Prevent rotation pitch calculations from running post-rotation

[Georacer]

Summary

This PR prevents the nav_pitch calculations related to takeoff rotation (Plane::takeoff_calc_pitch()) from taking place after the plane has completed the rotation.

It addresses an issue reported for ArduPlane 4.6beta.

Details

The nav pitch during rotation is set to scale linearly based on the groundspeed/airspeed_cruise ratio.
After that, the rest of the pitch calculations (e.g. calc_nav_pitch() when airspeed is enabled) can resume.
Also, at some point, if enabled, the level-off calculations will take over and reduce the demanded pitch.

But, if due to misconfiguration or a sudden strong headwind the groundspeed falls below cruise airspeed, the rotation calculations will take effect again and override the rest.

One result can be that pitch will be held high and the level-off calculations will be ignored.
In the following SITL test, the red cursor is set on the point where a strong headwind is turned on:

Another user has reported that there's also a chance to lead to a ping-pong effect, when the groundspeed oscillates around cruise airspeed:

The fix declares a new state flag, which gets set when the rotation is first complete.
Then, it will never let the rotation calculations to run again in the same takeoff.

An autotest has been created to prevent future regression.

Additional test fix

In my local testing the autotest Plane.TakeoffGround() would fail locally, even though it has recently passed in CI.

I have found that this is related to the difference between VHR_HUD.groundspeed and gps().groundspeed(), both in value and publication rate.

The autotest waits for the VFR_HUD.groundspeed to check the nav_pitch angle, which comes from AHRS.grounspeed.
But Plane::takeoff_calc_pitch() uses gps().groundspeed(), which is both lower and has lower refresh rate.
As a result, at the time of the check, the nav_pitch angle was outside of the test interval (14.69<14.9) and fail the test:

The test shifts the check for a bit later.
It was also necessary to push back the loiter part of the takeoff, to remove the effects of level-off and stall prevention (during banks) on nav_pitch.

Testing

Testing in SITL has been done:
takeoff_rotation_vs_leveloff_tests.zip

[IamPete1]

This PR is against 4.6? Do we have the same issue in master?

[tridge]

thanks for this! just need to make sure we reset for takeoff mode

[tridge]

@Georacer we also need a PR against master, should go into master first

[Georacer]

@Georacer we also need a PR against master, should go into master first

Here have it! #29860

fixed

[rmackay9]

@Georacer,

I've re-run the failing test but it doesn't seem to be happy for some reason. Maybe you could have a peek and see if you can figure out why it won't pass?

[Georacer]

@Georacer,

I've re-run the failing test but it doesn't seem to be happy for some reason. Maybe you could have a peek and see if you can figure out why it won't pass?

I will try locally. Thanks Randy!

[tridge]

@Georacer forced push change to try to make this pass CI

[Georacer]

@tridge it still fails two builds, in what I think is not related to my change.
Could you take another look?

[rmackay9]

This has been included in 4.6.0-beta via PR #29888