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Revert to use of cos^2 in LiftDrag plugin #2273

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Merged
merged 5 commits into from
Jan 8, 2024
Merged

Revert to use of cos^2 in LiftDrag plugin #2273

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ae85a48
Default CMA in LiftDrag pluginto zero
arjo129 Dec 26, 2023
67850c4
remove cos change to address one problem at a time
arjo129 Dec 26, 2023
a645be8
Revert to use of cos^2 in LiftDrag plugin
arjo129 Dec 27, 2023
6d35bfa
Update src/systems/lift_drag/LiftDrag.cc
arjo129 Dec 31, 2023
71dcdb8
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arjo129 Jan 3, 2024
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26 changes: 14 additions & 12 deletions src/systems/lift_drag/LiftDrag.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -74,7 +74,7 @@ class gz::sim::systems::LiftDragPrivate
/// \brief Coefficient of Moment / alpha slope.
/// Moment = C_M * q * S
/// where q (dynamic pressure) = 0.5 * rho * v^2
public: double cma = 0.01;
public: double cma = 0.0;

/// \brief angle of attach when airfoil stalls
public: double alphaStall = GZ_PI_2;
Expand Down Expand Up @@ -327,8 +327,10 @@ void LiftDragPrivate::Update(EntityComponentManager &_ecm)
double sinSweepAngle = math::clamp(
spanwiseI.Dot(velI), minRatio, maxRatio);

// get cos from trig identity
double cosSweepAngle = sqrt(1.0 - sinSweepAngle * sinSweepAngle);
// The sweep adjustment depends on the velocity component normal to
// the wing leading edge which appears quadratically in the
// dynamic pressure, so scale by cos^2 .
double cos2SweepAngle = 1.0 - sinSweepAngle * sinSweepAngle;
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@frede791 will this break your models?

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No, shouldn't be an issue for the PX4 models.

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No this is fine.

double sweep = std::asin(sinSweepAngle);

// truncate sweep to within +/-90 deg
Expand Down Expand Up @@ -390,20 +392,20 @@ void LiftDragPrivate::Update(EntityComponentManager &_ecm)
{
cl = (this->cla * this->alphaStall +
this->claStall * (alpha - this->alphaStall)) *
cosSweepAngle;
cos2SweepAngle;
// make sure cl is still great than 0
cl = std::max(0.0, cl);
}
else if (alpha < -this->alphaStall)
{
cl = (-this->cla * this->alphaStall +
this->claStall * (alpha + this->alphaStall))
* cosSweepAngle;
* cos2SweepAngle;
// make sure cl is still less than 0
cl = std::min(0.0, cl);
}
else
cl = this->cla * alpha * cosSweepAngle;
cl = this->cla * alpha * cos2SweepAngle;

// modify cl per control joint value
if (controlJointPosition && !controlJointPosition->Data().empty())
Expand All @@ -421,16 +423,16 @@ void LiftDragPrivate::Update(EntityComponentManager &_ecm)
{
cd = (this->cda * this->alphaStall +
this->cdaStall * (alpha - this->alphaStall))
* cosSweepAngle;
* cos2SweepAngle;
}
else if (alpha < -this->alphaStall)
{
cd = (-this->cda * this->alphaStall +
this->cdaStall * (alpha + this->alphaStall))
* cosSweepAngle;
* cos2SweepAngle;
}
else
cd = (this->cda * alpha) * cosSweepAngle;
cd = (this->cda * alpha) * cos2SweepAngle;

// make sure drag is positive
cd = std::fabs(cd);
Expand All @@ -444,20 +446,20 @@ void LiftDragPrivate::Update(EntityComponentManager &_ecm)
{
cm = (this->cma * this->alphaStall +
this->cmaStall * (alpha - this->alphaStall))
* cosSweepAngle;
* cos2SweepAngle;
// make sure cm is still great than 0
cm = std::max(0.0, cm);
}
else if (alpha < -this->alphaStall)
{
cm = (-this->cma * this->alphaStall +
this->cmaStall * (alpha + this->alphaStall))
* cosSweepAngle;
* cos2SweepAngle;
// make sure cm is still less than 0
cm = std::min(0.0, cm);
}
else
cm = this->cma * alpha * cosSweepAngle;
cm = this->cma * alpha * cos2SweepAngle;

// Take into account the effect of control surface deflection angle to cm
if (controlJointPosition && !controlJointPosition->Data().empty())
Expand Down