In general when there the pitch and roll exist the formula for the aerodynamic load factor should be as follows:
aerodynamic_load_factor = cosf(radians(_ahrs.pitch))/cosf(radians(demanded_roll));
which in case of turns (in the horizontal plane) becomes
aerodynamic_load_factor = 1.0f/cosf(radians(demanded_roll));
formulas can be obtained from equations of balanced spiral:
liftForce * cos(roll) = gravityForce * cos(pitch);
liftForce * sin(roll) = gravityForce * lateralAcceleration / gravityAcceleration; // as mass = gravityForce/gravityAcceleration
see issue #24320 [#24320].
To connect loadFactor to airspeed we can use formula of balancing between lift force and gravity force:
liftForce = loadFactor * gravityForce; on the other hand lift force can be expressed as
liftForce = 0.5 * lifCoefficient * airDensity * sq(airspeed) * referenceArea; minimum airseepd is at loadFactor = 1
and lift force only balances the gravit force, so gravity force (which is same as lift force at minimum airspeed) with minimum airspeed can be expressed as
gravityForce = 0.5 * lifCoefficient * airDensity * sq(airspeed_min) * referenceArea; substituting gravit force in previous formula gives us
0.5 * lifCoefficient * airDensity * sq(airspeed) * referenceArea = loadFactor * 0.5 * lifCoefficient * airDensity * sq(airspeed_min) * referenceArea;
from where we get:
loadFactor = sq(airspeed / airspeed_min);
These changes also require changes in ardupilot/libraries/AP_TECS/AP_TECS.cpp
Line 418 (according to the comments by Peter Hall): _TASmin *= _load_factor; should be changed to _TASmin *= safe_sqrt(_load_factor);
See details here: #24320
Updated the forward throttle battery voltage compensation feature to
disable the throttle entirely when the sag-compensated voltage drops
below the new parameter FWD_THR_CUTOFF_V.
Key changes:
- Added new parameter FWD_THR_CUTOFF_V to control the voltage threshold
for this feature. The default value of 0 matches the original behavior
of never cutting the throttle due to low voltage.
- Modified forward throttle battery voltage compensation logic in the
servos code to cut off the throttle in auto-throttle modes if the
resting voltage estimate of the FWD_BAT_IDX battery is under
FWD_THR_CUTOFF_V.
../../ArduPlane/quadplane.cpp:4260:15: warning: Value stored to 'approach_speed' during its initialization is never read [deadcode.DeadStores]
float approach_speed = cruise_speed;
^~~~~~~~~~~~~~ ~~~~~~~~~~~~
1 warning generated.
57a3bc1397 changed the code from "internal" to "in-flight
It seems the old value of "1" was no longer valid
It also changed things to that the learning system saved the offsets.
When an airspeed sensor is not used, during a takeoff, the pitch angle
is asymptotically driven to 0 as the takeoff altitude is approached.
Some airplanes will then stop climbing and fail to reach altitude.
To prevent an indefinite wait for the takeoff altitude to be reached, a
dedicated level-off timeout has been introduced.
