Can airflow over turret guns be modeled?

[Snap_Roller]

There was an update a while ago that dealt with airflow over the guns at different airspeeds effecting how fast they overheat when they fire. Problem is, bomber turret guns seemed to have been entirely overlooked. You can hop in any plane in this game, accelerate to 300 KPH; then go on to fire all rounds of ammunition from fixed forward guns without overheating. But you hop in a turret gun of the same plane ( JU-88 C6 for example in this case) and the guns overheat as fast as if the plane is on the ground not moving. Now turret guns fire like 1 burst and are inaccurate forever now. 

 

Surely, if a planes forward guns can fire forever at 300 kph, the rear guns could too. I don’t think it’s extra ram air being modeled, but an oversight. This would make the AI on magazine fed bomber gunners like A-20 and H-6 111 go from useless to useful now too. 

[Stonehouse]

It's already included in the turret definitions. No idea of whether what it does is right or wrong but as far as I understand things it is already considered.

 

I think the issue with bomber turrets could likely be the burst length used and how often the gunner fires a burst. All turrets in game use the same gunner bot definition and burst length is always between 1 and 1.5 secs in length and a gunner will wait between 1 and 2 secs between each burst as I understand the details in the bot definition file.  I don't know for sure, but tests I've done indicate that burst length and wait time is randomly chosen from the ranges above. 

 

Snip from A20 top turret definition, relevant section for barrel temp and airflow highlighted. Translation is via google.

[Stonehouse]

Follow up using the M2 as an example.

TM 9-225 Browning Machine Gun Caliber ,50, AN-M2 Aircraft, Basic states the info shown below. Using game values of 850 rounds per min, I calculate that an M2 fires 14.16667 rounds per sec.

 

So, about 15 rounds is where a 1 sec burst in game falls. Now according to the bot files bursts are between 1 and 1.5 sec. IE approx 15 - 21 rounds fired.

 

Bot definitions in game restrict the wait time to 1-2 secs between bursts. At the limits of the game definitions, we are looking at:

• Best case 1 sec burst with a 2 sec wait followed by another 1 sec burst, so about 14-15 rounds initial and then after a wait of 2 secs another 14-15 rounds. 
• Worst case 1.5 sec burst with a 1 sec wait followed by another 1.5 sec burst, so about 21 rounds initial and then after 1 sec waiting another 21 rounds.

Also using game data, a 1 sec burst of fire raises the temp of the M2 66.0025 deg (centigrade I believe but cannot be sure) - I can quote the cooling coefficient of 0.045 and as you can see from my first post at 300 km/h or more there is a temp decrease coefficient correction of 4 applied but don't know how either is used.

 

I don't think 1 - 2 secs wait time would cool the gun much. Even if it took off say 20 deg C (which seems quite a lot for 1 to 2 secs and I think it would be less) bringing the temp to 46 deg the next burst would make it 112 deg, waiting gives 92 deg, 3rd burst is 158 etc. By the 6th burst it would be about 300 deg C if my math is correct. 

 

This seems to imply to me based on the table of real-life burst/cooling info below that probably the burst length and short wait times between bursts used by the gunners in game would overheat the M2 pretty quickly and possibly cause a stoppage. So based on the table info in regard to the cooling times it may well be that the air cooling in game is fine and simply the bots are mistreating their weapons. 

 

            

          

 

 

[FeuerFliegen]

I made a post about this same thing last year.  I was told it the suggestion would be passed onto the devs.
 

 

[Stonehouse]

As far as I understand, the cooling effect does kick in at over 300kph, that is the significance of the 300 parameter in the line from the turret definition. 

 

    BarrelTemperatureDecreaseCorrectionData = 1.0, 4.0, 300.0 

 

As best I can determine all turret definitions are the same in this regard. I would think that thermodynamic theory was used to pick the values (at least generally even if they were later tweaked for playability) so while you could mod in a lower speed easily enough you would need to understand how it all worked to give the middle number a correct value.

[Charon]

I think that thermally, the turret and fixed guns seem to be equivalent now. You can test this with the He 111 and the bf 109G-6, which both mount the MG 131: at about 320kph, they both seem to suffer stoppages in the 100-250 round range, although if speed is increased to 400 then the bf 109 is able to fire off all of its MG ammunition without stoppage.

 

I still think this is just a fundamentally flawed approach, though. The approach seems to be to model the gun temperature as the only factor in a jam, the only thing that can cause a jam, and the historical evidence for that seems flimsy. John Bushby in Gunner's Moon talks about the belt feeds in the Lancaster being jam-prone, not because of overheating, but because the feed-rails were dangerously exposed and could easily be dented (p141). Sid Zimmerman in Memoirs of a WWII Marine Dive Bomber Gunner talks about needing to straighten his belts after they recovered from a dive (p52). Passmore in Blenheim Boy I can't recall ever mentioning any jams. I have a vague memory of an account of a B-17(?) maneuvering hard and upsetting all the ammunition in back which the gunners had to scramble to right; this might have been in Bert Stile's book, but I can't find the reference now. B-17 tail-gunner Ron Mclnnis doesn't seem to ever mention any jams, nor does John Gabay. Regardless of the potential for overheating to cause a jam, the material quoted above still seems to describe it as a possibility, not a certainty, and every memoir I can find seems more concerned with keeping the belts straight and undamaged.

 

Meanwhile you've got memoirs like that of Lipfert, who frequently describes the guns of his bf 109 jamming. Sometimes he's reduced to firing with just one gun, sometimes not even that. Yet this is the inverse of what we see in game, with jams a constant problem for gunners (seemingly irrespective of attitude or G) and a complete non-issue for fighter pilots in practice.

Edited March 30, 2024 by Charon

[Stonehouse]

6 hours ago, Charon said:

I think that thermally, the turret and fixed guns seem to be equivalent now. You can test this with the He 111 and the bf 109G-6, which both mount the MG 131: at about 320kph, they both seem to suffer stoppages in the 100-250 round range, although if speed is increased to 400 then the bf 109 is able to fire off all of its MG ammunition without stoppage.

 

Just curious - do you see the same amount of jamming with the different burst patterns I've implemented in the AI Gunnery mod? Has that alleviated the issue at all?

I didn't think I could see any gunners having too much trouble with such in my testing of the mod.

 

FYI there is also a max misfires per magazine in the turret definition, all set to zero for WW2 and a BulletMisfireData config item in the weapon definition. 

 

Lately I have started classifying turret weapons by overheating characteristics to see if I can fiddle with the burst lengths and wait times in conjunction with what I have now based on ammo supply to try to come up with something better for AI gunnery. ie a composite rating based on overheating tendencies and ammo supply to give a burst length and wait time category.

 

As far as I can tell there are only 12 different weapon types across WW1 and 2 and all turrets so it is probably less work than I thought to add it to the mod.

 

In the weapon definition for the MG131, which is fairly representative these are the overheating related lines (translation of comments via google):

Spoiler

BarrelTemperatureIncreasePerShot = 4.4
BarrelTemperatureDecreaseCoefficient = 0.045

BulletDispertionAngleData = 0.0, 0.6, 700.0, 3.5 //the spread of the fixed gun at 0K is zero, the spread of the overheated gun is 0.6°
BulletSpeedReducingData = 0.01, 700.0, 0.25, 0.05, 3.5
BulletMisfireData= 0.0, 0.02, 280.0, 700.0, 2.0 // 280K - the temperature at which a techno-chat message appears (see OverheatLimit)

CartridgeCasesEjectionPosition = -1.150, 0.025, 0.0
CartridgeCasesEjectionSpeed = 0.0, -2.0, 0.0

OverheatLimit = 0.4f // 0.4=700/280

 

I assume that the above is the base and the turret values modify this base and account for mounting type, overheating modifier due to situation etc. Interestingly the turret definition also lets you define the ratio of tracer rounds to normal rounds.

[Charon]

1 hour ago, Stonehouse said:

Just curious - do you see the same amount of jamming with the different burst patterns I've implemented in the AI Gunnery mod? Has that alleviated the issue at all?

I don't see the issue with AI at all -- maybe it occurs, but it's impossible for me to tell on the receiving end. But it's something that quickly becomes very frustrating when riding as a gunner.