Spitfire Mk IIa performance tests - Patch 1.07.18301

[klem]

Originally Posted by bongodriver

Why dont you guys set altimeter to 1013? this is what will give you standard pressure altitude which is what most charted data is based on, theres not much need to actualy test at sea level, simply start the testing at 1000ft and the data can be projected for the last 1000ft to sea level.

Manstons surveyed elevation was 150ft during wartime and tides are never factored, an elevation is based on mean sea level i.e. the average of all tide heights.

are you guys using the density altitude conversion for the tests?

Because the CoD environment doesn't seem to be set to 1013. In any case the True Airspeeds are calculated in the script using IAS, Altitude and the CoD environment data (apparent pressures and temperatures) including Density Altitude:

//calculate TrueAirspeeds and MACH
//Pressure Altitude P_alt=Ind_Alt+145442.2*(1- (alt_set/1013.25)^0.190261)
Pressure_Alt = I_Altitude+145442.2*(1- Math.Pow((C_AltimeterPinion/1013.25),0.190261));
//Density altitude (D_Alt) = P_Alt +(StdTemp0/.0019812)*(1-(StdTemp0/OAT)^0.2349690) ; = P_Alt +(273.15/.0019812)*(1-(273.15/OAT)^0.2349690)
Density_Alt = Pressure_Alt + 137870.9872804361 * (1 - Math.Pow((273.15 / Z_AmbientAirTemperature),0.2349690));
//TrueAirspeed_mph = CS/(1-6.8755856*10^-6 * ''DA'')^2.12794 (NB assume IAS = CS)
TrueAirspeed_mph = I_VelocityIAS / Math.Pow((1 - 6.8755856 * Math.Pow(10, -6) * Density_Alt), 2.12794);
TrueAirspeed_kph = TrueAirspeed_mph / 0.621371192;
TrueAirspeed_kt = TrueAirspeed_mph / 0.868976242;
//Mach Number (M) = TAS/CS; CS = sound speed= 38.967854*sqrt(T+273.15) where T is the OAT in celsius; TAS is true airspeed in knots.
MACH = TrueAirspeed_kt / (38.967854 * Math.Sqrt(Z_AmbientAirTemperature + 273.15));

There is no CoD C# parameter for Pressure to set the Altimeter by so I have to measure it and/or set it by reference to True Height. I am assuming 'True Height' is from Mean Sea Level. Can't think what else it would be. I set the Altimeter to read as near as possible to True Height when on the runway so I won't hit the sea on low level tests and I'll have near-correct Altitude reading on he Altimeter. Having said that, at a setting of 992mb its about 4 feet out at sea level but its about 2,000 feet out at 20,000 ft. something wrong somewhere. I don't thionk it matters at the moment as he performance is so far off but I'll include some mB vs Altitude error checks after the next patch.

EDIT: Did some tests.
Max Alt setting available is 1045mB. At True Height 20,000 ft, Alt reading ~19,900. Closest I could get.
Alt setting 1045mB at TH 15,000ft, Alt reading ~15,500. Alt setting for correct TH reading 1027mB
Alt setting 1027mB at TH 10,000ft, Alt reading ~10,500. Alt setting for correct TH reading 1007mB
Alt setting 1007mB at TH 5,000ft, Alt reading ~5,800. Alt setting for correct TH reading 998mB

Am I missing something?