Forum: F-16 Armament & Stores

Last edited by Attila on Nov 05, 2005 - 11:53 PM; edited 1 time in total

Anyone in here who knows the direction generated by the recoil?
Being a rifle and pistol shoter myself gives me the general understanding of recoil on single-barrel weapons.

But my question is due to the rotating barrels on the 6000 rpm Gatling.
Do the barrels generate mass and speed to get the gyroscopic effect of precession?
In that case, the recoil will move 90 deg.

The fwd mounts will in that case act as push-pull absorbers of the recoil.

(If not, the fwd mounts will act as pivoting points, letting the aft mount absorb all recoil.)

This is only a theory of mine.
Can any one confirm if my thery is right or wrong?

Thanks.
Attila

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Elite 1K Joined: May 26, 2005 - 08:39 PM Posts: 1496

The cannon does not rotate at all when fired, the shock mounts allow it to recoil but not spin. The M61A1 has a max recoil travel of 0.25 inches. and the average recoil force (ie not instantanous) is 3,800 lbs at 6,000 RPM. When you look at the gun from behind it rotates counterclockwise and the barrels have a right hand twist, so they spin opposite the barrel cluster. I don't know exactly what effect that has on precession, but I think it tends to cancel out.

You seem to be asking two different questions, and possibly confusing gyroscopic precession with torque:
1. "Anyone in here who knows the direction generated by the recoil?"
That's easy. The recoil is directly backwards from the projectile's forward path (for every action, there is an equal and opposite reaction--thanks Isaac). Of course the barrel isn't on the aircraft centerline, so there's a bit of yaw to the left induced by the recoil of the gun firing. But the F-16 knows this, and compensates for it automatically by adding a little right rudder (without any input from the pilot). Fly-by-wire offers so many advantages.

2. "Do the barrels generate mass and speed to get te gyroscopic effect of precession?"
The barrels spin up to speed very fast when the trigger is pulled, and then stop spinning about as fast after the trigger is released. Gyroscopic precession would require constant (or near constant) spin speed (aka rotational inertia), and probably more mass further from the center of rotation to create a gyroscopic effect. There may be some torque and counter-torque effects of the gun barrels spinning up and slowing down, but not any gyroscopic precesson.

Hi there....

My question was more along the recoil effect alone.
Not the torque or off-set positioning of the gun.

Bare with me here.......

When the 10 o'clock barrel is being fired, will the mass of the rotating barrels cause precession.
In that case the force applied to the airframe from the gun would be as if a single barrel at 7 o'clock being fired.
This means that the aft end of the gun is being forced up towards 1 o'clock.

Say if you were holding, god forbid, the gun at the fwd mounts.

Would you feel that the gun was push-pulling your arms? (Recoil at 7 o'clock.)

OR:

Would you feel that the gun was twisting in your palms? (Recoil at 10 o'clock.)

I know that this is maby a weird question, but me and a couple of guy's at work have being talking about it.
And this is a great site for getting an answer on a weird topic Smile

Yeah your right about the Fly-by-wire system, Flight Test Jim, it's a great system for getting a stable platform.
The F-104 pilots would have loved it......compensating for torque with flapperons and recoil with rudder.

Thanks again.
Attila

Elite 1K Joined: May 26, 2005 - 08:39 PM Posts: 1496

The torque is negligible since its bolted to the airframe. The recoil force is directly to the rear, as Jim said "equal and opposite...".

Are you thinking muzzle flip instead of recoil? The reason you get muzzle flip on a pistol or rifle is the barrel is pretty far above the pivot point of the gun (shoulder in a rifle, wrist in a pistol). The M61's recoil mounts are inline with the firing barrel, so there is no "flip".

It's hard to answer the "hand firing" question. If you were strong enough to lift the cannon and stand the recoil, well then you'd be strong enough where the torque of spinning up the barrels would be moot, right? See my point? If you are strong enough to heft the cannon the torque isn't a problem. If you're weak enough for the torque to be a problem, then you aren't going to be lifting the cannon in the first place.

I think i realize what you are trying to get at Attila. Basically you are trying to determine what forces are exerted on the gun, airframe, bullets when the gun spins and how the spinning of the gun effects the bullets and airframe in flight. Well seeing how the gun's mass compared to that of the airframe is small, there is a small, noticeable but compensated for recoil effect that causes the aircraft to yaw to the left. In the F-15 this happens to the right and in A-10 and the F/A-18 there is no yaw due to the gun being mounted on the centerline of the aircraft. Now since the barrels are rotating in a counterclockwise-wise direction, i believe that a small lateral momentum is imparted on the bullet as it travels down the barrel. Now you have to realize this, being a shooter, that the total time that the bullet is in the barrel compared to the speed of the rotating gun is minimal. if the bullet is fired from the 1 o'clock barrel the bullet is only in the barrel within a few degrees of 1 o'clock. though, like i said a little angular momentum is is still imparted on the bullet. this is accepted with this gun due to the fact that as a weapons guy told me you want a "shotgun effect" when firing. A bullet pattern when firing will look like you shot the target with a shotgun rather then a linear pattern with holes lined up next to each other. this gives the Vulcan a better hit probability due to the number of rounds expended on one trigger pull. As for the torque effects of the gun rotating, as i said before the mass of the gun compared to mass of the airframe is small and the aerodynamic forces acting on the aircraft would cancel out any torque effects.

This was the general idea:
The yellow being the barrel fired and the forces that should be applied on the hub. (With no rotation.)
The red is the force-effect on the hub due to precession when the wheel is rotating.
The green is an angle of approx. 90 deg.
Blue is of course, rotation.

Thanks
Attila the Geek Rolling Eyes

Your angle of fire from the illustration is 90 degrees off of what the gun fires at. Since the gun spins on the long axis of the airframe the gyroscopic effects are not exerted to the airframe (if I follow all this right). The bullet (if we slow time and speed) will exit the muzzle at a velocity greater than the barrel spin has time to mount effect on the bullet its self.

In the picture the wheel is spinning on a different axis than the gun in the airframe does. Please use a different example that reflects the rotational axis of the gun. Or maybe I just looked at it wrong.

IDCrewDawg, just realized that I put in the Red and Yellow arrows on the wheel wrongly.
It's supposed to be 180 deg. of what I indicated. But the arrows on the hub is as I intended.
Sorry for the confusion.....my fault.

I'll try with this drawing.
It indicates what kind of force may be applied to the fwd mounts.
The yellow indicates no precession, red is with precession.

Atilla, can I take that thing dear hunting?

I didn't use that one on this years moose hunt,
but my 9,3 x 62 did the job.
But if you want instant meat loaf, the m61 is a great choise.

you asking if the power of the bullet exiting the gun causes a recoil on the mounts. (I don't know what procession is) So if I understand your question correctly, the bullet exiting the muzzle should cause the gun to recoil in the opposite direction (this is established by Issac). What effect does the rotation have on the recoil is what your getting at. The answer is none. Then again, this could all just be over my head.

Sorry for the many edits. I think there will be induced precession, which will more than likely be damped by the mounts of the gun, causing the aircraft to yaw, pitch and roll (depending on mount position) if it is not compensated.

There is the recoil of the gun which will induce both a torque (since it is not in the center of rotation) and a backwards force if the force is not orthogonal to the distance vector to the rotational axis (center of mass if unmounted). If the round is fired from the top barrel, it will cause a barrel-up flip as it is pushed away.

When mounted asymmetrically as in the F-16 , the aircraft-gun absorbs the recoil causing it to yaw and pitch.

The motor of the gun starts spinning in one direction, causing the barrel to spin in the opposite direction. As the motors axis spins up or down, it will generate torque on the barrel causing it to spin up or down in the opposite direction.

When mounted, it will cause the airplane to roll.

IDCrewDawg wrote:

you asking if the power of the bullet exiting the gun causes a recoil on the mounts. (I don't know what procession is) So if I understand your question correctly, the bullet exiting the muzzle should cause the gun to recoil in the opposite direction (this is established by Issac). What effect does the rotation have on the recoil is what your getting at. The answer is none. Then again, this could all just be over my head.

I know about the recoil and the laws of Newton, but my thoughts are regarding the laws of gyros.
We all know that if you take a bicycle wheel and spin it up.
Then apply a force to the hub will make the wheel tilt at approx. 90 deg. in the spinning direction of the applied force.

You do not need a great speed for the bicycle wheel to have this effect called pressecion.
And since the barrel set has quite a great mass and speed my theory is that this will apply to the gun mounts as well.

And IDCrewDawg, I'm wayyyyyyy over my head on this one myself. Wink

But.....I suddenly got this idea, and I'm not quite sure if I'm right.
I was hoping that a Gun-geek from LM would know.

Elite 1K Joined: May 26, 2005 - 08:39 PM Posts: 1496

If I understand your question, what you're asking has nothing to do with the recoil of the gun, correct? The force you're talking about could be created by dry firing the cannon. Or no?

And saying the barrel cluster has a large amount of mass really, really depends on your frame of reference. Compared to the weight of an F-16, it's a fairly trivial amount of mass.

Forum: F-16 Armament & Stores

Recoil effect on the gun