Well, well, after 53 years of flying, I did something new and learned something new today! I was flying a Bellanca Scout towplane and I looked at the stick-free behaviour when lowering full-flap. The Scout only has 27º flaps, not the C182's 40º barn-door flaps, but adequate for this experiment.
I was in the first stage of descent after glider release - flaps up, 2100 RPM, trimmed for 80 mph. With hands off the stick, I then quickly applied full flap. The nose pitched up to 15-20º above the horizon and the IAS reduced to a minimum of 55 mph. The Scout then entered a phugoid with about a 15 second period. During the first cycle, the maximum IAS was 85 mph (Vfe is 100 mph). Subsequent cycles were significantly damped compared to the first one, but the phugoid was still present after six cycles, with the IAS oscillating around a nominal 65 mph.
After stabilizing the IAS, I then tried the obvious thing - raising the flaps. A very similar experience, but in reverse. The nose pitched down and the IAS reached 90 mph, before oscillating with 15 second phugoids and eventually beginning to stabilize around 80 mph.
I'm going to try that again, but with a flight recorder. I'm also going to look at the difference in trim position between the stick-free flaps-down speed and after retrimming when putting the flaps down.
Last edited by India Four Two; 3rd Jul 2020 at 02:31.