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MKelly
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Re: What am I doing wrong with these models?
Reply #1 - Nov 7th, 2021 at 11:27am
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Hi Dan - from your description it certainly sounds like thrust adjustments are needed.  My Spitfire started out the same way - great glide, first powered flight with just a hundred turns or so stood it on it's nose.  Recommend adding down thrust and trying again at the same low turns.  Keep doing this until the model flies out without raising the nose - add some right thrust if it seems to be getting pulled over to the left.

Once it'll fly out roughly level start working up in turns - you'll probably have to add a bit more down and right thrust as you get to higher turns.

One other thing to look at is how much difference you have between wing and stab incidence.  If the stab is more than 3-4 degrees leading edge down with respect to the wing you may want to move the CG slightly back and repeat your glide tests.  Too much negative incidence on the stab (LE down with respect to the wing) may glide test OK, but as the prop increases airflow across the stab and the model moves faster it'll make the model pitch up. 

I like to use an incidence meter (there's instructions to build a simple one in the tips and tools section of the forum) to measure this before starting powered flights.  If the difference between wing and stab incidence is more than 3 deg I'll adjust CG and repeat glide tests before moving on.

Hope this helps,

Mike
  
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DanSnow
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What am I doing wrong with these models?
Nov 7th, 2021 at 2:39am
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Here's the back story. I have 40+ years flying RC, stopped about 15 yrs ago, then got into rubber power about 4+ years ago. So I thought I knew a little about trimming new models. But that was using trim tabs, etc etc.

Yesterday took 4 new models out for their maiden trim flights. First up was an IL-2 from Ozark Model Aviation, 32" span. Balanced per designer recommendation, without prop, test glide in back yard resulted in flat straight glide, no stalling or turning. To the field, prop and motor installed, rebalanced same point. About 75 turns or so just to keep prop turning. Sharp pitch up, stall, splat. Rechecked CG, checked wing and stab setting. Another 75-100 turns, same result, pitch up, stall, splat.  Embarrassed

So what is wrong? No noticeable warps in wing or stab. Is it thrust setting? Seems like there wasn't enough turns for it to be that. Or is it wing or stab incidence? Need help on where to start.
What made it a rough day was 2 of the remaining 3 did the same dang thing. Initial glides without power reasonable results. Initial trim launch with minimal power pitch up, stall, splat.
Tally for the day, one model, 21" Otter built from Pres Bruning plans, flew fine, no stalling, gentle RH turn. After 2 flights put away till I make a stronger motor. The others, 2 broken props, one broken stringer, one broken wing strut.
  

Curse You, Red Baron!!!!
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