How many mph does B-25H lose when firing cannon?

[Sol75]

Which is exactly how A-10 pilots describe it.....

I was reading this thread, and saw the post about the A-10, I was interested so I called my cousin, who used to fly them.
Firing the cannon on it DID induce deceleration, not enough to cause the plane to STOP or stall in any way, but it WAS noticiable.  The other thing was that when they fired, the smoke from the gun, would be ingested by the engines, reducing thrust, and if fired for too long continuously (approx 3 seconds) it could even cause a flameout!

 

[JunkyII]

Noobs
do not fire your guns ingame to try for overshoot......just saying...

[SEseph]

A long time ago I read something on an AC-47 nicknamed Puff the Magic Dragon. She had 3 massive gatlin guns each capable of firing 6000 rounds a second out one of her sides, able to cover a football field in just over 3 seconds of fire. But the reason I bring it up (unfortunately I couldn't locate anything for or against to post as well) is I remember it saying that if she fired all her guns at once for too long it would cause her to slow enough to stall and drop from the sky. If anyone could confirm or deny this, please, as like I said, I can't remember where, just the name and the story.

[Bronk]

A long time ago I read something on an AC-47 nicknamed Puff the Magic Dragon. She had 3 massive gatlin guns each capable of firing 6000 rounds a second out one of her sides, able to cover a football field in just over 3 seconds of fire. But the reason I bring it up (unfortunately I couldn't locate anything for or against to post as well) is I remember it saying that if she fired all her guns at once for too long it would cause her to slow enough to stall and drop from the sky. If anyone could confirm or deny this, please, as like I said, I can't remember where, just the name and the story.

Spooky

http://en.wikipedia.org/wiki/AC-47_Spooky

Since it fired out the side...hard to slow it down. Now push it sideways?

[33Vortex]

The sideway push can (and probably will) slow it down because of the added drag. If that'd be enough to stall the aircraft I don't know, but consider that it must fly in a wide circle and bank to get guns on target in the first place. So the pushing motion would be outwards and upwards in the turn. The C47 isn't very fast, nor has it very powerful engines, so I can believe there would be a stall if the guns were fired continuously as the aircraft is very heavy laden with the guns and ordnance on board.

[Devonai]

I can certainly admit to being wrong, but I just can't get my head around this.  Any physics geeks out there who can better explain the forces at work?

[33Vortex]

http://www.youtube.com/watch?v=iH48Lc7wq0U

[Devonai]

Thanks for the video.

So, the kinetic energy generated by the fired projectile acts against the forward movement of the aircraft? Let's look at the numbers.

The A-10 Thunderbolt II has an average loaded weight of 42,000 pounds (as listed on Wikipedia for anti-armor missions).  At 340 mph (cruise speed, approx. 500 fps), this translates into about 163.2 million foot-pounds of energy (Weight in grains times velocity in fps squared divided by 450,240).

The GAU 8/A generates approximately 178,482 foot-pounds of energy with each shot (6560 grain projectile at 3500 fps).  This is about 0.00109 the kinetic energy of the aircraft.  Added together, this makes a 1 second burst (65 rounds) from the GAU 8/A about 11.6 million foot-pounds, or about 0.071 the kinetic energy of the aircraft.

So according to my calculations (please check my math), a one second burst from the cannon translates into a 7.1% loss in the forward velocity of the aircraft.  One can presume longer bursts have a greater effect, but at some point the continued thrust of the engines would have to mitigate the effect of the cannon.

I should have crunched the numbers first and saved myself the embarrassment.

[33Vortex]

Ok I've not checked the numbers on this so this won't be exact. However, consider that the entry speed on the attack run is not 'cruise speed' but full throttle and as much speed as you can get. So I'm assuming that'd be closer to 500 mph than 340. Then, a burst with the GAU would be against a group of vehicles perhaps a couple seconds long. Again using your numbers of 7.1% speed loss per second, that's 14.2% of 500 mph in 2 seconds which add up to just over 70 mph in 2 seconds. Now tell me that decrease in speed will not be noticeable in the cockpit. It's a deceleration more violent than what most stock cars can perform on the strip in acceleration.

[Krusty]

Making strafing runs at maximum speed is contrary to accuracy, aim, stability, and plane control.

Would be silly to assume it's flying 500mph or so, especially when the A-10 loiters at cruising speed (sometimes shutting off 1 engine?) waiting for a call to come in.

[Krusty]

Also, you're not just looking at the projectile, it's the giant jet of expanding gasses that project the shell as well. A space shuttle is extremely massive, and heavy, but it only takes a tiny burst of jets (thrusters) to move it about. A plane flying in-air can be slowed by the gasses shooting forward from gun barrels.

A giant cargo plane can be launched from a standstill to takeoff speed in a split second by a few (small diameter) rockets on its side [ED: I'm thinking Blue Angels C-130 here, but many other instances apply]

Don't discount firing super-high-caliber guns while flying at slow speeds as a means for slowing/impeding forward speed.

The question is: How much does it do in-game already on our B-25H?

[33Vortex]

Making strafing runs at maximum speed is contrary to accuracy, aim, stability, and plane control.

Would be silly to assume it's flying 500mph or so, especially when the A-10 loiters at cruising speed (sometimes shutting off 1 engine?) waiting for a call to come in.

Coming in hot with the possibility of taking return fire, I don't know about you but I'd want to move as fast as possible. The loss in accuracy is a moot point as the cannon on the A10 was never known to be a precision weapon. If you want precision, drop laser guided munitions from 20,000 feet.

[Beefcake]

Speaking from game play experience, when you fire the B25's cannon you can sometimes notice the speedometer "shaking" abit from the shot. However the recoil is not enough to have any real affect on the aircraft as the B25's gun fires far to slowly for this.

On a side note though, and as stated earlier in the tread, if you "unlock" your wheels and fire the B25's guns on the runway it will start rolling backwards. But again this is true for any plane with a large gun package.

[bj229r]

Used to fly H2H a lot, and with their silly ammo loadouts, jug would have like 15 THOUSAND rounds, and consequently handle even more poorly than normal. Keeping trigger held down for 2-3 min on climbout would drain lots of excess ammo, but it REALLY impeded acceleration

[Krusty]

That's a misconception.

When ammo multiplier is turned UP, the ammo does not weigh more than the standard ammo loadout would weigh. Otherwise you'd have P-47s weighing in at 150,000lbs and never go anywhere.