According to the plots we made the rate of speed decay was kept constant from 1.3 Vs to stall. We plotted the speed over the time in one plot and in to other pitch rate and elevator position over time in the other. All stalls on both aircraft were performed by the same pilot. The stall speed was determined as the speed where the elevator reached the up stop and the nose down pitching. Interestingly this happened more or less at the same time for all performed stalls. For each configuration a number of 5 stalls were performed and the resulting stall speed were within 1 kt.
During our investigation the question about the trim condition came up. The regulation states that the airplane has to be trimmed at 1.5 Vs. Does that mean that the airplane has to be trimmed in power idle which would result in a descent or in power for level flight at 1.5 Vs and than the power will be reduced from there before the stall maneuver?
There was indeed a difference of about 2° in the trim tab position between the two airplanes during the tests.
We don't have any information on the idle rpm, but from what I remeber the difference was not more than 100 rpm. Does 100 rpm have an effect?
From what I can take from your replays we should concentrate on the trim tab position, idle rpm and decay rate. Are there any other recommendations?
Thank you very much for your help.