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Doug_Kibbey · Posted: Sun Feb 05, 2006 2:59 pm Post subject: Re: Recoilless Rifle Question

'Weed,
Easy...it's really a conventionally assembled round, but with a lot of perforation holes in the case sides that permit a lot of the propellant to vent. It vents through the breech which itself has large vent holes (which is why it's very dangerous to be behind a RR when it fires). The principle is just to counter the thrust rearwards under recoil with an offsetting thrust to the front. Because there is no resistance of a round in the barrel to the rear, in fact most of the propellant energy is "wasted" in this quest for the "equal and opposite" recoil effect.

tankmodeler · Posted: Sun Feb 05, 2006 3:14 pm Post subject: Re: Recoilless Rifle Question

To elaborate a little on Doug's reply, in physics terms the mass of the projectile exiting out the front of a tube imparts an opposite reaction on a normal cannon, i.e. the recoil. The force generated is equal to the mass of the round times the velocity of the round, Newton's old F=MxA.

For the piece to be "recoilless" the recoil force generated by the shell exiting the front has to be countered by something creating the same force going out the back. For a recoilless rifle there is a relatively high mass shell propelled at a relatively low speed. To counter this you have the relatively small mass of the burnt propellant gasses exiting the breech at a very high speed.

In fact the most efficient RRs use venturies at the breech to increase the speed of the exiting gasses out the back, thus allowing more of the propellant to accellerate the shell.

Paul

Doug_Kibbey · Posted: Sun Feb 05, 2006 5:46 pm Post subject: Re: Recoilless Rifle Question

More details and pics:

en.wikipedia.org/wiki/...less_rifle

Oh...and some RR's either are rocket propelled, or rocket-assisted after firing...but this is an evolution of the classic recoilless rifle.

Kurt_Laughlin · ***Power User*** Offline Joined: Jan 24, 2006 Posts: 577

IIRC on the old board someone had a link to somebody firing a RR off the shoulder and nearly getting their head torn off by the sight and bracket. Those venturis Paul mentioned are eroded by the exiting gas. As they get worn bigger the Mv (it's more a momentum balance than force balance) going out the back get overwhelmed by the Mv going out the front and the actual recoil keeps increasing until you get what you saw in the film clip.

(C'mon Paul: "mass . . . times the velocity . . ., Newton's old F=MxA". . . You're not using that formula to design anything important are you? :-))

KL

tankmodeler · Posted: Sun Feb 05, 2006 8:49 pm Post subject: Re: Recoilless Rifle Question

- Kurt_Laughlin

(C'mon Paul: "mass . . . times the velocity . . ., Newton's old F=MxA". . . You're not using that formula to design anything important are you? :-))

F=MA and "You can't push on a rope".

The two cardinal rules of mechanical engineering.

I use them to design _everything_!

Paul

Kurt_Laughlin · ***Power User*** Offline Joined: Jan 24, 2006 Posts: 577

- tankmodeler

- Kurt_Laughlin

(C'mon Paul: "mass . . . times the velocity . . ., Newton's old F=MxA". . . You're not using that formula to design anything important are you? :-))

F=MA and "You can't push on a rope".

The two cardinal rules of mechanical engineering.

I use them to design _everything_!

Yeah, F=ma is important, but you described it as force equals mass times velocity . . . That's what made me think I didn't want to stand under it

KL

bsmart · Posted: Mon Feb 06, 2006 10:28 am Post subject: Re: Recoilless Rifle Question

I think the 'velocity'sion of the formula is
F=MV(2) or as I heard it on the flightline

"Force eguals Mass time velocity squared or a couple pounds of feathers hitting a 400 mph plane makes a a hellavu mess"

Also I remember reading somewhere that Recoiless rifles require up to six times as much propellent as standard guns because so much energy is 'lost' creating the 'equal but opposite' reaction.

Another cardinal rule I was taught back in engineering classes in the days before calculators (Three digit accuaracy is all you get from a slide rule)
was '40.9, 41, 41.1 they are all correct as long as you aren't spanning a 41' river. Then 40.9 and maybe even 41 are the wrong answers'

arfraser · ***Power User*** Offline Joined: Jan 24, 2006 Posts: 8

- bsmart

Also I remember reading somewhere that Recoiless rifles require up to six times as much propellent as standard guns because so much energy is 'lost' creating the 'equal but opposite' reaction.

The Germans fielded light reciolless rifles (IG1 - 75mm and IG40/41 10.5cm) through to 1944 (predating the Brit work on the Wombat series???). Development started in the 1930's. The rifles were issued to the german para units and rode on a light two-wheeled carriage that folded into a light tripod.

The weapon was retired as soon as the resource demands for the projectiles began to bite (in much the same way that taper-bore AT guns were abandoned).

tankmodeler · Posted: Tue Feb 07, 2006 12:23 pm Post subject: Re: Recoilless Rifle Question

Yeah, F=ma is important, but you described it as force equals mass times velocity . . . That's what made me think I didn't want to stand under it
KL

Ah, I see what you're getting at.

Fair enough, it was one simplification too many. Smile

Paul

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