The Law of Diminishing Returns (Resurected)

[Robmoff]

The Law of Diminishing Returns
« on: February 16, 2013, 10:39:47 AM »
Not many people seem to be aware of this natural law, put briefly it states that on return from a flying session, however perfect the conditions may have been, the modeller will always have fewer models in flyable condition than when he started.

I am reminded of this because I just had a brief, VERY BRIEF, session with two mini R/C planes. The first was a maiden flight of a home brew, all depron Whittman Buster at 18” span. It was fairly nose heavy and needed full up trim to fly, even though the CG was on the spar line. Still everything else was OK, plenty of urge, reasonable roll rate and all looks promising, but turning for the landing with that much up trim close to the ground resulted in a busted tail. Should be fixable though and with the battery moved back a bit I’ve got a flyer.

No. 2 was and ERC micro Mustang. Now in strict terms this should not have been a flyer anyway, I bought it as a crashed wreck on Fleabay for next to nothing to scavenge the R/C stuff for small scale (16-20”) stick and tissue R/C. But the damage was all repairable, the wings had folded and detached from the carbon spar, the fin was off and it needed a new propshaft, but it was still easily  fixed up. Last time out it caught some rough grass on landing and I did not notice that it had a new crack in one wing, certainly showed up on the next launch though! Still, I decided it warranted at least one more fix. Today it flew fine, they are really fun to fly, and being blown about by every minor gust just adds to the excitement. However a loop from a high speed dive showed that the wings had had just one too many folds and repairs. Now I shall have to dig out the R/C gear and start planning how to get it all into a Guillows Avenger that’s waiting at the back of the bench.

So today I started out with two, came back with one repairable and one write off, but I am not at all disappointed with that score. In the past however..........

The last really good flying session that I had was in about 1985. The kids had all foam rubber powered Bentom planes. One was a Zero, the other a Mustang. Both were about 20” span with a 5:1 gearbox and flew quite well, though the Zero was always better than the Mustang. I had a shoulder wing non scale plane from the same range with a Telco CO2 motor, now that really did fly well considering that it took all of 20 minutes to make! I also took a CO2 powered own design mini pylon model, think of a Ramrod at 24” span and built really light, first flight for this one and easiest trim I’ve ever done. Tried a long slow climb on a low throttle with nice wide turns right under power, left glide. Two minute flights even with no great height gain. Next I turned the wick up and added some more right thrust (with a bit of grass stalk IIRC) and got a more spiral climb to a decent height and flights of about the same duration, magic. Decided not to risk more flights with this until I’d fitted a DT. So I flew my KK Senator, this was the second one I had built since the other had been such a reliable flyer but had been given away when we moved house. That too was a maiden flight and trimmed out well. So by this stage in the afternoon the kids are still flying, I have a Senator in the air and sometimes manage to get my CO2 foamie up at the same time, and so far nothing has broken. Now I come to the one I have been ‘saving up’ for. A KK Starjet. This is a Jetex PAA loader powered duration model, very light build with sparless wings and tail and slim fuselage, and newly built. A few unpowered launches from a small hill show that the glide trim (mostly from a tilted tail) is pretty good, and I load the motor with a single pellet (PAA Loaders take up to three), I’m all fused up and ready to go and at this very moment the  farmer turns up with his brother, wife and kids. Now I know this is the kiss of death, but I just have to do it. Light the wick, wait for the FIZZZZZZ and a steady launch followed by a rapid acceleration into a nose up spiral climb that quickly turns vertical, JUST LIKE IT’S SUPPOSED TO. I can’t believe it, a perfect flight, in front of witnesses. Well there was lots of chat and much interest from the extended party, and I just have to go for a full load. ANOTHER PERFECT FLIGHT. All my Christmases and birthdays have come at once, I started with six planes, I’ve flown all afternoon, and I’ve still got six planes.

Well we all go back to the farmyard where the car is parked, and all six still working models get carefully put in the car. I now go to help the farmer’s brother put his new caravan into one of the barns (That + haymaking etc is how I pay for the ‘rental’ on the field). This new caravan is bigger that the old one, and it takes a bit of time to get the angle of approach right before it all goes in. But it all gets done and I can go home with my six planes. Well, actually, no. The dog; did I forget to mention the dog, lovely animal, an English Setter, beautiful markings and the friendliest nature you could possibly imagine, has become bored shut in the car on her own and has knocked down the dog guard that keeps her in the back and has bounced all over the aircraft on the back seat trying to get comfortable. And she’s done a good job, there were no large bits left to get in her way, in fact there were no bits left large enough to actually recognise. Six complete write offs and the end to my best, and worst, day’s flying ever.

Rob

[Robmoff]

Part Two, in which our hero comes of age.

OK, so I had built and flown a few rubber models and gliders as a kid, I even had a dabble with Jetex power, but I had never owned an engine. I sort of drifted out of modelling when the succession of GFs turned into a wife and kids when I wasn’t paying sufficient attention. Still, they were an excuse to start again, partly prompted by a friend giving me an ED Bee that he could not get to work. Well I managed to sort that out (I’ve still got it and it still runs, though it’s a sod to start now  since it needs a rebore!). So I made a KK Phantom and began a long love affair with control line, but that is another story. This one deals with my first foray into SERIOUS modelling. I built a Keil Kraft Gaucho. 44 inch span power duration model with whistles and bells. Washout on the tips, washin on one inboard panel, tilted tail, dethermaliser and an engine! All stuff that was new to me at the time (about 1973 IIRC). I bought a new motor, an Enya09 and a clockwork timer; I’m in the big league now!

Once the Gaucho was finished I put it in the car to try to grab some trim time, the job I had then involved a fair amount of driving about rural countryside, and a suitable opportunity would soon appear. So returning to the office in the late morning I make a detour to a small park. The glide trimming goes really well, and I am soon ready for power. I have seen a tip (probably in Aeromodeller) about using a short length of fuel tubing as an engine run timer; basically you start as normal using the tank built into the model, then just as you launch you pull off the fuel tube at the tank end. Once the fuel in the line is used the engine stops, simples. I have a tube fitted that will give me 2½  to 3 seconds run, so I’m not going to need the D/T. With the motor started I pull the fuel tube, wait about a second or so and launch. I am AMAZED by the speed at which the horizontal launch becomes a vertical climb. This is magic. But the short motor run did not really get enough height to really judge if the trim is right, but it’s obviously not bad! So this time I want an absolute minimum of delay between pulling the fuel tube and getting the launch away. Isn’t it funny how trying to hurry creates so many cock-ups.

The launch went well, rapid transition to a vertical spiral climb went well, engine cut off at three seconds did not go so well. I am watching the model climbing like a rocket and it slowly dawns on me that I must have fumbled disconnecting the fuel tube, 10 seconds in and the model is still on its way to heaven with the motor just about audible, 5 seconds later I can no long hear the engine and as the plane passes into the cloud layer I can’t see it either. Bugger! I hang around for the rest of my lunch time but no sight nor sign of a model. I make some estimates of the wind direction and speed, basically only a slight drift northeast wards, and go back to work. Straight after work I go home, pick up some maps, a sandwich and flask of coffee and I off hunting. Well I looked for hours, and with the light going make my way despondently home. Nothing. When I get home the wife tells me that I’ve had a phone call from someone who has my model. I ring her back, yes it’s my Gaucho, it landed in her back garden and her kids carefully brought it indoors. I thank her, get her address, and I’m off to collect it. I am a bit surprised as to the location, it’s much further downwind than I had expected.

When I arrive at the address, the model is in good order, so the kids really have been careful and deserve the bag of sweets I’ve brought as their reward. I casually ask what time it landed, thinking ‘I wish she’d phoned earlier and I need not have tramped over miles of countryside looking for it.’ The answer was ‘Oh about quarter to seven, just after my husband got in from work’ So It was STILL FLYING when I was looking for it! It was STILL FLYING six and a half hours after I launched it. SIX & A HALF HOURS. This is some plane, I’m going to take the modelling world by storm, they won’t know what’s hit em!

Well a couple of weeks later, it’s a club day. I was a member of the Shuttleworth Collection at Old Warden at the time, and the model section flew there once a month, but being a working airstrip there were rules about flying when there were full size aircraft around. As luck would have it I am all fuelled up raring to go and show everyone around what a top class model can really do and some joker in a Tiger Moth comes into view about ½ mile upwind of the airfield, so flying is suspended while he is on approach. After about five minutes I have a discussion with the club captain about whether messing about performing dodgy aerobatics at low level a few hundred yards upwind of an active runway constitutes ‘being on approach’ but he rightly says we have to be cautious. And we are, for the next ½ hour. Then the Moth gains height turns south and disappears from view! I am annoyed. Isn’t it funny how being annoyed creates so many cock-ups. Now that we are clear to fly I quickly get the motor running, check over the plane, set the D/T and shape up to launch. I’ll show them some flying now, something they will all remember. Oh how right I was. As I launched one of the wing bands came shooting backwards and just missed my head, it had snapped. With not enough bands on the wing, and those that were still there unbalanced, the wing shifted on the pylon and the vertical spiral climb never happened. Instead the sequence was launch, corkscrew loop, shattering collision with ground, and all in a lot less time than it’s just taken for you to read.

The timer survived, the motor survived, everything else was in bits the size of a matchbox, but I felt even smaller than that. Bugger.