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Message no. 1
From: shadowrn@*********.com (Martin Little)
Subject: Bullets lifting was Re: Crossbows
Date: Thu Apr 18 12:15:01 2002
On Thu, 18 Apr 2002, Gurth wrote:

> According to Lone Eagle, on Wed, 17 Apr 2002 the word on the street was...
>
> > Just to clarify this posting I think (although how it's supported by the
> > rules I can't remember) that a smartgun would have to be heavily
> > reprogrammed before it would function in conjunction with a crossbow, the
> > aerodynamics and ballistic characteristics are too different, a bullet
> > fired at 45 degrees to the horizontal (upwards) will describe a near
> > perfect parabollic curve
>
> Are you sure? Bullets experience lift as they fly through the air, which is
> why you can shoot _over_ the target even if you point the weapon straight
> at it.
>

Do you have a reference to this Gurth? Offhand I can't think of a reason
that a symetrical spinning object would generate lift.
I'm having flashbacks to old physics films in high school where they drop
a bullet at the same time as one leaves the barrel and they both hit the
ground at the same time.
Message no. 2
From: shadowrn@*********.com (Daniel Powell)
Subject: Bullets lifting was Re: Crossbows
Date: Thu Apr 18 12:25:01 2002
>Do you have a reference to this Gurth? Offhand I can't think of a reason
>that a symetrical spinning object would generate lift.
>I'm having flashbacks to old physics films in high school where they drop
>a bullet at the same time as one leaves the barrel and they both hit the
>ground at the same time.

I can verify that bullets fire in an arc which is why you have to site in a
rifle based on the distance you are planning to shoot. If you site in your
rifle at 300 yards then shoot at a deer at 100 yards, you will hit high on
your target. I don't know what causes the arc (lift sounds good to me) but
I know it happens.

Daniel Powell
"Friends come, and friends go, but enemies accumulate."

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Message no. 3
From: shadowrn@*********.com (Meph)
Subject: Bullets lifting was Re: Crossbows
Date: Thu Apr 18 12:30:02 2002
Now I haven't been following every message in this thread so forgive me
if this has been covered...But in Cannon Companion is states that you can
have smartlink on bows and crossbows.

Meph
Message no. 4
From: shadowrn@*********.com (Danyeal De La Luna)
Subject: Bullets lifting was Re: Crossbows
Date: Thu Apr 18 12:35:02 2002
On 4/18/02 11:31 AM, "Martin Little" <grimjack@******.com> wrote:

> On Thu, 18 Apr 2002, Gurth wrote:
>
>> According to Lone Eagle, on Wed, 17 Apr 2002 the word on the street was...
>>
>>> Just to clarify this posting I think (although how it's supported by the
>>> rules I can't remember) that a smartgun would have to be heavily
>>> reprogrammed before it would function in conjunction with a crossbow, the
>>> aerodynamics and ballistic characteristics are too different, a bullet
>>> fired at 45 degrees to the horizontal (upwards) will describe a near
>>> perfect parabollic curve
>>
>> Are you sure? Bullets experience lift as they fly through the air, which is
>> why you can shoot _over_ the target even if you point the weapon straight
>> at it.
>>
>
> Do you have a reference to this Gurth? Offhand I can't think of a reason
> that a symetrical spinning object would generate lift.
> I'm having flashbacks to old physics films in high school where they drop
> a bullet at the same time as one leaves the barrel and they both hit the
> ground at the same time.
>
>
I don't have a specific reference for this, but I think that the Ranger
Handbook talks about it. I know that when you shoot at extreme range, you
actually aim below the target. I don't, however, think that this applies to
missiles like arrows or bolts. My experience with that is that they drop in
a nice arc. I could be wrong, though.

Lunatec
Message no. 5
From: shadowrn@*********.com (Gurth)
Subject: Bullets lifting was Re: Crossbows
Date: Thu Apr 18 13:35:07 2002
According to Martin Little, on Thu, 18 Apr 2002 the word on the street was...

> Do you have a reference to this Gurth?

None that I can remember, let alone give you a URL to. I just know it
happens :)

--
Gurth@******.nl - http://www.xs4all.nl/~gurth/index.html
Dat is de kip voor het ei spannen.
-> NAGEE Editor * ShadowRN GridSec * Triangle Virtuoso <-
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Incubated into the First Church of the Sqooshy Ball, 21-05-1998
Message no. 6
From: shadowrn@*********.com (Martin Little)
Subject: Bullets lifting was Re: Crossbows
Date: Thu Apr 18 14:20:01 2002
On Thu, 18 Apr 2002, Gurth wrote:

> According to Martin Little, on Thu, 18 Apr 2002 the word on the street was...
>
> > Do you have a reference to this Gurth?
>
> None that I can remember, let alone give you a URL to. I just know it
> happens :)
>
>
The explanation on this page would seem to indicate that it's not a case
of the bullet 'lifting' but that the barrel is sighted on an angle to arc
the bullet to hit the sighted position.

http://www.molonlabe.net/johns/extbal.htm

Which seems to agree more with what I've observed.




----------------
"When you force someone to give you something, it's
no longer giving, it's stealing. Persons of leisurely
moral growth often confuse giving with taking."
-- Larry Wall
Message no. 7
From: shadowrn@*********.com (Daniel Powell)
Subject: Bullets lifting was Re: Crossbows
Date: Thu Apr 18 14:25:02 2002
>The explanation on this page would seem to indicate that it's not a case
>of the bullet 'lifting' but that the barrel is sighted on an angle to arc
>the bullet to hit the sighted position.

I remember seeing a poster on this guy's wall from college that showed a
bullet's tragectory and indeed it did arc up. But that's many years ago.

Daniel

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Message no. 8
From: shadowrn@*********.com (malcolm)
Subject: Bullets lifting was Re: Crossbows
Date: Thu Apr 18 14:30:01 2002
> >Do you have a reference to this Gurth? Offhand I can't think of a reason
> >that a symetrical spinning object would generate lift.
> >I'm having flashbacks to old physics films in high school where they drop
> >a bullet at the same time as one leaves the barrel and they both hit the
> >ground at the same time.
>
> I can verify that bullets fire in an arc which is why you have to site in
a
> rifle based on the distance you are planning to shoot. If you site in
your
> rifle at 300 yards then shoot at a deer at 100 yards, you will hit high on
> your target. I don't know what causes the arc (lift sounds good to me)
but
> I know it happens.

picture a line of string , right , that is the path of the bullet without
gravity , now add in gravity , the effect equal regardless of any
directional movement , so it starts to fall , hence it shoots low now you
sight your rifle at 300 yards , stretch your piece of string to allow for
gravity you will have to sight higher , then at a distance of 100 yards ,
you would sight lower

but this effects all objects equally from cannon to crossbows what
"reduces" the effect is the horizontal speed of the projectile it doesn't so
much reduce the effect of gravity as it's forward speed means it covers more
distance before falling an equal distance as the slower projectile did in
the same period of time

mil sights tend toward preset , 300 metres and 500 metres , this takes care
of most problems , your drop on a sub-sonic bullet over fractions of a
second means it has already covered that distance so at close ranges
sighting at 300 does little harm

now with slower projectiles this effect is greater , this as far as i am
concerned ( with the possible exception of difficulty in training ) is the
reason for the ascendancy of firearms over bow projectile weapons , after
all what general is his right mind wants a weapon that has a weapon with an
effective range of 40 yards that shoots once every minute over a weapon with
an effective range of 250 yards with a rate of fire of 5 every minute

hope this helps
Kanniemeernie , Korperaal
" the important thing in a military operation is victory not pesistance"
Sun-Tzu , the art of war
Message no. 9
From: shadowrn@*********.com (Lone Eagle)
Subject: Bullets lifting was Re: Crossbows
Date: Fri Apr 19 07:50:01 2002
>From: "Daniel Powell" <l0_jak@*******.com>
>I can verify that bullets fire in an arc which is why you have to site in a
>rifle based on the distance you are planning to shoot. If you site in your
>rifle at 300 yards then shoot at a deer at 100 yards, you will hit high on
>your target. I don't know what causes the arc (lift sounds good to me) but
>I know it happens.

Gravity is what causes the arc, the reason you hit high on a target at 100
yards when your rifle is zeroed at 300 is that the barrel of the rifle is
pointing upwards (to compensate for the fact that the bullet will drop as it
travels). Gravity effects the bullet less (i.e. the distance through which
the bullet drops is less) by about on third over a range of 100yrds compared
to over 300yrds. you shoot high because you're overcompensating (or rather
your scope is) for gravity.

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Message no. 10
From: shadowrn@*********.com (Lone Eagle)
Subject: Bullets lifting was Re: Crossbows
Date: Fri Apr 19 08:05:00 2002
>From: "malcolm" <mcuthbertson@***.co.za>
>but this effects all objects equally from cannon to crossbows what
>"reduces" the effect is the horizontal speed of the projectile it doesn't
>so
>much reduce the effect of gravity as it's forward speed means it covers
>more
>distance before falling an equal distance as the slower projectile did in
>the same period of time

Drag is also a factor, and as quarrells and arrows have vastly higher drag
characterisics they slow down quicker and more noticably, therefore their
flight path drops a lot "quicker" in the second half of their flight than
that of a bullet.

>all what general is his right mind wants a weapon that has a weapon with an
>effective range of 40 yards that shoots once every minute over a weapon
>with
>an effective range of 250 yards with a rate of fire of 5 every minute

The best units in the napoleonic wars could only manage a rate of fire of
three times a minute.

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Message no. 11
From: shadowrn@*********.com (shadowrn@*********.com)
Subject: Bullets lifting was Re: Crossbows
Date: Fri Apr 19 10:00:01 2002
> According to Lone Eagle, on Wed, 17 Apr 2002 the word on the street was...
>
> > Just to clarify this posting I think (although how it's supported by the
> > rules I can't remember) that a smartgun would have to be heavily
> > reprogrammed before it would function in conjunction with a crossbow,
the
> > aerodynamics and ballistic characteristics are too different, a bullet
> > fired at 45 degrees to the horizontal (upwards) will describe a near
> > perfect parabollic curve
>
> Are you sure? Bullets experience lift as they fly through the air, which
is
> why you can shoot _over_ the target even if you point the weapon straight
> at it.
>

>Do you have a reference to this Gurth? Offhand I can't think of a reason
>that a symetrical spinning object would generate lift.
>I'm having flashbacks to old physics films in high school where they drop
>a bullet at the same time as one leaves the barrel and they both hit the
>ground at the same time.

Speaking as a soldier I can tell you that firing an m-16 at 100 yrds the
bullet will be aprox 1" above the point of aim. At 200 yrds it's right on
target. I believe that the bullet travels in a circular orbit because of
the spin and this causes the lift. It's similar to the concept of a curve
ball in baseball.

Coyote
Message no. 12
From: shadowrn@*********.com (Marc Renouf)
Subject: Bullets lifting was Re: Crossbows
Date: Fri Apr 19 10:45:07 2002
On Fri, 19 Apr 2002 York.GA@******.ca wrote:

> Speaking as a soldier I can tell you that firing an m-16 at 100 yrds the
> bullet will be aprox 1" above the point of aim. At 200 yrds it's right on
> target. I believe that the bullet travels in a circular orbit because of
> the spin and this causes the lift. It's similar to the concept of a curve
> ball in baseball.

That's not lift. It's that your rifle is sighted in at 200 yrds
(or meters, more likely). As such, at 100 yds, your sight profile is
undercompensating for the drop of the bullet.

Marc
Message no. 13
From: shadowrn@*********.com (Achille Autran)
Subject: Bullets lifting (was Re: Crossbows)
Date: Fri Apr 19 12:50:01 2002
>From: Martin Little <grimjack@******.com>
>The explanation on this page would seem to indicate that it's not a case
>of the bullet 'lifting' but that the barrel is sighted on an angle to arc
>the bullet to hit the sighted position.
>
>http://www.molonlabe.net/johns/extbal.htm

This page mainly concentrates on the effects of drag depending on bullet
shapes. There are numerous other forces applied to a bullet while it is
flying through air, here is a page that explains that stuff pretty nicely
(lifted off Raygun's site, http://matrix.dumpshock.com/raygun/ ):

http://www.povn.com/%7E4n6/index.htm

The force that may cause bullet lift is the Magnus effect, but depending on
crosswind direction and wether the barrel rifling is clockwise or
counterclockwise. The Magnus effect is what makes, say, baseball balls have
insanely twisted trajectories when given the proper spin, and cut tennis
balls well, lift. But balls can spin on all axis, and it's the backward
spin (opposite to a rolling ball) of a tennis ball that gives it upward
lift and "floating" effect - make it spin the other way, and you have a
"lifted" ball that falls faster - yeah, tennis semantics are screwed.

Bullets only spin longitudinaly, so global upward bent of the trajectory
woud be a pretty tiny effect as average crosswind is almost negligible
compared to the cross air flow generated by a trans- or supersonic bullet
yaw angle, probably significant only in lab coundition. That maybe what
Daniel's college collegue had displayed on his poster. One can do wonders
with curvilinear coordinates based on a trajectory not taking into account
this effect.

If this isn't very clear, that's normal. We're dealing with non-trivial
(aero)dynamics here, which would be much better explained with a few
schemes and hand movements. ;-) And the effect I'm describing here is /not/
the wind force (divided in drag and cross-wind force, the later often
misnamed lift force. The cross-wind force does not produce any global lift
because it precesses along with bullet yaw, causing a spiralling trajectory
and general bullet side drift.)

Molloy
Message no. 14
From: shadowrn@*********.com (Paul J. Adam)
Subject: Bullets lifting was Re: Crossbows
Date: Tue Apr 23 13:25:00 2002
In article
<Pine.LNX.4.10.10204181327170.1068-100000@*******.vegamuse.org>, Martin
Little <grimjack@******.com> writes
>On Thu, 18 Apr 2002, Gurth wrote:
>> Are you sure? Bullets experience lift as they fly through the air, which is
>> why you can shoot _over_ the target even if you point the weapon straight
>> at it.
>
>Do you have a reference to this Gurth? Offhand I can't think of a reason
>that a symetrical spinning object would generate lift.
>I'm having flashbacks to old physics films in high school where they drop
>a bullet at the same time as one leaves the barrel and they both hit the
>ground at the same time.
>
>
>
>
>

--
Paul J. Adam
Message no. 15
From: shadowrn@*********.com (Paul J. Adam)
Subject: Bullets lifting was Re: Crossbows
Date: Tue Apr 23 13:35:01 2002
In article
<Pine.LNX.4.10.10204181327170.1068-100000@*******.vegamuse.org>, Martin
Little <grimjack@******.com> writes
>On Thu, 18 Apr 2002, Gurth wrote:
>> Are you sure? Bullets experience lift as they fly through the air, which is
>> why you can shoot _over_ the target even if you point the weapon straight
>> at it.
>
>Do you have a reference to this Gurth? Offhand I can't think of a reason
>that a symetrical spinning object would generate lift.

It's called the Magnus effect.

Magnus effect - A moving, rotating bullet in the air, drags some of the
air around with it, in its direction of rotation. This increases the
speed in that region, and thus the pressure is lower. Consequently,
there is a net force on the bullet in the direction of spin,
perpendicular to the forward movement of the bullet. This is called the
Magnus effect.

http://www.snipercountry.com/Compendium/Comp_M.htm

>I'm having flashbacks to old physics films in high school where they drop
>a bullet at the same time as one leaves the barrel and they both hit the
>ground at the same time.

That's gravity unaided by aerodynamics :)



>
>
>
>
>

--
Paul J. Adam
Message no. 16
From: shadowrn@*********.com (Joel Agee)
Subject: Bullets lifting was Re: Crossbows
Date: Wed Apr 24 15:20:02 2002
>Date: Tue, 23 Apr 2002 18:31:46 +0100
>To: shadowrn@*********.com
>From: "Paul J. Adam" <ShadowRN@********.demon.co.uk>
>Subject: Re: Bullets lifting was Re: Crossbows
>
>In article
><Pine.LNX.4.10.10204181327170.1068-100000@*******.vegamuse.org>, Martin
>Little <grimjack@******.com> writes
> >On Thu, 18 Apr 2002, Gurth wrote:
> >> Are you sure? Bullets experience lift as they fly through the air,
> which is
> >> why you can shoot _over_ the target even if you point the weapon straight
> >> at it.
> >
> >Do you have a reference to this Gurth? Offhand I can't think of a reason
> >that a symetrical spinning object would generate lift.
>
>It's called the Magnus effect.
>
>Magnus effect - A moving, rotating bullet in the air, drags some of the
>air around with it, in its direction of rotation. This increases the
>speed in that region, and thus the pressure is lower. Consequently,
>there is a net force on the bullet in the direction of spin,
>perpendicular to the forward movement of the bullet. This is called the
>Magnus effect.
>
>http://www.snipercountry.com/Compendium/Comp_M.htm

But, since the bullet is rotating orthogonally to its direction of travel,
why is the force upwards? It could just as easily be right, left, down,
whatever. Of course, this assumes a symmetrical bullet, but I'm still not
sure how even an asymmetrical bullet, rotating along its direction of
travel, would generate lift. If it had backspin, sure. It would also
generate lift or sink (depending on direction) if the wind was coming from
the side, though I doubt it would be significant.

> >I'm having flashbacks to old physics films in high school where they drop
> >a bullet at the same time as one leaves the barrel and they both hit the
> >ground at the same time.
>
>That's gravity unaided by aerodynamics :)

Yes, but if the dropped bullet is spinning it should move slightly to the
side -- turn your head 90 degrees and notice the backspin perpendicular to
the direction of travel.

<sigh> Where's a chalkboard when you need one...


--
Joel

"Intelligence has no place in politics!"
--Ambassador Londo Molari, Babylon 5
Message no. 17
From: shadowrn@*********.com (Achille Autran)
Subject: Bullets lifting was Re: Crossbows
Date: Thu Apr 25 14:05:02 2002
>From: Joel Agee <jagee@******.com>
>
>But, since the bullet is rotating orthogonally to its direction of travel,
>why is the force upwards? It could just as easily be right, left, down,
>whatever. Of course, this assumes a symmetrical bullet, but I'm still not
>sure how even an asymmetrical bullet, rotating along its direction of
>travel, would generate lift. If it had backspin, sure. It would also
>generate lift or sink (depending on direction) if the wind was coming from
>the side, though I doubt it would be significant.

A bullet in flight is not directed absolutely straight at its target
however. It has a yaw angle, that can be as large as 10° right out of the
barrel (angle delta in the following figure:
http://www.povn.com/%7E4n6/fig10.htm ). At such angles, almost 17%
(sin(delta) actually) of the forward velocity can be considered side
velocity - that's why there a sin(delta) in the Magnus force formula
http://www.povn.com/%7E4n6/magnusf.htm

Now, you're right when you say that the direction of the Magnus is not
necessarily upward, in is dependant on yaw angle, rifling orientation
(clockwise or counterclockwise), as well as direction of cross wind (true
cross wind, not the "virtual" side wind caused by yaw angle.) The vast
majority of Magnus force is caused by that "virtual" side wind, and this
force precesses along with bullet tip orientation (see
http://www.povn.com/%7E4n6/fig18.htm ) causing a slightly spiralling
trajectory. On the yawing motion graph above though, you can see that
precession is not regular: there is a favored "lobe" upward. This will
cause /on avarage/ a slighty stronger Magnus force to the left for a
clockwise rifling (I let you as an exercise in spatial representation with
the first figure to see how this runs) and thus, a trajectoory slighty
skewed to the left. Had the favored lobe been to the right, the global
effect would have been upward (downward with a counterclockwise rifling.)

I doubt one can accurately predict this favored lobe, though. The only
consistent effect is the one caused by real cross wind, and compared to
wind drift and turbulences the lift or fall would indeed most probably be
negligible.

Molloy
Message no. 18
From: shadowrn@*********.com (Joel Agee)
Subject: Bullets lifting was Re: Crossbows
Date: Fri Apr 26 14:05:01 2002
>Date: Thu, 25 Apr 2002 20:03:21 +0200
>From: Achille Autran <aautran@****.fr>
>Subject: Re: Bullets lifting was Re: Crossbows
>
>A bullet in flight is not directed absolutely straight at its target
>however. It has a yaw angle, that can be as large as 10° right out of the
>barrel (angle delta in the following figure:
>http://www.povn.com/%7E4n6/fig10.htm ). At such angles, almost 17%
>(sin(delta) actually) of the forward velocity can be considered side
>velocity - that's why there a sin(delta) in the Magnus force formula
>http://www.povn.com/%7E4n6/magnusf.htm

Is this because, for it's last ~œ bullet length of travel before exiting
the barrel, it's guidance (the barrel) exists only behind the center of
mass? A slight kick sideways would cause the bullet to be slightly off
true, which would then precess around due to the gyroscopic action of the
rifling translating the restoring force of air resistance 90 degrees one
way or the other (depending on rifling direction).

>Now, you're right when you say that the direction of the Magnus is not
>necessarily upward, in is dependant on yaw angle, rifling orientation
>(clockwise or counterclockwise), as well as direction of cross wind (true
>cross wind, not the "virtual" side wind caused by yaw angle.) The vast
>majority of Magnus force is caused by that "virtual" side wind, and this
>force precesses along with bullet tip orientation (see
>http://www.povn.com/%7E4n6/fig18.htm ) causing a slightly spiralling
>trajectory. On the yawing motion graph above though, you can see that
>precession is not regular: there is a favored "lobe" upward. This will
>cause /on avarage/ a slighty stronger Magnus force to the left for a
>clockwise rifling (I let you as an exercise in spatial representation with
>the first figure to see how this runs) and thus, a trajectory slighty
>skewed to the left. Had the favored lobe been to the right, the global
>effect would have been upward (downward with a counterclockwise rifling.)

That seems obvious, once given the wobble that I left out in my original
assumption. I don't understand why the precession favors that upwards
lobe, though -- is it because, in any long range test, the gun must be
aimed slightly upwards? Or is it the downwards fall of the bullet through
the air (which would require the bullet to come out of the gun with the
barrel level -- if the barrel is inclined upwards, there's going to be
upwards motion of the bullet until its vertical velocity is reversed by
gravity)?

>I doubt one can accurately predict this favored lobe, though. The only
>consistent effect is the one caused by real cross wind, and compared to
>wind drift and turbulences the lift or fall would indeed most probably be
>negligible.

And I still don't see anything aerodynamic causing this claimed "lifting"
effect, wherein *all* bullets rise (or fail to fall as fast as they should)
upon leaving the barrel.

--
Joel Agee
Visitalk.com
Phoenix, AZ

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