The physics of crossbow bolts in HL2 (was: The sniper rifle ...)

[Cyde Weys]

How come we never get to use the sniper rifle? You know, the
cool
one with the green laser sight that the enemies use against you? I
got very eager when the sniper part of the game came up because I
was hoping I'd be able to get a sniper rifle from killing one of
them ... but it didn't happen. Instead all we get is this stupid
crossbow, which is better than nothing (it's the only weapon that
can zoom), but its long travel time makes it hard to hit moving
targets at range. And if they had made it realistic and actually
added drop, well then, it'd be even harder to use.

Eh???? It DOES drop.

Well then, not enough to be noticeable :-/
(Err, I should say, given its travel time, it should drop a lot more
than the paltry bit it currently does. I'm saying it's not
influenced by -9.81 m/s^2 as it should be).

Do you think its velocity might affect it a little? Does an arrow drop
quicker than say, a stone when fired at the same speed?

??? Dude, that makes no sense. Velocity is a vector that has three
components ... x, y, and z. For the purposes of making it simpler, let
us only consider movement in two directions, x and y. The x component
of velocity is unchanging (unless you account for air resistance), while
the y component of velocity will accelerate at -9.81m/s^2. It doesn't
matter whether you are considering an arrow, a stone, or a feather ...
everything drops at the same speed (again, neglecting air resistance).
And everything drops at the same speed independent of its horizontal
velocity. Try a simple thought experiment ... dribble a basketball
while standing still. Then dribble a basketball while moving really
quickly. It doesn't take any longer for the basketball to return to
your hand when you are moving quickly because the x and y components of
the velocity are independent.

Anyway, I'm x-posting this to sci.physics so they can have their say.

[Walter Mitty]

Post by Cyde Weys

How come we never get to use the sniper rifle? You know, the
cool
one with the green laser sight that the enemies use against you? I
got very eager when the sniper part of the game came up because I
was hoping I'd be able to get a sniper rifle from killing one of
them ... but it didn't happen. Instead all we get is this stupid
crossbow, which is better than nothing (it's the only weapon that
can zoom), but its long travel time makes it hard to hit moving
targets at range. And if they had made it realistic and actually
added drop, well then, it'd be even harder to use.

Eh???? It DOES drop.

Well then, not enough to be noticeable :-/
(Err, I should say, given its travel time, it should drop a lot more
than the paltry bit it currently does. I'm saying it's not
influenced by -9.81 m/s^2 as it should be).

Do you think its velocity might affect it a little? Does an arrow drop
quicker than say, a stone when fired at the same speed?

??? Dude, that makes no sense. Velocity is a vector that has three
components ... x, y, and z. For the purposes of making it simpler, let
us only consider movement in two directions, x and y. The x component
of velocity is unchanging (unless you account for air resistance), while
the y component of velocity will accelerate at -9.81m/s^2. It doesn't
matter whether you are considering an arrow, a stone, or a feather ...
everything drops at the same speed (again, neglecting air resistance).
And everything drops at the same speed independent of its horizontal
velocity. Try a simple thought experiment ... dribble a basketball
while standing still. Then dribble a basketball while moving really
quickly. It doesn't take any longer for the basketball to return to
your hand when you are moving quickly because the x and y components of
the velocity are independent.

Another example of a little knowledge being a dangerous thing.

OK, here's a simple example for you.

Take a piece of paper and make it into a winged dart. Throw that. Get
another piece of paper and chew it up. Throw that at the same speed.
Which goes the furthest?

Ah yes!

The key being, of course, pressure differentials (theory of flight), air
pressure (you conveniently chose to ignore it), air currents etc.

[Cyde Weys]

Post by Walter Mitty
Another example of a little knowledge being a dangerous thing.
OK, here's a simple example for you.
Take a piece of paper and make it into a winged dart. Throw that. Get
another piece of paper and chew it up. Throw that at the same speed.
Which goes the furthest?
Ah yes!
The key being, of course, pressure differentials (theory of flight),
air pressure (you conveniently chose to ignore it), air currents etc.

Ahhh, so you are saying that crossbow bolt has wings on it that produce
lift? If not, it's pretty much a standard projectile that should drop at
the same rate as anything else. And I didn't see any wings or fins on the
crossbow bolts in my game ...

[Walter Mitty]

Post by Cyde Weys

Post by Walter Mitty
Another example of a little knowledge being a dangerous thing.
OK, here's a simple example for you.
Take a piece of paper and make it into a winged dart. Throw that. Get
another piece of paper and chew it up. Throw that at the same speed.
Which goes the furthest?
Ah yes!
The key being, of course, pressure differentials (theory of flight),
air pressure (you conveniently chose to ignore it), air currents etc.

Ahhh, so you are saying that crossbow bolt has wings on it that produce
lift? If not, it's pretty much a standard projectile that should drop at
the same rate as anything else. And I didn't see any wings or fins on the
crossbow bolts in my game ...

No, No, you're right. A crossbow flight is made to drop at the same
speed and acceleration as a brick.

Sigh.

[Cyde Weys]

Post by Walter Mitty
No, No, you're right. A crossbow flight is made to drop at the same
speed and acceleration as a brick.

Not exactly the same speed, but pretty close to it. A crossbow bolt will
probably drop less because it's more aerodynamic, but gravity is still the
dominant factor (and that works equally on all objects).

[Walter Mitty]

Post by Cyde Weys

Post by Walter Mitty
No, No, you're right. A crossbow flight is made to drop at the same
speed and acceleration as a brick.

Not exactly the same speed, but pretty close to it. A crossbow bolt will
probably drop less because it's more aerodynamic, but gravity is still the
dominant factor (and that works equally on all objects).

Are you really this much of a dumbass or are you trolling? I think
you're trolling. We are talking real life environments here : not some
vacumm.

[Ben Cottrell]

Post by Walter Mitty
Are you really this much of a dumbass or are you trolling? I think
you're trolling. We are talking real life environments here : not some
vacumm.

I don't know if HL2 takes air resistance into account - I suspect it
doesn't, therefore it's probably a safe assumption that physics in HL2
would be closer to that of a vacuum than of a 'real life environment' :-)

[Paul Catley]

Post by Ben Cottrell
I don't know if HL2 takes air resistance into account - I suspect it
doesn't, therefore it's probably a safe assumption that physics in HL2
would be closer to that of a vacuum than of a 'real life environment' :-)

The only games I know of that take projectile physics into account are the
better combat flightsims. Possibly also sim-shooters with long ranges (e.g.
Operation Flashpoint), I'm not sure. I very much doubt that Half-Life 2 or
other non-simulation FPS games bother, except perhaps for slower projectiles,
like crossbow bolts. What would be the point?

--
Paul

[Daniel Vandersluis]

Post by Cyde Weys

Post by Walter Mitty
No, No, you're right. A crossbow flight is made to drop at the same
speed and acceleration as a brick.

Not exactly the same speed, but pretty close to it. A crossbow bolt will
probably drop less because it's more aerodynamic, but gravity is still the
dominant factor (and that works equally on all objects).

In that case, should not a bullet, which has no fins as you'll agree,
should drop as quickly as well...?

[Walter Mitty]

Post by Daniel Vandersluis

Post by Cyde Weys

Post by Walter Mitty
No, No, you're right. A crossbow flight is made to drop at the same
speed and acceleration as a brick.

Not exactly the same speed, but pretty close to it. A crossbow bolt
will probably drop less because it's more aerodynamic, but gravity is
still the dominant factor (and that works equally on all objects).

In that case, should not a bullet, which has no fins as you'll agree,
should drop as quickly as well...?

Here's a new word of the day Sidewayz : "rifling" :)

[Andrew Lias]

Post by Daniel Vandersluis

Post by Cyde Weys
Not exactly the same speed, but pretty close to it. A crossbow bolt will
probably drop less because it's more aerodynamic, but gravity is still the
dominant factor (and that works equally on all objects).

In that case, should not a bullet, which has no fins as you'll agree,
should drop as quickly as well...?

Actually, in the real world, bullets drop as quickly as other objects.
Their rapid horizonal velocity allows them to travel much further
than, say, a thrown rock, however, if you were to fire a bullet
parallel to level ground and drop a another bullet from your hand at
the same instant, both would intersect the ground at approximately the
same moment (modulo minor areodynamic effects, of course).

As for the person who implied that rifling keeps a bullet in the air
longer, the only thing that rifling does is to keep the bullets
orientation stable via gyroscopic effects. A tumbling bullet will,
however, travel less distance due to bad aerodynamics, but it's rate
of descent is about the same.

--
Andrew Lias
http://andrewlias.blogspot.com

[Paul Catley]

Post by Andrew Lias
Actually, in the real world, bullets drop as quickly as other objects.
Their rapid horizonal velocity allows them to travel much further
than, say, a thrown rock, however, if you were to fire a bullet
parallel to level ground and drop a another bullet from your hand at
the same instant, both would intersect the ground at approximately the
same moment (modulo minor areodynamic effects, of course).
As for the person who implied that rifling keeps a bullet in the air
longer, the only thing that rifling does is to keep the bullets
orientation stable via gyroscopic effects. A tumbling bullet will,
however, travel less distance due to bad aerodynamics, but it's rate
of descent is about the same.

Nice one Andrew, the first answer I agree with :)

Now I'm waiting for someone to say that the flights on a crossbow bolt provide
lift...

--
Paul

[Tomasso makes things]

Post by Paul Catley

Post by Andrew Lias
Actually, in the real world, bullets drop as quickly as other objects.
Their rapid horizonal velocity allows them to travel much further
than, say, a thrown rock, however, if you were to fire a bullet
parallel to level ground and drop a another bullet from your hand at
the same instant, both would intersect the ground at approximately the
same moment (modulo minor areodynamic effects, of course).
As for the person who implied that rifling keeps a bullet in the air
longer, the only thing that rifling does is to keep the bullets
orientation stable via gyroscopic effects. A tumbling bullet will,
however, travel less distance due to bad aerodynamics, but it's rate
of descent is about the same.

Nice one Andrew, the first answer I agree with :)

You guys are making this stuff up. You want to get lift on the trajectory of a
bullet? Well, here is what really happens. The spin imparted by rifling keeps
the bullet pointing in its original direction, BUT the trajectory dips below that.

Eg, Fred aims to hit a target at 800m. To do that, he's pointing above the target.
The bullet continues pointing that way. There is an increasing angle (with distance)
between the bullet's pointing and the trajectory.

THIS imparts lift, and raises the bullet above the quasi-parabolic path (I say quasi
to allow for drag slowing the bullet).

The lift also imposes a drag penalty, so the bullet slows.

An older shooter I knew explained this to me once: His example was hitting a
target at 1200m, and the height the bullet would be at at various distances.
Depending on calibre, projectile, powder load, rifling and even some things
like humidity (and thermals), the bullet (in his example) was about 50 metres
high at 350 metres, for a hit at 1200 metres. In practice, the simply sight by
taking practice shots and adjusting...

Even if the bullet is fired horizontal, there will be a lift effect.

In aerodynamic terms, this means there is a relative pitch (between projectile
heading and trajectory == lift + drag).

Post by Paul Catley
Now I'm waiting for someone to say that the flights on a crossbow bolt provide
lift...

If the flights act as tail drag (with no lift), they will cause the bolt to point into
the direction of air resistance, hence, following the basic quasi-parabola.

A paper dart is different, because the wings and weight distribution also
maintain stability against rolling. [A crossbow bolt doesn't do this].

This means you can make little trim adjustments to your paper dart, either
for more lift or less drag. The maximum distance is a result of experiment
and craft.

Tomasso.

[Paul Catley]

Post by Tomasso makes things
You guys are making this stuff up. You want to get lift on the
trajectory of a
bullet? Well, here is what really happens. The spin imparted by rifling keeps
the bullet pointing in its original direction, BUT the trajectory dips below that.
Eg, Fred aims to hit a target at 800m. To do that, he's pointing above the target.
The bullet continues pointing that way. There is an increasing angle (with distance)
between the bullet's pointing and the trajectory.
THIS imparts lift, and raises the bullet above the quasi-parabolic path (I say quasi
to allow for drag slowing the bullet).
The lift also imposes a drag penalty, so the bullet slows.
An older shooter I knew explained this to me once: His example was hitting a
target at 1200m, and the height the bullet would be at at various distances.
Depending on calibre, projectile, powder load, rifling and even some things
like humidity (and thermals), the bullet (in his example) was about 50 metres
high at 350 metres, for a hit at 1200 metres. In practice, the simply sight by
taking practice shots and adjusting...
Even if the bullet is fired horizontal, there will be a lift effect.
In aerodynamic terms, this means there is a relative pitch (between projectile
heading and trajectory == lift + drag).

Damn, that's good, I didn't think anyone would get that advanced :) I'm not a
shooter and I don't know much about ballistics, but I would have thought that
elevating the gun has more to do with counter-acting gravity than imparting
lift. However, I know a little about aircraft aerodynamics, and your point
seems very reasonable.

Lift is imparted by causing different relative air speeds on one side of an
object to the other in a smooth airflow. This decreases the air pressure on one
side to the other, which causes a lifting force towards the side with the lower
pressure. This difference in air speed is most easily achieved by having the
aerofoil meet the airflow at an angle. Your bullet as it leaves the muzzle
would not meet the airflow at an angle, it would meet it straight on, regardless
of the elevation of the rifle. However, as the trajectory arc decayed, the
gyroscopic effect of the spinning bullet would keep the nose pointed in its
original elevation, and now it *is* meeting the airflow at an angle, so some
lift would be generated. Probably not very much, since it is such a thin shape,
but enough to have an influence. A ballistics expert or a well-read rifle
enthusiast would know how much of an influence it has. As you said, lift
creates drag, so the bullet will slow down, perhaps counter-acting any benefit
from the lift. Nevertheless, it seems likely that if there is *any* lift, it
will be sufficient to reduce the effect of gravity and slow the bullet's descent
(by how much would need that ballistics expert again).

Humidity and thermals are not things that generally have much effect on powered
aircraft, but on the smaller scale of a bullet, I can believe it. Wind will
have a more noticeable effect, I would think. These air condition factors might
not act beneficially though.

That's excellent information, cheers :)

Post by Tomasso makes things

Post by Paul Catley
Now I'm waiting for someone to say that the flights on a crossbow
bolt provide lift...

If the flights act as tail drag (with no lift), they will cause the bolt to point into
the direction of air resistance, hence, following the basic
quasi-parabola.

Agreed. There is no gyroscopic effect with a bolt or arrow, so the tail drag
*will* keep the bolt aligned with the direction of airflow (more or less), so no
lift is created.

Post by Tomasso makes things
A paper dart is different, because the wings and weight distribution also
maintain stability against rolling. [A crossbow bolt doesn't do this].
This means you can make little trim adjustments to your paper dart, either
for more lift or less drag. The maximum distance is a result of experiment
and craft.

You've taken it as read there, but a paper dart has lift, because a well
designed one will adopt an attitude that causes its wings to meet the airflow at
an angle (while it is descending). That is the principal difference, and that's
why Walter's comparisons of a paper dart with crossbow bolts are irrelevant.

Good discussion, thanks.

--
Paul

[McGrandpa]

Post by Paul Catley

Post by Tomasso makes things
You guys are making this stuff up. You want to get lift on the trajectory of a
bullet? Well, here is what really happens. The spin imparted by rifling keeps
the bullet pointing in its original direction, BUT the trajectory dips below that.
Eg, Fred aims to hit a target at 800m. To do that, he's pointing above the target.
The bullet continues pointing that way. There is an increasing angle (with distance)
between the bullet's pointing and the trajectory.
THIS imparts lift, and raises the bullet above the quasi-parabolic path (I say quasi
to allow for drag slowing the bullet).
The lift also imposes a drag penalty, so the bullet slows.
An older shooter I knew explained this to me once: His example was hitting a
target at 1200m, and the height the bullet would be at at various distances.
Depending on calibre, projectile, powder load, rifling and even some things
like humidity (and thermals), the bullet (in his example) was about 50 metres
high at 350 metres, for a hit at 1200 metres. In practice, the simply sight by
taking practice shots and adjusting...
Even if the bullet is fired horizontal, there will be a lift effect.
In aerodynamic terms, this means there is a relative pitch (between projectile
heading and trajectory == lift + drag).

Damn, that's good, I didn't think anyone would get that advanced :)
I'm not a shooter and I don't know much about ballistics, but I would
have thought that elevating the gun has more to do with
counter-acting gravity than imparting lift. However, I know a little
about aircraft aerodynamics, and your point seems very reasonable.
Lift is imparted by causing different relative air speeds on one side
of an object to the other in a smooth airflow. This decreases the
air pressure on one side to the other, which causes a lifting force
towards the side with the lower pressure. This difference in air
speed is most easily achieved by having the aerofoil meet the airflow
at an angle. Your bullet as it leaves the muzzle would not meet the
airflow at an angle, it would meet it straight on, regardless of the
elevation of the rifle. However, as the trajectory arc decayed, the
gyroscopic effect of the spinning bullet would keep the nose pointed
in its original elevation, and now it *is* meeting the airflow at an
angle, so some lift would be generated. Probably not very much,
since it is such a thin shape, but enough to have an influence. A
ballistics expert or a well-read rifle enthusiast would know how much
of an influence it has. As you said, lift creates drag, so the
bullet will slow down, perhaps counter-acting any benefit from the
lift. Nevertheless, it seems likely that if there is *any* lift, it
will be sufficient to reduce the effect of gravity and slow the
bullet's descent (by how much would need that ballistics expert
again).
Humidity and thermals are not things that generally have much effect
on powered aircraft, but on the smaller scale of a bullet, I can
believe it. Wind will have a more noticeable effect, I would think.
These air condition factors might not act beneficially though.
That's excellent information, cheers :)

Post by Tomasso makes things

Post by Paul Catley
Now I'm waiting for someone to say that the flights on a crossbow
bolt provide lift...

If the flights act as tail drag (with no lift), they will cause the bolt to point into
the direction of air resistance, hence, following the basic
quasi-parabola.

Agreed. There is no gyroscopic effect with a bolt or arrow, so the
tail drag *will* keep the bolt aligned with the direction of airflow
(more or less), so no lift is created.

Post by Tomasso makes things
A paper dart is different, because the wings and weight distribution also
maintain stability against rolling. [A crossbow bolt doesn't do this].
This means you can make little trim adjustments to your paper dart, either
for more lift or less drag. The maximum distance is a result of experiment
and craft.

You've taken it as read there, but a paper dart has lift, because a
well designed one will adopt an attitude that causes its wings to
meet the airflow at an angle (while it is descending). That is the
principal difference, and that's why Walter's comparisons of a paper
dart with crossbow bolts are irrelevant.
Good discussion, thanks.

How come both you and Neil ignored my post about wings and 'lift'?
McG.

[Paul Catley]

Post by McGrandpa
How come both you and Neil ignored my post about wings and 'lift'?

I'm not sure which one you meant, so I'm answering them all :)

(The only one that seems to apply is the push/pull one, which didn't seem to
need further comment, but if you insist...)

--
Paul

[McGrandpa]

Post by Paul Catley

Post by McGrandpa
How come both you and Neil ignored my post about wings and 'lift'?

I'm not sure which one you meant, so I'm answering them all :)
(The only one that seems to apply is the push/pull one, which didn't
seem to need further comment, but if you insist...)

One said Pull, the other said Push. I say both :) It's a pressure
difference that gives the effect we call Lift. I figure one can't
exist without the other. It takes at least two things to create a
difference, right? What am I doing? Oh, trying to get both you guys
to agree with me :) LOL!
McG.[all things are true, from a certain point of view]

[Tomasso makes things]

Post by McGrandpa
How come both you and Neil ignored my post about wings and 'lift'?
McG.

Sorry Mr Gramp,

Ny newsreader only downloads 300 headers by default, unless I
tell it to do otherwise, and I didn't see your post. I've pulled done more
headers and read your post. I don't spend all my time in newsgroups,
so I'm sure I miss a lot of stuff that the enthusiasts adore and find
edifying.

What you wrote is a bit vague and folksy, and scattered amongst your
other posts which enthuse about rebarr (whatever that is) and the game.

It wasn't a waste of time to read, but I think I still would have written what
I did if I'd read what you wrote, first.

I expect I'll check out the game, too...

Tomasso.

[McGrandpa]

Post by Tomasso makes things

Post by McGrandpa
How come both you and Neil ignored my post about wings and 'lift'?
McG.

Sorry Mr Gramp,
Ny newsreader only downloads 300 headers by default, unless I
tell it to do otherwise, and I didn't see your post. I've pulled done
more headers and read your post. I don't spend all my time in
newsgroups,
so I'm sure I miss a lot of stuff that the enthusiasts adore and find
edifying.
What you wrote is a bit vague and folksy, and scattered amongst your
other posts which enthuse about rebarr (whatever that is) and the game.
It wasn't a waste of time to read, but I think I still would have
written what I did if I'd read what you wrote, first.
I expect I'll check out the game, too...
Tomasso.

Rebar is round steel rod with raised marks on it used in concrete, gives
it strength. It's plentiful and cheap. It's also heavy. Its the
heaviest single round you will carry. It's kinda for: "When a baddie
absolutely positively must stay put!" Thanks for the response, it's all
just to further enjoyment of a great game.
McG.

[McGrandpa]

Post by Tomasso makes things

Post by Paul Catley

Post by Andrew Lias
Actually, in the real world, bullets drop as quickly as other
objects. Their rapid horizonal velocity allows them to travel much
further than, say, a thrown rock, however, if you were to fire a
bullet parallel to level ground and drop a another bullet from your
hand at the same instant, both would intersect the ground at
approximately the same moment (modulo minor areodynamic effects, of
course).
As for the person who implied that rifling keeps a bullet in the air
longer, the only thing that rifling does is to keep the bullets
orientation stable via gyroscopic effects. A tumbling bullet will,
however, travel less distance due to bad aerodynamics, but it's rate
of descent is about the same.

Nice one Andrew, the first answer I agree with :)

You guys are making this stuff up. You want to get lift on the
trajectory of a
bullet? Well, here is what really happens. The spin imparted by rifling keeps
the bullet pointing in its original direction, BUT the trajectory dips below that.
Eg, Fred aims to hit a target at 800m. To do that, he's pointing above the target.
The bullet continues pointing that way. There is an increasing angle (with distance)
between the bullet's pointing and the trajectory.
THIS imparts lift, and raises the bullet above the quasi-parabolic path (I say quasi
to allow for drag slowing the bullet).
The lift also imposes a drag penalty, so the bullet slows.
An older shooter I knew explained this to me once: His example was hitting a
target at 1200m, and the height the bullet would be at at various distances.
Depending on calibre, projectile, powder load, rifling and even some things
like humidity (and thermals), the bullet (in his example) was about 50 metres
high at 350 metres, for a hit at 1200 metres. In practice, the simply sight by
taking practice shots and adjusting...
Even if the bullet is fired horizontal, there will be a lift effect.
In aerodynamic terms, this means there is a relative pitch (between projectile
heading and trajectory == lift + drag).

Post by Paul Catley
Now I'm waiting for someone to say that the flights on a crossbow
bolt provide lift...

If the flights act as tail drag (with no lift), they will cause the bolt to point into
the direction of air resistance, hence, following the basic
quasi-parabola.
A paper dart is different, because the wings and weight distribution also
maintain stability against rolling. [A crossbow bolt doesn't do this].
This means you can make little trim adjustments to your paper dart, either
for more lift or less drag. The maximum distance is a result of experiment
and craft.
Tomasso.

OK, now apply all that to a length of red hot rebarr fired from a
specially worked over crossbow! That's what we have in this game :)

[Tomasso makes things]

Post by McGrandpa

...Tomasso.

OK, now apply all that to a length of red hot rebarr fired from a
specially worked over crossbow! That's what we have in this game :)

Is that 500 C and 900Km/h? Massive and dense? No flights?

Still no lift.

Given the mass, consequence of drag would be minor. There must be
an artillery manual that describes it somewhere.

But how do you keep it cherry red?

Tomasso

[McGrandpa]

Post by Tomasso makes things

Post by McGrandpa

...Tomasso.

OK, now apply all that to a length of red hot rebarr fired from a
specially worked over crossbow! That's what we have in this game :)

Is that 500 C and 900Km/h? Massive and dense? No flights?
Still no lift.
Given the mass, consequence of drag would be minor. There must be
an artillery manual that describes it somewhere.
But how do you keep it cherry red?
Tomasso

Listen to it when the crossbow is reloaded, and watch the anim. You
hear the bzzzt-hmmmm of the rebarr making contact to a hot circuit and
the inductive loading. The rebarr is just a big low ohms resistor.
What I want to know is why the 'bow doesn't need batteries! Once fired,
the rebarr will cool, but will still be too hot for humans to take,
especially if it hits one :) Exploding barrels should explode instantly
when the rebarr hits it :)
McG.

[Andrew Lias]

Post by Andrew Lias

Post by Andrew Lias
Actually, in the real world, bullets drop as quickly as other

objects.

Post by Andrew Lias
Their rapid horizonal velocity allows them to travel much further
than, say, a thrown rock, however, if you were to fire a bullet
parallel to level ground and drop a another bullet from your hand at
the same instant, both would intersect the ground at approximately

the

Post by Andrew Lias
same moment (modulo minor areodynamic effects, of course).
As for the person who implied that rifling keeps a bullet in the air
longer, the only thing that rifling does is to keep the bullets
orientation stable via gyroscopic effects. A tumbling bullet will,
however, travel less distance due to bad aerodynamics, but it's rate
of descent is about the same.

[...]

Post by Andrew Lias
You guys are making this stuff up.

I'm not making anything up. It's physics 101. However...

Post by Andrew Lias
You want to get lift on the
trajectory of a bullet? Well, here is what really happens. The spin
imparted by rifling keeps
the bullet pointing in its original direction, BUT the trajectory dips below that.

[...]

Post by Andrew Lias
THIS imparts lift, and raises the bullet above the quasi-parabolic path

Unless I'm mistaken, what you are referencing is something known as
the Magnus effect (http://www.geocities.com/k_achutarao/MAGNUS/magnus.html)
which pertains to the way air flows over a rotating surface. If so,
you are correct that I did not account for that.

Be that as it may, a bullet has a very small surface area and air has
fairly low viscosity. Unfortunately, I haven't been able to find any
reference that discusses the exact degree of lift imparted on bullets
via this effect and I'm (frankly) a bit too lazy to work out the
calculations on my own. My guess, however, would be the the amount of
real lift imparted would be fairly nominal under ordinary
circumstances and would fit under what I called minor aerodynamic
effects, especially since the angle of airflow would tend to be fairly
shallow.

If someone has the patience to work through the calculations for some
realistic examples using various elevations, I would be more than
happy to stand corrected, however.

Post by Andrew Lias
Even if the bullet is fired horizontal, there will be a lift effect.

Again, I'm not convinced that it is a significant effect. I suspect
that the deviation from a bullet fired in a vacuum would be slight.

--
Andrew Lias
http://andrewlias.blogspot.com

[Paul Catley]

Post by Andrew Lias
Unless I'm mistaken, what you are referencing is something known as
the Magnus effect
(http://www.geocities.com/k_achutarao/MAGNUS/magnus.html)
which pertains to the way air flows over a rotating surface. If so,
you are correct that I did not account for that.

No, the Magnus effect relates to airflow *perpendicular* to the axis of a
rotating cylinder. The air flows faster where the air is moving with the
rotation (say over it), and slower where it is moving against the rotation (say
under it). The result is lift towards the faster air (which has lower
pressure).

With a bullet, the airflow is parallel with the axis of rotation, so I don't
think the Magnus effect is relevant. Having said that, I haven't followed your
link :)

What Tomasso is talking about I tried to explain in my follow-up post, but maybe
I didn't make a very good job of it. Basically, he's talking about gyroscopic
effects maintaining the attitude of the bullet.

Post by Andrew Lias
Be that as it may, a bullet has a very small surface area and air has
fairly low viscosity. Unfortunately, I haven't been able to find any
reference that discusses the exact degree of lift imparted on bullets
via this effect and I'm (frankly) a bit too lazy to work out the
calculations on my own. My guess, however, would be the the amount of
real lift imparted would be fairly nominal under ordinary
circumstances and would fit under what I called minor aerodynamic
effects, especially since the angle of airflow would tend to be fairly
shallow.
If someone has the patience to work through the calculations for some
realistic examples using various elevations, I would be more than
happy to stand corrected, however.

Post by Tomasso makes things
Even if the bullet is fired horizontal, there will be a lift effect.

Again, I'm not convinced that it is a significant effect. I suspect
that the deviation from a bullet fired in a vacuum would be slight.

I think so too, but since his shooting enthusiast friends are aware of a
relevant effect, I'm prepared to accept it has some minor influence. The
aerofoil area presented to the air to actually generate lift is titchy, though,
and dwarfed by the drag effects at the sides of the bullet. A bullet on a
horizontal trajectory is going to have a miniscule angle of attack to the
airflow as it descends. Then again, a bullet doesn't weigh much, so maybe a
miniscule lift effect is enough to delay its impact with the ground. We're
going to need a ballistics specialist to take it any further either for or
against lift being significant, so I'm afraid we have to leave it there :)

(AGHL breathes a sigh of relief)

--
Paul

[Andrew Lias]

Post by Paul Catley

Post by Andrew Lias
Unless I'm mistaken, what you are referencing is something known as
the Magnus effect
(http://www.geocities.com/k_achutarao/MAGNUS/magnus.html)
which pertains to the way air flows over a rotating surface. If so,
you are correct that I did not account for that.

No, the Magnus effect relates to airflow *perpendicular* to the axis of a
rotating cylinder. The air flows faster where the air is moving with the
rotation (say over it), and slower where it is moving against the rotation (say
under it). The result is lift towards the faster air (which has lower
pressure).

I presumed that the reason he was introducing the issue of a bullet's
attitude is that a rifled bullet will, during its descent, moving
across the air. Even with a shallow angle, the Magnus effect could,
conceivably, come into play *somewhat*.

If he's not talking about the Magnus effect, then I don't understand
his point.

Post by Paul Catley
What Tomasso is talking about I tried to explain in my follow-up post, but maybe
I didn't make a very good job of it. Basically, he's talking about gyroscopic
effects maintaining the attitude of the bullet.

But, sans the Magnus effect, what does that have to do with a bullet's
rate of descent. Since he specifically claims that this, somehow,
produces lift, what's the mechanism that would cause lift?

Post by Paul Catley

Post by Andrew Lias
Again, I'm not convinced that it is a significant effect. I suspect
that the deviation from a bullet fired in a vacuum would be slight.

I think so too, but since his shooting enthusiast friends are aware of a
relevant effect, I'm prepared to accept it has some minor influence.

I'm really not inclined to accept anecdotal evidence, especially when
it's second hand.

Post by Paul Catley
The
aerofoil area presented to the air to actually generate lift is titchy, though,
and dwarfed by the drag effects at the sides of the bullet.

Ah, he's saying that an inclined bullet is a kind of aerofoil.
Hmmm... okay, I can see something to that. I would agree that it is
titchy (and thanks for the new addition to my vocabulary ;-). I don't
think that a tiny cylinder is going to be a very efficient foil.
Again, I'd want to see some calculations before I'd be inclined to
move this out of the column of "minor aerodynamic effects".

Post by Paul Catley
A bullet on a
horizontal trajectory is going to have a miniscule angle of attack to the
airflow as it descends.

Just so. The pressure differential is going to be very negligible.
The shape of the bullet is going to also have an effect. There's a
reason that the cross-sections of aircraft wings aren't arbitrarily
shaped, after all.

Post by Paul Catley
Then again, a bullet doesn't weigh much, so maybe a
miniscule lift effect is enough to delay its impact with the ground.

Maybe. I'll wager a $20 that the delay is negligible.

Post by Paul Catley
We're
going to need a ballistics specialist to take it any further either for or
against lift being significant, so I'm afraid we have to leave it there :)

I think that you're right.

Post by Paul Catley
(AGHL breathes a sigh of relief)

Heh.

[Paul Catley]

Post by Andrew Lias
But, sans the Magnus effect, what does that have to do with a bullet's
rate of descent. Since he specifically claims that this, somehow,
produces lift, what's the mechanism that would cause lift?

An aerofoil which meets the airflow at an "angle of attack" will generate lift.
The gyroscopic effect maintains the bullet's original attitude. As the bullet
descends, its nose will therefore be above the trajectory path, and thus at an
angle to the airflow. This offers some potential for lift. How much is
anyone's guess.

Post by Andrew Lias

Post by Paul Catley
I think so too, but since his shooting enthusiast friends are aware
of a relevant effect, I'm prepared to accept it has some minor
influence.

I'm really not inclined to accept anecdotal evidence, especially when
it's second hand.

I got the impression that his shooting friend had theoretical knowledge in this
area (as you might, if you were a well-informed shooter, same as in any hobby),
so I wouldn't necessarily dismiss it as anecdotal, though we would need to know
more.

Post by Andrew Lias
Ah, he's saying that an inclined bullet is a kind of aerofoil.
Hmmm... okay, I can see something to that. I would agree that it is
titchy (and thanks for the new addition to my vocabulary ;-). I don't
think that a tiny cylinder is going to be a very efficient foil.

No, but if it was efficient it might never land at all ;)

Post by Andrew Lias
Again, I'd want to see some calculations before I'd be inclined to
move this out of the column of "minor aerodynamic effects".

I may have just the thing... (see below)

Post by Andrew Lias
Just so. The pressure differential is going to be very negligible.
The shape of the bullet is going to also have an effect. There's a
reason that the cross-sections of aircraft wings aren't arbitrarily
shaped, after all.

They are shaped to produce lift efficiently. That doesn't mean that an
inefficient aerofoil won't produce some lift. A paper dart does, after all.
All that is required is for airflow over the aerofoil to be faster than airflow
under it. A flat shape meeting the airflow at an angle will do exactly that, as
long as it is aerodynamic enough to prevent smooth airflow becoming turbulent
airflow (which is why a thrown brick won't produce any lift ;) ).

Post by Andrew Lias

Post by Paul Catley
Then again, a bullet doesn't weigh much, so maybe a
miniscule lift effect is enough to delay its impact with the ground.

Maybe. I'll wager a $20 that the delay is negligible.

You may lose that bet. I found a website with some bullet velocity and
trajectory figures. I have to check my calcs, but I believe they show less drop
for targets at various ranges than they theoretically should. It's very
irritating, I know :o/

I'll get back to you, though I think we are the only ones interested ;)

--
Paul

[Andrew Lias]

Post by Paul Catley

Post by Andrew Lias

Post by Paul Catley
I think so too, but since his shooting enthusiast friends are aware
of a relevant effect, I'm prepared to accept it has some minor
influence.

I'm really not inclined to accept anecdotal evidence, especially when
it's second hand.

I got the impression that his shooting friend had theoretical

knowledge in this

Post by Paul Catley
area (as you might, if you were a well-informed shooter, same as in any hobby),
so I wouldn't necessarily dismiss it as anecdotal, though we would need to know
more.

Well, it's anecdotal, by definition, until someone provides actual
data.

Post by Paul Catley

Post by Andrew Lias
Ah, he's saying that an inclined bullet is a kind of aerofoil.
Hmmm... okay, I can see something to that. I would agree that it is
titchy (and thanks for the new addition to my vocabulary ;-). I don't
think that a tiny cylinder is going to be a very efficient foil.

No, but if it was efficient it might never land at all ;)

/smirk

Post by Paul Catley

Post by Andrew Lias
Just so. The pressure differential is going to be very negligible.
The shape of the bullet is going to also have an effect. There's a
reason that the cross-sections of aircraft wings aren't arbitrarily
shaped, after all.

They are shaped to produce lift efficiently. That doesn't mean that an
inefficient aerofoil won't produce some lift.

Certainly. At this point, I'll conceed that a bullet, in flight, will
experience some degree of lift. It's the amount of lift, and whether
or not it significantly contibutes to the bullet's flight time, that's
in question.

Post by Paul Catley

Post by Andrew Lias

Post by Paul Catley
Then again, a bullet doesn't weigh much, so maybe a
miniscule lift effect is enough to delay its impact with the ground.

Maybe. I'll wager a $20 that the delay is negligible.

You may lose that bet. I found a website with some bullet velocity and
trajectory figures. I have to check my calcs, but I believe they show less drop
for targets at various ranges than they theoretically should. It's very
irritating, I know :o/

I'll be interested in seeing what you come up with. I'm still going to
guess that the flight time of a horizontally fired bullet from a
nominal height is going to be about the same as for a dropped bullet.
The fired bullet will, I agree, likely stay in flight longer, but I'm
inclined to suspect that the extended time will be measured in
miliseconds.

Post by Paul Catley
I'll get back to you, though I think we are the only ones interested ;)

Well, why shouldn't we be? ;-)

[Marshall]

Post by Andrew Lias

Post by Paul Catley
I'll get back to you, though I think we are the only ones interested

Well, why shouldn't we be? ;-)

Eh? Wot? Did youse guys say somethin'?
-Marshall

[Tomasso vs noise]

Post by Andrew Lias
...

Post by Paul Catley
What Tomasso is talking about I tried to explain in my follow-up post, but maybe
I didn't make a very good job of it. Basically, he's talking about gyroscopic
effects maintaining the attitude of the bullet.

But, sans the Magnus effect, what does that have to do with a bullet's
rate of descent. Since he specifically claims that this, somehow,
produces lift, what's the mechanism that would cause lift?

?

The angle of attack of a descending bullet, of course.

(1) Let's assume the target is at the same altitude as the gun (and the range is not point blank).
(2) The aimer will point above the target (the the intention of hitting it). This sets the initial attitude of the bullet.
(3) Spin will preserve the attitude of the bullet.

Therefore, there will be an angle of attack between the bullet and its motion. That creates a lift force (because of differential compression of streamlines above vs below the bullet - or however you want to understand Bernoulli).

That's LIFT, Andrew. I'd say LIFT 101.

Magnus is interesting, but does not take the cake here. [In fact, in volleyball, you can get some really interesting serves from non-spinning balls].

My old shooter friend was talking about things like how high a bullet went when you were trying to hit a target at long range. I recall (even though it was many years ago) that the bullet was 150 feet high at some point (but well less than half way). The range was very long but I don't recall exactly how far. This was a person who shot at ranges in the Outback of NSW (Australia), and it was certainly more than 1000 yards (yes, Australians still spoke about yards in those days), possibly over a mile. He use to shoot crows at > 1 mile (but not often) :-). These were high power, very well charged loads intended to shoot a long way. I skimmed some of the long range shooter websites, but they implied that you calibrate for the range and then try for a tight grouping. Discussion of trajectory didn't actually mention trajectory... (!).

My shooter friend is not online (and he's retired) and I haven't seen him for many years, despite trying to find him.

Here's a corollary question. The rules for javelin say the point must strike the ground point first, and javelin weight distributions usually ensure this. However if we used a spinning javelin, there would be lift (or maybe you've call it "glide"). How much further would the spinning javelin go? [Of course it would be disqualified because it would not strike point first].

Tomasso - who once put a javelin tip into the lobe of his right ear... ...good thing I didn't throw that time...

[Paul Catley]

Post by Tomasso vs noise
Here's a corollary question. The rules for javelin say the point must
strike the ground point first, and javelin weight distributions
usually ensure this. However if we used a spinning javelin, there
would be lift (or maybe you've call it "glide"). How much further
would the spinning javelin go? [Of course it would be disqualified
because it would not strike point first].

There is no way that you can manually put enough spin on a javelin to create a
gyroscopic effect, which is what preserves the attitude of the bullet. Even if
you could, it is too long, and the airflow would probably overcome the
gyroscopic effect and force its attitude in line with the trajectory. And even
if it didn't, the proportions of the javelin would mean that the airflow would
be turbulent due to the overwhelming edge effects compared to the sliver-thin
surface of the aerofoil, and turbulent airflow equals no lift. And even if
there *were* minimal lift, it would have negligible influence against the weight
of the thing.

In other words, it wouldn't go any further :)

--
Paul

[Tomasso vs noise]

Post by Paul Catley

Post by Tomasso vs noise
Here's a corollary question. The rules for javelin say the point must
strike the ground point first, and javelin weight distributions
usually ensure this. However if we used a spinning javelin, there
would be lift (or maybe you've call it "glide"). How much further
would the spinning javelin go? [Of course it would be disqualified
because it would not strike point first].

There is no way that you can manually put enough spin on a javelin to create a
gyroscopic effect, which is what preserves the attitude of the bullet. Even if
you could, it is too long, and the airflow would probably overcome the
gyroscopic effect and force its attitude in line with the trajectory. And even
if it didn't, the proportions of the javelin would mean that the airflow would
be turbulent due to the overwhelming edge effects compared to the sliver-thin
surface of the aerofoil, and turbulent airflow equals no lift. And even if
there *were* minimal lift, it would have negligible influence against the weight
of the thing.
In other words, it wouldn't go any further :)

Maybe so, but I've thrown javelins which spun. I've thrown javelins which didn't
nose down by impact.

It was too long ago to recall how they went...

T,

[Walter Mitty]

Post by Andrew Lias

Post by Daniel Vandersluis

Post by Cyde Weys
Not exactly the same speed, but pretty close to it. A crossbow bolt will
probably drop less because it's more aerodynamic, but gravity is still the
dominant factor (and that works equally on all objects).

In that case, should not a bullet, which has no fins as you'll agree,
should drop as quickly as well...?

Actually, in the real world, bullets drop as quickly as other objects.
Their rapid horizonal velocity allows them to travel much further
than, say, a thrown rock, however, if you were to fire a bullet
parallel to level ground and drop a another bullet from your hand at
the same instant, both would intersect the ground at approximately the
same moment (modulo minor areodynamic effects, of course).

I was under the impression that the rifling ket it straighter == better
aero dynamics == longer air time?

Anyway the argument was about a crossbow belt, and if that is flighted
would you not expect it to stay in the air for longer?

I stand corrected if this is not true.

[Paul Catley]

Post by Walter Mitty
I was under the impression that the rifling ket it straighter ==
better aero dynamics == longer air time?

Not longer air time, longer distance. Very different. As Andrew Lias pointed
out elsewhere in this thread, a dropped bullet will hit the ground at the same
time as a horizontally fired bullet, subject to *minor* effects of air currents
(which as far as I can see stand an equal chance of causing either bullet to hit
the ground last).

Post by Walter Mitty
Anyway the argument was about a crossbow belt, and if that is flighted
would you not expect it to stay in the air for longer?
I stand corrected if this is not true.

It isn't true.

The flights on a bolt or arrow aren't provided for lift, they are there for
stability in direction, like rifling on a bullet. They wouldn't generate lift,
since they are shaped symmetrically, and thus they have equal airflow and
pressure on each face of the flight. If they did generate lift, it would be in
the wrong place (not at the centre of gravity), which would unbalance the bolt
instead of stabilising it.

--
Paul

[Walter Mitty]

Post by Paul Catley

Post by Walter Mitty
I was under the impression that the rifling ket it straighter ==
better aero dynamics == longer air time?

Not longer air time, longer distance. Very different.

I realise that.

As Andrew Lias pointed

Post by Paul Catley
out elsewhere in this thread, a dropped bullet will hit the ground at the same
time as a horizontally fired bullet, subject to *minor* effects of air currents
(which as far as I can see stand an equal chance of causing either bullet to hit
the ground last).

Post by Walter Mitty
Anyway the argument was about a crossbow belt, and if that is flighted
would you not expect it to stay in the air for longer?
I stand corrected if this is not true.

It isn't true.
The flights on a bolt or arrow aren't provided for lift, they are there for
stability in direction, like rifling on a bullet. They wouldn't generate lift,
since they are shaped symmetrically, and thus they have equal airflow and
pressure on each face of the flight. If they did generate lift, it would be in
the wrong place (not at the centre of gravity), which would unbalance the bolt
instead of stabilising it.

I'll beta pound to a penny that a flighted arrow stays in the air longer
- less air resistance due to straighter flight in the horiziontal.

Now, wheres my atomic stop watch :)

[Paul Catley]

Post by Walter Mitty

Post by Paul Catley

Post by Walter Mitty
I was under the impression that the rifling ket it straighter ==
better aero dynamics == longer air time?

Not longer air time, longer distance. Very different.

I realise that.

Clearly you don't.

Post by Walter Mitty
I'll beta pound to a penny that a flighted arrow stays in the air
longer - less air resistance due to straighter flight in the
horiziontal.

What the heck has less air resistance got to do with anything? That isn't doing
anything to counter-act acceleration due to gravity. It's just letting the
arrow travel a long way before it hits the ground.

--
Paul

[Andrew Lias]

Post by Walter Mitty

Post by Andrew Lias
Actually, in the real world, bullets drop as quickly as other objects.
Their rapid horizonal velocity allows them to travel much further
than, say, a thrown rock, however, if you were to fire a bullet
parallel to level ground and drop a another bullet from your hand at
the same instant, both would intersect the ground at approximately the
same moment (modulo minor areodynamic effects, of course).

I was under the impression that the rifling ket it straighter == better
aero dynamics == longer air time?

It allows it to travel a greater horizontal distance as a tumbling
bullet is significantly less aerodynamic, but the rate of vertical
descent between a tumbling bullet and a stabilized bullet is, for all
practical purposes, the same .

Post by Walter Mitty
Anyway the argument was about a crossbow belt, and if that is flighted
would you not expect it to stay in the air for longer?

Again, no. The fins on an arrow serve the same purpose (although via
a completely different mechanism) as rifling does for a bullet: it
keeps the arrow from tumbling in flight. Again, that only has an
effect on the amount of horizontal distance it obtains since a
tumbling arrow encounters more resistence in the air and, thus,
travels more slowly through it. The rate of descent is still
uneffected.

Post by Walter Mitty
I stand corrected if this is not true.

It's a common misunderstanding, so no harm done. :-)

--
Andrew Lias
http://andrewlias.blogspot.com

[Walter Mitty]

Post by Andrew Lias

Post by Walter Mitty

Post by Andrew Lias
Actually, in the real world, bullets drop as quickly as other objects.
Their rapid horizonal velocity allows them to travel much further
than, say, a thrown rock, however, if you were to fire a bullet
parallel to level ground and drop a another bullet from your hand at
the same instant, both would intersect the ground at approximately the
same moment (modulo minor areodynamic effects, of course).

I was under the impression that the rifling ket it straighter == better
aero dynamics == longer air time?

It allows it to travel a greater horizontal distance as a tumbling
bullet is significantly less aerodynamic, but the rate of vertical
descent between a tumbling bullet and a stabilized bullet is, for all
practical purposes, the same .

If I fire a tumbling bullet and a rifled bullet at the same time at the
same initial velocity, then you're still trynig to tell me they hit the
ground at the same time? No way.

[Paul Catley]

Post by Walter Mitty
If I fire a tumbling bullet and a rifled bullet at the same time at
the same initial velocity, then you're still trynig to tell me they
hit the ground at the same time? No way.

Yep, though the rifled bullet will be much much further away.

(However, it seems we *may* have a little influence from lift, but not much.
This does *not* apply to bolts or arrows)

--
Paul

[Andrew Lias]

Post by Walter Mitty

Post by Andrew Lias

Post by Walter Mitty

Post by Andrew Lias
Actually, in the real world, bullets drop as quickly as other objects.
Their rapid horizonal velocity allows them to travel much further
than, say, a thrown rock, however, if you were to fire a bullet
parallel to level ground and drop a another bullet from your hand at
the same instant, both would intersect the ground at approximately the
same moment (modulo minor areodynamic effects, of course).

I was under the impression that the rifling ket it straighter == better
aero dynamics == longer air time?

It allows it to travel a greater horizontal distance as a tumbling
bullet is significantly less aerodynamic, but the rate of vertical
descent between a tumbling bullet and a stabilized bullet is, for all
practical purposes, the same .

If I fire a tumbling bullet and a rifled bullet at the same time at the
same initial velocity, then you're still trynig to tell me they hit the
ground at the same time? No way.

Since this topic has opened, the *only* thing I've found that could
possibly give a rifled bullet any lift is something called the Magnus
Effect. The Magnus Effect, however, would only come into play if the
bullets rotating surface were moving across the air. Since a rifled
bullet keeps its orientation, due to gyroscopic forces, the Magnus
Effect might make a minor contribution during the bullets descent as
the air cuts a shallow and increasing angle across the rotating
surface. Frankly, I'm very skeptical that this would be a significant
effect, especially given that bullets has very small surface areas and
are fairly dense objects.

Discounting that, the answer is yes: rifled or tumbling, both bullets
fall just as fast. The only difference is that the tumbling bullet's
*horizontal* velocity is retarded in comparison to the rifled bullet,
which means that it will not travel as far. The vertical component of
its velocity (i.e., its accelleration towards the ground) is going to
be identical.

This is basic physics. The only way an aerodynamic effect could alter
this is if there is some aerodynamic force that would provide a
significant amount of life to the rifled bullet. I have yet to see
anyone propose a lift mechanism that convinces me that there would be
a significant difference.

In summary: yes way!

--
Andrew Lias
http://andrewlias.blogspot.com

[Chung Leong]

Post by Andrew Lias

Post by Walter Mitty

Post by Andrew Lias

Post by Walter Mitty

Post by Andrew Lias
Actually, in the real world, bullets drop as quickly as other objects.
Their rapid horizonal velocity allows them to travel much further
than, say, a thrown rock, however, if you were to fire a bullet
parallel to level ground and drop a another bullet from your hand at
the same instant, both would intersect the ground at approximately the
same moment (modulo minor areodynamic effects, of course).

I was under the impression that the rifling ket it straighter == better
aero dynamics == longer air time?

It allows it to travel a greater horizontal distance as a tumbling
bullet is significantly less aerodynamic, but the rate of vertical
descent between a tumbling bullet and a stabilized bullet is, for all
practical purposes, the same .

If I fire a tumbling bullet and a rifled bullet at the same time at the
same initial velocity, then you're still trynig to tell me they hit the
ground at the same time? No way.

Since this topic has opened, the *only* thing I've found that could
possibly give a rifled bullet any lift is something called the Magnus
Effect. The Magnus Effect, however, would only come into play if the
bullets rotating surface were moving across the air. Since a rifled
bullet keeps its orientation, due to gyroscopic forces, the Magnus
Effect might make a minor contribution during the bullets descent as
the air cuts a shallow and increasing angle across the rotating
surface. Frankly, I'm very skeptical that this would be a significant
effect, especially given that bullets has very small surface areas and
are fairly dense objects.
Discounting that, the answer is yes: rifled or tumbling, both bullets
fall just as fast. The only difference is that the tumbling bullet's
*horizontal* velocity is retarded in comparison to the rifled bullet,
which means that it will not travel as far. The vertical component of
its velocity (i.e., its accelleration towards the ground) is going to
be identical.
This is basic physics. The only way an aerodynamic effect could alter
this is if there is some aerodynamic force that would provide a
significant amount of life to the rifled bullet. I have yet to see
anyone propose a lift mechanism that convinces me that there would be
a significant difference.
In summary: yes way!

Whatever happened to conservation of angular momentum?

[Andrew Lias]

[...]

Post by Chung Leong

Post by Andrew Lias
Discounting that, the answer is yes: rifled or tumbling, both bullets
fall just as fast. The only difference is that the tumbling bullet's
*horizontal* velocity is retarded in comparison to the rifled bullet,
which means that it will not travel as far. The vertical component of
its velocity (i.e., its accelleration towards the ground) is going to
be identical.

[...]

Post by Chung Leong
Whatever happened to conservation of angular momentum?

I'm sorry, but I don't understand what that has to do with a bullet's
rate of descent. Can you elaborate?

--
Andrew Lias
http://andrewlias.blogspot.com

[McGrandpa]

Post by Cyde Weys

Post by Walter Mitty
No, No, you're right. A crossbow flight is made to drop at the same
speed and acceleration as a brick.

Not exactly the same speed, but pretty close to it. A crossbow bolt
will probably drop less because it's more aerodynamic, but gravity is
still the dominant factor (and that works equally on all objects).

That's a fact. You overcome (briefly) the effects of gravity with mass
at velocity. The faster it's going, the farther it travels before
gravity pulls it down.

[Walter Mitty]

Post by McGrandpa

Post by Cyde Weys

Post by Walter Mitty
No, No, you're right. A crossbow flight is made to drop at the same
speed and acceleration as a brick.

Not exactly the same speed, but pretty close to it. A crossbow bolt
will probably drop less because it's more aerodynamic, but gravity is
still the dominant factor (and that works equally on all objects).

That's a fact. You overcome (briefly) the effects of gravity with mass
at velocity. The faster it's going, the farther it travels before
gravity pulls it down.

Who told you that? In that case your'e suggesting that a paper dart will
not travel as fast as a lump of lead when released at the same
(horizontal) velocity.

You're maybe confusing momentum and surface friction with aerodynamics?

[Alex Hunsley]

Post by Walter Mitty

Post by McGrandpa

Post by Cyde Weys

Post by Walter Mitty
No, No, you're right. A crossbow flight is made to drop at the same
speed and acceleration as a brick.

Not exactly the same speed, but pretty close to it. A crossbow bolt
will probably drop less because it's more aerodynamic, but gravity is
still the dominant factor (and that works equally on all objects).

That's a fact. You overcome (briefly) the effects of gravity with
mass at velocity. The faster it's going, the farther it travels
before gravity pulls it down.

Who told you that?

Modern physics, I think.

Post by Walter Mitty
In that case your'e suggesting that a paper dart will
not travel as fast as a lump of lead when released at the same
(horizontal) velocity.
You're maybe confusing momentum and surface friction with aerodynamics?

No, you're confused about what he said. All he's saying is that the
downwards component of the motion, and the effect of gravity on it, is
independent on the other components orthogonal to 'down'. (Neglecting
air resistance.)

[Walter Mitty]

Post by Alex Hunsley

Post by Walter Mitty

Post by McGrandpa

Post by Cyde Weys

Post by Walter Mitty
No, No, you're right. A crossbow flight is made to drop at the same
speed and acceleration as a brick.

Not exactly the same speed, but pretty close to it. A crossbow bolt
will probably drop less because it's more aerodynamic, but gravity is
still the dominant factor (and that works equally on all objects).

That's a fact. You overcome (briefly) the effects of gravity with
mass at velocity. The faster it's going, the farther it travels
before gravity pulls it down.

Who told you that?

Modern physics, I think.

Post by Walter Mitty
In that case your'e suggesting that a paper dart will not travel as
fast as a lump of lead when released at the same (horizontal) velocity.
You're maybe confusing momentum and surface friction with aerodynamics?

No, you're confused about what he said. All he's saying is that the
downwards component of the motion, and the effect of gravity on it, is
independent on the other components orthogonal to 'down'. (Neglecting
air resistance.)

I'm not confusing anything : the main crux was that someone suggested it
should fall (gravity blah blah) at same rate. It doesn't because the
other forces do indeed create components which offset the gravity.

Maybe its all in the wording, but whenever people start waffling on
about gravity you can guarentee that all the "real life" components get
forgotten. It's not an O-Level physcis v=u+at only in the vertical
situation.

[Paul Catley]

Post by Walter Mitty
I'm not confusing anything : the main crux was that someone suggested
it should fall (gravity blah blah) at same rate. It doesn't because
the other forces do indeed create components which offset the gravity.

What are they?

--
Paul

[Walter Mitty]

Post by Paul Catley

Post by Walter Mitty
I'm not confusing anything : the main crux was that someone suggested
it should fall (gravity blah blah) at same rate. It doesn't because
the other forces do indeed create components which offset the gravity.

What are they?

In the case of the paper dart, the ailerons.

[Paul Catley]

Post by Walter Mitty

Post by Paul Catley

Post by Walter Mitty
I'm not confusing anything : the main crux was that someone
suggested it should fall (gravity blah blah) at same rate. It
doesn't because the other forces do indeed create components which
offset the gravity.

What are they?

In the case of the paper dart, the ailerons.

LOL, no. Only a rather sophisticated paper dart would have ailerons. Look up
any discourse on how a plane's wing works :D

--
Paul

[Walter Mitty]

Post by Paul Catley

Post by Walter Mitty

Post by Paul Catley

Post by Walter Mitty
I'm not confusing anything : the main crux was that someone
suggested it should fall (gravity blah blah) at same rate. It
doesn't because the other forces do indeed create components which
offset the gravity.

What are they?

In the case of the paper dart, the ailerons.

LOL, no. Only a rather sophisticated paper dart would have ailerons. Look up
any discourse on how a plane's wing works :D

Oh FFS, I mentioned this ages ago.

A paper dart always has ailerons : you bend the rear of the wing up a
little before launch in order to generate lift and keep the dart in the
air. Paper dart or 747 the pressure differential cause by the air flow
creates lift.

[Paul Catley]

Post by Walter Mitty
Oh FFS, I mentioned this ages ago.

It's you who isn't keeping up :)

Post by Walter Mitty
A paper dart always has ailerons : you bend the rear of the wing up a
little before launch in order to generate lift and keep the dart in
the air. Paper dart or 747 the pressure differential cause by the air
flow creates lift.

You obviously don't know what ailerons are.

Now where's that discourse?

--
Paul

[Cyde Weys]

Post by Walter Mitty
A paper dart always has ailerons : you bend the rear of the wing up a
little before launch in order to generate lift and keep the dart in
the air. Paper dart or 747 the pressure differential cause by the air
flow creates lift.

Errr, no. Ailerons are roll-control flaps that are placed at the tips of
the wings. Basically, you use them to turn, not to generate lift.

And I'd be very impressed if someone could make a paper dart with ailerons.
You'd need some awfully small actuators to move them, and a microchip to
run them.

[Paul Catley]

Post by Cyde Weys
Errr, no. Ailerons are roll-control flaps that are placed at the
tips of the wings. Basically, you use them to turn, not to generate
lift.
And I'd be very impressed if someone could make a paper dart with
ailerons. You'd need some awfully small actuators to move them, and a
microchip to run them.

Indeed :)

(They do affect lift, but only in a less-lift-one-side, more-lift-the-other kind
of way to cause the aircraft to roll)

--
Paul

[Ben Cottrell]

Post by McGrandpa
That's a fact. You overcome (briefly) the effects of gravity with mass
at velocity. The faster it's going, the farther it travels before
gravity pulls it down.

That's wrong - gravity affects all objects all of the time. you cannot
"overcome" gravity, without a force to counter-act it.

Newtons first law:

An object at rest will stay at rest, and a body moving in a straight
line will continue to move in the same direction and at the same speed,
unless an external force acts on it.

Remember - Gravity is acceleration in a downwards direction.

Ignoring Air resistance, If you drop a small stone off a cliff into the
water, and fire a bullet horizontally from a gun at the same time, both
will land in the water at the same time

Why? Because, both start with a vertical velocity of 0. Gravity Does
not affect their horizontal velocity, so any force acting on the
horizontal is totally irrelevent to the downward movement of the object.

[Walter Mitty]

Post by Ben Cottrell
Why? Because, both start with a vertical velocity of 0. Gravity Does
not affect their horizontal velocity, so any force acting on the
horizontal is totally irrelevent to the downward movement of the object.

Which isn't true if a force (such as lift from an airplanes wings) is
countering gravity. This is how planes stay in the air :)

[Ben Cottrell]

Post by Walter Mitty

Post by Ben Cottrell
Why? Because, both start with a vertical velocity of 0. Gravity
Does not affect their horizontal velocity, so any force acting on the
horizontal is totally irrelevent to the downward movement of the object.

Which isn't true if a force (such as lift from an airplanes wings) is
countering gravity. This is how planes stay in the air :)

Yep, it's true for all forces - remember that wings are sloped, changing
the direction of the airflow to a downwards diagonal as it passes over
the wings! (while the diagonal is fairly shallow, it provides enough
vertical force to counter-balance gravity)

[Walter Mitty]

Post by Ben Cottrell

Post by Walter Mitty

Post by Ben Cottrell
Why? Because, both start with a vertical velocity of 0. Gravity
Does not affect their horizontal velocity, so any force acting on the
horizontal is totally irrelevent to the downward movement of the object.

Which isn't true if a force (such as lift from an airplanes wings) is
countering gravity. This is how planes stay in the air :)

Yep, it's true for all forces - remember that wings are sloped, changing
the direction of the airflow to a downwards diagonal as it passes over
the wings! (while the diagonal is fairly shallow, it provides enough
vertical force to counter-balance gravity)

Who are you replying to? This is what I said. I think .../scratches head
and decides to get some sleep/ :)

[Neil Jones]

Post by Ben Cottrell
Yep, it's true for all forces - remember that wings are sloped, changing
the direction of the airflow to a downwards diagonal as it passes over
the wings! (while the diagonal is fairly shallow, it provides enough
vertical force to counter-balance gravity)

That's not quite how a plane's wing works. The characteristic curve is
designed to speed up the airflow over the upper surface of the wing.
This results in reduced pressure on the top surface - the plane is
literally pulled into the air.

___
Neil
AKA HighVis

[McGrandpa]

Post by Neil Jones

Post by Ben Cottrell
Yep, it's true for all forces - remember that wings are sloped,
changing the direction of the airflow to a downwards diagonal as it
passes over the wings! (while the diagonal is fairly shallow, it
provides enough vertical force to counter-balance gravity)

That's not quite how a plane's wing works. The characteristic curve is
designed to speed up the airflow over the upper surface of the wing.
This results in reduced pressure on the top surface - the plane is
literally pulled into the air.
___
Neil
AKA HighVis

Pushed! The greater air pressure under the wing pushes toward lower
pressure :) Just like electricity, electrons always flow from most
positive area to most negative area.
However, the push/pull argument has gone on for decades! No sense in
stopping it now :) I see that both are correct, actually. Natural
law, pressure differences always seek to equalize. Air, hydraulics,
mechanics, electrical, anything that can have a pressure difference.
I've found in the last 25 years that for my troubleshooting to be
accurate (and safe!!!) I will see both as true. Otherwise, I'd get
electrocuted :)
McG.

[Paul Catley]

Post by McGrandpa
Pushed! The greater air pressure under the wing pushes toward lower
pressure :) Just like electricity, electrons always flow from most
positive area to most negative area.
However, the push/pull argument has gone on for decades! No sense in
stopping it now :) I see that both are correct, actually.

So no sense in arguing about it. There is no push or pull... the sky sucks!

--
Paul

[McGrandpa]

Post by Paul Catley

Post by McGrandpa
Pushed! The greater air pressure under the wing pushes toward lower
pressure :) Just like electricity, electrons always flow from most
positive area to most negative area.
However, the push/pull argument has gone on for decades! No sense in
stopping it now :) I see that both are correct, actually.

So no sense in arguing about it. There is no push or pull... the sky sucks!

LOL! Pressure difference. An object is obeying natural Law in a given
medium.

[Ben Cottrell]

Post by Neil Jones

Post by Ben Cottrell
Yep, it's true for all forces - remember that wings are sloped, changing
the direction of the airflow to a downwards diagonal as it passes over
the wings! (while the diagonal is fairly shallow, it provides enough
vertical force to counter-balance gravity)

That's not quite how a plane's wing works. The characteristic curve is
designed to speed up the airflow over the upper surface of the wing.
This results in reduced pressure on the top surface - the plane is
literally pulled into the air.

Well, i'm no avionics expert :-) But the principle is the same..
there must be a vertical force somewhere.

(OK, we're apparently all saying the same thing.. i'll keep shh about it
now ;-) )

[Paul Catley]

Post by Neil Jones

Post by Ben Cottrell
Yep, it's true for all forces - remember that wings are sloped,
changing the direction of the airflow to a downwards diagonal as it
passes over the wings! (while the diagonal is fairly shallow, it
provides enough vertical force to counter-balance gravity)

That's not quite how a plane's wing works. The characteristic curve is
designed to speed up the airflow over the upper surface of the wing.
This results in reduced pressure on the top surface - the plane is
literally pulled into the air.

Very good Neil, all that flightsimming is paying off ;)

You're right about how lift is generated, but the curvature only improves the
efficiency of the wing. A paper dart will also generate lift, with no
curvature. As it happens, Ben is also right about a sloping wing generating
lift, but not about how it works :)

This has very little to do with crossbow bolts, of course.

--
Paul

[McGrandpa]

Post by Ben Cottrell

Post by McGrandpa
That's a fact. You overcome (briefly) the effects of gravity with
mass at velocity. The faster it's going, the farther it travels
before gravity pulls it down.

That's wrong - gravity affects all objects all of the time. you
cannot "overcome" gravity, without a force to counter-act it.
An object at rest will stay at rest, and a body moving in a straight
line will continue to move in the same direction and at the same
speed, unless an external force acts on it.
Remember - Gravity is acceleration in a downwards direction.
Ignoring Air resistance, If you drop a small stone off a cliff into
the water, and fire a bullet horizontally from a gun at the same
time, both will land in the water at the same time
Why? Because, both start with a vertical velocity of 0. Gravity
Does not affect their horizontal velocity, so any force acting on the
horizontal is totally irrelevent to the downward movement of the object.

go back and read what I said, gee! For it to stay in the air longer
without dropping, considerably more force must be exerted to overcome
inertia and give it a velocity of say 600 fps rather than 300 fps. At
300, it will drop more and quicker than at 600.
You're right though, it comes down to simple mechanics :)
McG.

[Paul Catley]

Post by McGrandpa
go back and read what I said, gee! For it to stay in the air longer
without dropping, considerably more force must be exerted to overcome
inertia and give it a velocity of say 600 fps rather than 300 fps. At
300, it will drop more and quicker than at 600.

I know what you're getting at, but you're not phrasing it correctly. It won't
stay in the air longer without dropping, it will travel further. The duration
of the flight before hitting the ground will be the same (assuming that in this
branch of the thread, we're talking about rebar from crossbows, not rapidly
spinning bullets). If something gets in the way before it hits the ground, it
will hit the target higher up than the slower bullet, but that's because its
flight time was shorter. The 300ft/s bullet won't drop quicker, it will drop at
the same rate, but it will travel less distance before it hits the ground.

--
Paul

[McGrandpa]

Post by Paul Catley

Post by McGrandpa
go back and read what I said, gee! For it to stay in the air longer
without dropping, considerably more force must be exerted to overcome
inertia and give it a velocity of say 600 fps rather than 300 fps.
At 300, it will drop more and quicker than at 600.

I know what you're getting at, but you're not phrasing it correctly.
It won't stay in the air longer without dropping, it will travel
further. The duration of the flight before hitting the ground will
be the same (assuming that in this branch of the thread, we're
talking about rebar from crossbows, not rapidly spinning bullets).
If something gets in the way before it hits the ground, it will hit
the target higher up than the slower bullet, but that's because its
flight time was shorter. The 300ft/s bullet won't drop quicker, it
will drop at the same rate, but it will travel less distance before
it hits the ground.

Ok, I can see that. Not the specifics, we don't have the formulae to
work with. I think we may well be missing some of the criteria to work
with too :)

and yes, rebar, no rifling. Just literally shot off the bows string
with only the crossbow for alignment during launch. Its massive enough
and the flight short enough that windage won't matter. Only the
elevation logistics.

There are more variables affecting bullets and quarrels in the other
threads of the discussion. I work with rebar kind often. And if it's
even 3/8", for it to be redhot leaving the breech and for it to be
buried in stone or brick walls makes it one helluva weapon. And a
nasty one. Just imagine suddenly realizing you can't move cause you'r
head is stuck to a wall....and it hurts...and it's HOT...and its <you
die> ...[shudders]
McG.

[Paul Catley]

Post by Walter Mitty
No, No, you're right. A crossbow flight is made to drop at the same
speed and acceleration as a brick.
Sigh.

Hmm, sarcasm. Are you suggesting that it doesn't? Reasons please.

--
Paul

[McGrandpa]

Post by Cyde Weys

Post by Walter Mitty
Another example of a little knowledge being a dangerous thing.
OK, here's a simple example for you.
Take a piece of paper and make it into a winged dart. Throw that. Get
another piece of paper and chew it up. Throw that at the same speed.
Which goes the furthest?
Ah yes!
The key being, of course, pressure differentials (theory of flight),
air pressure (you conveniently chose to ignore it), air currents etc.

Ahhh, so you are saying that crossbow bolt has wings on it that
produce lift? If not, it's pretty much a standard projectile that
should drop at the same rate as anything else. And I didn't see any
wings or fins on the crossbow bolts in my game ...

In Half-Life, the crossbow bolt didn't drop. In HL2, the 'bolt' is a
length of induction heated steel rebarr! And, it DOES drop over
distance. That rebarr has a lot of mass. It would weigh easily over a
pound. So for short to medium range, the initial velocity will keep
drop very slight. For long range you would have considerable drop, and
it does in game. Just imagine a cherry hot chunk of rebarr fired at
you at say 600 mph. At that speed it will cover a half a mile pretty
quick. The concept model for this one in HL2 may not be super
realistic, but it sure is fun!
McG.

[Paul Catley]

Post by McGrandpa
In Half-Life, the crossbow bolt didn't drop. In HL2, the 'bolt' is a
length of induction heated steel rebarr! And, it DOES drop over
distance. That rebarr has a lot of mass. It would weigh easily
over a pound. So for short to medium range, the initial velocity
will keep drop very slight.

Over a set distance, yes. Over a set time, no.

--
Paul

[McGrandpa]

Post by Paul Catley

Post by McGrandpa
In Half-Life, the crossbow bolt didn't drop. In HL2, the 'bolt' is
a length of induction heated steel rebarr! And, it DOES drop over
distance. That rebarr has a lot of mass. It would weigh easily
over a pound. So for short to medium range, the initial velocity
will keep drop very slight.

Over a set distance, yes. Over a set time, no.

at given speed, time is distance.

[Alex Hunsley]

Post by Walter Mitty

Post by Cyde Weys

How come we never get to use the sniper rifle? You know, the
cool one with the green laser sight that the enemies use against
you? I
got very eager when the sniper part of the game came up because I
was hoping I'd be able to get a sniper rifle from killing one of
them ... but it didn't happen. Instead all we get is this stupid
crossbow, which is better than nothing (it's the only weapon that
can zoom), but its long travel time makes it hard to hit moving
targets at range. And if they had made it realistic and actually
added drop, well then, it'd be even harder to use.

Eh???? It DOES drop.

Well then, not enough to be noticeable :-/
(Err, I should say, given its travel time, it should drop a lot more
than the paltry bit it currently does. I'm saying it's not
influenced by -9.81 m/s^2 as it should be).

Do you think its velocity might affect it a little? Does an arrow drop
quicker than say, a stone when fired at the same speed?

??? Dude, that makes no sense. Velocity is a vector that has three
components ... x, y, and z. For the purposes of making it simpler,
let us only consider movement in two directions, x and y. The x
component of velocity is unchanging (unless you account for air
resistance), while the y component of velocity will accelerate at
-9.81m/s^2. It doesn't matter whether you are considering an arrow, a
stone, or a feather ... everything drops at the same speed (again,
neglecting air resistance). And everything drops at the same speed
independent of its horizontal velocity. Try a simple thought
experiment ... dribble a basketball while standing still. Then
dribble a basketball while moving really quickly. It doesn't take any
longer for the basketball to return to your hand when you are moving
quickly because the x and y components of the velocity are independent.

Another example of a little knowledge being a dangerous thing.
OK, here's a simple example for you.
Take a piece of paper and make it into a winged dart. Throw that. Get
another piece of paper and chew it up. Throw that at the same speed.
Which goes the furthest?
Ah yes!
The key being, of course, pressure differentials (theory of flight), air
pressure (you conveniently chose to ignore it), air currents etc.

... and you obviously missed the part of his post where he noted he was
neglecting air resistance. Twice.

[Walter Mitty]

Post by Alex Hunsley
... and you obviously missed the part of his post where he noted he was
neglecting air resistance. Twice.

You can neglect all you like : but its not valid. Its like saying this
program is 100% bug free if you neglect all the bugs.

[Paul Catley]

Post by Walter Mitty
Another example of a little knowledge being a dangerous thing.

Likewise.

Post by Walter Mitty
OK, here's a simple example for you.
Take a piece of paper and make it into a winged dart. Throw that. Get
another piece of paper and chew it up. Throw that at the same speed.
Which goes the furthest?

What has that got to do with crossbow bolts? (Be very careful)

Post by Walter Mitty
Ah yes!
The key being, of course, pressure differentials (theory of flight),
air pressure (you conveniently chose to ignore it), air currents etc.

And? What are you suggesting these factors do? I'm interested; you've been
very critical but very non-specific in all your responses.

--
Paul

[Walter Mitty]

Post by Paul Catley

Post by Walter Mitty
Another example of a little knowledge being a dangerous thing.

Likewise.

Post by Walter Mitty
OK, here's a simple example for you.
Take a piece of paper and make it into a winged dart. Throw that. Get
another piece of paper and chew it up. Throw that at the same speed.
Which goes the furthest?

What has that got to do with crossbow bolts? (Be very careful)

Post by Walter Mitty
Ah yes!
The key being, of course, pressure differentials (theory of flight),
air pressure (you conveniently chose to ignore it), air currents etc.

And? What are you suggesting these factors do? I'm interested; you've been
very critical but very non-specific in all your responses.

Look up any discourse on how a planes wing work. With regard to air
currents etc, clearly a slight upbreeze or temperature differential is
not going to alter a bricks rate of fall in the same way as a paper dart.

With Gordons bow, which appears to fire a lump of metal all this might
have no impact whatsoever :)

[Paul Catley]

Post by Walter Mitty

Post by Paul Catley

Post by Walter Mitty
The key being, of course, pressure differentials (theory of flight),
air pressure (you conveniently chose to ignore it), air currents etc.

And? What are you suggesting these factors do? I'm interested;
you've been very critical but very non-specific in all your
responses.

Look up any discourse on how a planes wing work.

LOL! :D I'll be sure to do that :)

But hang on, you've looked up one of these discourses yourself, haven't you?
Can *you* tell me how a plane's wing works? That would save me the effort.

Post by Walter Mitty
With regard to air
currents etc, clearly a slight upbreeze or temperature differential is
not going to alter a bricks rate of fall in the same way as a paper dart.

I ask again: what have paper darts got to do with crossbow bolts?

Post by Walter Mitty
With Gordons bow, which appears to fire a lump of metal all this might
have no impact whatsoever :)

That at least is true.

--
Paul