Author Topic: Hub cannon (Read 1081 times)

SMIDSY · « **on:** January 11, 2006, 03:58:33 AM »

how do they work? i just cant figure out how you can have a cannon and a prop shaft in the same space. especially in rear-engined fighters like the P-39.

Charge · « **Reply #1 on:** January 11, 2006, 04:06:53 AM »

"http://www.cobrasoverthetundra.com/images/p39_engine_canon.jpg"

-C+

Ghosth · « **Reply #2 on:** January 11, 2006, 06:37:51 AM »

Whoaa! Nice pic!

TY charge

frank3 · « **Reply #3 on:** January 11, 2006, 07:24:19 AM »

Wow, nice picture indeed, says more than a thousand words

Wouldn't this setup affect the performance of the prop?

Lusche · « **Reply #4 on:** January 11, 2006, 07:46:51 AM »

IQUOTE]Originally posted by frank3
Wouldn't this setup affect the performance of the prop? [/QUOTE]

I think the performance of the prop itself is not affected.
The cannon is simply firing through hollow shaft & prop, was done on many planes.
The only thing coming to my mind are potential problems with vibrations resulting from a shaft that long. But it can be overcome with proper engineering. Don´t know that much about the P-39, but never heard of any trouble of this kind.

The Do335 had a similar long shaft for the rear prop, and the special single shaft of He 119 was over 7ft long.

nirvana · « **Reply #5 on:** January 11, 2006, 03:04:58 PM »

Cannon's inside the prop shaft. Think of it as a secondary muzzle, kind if.

MiloMorai · « **Reply #6 on:** January 11, 2006, 05:48:54 PM »

There is a little thing called a reduction gear box in an a/c like the 109. The crankshaft is not connected in a straight line to the prop. It is #3 in the diagram. http://www.axiomdigital.com/db605.htm The blast tube runs in the V of the cylinders.

A drawing showing the crankshaft line and the blast tube line.

Sorry for the LARGE size.

Another drawing,

On the P-39, there was a myth the pilots would go sterile from the vibration/buzz from the extension shaft.

Pics come from http://www.military-meshes.com/forums/showthread.php?p=8255#post8255

Angus · « **Reply #7 on:** January 11, 2006, 05:58:55 PM »

Hehe, nice.
The way the 109 put it up was AFAIK rather good.
The pilots complained abut the "dirty" cockpit though.
Now, the P39/63 had the engine behind the pilot and the shaft (being a long one) between the pilot's legs. Legend goes that the pilots rather didn't like that, and I very well belive that one.
Sit on top of a little seat with a PTO between your legs pulling some 1200+ hp's....ehhhh, better wear thick underwear!

Debonair · « **Reply #8 on:** January 11, 2006, 08:05:00 PM »

"In the summer of 1918, a group of soldiers of the 301st Tank Brigade, which I commanded, was having 37mm gun practice which I was observing. One defective round exploded in the muzzle, wounding two or three men. The next round exploded in the breech, blowing off the head of the gunner. The men were reluctant to fire the next round, so it was incumbent on me, as the senior officer present, to do so. In fact, I fired three rounds without incident. This restored the confidence of the men in the weapon. I must admit that I have never in my life been more reluctant to pull a trigger."
This is from Patton.

What would happen if this 37mm gun was in a P-39 or it was a MK108 in a 109?
Was the extra metal of the prop shaft enough to contain this or would it be the end of the plane or pilot?
...I remeber reading somewhere that firing the 37mm in a P-39 would turn the cockpit into an IMC envronment

Tony Williams · « **Reply #9 on:** January 11, 2006, 08:15:46 PM »

Quote

Originally posted by Debonair
What would happen if this 37mm gun was in a P-39 or it was a MK108 in a 109?
Was the extra metal of the prop shaft enough to contain this or would it be the end of the plane or pilot?
...I remeber reading somewhere that firing the 37mm in a P-39 would turn the cockpit into an IMC envronment

If the shell exploded at the muzzle it would probably take the prop off. If it exploded in the breech it would be even worse because it would be close to the pilot (particularly in the 109 - the gun action intruded into the cockpit).

Tony Williams: Military gun and ammunition website and discussion forum

Bruno · « **Reply #10 on:** January 11, 2006, 08:31:15 PM »

Norbert Hannig wrote that while flying an A-4 he engaged a Lagg-3 and scored hits. As he closed to finish the Lagg a round detontated within the barrel of his right inboard cannon (MG151/20mm). Hannig states (pg 73 Luftwaffe Fighter Ace) that the barrel 'had been split open back to the breech). His engine was damaged badly and his right gear was left dangling. He also says that a one meter square whole was blown in his right wing from the leading edge back to the main spar.

Hannig and his wingman were still enaged with the the enemy at the time but Hannig was lucky to make it back over the line and ditch (very ugly ditch) at an emergency airfield while his wingman covered him.

Debonair · « **Reply #11 on:** January 11, 2006, 08:55:20 PM »

Hey I saw his book for sale recently.
Sounds action packed.
Thanks for the info

SMIDSY · « **Reply #12 on:** January 12, 2006, 03:35:08 AM »

i still dont understand the mechanism behind the P39...wait, i get it. took a second but i get it.

Charge · « **Reply #13 on:** January 12, 2006, 09:27:37 AM »

The engine power is brought to the propeller via a shaft running under the cockpit. The gearbox is attached to the fuselage just behind the propellor. So the "raw power" and high RPM is lowered in the geartbox at the propellor and transferred to a hollow shaft in which the propellor is attached, too. (I guess that the gear box has to be put forward because the bearing for the propellor shaft is easiest and most reliably done in the gearbox rather than using a bearing arrangement attached to fuselage.)

In 109s DB601-605 the cannon does not shoot "through the crank shaft" as is erroneously claimed in many sources, but from between the cylinder banks. The big shaft protruding from the gear box is hollow (actually a pipe more than an axle) and that is where the cannon and its flash tube are inserted. This is seen very well in Milo's pictures.

-C+

Krusty · « **Reply #14 on:** January 12, 2006, 09:29:46 AM »

Quote

Originally posted by Tony Williams
If the shell exploded at the muzzle it would probably take the prop off. If it exploded in the breech it would be even worse because it would be close to the pilot (particularly in the 109 - the gun action intruded into the cockpit).

Tony Williams: Military gun and ammunition website and discussion forum

What do you mean? I've never seen anything to indicate this is so. The hub cannon wouldn't need to extend into the cockpit as there was plenty of room, and I believe there was a firewall between the two.