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E-Flite Ultimate 20-300 strange rolling under positive-G

Old 12-14-2010, 10:51 PM
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hogarthd
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Default E-Flite Ultimate 20-300 strange rolling under positive-G

I've been lurking here for a year, it's nice to finally post something

I've been flying RC airplanes since I was 12. I'm 34 now, and I've only recently gotten into brushless electric flight. I had a beat-up Parkzone Spitfire that I flew at my office for a year, but I "retired" it (only partially on purpose) and decided to move up to a really nice, brushless aerobatic airplane.

I bought an E-Flite Ultimate w/a Spektrum radio, Hitec HS-65b servos, and the recommended E-Flite Power 10 setup. It is a GREAT flying airplane! I've been having a blast with it for the last month. The included linkage hardware is of terrible quality, but otherwise, I love this thing.

Recently, however, I've noticed a strange behaviour that has developed in the little bipe - when I pull hard positive-G, the airplane rolls to the right. If I do a hard loop, for example, particularly on full rates, it ends up barrel-rolling to the right. If I do a less aggressive loop, it tracks pretty well. I can't figure out what's going on. I worried that maybe the dual elevator was decoupling, but it seems totally solid. I thought that maybe I was accelerated-stalling it and it was stalling the right wing first, but it just seems too consistent/predictable for that. The ailerons seem to be rigidly attached - no play, etc. I'm wondering if anyone else has seen this in a 4-aileron biplane or any other airplane for that matter.

If I keep the aggressiveness down, it's fine. It's strange to pull G's so suddenly anyway - I fly a real Pitts S2C on occasion (when I can afford it) and it's horrifying to imagine yanking the elevator around like I do with the RC Ultimate, but it seems to be the way the model is supposed to be driven for maximum awesomeness.

Anyone have any ideas?

thanks!

Hoagy
Oakland, CA
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Old 12-14-2010, 11:14 PM
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JetPlaneFlyer
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Hoagy,
It's not unusual to roll out of loops if you pull back too hard on the stick. All that's happening is you are stalling the wing, usually one wing stalls fractionally before the other and the plane rolls in that direction. It comes as a surprise to some but if you pull enough 'g' planes will stall at high speed just as easy as they do at low speed .

If it always goes right then you may find the right wing might be twisted a little which is worth checking and it's also worth checking that the model balances laterally (i.e. balances 'side to side') but the real solution might simply be not to haul back on the stick quite so aggressively. The problem is always much worse if the plane is heavy. If you for instance added a larger battery thus increasing the wing loading then that would make the model more likely to stall out of high g manoeuvres.

Steve
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Old 12-14-2010, 11:19 PM
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newjak
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That plane uses a joiner rod for the elevator halves. The control horn is on the right elevator. Double check to see if the joiner has widened out the hole in one of the elevator halves. It sounds like the right elevator may be deflecting more than the left under load.
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Old 12-15-2010, 01:44 AM
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hogarthd
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Default Great!

This is great advice, thanks guys!
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Old 12-15-2010, 08:52 AM
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Newjak's suggestion is a good one.
The nature of the roll would probably indicate if it's a stall or just slop in the elevator joiner. I'd expect the elevator issue to cause a quite slow steady roll to the right. Stall will usually give you a sudden snap roll.

Steve
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