Question about cb calculations

[Stickler]

Did some experimenting with Dive Toss lately and different sources providing different cb settings for specific release parameters have me somewhat confused.

Take this example from the kneeboard, which is taken from RL documentation available at F-4E Squadron Weapons Pamphlets (digitalcombatsimulator.com):

Assuming these parameters are for a standard day, release speed at 8200 ft MSL corresponding to 500 KCAS is 554 KTAS.

Entering these parameters in the bombing calculator, the resulting cb setting is 1.06, whereas the RL table has 1.10.

The above source also provides a formula to manually calculate cb.

While the letter in which this formula is contained does not explicitly state whether the formula applies to the BDU-33 only or to all munitions, I was able to re-calculate the cd values given on a previous page of the kneeboard for Mk 82 LDGP releases very accurately. This could be because the BDU-33 replicates Mk-82 ballistics IRL, or because the formula is applicable to all munitions. I don't know.

In any case, entering the RL parameters above in the formula yields a cb of 1.22.

An actual Mk-84 LDGP released in DCS at the above parameters has a bomb range of approximately 6538 ft. This is significantly longer than IRL since DCS free-fall munitions do not have an ejection velocity (it is noteworthy that the above tabulated RL bomb range would be reached in DCS if the Mk-84 had an ejection velocity of 21.2 ft/s, which happens to be a typical RL figure for Mk-82 ejections).

Using the above formula to calculate cb for the actual bomb range in DCS yields 0.97.

Using the formula with the bomb range from Heatblur's ballistic calculator (30524 ft) yields -0,65.

Overview

Source	cb
Heatblur's bombing calculator	1.06
RL table	1.10
RL formula with RL parameters	1.22
RL formula with DCS bomb range	0.97
RL formula with Heatblur's bomb range	-0.65

This leads me to first actual question: Which cb value do we use in the game for maximum accuracy?

1. The cb value from Heatblur's bombing calculator even though the calculator outputs a vastly inaccurate bomb range for any dive angle except 0°, the cb value being very sensitive to deviations in said range?
2. The values tabulated in RL sources, even though RL ballistics differ significantly from DCS ballistics, mostly due to a non-simulated ejection velocity?
3. The result of the RL formula, even though we do not know (I think) whether it applies to munitions other than the BDU-33 IRL, and even though we know that it applies strictly only for RL ballistics which do not match DCS ballistics?
4. Any other option I'm not aware of right now.

My second question:

Has Heatblur elected to use the above formula to calculate cb? If so, would you be willing to release the constants used for particular weapons (since the ones in the RL source obviously do not provide the same results as your calculator for all munitions)? If not, would you be willing to release the formula used to calculate cb instead?

P.S. It seems unlikely do me that the calculator's cb values are directly derived from the RL formula, unless the visible bomb range output is not re-used to calculate cb, but cb is based on a different bomb range calculated behind the scenes.

[Zabuzard]

The math is pretty much the same as IRL and solves the equation used by the Dive Toss math. But parts of it (release range computation, i.e. how far this specific bomb will travel when released in the DCS engine) are using DCS built-in methods that are also a blackbox to us. The real world formulas dont work very well for DCS and you are supposed to use our calculator. Which is also part of why we even provide such a tool to begin with. Without it, it is simply impossible to compute solutions that work in-game.

If our calculator spits out values that dont work well in-game (despite you flying the procedure correctly that is), then you found a bug and we will fix it.

Edited September 3, 2024 by Zabuzard

[Stickler]

Update: The RL formula posted above yields the same results as the bombing tool if the 7.5 ft/s ejection velocity is replaced with the 0.0 ft/s used in DCS. Deviations from RL tables are likely due to slightly different ballistics in-game vs. IRL, tabulation inaccuracies and - especially - different ejection velocities.

Reference the thread below for more relevant info.