Aerodynamic Forum

摘要

"Hi Alasdair, I have a Graupner Extra 300S (63" with 91 2-stroke) and a Black Horse Sukhoi Su-31 (54" with 70 4-stroke) which both exhibit a strange trait although the Sukhoi is the worst. Both models fly superbly in most circumstances and offer beautifully accurate rolls, loops, stall turns etc. but if you are a bit insensitive with the elevator they flick roll to the right - quite viciously in the case of the Sukhoi. By 'insensitive' I don't mean screaming along at full chat before whacking in full up - you would be asking for trouble doing that. But if you apply up elevator a little too quickly then - oops, there you go and you're off on another heading. Typically this might be at the bottom of a loop when you need to tighten it slightly or even during a 'bank & yank' turn - roll to 45 degrees apply a bit of up and round she comes, bit more to tighten it and oops, there we go again. It seems to be mainly to do with the speed of application of the elevator in that if you steadily apply increasing amounts of up then the loops just get tighter. Apply 'up' too quickly & it flicks out to the right (always the right), even from straight and level cruising. Both are a bit awkward to land and need flying right down to the deck as they seem to stall, at what looks to me and onlookers, a pretty high speed. They are not easy to get down without a head wind! As far as I can tell C of G, lateral balance, incidence and thrust lines are all as recommended. Many theories have been put forward by club mates, mainly to do with it being a high-speed stall causing a wing to drop. Can you shed any light please? It's putting me off flying them!" Steve Hargreaves.