[REQUEST] Controlling aircraft pitch with flaps

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I’m re-opening this old topic as, after eight months and three people working on it -including a qualified aerodynamicist- we have been unable to get correct pitching motion with flap deployment.

First of all, to set the target behaviour, this is how the aircraft behaves in reality and what we are trying to reproduce:

START STATE: Flaps 0, 160kts, gear up. Pitch 0 degrees.

  • Deploying flaps 15: pitch will remain 0, AoA will gradually decrease to -2 degrees (the plane will climb). After a bit the nose will start dropping very slowly.

BEFORE DEPLOYMENT OF 30, START STATE: Trimmed straight and level at flaps 15, 130kt, pitch 0 degrees, AoA 0 degrees.

  • Deploying flaps 30: pitch will remain steady initially, with AoA going from 0 to -2 degrees and +500fpm. The plane then slowly drops the nose and stabilises to -5 degrees, while the AoA indexer ends up at 0 degrees (-5 AoA). Final attitude straight and level, 5 degrees nose down.

BEFORE DEPLOYMENT OF 40, START STATE: Trimmed straight and level at flaps 30, 125kt, pitch -5 degrees, AoA -5 degrees.

  • Deploying flaps 40: At 125kts, the plane will slightly increase VS by less than 100fpm and AoA will go from -5 to less than -6 degrees. The nose will then drop 2-3 degrees and AoA will stabilise at -5 to -6 degrees. Approach attitude at 105kts will be -7 degrees, at 90kts will be -3 degrees.

We were able to get correct approach settings, but the deployment is very problematic, with the plane nosing up aggressively.

  1. Adding camber to get a nose-down pitching moment: to get a pitching down effect we’ve had to use values in excess of 26. At that point, the induced drag is so high that it is impossible to achieve a negative AoA for approach. Reducing drag had little effect, increasing lift caused the AoA to drop even more
  2. Adding aft CL: It was possible to use aft CL to get a reasonable deployment at flaps 15, but when negative AoA is needed the effect is not enough to stop the nose-up from happening.
  3. Combining aft CL and Camber: Increasing camber and adding aft CL helps control deployment to some extent, but we move the wing so far aft that we are losing pitch authority and can’t flare

Overall we need a pitching moment scalar or some way to make the plane pitch down like FSX had.

It is worth noting that Leonardo’s MD-82 for MSFS had it close to perfect, until the pitching moment for the flaps was deactivated.

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