PDA

View Full Version : Weapon recoil effect



Manu-6S
06-12-2007, 01:45 PM
More that once I read that firing with HMGs and cannons at low speed could make the plane stall because of recoil.

I always feel strange about this game the possibility to hang on the prop in a candle manouvre firing with all the weapons without problem, even when you are a almost stall speed.

I think this should be a problem above all for wing weapon since, maybe, the engine mass could block the recoil effect in a better way. The same for firing at really high speed could make the cannons to explode (like happened to italian pilot Gorrini in his MC205) or rip the wings.

What do you think about this?

Manu-6S
06-12-2007, 01:45 PM
More that once I read that firing with HMGs and cannons at low speed could make the plane stall because of recoil.

I always feel strange about this game the possibility to hang on the prop in a candle manouvre firing with all the weapons without problem, even when you are a almost stall speed.

I think this should be a problem above all for wing weapon since, maybe, the engine mass could block the recoil effect in a better way. The same for firing at really high speed could make the cannons to explode (like happened to italian pilot Gorrini in his MC205) or rip the wings.

What do you think about this?

Freelancer-1
06-12-2007, 01:50 PM
What do I think about this?

Eight pages, minimum, is what I think http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

reisen52
06-12-2007, 02:00 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Freelancer-1:Eight pages, minimum, is what I think http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif </div></BLOCKQUOTE>

And no effective resolution http://forums.ubi.com/images/smilies/35.gif

K_Freddie
06-12-2007, 02:08 PM
Where's Raaaid on days like these ? http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

I've seen some reports where a plane slowed down by ~20mph when firing all guns. But it doesn't say how long he fired for, as most bursts tend to be for a second or two.
It is physically possible and is modelled in the game. But only a turkey would try this when 'stalling'
http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

VW-IceFire
06-12-2007, 04:39 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Manu-6S:
More that once I read that firing with HMGs and cannons at low speed could make the plane stall because of recoil.

I always feel strange about this game the possibility to hang on the prop in a candle manouvre firing with all the weapons without problem, even when you are a almost stall speed.

I think this should be a problem above all for wing weapon since, maybe, the engine mass could block the recoil effect in a better way. The same for firing at really high speed could make the cannons to explode (like happened to italian pilot Gorrini in his MC205) or rip the wings.

What do you think about this? </div></BLOCKQUOTE>
I nose over when trying to do something like that. Seems to be modeled to me.

FritzGryphon
06-12-2007, 04:59 PM
Someone in the know will post a detailed explanation and calculation of recoil forces.

This will be conveniently ignored by everyone who wants to believe the lie.

So in a naive effort to stop the thread here, I would suggest that everyone who wants to know if it's modeled will go into the game, start a mission, and fire your guns on the ground. The guns will push your plane around, proving that IL-2 models recoil forces!

I would also suggest they read this article, which explains why recoil forces will never make a plane stall unless it was already going to anyway.

http://en.wikipedia.org/wiki/GAU-8_Avenger
See "Recoil Myth"

Lurch1962
06-12-2007, 05:02 PM
If you fire guns while on the ground (no chocks), your plane will slowly drift backward and perhaps wobble a bit while doing it.

One could calculate the recoil force of a single round as it works against the mass of the plane, and sum the results over a given firing time. I did this a couple of years ago and arrived at the conclusion that it's unlikely a MG-equipped plane would slow by 20-30 mph over a typical firing time.

After all, a mere 150-pound man can operate a 30 cal MG without being thrown off his feet. Even 12 such guns won't to any great degree accelerate a 3,000 kg mass.

--Lurch--

DooDaH2007
06-12-2007, 05:25 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">More that once I read that firing with HMGs and cannons at low speed could make the plane stall because of recoil </div></BLOCKQUOTE>

I would seriously have my doubts about the engine management and speed observations of a guy who is fireing Mg and cannons at near stall speeds...

Though it is theoratically possible offcourse...

The forces are modeled, as Lurch1962 wrote...
Fireing mg and cannons on ground will make the plane go backwards...

rnzoli
06-13-2007, 03:54 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">hang on the prop in a candle manouvre </div></BLOCKQUOTE>
If you mean going up vertically, you never stall in that manouver.
The angle of attack is not going to increase, so your speed can go down to 0 km/h, without stalling. Firing the guns should slow down the plane's zoom climb and limiting it's maximum altitude that it can reach. But aiming should be quite poor in that low-speed situation, controls are not effective, even small changes need a lot of input from elevator, rudder etc.

Anyway, the recoil is modellled for sure. This is why US Navy planes were yawing due to asymmetric ROF from the wing guns in 4.04 version (now it is corrected).

Manu-6S
06-13-2007, 08:33 AM
I knew about the recoil in il2, but i wanted your thought about how is it modelled.

Bud Anderson:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I close to within 250 yards of the nearest Messerschmitt--dead astern, 6 o'clock, no maneuvering, no nothing--and squeeze the trigger on the control stick between my knees gently. Bambambambambam! The sound is loud in the cockpit in spite of the wind shriek and engine roar. And the vibration of the Mustang's four. 50-caliber machine guns, two in each wing, weighing 60-odd pounds apiece, is pronounced. In fact, you had to be careful in dogfights when you were turning hard, flying on the brink of a stall, because the buck of the guns was enough to peel off a few critical miles per hour and make the Mustang simply stop flying. That could prove downright embarrassing. </div></BLOCKQUOTE>

Dtools4fools
06-13-2007, 11:16 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">After all, a mere 150-pound man can operate a 30 cal MG without being thrown off his feet. Even 12 such guns won't to any great degree accelerate a 3,000 kg mass. </div></BLOCKQUOTE>

That seems a bit too simply to me...

If the 150 pound man is just standing like he does when falling in line at the cashier at the local supermarket it might throw him of his feet. If he's standing on ice he might have problems too. If he's suspended in the air it might have a different effect.
Sure if a plane is parked on a grass field and the brakes engaged it would no move at all.
But in flight is different. No brakes there, less friction.
*****

reisen52
06-13-2007, 11:31 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Dtools4fools:But in flight is different. No brakes there, less friction.***** </div></BLOCKQUOTE>

But 8,000 to 10,000lbs of mass going 300mph against the direction of the recoil force might be a little more difficult to counteract then a 150lbs guy in combat boots on dirt.

The 20mph slow down is one of those urban legends that exist because people want it to exist not because it can be supported with any logic.

Also it always seems to be 20mph regardless of the plane or weapons involves. 20mph must be the magic number.

stalkervision
06-13-2007, 11:35 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Freelancer-1:
What do I think about this?

Eight pages, minimum, is what I think http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif </div></BLOCKQUOTE>

between 12 and fifteen.. http://forums.ubi.com/images/smilies/winky.gif

stalkervision
06-13-2007, 11:37 AM
Does anyone know that when the 30mm cannon on the "wart hog" is fired it actually flies backwords for a moment! http://forums.ubi.com/groupee_common/emoticons/icon_eek.gif

ploughman
06-13-2007, 11:57 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by stalkervision:
Does anyone know that when the 30mm cannon on the "wart hog" is fired it actually flies backwords for a moment! http://forums.ubi.com/groupee_common/emoticons/icon_eek.gif </div></BLOCKQUOTE>

No it doesn't, maybe it slows down a bit, but it certainly doesn't decelerate from 200mph to -15mph and then accelerate right back up to 200mph again just because the pilot pulls the trigger. If it did the pilot would be dead with his brain pooled over the inside of his visor, the plane would be in bits and the Saturn V rocket engines needed to accelerate the plane back from -15pmh to 200mph in a 'moment' would be headed to Mars.

stalkervision
06-13-2007, 12:01 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Ploughman:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by stalkervision:
Does anyone know that when the 30mm cannon on the "wart hog" is fired it actually flies backwords for a moment! http://forums.ubi.com/groupee_common/emoticons/icon_eek.gif </div></BLOCKQUOTE>

No it doesn't, maybe it slows down a bit, but it certainly doesn't decelerate from 200mph to -15mph and then accelerate right back up to 200mph again just because the pilot pulls the trigger. If it did the pilot would be dead with his brain pooled over the inside of his visor, the plane would be in bits and the Saturn V rocket engines needed to accelerate the plane back from -15pmh to 200mph in a 'moment' would be headed to Mars. </div></BLOCKQUOTE>

just kidding of course. I wondered who would believe it.. http://forums.ubi.com/images/smilies/winky.gif


It does slow down a lot though.. http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif
Recoil myth

The GAU-8/A "Avenger" gatling gun next to a VW BeetleA persistent urban legend is that the recoil force of the Avenger matches that of the A-10's engines and as such the plane would slow down, stall, and subsequently crash if the gun was to be fired for long periods of time (some even claim that the aircraft would begin to fly backwards). However, these claims can be demonstrated to be false through the use of simple mechanics.

The average recoil force, F, can be calculated using fundamental principles of mechanics. The operative principle is change in momentum equals impulse. mv = Ft, where m is the projectile mass, and v is the muzzle velocity, t is time. For a burst of fire,

,
which reduces to

F = mvr,
where

m is the mass of the projectile (0.425 kg),
v is the muzzle velocity (1067 m s-1),
r is the rate of fire in rounds per second (70 s-1).
At 4200 rounds/minute, 70 rounds are fired each second. A 0.425 kg projectile is accelerated to 1067 m/s every one seventieth of a second. This gives a recoil force of approximately 30 kN based on the relation above. ( On the GAU-8/A product homepage the recoil force is stated as 10,000 pounds-force, or about 45 kN, probably due to additional recoil from exhaust gas from the muzzle. The maximum combined output of the A-10 engines is 80 kN. Hence the recoil force of the gun is slightly more than half of the total thrust of the engines. While this is quite significant, it is not sufficient to stop the aircraft but it can noticeably slow the aircraft.) In fact during test firing of the gun in the A-10 in the early 90's the USAF experimented with putting a muzzle brake on the end of the gun and extending the nose of the plane out around this muzzle brake to vent the gun gases backwards. It was decided during this testing that the effect of the gun was not significant enough to warrant the added expense and complexity of adding this to every plane in the inventory.

The recoil of the gun is also evident in the mounting position of the gun. The gun is mounted off the centerline of the plane as the bullets leave the gun when the barrels reach roughly the 9 O'clock position when looking at the nose of the plane, thus the recoil forces of the gun are directed down the centerline of the plane. This was done because it was discovered during development of the platform that having the gun mounted on the centerline and thus the recoil forces off the centerline was enough to push the plane off target when firing the gun.

According to 355th Fighter Wing Weapons and Tactics Chief at Davis-Monthan AFB in Tucson, AZ, there is no recoil problem with the GAU-8/A. The GAU-8/A utilizes recoil adapters. They are the interface between the gun housing and the gun mount. By absorbing (in compression) the recoil forces, they reduce the magnitude of the felt recoil, spread the time of the recoil impulse, and counter recoil energy transmitted to the supporting structure when the gun is fired.

Some claims have been made that the A-10 engines are susceptible to flame-out when subjected to gunpowder gases, such that when the GAU-8 firing, the smoke from the gun can make the engines stop, and this did occur during initial flight testing. Gun exhaust is essentially oxygen-free, and is certainly capable of causing flame-outs of gas turbines. However, the A-10 is now designed so that the gun exhaust passes underneath the fuselage, and never ventures near the high-mounted turbines, even during negative-G maneuvers.

reisen52
06-13-2007, 12:21 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by stalkervision:
Some claims have been made that the A-10 engines are susceptible to flame-out when subjected to gunpowder gases, such that when the GAU-8 firing, the smoke from the gun can make the engines stop, and this did occur during initial flight testing. Gun exhaust is essentially oxygen-free, and is certainly capable of causing flame-outs of gas turbines. However, the A-10 is now designed so that the gun exhaust passes underneath the fuselage, and never ventures near the high-mounted turbines, even during negative-G maneuvers. </div></BLOCKQUOTE>

This caused a number of crashes of the YP-104 test aircraft before they figured out what was happening & modified the gun mounting & gas venting in the airframe to compensate for it.

The 104 was the first US plane to mount the M-61 Vulcan gatling gun so the phenomenon was completely unexpected.

BaronUnderpants
06-13-2007, 03:11 PM
IIRC the 20 mph or there abouts reduction in speed came up a few times reading about very heavy cannon equiped ac`s..like Bf109, B-25 and Mosqito, all at some point or as standard carried 30mm, 40mm or even 50mm cannons ( As big as 70mm in the B-25?...not sure?)

shotdownski
06-13-2007, 03:53 PM
This sounds like the same type "urban myth" as the one about a battleship being pushed sideways 30 feet when firing a full broadside. The physics just don't add up.

Manu-6S
06-14-2007, 12:45 AM
Thanks for the answers http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Lurch1962
06-14-2007, 06:14 PM
Another way to look at it...

Let's consider that a 12-MG plane, which weighs 3,000 kg, is sitting on a frictionless sled. Each fired bullet leaving the muzzle weighs, say, 7g and travels 850 m/s.

The mass ratio of bullet to plane is 1:428,571. Therefore each bullet will accelerate the plane by an amount equal to the muzzle velocity times this ratio, i.e., 850 x 0.0000023 = 0.002 m/s. So even a 1000-round burst would push the plane/sled backwards only 2 m/s, or 7.2 km/h.

--Lurch--

Deadmeat313
06-15-2007, 01:59 AM
A couple of anecdotes I remember:

During the Battle of Britain, the RAF was concerned at a very high altitude Luftwaffe recon aircraft that kept flying over their bases at heights their Spitfires could not reach. One squadron went as far as to strip down a spitfire of all non-essential equipment to maximise its high altitude performance. It was armed with two hispano cannons with a few rounds of ammo.

They sent the spit up against the recon plane next time it came over. the spit was at the very edge of stall as it climbed to firing position. When the pilot opened fire one of the hispanos jammed, and the other threw the plane into a spin. The recon plane escaped.

On these forums there was a link to an interview with a russian VVS pilot. He told a fairly lighthearted story of how one day he was coming in to land too fast, so fired his nose cannon to slow himself down, then landed perfectly. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif


T.