216 lines
8.2 KiB
Text
216 lines
8.2 KiB
Text
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##########################################################################
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# Simple Brake Simulation System
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# 2010, Thorsten Brehm
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#
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# Simple simulation of brake energy absorption and cooling effects.
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#
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# This module computes (approximates... :-) ) an energy level which
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# (faintly) resembles the kinetic energy absorption and cooling effects
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# of a brake system. But instead of computing real temperatures, this
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# is just meant to distinguish normal energy levels from exceptionally
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# high levels. The target is to drive EICAS "brakes overheat" messages
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# and gear effects only, to "reward" pilots with exceptionally bad
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# landings...
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#
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# To avoid complicated calculations of different braking effects (roll/air
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# drag, reverse thrust etc), we simply assume the brake system to cause a
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# fixed deceleration (me.BrakeDecel). With this deceleration we approximate
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# the speed difference which would be caused by the brake system alone for
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# any given simulation interval. The difference of the kinetic energy level
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# at the current speed and the decelerated speed are then added up to the
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# total absorbed brake energy.
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# Units (knots/lbs/Kg) do not matter much here. Eventually a magic scaling
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# divisor is used to scale the output level. Any output > 1 means
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# "overheated brakes", any level <=1 means "brake temperature OK".
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# No exact science here - but good enough for now :-).
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##########################################################################
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var BrakeSystem =
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{
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new : func()
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{
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var m = { parents : [BrakeSystem]};
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# deceleration caused by brakes alone (knots/s2)
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m.BrakeDecel = 1.0; # kt/s^2
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#m.LBrakeDecel = getprop("systems/hydraulic/brakes/pressure-left-psi") / 1000 * getprop("controls/autobrake/decel-error"); # kt/s^2
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#m.RBrakeDecel = getprop("systems/hydraulic/brakes/pressure-right-psi") / 1000 * getprop("controls/autobrake/decel-error"); # kt/s^2
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# Higher value means quicker cooling
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m.CoolingFactor = 0.005;
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# Scaling divisor. Use this to scale the energy output.
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# Manually tune this value: a total energy output
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# at "/gear/brake-thermal-energy" > 1.0 means overheated brakes,
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# anything below <= 1.0 means energy absorbed by brakes is OK.
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#m.ScalingDivisor= 700000*450.0;
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m.ScalingDivisor= 1;
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m.LSmokeActive = 0;
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m.LSmokeToggle = 0;
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m.RSmokeActive = 0;
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m.RSmokeToggle = 0;
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m.nCoolFactor = math.ln(1-m.CoolingFactor);
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m.reset();
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return m;
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},
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reset : func()
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{
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# Initial thermal energy
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setprop("gear/Lbrake-thermal-energy",0.0);
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setprop("gear/Rbrake-thermal-energy",0.0);
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setprop("gear/Lbrake-smoke",0);
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setprop("gear/Rbrake-smoke",0);
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setprop("sim/animation/fire-services",0);
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me.LastSimTime = 0.0;
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},
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# update brake energy
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update : func()
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{
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var CurrentTime = getprop("sim/time/elapsed-sec");
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var dt = CurrentTime - me.LastSimTime;
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if (dt<1.0)
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{
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var OnGround = getprop("gear/gear[1]/wow");
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var LThermalEnergy = getprop("gear/Lbrake-thermal-energy");
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var RThermalEnergy = getprop("gear/Rbrake-thermal-energy");
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if (getprop("controls/gear/brake-parking"))
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{
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var LBrakeLevel=1.0;
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var RBrakeLevel=1.0;
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var BrakeLevel = (LBrakeLevel + RBrakeLevel)/2;
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}
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else
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var LBrakeLevel = getprop("fdm/jsbsim/fcs/left-brake-cmd-norm");
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var RBrakeLevel = getprop("fdm/jsbsim/fcs/right-brake-cmd-norm");
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var BrakeLevel = (LBrakeLevel + RBrakeLevel)/2;
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if ((OnGround)and(BrakeLevel>0))
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{
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# absorb more energy
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var V1 = getprop("velocities/groundspeed-kt");
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var Mass = getprop("fdm/jsbsim/inertia/weight-lbs")/(me.ScalingDivisor*200000000);
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# absorb some kinetic energy:
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# dE= 1/2 * m * V1^2 - 1/2 * m * V2^2)
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var V2_L = V1 - me.BrakeDecel*dt * LBrakeLevel;
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var V2_R = V1 - me.BrakeDecel*dt * RBrakeLevel;
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# do not absorb more energy when plane is (almost) stopped
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if (V2_L>0)
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LThermalEnergy += Mass * (V1*V1 - V2_L*V2_L)/2;
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if (V2_R>0)
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RThermalEnergy += Mass * (V1*V1 - V2_R*V2_R)/2;
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}
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# cooling effect: reduce thermal energy by factor (1-m.CoolingFactor)^dt
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LThermalEnergy = LThermalEnergy * math.exp(me.nCoolFactor * dt);
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RThermalEnergy = RThermalEnergy * math.exp(me.nCoolFactor * dt);
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setprop("gear/Lbrake-thermal-energy",LThermalEnergy);
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setprop("gear/Rbrake-thermal-energy",RThermalEnergy);
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if ((LThermalEnergy>1)and(!me.LSmokeActive))
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{
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# start smoke processing
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me.LSmokeActive = 1;
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settimer(func { BrakeSys.Lsmoke(); },0);
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}
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if ((RThermalEnergy>1)and(!me.RSmokeActive))
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{
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# start smoke processing
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me.RSmokeActive = 1;
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settimer(func { BrakeSys.Rsmoke(); },0);
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}
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}
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me.LastSimTime = CurrentTime;
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# 5 updates per second are good enough
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settimer(func { BrakeSys.update(); },0.2);
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},
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# smoke processing
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Lsmoke : func()
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{
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if ((me.LSmokeActive)and(getprop("gear/Lbrake-thermal-energy")>1))
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{
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# make density of smoke effect depend on energy level
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var LSmokeDelay=0;
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var LThermalEnergy = getprop("gear/Lbrake-thermal-energy");
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if (LThermalEnergy < 1.5)
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LSmokeDelay=(1.5-LThermalEnergy);
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# No smoke when gear retracted
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var LSmokeValue = (getprop("gear/gear[1]/position-norm")>0.5);
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# toggle smoke to interpolate different densities
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if (LSmokeDelay>0.05)
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{
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me.LSmokeToggle = !me.LSmokeToggle;
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if (!me.LSmokeToggle)
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LSmokeValue = 0;
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else
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LSmokeDelay = 0;
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}
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setprop("gear/Lbrake-smoke",LSmokeValue);
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settimer(func { BrakeSys.Lsmoke(); },LSmokeDelay);
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}
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else
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{
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# stop smoke processing
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setprop("gear/Lbrake-smoke",0);
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setprop("sim/animation/fire-services",0);
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me.LSmokeActive = 0;
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}
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if (getprop("gear/Lbrake-thermal-energy") > 1.5)
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setprop("sim/animation/fire-services",1);
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else
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setprop("sim/animation/fire-services",0);
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},
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# smoke processing
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Rsmoke : func()
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{
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if ((me.RSmokeActive)and(getprop("gear/Rbrake-thermal-energy")>1))
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{
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# make density of smoke effect depend on energy level
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var RSmokeDelay=0;
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var RThermalEnergy = getprop("gear/Rbrake-thermal-energy");
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if (RThermalEnergy < 1.5)
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RSmokeDelay=(1.5-RThermalEnergy);
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# No smoke when gear retracted
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var RSmokeValue = (getprop("gear/gear[2]/position-norm")>0.5);
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# toggle smoke to interpolate different densities
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if (RSmokeDelay>0.05)
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{
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me.RSmokeToggle = !me.RSmokeToggle;
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if (!me.RSmokeToggle)
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RSmokeValue = 0;
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else
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RSmokeDelay = 0;
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}
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setprop("gear/Rbrake-smoke",RSmokeValue);
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settimer(func { BrakeSys.Rsmoke(); },RSmokeDelay);
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}
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else
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{
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# stop smoke processing
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setprop("gear/Rbrake-smoke",0);
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me.RSmokeActive = 0;
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}
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if (getprop("gear/Rbrake-thermal-energy") > 1.5)
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setprop("sim/animation/fire-services",1);
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else
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setprop("sim/animation/fire-services",0);
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},
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};
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var BrakeSys = BrakeSystem.new();
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setlistener("sim/signals/fdm-initialized",
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# executed on _every_ FDM reset (but not installing new listeners)
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func(idle) { BrakeSys.reset(); },
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0,0);
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settimer(func()
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{
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BrakeSys.update();
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}, 5);
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