# Can gun recoil really slow a fighter?



## CobberKane (Oct 26, 2013)

This one comes up time and again in pilot combat reports; that recoil from the guns significantly slows a fighter aircraft. I'm not going to spoil the fun by doing the maths straight off, but to me this seems highly unlikely. I suspect the idea comes from seat of the pants impressions but doesn't hold up to the laws of physics, but if anyone can prove otherwise, go for it.


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## vikingBerserker (Oct 26, 2013)

I certainly think there is the potential from the recoil. IMHO it depends on the number and type of guns firing versus the weight of the aircraft.


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## CobberKane (Oct 26, 2013)

vikingBerserker said:


> I certainly think there is the potential from the recoil. IMHO it depends on the number and type of guns firing versus the weight of the aircraft.



Absolutely. The weight of the projectile and it's muzzle velocity will give a figure for the recoil of each weapon upon each discharge. Rate of fire should then give us an idea of how much reactionary force is created per second of firing, and with reference to the mass of the aircraft we could then estimate how much the recoil of the guns would slow it over a given period.. Shouldn't be too difficult. Personally though, I'm about to head off fishing, so I'll check back later.


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## turbo831 (Oct 26, 2013)

Stars and Stripes article addressing this on the A-10 Does the A-10's gun slow the plane when fired? - The Rumor Doctor - Stripes


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## syscom3 (Oct 26, 2013)

vikingBerserker said:


> I certainly think there is the potential from the recoil. IMHO it depends on the number and type of guns firing versus the weight of the aircraft.



You mean the energy state of the aircraft. If its going fast, the recoil has less of an effect.


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## vikingBerserker (Oct 26, 2013)

If you are referring to speed in relation to mass then I would agree somewhat. I would think speed would certainly come into play but I would assume mass/weight would have a greater impact. The recoil of a 30mm would probably stop a paper airplane in flight going 100mph, but would have no effect on a 747 sitting still.


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## parsifal (Oct 26, 2013)

The physics certainly says that gun recoil could theoretically have an effect. Its basically the aircrafts engines are applying a certain force in one direction, that is forward, whilst the projectile, according to newtons laws, are applying a force in exactly the opposite direction.

whether the discharge of the weapons affects aircraft velocity in applied terms, is another, and interesting question. heres my school boy bash at it be advised my maths is terrible.....

Say an aircraft is travelling at 500kmh and weighs 1000 kg. We have to convert the airspeed to m/s. 
500kmh = 500x1000/60x60
= 140m/s


Assume the armament is 4 x 40mm cannon (AFAIK nobody ever carried that much). Assume a projectile weight of 1.6 lbs (0.8 kg). Assume a MV of 4000m/s and a rof of 250rpm for each gun. Effectively for the entire armament we have an rof of 1000 rpm

The kinetic energy of the aircraft is equivalent to its moments of force, which is expressed as a vector

P=MV where P= Momentum, m= mass and V=velocity
= 1000x 140 m/s (approx)
= 140000 units of momentum

This measuremnt of momentum (which is a moment of force) is in the same direction as the direction of the aircraft (assume straight line flight). 

Force generated by the discharging armament

P=MV
=(rof of a/c x projectile weight)xv
=(1000x0.8) x 4000
= 3,200,000 units of momentum (ne force) in the reverse.

On that basis the armament discharging will very quickly cause the aircraft to lose speed and go into a stall. To maintain some speed the armament needs to be reduced, and the aircraft needs to be in a dive with the engines at full throttle.

But there should be little doubt, the armament, if heavy eanough, will affect airspeed


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## wuzak (Oct 26, 2013)

"The kinetic energy of the aircraft is equivalent to its moments of force, which is expressed as a vector"

I don't follow that reasoning at all.

Firstly, kinetic energy is proportional to mass and the square of the velocity. Momentum is proportional to mass and velocity.

Momentum is also not a "moment of force".


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## GregP (Oct 26, 2013)

According to a copuple of friends of mine who flew the A-10, the recoil of THAT gun slowed the aircraft considerably. Fortunately, you could not fire many rounds or the accumulation of gun gas in front of the plane would flame out the engines and the pilot would be in a panic to restart, usually melting the APU in the tail.

Whether or not the recoil of six .50 caliber MG for a short hurst would slow a Mustang is another story, but four 20 mm cannon would. The trick is to aim, get in a shooting solution, and fire a few rounds for effect ... and do it again. The trick is NOT to hose the ammo all over the sky, slow down and be happy with your ONE victory.


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## Greyman (Oct 26, 2013)

The physics clearly points to this being the case.

I've also read many anecdotes where pilots felt the aircraft slow down when they fired, being pressed forward into their straps, etc.

I've even read of a few anecdotes of pilots in dogfights with enemy fighters and not being able to fire at their opponent due to being at stall speed, even though the enemy was right in their sights. This was always at extreme low level where they weren't going to risk it. Must have been insanely frustrating.


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## Cave Tonitrum (Oct 26, 2013)

"significantly slows a fighter aircraft"

No.


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## Greyman (Oct 26, 2013)

Depends what you mean by 'significant', I suppose.

Flying right on the edge of a stall in a turn just above the waves ... that'd be significant in my books.


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## turbo831 (Oct 26, 2013)

From Stars and Stripes article :


> But while the A-10's endurance and firepower are legendary, the myth that its cannon drastically decelerates the aircraft is pure "Hawg-wash," said retired Air Force Col. Steve Ruehl.
> 
> "I have fired as many as 500 rounds in one trigger burst, that takes just about seven, eight seconds, and [it had] no impact on the air speed of the aircraft," said Ruhel, who has logged 3,500 hours flying A-10s.
> 
> ...


Does the A-10's gun slow the plane when fired? - The Rumor Doctor - Stripes


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## GrauGeist (Oct 26, 2013)

The GAU-8/A in a full 5 second burst may slow the A-10 about 3 knots and the self-sustaining combustion modules in the engines engage when the A-10 fires it's weapon to prevent oxygen starvation.


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## CobberKane (Oct 26, 2013)

Greyman said:


> The physics clearly points to this being the case.
> 
> I've also read many anecdotes where pilots felt the aircraft slow down when they fired, being pressed forward into their straps, etc.
> 
> I've even read of a few anecdotes of pilots in dogfights with enemy fighters and not being able to fire at their opponent due to being at stall speed, even though the enemy was right in their sights. This was always at extreme low level where they weren't going to risk it. Must have been insanely frustrating.



Absoultely no doubt that a fighter WILL slow when it fires it's guns - Newtons third law demands it. The question is, how much?
Here’s my take on this with, say, a P-51D.
A .50 bullet weighs about 45g. I don’t know how much the propellant in the cartridge weighs, but we have to take that into account as well because it’s also being ejected from the muzzle, adding to recoil. I’ll double the weight of the projectile to 90g to cover it.
At 750rpm the Mustang will be ejecting about 13 rounds plus propellant per gun per second, for a total ejected weight of about 7kg per second. To my thinking it would make no difference if the mustang fired seventy eight .50 cal rounds per second weighing 7kg total or one 7kg round; the equal and opposite force accelerating the fighter in the opposite direction would be the same over the course of one second.
The muzzle velocity of 7kg/sec of stuff coming out of the guns is about 750 mps. Therefore, if the Mustang could weigh exactly seven kilograms, and (for the sake of simplification) it fired a single 7kg projectile with a muzzle velocity of 750mps, the Mustang would go backwards at 325mps and the projectile would for forward at 325mps. But of course the mustang is much heavier than one second’s worth of its firepower: at nine metric tons its about 1300 times heavier, in fact. So divide the 325 mps of force on Mustang by 1300 and we get .25 mps or 9kph – about five and a half mph. Ergo, each second of fire will take about five and a half miles per hour off the mustangs speed. That would be irrespective of whatever speed the Mustang was travelling at when it fired.
Is that a significant amount? Probably not if the Mustang is travelling at a fair clip to start with, but given that a five second burst would slow the plane by nearly 30mph, I can see how a fighter would be pushed over the edge into a stall during a low speed dogfight, or if the wings were at a high angle of attack.


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## bob44 (Oct 27, 2013)

I remember a watching documentary years ago, a P47 pilot said firing the 8 50cals would slow the plane down considerably (cannot remember the exact words).
I remember I was very impressed by how much it did slow down.


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## silence (Oct 27, 2013)

CobberKane said:


> Absoultely no doubt that a fighter WILL slow when it fires it's guns - Newtons third law demands it. The question is, how much?
> Here’s my take on this with, say, a P-51D.
> A .50 bullet weighs about 45g. I don’t know how much the propellant in the cartridge weighs, but we have to take that into account as well because it’s also being ejected from the muzzle, adding to recoil. I’ll double the weight of the projectile to 90g to cover it.
> At 750rpm the Mustang will be ejecting about 13 rounds plus propellant per gun per second, for a total ejected weight of about 7kg per second. To my thinking it would make no difference if the mustang fired seventy eight .50 cal rounds per second weighing 7kg total or one 7kg round; the equal and opposite force accelerating the fighter in the opposite direction would be the same over the course of one second.
> ...



Not too sure about the propellant being ejected: its being burned and converted into energy to drive both the projectile and the recoil. These may balance out, or one may mitigate the other to a certain degree. Hmmm... been too long since I studied dynamic mechanics. I'm not even sure I'm making sense here. Wouldn't be the first time.

I shouldn't have read this thread: now my brain will be mulling this over whether I want it to or not. Hope someone can clear this up for me so I don't lose too much sleep!


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## CobberKane (Oct 27, 2013)

silence said:


> Not too sure about the propellant being ejected: its being burned and converted into energy to drive both the projectile and the recoil. !



A chemical reaction such as the burning of the propellant in a cartridge does not destroy matter, i.e. the propellant is not 'converted' into energy. The mass of the gases produced by combustion in the cartridge would be exactly the same as the mass of the propellant before ignition, and as these gases are ejected they would contribute to recoil accordingly.
Incidentally, I don't know how much energy would be released to the propellant in a .50 cal round WERE fully converted to energy, but you are talking about the equivalent of a number of decent hydrogen bombs. We might need to make the breach and barrel a bit heavier.


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## pattle (Oct 27, 2013)



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## stona (Oct 27, 2013)

silence said:


> its being burned and converted into energy to drive both the projectile and the recoil.



It is being largely converted into gas (albeit by an exothermic process) not energy, otherwise each cartridge would go off like a nuclear explosion  All the laws of conservation still apply. The problem becomes somewhat tricky as not all the gas and other combustion products are ejected forwards, the action of the gun is driven by a component for example.

The answer to the original question must be yes, as already noted, as not even the USAAF cannot defy the laws of physics.

Cheers

Steve


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## drgondog (Oct 27, 2013)

Simple answer - Yes. The negative acceleration due to recoil is expressed from F=d/dt(m*v)

The 'system' during cannon firing is characterized by a rapid change of MASS (i.e cannon projectiles) leaving the 'system') with respect to time


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## Shortround6 (Oct 27, 2013)

The formula for recoil velocity (not energy) is bullet momentum ( bullet weight x bullet velocity) + propellant momentum (propellant weight x propellant velocity) divided by gun/aircraft weight.

Propellant velocity is about 1200 meters/sec (+ or - 10%) for most rifles, machineguns and automatic cannon. 

IF I am doing the math right it would take 100 rounds of .50 cal ammo to slow a 4000kg aircraft down by just under 1.5 meters a second. 

Or look at it this way. A .50 cal round has about 5 times the recoil impulse of a .308 round, but the 4000kg airplane weighs 1000 times what the M-14 rifle does.


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## R Pope (Oct 27, 2013)

I have a pic somewhere of the Missouri firing a broadside. You can see a wave at the bow, where the recoil is driving the ship sideways at a noticeable speed. And that's a 60K ton ship! Somewhat bigger guns, too, but still....


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## pattle (Oct 27, 2013)



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## parsifal (Oct 27, 2013)

parsifal said:


> The physics certainly says that gun recoil could theoretically have an effect. Its basically the aircrafts engines are applying a certain force in one direction, that is forward, whilst the projectile, according to newtons laws, are applying a force in exactly the opposite direction.
> 
> whether the discharge of the weapons affects aircraft velocity in applied terms, is another, and interesting question. heres my school boy bash at it be advised my maths is terrible.....
> 
> ...




When I refer to "moment of force", i certainly stuffed my description of what was happening. This is what I think....What I was intending was that there is no force being applied (assuming no effects from friction or the like) when a body is not changing its weight or velocity. A moving body whose velocity is not changing has momentum, but it has no force being applied to it. Force is mass x accelaration, since there is no accelarartion there is no force, and no Work being done (work - Force x Distance). I also think the aircraft altitude is potential energy. 

However if the mass (ie the aircraft) starts to alter its velocity, that momentum starts to translate to Force, even if decelarating. a car crashing has force being applied to it, by its own loss of velocity.

To describe it as a moment of force is technically wrong, I know, but it sometimes is used to describe (wronly) the amount of force being applied over a short period, say less than a second.


The second thing wrong with what I did above is I got my energy momentum calcs and gun estimates totally screwed up. The aircraft momentum calculations are per sec (ie the velocity is metres per second), but the gun component.....the thing applying force in the reverse direction......Ive calculated with rof measured in rounds per minute. They should be rounds per second. ive also gotten the the guns MV wrong

Correcting these errors, the estimated effect by the discharging guns should be as follows

P=MV
=(rof of a/c sec-1 x projectile weight)x projectile velocities (this falls down as well, it will not be 4000m/s, more like 1500, as the projectile is still accelarating when it leaves the barrel and in any case wil never get to 4000)

=(1000x0.8/60 kg/sec) x 1500 (m/sec)
= 13.33 x 1500 
= 20000 units of force

The aircraft was producing 140K units of momentum, which will be reduced by 20000 units of force each and every second the weapons are firing. Of course the engines are producing a certain amount of power each and every second. So whilst the guns are applying a significant negative effect on the aircrafts momentum, the engines are applying a positive effect. If the aircraft is diving, almost certainly this will act to also counterbalance the loss of momentum caused by the guns. you would have to say there is probably very little effect I think.


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## silence (Oct 27, 2013)

That's what I get for trying to think at night. Shame on me!



R Pope said:


> I have a pic somewhere of the Missouri firing a broadside. You can see a wave at the bow, where the recoil is driving the ship sideways at a noticeable speed. And that's a 60K ton ship! Somewhat bigger guns, too, but still....



Here's an interesting short paper on that very topic: Do Battleships move sideways when they fire?


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## syscom3 (Oct 27, 2013)

The only aircraft that I have heard of that actually slowed down to a considerable degree was the B25 gunship. Having a dozen .50's, or the firing of the 75mm cannon would slow it up. But not to any big degree.


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## fastmongrel (Oct 27, 2013)

Mosquito Tsetse 6 pounder. It certainly bounces about on the ground when firing. 
_View: https://www.youtube.com/watch?v=M00f5RxhxLY_


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## GregP (Oct 27, 2013)

According to the A-10 pilots I knew back in Arizona (they flew them from Tucson), the aircraft slows significantly when the GAU-8 is fired. They said they were limited in how many shots could be fired in a row before flameout occurred. The self-sustaining combustors are not oxygen-supplying items, they simply keep the igniters on. If you fly though enough gun gas, the engines will flame out. They train so this doesn’t happen … but it certainly CAN. 

Talking with former pilots and crew members who flew the B-25 gunship, I heard them state the plane could lose 15 - 20 mph when firing the big gun. Now memory can play tricks on you, but these memories must have been pretty vivid because when one former pilot said it, the rest immediately nodded and agreed. The original field modification airframe to create the gunship B-25 only fired about 20 shots from the 75 mm cannon before the airframe was scrap due to the recoil loosening the rivets! If that isn’t significant force, I don’t know what would be.

The later North American Aviation gunships had a good recoil absorption mechanism to reduce the impact on the airframe and crew. It perhaps was a different story, but the group I heard at the former Champlin Fighter Museum in Mesa, Arizona were from the first squadron to fly these field mods. They flew with Pappy Gunn, who helped invent the plane. One was Paul Cherry, who was on Pappy Gunn's crew. I can't remeber the names of the others. The only reason I remember Paul is I worked with him at Motorola in Scottsdale, Ariziona for some years.


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## GrauGeist (Oct 27, 2013)

As mentioned before, the A-10 can't "flame out" it's engines from cannonfire because it's equipped with a Self-Sustaining Combustion Section in each engine. This was developed during production and retro-fitted into early models based on performance of the very early models.

The GAU-8 is designed with recoil in mind as well as offest mounting to compensate for the recoil.

The Cannon can be held to long burst but speed equates to time over target and a long burst isn't nessecary for several reasons. One being the aforementioned ToT and the other is overkill/waste. A short burst from the Cannon is all it takes to re-arrrange devestate the landscape/buildings/armor/small nations and is a waste of ammo otherwise.

Pilots report deacceleration is negligible and a moderate burst will register about a 3 knot braking in a shallow angle of attack.


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## wuzak (Oct 27, 2013)

GrauGeist said:


> The GAU-8 is designed with recoil in mind as well as offest mounting to compensate for the recoil.



How does that work?

I was always under th eimpression that the gun was off centre to allow room for th enose landing gear....


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## GrauGeist (Oct 27, 2013)

wuzak said:


> How does that work?
> 
> I was always under th eimpression that the gun was off centre to allow room for th enose landing gear....


From "A-10: Developement Description", authored by Greg Goebel:


> Each barrel fires when it reaches roughly the 9 o'clock position, when viewed from the front of the plane. Because the gun's recoil forces could push the entire plane off target during firing, the weapon itself is mounted off-center in the other direction, toward the 3 o'clock position, so that the firing barrel lies directly on the aircraft's center line. The firing barrel also lies just below the aircraft's center of gravity, being bore sighted along a line 2 degrees below the aircraft's line of flight. This arrangement accurately centers the recoil forces, preventing changes in pitch and/or yaw when fired. This configuration also provides space for the front landing gear, which is mounted slightly off-center on the right side of the nose.



While the cannon's recoil itself isn't enough to significantly slow the aircraft while firing, it is enough to skew the aim.


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## Shortround6 (Oct 27, 2013)

Some other aircraft may exhibit slewing or dipping when the guns fire, whether this is confused with the guns 'slowing' the aircraft I don't know but may be a possibility. 

Figuring out the recoil impulse of a gun or guns is relatively easy, as above. Projectile mass in grams times projectile velocity in meters per second plus propellant weight times 1200meters a second ( good enough for most guns). Divide by the aircraft mass in KG to get the rearward speed (or speed reduction) then multiply by number of shots.


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## Aozora (Oct 27, 2013)

About 19:27 on - the B-25Gs don't seem to slow down while firing their 75mm and they "get the hell out of there"...

_View: https://www.youtube.com/watch?v=DGjGJHrQxy8_


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## GregP (Oct 27, 2013)

Hi Wuzak,

The gun is mounted off-center so the barrel that is firing is exactly on centerline, helping to not throw off the aim. The A-10 absolutely CAN flame out its engines. To help prevent same, they keep the igniters on while firing (self-sustaining item), but if you fire long enough, it'll STILL flame out due to lack of oxygen ... unless you are suggesting they carry oxygen to inject, too. I can tell you they don't do that.

The many melted APU's are mute testament to flameout all by themselves.


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## GrauGeist (Oct 27, 2013)

Ah well, thought it was pretty well covered, I guess not...


GregP said:


> Hi Wuzak,
> 
> The gun is mounted off-center so the barrel that is firing is exactly on centerline, helping to not throw off the aim. The A-10 absolutely CAN flame out its engines. To help prevent same, they keep the igniters on while firing (self-sustaining item), but if you fire long enough, it'll STILL flame out due to lack of oxygen ... unless you are suggesting they carry oxygen to inject, too. I can tell you they don't do that.
> 
> The many melted APU's are mute testament to flameout all by themselves.


On 8 June 1978, an A-10 (73-1669) was lost due to engine fouling by secondary gases. The pilot had to eject because the engines cooled and wouldn't relight. This led to an investigation as to why it happened and thus the secondary gas problem was addressed. This was the only known A-10 to ever experience total failure resulting in a crash.

The initial fix:


> The Battelle device was developed by Battelle Laboratories as a gas diverter to be fitted to the barrel muzzles of the GAU-8/A. It was a relatively cheap fix but it was soon found to contribute to unacceptable stress fractures of the airframe along various locations of the forward fuselage. As such, the Battelle device was dropped from consideration.





> *Instead, the engines were fitted with a system that maintained continuous ignition for every moment that the 30mm gun was to be fired and for a short time after the trigger was depressed.* Additionally, maintenance requirements now stipulated that engines were to be washed once for every 1,000 rounds fired.



Never heard of an APU "melting" in an A-10 due to engine fouling via secondary gas, but I'd be more than happy to read about it if you have the publication handy.

_** Forgot to add a bit of info! **_
Regarding the incident on 8 June, this was gunnery testing and the excersize was to make 5 passes, firing 100 rounds per pass. The engines fouled on the 4th pass.
Also, Maj. Gideon Jr. ejected safely, but he ejected at 2,000 feet approx. and suffered injuries.


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## GregP (Oct 27, 2013)

I don't have an article on the melted APU's but did manage to see a couple of them at Honeywell in Phoenix, AZ in the 1980's.

Let's say I don't buy what you're selling but, that's OK. It likely won't shorten or extend the lifetime of the A-10 anyway. Cheers.

Speaking of the lifetime of the A-10, I wonder what we will get to replace it? I'd sure hate to hear the F-35 because the A-10's fly around at low altitude and are a bit vulnerable for an aircraft with the sticker price of an F-35.


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## CobberKane (Oct 27, 2013)

As has been stated, firing the guns WILL slow the fighter, so the question is by how much, and whether it’s significant. I guess under the right circumstances, for example just above stall speed, its something the pilot would have to take into account. That said, there seems to be a disconnect between the pilot’s seat of the pants impression and the actual slowing of the plane. I’ve read numerous accounts where pilots have described the sensation of firing the guns with terms like ‘hitting a wall’, where some quick notepad calculations demonstrate that the effect was actually negligible. On a similar note, I have heard an experienced pilot claim that he rolled a railway carriage over with only the impact of his P-47s guns, which is obviously impossible, and whereas the Thunderbolt is generally touted as the best diver of the war, comparisons with the P-51 seem to generally have that fighter out-diving it. I guess the moral is, be careful of truisms, no matter how well established. Or as Scotty would say “Ye canna change the laws ‘o physics, captain!”


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## GregP (Oct 27, 2013)

Hi Cobber,

Like I've said before, the real-life recollections of a former combat pilot must be weighed against experience. I have spoken with many former P-51 pilots who stated it was the best fighter in the world. Later, when I asked them how many other fighters thay had flown, the answer was many times, "none," so their estimation of "the best" would have to be taken with a grain of salt ... at least in my book.

However, it stands to reason by simple Physics that a plane in steady flight with a steady engin epower ... that suddenly experiences firing of the guns would probably experience some small negative acceleration related to the sum total of the muzzle energy of the weapons. It is also quite possible that a 1 - 3 second burst, while it WOULD generate retarding energy, might not be sufficient to materiialy affect the speed of the aircraft unless the burst were sustained awhile.

I have seen a statement about the GAU-8, the cannon in the A-10, that the recoil force was on the order of 10,000 pounds ... but the article didn't cite any reference for it. So, the accuracy of the statement is a roll of the dice ... I make no claims for it or against it.

I have only the statements of pilots, who SHOULD know whether or not they lost speed. Can't say for sure myself; I wasn't there flying an armed fixed-wing aircraft and discharging the armament. When I was in Vietnam, I never noticed the Huey sliding sideways when someone fired a fixed M-60 out the side. But I also wasn't exactly trying to look for it, either. I was hoping the bad guys weren't good shots. Since I'm here, they weren't that good at that exact point in time, though we DID take some hits.

Maybe the combat recollections of pilots would be a bit suspect, but firing in practice runs during training would be a different story with little or no stress of combat to deal with. They SHOULD know, but that is only my opinion. Others may well feel differently.

I like that movie Aozora posted, but since there were nine B-25G's, they were very probably factory North AMerican planes with recoil absorption mechanisms, not the early hard-mounted 75's. Those didn't last very long and the recoil was murderous, if one can believe the first-hand accounts of the pilots and crewmen who flew them. 

If you can't believe them, then what WOULD be believable? Hopefully not some opinion from someone who has never flown a B-25, much less an armed one. In any case, it'll be tough to prove one way or the other, so I won't try.

Cheers.

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## GrauGeist (Oct 27, 2013)

GregP said:


> Let's say I don't buy what you're selling but, that's OK. It likely won't shorten or extend the lifetime of the A-10 anyway.


Sorry if fact isn't as exciting as opinion or speculation 



GrepP said:


> Speaking of the lifetime of the A-10, I wonder what we will get to replace it? I'd sure hate to hear the F-35 because the A-10's fly around at low altitude and are a bit vulnerable for an aircraft with the sticker price of an F-35.


They would be stupid to shelve the A-10 as it's a ground support force-multiplier of the highest order and has proven it's value on the battlefield countless times. They can keep the B-52 in service well over 60 years, they can certainly keep the A-10 around for a while longer as well.


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## GregP (Oct 27, 2013)

I hope they DO keep the A-10's in service. With today's avionics, an avionics upgrade for teh A-10's might not be a bad idea, either.

I believe the experiences of pilots in a type are sufficiently factual for me, but I don't wish to continue to argue about it. Though we disagree, it isn't exacly a cosmic argument, is it? Cheers to you.

I'd purely LOVE to fly an A-10 and find out for sure, but I stand a better chance of marrying Sandra Bullock than I do of flying an A-10. One can hope ... and maybe pigs CAN fly.


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## tyrodtom (Oct 27, 2013)

When a OH-6 (Loach) was armed with a minigun, it was stuck out on a pylon on the left side.
If it was fired from a hover, the helicopter would yaw left, but the pilot could easily compensate with right pedal.

If fired in flight, it had the same effect, but less so. 
The minigun had two rates of fire, 2000 rpm, and 4000 rpm. The yaw effect was greater at the high rate.

I wouldn't even have noticed it myself, until it was remarked on by the pilot.


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## CobberKane (Oct 28, 2013)

Noticed a dumb mistake I made in my calcualtions on page one - somehow I attributed the P-51 a weight of nine metric tons (!!). Actually its about half that, so firing the guns should slow the aircraft by about eleven miles per hour, per second. If a five second burst slowed the fighter by 44mph, that really is getting quite significant, even at high speeds.


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## Francis marliere (Oct 28, 2013)

R Pope said:


> I have a pic somewhere of the Missouri firing a broadside. You can see a wave at the bow, where the recoil is driving the ship sideways at a noticeable speed. And that's a 60K ton ship! Somewhat bigger guns, too, but still....



I am afraid that is an urban myth : battleships don't move sideway when they fire (anyway, they should rather capsize). What you see on the picture is the effect of blast on the water.

Best,

Francis Marliere


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## vikingBerserker (Oct 28, 2013)

I don't think it's a myth.  It was said the HMS Rodney did the same thing when firing broadsides.


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## Shortround6 (Oct 28, 2013)

I can believe the battleship moves sideways, but part of the question is at what speed. I have moved a 30 ft Ketch that weighed over 4 tons without much trouble using one leg as have many people who have pushed a boat of that size away from a dock. 

Sure doesn't mean I can stand in the road and slow a 2 ton car moving at 40mph very much by kicking it as it hits me


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## drgondog (Oct 28, 2013)

nine 16 inch guns firing a 2000 pound projectile at 2800 ft (?) per second would cause both a lateral displacement and a rolling moment. How much? 60,000 tons is a lotta weight being buoyed in much more viscous fluid...


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## drgondog (Oct 28, 2013)

tyrodtom said:


> When a OH-6 (Loach) was armed with a minigun, it was stuck out on a pylon on the left side.
> If it was fired from a hover, the helicopter would yaw left, but the pilot could easily compensate with right pedal.
> 
> If fired in flight, it had the same effect, but less so.
> ...



A simple comparison between the OH-6 and the Mustang is to assume MV ~ same, 150gr 7.62, 700gr .50 Cal :

At 2000 rpm for mini gun and 600 x 6 (3600) rpm for 50
2000/60=33.3 per second
150gr x 33.33 = 5000 grains per second = .7 pounds/sec at 4000rpm = 1.4 pounds/sec
3600/60= 60 per second
700gr x 60 = 42000 grains per second = 6 pounds/sec

50 caliber battery ~ 8 times the mini gun at 2000 rpm

T


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## drgondog (Oct 28, 2013)

GregP said:


> I hope they DO keep the A-10's in service. With today's avionics, an avionics upgrade for teh A-10's might not be a bad idea, either.
> 
> *The A-10C has a major upgrade in avionics. The cockpit layout is not so different but the image panel on right center for both guidance purposes and 'seeing' is larger. Also DM has a complete IRAN facility which is also rebuilding and installing new wings for the A-10A which is reaching end of life on fatigue cycles. There is also an engine shop that brings all the A-10 fans to spec.*
> 
> ...



I have flown the A-10A and A-10C simulators as well as the F-15E and A-7D (long time ago). My daughter has never flown before, but I was able to teach her (A-10 simulator) to take off, pull high G level turns, roll, Cuban 8 and chandelle - then land with only one prang.. the A-10 instructor put me in my place by simulating an ILS approach below minimums - then cut the hydraulic system at low speed on final. I did not survive it. 

BTW - the A-10 has a noticeable reduction in airspeed from my perspective as an observer on the range when the 30mm is zipping away.


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## tyrodtom (Oct 28, 2013)

+Those guns on battleships aren't mounted solid, they recoil thru many feet, the recoil soaked up by different systems, you'll still have some left over recoil, but only a fraction of what the gun produces.

Hasn't anyone ever seen a real Civil war era cannon fire a solid shot ? They're driven back several feet. Don't go by what you see in the movies, they're firing blanks, usually through a subcaliber adapter.
One of the great advances in artillery was the invention of the recoil absorbers in the French 75mm in the late 19 century, or early 20th century.
It meant artillerymen didn't have to move the cannon back to position after every shot to aim it.

Most aircraft automatic armaments are recoil operated, the main body of the weapon has to be mounted fairly solid or the weapon won't function.
Even a M1911A1 ( 45 auto ) won't fire the second shot if the firer doesn't hold it firmly, it's called "limp wristing"

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## Shortround6 (Oct 28, 2013)

The recoil impulse didn't go away. It is just spread out over time, the total energy is the same. A long shove instead of quick punch. 

The French 75 used a recoil spade and locked wheels to prevent rolling while the barrel recoiled. The lower _peak_ load meant the carriage could be lighter without breaking or flipping. Put a castor under the recoil spade and unlock the wheels and you might be surprised at how far the the gun would actually move.

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## silence (Oct 28, 2013)

On Battleships moving sideways, please read this paper, complete with calcs and addendums:

Do Battleships move sideways when they fire?

Landgraff - if his is still alive - was a Naval Architect Technician at the Long Beach Naval Yard for almost 40 years. You can read a short bio here: Richard A.Landgraff Biography.


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## silence (Oct 28, 2013)

drgondog said:


> I have flown the A-10A and A-10C simulators as well as the F-15E and A-7D (long time ago). My daughter has never flown before, but I was able to teach her (A-10 simulator) to take off, pull high G level turns, roll, Cuban 8 and chandelle - then land with only one prang.. the A-10 instructor put me in my place by simulating an ILS approach below minimums - then cut the hydraulic system at low speed on final. I did not survive it.
> 
> BTW - the A-10 has a noticeable reduction in airspeed from my perspective as an observer on the range when the 30mm is zipping away.



I got on the SR-71 simulator once. What a rush!


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## bobbysocks (Oct 28, 2013)

i read that comment by the p47 pilot and iirc he was approximating a 25-40mph loss of airspeed......which i find damn near impossible. IF you had a plane on the tarmac and idling with the brakes off and fired the machine guns...it would probably roll the plane back a little....but so could a man pushing it. IF you were flying right at stall speed...you would probably lose a few mile an hour and break into the stall. but a 10 to 15,000 lb ac moving at 300+ mph isnt going to feel hardly a loss of speed. you will get vibration and probably plenty of it.. as witnessed in gun camera footage. here is the recoil of a semi auto 50 cal. the guy in the first video is shooting one handed with the bipod resting on the table then with arms extended. the guy in the second is shooting semi from the hip. yes i understand that there were 6 MGs on the mustang ( and 8 on the 47...but the 47 was also a couple thousand lbs heavier too ) and firing at ~ 600 rpm. the reverse thrust from those guns is going to be minimal at best....



_View: https://www.youtube.com/watch?v=RzUAQoyvrOw_


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## bobbysocks (Oct 28, 2013)

_View: https://www.youtube.com/watch?v=DoJAA5JIa1I_


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## tyrodtom (Oct 28, 2013)

The Barrett has a very effective muzzle brake, and other modern recoil reducing features, it can't hardly be compared with recoil of a M2 .50 cal. designed and refined in the early 20th century.


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## CobberKane (Oct 28, 2013)

There seem to be a few misconceptions floating around. Firstly, whatever effect the recoil of the guns has on the forward speed of the fighter will remain constant, irrespective of the speed of the fighter prior to firing. Ergo, if a five second burst slows my Mustang by 30mph, it will do so whether the Mustang is travelling at 400mph or 150 mph. Of course, the degree to which the Mustang slows expressed as a percentage of it's inital speed will change, but the the actual speed it looses will be the same.
Secondly, recoil damping devices will do nothing to reduce the negative acceleration imparted by firing the guns on a fighter, battleship or anytying else (including a rifle). The force of the recoil will be spread over a longer time period, but it wil be the same. The only way to completely isolate a fighter from the effects of recoil is to have the projectile carry its propellant with it as it leaves, as with a rocket.
Regarding the P-47, as Bobbysocks mentioned it has more guns than the P-51 but also more weight. 25mph loss of speed for a five second burst seems in the ballpark, maybe 40mph for a few long bursts fired in close succession.


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## tyrodtom (Oct 28, 2013)

Actually a muzzle brake doesn't spread the recoil over a longer period, it pushes the rifle forward against the recoil, reducing felt recoil.


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## bobbysocks (Oct 28, 2013)

CobberKane said:


> 25mph loss of speed for a five second burst seems in the ballpark, maybe 40mph for a few long bursts fired in close succession.



i dont think its going to be anywhere near 25mph....maybe closer to 5 tops if that much.

and yes the Barrett has an very efficient muzzle break and dampening system....but it doesnt reduce recoil by more than 50% over a ma duce....its going to take a heck of a lot more than 6 ot 8 of them to slow down a 5+ ton ac with inertia.


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## GregP (Oct 28, 2013)

Hi Bobbysocks,

We operate a P-47. A man pushing for all he is worth won't move a P-47 unless he is strong and pushing against a wall. We've seen a small tow tractor simly spin the tires when trying to move it on smooth concrete.

If the engine is idling, the man might get dragged forward or run over, but he won't move it at all.


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## snelson (Oct 28, 2013)

tyrodtom said:


> The Barrett has a very effective muzzle brake, and other modern recoil reducing features, it can't hardly be compared with recoil of a M2 .50 cal. designed and refined in the early 20th century.




yes, but the M2 weights 4 times as much so it would have 1/4 the recoil of the barrett


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## GregP (Oct 28, 2013)

Nope, the M2 does NOT have the recoil attenuation of the Barrett. It has no muzzle brake, no table or soft shoulder. It has full recoil and kicks like mule.

The gun does NOT get a chance to recoil by a few inches or a foot or whatever. It is bolted to the wing or fuselage. The entire recoil, without benefit of recoil absorption, is transmitted to the wing. Big difference.


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## CobberKane (Oct 29, 2013)

bobbysocks said:


> i dont think its going to be anywhere near 25mph....maybe closer to 5 tops if that much.
> 
> and yes the Barrett has an very efficient muzzle break and dampening system....but it doesnt reduce recoil by more than 50% over a ma duce....its going to take a heck of a lot more than 6 ot 8 of them to slow down a 5+ ton ac with inertia.



I extrapolated my figures for the P-47 from the ‘back of an envelope’ calculations I did on page one of this thread. To date no one has pulled me up on the maths (surprisingly) but if anyone can offer some figures to indicate the recoils would have less effect than I arrived at, let me know. In the meantime the figure of a 40mph loss of speed from several long bursts fired in succession seems reasonable. 
BTW, does anyone know the weight of the propellant a .50 cal round?


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## parsifal (Oct 29, 2013)

according to that learned source wiki, 42g to 52g. not sure what "g" stands for in this case.


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## CobberKane (Oct 29, 2013)

parsifal said:


> according to that learned source wiki, 42g to 52g. not sure what "g" stands for in this case.



My brain hurts. Would someone with some schoolboy physics take over and use this data (rounded off for simplicity and attributing the same velocity to the bullets and the muzzle gasses:

.50 cal round plus gasses = 100 g
Muzzle velocity = 750mps
ROF = 750 rounds per minute
Mass of a P-51 = 4000 kg 

If our Mustang was at a constant speed of 300kph and fired a five second burst, how much would it slow? If no one takes up the challenge I'm going to handball it to my son, who is doing physics at university


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## bobbysocks (Oct 29, 2013)

GregP said:


> Hi Bobbysocks,
> 
> We operate a P-47. A man pushing for all he is worth won't move a P-47 unless he is strong and pushing against a wall. We've seen a small tow tractor simly spin the tires when trying to move it on smooth concrete.
> 
> If the engine is idling, the man might get dragged forward or run over, but he won't move it at all.



and neither will a 50 cal! or 8 of them! that is a hell of a lot of weight to move or slow down...by 5, 10, yea 40 mph....and that is standing still. if it had the inertia and kinetic energy of that 6 to 7 tons moving @ 350 mph those guns arent going to slow it one iota. let me put it this way. anyone who has read pilot accounts, combat reports, talked with those men who flew them...knows they tried every trick in the book and invented a few to get an advantage over their enemy at critical times. when faced with the prospect of "over shooting" (flying past ) the foe they were behind...you will read they: chopped throttle, dumped 10, 20+ degrees of flaps, threw their plane into violent a skid/slip sideways, even dropped landing gear...all in an attempt to slow down quickly and not fly past their foe and thus become the prey themselves. ergo....if firing their guns would have slowed them down that 20 - 40 mph they would have laid on the trigger and shot a burst to help them slam on the brakes and stay behind their enemy. but i have yet to run across anyone who did this as a tactic to bleed off air speed.. i have also read reports where they were flying at the edge of a stall when they fired on the EA....their next comment wasnt " that threw me into a stall/spin and...". I have yet to hear a pilot claim that by firing their guns resulted in them stalling or causing them to lose control. were it the case....the stories would abound...you would read it in the manuals for the ac. it would be well known as flying with the fuse tank on a 51 full with tons of supporting documentation. but in this case we have ONE jug pilot that makes a claim ( for god knows what reason ) and it is sucked down as gospel. anytime we discuss issues on this forum sources of reference and documentation are presented ( or asked for ) as proof of claim. i have yet to read any source....trial test...first hand account ( other than this 47 jockey ) to further substantiate his claim. if anyone else has i would appreciate them posting it.

If it caused that significant a drop in airspeed it would have been given a "V" rating on the air speed indicator....you have V speeds for stall...do not extend flaps, do not extend gear, do not exceed ( max speed ) in calm air...do not exceed in rough air....it would have been a "do not fire guns below speed" indicated for fear of stalling and crashing.


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## bobbysocks (Oct 29, 2013)

parsifal said:


> according to that learned source wiki, 42g to 52g. not sure what "g" stands for in this case.



"G" stands for grain....and it is a weight of ball powder ( and actually the weight of the projectile as well ) a smokeless slow burning propellant....the standard gun powder ( or was ) of the US military. its use became an issue with the m-16 during vietnam. the original trials for the gun were preformed with a different cleaner powder. when it was deployed in the field with the standard powder which was not as clean the guns soon jammed and didnt perform as designed and thus gave the gun a bad rap. once that was changed the rifle didnt have that issue....


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## Greyman (Oct 29, 2013)

'g' is gram. Grains are usually abbreviated 'gr'

A 1943 Ordnance manual gives the following weights:

M2 Armour-Piercing Bullet: 710 grains
M2 Armour-Piercing Propellant: 235 grains

This is 46.00 grams and 15.23 grams respectively.


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## fastmongrel (Oct 29, 2013)

Has anyone analysed gun cam footage to see if the attacking plane drops behind its target when shooting.


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## Shortround6 (Oct 29, 2013)

CobberKane said:


> My brain hurts. Would someone with some schoolboy physics take over and use this data (rounded off for simplicity and attributing the same velocity to the bullets and the muzzle gasses:
> 
> .50 cal round plus gasses = 100 g
> Muzzle velocity = 750mps
> ...



100 rounds of .50 cal ammo (2 second burst for a 4 gun P-51B/C) will slow the plane down by 1.5m/s so a 5 second burst will slow it down 3.75m/s or about 8.4 mph. 

For our P-47 lets try working it out. 

.50 cal bullet 43 grams times MV of 890ms= 38270
propellant weight 15.6 times gas veleocity 1200ms=18720

Impulse of single shot= 56990 divide by 1000 to convert to Kilograms = 56.99

Weight of P-47= 12500lbs = 5681kg

Divide impulse by weight 56.99/5681= .0100031 meters per second

Multiply by shots in the burst. 800 rounds per minute = 13.33 rounds per second times 8 guns = 106.66 rounds per second = 1.006699 meters per second loss of speed per second of firing time. or 2.251 mph loss of speed for each second of firing time. 
or 11.26mph over 5 seconds.

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## yulzari (Oct 29, 2013)

So the airspeed will reduce, but not dramtically and the slowing effect will allow slightly more time for the guns to bear onto the target.

But I wonder of a more significant effect upon effective accuracy is any vertical difference between the gun line and the centre of gravity. Hurricane IIDs and IVs with underslung 40mm guns suffered a noticeable change in pitch as the recoil under the centre of gravity pitched the aeroplane nose down during firing. Possibly this is a more extreme example than in most fighters however. 

I do recall a Spitfire pilot stating that a single cannon failure meant that firing the remaining one, out on the wing, gave a swing towards the firing side when using the working cannon.


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## drgondog (Oct 29, 2013)

bobbysocks said:


> "G" stands for grain....and it is a weight of ball powder ( and actually the weight of the projectile as well ) a smokeless slow burning propellant....the standard gun powder ( or was ) of the US military. its use became an issue with the m-16 during vietnam. the original trials for the gun were preformed with a different cleaner powder. when it was deployed in the field with the standard powder which was not as clean the guns soon jammed and didnt perform as designed and thus gave the gun a bad rap. once that was changed the rifle didnt have that issue....



52 g refers to gram. a 7.62x51 with 150gr bullet is loaded with ~ 45 grains of powder which is 45/7000 pounds.

Loaded M2 Ball is about 5.5 0z or 3 per pound.


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## tyrodtom (Oct 29, 2013)

snelson said:


> yes, but the M2 weights 4 times as much so it would have 1/4 the recoil of the barrett



I don't know where you got those weights, but the Barrett M82 weight is 31 lbs.
The M2 .50 cal heavy barrel is 83 lbs., just the weapon not including tripod.
 The AN/M2 light barrel, used in WW2 aircraft weight was 61 lbs.

I'm don't think there is a direct corollation between gun weight and felt recoil, it's not that simple.


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## bobbysocks (Oct 29, 2013)

drgondog said:


> 52 g refers to gram. a 7.62x51 with 150gr bullet is loaded with ~ 45 grains of powder which is 45/7000 pounds.
> 
> Loaded M2 Ball is about 5.5 0z or 3 per pound.



yes it is..i stand corrected. its been many years since i reloaded anything.

SR what speeds are the 51 and 47 flying at to get that rate of loss? i would think it would go on a curve...the slower the plane the more severe the loss and the faster it was travelling the less severe. like stopping a car. more resistance is needed for a car going 60 mph than 10. if i am reading your calculations correctly you just divided the impluse only to the weight of the plane alone...like it was sitting on the tarmac. or doesnt it matter what speed? i would think KE = 1/2 MV2 would have to figure in this somehow..


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## Ascent (Oct 29, 2013)

Remember it's the sum of all forces that dictate what the aircraft does. There is still the thrust from the propellor pulling the aircraft forward. It''s not simply the force of the recoil pushing it backwards.


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## Shortround6 (Oct 29, 2013)

true but unless the aircraft is at part throttle the engine/prop are already exerting max force on the airplane. The plane is either already at top speed, is accelerating or climbing. The guns act like little retro rockets. Mighty little ones unless you have really big guns


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## bobbysocks (Oct 29, 2013)

Shortround6 said:


> The plane is either already at top speed, is accelerating or climbing.



so if i get you right you are saying the exact same force applied to two 12000 lb planes....1 travelling at 300mph and the other travelling at 150mph will both slow down by the exact same speed? the force of the same number of bullets being fired for the same duration is a constant whereas the mass x velocity is doubled?


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## swampyankee (Oct 29, 2013)

wuzak said:


> How does that work?
> 
> I was always under th eimpression that the gun was off centre to allow room for th enose landing gear....



Vice versa: the nose gear is off center. Take a gander at this picture: Google Image Result for http://airpigz.com/storage/2010-may/A-10-Warthog-Front-View.jpg?__SQUARESPACE_CACHEVERSION=1275348107863


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## Greyman (Oct 29, 2013)

Looks like they're both off centre.


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## Shortround6 (Oct 29, 2013)

The gun is but the firing barrel position is not. The barrels fire in the 9 o'clock position facing the aircraft.


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## Aozora (Oct 29, 2013)

Shortround6 said:


> The gun is but the firing barrel position is not. The barrels fire in the 9 o'clock position facing the aircraft.



That A-10 ain't gonna live long if the barrels fire while facing the aircraft...


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## tyrodtom (Oct 29, 2013)

And you ain't going to live long if the barrels fire while you're facing the aircraft.


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## CobberKane (Oct 29, 2013)

bobbysocks said:


> yes it is..i stand corrected. its been many years since i reloaded anything.
> 
> SR what speeds are the 51 and 47 flying at to get that rate of loss? i would think it would go on a curve...the slower the plane the more severe the loss and the faster it was travelling the less severe. like stopping a car. more resistance is needed for a car going 60 mph than 10. if i am reading your calculations correctly you just divided the impluse only to the weight of the plane alone...like it was sitting on the tarmac. or doesnt it matter what speed? i would think KE = 1/2 MV2 would have to figure in this somehow..



The loss of speed due to recoil would be the same, irrespective of the speed of the aircraft before the guns were fired. Shortrounds figures for the P-47 give us a rive us a de-accelleration of about 11 m/ps from a five second burst. So, while several long busts in quick succession might reach the 25-40 mph de-accelleration you spoke of earlier, on the whole you would have to think that the effect of recoil on a fighters speed was actually a lot less than suggested by seat of the pants impressions (given the way pilots talk of it). It seems to me that a pilot who was concerned about gun recoil pushing the fighter into a stall during hard manoeuvering would have had to have been right on the edge for this to be a risk.


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## snelson (Oct 30, 2013)

tyrodtom said:


> I don't know where you got those weights, but the Barrett M82 weight is 31 lbs.
> The M2 .50 cal heavy barrel is 83 lbs., just the weapon not including tripod.
> The AN/M2 light barrel, used in WW2 aircraft weight was 61 lbs.
> 
> I'm don't think there is a direct corollation between gun weight and felt recoil, it's not that simple.



you are right about the weight of the M2 i was including the weight of the tripod which weights 127 lbs.

but even with the light air craft gun it would still cut the recoil by 1/2.

it's well known in the gun world that if the gun has to much recoil you make the gun heavier, twice the weight half the recoil. if you add the weight of the plane the recoil goes to almost nothing.

Recoil Calculator

here's a recoil calculator where you can punch in any set of numbers to help you find out how much recoil velocity you get.


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## tyrodtom (Oct 30, 2013)

snelson said:


> you are right about the weight of the M2 i was including the weight of the tripod which weights 127 lbs.
> 
> but even with the light air craft gun it would still cut the recoil by 1/2.
> 
> ...



And the the very site you posted says in the first sentence, the numbers calculated here DO NOT relate to felt recoil.


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## pbehn (Oct 30, 2013)

Hi Guys my first pot although I've been lurking for months............great forum.

I think there are some errors here (though I may be wrong). The maximum recoil felt by the pilot would be when all guns fire at the same time in effect the weight is that of one bullet and charge 6 or 8 times larger the lowest recoil would be when they fire at different times equally spaced in a cycle (like the firing of the cylinders in an engine). In practice I'm sure there are millie seconds of difference. Some have averaged the weight of shot per second however I think to calculate the maximum this should be the weight x velocity of charge and bullets (muzzle velocity) / the time taken from firing to the bullet exiting the barrel. 

When a plane is in level flight at maximum power and has achieved maximum peed all forces are in equilibrium. The recoil from the guns would introduce a new force eqivilant to an increase in drag, the plane would then slow down to a new equilibrium, it would not continually slow down or theoretically it would go from max speed to stall even on full power (I know no plane carries so much ammo).

As I was thinking of this I thought what is the effect of pumping large volumes of hot gas and particles into the airflow of (for example) a Mutang. The guns firing stained the wing so obviously this gas and particles are in the air directly in contact with the wing, would this increase drag?

The human body is very sensitive to forces, when a plane is in level flight not only are the forces on the plane balanced but also on the pilot if the plane slows by even 1/2 of 1 MPH instantaneously the pilot would feel it in the same way that those of us old enough to travel on old trains connected by chains felt a jolt as the slack on the train was taken up, in a small fraction of a second the train goes from standstill to maybe 1/2 a mph but it can give a helluva jolt. I imagine the sensation would be a bit like hitting standing water in a car.

An aircraft on the ground is hard to move but this isnt due to the weight but the rolling resistance of the tyres, suspend the same craft from a wire as in a museum and its a whole lot easier, a 10 ton fabrication on a crane can be easily be manouvered by one man. A plane in flight is free to move in reaction to forces acting upon it.

To answer the original post the guns firing must slow the aircraft, its the laws of physics. Would the pilot feel it? possibly I think although I think its possible the disturbed airflow may have more effect than the weight of the actual bullets. Many plane had the firing port covered with tape, therefore firing the guns immediately puts 8 holes in your early spit and hurricane leading edge, this must increase drag, the ground crews could hear the whistling noise when BoB planes came into land after firing their guns


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## Shortround6 (Oct 30, 2013)

Felt recoil it what your shoulder or hand _feels_ 

Let me whittle down the butt of rifle to about 1/2 it's original thickness so it hit's 1/2 of the shoulder area with the same force total and tell me how it "feels". 

Or use rough checkered grips on a hand gun with raised edges to the checkering instead of smooth wood. 

Or a lot of drop to a stock and a narrow, low comb so as the rifle/shotgun pivots up it smacks your cheek bone. 

Punishment you _feel_ has a lot more variables than just the velocity of the recoiling gun of the ft/lbs-jules of energy.


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## GrauGeist (Oct 30, 2013)

snelson said:


> you are right about the weight of the M2 i was including the weight of the tripod which weights 127 lbs.
> 
> but even with the light air craft gun it would still cut the recoil by 1/2.
> 
> ...


I have two shotguns, one is a Winchester model 12 and the other is a Remington squareback autoloader. Both have comparable barrel lengths and both are 12 gauge and can fire the same ammunition.

I can fire the Remington from the hip but I cannot do that with the Winchester. The reason is that the Remington is using the energy from the discharge to cycle the eject/load sequence while the Winchester simply discharges the round and waits for somebody to eject the shell and load a fresh one manually, so in this case, the energy is not being used but is driven right back to the shoulder instead.

So in the recoil world, it's not the weight of the gun, it's how it's designed.


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## Shortround6 (Oct 30, 2013)

If the guns weighs the same you have the same total recoil. In the Winchester you get it all at once, in a hundredth of a second. With the Remington you get it slowly. The Barrel moves back against a big spring compresses the spring. the gun picks up speed slowly as the spring compresses. The peak recoil force is much reduced but the total recoil force is unchanged. 

Video : 
_View: https://www.youtube.com/watch?v=CDaWnO4s8Vo_

Go to 5:29 

This is one reason "felt" recoil is so variable. 

10lbs is 10lbs wither it is on a table, a chair or sitting on a compressed spring.


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## tyrodtom (Oct 30, 2013)

` I don't know what the percentages are, but some of the recoil energy is absorbed in working the action, moving the belt, stripping the round out of the links, feeding it into the chamber, ejecting the spent cartridge.
Plus the M2 had two buffer systems , a oil buffer that forced oil thru small passages, and disk buffers, both absorbed recoil, didn't just spread it out over time.
Both of these systems in the same weapon.


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## Shortround6 (Oct 30, 2013)

tyrodtom said:


> ` I don't know what the percentages are, but some of the recoil energy is absorbed in working the action, moving the belt, stripping the round out of the links, feeding it into the chamber, ejecting the spent cartridge.
> Plus the M2 had two buffer systems , a oil buffer that forced oil thru small passages, and disk buffers, both absorbed recoil, didn't just spread it out over time.
> Both of these systems in the same weapon.



What did they do with the recoil energy? it just doesn't _go away._

Some of it they turned to heat. the buffers heat up and yes the buffers spread out the time. They slow down the moving parts, they were there to minimize the internal parts battering themselves, not as recoil reducers for the gun. Take them out and the gun will speed up it's rate of fire. You will also wind up breaking parts much quicker. 

The amount of energy used to 'work' the action is minimal.


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## snelson (Oct 30, 2013)

tyrodtom said:


> And the the very site you posted says in the first sentence, the numbers calculated here DO NOT relate to felt recoil.



you are right again, there is noway to tell how something feels. what might seem lot to me may mean nothing to you. things like rubber butt pads and stock design help take the bite out of them.

here this site explains it better than i do.


Rifle Recoil Table


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## bobbysocks (Oct 30, 2013)

you have the same amount of recoil force from the spent shell as it is moved in the opposite direction of the projectile... but the design of the some guns will dissapate that and use that energy to work mechanisms and thus bleed off that energy.


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## snelson (Oct 30, 2013)

GrauGeist said:


> I have two shotguns, one is a Winchester model 12 and the other is a Remington squareback autoloader. Both have comparable barrel lengths and both are 12 gauge and can fire the same ammunition.
> 
> I can fire the Remington from the hip but I cannot do that with the Winchester. The reason is that the Remington is using the energy from the discharge to cycle the eject/load sequence while the Winchester simply discharges the round and waits for somebody to eject the shell and load a fresh one manually, so in this case, the energy is not being used but is driven right back to the shoulder instead.
> 
> So in the recoil world, it's not the weight of the gun, it's how it's designed.




if the shotguns weight the same, then amount of recoil energy will be the same. but the semi auto spreads the recoil velocity will be spread out over a longer time reducing felt recoil. the same thing happens when you add weight to the gun.


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## bobbysocks (Oct 30, 2013)

Shortround6 said:


> What did they do with the recoil energy? it just doesn't _go away._
> 
> Some of it they turned to heat. the buffers heat up and yes the buffers spread out the time. They slow down the moving parts, they were there to minimize the internal parts battering themselves, not as recoil reducers for the gun. Take them out and the gun will speed up it's rate of fire. You will also wind up breaking parts much quicker.
> 
> The amount of energy used to 'work' the action is minimal.



it depends on the design of the gun how timing is accomplished. if it fires from an open bolt....the bolt is in the rearward position until the trigger is pulled...the firing pin is fixed to the bolt head....the weight of the bolt and the return springs are proportional to the acceptable loads of the ammunition. too mild a load and the firearm will not cycle...too hot it will over compress the return.recoils springs and could damage the firearm.
if the firearm fires from the closed position and has a hammer it will need to be mechanically times so that the hammer is held back and not riding on the firing pin when the bolt slams the shell into the breech. if it didnt the potential for a slamfire or pre-ignition firing could occur. there is usually a system of levers that are actuated by the bolt at different stages.

a lot of the recoil force is absorbed in moving the bolt rearward and compressing springs.


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## parsifal (Oct 30, 2013)

genuine question guys. i dont even know if this is possible....but what happens to the reactive forces on the aircraft once the shell has left the barrel? What if the potential energy locked away in the chemical reaction isnt fully realeased as the shell leaves the barrel. If only a part of the shells propellant has been spent, or the shell loses some of its weight as it leaves the barrel (such as with a discarding sabot round), would this not reduce the recoil effect on the aircraft?. I talking theoretically rather than practically initially.


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## tyrodtom (Oct 30, 2013)

snelson said:


> you are right again, there is noway to tell how something feels. what might seem lot to me may mean nothing to you. things like rubber butt pads and stock design help take the bite out of them.
> 
> here this site explains it better than i do.
> 
> ...



I'm not trying to deny that gun weight is a factor in recoil, especially in solid weapons like bolt action rifles, and revolvers. 
But we're talking about automatic weapons here, and in them there are several other factors to consider also.

I've never fired a Barrett of any sort, but I have fired a M2 .50 cal, heavy barrel many times.
If you tried the same trick with a M2, as they did with that Barrett on the table. The M2, 83 lbs and all, would not stay on the table.


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## CobberKane (Oct 30, 2013)

parsifal said:


> genuine question guys. i dont even know if this is possible....but what happens to the reactive forces on the aircraft once the shell has left the barrel? What if the potential energy locked away in the chemical reaction isnt fully realeased as the shell leaves the barrel. If only a part of the shells propellant has been spent, or the shell loses some of its weight as it leaves the barrel (such as with a discarding sabot round), would this not reduce the recoil effect on the aircraft?. I talking theoretically rather than practically initially.



It seems to me that recoil depends of two things; the amount of mass ejected from the barrel and the speed at which it exits. FELT recoil is also dependant on the mass of gun or gun/plane combination, but the actual energy of the recoil is constant. If some of the propellant left the barrel before combustion, it would not affect the mass leaving the barrel because mass is not consumed in a chemical reaction; the amount of material exiting the barrel would be the same. However, as the unburnt propellant did not contribute its energy to accelerating the projectile, recoil would be less for this reason. Many cartridges can be used in both hand guns and rifles, but as the short barrel of handgun means the round exits the muzzle before all the propellant is burned, a portion of the available energy is lost as muzzle flash after the propellant leaves the barrel and thus does not contribute to muzzle velocity or, by definition, recoil. Hence the recoil will be greater in the rifle, even though the cartridge is the same. FELT recoil may be greater for the handgun though, due to its lesser mass. I think.
In respect to the reciprocating parts of an automatic or fully automatic weapon reducing recoil, this must be the case, though by how much I wouldn’t know. I believe bolt action rifles and revolvers typically have higher muzzle velocities than semi-automatic weapons, perhaps for this reason. I’m sure someone out there who is in to bench rest shooting could give us an idea of the different muzzle velocities of the same round fired from a bolt action and a semi auto (not me, semi autos are largely banned in Australia). For the effect on a fully automatic weapon I guess it would be easy enough to measure by disabling the mechanism for one round, then comparing muzzle velocity or recoil with that of a single round fired with mechanism in action.

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## Shortround6 (Oct 30, 2013)

It is Newtons 3rd law; The momentum of the "stuff" going out the muzzle *HAS* to equal the momentum of gun, mount, plane, ship. 

Momentum is mass times velocity. 

Now the "stuff" going out the muzzle may have different velocities. Projectile( and sabots leave at the same velocity as the cores, they just slow down much quicker upon leaving the muzzle), powder gases, unburned powder, still burning powder. 

As for how much "power" is lost due to the action......not much. Most gas operated weapons have the gas port well down the barrel and the gas pressure has dropped considerably by the time the projectile passes the gas port. Pressure may have peaked at 50-65,000psi (depending on measuring system, I am old enough to think in copper crusher terms and not transducers) a few inches in front of the chamber but be down to 6-8,000psi at the gas port.

For a better explanation see; M1 Garand Gas Pressure 

You can have a greater variation between otherwise identical rifles than the difference between a gas gun and a manual rifle. 
Revolvers have a cylinder gap which bleeds off some pressure right away, but revolvers have a 'secret' advantage. A 4 inch revolver has 4 inches of barrel _in front_ of the chamber/cylinder while a 4in automatic barrel has the chamber cut into the rear of the 4 inch tube. Mkae sure you are comparing like to like


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## CobberKane (Oct 30, 2013)

Shortround6 said:


> It is Newtons 3rd law; The momentum of the "stuff" going out the muzzle *HAS* to equal the momentum of gun, mount, plane, ship.
> 
> Momentum is mass times velocity.
> 
> ...



On further consideration, it occurrs to me that the reciprocating parts in a machine gun or cannon would have effectively ZERO effect on recoil. Some of the energy from each round goes into re-cocking the weapon for the next round, but the movement of the reciprocating parts themselves would still pass on the energy to the aircraft as a whole. There might be some damping effect, but the deaccelleration would be unchanged.


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## parsifal (Oct 31, 2013)

> It is Newtons 3rd law; The momentum of the "stuff" going out the muzzle HAS to equal the momentum of gun, mount, plane, ship.



Is it momentum (MV) or Force (MA) that we need to look at? Does a cannon ball weighing 100 lbs and travelling at 50m/s generate the same recoil as a bullet weighing 1lb travelling at 5000m/s. Disregard all other extraneous variables like friction and wind resistance for the moment.... If the velocity of that cannon ball is not changing, does it generate any recoil at all? Is a cannon ball that is accelarating as it leaves the barrel generating more less or the same recoil as a cannon ball that leaves the barrel having a stable, unchanging velocity?


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## CobberKane (Oct 31, 2013)

parsifal said:


> Is it momentum (MV) or Force (MA) that we need to look at? Does a cannon ball weighing 100 lbs and travelling at 50m/s generate the same recoil as a bullet weighing 1lb travelling at 5000m/s.
> Disregard all other extraneous variables like friction and wind resistance for the moment.... If the velocity of that cannon ball is not changing, does it generate any recoil at all? Is a cannon ball that is accelarating as it leaves the barrel generating more less or the same recoil as a cannon ball that leaves the barrel having a stable, unchanging velocity?


Yes, the 100lb and the 1lb cannon ball would give the same recoil. 
In regards to the second scenario, the cannon ball accelerates from a stationary position relative to the cannon, to a given speed relative to the cannon. This MUST create recoil (Newton's third law of motion). The cannon ball will accelerate while in the barrel, but it will NOT accellerate after it leaves tha barrel as there is no longer any force compelling it to do so. Hence, muzzle velocity, measured as the projectile leaves the muzzle, is the highest speed reached by a projectile and therefore is the measure we would use in calculating recoil. The only exception I can think of to this is with a dud round, where the projectile might be accelerating negativeley when it leaves the muzzle.


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## Rick65 (Oct 31, 2013)

Long time since I did physics but isn't the force (recoil) generated a function of the velocity squared of the projectile as it leaves the end of the barrel? 
As such a 1lb projectile exiting at 5000m/sec will generate 100 times the force(recoil) of a 100lb projectile exiting at 50m/sec.
Simplistically
F=m(v squared)/2s
where
F= force (recoil)
m = mass of projectile (bullet plus propellant?)
v = exit velocity of projectile having accelerated from a relative velocity of zero
s = length of barrel

Or should I have stayed retired from physics?


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## Shortround6 (Oct 31, 2013)

The momentum is not the force (kinetic energy) the projectile has. 

And as Newtons 3rd law states BOTH the 'bullet' and the 'gun' are projectiles. the gun just moves a LOT slower 

This can be seen or tested by firing different loads out of the same gun. A fast, light bullet can have more "energy" than a slow heavy bullet but the gun will recoil less with the light bullet. This was remarked on quite a bit with the change over from 10-14.7 mm military black powder rifles to the 6-8mm smokeless powder rifles. 

as to the recoil we are also back to the momentum and energy question and this is part of the "felt" recoil problem. A 6lb rifle and an 8lb rifle firing the same cartridge _will_ recoil at different speeds. the _energy_ the rifle hits the shoulder with is the result of the mass of the rifle times the velocity of the rifle squared. 

BTW "s = length of barrel" has absolutely nothing to do with recoil or even velocity of the projectile in this question. Longer barrels allow for more velocity but that is getting into the subject of _internal ballistics_ (what happens inside the barrel. 

You do have to figure the bullet and propellant seperately however as they have vastly different "exit' velocities.


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## Rick65 (Oct 31, 2013)

Newton's 2nd F(recoil)= mass x acceleration.
If we assume that a projectile accelerates uniformly until it reaches muzzle velocity as it leaves the barrel (is this correct or do projectile reach maximum velocity sometime before the end of the barrel?), the length of the barrel is significant as it allows us to calculate the acceleration of the projectile as it changes from stationary to moving at muzzle velocity over the length of the barrel.
v squared = u squared +2as
Where
v=end velocity (muzzle?)
u= initial velocity (=0 in this case)
a= acceleration
s = distance traveled (barrel length?)


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## Shortround6 (Oct 31, 2013)

But we don't _need_ to calculate the acceleration of the projectile in order to figure out the recoil. 


_ALL_ we need is the mass of the "stuff" leaving the barrel and the velocity/s of the different "stuff/s" (projectile and powder gases). It doesn't make any difference if the projectile took 700mm of barrel or 900mm of barrel travel to reach 700 meters a second. 

Your formula may be correct but it is solving the wrong question.


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## syscom3 (Oct 31, 2013)

The formula to use is the kinetic energy (in joules) of the airplane of "x" weight at "Y" speed. And in the other direction, the force created by the kinetic energy (in joules) of the projectiles of "a" weight going at "b" velocity at the muzzle.

And if the ratio between the two is high, you can bet that the speed of the aircraft that is lost , would be quite low.


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## Rick65 (Oct 31, 2013)

Thanks Shortround - much better
Ke=m(v squared)/2 
Further proof that a little knowledge (on my part) is dangerous.


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## OldSkeptic (Nov 1, 2013)

You can calculate in different way ... and still pretty much get the same answer. Either a delta KE calc (same as space craft engine calcs) or as an impulse one or as a momentum transfer.

More of an issue in the older planes as they were so much lighter, unless you have really big guns like a A-10. 
People forget just how heavy modern planes are. For example a fully loaded F-15C is similar to fully loaded Lancaster Bomber.


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