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Message no. 1
From: rothgefa@*******.com (Robert Fanning)
Subject: Missile Launchers and Recoil
Date: Mon, 19 Jan 2004 17:34:54 +1000
There are reasons you want missiles to actually have recoil.

Imagine you are standing up and firing a missile (same applies for
grenades).

1) You want the missile to actually leave the tube.

2) You want the missile to leave the tube fast enough so that it travels in
the direction you want.

3) You want the missile to have enough velocity that it does not drop short
at your feet.

4) You want the missile to travel fast enough in the arming time to not blow
yourself sky high.

5) You want to propel the missile far enough in front of you, so that it
does not fry you with the exhaust gases. (some systems use a two stage
charge like a mortar, others have a long tube that protects you, while
flamethrowing everything behind you).

However, if you are intending to autofire missiles, please do not stand near
me - even if it is a 4 pack multiple barrelled launcher.

If a gun overheats and backfires, you will probably be the only one to
suffer (with the bolt driven back through the eye that you aim through).
Even with an ammunition cookoff, chances are, nobody else will be hurt
because the bullets can't develop muzzle velocity without a barrel.

If an autofire missile launcher overheats and jams, back oopsies. A lot of
vehicle mounted versions are attached with explosive bolts to be ejected in
an emergency. Many also have blowback protection for the armoury and
cellular ammunition storage.

<@^@> put "Hey Robert!" (without quotes) in the subject line to bypass my
junk mail filter and do not mention any sort of word associated with
commercial transactions.

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Message no. 2
From: gurth@******.nl (Gurth)
Subject: Missile Launchers and Recoil
Date: Mon, 19 Jan 2004 11:02:38 +0100
According to Robert Fanning, on Monday 19 January 2004 08:34 the word on
the street was...

> There are reasons you want missiles to actually have recoil.
>
> Imagine you are standing up and firing a missile (same applies for
> grenades).
[snip 5 reasons]

AFAIK it will do all these things regardless of whether it imparts any
recoil to you. The fact that it's throwing plenty of exhaust gases out the
back of the missile itself already means it will move, fast. The reason
for recoil in a regular gun is because it works the other way: it pushes
the gun into your shoulder, and incidentally drives the bullet out of the
barrel with the propellant gas. With a rocket launcher that has a
completely-open launch tube, the only recoil you should feel, is probably
the result of the missile touching the tube's sides in a few locations,
and thereby causing a backward force on the tube.

> If an autofire missile launcher overheats and jams, back oopsies. A
> lot of vehicle mounted versions are attached with explosive bolts to be
> ejected in an emergency. Many also have blowback protection for the
> armoury and cellular ammunition storage.

Are you talking IRL, or SR here? Because IRL, there are only a small number
of vehicles carrying multiple rocket launchers, and even fewer of those
carry any spare ammunition. A large number are even totally unarmored,
being just trucks with a big launcher on the back.

--
Gurth@******.nl - Stone Age: http://www.xs4all.nl/~gurth/index.html
You've been touched by the doubt of man
-> Probably NAGEE Editor * ShadowRN GridSec * Triangle Virtuoso <-
-> The Plastic Warriors Page: http://plastic.dumpshock.com <-

GC3.12: GAT/! d- s:- !a>? C++(---) UL+ P(+) L++ E W--(++) N o? K w(--)
O V? PS+ PE@ Y PGP- t- 5++ X(+) R+++$ tv+(++) b++@ DI- D+ G+ e h! !r y?
Incubated into the First Church of the Sqooshy Ball, 21-05-1998
Message no. 3
From: davek@***.lonestar.org (David Kettler)
Subject: Missile Launchers and Recoil
Date: Mon, 19 Jan 2004 17:36:34 +0000
On Mon, Jan 19, 2004 at 05:34:54PM +1000, Robert Fanning wrote:
> There are reasons you want missiles to actually have recoil.
>

I am confused. This is not a question of wants but of facts. Missiles do not have
recoil, both IRL and in Shadowrun.

> Imagine you are standing up and firing a missile (same applies for
> grenades).
>

The same does *not* apply to a grenade launcher at all. More on this below.

> 1) You want the missile to actually leave the tube.
>
> 2) You want the missile to leave the tube fast enough so that it travels in
> the direction you want.
>
> 3) You want the missile to have enough velocity that it does not drop short
> at your feet.
>
> 4) You want the missile to travel fast enough in the arming time to not
> blow yourself sky high.
>
> 5) You want to propel the missile far enough in front of you, so that it
> does not fry you with the exhaust gases. (some systems use a two stage
> charge like a mortar, others have a long tube that protects you, while
> flamethrowing everything behind you).
>

<snip>

This is a very simple physics problem. If you want something to go in one direction (a
bullet, a missile, a grenade, whatever) then you have to conserve momentum. When firing a
gun the bullet gets a momentum p going one direction and so the gun pushes on you with the
same momentum. This is recoil. The same applies to grenade launchers or anything else
with a closed tube.

When firing a missile, the missile obtains its momentum by shooting gases out the back.
The missile itself conserves momentum, without the need to look at a bigger picture.
Since the missile tube is open, these gases are free to shoot out the back and do not
impart any momentum to the launcher.

A recoilless rifle works on the same principle. Actually, a recoilless rifle is basically
just a rocket launcher for rockets that burn up all their fuel before they even leave the
tube. But here we see the disadvantage of this approach: For a recoilless rifle to fire
a round with the same velocity of an equivalent sized gun with recoil it has to use twice
as much propellent. And you have to deal with the backblast of course.

--
Dave Kettler
davek@***.lonestar.org
http://davek.freeshell.org
SDF Public Access UNIX System - http://sdf.lonestar.org
Message no. 4
From: gurth@******.nl (Gurth)
Subject: Missile Launchers and Recoil
Date: Mon, 19 Jan 2004 19:11:24 +0100
According to David Kettler, on Monday 19 January 2004 18:36 the word on the
street was...

> A recoilless rifle works on the same principle. Actually, a recoilless
> rifle is basically just a rocket launcher for rockets that burn up all
> their fuel before they even leave the tube.

Well... yes and no. A rocket is generally thought of as a projectile that
contains its own propellant; recoilless rifles use cased projectiles, in
which the propellant is not stored in the projectile. They really are
conventional guns that vent much of the propellant energy backward to
counter-act the projectile's recoil, rather than rocket launchers.

But this is not relevant to SR :)

--
Gurth@******.nl - Stone Age: http://www.xs4all.nl/~gurth/index.html
You've been touched by the doubt of man
-> Probably NAGEE Editor * ShadowRN GridSec * Triangle Virtuoso <-
-> The Plastic Warriors Page: http://plastic.dumpshock.com <-

GC3.12: GAT/! d- s:- !a>? C++(---) UL+ P(+) L++ E W--(++) N o? K w(--)
O V? PS+ PE@ Y PGP- t- 5++ X(+) R+++$ tv+(++) b++@ DI- D+ G+ e h! !r y?
Incubated into the First Church of the Sqooshy Ball, 21-05-1998
Message no. 5
From: arclight@*********.de (Arclight)
Subject: Missile Launchers and Recoil
Date: Mon, 19 Jan 2004 19:34:03 +0100
At 19:11 19.01.2004 +0100, Gurth wrote:

>According to David Kettler, on Monday 19 January 2004 18:36 the word on the
>street was...
>
> > A recoilless rifle works on the same principle. Actually, a recoilless
> > rifle is basically just a rocket launcher for rockets that burn up all
> > their fuel before they even leave the tube.
>
>Well... yes and no. A rocket is generally thought of as a projectile that
>contains its own propellant; recoilless rifles use cased projectiles, in
>which the propellant is not stored in the projectile. They really are
>conventional guns that vent much of the propellant energy backward to
>counter-act the projectile's recoil, rather than rocket launchers.
>
>But this is not relevant to SR :)

You forgot "Oh, and recoilless rifles aren't" ;) And missile launchers DO
have some recoil.


--
Arclight

Quitters never win, winners never quit,
but those who never quit and never win are idiots
Message no. 6
From: gurth@******.nl (Gurth)
Subject: Missile Launchers and Recoil
Date: Mon, 19 Jan 2004 19:38:43 +0100
According to Arclight, on Monday 19 January 2004 19:34 the word on the
street was...

> You forgot "Oh, and recoilless rifles aren't" ;)

Yeah, but "mostly-recoilless rifles" sounds so lame ;)

> And missile launchers DO have some recoil.

I mentioned a possible reason for this in my initial post in this thread.

--
Gurth@******.nl - Stone Age: http://www.xs4all.nl/~gurth/index.html
You've been touched by the doubt of man
-> Probably NAGEE Editor * ShadowRN GridSec * Triangle Virtuoso <-
-> The Plastic Warriors Page: http://plastic.dumpshock.com <-

GC3.12: GAT/! d- s:- !a>? C++(---) UL+ P(+) L++ E W--(++) N o? K w(--)
O V? PS+ PE@ Y PGP- t- 5++ X(+) R+++$ tv+(++) b++@ DI- D+ G+ e h! !r y?
Incubated into the First Church of the Sqooshy Ball, 21-05-1998
Message no. 7
From: davek@***.lonestar.org (David Kettler)
Subject: Missile Launchers and Recoil
Date: Mon, 19 Jan 2004 19:48:42 +0000
On Mon, Jan 19, 2004 at 07:11:24PM +0100, Gurth wrote:
> Well... yes and no. A rocket is generally thought of as a projectile that
> contains its own propellant; recoilless rifles use cased projectiles, in
> which the propellant is not stored in the projectile. They really are
> conventional guns that vent much of the propellant energy backward to
> counter-act the projectile's recoil, rather than rocket launchers.
>
> But this is not relevant to SR :)
>

We're discussing technicalities here. I was talking more from a general "how it
works" standpoint than an actual design standpoint.

Incidentally, after your last post I re-read your first post on this topic, and I don't
buy your explanation for why a missile launcher has some recoil. If you just look at the
friction between the rocket and the tube then that is going to want to pull the launcher
forwards, along with the rocket, not push it backwards. Essentially it's the opposite of
recoil.

I'd say the actually reason a rocket or missile has some recoil is a bit more subtle. If
you look at the individual gas particles coming from the rocket's engine, there is no
reason they have to fly straight backwards. It's more likely that they will come off with
some angle. If this angle is steep enough, then they can impact the tube, imparting
momentum. For instance, a particle traveling down and back from the rocket could hit the
tube giving it momentum down and backwards. Now, there is absolutely no radial preference
in direction, so there will on average be just as many particles traveling up and back, so
the side and back, and so on. Thus the radial component of this momentum cancels out (as
we would expect since the launcher shouldn't fly up, down, or to the side), however the
backwards component of the individual momenta does not cancel at all, but rather sums. So
even with an open tube there is some recoil. Futhermore, how much recoil will vary as a
function of how much extra tube you have behind the rocket's starting position, since a
longer tube will allow for gas particles coming off at less steep angles to impact the
tube. I would go so far as to say that a missile placed in an infinitely long tube will
impart as much momentum to the tube as a missile placed in a closed tube, but now I'm
talking like a physicist ;)

--
Dave Kettler
davek@***.lonestar.org
http://davek.freeshell.org
SDF Public Access UNIX System - http://sdf.lonestar.org
Message no. 8
From: arclight@*********.de (Arclight)
Subject: Missile Launchers and Recoil
Date: Mon, 19 Jan 2004 21:21:17 +0100
At 19:48 19.01.2004 +0000, David Kettler wrote:

<snip>

>Incidentally, after your last post I re-read your first post on this
>topic, and I don't buy your explanation for why a missile launcher has
>some recoil. If you just look at the friction between the rocket and the
>tube then that is going to want to pull the launcher forwards, along with
>the rocket, not push it backwards. Essentially it's the opposite of recoil.

No, the rocket is pushed out of the tube. A normal cannon round is
certainly not trying to pull the gun with itself, and it has friction all
the way until leaving the bore *g*

>I'd say the actually reason a rocket or missile has some recoil is a bit
>more subtle. If you look at the individual gas particles coming from the
>rocket's engine, there is no reason they have to fly straight
>backwards. It's more likely that they will come off with some angle. If
>this angle is steep enough, then they can impact the tube, imparting
>momentum. For instance, a particle traveling down and back from the
>rocket could hit the tube giving it momentum down and backwards. Now,
>there is absolutely no radial preference in direction, so there will on
>average be just as many particles traveling up and back, so the side and
>back, and so on. Thus the radial component of this momentum cancels out
>(as we would expect since the launcher shouldn't fly up, down, or to the
>side), however the backwards component of the individual momenta does not
>cancel at all, but rather sums. So even with an open tube there is some
>recoil. Futhermore, how much recoil will vary as a function of how much
>extra tube you have behind the rocket's starting position, since a longer
>tube will allow for gas particles coming off at less steep angles to
>impact the tube.

The problem with this is, that the missile is blown out of the tube by a
smaller starter charge, the real rocket motor isn't started after the
missile travelled at least a dozen or so meters. Otherwise the hot gases
would seriously injure the soldier firing the weapon.

> I would go so far as to say that a missile placed in an infinitely long
> tube will impart as much momentum to the tube as a missile placed in a
> closed tube, but now I'm talking like a physicist ;)

I couldn't care less about physics, but when the gases from the starter
charge never reach the end of the tube they will just expand until they
have lost all energy. So - almost no recoil or at least a LOT less than in
a short closed tube.


--
Arclight

Quitters never win, winners never quit,
but those who never quit and never win are idiots
Message no. 9
From: davek@***.lonestar.org (David Kettler)
Subject: Missile Launchers and Recoil
Date: Mon, 19 Jan 2004 21:56:23 +0000
On Mon, Jan 19, 2004 at 09:21:17PM +0100, Arclight wrote:
> At 19:48 19.01.2004 +0000, David Kettler wrote:
>
> No, the rocket is pushed out of the tube. A normal cannon round is
> certainly not trying to pull the gun with itself, and it has friction all
> the way until leaving the bore *g*
>

I'm sorry, but you are wrong. A normal cannon round *is* trying to pull the gun with
itself. That's what friction does. Place a heavy object on top of a piece of paper and
push it forward. The object will pull the paper along with it, not push it back. Of
course, this effect is much less the effect of the expanding gases pushing back on the gun
so you don't notice it. If it wasn't the round would never go anywhere in the first
place.

> The problem with this is, that the missile is blown out of the tube by a
> smaller starter charge, the real rocket motor isn't started after the
> missile travelled at least a dozen or so meters. Otherwise the hot gases
> would seriously injure the soldier firing the weapon.
>

So? This doesn't change anything I said, it just means that the recoil is small. And it
is small.

> I couldn't care less about physics, but when the gases from the starter
> charge never reach the end of the tube they will just expand until they
> have lost all energy. So - almost no recoil or at least a LOT less than in
> a short closed tube.
>

I care about physics ;)

Anyway, all I was saying about the infinite tube is that eventually the same amount of
momentum will be transferred. Of course, it does not happen in the same timeframe. In
the case of a closed tube it happens almost instantaneously, while in the case of the
infinite tube it will happen over a very long time. But it will happen. Every particle
will come off at some angle (mathematically the probability of a particle going directly
backwards is zero) and will therefore impact the tube at some point. And it is true that
the gases will lose energy. Now where do you think that energy goes?

--
Dave Kettler
davek@***.lonestar.org
http://davek.freeshell.org
SDF Public Access UNIX System - http://sdf.lonestar.org
Message no. 10
From: gurth@******.nl (Gurth)
Subject: Missile Launchers and Recoil
Date: Tue, 20 Jan 2004 11:08:48 +0100
According to David Kettler, on Monday 19 January 2004 20:48 the word on the
street was...

> Incidentally, after your last post I re-read your first post on this
> topic, and I don't buy your explanation for why a missile launcher has
> some recoil. If you just look at the friction between the rocket and
> the tube then that is going to want to pull the launcher forwards, along
> with the rocket, not push it backwards. Essentially it's the opposite
> of recoil.

Yes, you're right -- I didn't think it through well enough. Now if the
missile had little wheels on the tips of its fins... :)

--
Gurth@******.nl - Stone Age: http://www.xs4all.nl/~gurth/index.html
You've been touched by the doubt of man
-> Probably NAGEE Editor * ShadowRN GridSec * Triangle Virtuoso <-
-> The Plastic Warriors Page: http://plastic.dumpshock.com <-

GC3.12: GAT/! d- s:- !a>? C++(---) UL+ P(+) L++ E W--(++) N o? K w(--)
O V? PS+ PE@ Y PGP- t- 5++ X(+) R+++$ tv+(++) b++@ DI- D+ G+ e h! !r y?
Incubated into the First Church of the Sqooshy Ball, 21-05-1998
Message no. 11
From: ShadowRN@********.demon.co.uk (Paul J. Adam)
Subject: Missile Launchers and Recoil
Date: Tue, 20 Jan 2004 18:48:10 +0000
In article <BAY2-F118gpwqWXf8om00016ffe@*******.com>, Robert Fanning
<rothgefa@*******.com> writes
>There are reasons you want missiles to actually have recoil.
>
>Imagine you are standing up and firing a missile (same applies for
>grenades).
>
>1) You want the missile to actually leave the tube.

Ever since the Davis Gun, the solution has been "equal and opposite".
So, fling equal amounts of momentum out of the back to match the
launched projectile coming out of the front.

The normal method used by rocket/missile launchers and recoilless rifles
is to launch a heavy, low-velocity projectile out of the front, and a
lot of light but high-velocity gas out of the back. Resultant force,
zero, hence no momemtum (but uncomfortable backblast).

Other alternatives include launching 'payloads' out of the back: plastic
flakes are sometimes used nowadays, the original Davis Gun used buckshot
in grease. MILAN reduces its backblast by launching the missile from its
storage canister, and flinging that backwards off the launcher when
firing. The UK Javelin MANPADS blows a heavy metal base plug out of
_its_ launch tube (because it's got to be fired at elevated angles, and
reflected backblast off the ground would be bad for the firer)

>2) You want the missile to leave the tube fast enough so that it
>travels in the direction you want.

Or you want it out of the tube fast enough that when it fires its main
motor, it doesn't cook the firer.
>
>3) You want the missile to have enough velocity that it does not drop
>short at your feet.

Again, typical solution is to use an inital charge to lob it off the
launcher, then a main motor to get it to working speed.

>4) You want the missile to travel fast enough in the arming time to not
>blow yourself sky high.

Setback counters (boost and main both have to fire) are an easy way of
implementing that.


--
Paul J. Adam

Further Reading

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