Revisiting A Gunnery Wish.

[bustr]

As most are aware, the fighters in our game with cannon mounted inside of the engine shot tube, or mounted to the engine block parallel to the crankshaft, and firing through the hollow prop shaft. Can be tilted up through the engine or hollow airscrew shaft to allow arching rounds up in response to the convergence application in the hanger. The P39 cannons both 20mm and 37mm in the real world had to be mounted with the barrel parallel to the drive shaft. This configuration was to allow the barrel to pass through the 2ft tube passing through the reduction gear housing out through the hollow airscrew shaft.

Up or down tilting was physically impossible with the gun to engine mountings in the real aircraft. We do have an example of the correct mounting with our B-25H and it's 75mm cannon. It is set parallel to the datum line, and after parking the bomber offline with the nose wheel slightly down slope on a cliff to level the bomber. I tested the round drop at 15yd, 25yd, 50yd and 100yd, to which the rounds dropped as expected from a "0" azimuth mounting.

My wish is for this to be corrected for authenticity in the Bf109 series, Ta152, Yak series, and P-39 series. We have been using the B-25H for a number of years now with no problems aiming the cannon locked parallel to the datum line.

DB601, DB605, Jumo 213 mounting methods for the MG151/20 and MK108 motor cannons.

The DB601\605 and Jumo 213 engines had 65mm diameter shot tubes that passed through the engines. This allowed the mounting of an MG151/20 or MK108 30mm cannon with it's barrel into the tube bolted onto the back of the engine's with adaptor units called "MoL"(Motor Lafette).

Cutaway views of DB60x and Jumo 213 showing the "Shot Tubes".





Methods for mounting the Cannons.

Below this DB60x has an MG151/20 mounted in it, bolted on to the aft end of the engine with a standard MoL unit. The following pictures will show the engine. A look down the "Shot tube" from the front showing the 20mm barrel and the star washer mounted to it to center the barrel in the "Shot Tube". No "Up Tilting" is physically possible. This is why the Revi gunsight line of sight was set to intersect the 20mm trajectory down 210cm at 400m below the end of the "Shot tube".

You can just see the end of the MG151/20 to the right.



DB60x view through the "Shot Tube".



View in the "Shot Tube" and the barrel end of the MG151/20 centered and locked in place with the star washer.



That MG151/20 and MoL now removed and see to the left of the gentleman's hand the star washer.



Close up of the MG151/20 bolted into the MoL unit which is "Bolted" in to back of the engine. No tilting possible.



Aft view through a DB60x "Shot Tube". Note the four mounting bolt locations for the MoL unit.



Illustrations like this from the manuals assume the reader knows about the star washer.



And this very early 109F illustration for star washers to adapt to the not yet standardized 65mm "Shot Tube" is a tension pressure slide on instead of a four blade screw clamp on. But, no tilting of the barrel is possible.





 

[bustr]

The MK108 was mounted with a MoL unit that centered the barrel to the center line of the "Shot Tube" with just the tip of barrel into the "Shot Tube". As you see from the pictures and illustrations below, "No Tilting of the Barrel Possible".

Rear end of a DB605 "Shot Tube" and bolting flang.



MoL unit "Bolted" to the end of the "Shot Tube". MK108 not inserted yet.





MK108 mounted and locked to the DB605. No possible titling here.



Technical drawings illustrating the MoL, MK108 and DB605 relationship. It will be the same for the Jumo 213 in the Ta152.

[MrKrabs]

@__________@

[bustr]

Russian fighters with M105P or M107P that have the ShVAK 20mm, NS-37, or Sh-37 (LaGG3) mounted to fire through the hollow airscrew.

Origin of the Kilmov M10x engines.

The M10x series of engines came from the license built Hispano-Suiza 12Y French engine (M100) designed for the Hs404 20mm cannon to fire through the hollow airscrew.

Pictures of the HS 12Y and cannon mounts. The length of the hollow airscrew shaft makes it impossible to tilt the cannon barrel.







The ShVAK 20mm cannon fired flat to 200m. By 400m the Hisso 20mm round has dropped more. With the ShVAK or NS-37 mounted, the PBP gunsight was set so it's line of sight intersected down to the bullet trajectory at 200m. Below is an original ballistics data set for the ShVAK 20mm. Note by 200m the bullet drop is only .01 meters.



Just as with the HS 12Y and the Hs404 20mm cannon mounting method. Below is the method for M10x engines and ShVAK 20mm or NS-37\Sh-37.

[artik]

You know to configure convergence you can either:

1. Tilt the canon
2. Change the sight

In fact the table of the   ShVAK canon refers to a sight calibration - the correction angle as function of distance.

So technically you don't tilt the canon but you correct the sight.

Additional small note - the convergence for the central mounted gun is almost non-issue.

[bustr]

Bell P-39 20mm and 37mm cannon mounting was in the same method as the Hs404 to the Hs Y12. In the case of the P-39 the cannon was mounted parallel to the drive shaft to pass through the 2ft hollow shaft inside of the gear box and hollow airscrew shaft. The gunsight was set to intersect the 37mm down at 400 yards. At SL about 48 inches.

Below are pictures and illustrations of the cannon setup.

P-39K and N illustrations from their Manual's.





Cleary illustrated mounting.





Illustration of the ammo feed unit and it's mounting relationship to the M4 cannon.



Cannon compartment photos. Note the shape of the ammo feed unit is also part of the support for the compartment cover. The ammo feed unit from the mounting illustration is fixed to the M4 receiver. So no tilting is possible.



A recently recovered P-39. Note the nose is intact and the cannon compartment or cover were crushed by the crash. the shape and mounting of the ammo feed unit was integral to the structure of the ammo compartment. No barrel tilting possible.





Gun harmonizing tables for the Bf109 with MG151/20 and Mk108 motor cannons mounted.

MG151/20



MK108 30mm

[bustr]

You know to configure convergence you can either:

1. Tilt the canon
2. Change the sight

In fact the table of the   ShVAK canon refers to a sight calibration - the correction angle as function of distance.

So technically you don't tilt the canon but you correct the sight.

Additional small note - the convergence for the central mounted gun is almost non-issue.

Park any of these fighters off the end of a cliff so the wheels are just down slope to level the center of the spinner to the center horizontal red line of the offline target. Usually you set between 3.5yd and 4yd. From F3 using Num_2 you will see the tip of the spinner just poking through the target. From level you will find at all convergence 150-650 the cannon barrel is tilted up through the engine.

For the MK108 and M4 it is actually of great significance. At 425conv, if you level the the K4, rounds pass above the datum line of the DB605, or the Shot Tube Line. Same for the Ta152. This did not happen and in the game in effect the player is being allowed to make a slow straight shooting cannon round to 425yds. By 400m in the real world the round has dropped 12ft below the DB605 Shot Tube line. Yes the Revi visierlinie was adjusted down 338cm(12ft) to 400m. That gave a visual illusion of the round shooting almost flat but, the nose of the fighter had to be lifted to make shots much past 100m. Right now in the game we point and click due to the convergence app up tilting the barrel. The 5.5Mil needed to accomplish center at 425conv in the game would blow destroy the engine on the first firing of a round.

Why does this even bother you? You like the gamey slow laser soft ball and Don't want the MK108 to drop 12ft at 400m(437yd)? You don't want the physical systems in the game to accurately represent themselves?

In the real airplanes, could the cannons in question have their barrels tilted for azimuth adjustments with the technical information I've just posted? Why do you have a problem with them being corrected? 

[artik]

Why does this even bother you? You like the gamey slow laser soft ball and Don't want the MK108 to drop 12ft at 400m(437yd)? You don't want the physical systems in the game to accurately represent themselves?

In the real airplanes, could the cannons in question have their barrels tilted for azimuth adjustments with the technical information I've just posted? Why do you have a problem with them being corrected? 

You assume that I don't care about the physics - actually I really do. The only point I want to tell that we don't need to remove the convergence as itself - that is what looks like from the your original post:

My wish is for this to be corrected for authenticity in the Bf109 series, Ta152, Yak series, and P-39 series. We have been using the B-25H for a number of years now with no problems aiming the cannon locked parallel to the datum line.

It looks like you suggest remove the convergence for spinner mounted canons at all.

I would write as suggesting changing the model of spinner canon convergence - by adjusting the sight rather than tilting the canon - this is something that isn't clear from your posts. That's it.

 

[Xavier]

Why does this even bother you? You like the gamey slow laser soft ball and Don't want the MK108 to drop 12ft at 400m(437yd)? You don't want the physical systems in the game to accurately represent themselves?

In the real airplanes, could the cannons in question have their barrels tilted for azimuth adjustments with the technical information I've just posted? Why do you have a problem with them being corrected? 

Those posts have been the most interesting read I've had in a long time. I wish the convergence settings for the motorkanone adjusted the gunsight's position instead of tilting the cannon on the vertical axis. I don't really know if it would be easy to implement, but it would add a lot to the aerial gunnery realism  . Do you know if the cowling weapons were capable of vertical adjustments? I'm only sure that the gondolas could be adjusted in both axis.

And I would absolutely love the telescopic sight for the Me-410A1/U4! 

[ink]

dont care one way or the other....

but I must say, some damn cool pics.

love the shot of the "mounting" those are some hefty rounds

[bustr]

Xavier,

German cowling MG could be adjusted. But, in the 109 series with motor cannon, pretty much what you see in the two charts is it. Also cowling or hood guns across all countries did not point inward to a convergence point. They fired parallel. Two reasons for that. First to aid synchronization with the props. Second, they were so close together it didn't matter. Dispersion at distance took care of any rational for a distant convergence point.

If you look at the Russian groups of fighters with cowling mounted MG and cannon. They were mounted with the expectation of shooting flat and parallel to 200m. The ShVAK 20mm, NS-37\Sh-37, and UB 12.7\20mm all shot flat to 200m. The Yak3 hand book shows adjusting the PBP gunsight before takeoff to the 200m centering mark on the back of one of the prop blades. When you look at La pictures with the gun hatch cover off. The cannon barrels at the front are slipped into tiny holes in the support structure inside of tightly fitted grommets. The rear end of the cannons are locked against a steel tubing support bar structure. There is almost no space for azimuth adjustments in the space other than to ensure the bores are shooting parallel and level with the datum line.

[waystin2]

dont care one way or the other....

but I must say, some damn cool pics.

love the shot of the "mounting" those are some hefty rounds

While informative, my view is this as well.  Love the pics!

[bustr]

I figure with everything else being reworked around here. And one of this game's strongest points is it's realistic physics modeling. It's about time to make real the gunnery physics on these aircraft from the moment the rounds leave the barrel.

Yes the origination azimuth matters in gunnery. When you figure azimuth adjustment in real life was up to 3.5 degrees for some wing guns. And in the game I'm seeing the HUB cannon with an azimuth of about 6Mil angled up and not even a pretense at a "0" azimuth setting. None of those engines should be able to run in real life with the cannon barrel angled like that, let alone the MK108 blowing up the DB605 or Jumo 213. We are not WT.

The convergence app in the hanger supports a cannon set to 0 azimuth while the MG are adjustable. Look at the B-25H. The line of sight for the gunsight would have to be set to the motor cannon in the fighters as in the real world.
 

[steely07]

Now this is how a wishlist wish should be done, kudos bustr.

And have to say, I agree with all your points, if they weren't adjustable in the real aircraft, they shouldn't be here either.

Salute

Steely

[TheCrazyOrange]

I'm already using minimum convergence in the K4, less to account for in vertical shots. Besides, if you're shooting from more than 400 out, you're doing it wrong.