True Altitude?

[Soldier_Fortune]

Hi again Jeremiah

I would like to coment some points of your posts:

It looks like you already know these maps are somewhat based on ISA (International Standard Atmosphere) and also that temp rises by .0065 deg C per meter. Also, that 15 deg C is the temp at sea level for ISA normal, at least for one, so I don't really need to go into any detail about that. (I believe there is another ISA that starts at 0 deg C, but we'll ignore that one)

As far as I tested, ALL maps in IL2-1946 are based on ISA.
In all of them the OAT decreases from the given free air temperature @MSL at a lapse rate of -6.5 ºC/km_altitude. It can be checked reading the OAT gauges in diferent planes, while flying whatever map.
Under ISA, the lowest temperature of the troposphere is -56.5 ºC; and, for the standard condition (15ºC @MSL), that temperature is constant from 11,000 m up to 25,000 m. But, what if the OAT @MSL is not the standard?
Well... if the OAT @MSL is greater than 15ºC you will find the lowest temperature at a higher altitude than 11,000 m; and if the OAT is smaller than 15ºC you will find the lowest tropospheric temperature at a lower altitude than 11,000 m.
Since the OAT at a given altitude affects the air density, it also will affect the TAS.

So, on to one of the formulas. While looking at the IAS/TAS chart, I was able to derive a formula that came up with their numbers:

(IAS * .0657 * (ALT/1000)) + IAS = TAS

I quickly realized that this formula didn't take into account changes in OAT (Outside Air Temperature) and it wouldn't have been on a curve...so I modified it. What I came up with is this:

((IAS * .066 * (ALT/1000)) + IAS) * (1 + ALT/100,000) = TAS

- First of all: what IAS/TAS chart were you looking at, exactly?
Is it the kown IAS/TAS chart used since 6 years ago?

- 2nd: Both of your equations give a TAS higher than that obtained with the ISA's equations, or than that measured in-game.
I.e.: altitude = 5000 m; IAS = 250 km/h; OAT = -7.5 ºC (25 ºC @MSL)

With your 2nd equation, TAS = 349 km/h
With an E6-B, TAS = 320 km/h
With the published IAS/TAS chart, TAS = 332 km/h
With ISA equations: 319,5 km/h

It's easy to check what TAS is right: at least there are 2 aircrafts equiped with TAS gauges: Me-262 and B-25J. Any pilot can ride them to fly at that altitude over Crimea, and read both IAS and TAS.

3rd: Regardless the mathematical method used to relate variables, constants of proporcionality found or made during the process must be consistent with what those variables are representing. That formal consistency must cover the measurement units also.

((IAS * .066 * (ALT/1000)) + IAS) * (1 + ALT/100,000) = TAS

I gather 0.66 is measured in 1/km in the above equation, and 1000 is measured in m/km. In this way the first parenthesis gives outcomes in km/h, and it is consistent. Right?
But... what does 100,000 within the second parenthesis mean?
If ALT is measured in meters, 100,000 must be measured in meters also, because 1 in this case has not dimension.
But then, why "100,000" and not any other arbitrary value? If "100,000" would mean "100,000 m", it is far beyond where our planes can fly... and I see no reason to consider a value of altitude unattainable for any aircraft, including the most modern ones.

4th: You've found diferent constans of proporcionality for diferent planes: 0.066 for B5N1; 0.084 for Russian bombers; 0.046 for G4M11; 0.026 for He-111 H2 and 0.046 He-111 H6... In few words: a diferent constant for each bomber, for one only map, and for altitudes below of 6000 m.
Perhaps I'm unable to get your point but... why one should use so complicated methods instead of the more realistic and simple ISA equations, already implemented in any 'wizz wheel' or in the 'Warbirds of prey' calculator?
And: will those constants be valid when you enter the wind?

Also, I forgot to mention, if you're testing out the Lofte/Norden type bombsights there's a trick to them. Don't try to track your target forever. They aren't designed for that. Only track your target about 3 or 4 degrees at the most. For instance, if you find the bombs release around 35 degrees at a given altitude, manually move the bombsight angle no farther than 38 or 39 degrees. As your sight moves over the target, enter it into auto mode and let it do its job. If you don't try to track your target forever, they're just as accurate as the OKPB-1 sights.

You can also "tweak" it a bit before you enter into auto mode. If the actual TAS is 2 or 3 kph HIGHER than what you entered as the bombsight velocity, you can move the bombsight altitude DOWN 10 or 20 meters in elevation for fine adjustment. The reverse is also true.

This is a very good advise for a 'auto track and targeting' with the Norden/Lofte bombsights, and perhaps it could be combined with the 'ISA method'. I'll test it when I come home (sadly I've not IL2 installed in this computer )

OK... You've been working very hard and I hope my comments are not offensive for you. But, under my own experience, I see you might be getting into a method of analysis which may give you more problems than solutions, despite its apparent simplicity.

See you soon.