MIG-15bis: Cannons and Bullets Data.

[Curly]

Some parameters on the MiG-15bis guns do not match the historical data.  These errors tend to reduce the effectiveness of  guns.  I’ve created a mod to match the historical data as closely as possible. You can find a link to that here. Of particular concern are the dispersion values and weights of the projectiles in DCS. Perhaps some of these proposed changes could make it in before Flaming Cliffs 4 comes out.

https://www.dropbox.com/scl/fo/0vg8jko4cdn5dsfx4k3ri/AFeR-Qst2XAl69xxI6Wx_LY?rlkey=vevkaqfqxvt4hkw3k0pxyekyq&st=5dcqhkr1&dl=0

 Of particular concern are the dispersion values and weights of the projectiles in DCS.

The proposed changes to the bullets are:

 

	23MM HEI-T	23MM API	37MM HEI-T	37MM AP-T
Dispersion Old	0.0007	0.0007	0.0017	0.0017
Dispersion New	0.0012	0.0012	0.00083	0.00067
Bullet Weight Old	0.196	0.199	0.722	0.765
Bullet Weight New	0.196	0.199	0.735	0.753
Filler Weight Old	0.011	0	0.41	0.41
Filler Weight New	0.014	0.006	0.041	0.008
Tracer Off New	2.5	2.5	3	3
life_time New	8	8	8	8

 

The 23MM and 37mm should also be changed to match the data from the historical data.

Those proposed changes are:

 

	NR-23MM	N-37MM
Rate of fire Old	850	400
Rate of Fire New	860	400
Ratio of HE/API in Gun Belt,
Old Ratio	2 HEI-T / 4 API	2 HEI-T / 4 API
New Ratio	5 HEI-T / 2 API	5 HEI-T / 2 API

 

The proposed values correspond to data from official documents.

 

The primary sources are:
The Soviet Technical Manual for Aircraft Guns

https://disk.yandex.com/i/YVj0XI6O3Mu4LM

 

MiG-17 The Flying Techniques and Combat Manual: Link below

https://annas-archive.org/md5/bd31e5163d094e0ba055e8dccaaa0a0c

 

Volume of 2 of Technical Manual for the MiG-15bis: Armament.

 

 Evaluation of Soviet Automatic Aircraft Guns 37mm NS and 37MM N 1952

 

 

Link: https://apps.dtic.mil/sti/tr/pdf/AD0004232.pdf

 

The change are discussed in detail below

37MM

The dispersion is too large on the N37 HEI-T. Currently Da0 is set to 0.0017
The weapons manual indicates the mean error is 0.5 meters at a range of 600m

 

 

The appropriate value for the DCS N37 HEI-T is = 0.5 / 600 or 0.00083

In DCS the mass of projectile is off, It’s 0.722 kg and should be 0.735 kg

 

The weight  of the explosive in  DCS 37MM HEI-T is 100 times greater than the data from the technical manual.

 

 In DCS the charge weighs 0.410 kg. The weight of the HEI charge in the real shell is 0.037kg. The weight of the tracer chemical is 0.008 kg. So max weight of explosive should be between 0.041 or 0.037 in DCS.

The tracer in DCS also turns off too early. In DCS it shuts off after 1.5 seconds. Based on the time of flight of the projectile from the American evaluation.

The DCS tracer turns off after traveling 1000 meters, 500 meters short of the burn distance given in the Russian Aircraft Weapons manual on page 47.

From the previous TOF chart. We can estimate the TOF at 1500 meters to be around 2.5 to 3 seconds. So I’ve set tracer_off to = 3 for both the APT and HET projectiles.

Given the duration of the tracer burn, I believe the life time of the projectile should be increased to at least 8 seconds.

In DCS  the projectile life time is set to 5 seconds. Thus after 5 seconds the DCS bullet explodes. The manual does not indicate there is a self destruction feature on this shell. So the lifetime of the bullet should be greater than the burn time of the tracer.  

37MM APIT

The dispersion is also too high for the 37MM APIT shell in DCS. In DCS the dispersion value Da0 is set to 0.0017. That value corresponds to a probable error of 1.02 meters at 600 meters. The Soviet Manual notes the largest acceptable probable error at 600 meters is 0.4 meters. Thus, the appropriate value for Da0 is = 0.4/600 or 0.00067.

Similarly to the DCS 37MM HEI -T, The API-T tracer turns off too early, at 1.5 Seconds. It also self-destructs after 5 seconds.  Based on the time of flight of the projectile, Both the tracer duration increased to 3 and  the projectiles lief time to 8 seconds.

 

23MM  Bullets:

The dispersion in DCS is too low for both 23MM projectiles the MIG-15bis fires.

The dispersion for both, the API and HEI-T, is  Da0 = 0.0007. The DCS version of these bullets have a probable error of only 0.35 meters at a range of 500 meters.  The actual dispersion for these bullets was 1.714 times larger.   

As the Aircraft weapons manual gives the probable error as 0.6 meters at 500 meters, Da0 should be = 0.6/500 or 0.0012.  

 

 

An increase in the dispersion will likely improve the effectiveness of the 23MM in game. An appropriate amount of dispersion keeps a lethal density of projectiles down the entire range of the sight line. As indicated by the MiG 17 Combat Manual, the designers at the BBC optimized the sight setup to account for this.

 

The sight was angled downward to account for the angle of attack at the assumed optimal firing parameters as well.

 

Given the 50 meter boresight target in the Armament Technical Manual for the MiG-15bis is identical to the one in the MiG -17 Combat manual. We can assume that, the MiG-15bis sight and weapons are angled the same.  

Above MiG 17 50 meter boresight target.

 

Above: MiG 15bis 50 meter boresight target.

 

For the 23MM HEI shell I also increased the weight of by 3 grams to account for the tracer material. As the tracer substance can have an incendiary effect.

 

 

A payload of 0.006 kg of incendiary was added to the 23mm API. As the real projectile contains 6 grams of incendiary agent.   

The tracer time for the 23MM HEI-T was increased to reflect the tracer length of 1200 meters given on page 34 of Soviet Aircraft Weapons and Bullets manual.

 

The current trace duration is 1.5 seconds and seems low based on the ballistic tables for similar
projectiles. I’ve set changed to 2.5 seconds based on the ballistic tables for the 23MM Vya

 

 

 

For comparison, The HEI fired from  23MM VYa cannon with a muzzle velocity of 890 mps takes 1.81  seconds to travel 1200 meters. Given the lower muzzle velocity of DCS projectile, the tracer is likely to burn out before it travels 1200 meters.

 

 

We can use this table to estimate the tracer burn time for MIG-15’s 23MM HEI-T bullet.

The velocity of the VVY projectile at 600 meters (675mps) is comparable to muzzle velocity of MIG-15’s  HEI-T (680mps).  If the firing table listed the time of flight to a range of 1800 meters. We could have used the TOF’s to 600 and 800 meters as the duration of the tracer lifetime.  As the  Tof 1800 - TOF 600 = TOF over 1200 meters = Tracer burn time.

However, the chart only goes to 1200m meters. We are forced to make an estimate of the TOF to 1800 meters.  We’ll do this by examining  the rates of change of the TOF and the change of this change.  Thus we estimate the  TOF to 1800 meters as ~ 2.95 seconds.

 

 

As the TOF to 600 meters is 0.774. We compute the tracer burn time  as 2.2 second, as:   
TOF 1800 - TOF 600 = Tracer Burn Time
2.98-0.774 = 2.21.

We can assume this estimate is somewhat accurate, as the projectile stays within the linear part of the mach drag curve. Thus a tracer burn time of 2.5 to 3 seconds seems reasonable.  

The ammo belts of all the guns have been changed to a mix of 70% HEI and 30 API. Which are the proportions given in the MIG-17 Combat Manual.

 

 

Currently the NR23 fires belt consisting of 2 HEI and 4 API.
The N-37 fires 3 HEI and 1 APIT.
I chose to implement a ratio of 5 HEI and 2 API on the 23MM and 37MM. This makes the ratio of HEI to API  equal to  2.5.  Close enough to the ratio given in the manual 70/30 or 2.333.
 
To ensure both 23MM cannons do not fire a tracer at the same time. The placement of the tracers is 23MM cannons are different from one another.

These changes are made at line 375 in the lua file in the Guns table. The rate of fire of the cannon was changed in this section of the LUA to. The ROF of both cannons is offset by +-1 RPM. DCS doesn’t always deal with two guns with same rate of fire on the same aircraft. The RPM offset mitigates this.

The rate of fire of the 23mm cannon was increased to 860 rpm. 860 being the mean rate of fire given in the MiG-15bis Technical Manual Volume 2 Armament.

 

The variable which controls the range at which the AI will open fire, tbl.effective_fire_distance,was also changed of both the 37mm and 23mm cannons. It was reduced from 1000 meters to 600 meters.

600 meters was chosen based on the effective range of the weapons and sight system as described in the MiG-17 The Flying Techniques and Combat manual.

 

As a result of this change,  the highest skilled AI will only open fire at 600 meters or less. The lowest skilled AI will begin shooting at approximately 420 meters. These values are based on the notes in \Scripts\AI\Skill_Factors.lua.

CANNON_FIRE_DISTANCE_COEFF = 29 --effective fire distance = fire distance * fire distance coeff
 
The value of lowest skilled AI is set to 0.7 and the most skilled is =1
[CANNON_FIRE_DISTANCE_COEFF] = 0.7,

For testing purposes, I’ve disabled the barrel heating mechanic by setting shot to 0 on all the guns. This was done to verify the accuracy of the dispersion changes.

It may also be worth considering reducing the recoil coefficient on all the guns. The magnitude of the effect seems overdone, shaking the aircraft considerably when firing. While the N37 is a large weapon with considerable recoil force, it does have a muzzle brake to reduce these forces.

 

The  recoil effect is governed by the parameter, recoil_coeff. It is currently set 1 on both guns. At 0.5 the forces are reduced considerably. When computing the recoil force DCS only seems to consider the projectile mass and the muzzle velocity, whatever other transforms it applies .  

If you made it this far, Thanks for taking the. Please let me know if you have any question or concerns.

 

 

 

[AeriaGloria]

Whether these gun changes are more realistic or not, which your evidence definitely suggests is the case, I do think it will be more “fun” having a more accurate 37mm and less accurate 23mm. It makes sense the Soviets would intent the crews to have higher standards on the low ROF 37mm that was truly meant for long range bomber pounding, vs the faster firing 23mm 

Also I was finding bullet alignment charts and instructions for MiG-19 also: they are identical. So it’s sight likely has same 25’ (0.4 degree)) down turned sight 

Edited June 16, 2024 by AeriaGloria

[AeriaGloria]

As if note, I would like to bring extra attention to how barrel heat is having massive effects on accuracy after just 3-4 shots. Should really be looked into