77e21b26d2
Stub in hooks for Propeller feathering controls and the turbo prop "condition" lever. I added a line in FGFDM.cpp to force control properties to exist if they don't already. This way you can specify anything you want and find them in the property browser, otherwise no one else may create them and you are stuck. In PropEngine::solve() the code original sets _running = true at the beginning and then sets running = false at the end. I changed this to save the current value at the start, set to true, solve(), and then restore the original value at the end. That way if we start off with _running = true, we don't have to hack up the calc() routine which wasn't using the value anyway. Finally I added some very initial support to shut down a turbine engine (_running = false) when the condition lever goes to zero.
115 lines
3.3 KiB
C++
115 lines
3.3 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::modPitch(float mod)
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{
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_j0 *= mod;
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if(_j0 < 0.25f*_baseJ0) _j0 = 0.25f*_baseJ0;
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if(_j0 > 4*_baseJ0) _j0 = 4*_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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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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