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ArduPlane: Fixed formulas for load factor and roll, also corrected _TASmin in AP_TECS accordingly #24509

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ArduPlane: Fixed formulas for load factor and roll, also corrected _TASmin in AP_TECS accordingly #24509

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bacdea6
ArduPlane: Fixed formula for load factor
abaghiyan Aug 4, 2023
c44665b
AP_TECS: Corrected formula for _TASmin according to fix in formula fo…
abaghiyan Aug 4, 2023
a72bb39
ArduPlane: moved justifications to commit description
abaghiyan Aug 14, 2023
0009b9d
AP_TECS: moved justifications to commit description
abaghiyan Aug 14, 2023
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11 changes: 7 additions & 4 deletions ArduPlane/Attitude.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -607,7 +607,8 @@ void Plane::update_load_factor(void)
// limit to 85 degrees to prevent numerical errors
demanded_roll = 85;
}
aerodynamic_load_factor = 1.0f / safe_sqrt(cosf(radians(demanded_roll)));
// loadFactor = liftForce / gravityForce, where gravityForce = liftForce * cos(roll) on balanced horizontal turn
aerodynamic_load_factor = 1.0f / cosf(radians(demanded_roll));

#if HAL_QUADPLANE_ENABLED
if (quadplane.available() && quadplane.transition->set_FW_roll_limit(roll_limit_cd)) {
Expand All @@ -630,8 +631,9 @@ void Plane::update_load_factor(void)
return;
}
#endif

float max_load_factor = smoothed_airspeed / MAX(aparm.airspeed_min, 1);

float max_load_factor = sq(smoothed_airspeed / MAX(aparm.airspeed_min, 1));

if (max_load_factor <= 1) {
// our airspeed is below the minimum airspeed. Limit roll to
// 25 degrees
Expand All @@ -644,7 +646,8 @@ void Plane::update_load_factor(void)
// allow at least 25 degrees of roll however, to ensure the
// aircraft can be maneuvered with a bad airspeed estimate. At
// 25 degrees the load factor is 1.1 (10%)
int32_t roll_limit = degrees(acosf(sq(1.0f / max_load_factor)))*100;

int32_t roll_limit = degrees(acosf(1.0f / max_load_factor))*100;
if (roll_limit < 2500) {
roll_limit = 2500;
}
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3 changes: 2 additions & 1 deletion libraries/AP_TECS/AP_TECS.cpp
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Expand Up @@ -415,7 +415,8 @@ void AP_TECS::_update_speed(float DT)
if (aparm.stall_prevention) {
// when stall prevention is active we raise the minimum
// airspeed based on aerodynamic load factor
_TASmin *= _load_factor;

_TASmin *= safe_sqrt(_load_factor);
}

if (_TASmax < _TASmin) {
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