Re: Approaching the new rules from a design standpoint

From: <joshuawfinn_at_gmail.com>
Date: 17 Apr 2014 05:03:25 -0700

Mike,
  
  This is why I went to .015 motorsticks, and not light wood either. Most of mine is 5 lb. I used a piece of sub-3 lb for the record model, but that was .017 balsa, too. And it exploded on me on Saturday. Might have something to do with having several hundred flights on it, though. In my most sarcastic southern drawl: For reasons I simply don't understand, repeated launches in 90-115 F conditions at .55 in-oz eventually seem to break down the wood.
  
 I read about wing twist at launch a lot when I got into F1D. My own tests showed very quickly that if I could get the model to remain stable at launch, the less wing twist, the higher it would go. Trouble was that less wing twist equates to more tendency to straighten out shortly after launch, pull to the right, and stall. I kept slowly enlarging my rudders, and then Nick Ray mentioned that I wasn't using as much wing offset as a lot of other folks. So I increase it to .75", then to 1", and finally to 1.25", at which point I could launch in whatever configuration I wanted to, with minimal wing twist, and get the model to climb in perfect circles, provided that the stab didn't tuck (I've got one that likes to do that when the airspeed gets above a certain level, and my models are trimmed pretty hot on launch torque). I saw no loss of cruise or descent performance from the increases in wing offset. I'll add that these changes were done prior to switching to reduced-area wings. I've done some experiments which indicate that they don't need quite as much offset. Time will tell. I've never flown one on a fixed pitch prop.
  
 The new rules will likely reward continuing with this setup, though motors may get a little thinner, allowing us to reduce the offset back to, say, 1". Proper flight trim will become critical...the models will likely be trimmed even hotter than before. Wing spars are already being seen that are less than .040 deep. Will we see .030 now with 6 borons per spar in the center section? Will stabs go to .020 deep spars with 4 borons, or will they go all carbon? It will be interesting, to say the least.

 Good flying,
 Joshua
  
Received on Thu Apr 17 2014 - 05:03:25 CEST