Rotary cannons
 

This thought popped into my head today as I was reading an article about the A10, and the rate of fire of the cannon. When the bullet is fired and the projectile is in the barrel, does the barrel start rotating while the projectile is still in it, or does it rotate after the projectile has left the barrel?

The barrels rotate continuously. They spin up at trigger press and spin down after trigger release.

Now, I wonder if your next question might be about how that affects the direction of the bullets. And, of course, aiming.

Courtney,

Does the rotation affect the direction of the bullets, and of course the aiming?

CG:ok:

Hadn't occurred to me before but I suppose the amount the barrel moves between firing and the bullet leaving must impart a lateral component to the bullet.

Which presumably can be corrected by spin and coriolis.

Now there is a problem if you use your big gun south of the equator.

Slightly off thread..............................

I was on exchange with the USN at China Lake when the competition for the gun for the AV-8B was being run. Some of us went out to the ranges to watch a demo. The three competitors were the Brit 30mm Aden, the standard issue USN 20mm gatling, and a development of the 30mm GAU8, the 25mm GAU 12.

The guns were static, mounted on trestles on the ground.

The target was an armoured vehicle.

First off was the Aden. you could hear the pop, pop as each bullet left the barrel, arced gracefully upwards, to fall gracefully down to hit the target with some pleasing flashes.:hmm:

Second to go was the 20mm gatling. A lady-like f@rt and a stream of bullets flying pretty much in a straight line to hit the target with some very pretty flashes.:ooh:

Then they fired the GAU12. A manly f@rt, followed by a stream of bullets going - as far as the naked eye was concerned - in a straight line - with no discernable gravity drop - straight to the target which instantly returned to Airfix components.:E

We looked at each other and said "We want one of those please!":ok:

Guess which one we got?:{

It's a good question and I'm glad you all asked. Simply, yes, but not much. It is yet another known component once the gun is up to speed. It's not the distance the barrel rotates whilst the projectile is in it (barrel length is not a factor) it's the tangential speed of the barrel as the round leaves the muzzle. RPS x pi x 2 x r. A couple of m/s, maybe, compared to a muzzle velocity of some 1,000 m/s. That's my guess.

Answer D - None of the above!

Whereas the USMC got the very impressive GAU-12 for their AV-8Bs... :ugh:

-RP

I must say I had never thought of that one, although CM is right - the spin may look fast but the actual velocity of the barrels about the axis is not much compared to the M/V.

Fortunately, the mechanism that activates the loading/firing/clearing of each rifle barrel is very robust and foolproof (cams inside a fixed drum surrounding the rotating cluster of barrels), so that the projectile invariably exits the barrel when it is lined up with the corresponding hole in the airplane, because anything else would be messy and inconvenient.

:ok:

More fun than dropping bombs and firing rockets any day of the week. The pregnant pause between pulling the trigger and then the nose tucking down and left(??) due to the torque on the gun and then the noise, even sitting in front of a Pegasus donk :} Pull back and right (??) to keep the pipper on the target and then definitely no following the rounds to get a look and see the target twinkling away as a bagillion bullets hit it. Great way to while away the hours. The mighty Aden......meh.

Great to hear on the ground too. First the whoosh of the impact, the sonic boom, followed by the whoosh as they are fired. Surreal.

"so that the projectile invariably exits the barrel when it is lined up with the corresponding hole in the airplane, because anything else would be messy and inconvenient."

???????????


Might be worth using google and reading up on it.

ISTR reading about gatling v's revolver cannons, that for A to A the initial rate of fire was better from the revolver as it didn't need to spin up. The problem was the barrels wearing out 6 times faster.
I think it claimed that this would provide more rounds on target for snap shots (if that is the right term).
The calibre was also discussed re the velocity, mass, trajectory and the optimum size required to provide the damage effects needed to disable a FJ or certain types of ground target.
I think the article favoured the 27mm mauser as the best on paper, but isn't it v. expensive and eats barrels.

Any of you knowledgeable chaps confirm any of this or not?

How long until lasers replace them?

Used to love watching the A-10s on the range, didn't even have to watch them the sound (all three sounds) was always impressive :ok:

It doesn't matter what the round is, if you fire a gun continuosly
it will wear out the barrel faster than shorter or shorter bursts.

500N, didn't IR mean that the rotary cannon fires fewer rounds per barrel therefore barrel replacement (all barrels at the same time) would be less frequent?

Strafing in an F4 is the best fun you can have with your trousers on.

Nothing matters very much, most things don't matter at all.

Indeed, all the rounds go down one barrel, therefore more internal wear. However, changing 6 barrels less frequently would be just as expensive. The main factor with the Mauser is the ammo - having a steel driving band, which is what eats the lands in the barrel.

As for spin up time, the greater mass of a gatling does require more time to get up to speed, but to be honest it happens very quickly and the first rounds out of the barrels still work just as well and bullet density is comparible to the revolver. Remember that the entire mechanism isn't accelerating from zero as the fly-wheel (design dependent) is rotating all the time the gun is selected, just not at full chat.

Now this is a mod I'd like ... especially this weekend ... were do all those caravans hibernate during the winter :E

For those interested it's a Dillon Aero M134D Gatling Gun :8

http://media.popularmechanics.com/im...4D-Gatling.jpg

Coff.