109 nose cannon

[trap78]

...the barrel rubbing on the inside of the rotating hollow shaft...

I noticed this the other day; the crankshaft is geared to drive the supercharger which in turn is geared to the "cannon tunnel" which then appears to drive the overhead cam via a shaft. It seemed to me the cannon tunnel would have to rotate at one-half the crankshaft speed (most likely) for this to work.


This is a good picture of the bare block with the front of the engine facing towards us. It shows what looks to me like the through hole cast as part of the block that housed the cannon barrel. This is where a camshaft would have gone in a conventional push rod design. Since the DB was an overhead cam arrangement this "tunnel" could be utilized for the placement of the cannon barrel.

[nrshida]

Great links bustr.

It's way more logical in design terms to fix the cannon to the engine without any recourse for adjustment, and then simply adjust the sight, similar to a rifle as many posters have observed.

The four bolt flange was fixed (I mean non-rotating) as it also served as the bearing surface for the cam drive gear set. If the cannon tunnel had an actual blast tube within it there would be absolutely no need for it to rotate.

Hopefully this picture will help. It's from a Jumo engine manual but the similarities are sufficient. It illustrates both the cam gear (right side of the picture) and the prop reduction gear (left side of the picture). You can see the cam drive gear is just a ring which would have rotated around what would be the four bolt flange shaft on the DB engine. Sorry the picture is a little small:

[bustr]

Then the fixed four bolt flang being ridgid seems to make it clear that the cannon is locked to the 0-datum line of the engine. Only thing now would be to suggest that cannon in german plane HUB mountings be set to the 0-datum line with no adjustment.

After all the Revi graticules were changed to include stadia marks after the 109E Revi3c version when the motorkanon became standard armament with the 109F series that used the ReviC/12. Below center inside of the 50mm ring two stadia marks became standard which probably aproximate to roughly 400 meters and 600 meters off the engines 0-datum line.

My early comment about the Yak and its graticule referenced to stadia lines because the Yak has a HUB cannon. I wonder if any of our audience has schematics showing the russian engine/HUB cannon configuration to see if they also had a fixed flange.

If the flange is fixed and ridgid, I wonder why we have the ability to change the HUB cannon's convergence in the hanger??

[Stoney]

If the flange is fixed and ridgid, I wonder why we have the ability to change the HUB cannon's convergence in the hanger??

Well, we could ask HTC, but I'd assume it was for simplicity/omitted detail.

[Krupinski]

While we're on the topic of 109s, I want my two radiators! 

[Ardy123]

While we're on the topic of 109s, I want my two radiators! 

With the shutoff valve between them...

[bustr]

Well, we could ask HTC, but I'd assume it was for simplicity/omitted detail.

Since the 109 and 190 seem to be the most piciunely argued over for detailed accuracy in the games aircraft offerings. This point would fit nicely with that venue and give the expertin another badge of courage in their kit for the super human requirments to master the "Way of the Jagdflieger".

But then again check this picture: http://ww2db.com/image.php?image_id=10369

My whole effort at research could be to nill by this gentelman and his bore sighter. Or he could be using it to make sure the cannon is centered in the 70mm tube.

[trap78]

Remember that bore sighting is aligning the center of the barrel with a target at a specific distance. Since the technician in the photo can't look down the cannon barrel from the breach end he uses that nifty tool that allows him line up the center of the barrel with the target visually. The next step would be to adjust the sight so the pipper is on the target. At this point the weapon isn't "sighted in" but should register hits "on the paper". Then fine adjustments can be made to the sight to bring everything dead on.

In the photo you'll notice the rear of the aircraft is supported on adjustable jack stands. These could be used to move the nose up and down. The target itself could be moved left or right. This would give you x and y adjustments to bore sight the cannon.

[nrshida]

Yup, Trap is correct about what that person is doing.

The Bf109s modelled in Aces High have other differences from the real thing in the interests of simplicity. So do a lot of planes come to that. Why don't we just agree to not campaign against the convergence setting until there is a wide scale addressing of all those little inaccuracies?

[trap78]

I'm more interested in how real life 109's were designed and worked than I am in trying to convince HTC to make changes to the game. How these aircraft functioned in "the world" I find pretty amazing. It's up to HiTech how realistic he wants the game to be.

[bustr]

WW2 reflector gunsights did not have an elevation adjustment other than a few allowed a change in the angle of the reflector plate to lower the dot for use with rockets and shallow dive bombing.

They were a line of sight aid evolved from the earlier iron ring and telescopic tube sights. Gun convergence and harmonization was adjusted to cause the rounds to pass through the "line of sight" at some set distance. The gunsight nor the graticule was adjustable to compensate for bullet drop like a rifle scope. The armorer adjusted for the paralax lense table to be level while the aircraft was propped up level for gun adjustment. The guns were adjusted to patterns that converged at the line of sight based on the center pipper of the graticule. The mounting was standardised to the average hight distance from the pilots seat to his eye for a direct line of sight over the nose of the aircraft.

FW convergence charts show the line of sight level to the datum line and all of the guns adjusted to fire over the line of sight and drop the rounds in between 400 meters and 550 meters. None of the Fw A to F series had HUB mounted cannon. In the chart for the G6 with MK 108 motrkanon, the MK 108 is shown firing level to the 0-datum line while the line of sight is down over the nose to 400 meters at a point 340cm(11ft) below the 0-datum line.

The Revi installation in the 109 cockpit is preaty much fixed because there is absoultly no room to raise the pilots line of sight up any higher.(Berlin Phone book 1944 seat cusion) Thats why you have 20 mil stadia marks along the cross hair. The effective straight line of sight shot for the MK 108 is 100 meters which has a drop of about 12 inches. The line of sight angling down to a convergence of 400 meters will align with about the 40 mil (second down) stadia mark below the center of the Revi graticule(11 ft drop).

When you look at the diameter of a MG151/20 barrel and how far it extends into the cannon tube past the flange I can see up to 2 degrees of elevation possible down the 70 mm engine tube. I'm still looking for the information about factory setting of MG151/20 had two choices of 200 or 400 meters. Based on the chart I bet 200m was more common for the MG151/20. About a 24inch drop at 200meters.

With a 30mm round from a short barrel that barly makes it to the tube without an adaptor, you want it going straight down the center of the tube and not impacting the sides. Reference back to the G6 chart showing the 30mm at a flat trajectory from the left of the chart.

HiTech has been very good about fixing things over the years if you present the data or a solid argument. Pyro is interested in updating the realism of the ordenance.

[trap78]

bustr - do you have a picture that illustrates what your saying? I think I understand but want to be sure.

[bustr]

Here's a few pages I used along with researching concepts to other pages.

How else did I create the Reflexvisiere graticules in my Historic gunsight pack? You can use the tech graph included in this thread for the MK108 balistics related to the stadia marks on the Revi graticules. Other discussions at Historic web forums have beaten the 30mm balistics to death. Rougly 12 inches at 100 meters, roughly 11 feet at 400 meters, past that it drops down a well. You can see where stadia marks were added to the Revi graticules around the same time 20mm cannon became standard armament on fighters. The ReviC/12A without stadia marks was used in gun turrents. You notice the germans kept using iron rings on hand held manned gunner positions till the end of the war MG or 20mm.

Reflexvisiere Manuals: http://deutscheluftwaffe.de/
Reflexvisiere discusson group in german: http://208090.homepagemodules.de/t103f25-Revi-Baumuster.html

http://www.ww2aircraft.net/forum/
http://www.ww2incolor.com/forum/showthread.php?4127-Luftwaffe-Cannons-amp-Machineguns.
http://forum.axishistory.com/viewtopic.php?f=114&t=17850

Check some of the links I added to this post back a few page also. I suspect some of our membership have books with diagrams that show detailed info on the Motrkanon installation along with factory data on convergence.

I could be wrong but, the motorkanone MG151/20 bottom of the page picture in this link has a collor to fit down the hollow airscrew cannon tube on the DB601. And that looks like the 4 hole flang that bolts to the fixed flang on the back of the DB601.....

http://www.ww2incolor.com/forum/showthread.php?4127-Luftwaffe-Cannons-amp-Machineguns./page3

[W7LPNRICK]

(Image removed from quote.)
I noticed this the other day; the crankshaft is geared to drive the supercharger which in turn is geared to the "cannon tunnel" which then appears to drive the overhead cam via a shaft. It seemed to me the cannon tunnel would have to rotate at one-half the crankshaft speed (most likely) for this to work.

(Image removed from quote.)
This is a good picture of the bare block with the front of the engine facing towards us. It shows what looks to me like the through hole cast as part of the block that housed the cannon barrel. This is where a camshaft would have gone in a conventional push rod design. Since the DB was an overhead cam arrangement this "tunnel" could be utilized for the placement of the cannon barrel.

yup, good picture.... right through the upper reduction gear to exit the nose cone/prop. 

[bustr]

Page 15 of the 109-G6/U4 manual says the MK108 fits parallel to the engine and is not adjustable. Roughly translated. 0-datum line convergence.

http://deutscheluftwaffe.de/archiv/Dokumente/ABC/m/Messerschmitt/Me%20109/Bf%20109%20G-6%20U4%20Bedienungsvorschrift%20-Wa.pdf

109F2-F4 manual shows similar things by the fact it shows the MG151/20 round drops 8cm at 100 meters out the barrel. But it says roughly the ReviC/12b is line of sight to 400 meters. ReviC/12b graticule introduced stadia marks on the cross hairs at every 20 mil.

http://deutscheluftwaffe.de/archiv/Dokumente/ABC/m/Messerschmitt/Me%20109/Bf%20109%20%20F-2%20F-4%20Wa.pdf

I will venture the motorkanone is mounted inline with the engine datum line fixed and there is no elevation adjustment. The inverted "V" mounting of the engine allowed an unobstructe line of view down over the nose to 400 meters. One would think then in the game the HUB cannon on  german fighters should be locked at about 100-125 meters due to no adjustemt possible in the engine tube mounting..