040c508aa8
implicitly in PropEngine by disallowing negative torques, but that was removed at some point. We really need the explosion protection here at the source.
98 lines
2.5 KiB
C++
98 lines
2.5 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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}
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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::calc(float density, float v, float omega,
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float* thrustOut, float* torqueOut)
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{
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float tipspd = _r*omega;
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float V2 = v*v + tipspd*tipspd;
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// Clamp v (forward velocity) to zero, now that we've used it to
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// calculate V (propeller "speed")
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if(v < 0) v = 0;
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// The model doesn't work for propellers turning backwards.
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if(omega < 0.001) omega = 0.001;
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float J = v/omega;
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float lambda = J/_j0;
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float torque = 0;
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if(lambda > 1) {
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lambda = 1.0f/lambda;
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torque = (density*V2*_f0*_j0)/(4*_etaC*_beta*(1-_lambdaPeak));
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}
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// There's an undefined point at 1. Just offset by a tiny bit to
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// fix (note: the discontinuity is at EXACTLY one, this is about
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// the only time in history you'll see me use == on a floating
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// point number!)
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if(lambda == 1.0) lambda = 0.9999f;
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// Calculate lambda^4
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float l4 = lambda*lambda; l4 = l4*l4;
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// thrust/torque ratio
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float gamma = (_etaC*_beta/_j0)*(1-l4);
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// Compute a thrust, clamp to takeoff thrust to prevend huge
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// numbers at slow speeds.
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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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if(torque > 0) {
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torque -= thrust/gamma;
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thrust = -thrust;
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} else {
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torque = thrust/gamma;
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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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