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Can someone answer the old myth for me : does firing the A-10's canon slow the aircraft down? A-10 drive once said that was BS but I forget in my old age.

The physics of firing the Avenger would make me think yes. If you consider the mass that is being expelled by the jet, in ammunition, that is going to slow the acceleration of the dive, as well as the sheer force acting against the forward motion of the aircraft. Objects in motion will stay in motion until acted upon by another force. The force of a few hundred 30mm shells with a muzzle velocity higher than the velocity of the aircraft would most definitely have to create a slow down in airspeed...which would explain firing the gun while in a dive and not level flight (plus the target is usually on the ground.)

--Raven

"Work Hard, Party Hard, Hardly Sleep"

Any loss in speed due to the gun firing does not amount to more than a knot or two. We fire the cannon in a dive because you have less dispersion in a dive and the HUD elevation matters less. Obviously there are many other factors (weather, tactics, etc.), however in general you can say the gun is never fired in level flight or a climb.

I have fired many thousands of rounds from the cannon and have not once noted a loss in airspeed, in the air or in reviewing the tapes on the ground. In fact, the airspeed in usually increasing because of the dive angle.

Edited by - tinygiant on Dec 14 2002 6:36 PM

Can someone give me the specific measurements of the velocities and the forces acting upon the airplane? I got some friends who love physics and would love to figure this out. If it's ok with OPSEC/COMSEC, that is.

The object of war is not to die for your country but to make the other bastard die for his. -General George Patton

BR:
If I had some numbers, I'd crunch them myself <img src=icon_smile.gif border=0 align=middle> I always did like physics. Also, I should amend my statement...I meant thath there would be a loss of speed, but I should have said that it MAY be negligible. Thanks for the input TinyGiant.

--Raven

"Work Hard, Party Hard, Hardly Sleep"

<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>
The guys in Vermont understand the physics of it I guess. My recollection, which is unreliable at this point, is that the instantaneous recoil (just after the first round is fired) on the mounts is 18000 lbs peak and it settles down to 9000 lbs peak for the next rounds. Remember, this is not a steady value. It occillates wildly and depends on the mass properties and recoil mechanism in the gun, and the stiffness and mass of the fuselage. GE Burlington had an A-10 forward fuselage facsimile to mount the gun in for testing to make sure there weren't serious resonances. You could probably estimate the speed change by calculating the momentum of each round and say that the change in airplane momentum per round is the same. Total rounds fired would dictate the speed change during the burst. I'm pretty sure the speed change would be negligible since the jet is 40,000 times heavier than the bullet, but you do the math.

Mc/I + P/A
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

OMG <img src=icon_smile_shock.gif border=0 align=middle><img src=icon_smile_shock.gif border=0 align=middle><img src=icon_smile_shock.gif border=0 align=middle><img src=icon_smile_shock.gif border=0 align=middle><img src=icon_smile_shock.gif border=0 align=middle>...I will never talk about the A-10 again..I can't keep up with this!!!

Ugly but well hung!

Old dogs and new tricks, eh, Dice!<img src=icon_smile_evil.gif border=0 align=middle><img src=icon_smile_wink.gif border=0 align=middle>

King George II on Gen. James Wolfe: "Mad, is he? Then I wish he'd bite more of my other generals!"

_________________
\"Those who hammer their guns into plows
will plow for those who do not.\"
- Thomas Jefferson

a10stress:
There will be an oscillation as each and every round is fired. My question is how they got the recoil and firing rate set properly so as not to induce harmonic vibrations that I would imagine would wreak havoc with the pilot and probably some com/nav equipment. Also, the slowdown would depend on the number of rounds fired, and I am sure that one does not typically fire enough rounds at one time to really slow the aircraft down noticably.

I wonder how noticable the slowdown may be in a positive AOA though...hmmm

--Raven

"Work Hard, Party Hard, Hardly Sleep"

A responce I got from an FCF pilot (Ragman) from McClellan AFB CA. with 15 years flying the Hog.


<b>Ragman-</b> The old wive's tale of the A-10 slowing down in flight when the gun is fired was generated by the early jokes bureau when the airplane first came to be...you know, A-10 simulator - put the pilot in a metal trash can and throw rocks at it. That kind of thing. Since bullets are expensive and chances to shoot on the range are limited, most pilots get in the habit of shooting short bursts: less than one second. Best chances for a kill on most targets (PK) is with a one second burst or around 70 rounds. In that length of time there's never any noticeable slowdown of the plane in flight.

When I was flying test sorties out of McClellan in the 80's, we were testing the Batelle gun gas diverter, a huge metal baffled wheel apparatus attached to the barrels that would sling all the gun gas down and away from the engines. A dismal failure of an idea because of weight and excess spinup of the gun. During the firing tests we were shooting four and six second bursts: what seemed like an eternity on the trigger. Even with that there was never any noticeable speed reduction during firing in the cockpit, but a slight evidence by the chase aircraft on the wing while trying to film.

<b>Dice-man-</b> Ragman what about noise, vibs and gun gas...

<b>Ragman-</b> As for vibration and noise, it's kind of like hitting those little grooved ridges on the shoulders of some two-lane roads in your car with only a muted growl for noise. The smoke is hardy noticeable. It's fun to shoot because it does have some feeling to it, unlike the 20mm in the F-5 that was kind of a joke after the Hog.

BTW Ragman flew F-5 for a couple of years...and that's from the horse's mouth or in this case the Hog's mouth!




<img src=icon_smile_cool.gif border=0 align=middle>

Ugly but well hung!

Somebody get the Extra Strength Tylenol, please?! <img src=icon_smile_clown.gif border=0 align=middle><img src=icon_smile_wink.gif border=0 align=middle>

King George II on Gen. James Wolfe: "Mad, is he? Then I wish he'd bite more of my other generals!"

_________________
\"Those who hammer their guns into plows
will plow for those who do not.\"
- Thomas Jefferson

a10stress: That calculation seems right to me. That would be considering firing at level, and doesn't account for the nose up effect which gives you a larger cross section to induce drag. Now, when you look at the way the gun is typically fired, the slow down becomes 1-2 knots or less with the AOA and Pitch-Trim compensation taken into account. This sound right to everyone?

--Raven

"Work Hard, Party Hard, Hardly Sleep"

And I seriously doubt many of us could discern +/- 5mph @ 400mph!<img src=icon_smile_wink.gif border=0 align=middle>

King George II on Gen. James Wolfe: "Mad, is he? Then I wish he'd bite more of my other generals!"

_________________
\"Those who hammer their guns into plows
will plow for those who do not.\"
- Thomas Jefferson

What about the thrust of the engines? The calculations only seem to take into account a level, steady state condition. If the aircraft is in a dive, which is how it is fired most of the time, gravity will cause the aircraft to accelerate even when the engines are in idle.

It really doesn't happen.

<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>...the slow down becomes 1-2 knots or less with the AOA and Pitch-Trim compensation taken into account. <hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

Coach...the AOA (angle-of-attack) would be the dive. But then you have acceleration due to gravity vs. lift of the airfoil, plus it is at an angle and not a full down dive, so it is not a full 9.8 m/s/s acceleration.

--Raven

"Work Hard, Party Hard, Hardly Sleep"