ArduPlane: Fixed formulas for load factor and roll, also corrected _TASmin in AP_TECS accordingly #24509
+9
−5
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
I am happy with the change to a standard definition for load factor, but would like to see the justifications moved into the text field for the commit. |
abaghiyan
force-pushed
the
loadFactorFix
branch
from
2174843 to
a3f97d1
Compare
|
@priseborough this PR has been updated. Please re-review |
See details here: ArduPilot#24320
…r the load factor See details here: ArduPilot#24320
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 ArduPilot#24320 [ArduPilot#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);
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); and_TASmin should be _TASmin *= safe_sqrt(_load_factor);
abaghiyan
force-pushed
the
loadFactorFix
branch
from
8a78b20 to
0009b9d
Compare
priseborough
approved these changes
Aug 26, 2023
This was referenced Jan 16, 2025
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
No description provided.