109 nose cannon

[Stoney]

According to this website, the Mk 108 was fixed in the engine with a conversion of 400m...

http://www.luft46.com/armament/mk108.html

[MiloMorai]

The gunsight moves too.

How is that accomplished?

[trap78]

Interesting article Stoney. Evergreen Air and Space museum is about an hour from my home. They have a 109G-10 manufactured in Austria in early '44. I'll have to make a trip up there to check out the bird and ask a few questions. I used to be a volunteer there. I also seem to remember the 109 having a rudder trim tab as well. The tab wasn't adjustable in the cockpit but rather "fixed" and could be bent to the desired angle with a special tool. Technicians at the factory would set the trim tab angle to the  manufacturer's spec and once in the field, pilots could have their mechanics make additional adjustments until the aircraft felt right to them.

[nrshida]

Looking at it again the barrel must have been fixed. Direct your attention to the H-shaped cylindrical connection flange on the front of the cannon and then look at the diameter of the airscrew shaft at the frontmost part of the engine. Not enough room to even shim the bore up and down. You can't move the 'propeller assembly' because it's constrained by the airscrew reduction gear.

I'd imagine the barrel was fixed during manufacture and then the sight adjusted to suit. A subordinate advantage might be more accuracy (or should I say less dispersal of shot?) due to the cannon being rigidly mounted to the engine That has to be superior to wing mounting. Wonder if this announces in tests on a target in Aces High with the same armament (Bf109 / FW190 for instance)?

Cams are gear driven in the Merlin engine also.

[bustr]

So with a hub mounted cannon that is bore aligned with the engine datum line between the cylanders, 20mm or 30mm. What is the point of impact range for the center of the graticule in Aces High?? Shouldnt that be set at the factory and unchangable versus a P38 or 262?

I have not seen references to reflector gunsight's bore sight center dot having a dial to allow raising or lowering it like you would for drop compensation in a rifle scope. They all seem to be line of sight to infinity for a standard torso hight human's eye and the guns are raised or lowered to achive a bullet dropping or crossing onto the line at known distances. The ring can be adjusted in diameter for distance gauging against wingspan or some set of dots or bars. There is the ability to adjust the angle of the reflector plate to lower the bore pipper on some to fire rockets or drop bombs.

The cowl MG can be adjusted for distance. But, I will ventur most hub cannon are set at the factory and left alone. So again what is the datum line bore range of the hub cannons seen by the graticule pipper? On 109 the lower stadia lines in the Revi vertical bar would seem to become very important to placing the hub cannon rounds on target.

[Ardy123]

So with a hub mounted cannon that is bore aligned with the engine datum line between the cylanders, 20mm or 30mm. What is the point of impact range for the center of the graticule in Aces High?? Shouldnt that be set at the factory and unchangable versus a P38 or 262?

I have not seen references to reflector gunsight's bore sight center dot having a dial to allow raising or lowering it like you would for drop compensation in a rifle scope. They all seem to be line of sight to infinity for a standard torso hight human's eye and the guns are raised or lowered to achive a bullet dropping or crossing onto the line at known distances. The ring can be adjusted in diameter for distance gauging against wingspan or some set of dots or bars. There is the ability to adjust the angle of the reflector plate to lower the bore pipper on some to fire rockets or drop bombs.

The cowl MG can be adjusted for distance. But, I will ventur most hub cannon are set at the factory and left alone. So again what is the datum line bore range of the hub cannons seen by the graticule pipper? On 109 the lower stadia lines in the Revi vertical bar would seem to become very important to placing the hub cannon rounds on target.

I'm with bustr on this, I build a 109 from scratch, albeit an RC plane, but I did it by looking and basing my plans of what I could find on the internet. What I found was...
1) the nose cannons were fixed, and could not be adjusted... made them more accurate but less flexible.
2) its a super tight fit, and the cannon itself is right in front of the stick, between the pilots legs. The cannon, is behind the engine, with part of the barrel being the shaft through the engine. I'm assuming that the longer barrel increased accuracy?

[MiloMorai]

There had to be some adjustment for the Mk108 due to manufacturing tolerances between all the components (engine, motor mounts, blast tube and so on).

[Stoney]

Well, you may be right Milo, but what sort of adjustment?  Certainly not one that would allow for a wide range of convergence.  I would assume any "slop" in the mount would be merely to account for those manufacturing tolerances, not to allow pilots to adjust the convergence of the rounds.  Given that the round is passing through the propeller shaft, I can't see there being a lot of variation allowable.  Once the thrust line of the engine is set in the mounts, so to goes the trajectory of the cannon rounds.  I.e. you can't change the trajectory without changing the thrust line of the engine.  That could only be done by adjusting the engine mounts, but ultimately, the thrust line needs to be within whatever the factory specs dictate, otherwise you'd get some pretty wild performance variation out of the engine, right?  While this certainly provides the gun with a much more stable mount, changing the convergence would not be possible.  If someone has data that shows the thrust line of the engine, it would show what the initial trajectory would be.  Obviously, the 110/163/262/190 mounts wouldn't suffer the same limitation.

Now, that being said, I don't have any serious heartburn with the way its modeled in-game, but I also would respect a choice by HTC to fix the convergence much like the 75mm on the B-25H.

[edit] And that page I linked above doesn't contain the 400m convergence setting I listed.  It does support the lack of adjustment for "harmonization" I stated.  I'll have to look around to find the information that stated a 400m convergence setting.

[MiloMorai]

The only point that of interest is the point at which the shell exits the prop spinner. The 50mm blast tube could be move in the x-y axis as could the MK108 as long as it was a straight line. The thrust line of the engine only sets the general line of the trajectory.

[trap78]

Posted by MiloMorai

The 50mm blast tube could be move in the x-y axis as could the MK108 as long as it was a straight line.

Do you have any photos, drawings, etc. showing how this could be done so as to compensate for bullet drop at 200+ yards?

[nrshida]

Respectfully, I think the tolerances in mounting the cannon and having it fire through the cannon tunnel accurately are a good deal less critical than those within the engine and easily within reach of precision manufacture.

The most natural solution is to mount the cannon rigidly to the engine to take advantage of the mass to dampen the recoil and take advantage of the engine mountings, and then to make the gunsight adjustable to suit an optimal setting or a pilot preference.

[MiloMorai]

[trap78]

^
This looks like a ballistic chart for several different cannon rounds. If there's anything you can add in the way of an explanation of what the data means I'd be interested to hear it.

[Blooz]

^
This looks like a ballistic chart for several different cannon rounds. If there's anything you can add in the way of an explanation of what the data means I'd be interested to hear it.

It's a chart that shows the BF109g6 with 20mm gondolas line of fire as it relates to the line of sight.

The straight diagonal line from upper left to lower right is the pilots line of sight. Each curved line is a different ammo from the place it starts on the plane out to about 450 meters range. The dashed lines are above the line of sight. The numbers at left are the drop in centimeters. Range is across the top in hundreds of meters.

The 109g6's 30mm and the 13mm's are dead on at 400 meters. That's the "zero". The 20mm's are on at about 140 meters and are still above the line of sight at 450 and dropping back to the line of sight at probably 500 or so.

You'll notice that all converge at 275 - 300 meters. If the pilot raises his pipper up a bit, all his weapons would be dead on his gunsight at 275 meters.

[pumaclaw]

i think that the cannons and mg's had the engine built around them...not sure tho