday, September 4, 2020

Flying a small glider off a High Start: Lulu wing on Crofter

The Peterborough Model Flying Club specify a high start for small gliders as 7.5m of rubber (they recommend 1/8" strip) attached to 22.5m of line. This works beautifully. Here are some details of mine. First, this is how I store it, on a 1cm thick Depron foam board stiffened with a piece of wood (a bit of old fencing!):


This works very well. Simply remove the split ring from the knob of Depron, fix it to the ground with a decent stake, and unwind the foam board as you walk back downwind. To put it away, start by putting the glider end split ring onto a Depron knob, then wind it up as you walk forward to the stake, making sure that the rubber goes on slack. Use a hand over hand movement, otherwise the line will twist.  Knots wise, I use a Palomar knot to tie the rubber to the stake ring, a Figure 8 (Flemish) bend to join rubber to line, and an Anchor Hitch to join the line to the ring at the glider end. I also add half hitches and overhand knots on top of these to prevent slippage. If the kite line at the Figure 8 bend cuts into the rubber, then I'll do something else, but so far, it's held up well.  

Following on from posts about the CROFTER, I had a 24" wing that was made by my son for a school project. It's based on the LULU wing, scaled down.  Here it is attached to the CROFTER fuselage:


If you look carefully, you can see that all I've done is add a couple of 1/16" tabs in front and behind the wing platform, before banding the wing on. It means that the band pegs are a bit awkward to reach, but it's not a big deal. 


No idea why my son went for a German/Belgian flag look with the tissue! 

Balanced at 49% of chord (90mm, so at 44mm behind the leading edge), all up flying weight was 36.7g. That means it's about 10% lighter than the CROFTER with roughly 20% more wing area. Wing loading hugely improved. 

A quick shoulder glide, showed it needed a 1/32" shim of up on the stab, and it had a slight right turn which I encouraged with an Al foil tape trim tab on the fin. Then on to the high start. First flight was over 1min. I had a go at trying to take videos myself, but it was pretty lousy trying to do it myself and launch. First a 4s clip of the end of the high start launch. 


Now a longer video of part of one of today's flights. It starts off doing right hand turns, but then goes downwind in a straightish glide before turning a little and landing. 



It's abundantly clear that the LULU wing on the CROFTER fuselage is far better than the original CROFTER wing. A tribute to John Barker, who originally designed the LULU. RIP Hepcat. 

  

Monday, August 31, 2020

Herr Starlite evening flying: Aerobatics with a R/E 3 channel model aircraft


The perfect plane for a calm evening. STARLITE is a well behaved, light, 3 channel model from SIG mfg, HERR. It was a pleasant kit to build. Mine came out at 160g all up weight ready to fly (balanced under the front half of the wing spar). It's fitted with a small brushless motor, 6A ESC, 450mAh 2s LiPo battery, EP5030 prop, and two 8.5g EMAX ES08AII servos. Here's a photo of them in position on my quick build servo mount:


I find these EMAX servos to be really good value for money - smooth, powerful, reliable and cheap. They are firmly at the budget end, and I don't think they centre as accurately as some others (in my tests, some Hitecs were better). But it's a tiny difference and I still like them. The pushrods are carbon rods bound with kevlar to wire at each end. You can't see the carbon rod in the photo above, but you can at the other end:

All designed by Herr to be light weight. And below, another photo of my Ferrari inspired wheels on the STARLITE'S somewhat spindly undercarriage: 


So, with a R/E plane what can you do in terms of aerobatics and manoeuvres? When you think about it, there's actually quite a lot - look under the photo below for a list. 
 

AEROBATICS & MANOEUVRES WITH 3 CHANNEL RC MODEL PLANE


DO-ABLE ON MOST R/E PLANES


  1. Circuits: left hand and right hand. 

  2. Procedure turns (to change circuit directions)

  3. Aerobatic 360º (a wide circle turn in the horizontal plane)

  4. Steeply banked turns

  5. Chandelle/Wingover

  6. Figure of 8 (two 360ºs, crossover point in front of pilot, entry and exit in the same direction)

  7. Inside Loop (a big standard loop, canopy on the inside, in the vertical plane)

  8. Humpty bump (entry and exit direction the same, no rolls)

  9. Hammerhead/stall turn (entry and exit in opposite directions)

  10. Lines: Vertical and 45º, up and down

  11. Landing approach practice. Dead stick and/or low power. Over long grass or other unsuitable surface, bring the plane to under 6’ height, then power up and climb out.


WITH UNDERCARRIAGE OVER GOOD GROUND SURFACE 


  1. Touch and Gos (like landing approach practice above, but touch the wheels on the ground)

  2. Taxi practice, ground turns, figures of 8, alignment drills, etc. 


PERHAPS DO-ABLE ON SOME R/E PLANES?


  1. Outside Loop (canopy outside) 

  2. Spin (1x or 1.5x) 

  3. Barrel Roll

  4. Tailslide

  5. Loop to inverted. Exit with either: a dive (basically, a stretched loop); or a barrel roll out (e.g. a 'Barrelly' Immelmann turn/half Cuban 8 - it may not be easy to distinguish them!)

  6. Square Loop

  7. Inverted 360º


Are there any more? Today I had a go at 1-9, 11, and 19 (a stretched loop). All went reasonably well except the stall turn, which ended up more like a prop hang. I need more finesse on the airspeed, but I've no doubt STARLITE will do it if given the right instructions. Also, on the Figure 8, I kept doing one turn bigger than the other. I haven't tried spinning, or barrel rolling STARLITE yet. 

Bags of fun. Flying always leaves me with memorable images. A major one today was STARLITE gliding slowly in the orange sunlight on deadstick landing approach practice. 

The only problem with autumn evenings is the dewey damp grass. Wrinkles up the tissue...

 
But it dries out and stretches back fine. 

Sunday, August 30, 2020

Flying wing maiden



Today I maidened this 900mm (35") span foam wing. It was easy to put together and flew beautifully. Basically, a maiden with no surprises or dramas whatsoever. All it needed was a bit of up trim (it always surprises me how high the elevons need to be centered on a wing). I have to experiment with CG - will probably move it a little forward first.  


The battery and receiver hatch is cut out of overhead projector slide (remember them?) covered with coloured parcel tape. All up weight ready to fly is 197g. It also has a tow hook for pinging it off high starts. The wire hook is attached to a ply bracing spar that is pushed into a slot in the wing. Here it is being glued in with white wood glue (pva resin type, which I find works well on foam). 


Details below of the hook and ply bracing spar. Kevlar thread bound on and sparingly smothered with superglue. Very strong. 

I'm wondering now whether to keep it as a glider, or add a pusher motor. It came with a geared brushed motor and huge looking prop. If I do put a motor on it, I'll probably go for a small brushless and 5mm dia shaft smaller prop (EP5030 should be ok, I reckon). 

I think I'll slope it first before deciding. I also have a 48" Genesis flying wing that also configured as a glider and it's great on the slope. 

Thursday, August 27, 2020

Crofter first flights


Evening hardly any wind, on the day I maidened the CROFTER 24" simple glider. I found it very hard to trim. Took me a long time to get it to tow on the High Start (30m), and the glide starts stally, then tends towards a spiral dive. 

I think the fin is too big, and have since cut it down. I've also experimented with moving CG forward to 40% (it was about 50% on the plan), but it didn't help very much. I may try to move CG backwards to about 55% and see if that helps. 

However, I now believe that this glider for a newbie would not be as satisfying to build and fly as compared with a simple well-designed model with tissue covered wing. 

So, to check that, my daughter has agreed to build a West Wings Merlin 35" wing span, which is a well regarded kit. We'll compare it with this one for ease of launching and trimming - and overall satisfaction. Not really a fair test though, because it has a bigger span and more complex construction.

But I also have a 24" wing that was built a few years ago by my son for a school competition. It's based on John Barker's famous LULU. Here it is after steaming, banded to a board to get a warp out:

I should be able to to fix this wing temporarily onto the CROFTER fuselage. It weighs 8.43g as compared with the CROFTER'S which is 12.3g - that's 30% lighter! It also has significantly more wing area (90mm chord vs. 75mm on the CROFTER, giving about 20% more area if my maths is right). I'll balance it at about 50% and see how it behaves. It will be an interesting experiment!

Newcomers need something that gives good results relatively easily, in my view.

Sunday, August 23, 2020

Crofter 24" simple glider: revisiting my first ever model plane

Most aeromodellers seem to have memories of one sort or another about the first plane they ever built. As advertised in a previous post, my first attempt was a Crofter glider by Ian Barret published in Aeromodeller in 1973.
 

As a boy, the build felt like I had slaved away for ages to produce a small glider. While I had a sense of satisfaction, trimming and launching it properly evaded me. I had no real support for that, and didn't know who to ask. This was obviously pre-internet. I was 11y old and although I managed to get it to release off a hand tow launch, the overwhelming feeling was of frustration. 

I've always wanted to revisit this model. With the benefit of some years of experience of full size gliding, building chuck gliders and many other models, construction this time round was really easy, taking me essentially one evening. The decoration and ballasting happened the next day. Here's a picture of the final model. 

Who doesn't like tissue flames?! Perhaps they signify my boyhood frustration with this thing! 

Today, I'm an experienced aeromodelling chappie and I see two main issues with this design. Let me start with the weight: 

Wing: 12.3g

Fuselage: 11.9g

Stab: 2.3g

Ballast and rubber bands: 13.9g!!

AUW ready to fly: 40.4g

The built weights of the wing, stab and fuselage are pretty good, but that is a massive amount of ballast required to achieve the plan-marked CG of 38mm behind LE. It indicates a heavy tail, a long lever arm, a short nose, a forward CG, or all of them! 

Not surprising then that first glides from the shoulder indicate to me a higher wing loading than even most of my chuckies! It's stable due to the CG and dihedral, but has to glide relatively fast compared to really lightweight tissue and balsa gliders. On the other hand, it seems to react well enough to the air, so it should thermal - that is if I can get it to launch and turn on the glide (without using auto-rudder and such). I've started with the tow hook a little bit further forward than indicated on the plan:

The second issue I see with the design, is the ease with which this wing can warp. Nothing wrong with a Jedelsky style wing (reminiscent of the Cloud Tramp rubber model, but also some really high performance free flight models of the past), but the Crofter's wing is not very "stable". Trimming becomes interesting, as one day it will turn left, and the next day right. This is purely because of the twistability of the wing design. It's like it has random ailerons! On the plus side, you can eyeball it quite easily, and steam changes in. Whether the changes stay in, only time will tell! But at least I know what I'm doing now with trimming, balance and warp changes. You can see a little stab shim in the photo above. If I had the trimming information guidance or sources as a kid, I think the model would have been a good teaching aid for aeroplane control surfaces. 

As I write this blog, I wait for good weather to maiden it on a small high start. It's gonna be fun! Whatever happens at the maiden, the catharsis of the build has been worthwhile already. Whether it zooms off to one side to crash sickeningly, or the wings fold in flames on its first high start launch, I've already tucked all that childhood frustration to bed. Basically, I understand what's happening and why at every step. That's such a good feeling. 



Pearl DLG, rudder-elevator discus launched glider from Impres, Ukraine

 This is one of a series of gliders that were produced by Impres of Ukraine. As far as I know, the company is defunct, but their models were jewels! Literally, named Pearl, Garnet, Ruby, etc. 

I have finally managed to kit out and maiden my Pearl R-E DLG. Here are some photos. Basically, the model is superb. With the 3 panel wing and R-E controls, it's not surprising that it feels a lot like the Gambler AG. However, the Pearl has a much flatter and floatier glide. The Pearl's 1.49m wing is beautifully made with lots of kevlar and carbon capping. Like a high tech free flight glider. In contrast, the Gambler has a thicker wing section 1.22m span, and a higher wing loading. Neither the Gambler or the Pearl will launch as high as modern composite DLGs.  


AUW ready to fly for my Pearl came out at 284g. Because there is not enough space in the pod, I found battery choice awkward. A 15g 120mAh NiMh pack gave me 25mins (better to be conservative and stop at around 18mins). A better alternative is a  Li-Fe 200mAh that weighs about the same.   





More build information is on RCGroups - here, including the "drama" on the maiden.  

I think it looks fantastic in the air. Looking forward to sloping it as well.  


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...