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hugohugo37
01-18-2006, 10:54 AM
How does this work exactly? Does anyone have a diagram? I just can't picture how the barrel of the gun and the driveshaft can be configured so as not to interfere with each other. This has always bothered me. Thanks.

hugohugo37
01-18-2006, 10:54 AM
How does this work exactly? Does anyone have a diagram? I just can't picture how the barrel of the gun and the driveshaft can be configured so as not to interfere with each other. This has always bothered me. Thanks.

Cajun76
01-18-2006, 11:06 AM
http://www.aviation-history.com/engines/db605.htm

Shaft is hollow, gun is mounted behind. This limits the size of the gum one can fit. The Mk 108 was very compact for a 30mm weapon, more of a grenade launcher. High ROF, lower muzzle speed.

hugohugo37
01-18-2006, 11:13 AM
But in another thread they are talking about the inverted V engine design and how this enabled them to place the gun between the cylinders. This would imply that the gun was not behind the engine rather on top of it. So I still can't picture this.

Cajun76
01-18-2006, 11:34 AM
In the first pic, see the hole? It sits between the cylinders. The crank is hollow, and fires straight through the crank and prop shaft. Some (all?) of the Yak fighters also fire through the crank, but iirc, they don't have an inverted V, it's a regular V.

If the gun were longer, it would extend between the pilots legs, where the firing bolt would produce an unpleasent effect. http://forums.ubi.com/images/smilies/blink.gif http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif

hugohugo37
01-18-2006, 11:55 AM
I'm sorry but I don't think the cannon fired through the crankshaft. I think the crankshaft was connected to a gear reduction unit which drove the prop shaft. I.e. the crankshaft and prop shaft were not the same. Correct me if I'm wrong but...

womenfly
01-18-2006, 11:56 AM
.... really the crank shaft is not hollow. Its a geared engine. The crank shaft is at the top where the connecting rods are attached to the pistons. There is a lower shaft, this is the hollow one that the gun fires through, this shaft is geared to the crank shaft and is the one the propeller is driven from. http://forums.ubi.com/images/smilies/heart.gif

hugohugo37
01-18-2006, 12:01 PM
Yes Womanfly, that's what I finally figured out. I guess Cajun learned something today too.

jimDG
01-18-2006, 12:50 PM
(on an upright V engine) the barrel of the cannon is bewteen the V of the cylinders, crankshaft is beneath. crankshaft ends with a gear. this gear turns another gear above it. the propeler is connected to that gear, and it so happens that its axis is exactly in line with the cannon. no propeler is ever direcly attached to the crankshaft. the 2 gears' ratio varries depending on size of prop, if it is a low alt or high alt fighter, how much torque the gears can handle without breaking (early spits had a problem with this), etc.

If you sit in a Bf109 cockpit then the cannon axis passes between your knees/legs (http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif), the crankshaft axis is slightly above and the 2 MG axis end where your shoulders are.

ddsflyer
01-18-2006, 02:50 PM
Glad you guys (gals) finally figured it out. Now the P-39.......

Chuck_Older
01-18-2006, 03:44 PM
..has an extension shaft for the prop, under the pilot's seat, roughly on the same level as the floor. In fact, the control column straddles it.

Since the center of the prop is not on the same plane (As in geometry) as the extension shaft, the cannon has no trouble being directly under two machine guns, and squarely behind the prop. I imagine a gearset transfers actual power, but I'd have to find a good cut-away to know for sure. But I do know where the extension shaft is, I have here a very clear cockpit interior photo from a magazine that covers the recovery of a P-39 that's been missing since 1944

han freak solo
01-18-2006, 08:50 PM
Cajun's link shows it correctly. The engine crankshaft is at the top of the DB engine. Look at the upper right side of the drawing. The crankshaft is geared (reduction gear) to a hollow shaft for the prop and gun.

The text is hard to make out, but the left side of the drawing has an arrow pointing to "TUNNEL FOR CANNON" and on the right side of the drawing is "HOLLOW AIRSCREW SHAFT".

Cajun76
01-18-2006, 09:13 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by hugohugo37:
Yes Womanfly, that's what I finally figured out. I guess Cajun learned something today too. </div></BLOCKQUOTE>

Every day Cajun learns something new, 'cause he ain't real smart.... just smart enough to be a danger to himself. http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif

Just give me 4 guns in each wing, where the Holy Republic intended. http://forums.ubi.com/images/smilies/11.gif http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

tigertalon
01-18-2006, 09:37 PM
Best thread in long long time here imo.

IL2-chuter
01-19-2006, 05:52 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">no propeler is ever direcly attached to the crankshaft. </div></BLOCKQUOTE>

Well . . . there are so many direct drive engine/propellers out there (to give one example 33,000 C172s were built although a very small number had geared engines) that this probably isn't quite the rule it might first appear to be.

http://forums.ubi.com/images/smilies/16x16_smiley-indifferent.gif

womenfly
01-19-2006, 06:02 AM
... front end of the P-39 showning gun and prop arrangement.

http://www.airheritage.org/images/P398C.JPG

Kurfurst__
01-19-2006, 06:17 AM
Here's how it looks like in the 109. You can see the back of the engine on the, and the shaft between the cylinder banks.

http://img108.imagevenue.com/loc290/th_15f23_11a.jpg (http://img108.imagevenue.com/img.php?loc=loc290&image=15f23_11a.jpg)

and here when the MK 108 is totally bolted on. It's actually right between the pilot's leg, you can see the gun cover on the game's cocpit.


http://img130.imagevenue.com/loc128/th_987a2_11.jpg (http://img130.imagevenue.com/img.php?loc=loc128&image=987a2_11.jpg)

major_setback
01-19-2006, 10:09 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by womenfly:
... front end of the P-39 showning gun and prop arrangement.

http://www.airheritage.org/images/P398C.JPG </div></BLOCKQUOTE>
Nice picture...it explains it all. I presume that the lower (brass-coloured) rod is the main driveshaft, and that the gun barrel remains stationary whilst the prop moves around it. I'd like a look inside that grey coloured gearing box though! I imagine it just has a couple of heavy duty cogs?

Cajun76
01-19-2006, 08:33 PM
Just for scale for that 37mm cannon on the P-39...

http://img.photobucket.com/albums/v30/Cajun76/p-39_c_23.jpg

BfHeFwMe
01-19-2006, 08:48 PM
http://static.howstuffworks.com/gif/gears-planet2.gif

Basically the inner workings of a typical prop gearbox system. Hollow out the center gear and put it on a heavy duty bearing and shaft, your ready to slap a gun through the middle.

Vike
01-19-2006, 08:50 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kurfurst__:
Here's how it looks like in the 109. You can see the back of the engine on the, and the shaft between the cylinder banks.

http://img108.imagevenue.com/loc290/th_15f23_11a.jpg (http://img108.imagevenue.com/img.php?loc=loc290&image=15f23_11a.jpg)

and here when the MK 108 is totally bolted on. It's actually right between the pilot's leg, you can see the gun cover on the game's cocpit.


http://img130.imagevenue.com/loc128/th_987a2_11.jpg (http://img130.imagevenue.com/img.php?loc=loc128&image=987a2_11.jpg) </div></BLOCKQUOTE>

Thanks for this! http://forums.ubi.com/images/smilies/25.gif

The more i learn about the Me109,the more i'm impressed... http://forums.ubi.com/images/smilies/11.gif