A return to model building and flying. Part 28
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Wrestling a Hellcat and ToughLon (again)
I said last month that if anything else goes wrong with the Toughlon covering film I would report it. Well it did, and I don't find it at all amusing. I was a very hot bright sunny day, just the sort of conditions that will show up any flaws in plastic covering. I also had a smaller model with the wings covered in Oracover/Profilm sitting in the same conditions, all that developed was one small blister about a one and a half centimetres long. This model was the first I had ever used Profilm on and did not really know what I was doing, so it's a testament to it tolerance.
These pictures speak for themselves. For a covering that is supposed to be resistant to slackening in hot weather it's a bit of a joke. I accept that part of the problem may be that I have not got the covering at the right temperature when applying it, but, if you read last months episode, you will will be aware of the problems I had with that. I managed to shrink it all down again, and hope that it does not happen again. There is no guarantee that it will not happen again, it does with Solarfilm. From now on I shall steer well clear of ToughLon and hope that I can get the existing model to stay together and not have to re-cover the wing, making those decals was not a quick job.
Sorting Out the Hellcat and Engine
Now that the throttle is tuned correctly I can turn my attention to the models flying trim. I was obviously nose heavy to start with, although it balances in a position I would have thought would have been OK, with a tendency to not want to rotate into a slow flying attitude and have quiet a fast steep glide when the engine cut. It was also pulling uncomfortably on a fast run, enough for the throttle ring to pull on my middle finger in a quite painful manner. I also noticed on slow throttle the engine had a slight tendency to hunt up and down the revs. There is also a tendency to Dutch roll quiet violently as the slow speed angel of attack increases.
[Quote] The Dutch roll motion is a "flat" yawing/side-slipping motion in which rolling is suppressed (Etkin and Reid, 1996)
[Quote] Dutch roll is a type of aircraft motion, consisting of an out-of-phase combination of "tail-wagging" and rocking from side to side. (http://en.wikipedia.org)
This is difficult to visualise and illustrate. If I ever manage to find a way of strapping my mini camcorder to my head, I might be able to record it happening.
Lead was added to the tail on a subsequent outing and an improvement in the slow flight handling as well as the dead stick glide were noted. Also, moving the wing leadouts forward helped with the excessive pull on a fast run. A change of prop to a finer pitch has all bet eliminated the slight rev hunting, but will obviously affect the fast speed. The Dutch roll is still there but for the moment I am not quite sure how to tackle the problem as it may be something to do with the Clark Y type wing section, it may reduce as the other things get sorted. Torrential rain on a hot summers evening stopped any more experiments. The covering stayed taught this time, but I will not be convinced until it has stood up to the mid day sun beating down on it for an hour or two.
Another thing of note is that the engine an S.C. 40A (Mk.I) I described test running last month.
It actually runs perfectly well, with only two provisos. The standard silencer is quite raucous when the engine comes in song and a 10 inch diameter prop exacerbates the problem. As is always the case I had loads of props up to 10 inch and quite a few 12 inch but no usefull 11 inch. Looking at the silencer that is supplied with a Mk.II the exhaust outlet is about 50% smaller than the Mk.I, so something will have to done to calm it down a bit. The other problem is that like my S.C. 15, it does not like hot weather and tends to sulk when asked to start nicely. However, having spent quite a few hours beating many a recalcitrant engine into life by shear force of will and brute force at times over the years, it succumbed in the end, and all without recourse to an electric starter, which I have never possessed anyway. I am pretty sure the cause is a borderline piston liner fit. so it may be worth investing in new parts, as like my original S.C. 15, it went like crazy when it did go. See Part 23 The Stupidity of a Failing Mind
However, awkward starting is not a desirable quality if I do get serious about competing, nor for sport flying, as I like to fly not crank engines all day. So, having the choice of two other S.C. 40's, a brand new Mk.I and a Mk.II (isn't eBay wonderful) I decided to replace the existing one with the Mk.II as I want to sort out the model and the Mk.I would take time to run in, if you have read any of my previous scribblings on ABC engines you will know that I do not exactly agree with the quick run in practice usually recommended. However the Mk.II has a conventional front mounted carb in a very vulnerable place, so I hope that I don't make any flip over landings until I can get a remote NVA assembly for it. The Mk.I RNVA carb will not fit the Mk.II so I could not swap them,
And while blathering on about S.C. engines (I have learnt a lot recently), the manufactures instructions recommend the use of a 20% Castor oil based fuel for all their two stroke glow engines. I am wondering if this would help the hot starting, it certainly did with my old Merco 35's. However I like a synthetic/Castor mix and I can't find such a commercial item, at least one that is readily available, up to now it's been a case of that's what we have in stock, take it or leave it! That situation has changed to certain extent now, as you will read later. So I am faced with adding Castor to an existing commercial fuel. Apart from the the fact that it would take up even more room in my small flat, it's tempting to buy the raw materials and mix up what I want, not have to use what someone tells me I should. There is an extremely useful page of information about fuel make up on the Just Engines site here, it seems I am not the only one the does not like ingredients being hidden.
As another hot still day announced itself; Hang on! this is not right? I must have been transported to an alternative dimension where it isn't wet and and windy all the time, I stole up to the flying field in the evening after dropping Paul off at work, trying another route and getting lost yet again in the depths of rural Leicestershire, to try out the Mk.II engine and the Model Technics Duraglo 5% nitro, with added Castor oil to bring it up to 20% oil.
What a difference. The engine is a one to two flick starter, hot or cold. I don't think that is all down to the extra oil. This is very good news as the weather was still hot and humid, once over the mid 20's C the weather here more often than not always seems to be uncomfortably humid, just the sort of thing to show up any starting difficulties that may exist. This engine also develops an embarrassing amount of power, with less noise, I think due to the smaller outlet pipe and better match of exhaust port to silencer area than the Mk.I. I now have to find some way of controlling this. On a 10x4 APC prop it will float along on just over a tickover which can make it bit difficult to settle it into a groove; or have it rock and roll itself out of one! The Dutch roll instability is beginning to annoy me now, it can make going really slow a handfull if it gets violent. Finding a solution to this problem is a priority. And yes, the model did flip over after a bumpy landing, fortunately going very slowly so the needle assembly survived, emphasising again the urgent need for the RNV conversion.
Flying on my own causes a few problems with launching. I mentioned in the past that most RC throttles have a spring loaded barrel, which forces the throttle to the open position. This means that I cannot let the engine tick over on it's own as it will spontaneously open up. My jury rigged couple of tent-pegs, string, and a meat skewer, works OK as a temporary remote release, but once or twice the arrest or hook has dropped down and caught on the pegs, thus leaving me stranded 18 metres away, looking at a released model running flat out but not moving. If I can't shake it loose by pulling on the lines, there is nothing I can do but run like hell, whilst praying that the model does not take off before I get there. At my age this is neither dignified nor proper, I should be sauntering in a genteel sedate manner.
It also does my M.E. no good at all, making me much more tired than I should be, and arriving home shattered after only a couple of hours at the field. It also brings home to me the difficulties I would encounter trying to travel any distance to competitions. There is nothing I can do about this, I have lived with the condition for long enough now to know the medical profession has no answers. Bit of a bummer really. I really get to loath, hate and detest the tiredness at times, but those feelings don't change anything. It's difficult to enjoy life when all I feel is the desire to shut my eyes and lie down, sometimes I have to, to prevent serious problems.
On the subject of spares: a recent phone call to John Haytree revealed that a rear needle conversion kit for the S.C. 40 Mk.II was in the region of £33.00 and the extension piece to make the silencer into a large second chamber quiet silencer would set me back £16.00. Needless to say I declined, when complete engines can be had for those sort of prices. Looking at Just Engines website, a complete Super Quiet silencer of almost the exact same size and shape that the existing one would have ended up like, price £18.00. A complete remote NVA and carb setup that looks exactly the same as an original S.C. one, £22.00. These are not small differences but either would make a big hole in my budget at present. As I want to be able to keep using my club site and not be barred because of noise, also not wanting to spend money on new needle valve assemblies every other week, or waiting for a Mk.II with RNV to show up on eBay and win it for £22.00, inc postage, I reluctantly hit the plastic.
The parts duly arrived two days later. Just Engines really do offer a very good service at good prices, increasingly rare these days, and fitted perfectly. I can now say that a Just Engines series3's' 13.5mm rear needle carb and NVA are exactly the same as S.C. 40 Mk.II original parts. The Super Quiet JENS3S/7 silencer looks like it could have rolled off the same production line as the original S.C. silencer, as did the carb conversion; I bet they all did. The silver bit in the middle of the silencer is what I was originally quoted at £16.00...???
Sunday spawned another very hot but slightly breezy day and found me at the flying field again. The second outing with the modified Mk.II S.C. in the Hellcat and I was beginning to wonder if the initial pleasant starting characteristics where going to disappear. I always use a glove to protect my hand when starting, apart from giving more feel, they protect my whole hand not just the starting finger. Willkinsons Hardware Stores do a nice pair of thick all leather gardening gloves that are quite quite cheap that are ideal, being fleece lined they also keep my hands nice and warm in winter. They also do a pair of knee protectors for around £2.00 which I find great for keeping my knees dry in winter and stopping the sometimes painful experience of kneeling on a hard surface. and they don't blow away in a wind like a kneeling mat. I might look like a oldie skate boarder but I am safe, dry, and void of too much discomfort.
However, this particular day I had managed to leave the glove at home, and had to use the finger stall. What an awkward thing! I could use stronger language but I wont. I just could not get my swing right. It always feels like the the blasted rubber thing is going to fly off my finger if I give the prop a good old diesel clout, as it has done on occasion in the past. That combined with a new carb, plus the phenomenon I have noticed with rear NVA's, of fuel syphoning back out of the fuel feed pipe when not running, caused some problems initially. On reflection I think the fuel syphoning is inevitable with a rear mounted needle. With the throttle fully open position there is a larger area hole exposed to atmosphere in the carb choke, the needle forms a much smaller restriction sitting on the backplate. Exposed to more atmospheric pressure at the choke end fuel will be pushed back until it reaches the needle where a much reduced area of exposed fuel exists. If the engine is started RC wise, with the throttle shut, this should no be too much of a problem as the slow running needle then restricts the exposed area of fuel. Indeed I have noticed if the throttle is shut the fuel ends to stay in the pipe. However I start engines at full throttle, hand flicking with the throttle shut just seems to result in an inert engine. Again with an electric starter this would probably be no problem. But, I have enough junk to carry to the field without adding a heavy battery and starter. So will give that a miss, thank you very much.
Once started there appear to be no problems with fuel supply or carburation through the whole throttle range. The only ones encountered have been those caused by the slow running needle not being set correctly. Quite where these reports of slow needle/throttle response with rear needles come from, or what the people in question are doing with them, I am not sure, I certainly have found none yet, apart from the starting quirk I have already mentioned, there seems to be no difference once running with a front mounted needle. And anything that keeps parts of my anatomy away from that high speed flesh shredder has got to be a good thing, and only for the cost of learning a slightly different starting technique. I found by experiment that giving the engine a squirt of fuel down the carb is usually sufficient to get the engine to fire and run long enough to draw fuel through the feed system which then takes over as the initial charge runs out. So after a couple of flights it was back to the 2-3 flick starts. The engine still has a bark at peak rev's, but more slightly more muted than the original Mk.I engine and silencer. The real difference is in the mid to low revs range where the exhaust note is markedly more muted. I may have to add some silicon tube to outlet to tame the bark a bit more. This is a problem I have to sort out one way or another, even if it means making an extra baffle for the rear chamber..
The first trial prop was a Kavan 11x6 (not one of the yellow nylon ones), the engine was not happy on it, plenty of top end power, read that as airspeed, but vibration and uneven running at slow throttle settings running. An APC 11x4 was OK at slow speeds but produces a few too many revs and noise flat out. A change to a Taipan 11x5, the only one of two Taipan props I possess, has increased the fast speed over the 11x4 , but still the slow speed is just a bit too close to a tickover for comfort. I don't like changing brands of props when trying this sort of thing, but props are not cheap and supplies are variable and fluctuate to say the least. Next I will try a range 10 inch and 12 inch props and keep experimenting, Although I suspect 10 inch diameter is the range of props I should be using, the noise emission will increase exponentially with it. Bit of a catch 22 situation
One serious problem I have to nail down somehow, is the throttle being biased to full open by an internal spring. This has caused me serious problems. It makes solo launches very iffy as you will have already read. On one flight, after touching down at a tickover, and almost at a standstill the lines caught a weed in the grass. This caused the model to swing into the circle, still at a tickover, until the lines lost tension. The result was an accelerating model heading strait for me. I was lucky, the trailing lines caught on another weed and gave full down stopping the engine when it nosed down. The worrying thing is, it could have equally given full up and took off. The only consolation in this situation, providing it did not end up taking my head off, was the fact that I have started to use wrist strap regularly, and it would not have been able to fly off and cause mayhem elsewhere. No other fliers about if it had but a flock of sheep could have had a nasty fright.
I desperately need some mechanism that is capable of holding the throttle in the closed position but not affect the rest of it's function. A friction damper may work but might remove some of the sensitivity of the throttle. Some sort of cam mechanism may also work. What ever it is it needs to be simple and easy to fabricate. I have been puzzling over this for weeks and I'm still no nearer to a solution. I am reluctant to remove the spring as the carb barrel has a lot of side play. This will affect the slow running to a greater or lesser degree, an unpredictable slow throttle response is something I do not want. So if anyone is reading this that has solved this problem please let me know how.?
I tried recently to lightly bias the throttle closed with an elastic band. This worked, but the side effect was a horribly insensitive throttle response, it always felt like it was not going to open up when I most needed it, and had a noticeable delay before anything happend. So although it worked, springs or elastic bands are not a good answer.
In an attempt to affect the slow flying Dutch roll characteristic. I reduced the line rake considerably by moving it from the position suggested on the plan to a more conventional one. The old rule of thumb was to have the front leadout parallel with the lateral span of the wing. This usually puts it a short distance behind the centre of gravity. The Hellcat has the bellcrank pivot much further back than normal, making the suggested leadout position a very long way back. My adjustment to the old rule of thumb layout made a marked improvement. But is early days yet. Lets just say the model has become a lot more pleasant to fly, but obviously this has had an effect flying slowly around the upwind part of the circle. Warping some washout into the tips of the fixed flaps did not cause any no ticable change, although I thought it should; maybe the whole wing needs washout. Piling tip weight on did seem to have some effect, but the screw attaching the lead to the wing hard point was too short to go as far as I wanted to, so things are on hold until the next flying session and with a longer screw and some huge pieces of lead.
I also increased the elevator movement in an attempt to give it a bit more authority. This caught me by surprise when the model took off at full chat and shot up to the top of the circle above my head. it took a few laps to get used to it and reduce my hand movements a little. I will get it all to work together eventually. I subsequently had to reduce this as on one run, the transition from fast to slow really exaggerated the interaction of the simple bellcrank arrangement and the model ended up in a high speed, almost too fast for me to handle, up and down oscillation that I thought was eventually going to stuff the model into the ground at high speed. Fortunately I managed to get the speed down without loosing control and at the first opportunity reset the elevator movement to safer parameters..
If you are not a C/L flier, my previous scribblings may give you some idea of how much work is actually involved in getting what deceptively appears to be a crude control system and model to perform properly. And why I always used to inwardly scowl at the phrase, 'Bricks on Strings'. Don't knock it until you have tried it. And if you do ever try it, be prepared for a very steep learing curve both physically and mentally. And don't use the excuse, "But I get dizzy." That's all it is, an excuse. It recedes the more you are exposed to it. Did anyone ever keep repeating, "But I can't keep my balance," when learning to ride a bicycle?
I suppose this is what I have always got from aeromodelling, tinkering with all the variables until something works properly and I feel that I have some idea of what is going on, and what I am doing, from building to flying to ultimately competing against someone else. Whilst looking at an all plastic (literally) scale RTF RC model during the club Sunday quiet hour (a gesture to the complainant in a nearby farm) I realised almost none of the previously mentioned satisfaction could be had from such a model. All that can be done is to hand over money, screw in the RC gear and engine, fly it. And that is it! If something breaks, all you can do is buy a replacement part, Modifications, improvements, how? Taking a ridiculous example. I could take one of my models saw the fuselage in half and lengthen it I chose to. I lengthend the nose on the Swift by 50 mm last week, with only a piece of plywood and some epoxy, and covered the modification with some spare matching Solarfilm. I can't help but think of the plastic RTF models as toys however I look at it. Apart from the flying, there is almost zero input from the purchaser, apart from the arduous task of handing over a credit card to the retailer.
Don't get me wrong I have nothing against RTF ARTF or anything else ending in TF; in the appropriate place or for a valid reason, after all, Cox, Testors, and even Keil Kraft were producing RTF plastic controlline models more years ago than I care to remember; they flew terribly by the way, and I often wonder how many young people were actually turned on to aeromodelling by them, and how many put off for life. I have even cast curious eyes over ARTF models with a view to converting some to CL scale or possibly carrier? No. it's the fact that in the same way that 'AEROMODELLING' these days sands for RC; 'MODEL', also stands for, what you can buy off the shelf that involves no effort. I find this a little disturbing and can't help the feeling that it does not bode well for the future.
What I think has been lost is something that is almost intangible, and often forgotten. Putting work and effort into something, more often than not, gives a lot back, even in seemingly negative ways; if you really have a bad time with something, at least you know what to avoid the next time, thus saving time and effort in the future. if you take a quick look at the ageing population on aeromodelling scene, some of the longest involved people have done it all, and the hard way in the past. If they derived no pleasure or satisfaction from what they have done over the years, would they still be interested...? When I think of all the things that Aeromodelling taught me, some seemingly very unrelated on the surface, I could never have got them from buying RTF models. For example the differing properties of adhesives, and what makes one more suitable than another for a specific job, has enabled me in the past to literally glue a spark plug into stripped thread in a cylinder head of an old car engine and drive home. I never really got much from building Airfix plastic kits. Maybe I did from the 6 penny balsa chuck gliders we used to buy nearly every week and either loose or destroy in the back streets or local park. But they could be modified, and were, I learned a lot about dihedral and effects of centre of gravity position from those. I can vaguely remember experiments with penny rockets as a propulsion system around Bonfire Night. And penny bangers as a payload on such rockets. Why am I grinning?
I guess I am just a symptom of a passing age. But then again, if there was such a thing as a Control Line Flight Sim, I would want one. I can't think of a better way to spend a rainy unable to fly day, than an on-line virtual team race with teams somewhere else in the world, attempting build a virtual speed model and fly it, or stunt comps. Pity I am not a software developer.
ToughLon Yet Again
The heat of the midday sun (temp around 30 C.) cause the ToughLon to slacken slightly in small patches on the wing, and a couple of bubbles appeared on the tailplane. I can live with that. But the Hallam Swift (left of picture) I had also taken along that is covered with Solarfilm also stood up well. So I can't really draw any conclusions yet. Obviously ToughLon is very critical on application temperatures
Try as I might, I cannot get away from the fact that ToughLon has some serious issues with the adhesive used. I am constantly finding edges and corners that have lifted off. This happens with other films even Oracover/Profilm, but they do tend to stay stuck down once found and re-heated. The ToughLon seems to be a lottery as to whether it will stay down or not, whatever heat setting is used. after every flying session I have to go over the whole model checking all seams an joints and ironing loose bits down again. This is just not good enough, I have better things to do with my life, even though people say, "but it looks good."
And yet more evidence that something is not right. These blisters on the underside of the tailplane were not there 24 hours ago. The model has not moved from the workroom, and room temperature is 25.1 degrees C. Hardly what you would call excessively hot.
And yet again, the two pictures above taken a day later after standing and flying in the hot sun, I am guessing around 30 degrees C. The blisters are actually worse than they appear in the picture with one that runs for half the tail plane span next to the hinge line. Again the Solarfilm covered Swift was there and survived better.
I am sick and tired if this, if you where me, would you touch the stuff ever again? But to re-cover would be too big a job, on a model that I am aware of most of the faults that exist (by the third model I will probably have it all sorted). It would be easier to build the next one from scratch and cover it with something more stable and reliable, although I am beginning to doubt a material that would fulfil my needs actually exists; so far Oracover/Profilm comes closest, but is still far from ideal.
Annoyed About Fuel Supplies
At this moment of time I have just had a experience that irritated the hell out of me. So I hope you will forgive forgive me for venting my feelings.
I am running out of glow fuel. I only have enough to last for two, maybe three at a push, flying sessions. If you read my previous writings you will know that my local model shop has gone out of business; not that getting what you wanted from there was always a successful venture. So I decided it might be a good idea to get some fuel now rather than wait until the last minute, then run around like a headless chicken trying to find a supplier. The nearest model shop is in Hinckley about an hour plus drive there and back, my days of using the motorway as race track are long gone.
Deciding it might be prudent to find out if they had any of the fuel I wanted in stock before I left, I telephoned. The conversation went along these lines.
"Hello, Do you stock Modeltechnics fuel."
"What fuel do you stock? I need an equivalent to Duraglow 5 or a 20% strait Castor mix"
"We stock the whole range of brand XXXX. a very reputable respected fuel in X% nitro to XX%nitro"
This sounds suspiciously like a sales pitch to me.
"OK. Any have a 20% strait Castor oil mix?"
"Sorry I don't have access to information about the make up of the fuel."
Think to myself, 'Well sorry, but I have no intention of buying something without knowing what's in it.'
And down went the phone.
Now I am p****d off! All I can do is order over the internet from Balsa Mart (Blackburn Models) and pay considerable transport costs, ordering twice as much as I really need to try and make best use of the postal charge. All at time when I need to conserve my outgoings. There is a kind of model shop in the city centre that is part of a big toy shop, but they seem to cater mostly for the model car brigade. Being faced with driving round until I am dizzy looking for a parking space or paying to park. I may as well use the internet. I could use public transport, but if you could see and hear some of primordial stagnant pond life I have to share it with, you would know why I would rather not.
I am not blaming Balsa Mart for any of this this, apart from one wrong sized prop I received as part of an order, they have served me well, and just lately they are proving a life saver. It's just the way the world is. But it does keep making ever larger holes in the modest amount of money that I do have to spend on this hobby. At least I have the consolation of getting to choose what I want, and not have someone trying to sell me an unknown composition fuel mixture, that HAS! to be OK, because it's supposedly developed by someone called Yurtis Wateryveins, or has some exotic name like 'Quark's Ion Booster Rocket Fuel with 50% added Boggle Juice. You know it's the best, it's expensive!' Some of these are in American pints and gallons, not even Imperial pints and gallons that the anti-metric reactionaries are so wedded to, it's strange how they never complain about those differences. So we can be short changed before we even start. And people wonder why I prefer the metric system?
OK. Moan over.