AP_TECS: blend weights when changed

[magate]

Context

Weights change in a step manner which can cause large pitch commands specifically for quadplanes after transition.

Proposal

Blend the speed weighting.

Testing: note this testing has the logging added for TECS SKE (ArduPilot#25287)

Initial testing

before_with_poor_handoff.BIN.txt

Figure: TECS weights with airspeed. 1) start of transition 2) end of transition

Figure: TECS weights with DesPitch. 1) Start of transition, TEC2.KEW steps and pitch steps in unison. 2) End of transition, TEC2.KEW steps and DesPitch steps in unison.

After change testing with blend factor 1 to test no effect

after_with_default_1.BIN.txt

Figure: TECS weights with airspeed. 1) start of transition 2) end of transition

Figure: TECS weights with DesPitch. 1) Start of transition, TEC2.KEW steps and pitch steps in unison. 2) End of transition, TEC2.KEW steps and DesPitch steps in unison. Default behavior remains the same.

After change with blend factor 100

after_with_blend_100.BIN.txt

Figure: Figure: TECS weights with airspeed. 1) start of transition 2) ~end of transition

Figure: TECS weights with DesPitch. 1) Start of transition, TEC2.KEW ramps and pitch steps to a lesser extend (-2.5 instead of -5). 2) End of transition, TEC2.KEW ramps and DesPitch remains smooth.

CAUTION

This change does result in significant altitude loss when performing detransition with a blend factor of 100. A smaller blend factor should likely be used.

For example, a blend factor of 10 results in -3.5 des pitch in transition (instead of -5.5) and ~ 1 meter of altitude lost in detranstion.