True Altitude?

[FrankB]

Originally Posted by Soldier_Fortune

But... How did you got "0 m ground altitude and shores" in the Moscow map?

In the Moscow map the ground is mostly flat... but the average ground altitudes are about 400 @MSL. If you've considered too low altitudes in your calculations, it may explain why your bombs fell short.

It is a known thing that water in IL2 has to be at 0 altitude, hence my choice to put the targets adjacent to the water surfaces.
On the Moscow map it is not a seashore, more like a river bank, but the altitude is still 0 (landed on the target marker just to be sure.)

Originally Posted by Soldier_Fortune

- Don't use the Speed Bar data as inputs to set the bombisght.
The Speed Bar readings are less accurate than the gauges readings, with the sole excepcion of the Heading.
Speed Bar gives IAS and ALT in steps of 10. It means that you could read 230 km/h in the Speed Bar, but 239 km/h in your IAS-meter. What is true? The latter. For altitude, a difference of 10 m is negligible. But a difference of IAS = 9 km/h, it's not.

Yep, that is what I do since I fly mostly with speedbar off.
But one has to mention that the gauges are often unreadable - either blurry or the ticks are crammed together so sightly that it is hard to read exact value - that is why I chose SB-2 - as it was added recently, the gauges are more readable.

Originally Posted by Soldier_Fortune

I hope these tips will help you to improve your enjoyment.

Good tips there!

[Soldier_Fortune]

Hi again FrankB.

I was reviewing the equations, and it seems the Air density calculation is wrong.

It's rare, because they are the ISA (International Standard Atmosphere) ones. But it would be possible.

The formula I've posted has given you a TAS = 367 km/h, right?
I've calculated TAS = 340 km/h with an E6-B, and I confirmed this result with an app for Android which I have.

It would explain why your bombs fall short: calculated TAS is greater than the real, and therefore the calculated drop angle also is greater by about 2 or 3º. Finally this angle causes that you drop your bombs too soon, missing the target.

Please, use the following equations:

- Pressure at bombing altitude:

P = 101325*[(Tmap-0.0065*ALT) / Tmap]^5.25

- Air density at bombing altitude:

AD = 0.0036*[P/(Tmap-0.0065*ALT)]

The temperatures must be converted into Kelvin before they're used in the equations above (T+273).
The pressures are given in Pa (Pascals).

These equations are also from ISA and I've checked them right now.

For your data:

Tmap = -17 ºC = 256 K
T @ 2000 MSL = -30 ºC = 243 K
Po = 101325 Pa
P = 77071 Pa
AD = 1.142 kg/m3
AD_std = 1.225 kg/m3

Then:

TAS = IAS * SQRT(AD_std/AD) = 330 * SQRT(1.225/1.142) = 342 km/h

With this TAS your drop angle should be right.

Please: test these equations, and let me know how they work for you.

[FrankB]

Originally Posted by Soldier_Fortune

The formula I've posted has given you a TAS = 367 km/h, right?
I've calculated TAS = 340 km/h with an E6-B, and I confirmed this result with an app for Android which I have.

Right.

Originally Posted by Soldier_Fortune

- Air density at bombing altitude:

AD = 0.0036*[P/(Tmap-0.0065*ALT)]

While your formula works ingame, this does not seem to compute the correct density according to the ISA tables (at 11000m it should be 22632 Pa), so I used the source formula

AD = (P*M)/[R*(Tmap-0.0065*ALT)]

where R and M is universal gas constant and molar mass of dry air and that gives me the constant 0,00348, giving same results as ISA tables.

Originally Posted by Soldier_Fortune

Please: test these equations, and let me know how they work for you.

Your equations (and my slightly altered one) were spot on on both test scenarios as defined above.
I also tried to increase the altitude to 5000m as you suggested before, and at least one of the bombs was still hitting the target pattern. Great!

...until I switched from SB-2 to Ju-88 or B-25.
On both maps and both altitudes the bombs fell always short. Too short. Maybe 2-3 bombsight degrees.

[Jack_Aubrey]

Have you seen the new videos from 4.13 updates???? i think for us bombardiers it's a must seen .....

[Soldier_Fortune]

Originally Posted by FrankB

...until I switched from SB-2 to Ju-88 or B-25.
On both maps and both altitudes the bombs fell always short. Too short. Maybe 2-3 bombsight degrees.

This has nothing to do with the equations, but with the plane's attitude.

Both, B-25 and Ju-88, tend to sink more than other bombers. Therefore, when you engage the Level Stabilizer, automatically the plane will increase the Angle of Attack (AoA) trying too keep the altitude while damps the sinking.
This action avoids the bomber flies leveled, even if the level indicator and the variometer indicate that, and thus the bombisght is aiming to certain forward angle by default. You should substract this angle to that you've computed for a manual drop.

I've found that forward angle is about +3º when the Level Stabilizer is engaged and it is combined with fully trimmed elevator. For other elevator trimming, this angle would be a bit less... but I've not found an "universal" linear ratio for this matter. Too many variables are involved: TAS, altitude, payload, wind...
Therefore it's all about how well the player knows his plane's behavior at different speeds and altitudes under different external cirumstances, how well skilled he is to fly it using the proper trimming, and his jugdement about what is the actual AoA.