Spitfire Mk IIa performance tests - Patch 1.07.18301

[klem]

Originally Posted by ACE-OF-ACES

Just got home and thought I would do a quick ROC TTC test..

In this test I set the Altimeter_set to 1025mB..

And note in the TTC you can see the I_Altitude changes (red) as I change mB.

Anyway, not a formal test, so don't draw any conclusions from these results.

OK, couple of things.

Rethinking what I said about:

if ( 15 - Pressure_Alt_ft*0.0019812 < -56.5) <--- determines the Tropopause altitude
{
TropAlt = PressureAlt - 56.5/0.0019812 <--- calculates altitude element above Tropopause
TempStd = 288.15 - 56.5;
Density_Alt_ft = Pressure_Alt_ft + (TempStd/0.0019812 + TropAlt) * (1 - Math.Pow((TempStd / I_AmbientAirTemperature),0.2349690));
else
TempLapse= Pressure_Alt_ft*0.0019812;
TempStd = 288.15 - Templapse;
Density_Alt_ft = Pressure_Alt_ft + (TempStd/0.0019812) * (1 - Math.Pow((TempStd / I_AmbientAirTemperature),0.2349690));
}
TempStd = 288.15 - TempLapse;
Density_Alt_ft = Pressure_Alt_ft + (TempStd/0.0019812) * (1 - Math.Pow((TempStd / I_AmbientAirTemperature),0.2349690));

I'm not sure about the part:
Density_Alt_ft = Pressure_Alt_ft + (TempStd/0.0019812 + TropAlt) * (1 - Math.Pow((TempStd / I_AmbientAirTemperature),0.2349690));

TempStd/0.0019812 is the correction of Pressure_Alt_ft within the Troposphere, beyond which there is no/negligible further Temperature Lapse so no correction seems to be required for that so I think the original formula applies, just
Density_Alt_ft = Pressure_Alt_ft + (TempStd/0.0019812) * (1 - Math.Pow((TempStd / I_AmbientAirTemperature),0.2349690));


EDIT 2: OK, regarding I_AmbientAirTemp, as you say it is only present where the gauge is fitted and it isn't in the Spitfire or Hurricane and returns zero.

so, how about this to get I_AmbientAirTemperature ?
if (I_Altitude / Z_AltitudeMSL_m > 2.5) //is I_Altitude in feet?
{
Z_TempLapse = (Z_AmbientAirTemp - 288.15) / Z_AltitudeMSL_ft;
else
Z_TempLapse = (Z_AmbientAirTemp - 288.15) / Z_AltitudeMSL_m;
}
I_AmbientAirTemperature = I_Altitude * Z_TempLapse;


Also, what are you using to create your charts? I tried plotting the Y axis as Altitude (as is often done for these tests) but Excel threw a wobbly when the Level Speeds or ROC reversed with altitude.

PS Further apologies to Felipe for turning his Spitfire thread into a general "Aircraft Performance Measurement" thread but I think it is just about On Topic