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(20.07.2021) [] [Radar SPAA] Ammo type selection can render the lead indicator incredibly inaccurate

# Circuit / Game Version

# Platform



# Description


The lead indicator for radar SPAA uses the shell velocity of the first shell in the currently selected belt. If that shell is HVAP, then the radar lead indicator will only be good for the HVAP rounds fired, while the rest of the shells actually require more lead. Even a small change in shell velocity of ~100 m/s between the HVAP and normal shells can render the lead indicator entirely useless.


The lead indicator for Radar SPAA changes depending on what belts are currently selected, seeming to determine lead based on the first shell listed in the belt. This is expected behavior, and in general, works without issues. However, some SPAA have belts where the velocity of the shells in that belt change somewhat significantly, and the lead required for these various shells in the belt are very different.


It's common for SPAA to have multiple belts on them at once to fight against ground or air targets, and with SPAA like the Wirbelwind, AMX-13 DCA, ADATS, etc., it's important to remember to swap between the two belts for the situation. However, not all SPAA are capable of hot swapping ammo belts, and need to perform a long reload of the entire feed to change belts. This causes a problem for SPAAs like the AMX-30 DCA, which has a 60s long reload (swap time).


The AMX-30 DCA has 4 belts to choose from, but considering it has a 60s reload, a player is likely only going to bring in 1 belt type. Since the they are going to need to defend themselves against ground targets, it's likely they'll want to choose the belt regarded as the 'ground' belt which is the only belt containing APDS (30x170 APDS-T). This belt's shell order is APDS / AP-I / AP-I / HEI-T* , indicating 2 important facts about this belt.

  1. The starting shot in the belt, is an HVAP round.
  2. The belt has only 1 HVAP (high velocity, armor piercing) round per every 4 shots fired.


The 1st point means that the radar lead indicator is going to be for the HVAP round, with a significantly higher muzzle velocity than the majority of the rounds in the belt. This fact, combined with the second point mean that the lead indicator is only indicating for 25% of the shells being fired. This means that the number of shots flying towards the target are significantly reduced, since most of them will be behind the target by a large amount. Furthermore, this 25% of the shells it provides an accurate indicator for are the shells for use against ground targets, rather than air. So if a player does manage to get a hit with the reduced number of shells, it's unlikely they'll do any meaningful damage to the target anyways.


The difference in shell velocity doesn't need to be all that large to have a great effect on the lead indicator either. For example, the shell velocity of the AP-I, HEI-T, and HEI rounds on the AMX-30 DCA are all 1080 m/s. The APDS shell is only about 100 m/s faster at 1175 m/s, but this results in a drastically different aim point for the lead indicator.


My suggestion is that the shell velocity used to determine the lead indicator for a radar SPAA, should be 1 of these 2 methods.

  1. Ensure that the first shell type in all radar SPAA belts is the shell type intended for use against air targets (HE shell types), and the current method of determining shell velocity can be used
  2. The velocity of the most common shell type found in the belt should be used


The first method would be the easiest brute-force solution, provided all relevant belts are changed. However, it would mean another point of standardization when releasing new radar SPAA, and thus another possibility to cause a bug on release or update to a radar SPAA.


The second method is preferred, as it would mean a relatively simple change (supposedly). It may require a change to how the lead indicator is calculated at runtime, or a programmatic change can be applied to any relevant (or all) SPAA belts to determine the new value to be used for shell velocity in radar lead calculations. Although this method does require some thought put into it to implement, once it's completed, there's no need to worry about this change affecting any other parts of the game, or causing bugs.


# Step to reproduce

(^ *Steps ?)

Test drive in the AMX-30 DCA and bring the HVAP belt as well as one of the air target belts. Lock onto the bomber once it flies overhead, and center your aim on the aircraft. Check the lead indicator when the turret is facing 120 degrees given by the compass ribbon at the top. Do this once for each belt type, and you'll notice the difference in the lead indicator. This difference gets significantly worse as the target begins to flank (move directly left or right of the player) harder, and diminishes as the target goes hot or cold (moves toward or away from the player).

# Additional Information

AMX-30 DCA using the 'Ground Belts' (30x170 APDS-T) showing the lead indicator for the HVAP round.



AMX-30 DCA using the 'Air Belts' (30x170 HE-I-T or 30x170 APHE-I) showing the lead indicator for the HE or AP round.


DxDiag.txt 2021_06_13_08_52_01__3004.clog

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  • Piciu713 changed the title to [] [Radar SPAA] Ammo type selection can render the lead indicator incredibly inaccurate
  • 2 weeks later...
  • Technical Moderator

Thank you for your interest and help improving the game.  

Your information has been forwarded to the Developers. 

If there is anything further regarding this report a Technical Moderator will contact you.

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  • Piciu713 changed the title to (20.07.2021) [] [Radar SPAA] Ammo type selection can render the lead indicator incredibly inaccurate
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