Dive flight recovery from -90 degrees pitch

ArduPlane
1

Hello to all,

It’s my first post here, I’m building an experimental plane, I was looking for solutions few days without success.

I recently crashed with some unusual issue. My drone (5 channel plane, 1+5 aileron, 2 elevator, 4 rudder, another channel for manual throttle control, T-tail) was in dive flight in AUTO mode, and it want to recover with pitch down output signal. It was -90 degrees dive flight and autopilot want to recover through inverted flight and then roll with ailerons to horizontal flight.

It was experimental flight with testing Vne speed and flatter durability. My plane don’t have exact +/- G’s durability. It’s less strong with -g force in Z axis (elevator forward/nose down).

Now I know that when in AUTO/FBWA mode and drone reach -90 degress, then autopilot in a moment change steering from pitch up to pitch down. In manned flight it is unusual to recover from dive to inverted flight through pitch down (elevator forward).

Is there possibility to change algorithm to make returns from dive to horizontal flight only with pitch up signal?

I’m flying with:
-cube black with SB, newest arduplane firmware and newest Mission Planner
-calibrated airspeed sensor
-internal compass
-gps
-external baro
-motor turned off (throttle assigned to manual channel, without A/P control)
-plane tuned in auto-tune mode, servos properly configured, manual and auto mode tested (without double reverse problems).

Best regards,
Peter

2

I suspect it just goes which ever way is the shorter to get back to the desired angle. I think it would require a code change to make it always pitch up I think. I’m interested as to why you would want to fly in such a steep dive?

3

In most cases it will be released from another UAV. I’m testing something like “dive takeoff”, regardless I think it’s better to recover always using pitch up command. It will be useful also in “normal” type of flight in stall avoidance or inverted spin recovery.

Best regards,
Peter

4

this might interest you Flight envelope protection: better stall prevention based on airspeed and g-load

Probably the first step would be to add a proper negative load factor limit to the code, then we can work out which way would get us back to level faster. ie pitching up at the positive load limit or pitching down at the negative load limit.

5

Thanks, I’ll look closer to this, but I’m not familiar with programming. I have to spend some time remembering basics, then I can try to change arduplane code.

I’ve found another solution: automatic takeoff command. NAV_TAKEOFF have two parameters, pitch up value and height. It will be perfect if height parameter could have negative value.