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Kari
When the wing is about to stall, any movement of ailerons may interrupt the flow and cause a stall there. In effect lift is lost and the wing drops. From the pilot's point of view it looks like reversal od aileron controls and hence is very dangerous.
To prevent this and make the aircraft safer, the wing is designed to stall at the mainplane first. This may be achieved either by a different less stall-prone profile on the wingtip or by the geometrical twist - changing the angle of atack on the wingtip, comparing to the root. Of course, penalties are paid for those sollutions.
I have a NIIVVS or CAGI test for La-7, I will dig it up and check the data there. Certainly there were performance data but I think also some discussion concerning loss of performance in series aircraft.
Another interesting thing is report filled by Hans-Werner Lerche after testing of captured La-5FN. It is not very favourable having some 40 km/h lower speeds comparing to series aircraft data. I have seen an explanation it was due to lack of automatics which caused proper settings rather hard. Of course a question arise - was it possible to achieve high performance figures in combat conditions?
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