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Yes it will be a great help in any future testing. It is silly to even discuss airplane performance without knowing the atmospheric conditions. You can tell if the game is modeling denisty altitude by looking at the FTH. If the FTH matches standard day conditions, the atmospheric model is not correct. |
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If the terrain is to scale in ClOD, you could try 'time vs distance' over varying alts to confirm atmospheric change effects on TAS. |
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Good to see you. Hope they get the P-40 in the game soon, LOL. That is a really good idea. You could even do T vs D in cardinal directions to check wind modeling, confirm the PEC, and TAS. |
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See the following REVIEW of your Java code. Before we do that, I took the liberty of re-wording the formulas you used from Williams site, i.e. http://williams.best.vwh.net/avform.htm#Altimetry I also added more detailed definitions all in all with the goal of making them easier to read and follow Quote:
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Density_Alt = Pressure_Alt + (T_std/TLR) * (1 - Math.Pow((T_std / Z_AmbientAirTemperature),0.2349690)); Code:
T_std = 288.15 - Alt_ind × TLR Code:
if ( height < tropopause ) then Code:
tropopause starts at 11.0km (36089.24ft) and ends at 20km (65,616.78ft) SUMMARY I don't know if I would use Williams formulas.. I have some concerns with how he handles some of the units, but since you were using his formulas I thought it best to review those formulas. Also not sure if you can use Z_AmbientAirTemperature directly in that it is not realitve to I_Altitude.. And as you know small temp differences can have a big effect on Density Altitude calculations, so hopefully these are small differences. Might be better of using the ISA Standard Temp formulas adjusted for temp. Hope this helps! S! PS see attached where I did a quick ROC test and ploted the different altitudes |
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But my point is it is NOT realitive to 'I_Altitude'.. As far as I can tell it is realitive to 'Z_AltitudeAGL' and/or 'Z_AltitudeMSL'. In short, the Z_AmbeintAirTemperature value your using may be the OAT realitive to another 'altitude' and not the one the plane is currently at.. For an example of which I speak, look at the TIME TO CLIMB picture I posted Note at the higher altitudes (around 17.5Kft) the "Z" altitudes are quite different (higher) from the indicated, pressure and density.. Thus in and around that area when you use Z_AmbeintAirTemperature (OAT) your getting the temperature 'realitive' to the "Z" altitudes and not the OAT realitive to indicated, pressure, and density. How big of an error that will introduce.. Not sure have not calcualed it yet, but knowing how a little temperature difference can have a big effect on the calcuation of density altitude one should take pause. Again, not 100% sure yet, need to test that to prove it to myself! I just wanted to bring it up should you come across it while testing |
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Now, regarding: Density_Alt = Pressure_Alt + (T_std/TLR) * (1 - Math.Pow((T_std / I_AmbientAirTemperature),0.2349690)); (now with I_AmbientAirTemperature) Where: T_std = 288.15 - Alt_ind × TLR TLR = 0.0065 and if ( height < tropopause ) then TLR = 6.49(°C/1,000m) = 1.98(°C/1,000ft) = 3.56(°F)/1,000ft else TLR = -56.5(°C) = 216.65(°K) I have two questions. 1. TLR is a rate so presumably below the Tropopause the Temperature Lapse is - Alt_Ind x TLR but above the Tropopause the Temperature Lapse is simply 56.5C ? and similarly...... 2. Within the DA calc, T_Std/TLR would appear to calculate an altitude. Does it hold good above the Tropopause where the lapse rate is zero or should I be capping T_Std at 288.15 - 56.5 = 231.65K once T_Std/TLR hits 56.5? EDIT: Sorry, ref Q.2, I meant should I replace T_Std/TLR with some other expression above the Tropopause?? EDIT2: Think I've got it if ( 15 - Pressure_Alt_ft*0.0019812 < -56.5) { TropAlt = PressureAlt - 56.5/0.0019812 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)); |
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I just don't recall if every plane had one? I noticed that when a plane does not have a guage for a said "I" value that said value is not aval to read/log. But we can use that value and log it along with the "Z" value (which is allways active) you were using to see if they are the same, or if they diverage at some point (alt). If they don't than I was worring for nuttin and we can continue to use the "Z" value. Quote:
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Take a look at any standard atmosphere table/graph and you will see that is indeed the case Quote:
So, one answer, one pending! ;) |
My bad..
When checking for the tropopause, i.e. Code:
if ( height < tropopause ) then Note I had this Code:
if ( height < tropopause ) then What we want to do is this Code:
if ( height < tropopause ) then Code:
T_Topopause = -56.5(°C) = 216.65(°K) |
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