FW Flaps on landing Abort

[ryanjAA]

Currently when you manually abort an auto-landing, the flaps retract immediately.

This is a problem because you can potentially be below the stall speed of a "clean" (flaps not extended wing). We saw several vehicles crash at MTOW like this.

This PR solves this by keeping flaps set to the landing flaps amount until the rotation airspeed is met.

Landing flap scale (FW_FLAPS_LND_SCL) was chosen rather than takeoff flaps as you may not use flaps on takeoff but are using them on landing.

Rotation speed (RWTO_ROT_AIRSPD) was chosen as that should be a comfortable airspeed at which you are getting ready to climb at the beginning of your mission, min speed didn't make sense given it could be much higher... Also, it is latching so you don't go slightly above rotation speed and then have the flaps retract and extend, I saw that in SITL testing early on.

Concerns would be climbing with flaps and hitting critical AoA of the flap, if that is an issue (or at least a valid concern) we can divide the landing flap value by 2 here to deploy half the flap amount or add a new param for abort flaps.

This was tested in SITL extensively on 1.14.x to not impact hold mode or scenarios where you were below rot speed and put it into hold, etc.

EDIT: updated airspeed to eas for main.

@sfuhrer

[ryanjAA]

https://review.px4.io/plot_app?log=fe488fa9-efda-46a9-a996-e9bd8cd8c47f

[ryanjAA]

1.14.x log:
https://review.px4.io/plot_app?log=67140054-7ebe-4827-abfc-cbe31f7f3bb5

[sfuhrer]

Hi @ryanjAA , thanks for the proposal. I though wonder if we cannot make it much simpler and without the airspeed dependency and just keep the flaps extended in the landing configuration until we have cleared the abort altitude. Have a look at #23877 thus please and let me know what you think!

[ryanjAA]

@sfuhrer, I’m with you on this, and I initially implemented a similar approach to what you proposed in #23877. However, after discussing it with our aero guy, we decided to change course because of a potential issue with climbing to the loiter altitude (especially if it's high). The problem is that with landing flaps deployed, a high angle of attack during climb could stall the airfoil, as landing flaps typically have a much larger deployment than takeoff flaps on a full-size aircraft.

Without dedicated takeoff flaps, there's a gap: we either need an "abort flap" setting (which isn't ideal because it introduces a new param and setting) or simply retract the flaps once sufficient airspeed is reached, hence rotation speed. The concern is that if the flaps remain deployed during the climb, the pitch-up could put the aircraft into a "flap-induced stall."

Landing flaps are designed (im sure you know this, just writing it for good measure) to create lift and drag, slowing the aircraft for descent. But in a climb, they can push the angle of attack beyond what the airfoil can handle at low speed and high power. This excessive drag, combined with a high angle of attack, risks causing a stall or preventing effective climb.