A return to model building and flying. Part 60


August 2009

Great Planes ARTF

Corsair 

Control Line Carrier Conversion



This project to convert a, Great Planes, Combat Corsair ARTF kit, to carrier use was turning out to be one of those, seemed like a good idea at the time, jobs. I seem to have been stumped and frustrated at every turn; repeatedly. My first big mistake was trying to alter the orientation of the engine to an upright position. this change has cause more headaches than anything else; from miscalculating where the centreline of the engine is causing many holes to be drilled, to problems with fitting the cowl. My advice for what it's worth, if you attempt to build one, leave the engine in the default position; it will save a lot of grief. The wooden bearer under the engine was to enable lead to be screwed on without removal of the cowl, as I know from experience that carrier models need a very forward CG. and this was probably going to be no exception. If you wanted this model for just sport flying the Magnum 36 (read that as ASP 36 or SC 36 as well) will have more than enough power.

Originally I intended to build this model as an experiment, and if suitable use it for Basic Carrier competitions  as it would make a change from the endless succession of profile models the proliferate this class. That was until a conversation with Andy Housden at the Old Warden Sams do, when he asked, "Would it suitable for class one?"  After some thought, I suppose I talked myself into it. If had known what I know, I may not have been so ambitious.

The difference between the two classes is stark. Basic is no moving surfaces except the elevator, and representative of a full size aircraft, no restriction on line length or engine, up to max 30° attitude for slow fight , with a 3m circle for the pilot to wander about in. Class 1 is scale, max capacity with a 3m circle for the pilot to wander about in 6.5cc/.40 engine, 18.28m/ 60' with no restrictions on control surfaces, flaps ailerons, and any other gadgetry you can stuff in it, and max  60° angle for slow flight, and a 0.9m pilot circle.

As my original intention was to only use this mode for Basic, ( I had limited time for preparation), I had to forego all the ancillary bits and bobs due to time restraints, that would have probably helped with the slow flight in Class 1; meaning that I hadn't a cats chance in hell of getting a decent placing, even if everything worked properly

One problem I had was getting hold of a suitable carb, the ASP 32/36 size engines do no have a throttle stop screw, all other engines in the range do? the only difference between a 40 carb and the 36 is  the choke diameter of 7.5mm instead of the 7.0mm for the 32/36. Spigot size is the same at 13mm. So that is what it had to have fitted. More choke area is no problem for high speed, but may be for slow running and hand starting. In practice it seems to work OK. I also used my now standard method of fixing the engine on alloy plates to allow easy engine changes. A .40 would fit if needed. The wooded bearer under the engine is for holding ballast weights to get the CG forward if need be, it can be accessed easily from the front of the cowling.

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Another hard lesson learned, was cut the slot in the cowl for the silencer first, before doing anything else; it's much easier to find the position of the other holes if you do. I didn't! The resulting mess took a week to sort out, and involved a lot of gluing and shaping of bits of wood, plus respraying the cowl. The method of fixing the cowl is a also a bit iffy, no doubt OK for the original RC purpose it was intended for a plywood ring clued to the rear of the cowl that is then screwed to the firewall is adequate, but with a bigger engine and the possibility of squeezing a 40 into it, there is not much room. The whole circular ring fixing idea is neat, and that's about all you can say about it.

corsair cowel

The undercarriage was reasonably strait forward. I could have just left the ply plates as they were but I wanted them to at least look like they were part of the wing section. Adding some balsa and sanding to section worked, but the whole process left me wondering if it had been worth the effort. I also incorporated an idea I had been wanting to try out for some time, that of insulating the wire where it is clamped with silicon tubing to try and get some shock absorbation. Time will tell if it has any effect.

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Tail wheel was reasonably straightforward as the last fuselage former is ply, so gluing the leg in into a small hardwood block and gluing that to the former was all that was required. The tail fairing is a flimsy plastic moulding that glues on. unfortunately it did not fit over the fuselage, requiring it to be stuffed with scrap balsa to give it something to glue to.

Fitting the elevator push rod required removing a large  section of the bottom fuselage for almost the full length. The snakes are glued into parts of the fuselage formers and directly in line with the path of the push rod, requiring then to be surgically removed. This did give me room to mount a ply plate to take the arrestor hook pivot. Just hope it's all strong enough.

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Fixing the bellcrank assembly ply plate became a bit of a nightmare, as I found it had to be further back than I wanted to allow the fuel tank to be accessed if need be, a pound to a penny it will need attention if I don't. This procedure also required a a cross member of the middle former to be removed to get the required clearance. The bellcrank arrangement I have used is almost 99% compensating, with no discernible interaction between the elevator and the throttle, and is remarkably straightforward to make, if you take the effort. It is only really suitable for fuselage or internal wing mounting though.

Fitting tip weight of around 50 grams, was a cut, glue, and cover job, and should have been strait forward, but for some reason no covering would stay stuck down, and it took me four attempts before it looked reasonable.

The most head scratching was caused by the leadout guides. I wanted to take advantage of the removable wing. This means complications when it comes to how to arrange the leadouts. I don't like having lines running through guides, full stop! there is strain and friction on the those contact points and I prefer to use larger cross section flexible leadouts, this means the guide has to be able to release the leadouts, or the fuselage and wing will always be connected even if separated. After a week of headache and false starts, I end up use in a tooth and comb arrangement, fiddly to make, but should work. And of course, afterwards, I thought of a much simpler way. (kicks self in the rear.. Ouch!) 

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Flying

The day dawned when I had to try it out as the clock was ticking for the Nat's, and once having talked myself into entering it for Class 1 (although it won't stand a cats chance in hell of coming anywhere) I was determined to at least, 'try', and get at least one complete qualifying flight in with it.

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It looked pretty, but how would it fly? After running the engine and making sure the throttle was at least behaving in a reasonable fashion, I attached the lines. A big Oops..... Shit! moment followed. In all the confusion of modifications and just being plain tired at times, I had somehow got the throttle bellcrank reversed. I pull the line to open up and let go to shut down. I have flown the other way round, so it's not too much of a problem; well it shouldn't have been! I decided to fly it any way and get some idea of how it would behave in the air. Ooooh! fatal mistake....! I had forgotten that I rely on line tension to naturally shut the throttle, with the system set up like it now was, any tension will open the throttle. I normally stake the handle to the ground with a screwdriver and pull the model away from it to start, then adjust the tick over by the simple expedient of moving the model lateraly. It's quite safe as any attempt to open up will result in the throttle closing as line tension increases, and if it doesn't the handle is staked in such a way that tension  is applied to the down line as the model progresses round the circle. Never the less, I always treat the whole set-up with caution, but in practice, in the years I have been using this solo technique, the worst that has happened is the engine stopping as I get to the handle: very annoying!

In the event I had to stake only the throttle line to the ground and make sure it was under tension. all seemed to be going OK until I released the throttle line and picked up the handle. The model immediately opened up and started a fast taxi; not only that, in the panic and surprise, somehow, the throttle connector had got hooked up with the down line. Things were getting out of control at this point. I did the only safe thing I could think of in the fraction of a second before things reached the point of no return, I grabbed the down line with my free hand and pulled hard, reasoning that hopefully the engine would stop as the prop hit the ground before the model had taken off. It worked but the model was going fast enough to make it flip over, this took off the fin. First evidence then that the whole rear end of the model needs a good rethink.

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First impressions were favourable when I finally got it into the air, it had a reasonable turn of speed, but but the slow flight was awful. it just didn't want to come down, especially in the 20-30mph winds what where consistent during this period, not the ideal way of setting up a model, but time was dictating everything. To my relief the undercarriage stood up to numerous hard landings on grass, from engine cut fall out of the sky ones, to half throttle fast landings. This tuned out to be the one thing that did work OK. The not coming down has turned out to have three causes, the model is slippery aerodynamically,  the centre of gravity is too far back and the piddlingly small scale elevator is not powerful enough to get the required leverage with a forward CG. As I had originally built the model for Basic Carrier, all the flying surfaces are fixed. Nothing I could do about that right now; but some hefty flaps would work wonders. the CG problem can partly be overcome by using a .40 and shifting it as far forward as possible. None of this was practical in the two weeks I had left before the Nat's.

Another day and and 75 grams of  lead in the nose improve the level flight but the slow flight was still barely controllable. Another 25 grams of lead in the wing tip helped slow flight stability a little. An eventual total of 150 grams was added to the nose to keep things from bouncing about in the breeze, yet it still flies too well at low speed.

I was also having trouble with the engine runs,and getting the carb settings somewhere near. The engine would consistently cut after half a tank was consumed; restart the engine and it would run the other half out. No I can't explain it either? But tank was  beginning to raise my suspicions on lots of counts, and different orientations tried.This meant even more surgery on the bulk head. But testes proved that the 150cc tank was way too big, I could do a competition flight on half the amount easily. When you consider that the original model built for it's original purpose was meant to be powered by a 15 -19 sized engine, a 125 cc tank seems a a little ridiculous.I was also becoming more and more frustrated with the stupid method of fixing the cowl in place with an internal ply ring at the rear, it made access a time consuming process, cutting another hole in the cowl to enable the midrange screw to adjusted with the cowl in situ helped.

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Reducing the capacity and using a smaller tank also required a new method of retaining it. I also decided  to use a fixed uni-flow brass pipe in stead of two clunks. This improved things to the state of being semi reliable. At this point I had a sense of  Déjà vu, as many years ago I gave up on clunk tanks on stunt models and went for metal uni-flow ones for very similar reasons; although I do know others use them very successfully.

During this period I was also trying out various prop sizes and pitches. I know from experience that a course pitch is no good on my models, OK for speed but not good or throttle response or rapid pick up; diameter is influenced more by model size and drag, in this case a big cowl was blocking a lot of it, 10 inch was about right for the diameter, 9 inch and there was a noticeable drop in speed. Pitch was a bit fine at 4 inch with the engine over revving to no effect, 6 inch too much, nice fast flight but sluggish take-offs and not good throttling, I settled on 5 inch.

I know some of the old stager's that fly carrier use 8x8 props on the 40's but this is only using the reduced diameter to make up for the load caused by the high pitch, in effect that is a speed or team race set-up. I don't claim any of these approaches is right or wrong, and it's only here for reference. Personally my mind set is that the model is flying more like a helicopter in the slow run, so it needs some blade area and a fine pitch to allow it to rev without pulling the model skyward on the smallest twitch of throttle. Where some of the pitch recommendations for RC motors come from, I have no idea?  I have never used a 7 or 8 inch pitch on anything, except a 1.5cc speed model I built once.

Another problem that reared it's head was that it was possible for the the arm that carries the two bellcranks to rotate through more than 180 degrees if shocked hard enough, leaving half the movement gone. I found this out the hard way and barley got the thing down on the ground again. It shot up like  a rocket on take off and nothing I did would bring it down, full down was having no effect. In the nick if time I remembered to shut the throttle, and managed to coax the model down to the ground for a barley in control, landing. On inspection I found the only control I had was neutral elevator to full up and no down at all. A screw stop has now been fitted to stop this happening again.

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Numerous heavy landings later, and the thin tailplane was showing signs of failure round the hinge areas, this was exacerbated by the lack of strength in the elevators caused by the manufacturers lightening holes. The elevator problem became ugly after one violent touch and go. I wondered why I was having difficulty controlling the level flight, only to find on landing that one half of the elevator was gone. The solution required thickening up the tailplane and elevator, and a short spruce implant in the tailplane to prevent flexing on heavy landings. This required a lot of major surgery and burning candles late into the night to implement. This repair of course added more weight to the tail and as consequence even more to the nose. The weight was building! of course  to graft in a .40 to replace the weights and get more power was the answer, but time dictated that was really not a practical option at this stage.

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At the same time I was increasingly worried that the hook mount would not stand the strain of pulling up an increasingly heavy model, so more surgery added a re-enforcing spruce cross member and the gap filled in with balsa; just hope it's enough.

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Another thing was niggling away at the back of my mind during this time; the hook release mechanism. The hook was released by the application off full  up elevator; as is common on a lot of carrier designs. This always seems to be a bit unpredictable in operation, as carrier models tend to use a lot of up elevator in all sorts of hairy situations as well as waiting to take off from the deck. Nothing wrong with it dangling in the breeze from take off, but it could loose a precious few centimetres when bouncing about near the stall and ground. A tell-tail clump of grass hanging from the hook can't be argued with; so I prefer to keep it up until needed. There followed one of the those epiphany moments lying in the bath, when it dawned on me that it would be much more sense if it released on full down, all this meant was reversing the push rod extension and making sure nothing fouled the hook on release or prevented full up elevator being utilised. In the event it works like a charm and seems a lot more predictable than the other way round

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More flight trials produced a succession of tail wheel wire breakages, something I have never encountered before, but it obviously needs further investigation. No time left, just keep gluing and soldering and pray.

The model was by now looking war torn, but at least reaching a semi reliable state, Carrier models rarely look pristine, and now you may have some idea why. The slow flight,,,,, is not! and I had not yet even attempted to land it on the club deck, time had run out as I wrote this, I would just go for broke on the day.

I reckon I had crammed about six months to a years worth of development into this two weeks, and would not be able to think dispassionately about the project until some time had lapsed after the Nat's.

UK Nationals 2009

Carrier Event

For the first time I didn't take one picture or piece of video. Paul my ex-boyfriend came with me as official photographer, but only managed to get a bit of video hopefully this will be available soon. Read on and you may realise why there are no pictures.

Saturday dawned bright, but windy; far windier than was really pleasant to fly in, and bordering on the, is it worth the risk, point. The wind was also cold, which also caught a lot of people out with the wrong clothing. I was surprised to see the all the controlline circles empty with almost no signs of life from anywhere except the carrier and combat circles. Now I find that odd, as carried models during the slow flight are bordering on falling out of the sky on the best of days, add a turbulent 30 mph gusting wind on top of the equation, and I find it remarkable that they cope so well with it.

I had company in the comp this year, in the form of  Andy Green, a fellow club member had also entered 'Basic Carrier' also using a profile Hellcat of the same design as mine; so what would pan out for Team LMAC? 

Meeting up with old acquaintances from the continent  in particular Herbert Harritsen who I have not seen for some time,  Jan Odeyn and the usual Belgian contingent, and the usual UK crowd, kept my mind off the weather a little. We were all treated to the sight of Jan flying lazy eights with a carrier model, just to prove you can fly in a strong wind. Way to go Jan! The flow of information and socialising at these events is one of the things that make it all worth while, and it's something sport flying can never give you for various reasons. If someone in the same competitive environment tells you A+B works, it's because it helps them get scores, it might not apply to your model, but it has been learned through experience, not just read in a magazine article, or half heartedly tried on a model only flown in calm weather on the odd weekend and made into the the gospel according to Joe the average fair-weather flier. So it's always worth listening to, I certainly do, I would be foolish not to.

My two flights in Basic Carrier where a no frills, no pushing the envelope, take off , hang on for the the fast run, shut throttle on downwind leg and full throttle up wind, and go for the deck landing no matter how many landing passes I had to make to make to get it down. This worked, crap score, but model in one piece. Strangely I was actually enjoying myself, unless it was just the adrenaline rush. It also may have been that I had just proved to myself that I can fly in adverse weather conditions. Second flight was a repeat of the first, but trying to increase the slow lap score a little. The whole focus of Carrier is the arrested landing, without it you a scuppered (literally), so two good landings left me felling more than a little elated.

Andy's first flight, and indeed first carrier comp, used the same technique as mine, but unluckily bounced of the deck on the first attempt. Second attempt was rewarded with good landing. I'm sure Andy felt good about it!

Neither of us had any engine problems, Andy's ASP 40 and my SC 40 bursting into song without much fuss. Andy was using 15% Nitro and me 10%

So we had both achieved qualifying scores and could go home for the night with models intact with a hope of the weather  improving on the Sunday.

Sunday ....! well the wind didn't drop, and the skies clouded over, if anything the wind was freshening to quite alarming gust levels. Andy and I were scheduled to fly between 16:00 and 17:00 hours, but as the flight order was very relaxed, we flew mid afternoon. Andy had bad luck by missing landings on two flights. This was not helped by the wind seeming to reach gale force every time Andy started his landing runs; one gust being strong enough to force me to take a step back wards to keep my balance. This was a shame as I am sure his fast and slow speed run difference was improving. Considering Andy has only really been flying carrier occasionally at our the club site for a couple of months this was no mean performance taking into account the conditions. My flights got a little better and I managed to get it down on the deck both on both flights, so I had at least achieve what I had set out to do.

corsair startThe number of bodies seemed to grow behind the carrier deck like a flock of vultures as I plucked up courage to fly the 'Class 1' Corsair, I got the feeling I was about to make a real fool of myself, but praying I didn't. Everything fired up and and set I took off and got the fast run out of the way stably. The slow run was just about that, on reduced power, with no sitting on it's tail. Then the part I was dreading, the landing! With no prior knowledge as to how it would behave, I was in uncharted waters. Getting it down to deck level was the usual problem in the tearing wind, but miraculously, after a few flybys I made it; then promptly fell off the deck! It turned out the arrestor wire had  broken, but I was generously allowed the flight. I opted to get the all the attempts out of the way as Monday's weather forecast was for stronger winds than we had already. Second flight, I lost it on one slow lap, when it decided to sink towards the ground. With the Magnum screaming at full throttle, it just managing to pull it over the deck but clipped it loosing me a flight; but I did manage to land it correctly. I went for the last attempt before my nerve went, only to find all the officials had all run off to an ice cream van for some refreshment, I can only assume the carrier was steaming along on auto navigation? This last flight was a much better attempt, and seeing it sitting on all its wheels with the engine idling and the hook firmly holding the arrestor wire was a a joy to behold, every modification had worked, making all the hard work seem worthwhile.

Then the heavens decided to open and the rain came, So Team LMAC got the timing right on that score.

There was not much to be achieved by driving back on the Monday, I was exhausted and tired, and weather forecast was for even stronger winds than the Sunday. In the final analysis myself and Andy Achieved 9th and 13th place respectively in Basic Carrier, with a total entry of 24 , and I came 4th in Class 1, out of an entry of 6. Andy also came first as best beginner in Basic Carrier. Not at all bad  bad considering the weather conditions.

Short video extracts of flights
Hellcat
Corsair

As you have read, Saturday had almost no CL flying going on so nothing to photograph. Sunday we arrived midday missing the swap meet, and I was so wrapped up in psyching myself up to fly in two classes in the appalling wind, that I didn't even think about it. My one trip around the trade tents, was disappointing, hardly anything of interest, and no bargains, at least not for CL. A few props and some hard to get odds and ends, and that was it. whether this is a sign of the times or the economic climate, I don't know.

Now all I want is to stay away from models for a bit and relax; and as it happened that was probably a wise decision, as I had a bout of falling asleep and feeling crap for a few days, as the activity had triggered my ME of again .At least for a week, as our monthly club time trials come team races needed to be flown. I must be a masochist! As it happened I won all three classes, one by default. Come on Bob sort your models and engines out, we need some competition! The Week after that found me at Old warden again with a fun time had by all. I did manage to test fly the Corsair in better conditions, and it will occasionally get to a 30° angle if I really work at it, so something drastic has to be done to the model or trim to get it to sit at 60°. But whatever, it will have to wait until I get a tooth problem sorted out that has had me going insane, being messed about with appointments, and various other, problems, and of course considerable discomfort, has left model aircraft a bit low on the list of priorities just now.

As a footnote, it's a great pity that there a not more ARTF RC models of this type and size around, that would make a good sport or semi scale CL models. If anyone knows of any that do exist that representing any full size carrier aircraft, and have maximum wingspan of 111.7cm/44 inch. They must be to scale for  for 'class 1' carrier carrier use;  please let me know. 





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