Plane: Disallow climbs during TRANSITION_AIRSPEED_WAIT

[WickedShell]

assist_climb_rate_cms() will bring in the altitude error in the mission as a desired climb rate on the quad motors. This is very poor as it adds a lot of load to the airframe, puts the VTOL motors into a mode where they are working harder (during which time on a single power source system you are usually experiencing the peak draw), adds drag to the airframe, and hurts the angle of attack.

This does allow the existing cases where we were accepting a decent during the transition for some reason, but since the most common missions (and pilot input) are to transition at the same altitude or climb to the next waypoint this is protecting those modes.

This could be done with Q_OPTIONS but from discussions with @lthall we thought the default behavior should be level transitions.

[Rolf-G]

@WickedShell
Just to understand that correctly. What do you mean by "Disallow climbs during TRANSITION_AIRSPEED_WAIT" ?

Disallowing climbs only while in auto-mode or generally (initiated by pilot due to switching from a q-mode to FBWA) ?

In the latter case, i want to disagree, because it would be an unnecessary and dangerous restriction of pilot authority. Afterabout 150 pilot initiated transtions (with tiltrotor, q-planes and vectored tailsitters) with arduplane i dont want to miss the possisbility to gain altitude before transition speed is reached, especially when you initiate the transition at low altitude.

[Halifacts]

@Rolf-G
My thoughts would be

1. If you desire more altitude during takeoff, why not just set or climb to a higher transition altitude?
2. Gaining airspeed is critical for fixed-wing, especially at low altitudes. You should not be trying to climb at low airspeeds.

[WickedShell]

@Rolf-G The intent was all transitions. The effect of using your vertical lift component to climb while trying to do the transition actually makes it harder on the vehicle to transition to forward flight which is where your faster climb rates are available. (And if you don't get a faster climb rate in fixed wing mode, then you should be able to be using the VTOL mode to easily clear obstacles before transitioning).

I've added the usage of LEVEL_TRANSITION Q_OPTION to make this opt in behavior, but I strongly think that's the wrong thing to do, as it makes the default out of box experience on a quadplane take longer to do transitions, and makes it more likely to fail.

[Rolf-G]

@Halifacts
Why not climb at low airspeeds, especialy in VTOLs ?!!!!. During transition_airspeed_wait its even safer as climbing with any other "normal" airplane. Worst case you will not reach transition speed (ARSPD_FBW_MIN) and have to give up the climb.
By the way: Without climbing at low airspeeds normal planes would not be able to take off from the runway ;-).

@WickedShell:
Thanks for making this behavior optional, so I am able to disable ;)
Still another question:
Will it be possible to climb after reaching the tranisiton speed or only after transtion is completed ?
There could be another 5 seconds of forced levelflight after reaching the tranistionspeed, if Q_TRANISTION_MS at a quadplane is still 5000 (i believe default value ).
Example of my last flight with the mini talon quad (Q_TRANISTION_MS = 2500)

Regards Rolf

[WickedShell]

@Rolf-G Planes climb once they reach Vr. This is above stall speed, and is used to ensure the vehicle is generating sufficient lift. It should also be noted that this patch strictly increases your ability to reach transition speed. By climbing with the VTOL motors you've reduced your angle of attack, increased the drag on the system, in the case of a single battery power source you've increased the load on the battery and decreased the power available to the forward motor. Also worth noting that if you look at your log this would have had no effect on limiting your climb performance. You didn't try and climb until after you had hit transition airspeed.

This limit only applies to before the transition airspeed is reached. I should note that during the entire transition the fixed wing surfaces are allowed to demand a climb or descent.