Spitfire Mk IIa performance tests - Patch 1.07.18301

[ACE-OF-ACES]

Hey klem..

Have not had a chance to work on it yet, got home friday night and the girl friend had 'other ideas' as to how I was going to spend my time this weekend! I am hoping to get some time tonight to work on it! S!

[ACE-OF-ACES]

Hey klem

Sorry this reply took so long.. I have been busy with some of my own stuff..

On that note I still have not writen the C# code for you yet, but wanted to share with you my matlab code, i.e.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% ISA Standard
Alt_Tropopause_m    = 11000.0;      % ISA Altitude of Tropopause in meters
Tmp_Tropopause_K    = 216.65;       % ISA Temperature of Tropopause in Kelvin
To_K                = 288.15;       % ISA Temperature @ SL in Kelvin [288.15(°K) = 15(°C) = 59(°F)]
Po_mB               = 1013.25;      % ISA Pressure @ SL in millibar [1013.250(mB) = 29.92126("Hg) = 101325.0(Pa) = 2116.2166(lbs/ft^2) = 760.0(mmHg) = 14.69595(psi) = 1.0(atm)]
Po_Hg               = 29.92126;     % ISA Pressure @ SL in inch of mercury [1013.250(mB) = 29.92126("Hg) = 101325.0(Pa) = 2116.2166(lbs/ft^2) = 760.0(mmHg) = 14.69595(psi) = 1.0(atm)]
TLR_Cpm             = 0.0019812;    % ISA Temperature Lapse Rate in Celsius/meter [6.5(°C)/1,000(m) = 1.9812(°C)/1,000(ft)]
TLR_Kpm             = 0.0019812;    % ISA Temperature Lapse Rate in Celsius/meter [6.5(°K)/1,000(m) = 1.9812(°K)/1,000(ft)]
PLR_ftpHg           = 1000;         % ISA Pressure Lapse Rate in feet/inch of mercury [1,000ft/"Hg]

% Where
% 29.92000 "Hg = 1013.207489 millibar
% 29.92126 "Hg = 1013.250158 millibar

if (units_si == 1)
    To = To_K;
    Po = Po_mB;
    PLR = 1;
    TLR = TLR_Cpm;
else
    Po = Po_Hg;
    To = To_K;
    PLR = PLR_ftpHg;
    TLR = TLR_Cpm;
end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% STEP 1) Find the PRESSURE DIFFERENCE
%
% Pdif = Po - Altimeter_Set
Pdif = Po - Altimeter_Set;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% STEP 2) Find the ALTITUDE CORRECTION due to the PRESSURE DIFFERENCE @ SL
%
% Alt_pcorr = (To/TLR) × [1 - (Altimeter_Set/Po)^0.190261]
%
% Or you can use the following simple approximation
%
% Alt_pcorr = Pdif × PLR
%
% Where:
% Altimeter_Set = Is the altimeter set/offset (CoD: Altimeter Pinion)
Alt_pcorr = (To./TLR) .* (1 - power((Altimeter_Set./Po),0.190261));

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% STEP 3) Find the PRESSURE ALTITUDE due to the ALTITUDE CORRECTION
%
% Alt_pressure = Alt_ind + Alt_pcorr
%
% Where:
% Alt_ind       = The Indicated Altitude
% To/TLR        = 44330.77(m) = 145442.15(ft)
Alt_pressure = Alt_indicated + Alt_pcorr;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% STEP 4) Find STANDARD TEMPERATURE due to the TEMPERATURE DIFFERENCE @ SL
%
% Tstd = To - TLR × Alt_pressure        
%
% Tstd = 15(°C) - 0.0019812(°C/ft) × 8,000(ft)
% Tstd = 15(°C) - 15.8496(°C)
% Tstd = -0.8496(°C) = 272.30(°K)
%
% or in Kelvin
%
% Tstd = 288.15(°K) - 0.0019812(°K/ft) × 8,000(ft)
% Tstd = 288.15(°K) - 15.8496(°C)
% Tstd = 272.30(°K)
Tstd = To - TLR .* Alt_pressure;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% STEP 5) Find DENSITY ALTITUDE
%
% NOTE: TLR, Tstd, and OAT must be in units of Kelvin for this formula to work!!
%
% Alt_denisty = Alt_pressure + (Tstd/TLR) × [1 - (Tstd/OAT)^0.2349690]
Alt_density = Alt_pressure + (Tstd. / TLR) .* (1 - power((Tstd ./ Temp_indicated),0.2349690));

I you have not used matlab, know that it does some things under the hood. The big thing being arrays, if you have an array, and you want to do stuff with it, you don't have to do the indexing for example, say we have an array called 'dog' that I want to apply an offset to, and create a new array called 'cat'. In matlab all you have to do is the following:

cat = dog + 100;

Where as in most other languages you would have to do the indexing yourself, i.e.

for (ii=0; ii<dog.Lenght-1;ii++)
{
    cat(ii) = dog(ii) + 100;
}

Same goes for mul or div

cat = dog .* 100;
cat = dog ./ 100;

The period before the * and / means apply this to each value (each index), instead of the sum of the array

Feel free to contact me if you have any questions

PS still debating on wether we can use the ingame temp, or not, ill keep you posted

[klem]

You'll understand if I don't take up matlab, C# is enough of a challenge!

Those formulas are generally what I am using.

btw I assume our TLR_Cpm is for altitude in feet not metres (TLR_Cpf?).

The problem we have for calculating Density Altitude is that there is no OAT indicator. Then there is the question of whether Z_AmbientTemp relates to the cockpit altitude.

I did calculate a lapse rate from Z_Temp and Z_AltMSL and assuming 288.15 at SL but that gave daft results.

So I have assumed Z_AmbientTemp as OAT. I crashed at SL and it returned 290.1K or ~17C. At 15000ft it gave 260.2, a lapse rate of 0.0019933 for the CoD environment so I guess its OK for our purposes.