Can gun recoil really slow a fighter?

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

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

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

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.
 
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.
 

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.
 
snelson said:
yes, but the M2 weights 4 times as much so it would have 1/4 the recoil of the barrett
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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.
 
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.
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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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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.
 
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
 
Shortround6 said:
The plane is either already at top speed, is accelerating or climbing.
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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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