86c3a3b5c4
propeller pitch stops for constant speed propellers. The default values are the same as the previous hard-coded values. The new attributes, "fine-stop" and "coarse-stop", are documented in the base package, Docs/README.yasim.
122 lines
3.5 KiB
C++
122 lines
3.5 KiB
C++
#include <stdio.h>
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#include "Atmosphere.hpp"
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#include "Math.hpp"
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#include "Propeller.hpp"
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namespace yasim {
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Propeller::Propeller(float radius, float v, float omega,
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float rho, float power)
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{
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// Initialize numeric constants:
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_lambdaPeak = Math::pow(5.0, -1.0/4.0);
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_beta = 1.0f/(Math::pow(5.0f, -1.0f/4.0f) - Math::pow(5.0f, -5.0f/4.0f));
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_r = radius;
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_etaC = 0.85f; // make this settable?
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_j0 = v/(omega*_lambdaPeak);
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_baseJ0 = _j0;
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float V2 = v*v + (_r*omega)*(_r*omega);
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_f0 = 2*_etaC*power/(rho*v*V2);
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_matchTakeoff = false;
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_manual = false;
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_proppitch = 0;
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_propfeather = 0;
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}
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void Propeller::setTakeoff(float omega0, float power0)
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{
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// Takeoff thrust coefficient at lambda==0
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_matchTakeoff = true;
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float V2 = _r*omega0 * _r*omega0;
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float gamma = _etaC * _beta / _j0;
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float torque = power0 / omega0;
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float density = Atmosphere::getStdDensity(0);
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_tc0 = (torque * gamma) / (0.5f * density * V2 * _f0);
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}
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void Propeller::setStops(float fine_stop, float coarse_stop)
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{
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_fine_stop = fine_stop;
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_coarse_stop = coarse_stop;
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}
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void Propeller::modPitch(float mod)
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{
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_j0 *= mod;
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if(_j0 < _fine_stop*_baseJ0) _j0 = _fine_stop*_baseJ0;
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if(_j0 > _coarse_stop*_baseJ0) _j0 = _coarse_stop*_baseJ0;
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}
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void Propeller::setManualPitch()
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{
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_manual = true;
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}
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void Propeller::setPropPitch(float proppitch)
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{
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// makes only positive range of axis effective.
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_proppitch = Math::clamp(proppitch, 0, 1);
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}
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void Propeller::setPropFeather(int state)
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{
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// 0 = normal, 1 = feathered
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_propfeather = (state != 0);
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}
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void Propeller::calc(float density, float v, float omega,
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float* thrustOut, float* torqueOut)
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{
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// For manual pitch, exponentially modulate the J0 value between
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// 0.25 and 4. A prop pitch of 0.5 results in no change from the
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// base value.
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// TODO: integrate with _fine_stop and _coarse_stop variables
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if (_manual)
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_j0 = _baseJ0 * Math::pow(2, 2 - 4*_proppitch);
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float tipspd = _r*omega;
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float V2 = v*v + tipspd*tipspd;
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// Sanify
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if(v < 0) v = 0;
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if(omega < 0.001) omega = 0.001;
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float J = v/omega; // Advance ratio
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float lambda = J/_j0; // Unitless scalar advance ratio
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// There's an undefined point at lambda == 1.
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if(lambda == 1.0f) lambda = 0.9999f;
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float l4 = lambda*lambda; l4 = l4*l4; // lambda^4
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float gamma = (_etaC*_beta/_j0)*(1-l4); // thrust/torque ratio
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// Compute a thrust coefficient, with clamping at very low
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// lambdas (fast propeller / slow aircraft).
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float tc = (1 - lambda) / (1 - _lambdaPeak);
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if(_matchTakeoff && tc > _tc0) tc = _tc0;
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float thrust = 0.5f * density * V2 * _f0 * tc;
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float torque = thrust/gamma;
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if(lambda > 1) {
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// This is the negative thrust / windmilling regime. Throw
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// out the efficiency graph approach and instead simply
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// extrapolate the existing linear thrust coefficient and a
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// torque coefficient that crosses the axis at a preset
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// windmilling speed. The tau0 value is an analytically
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// calculated (i.e. don't mess with it) value for a torque
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// coefficient at lamda==1.
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float tau0 = (0.25f * _j0) / (_etaC * _beta * (1 - _lambdaPeak));
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float lambdaWM = 1.2f; // lambda of zero torque (windmilling)
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torque = tau0 - tau0 * (lambda - 1) / (lambdaWM - 1);
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torque *= 0.5f * density * V2 * _f0;
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}
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*thrustOut = thrust;
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*torqueOut = torque;
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}
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}; // namespace yasim
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