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
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It seems the old value of "1" was no longer valid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.
- TAKEOFF and AUTO flight modes now should have identical takeoff
- Prevent behaviour switching past climb altitude in TAKEOFF mode.
- Refactor set_pitch_min/max methods.
Max was already there, now renamed.
Min is newly introduced.
behaviour.
- Remove enforcement of min takeoff throttle logic from servos.cpp.
It is now handled only by takeoff.cpp.
- Take TKOFF_LVL_ALT into consideration in AUTO as well.
- Fixed pitch setpoint when TKOFF_ROTATE_SPD>0.
- Roll navigation in mode TAKEOFF during climb should now work again.
- Now the TAKEOFF loiter waypoint is set by the bearing of the
aircraft while on TKOFF_LVL_ALT, as in the last stable release, instead
of TKOFF_ALT.
- Using TRIM_THROTTLE in takeoffs, when TKOFF_THR_MIN==0
this is principally for tailsitters where rangefinders would be
orientation with RNGFND1_ORIENT=12 (PITCH_180), but also allows for
custom orientations which will be useful if the rangefinder is tilted
forward
This is a rework so that servos.cpp is responsible for setting the
throttle limits under more circumstances and always notifies TECS when
it does so.
Additionally, the TAKEOFF mode has been improved with a new parameters
TKOFF_MODE and TKOFF_THR_MIN that extend the throttle behaviour.
This variable updated unpredictably, and it was easy to introduce bugs.
It was not used in many places and is clearer to calculate the error
directly when needed.
* Set position target used to just be used in scripting, now it's used
by DDS in external control
Signed-off-by: Ryan Friedman <ryanfriedman5410+github@gmail.com>
