Bullet lift, does it exist?

Catshooter, well said.

And thanks for the great explanation of what REALLY happens to a bullet. It's been too long for me since physics class, but you 're-ignited' some synapses that hadn't fired since my BS in Mathematics was fresh.

Thanks,
AJ

Blimey.



Catshooter,

What you are signally failing to understand is that it is the overturning moment itself that, through the process of gyroscopic stabilisation, ultimately causes a correctly spun projectile's nose to broadly follow the trajectory.





Can't stop to type more; I have to get a signal off to recall all the artillery point detonating fuzes we've been mistakenly using all these years.

Apparently the shells always land on their sides!

...an unknown ballistic expert has chosen LRH to release stunning new theories that projectiles always land at the same angle as they were launched..

..this ballistic expert has discovered that at 19km, 155 shells are point 43 degrees up in the air when they land. At 24.7km, they're landing pointing 47 degrees in the air.

...better recall all the forward looking radar fuzes too...they won't be sensing the ground if the shells are coming in looking 47 degrees up in the air.

Good thing he's pointed it out.



...and while I'm at it, recall all the 6DOF ballistic programs, the shells aren't adopting a yaw of repose either.

...apparently they're just rolling sideways.


...and the Earth is flat.

AJ Peacock said:

Catshooter, well said.

And thanks for the great explanation of what REALLY happens to a bullet. It's been too long for me since physics class, but you 're-ignited' some synapses that hadn't fired since my BS in Mathematics was fresh.

Thanks,
AJ

Click to expand...

It appears there may be a Flat Earth Society meeting in the offing

CatShooter,

Just wanted to let you know, that you got me thinking enough about this stuff, to actually dig out my copy of "Hatchers Notebook". There is a short section on page 555 that anyone reading this thread might be interested in. Of course, since most of the folks reading this probably don't have a copy. And may not even know who Julian Hatcher is, I'll include it here (I'm sure he won't mind ;-0 ). The comments in ()'s and CAPS are mine.

------------------------

Action of the Air

The air not only tries to hold the bullet back, but also causes it to drift in the direction of the spin. The action is as follows: as the bullet starts to fall from the action of gravity after it has started its flight, the air pressure under its point causes the point to deviate in the direction of rotation, because of the fact that the rapidly rotating bullet acts as a gyroscope, and any pressure causes the axis of rotation to swing at right angles to the direction of the pressure. Thus if the bullet is rotating to the right, the upward pressure on the nose causes it to swing very slightly toward the right, and as the bullet presents its elongated surface to the air resistance (BECAUSE THE POINT DOES NOT FOLLOW THE ARC OF TRAJECTORY!!), it is shoved bodily over to the right. The amount of drift is not great; in the service .30 M2 bullet it amounts to 6.7 inches to the right at 1000 yards.
While the most important effect of air resistance in exterior ballistic calculations has to do with the retardation of the bullet, the action of the air also makes necessary the provision of rifling, so that subject will be discussed here to get it out of the way before studying the effects of retardation of the bullet by the air.

-----------------------

Since Julian Hatcher believed that the air pressure increased under the nose of the bullet, I would wager that bullets tend to 'sail' or colloquially 'have lift'.

Later,
AJ

Brown Dog said:

It appears there may be a Flat Earth Society meeting in the offing

Click to expand...

Most excellent, the founding members can be Sir Isaac Newton and Julian Hatcher. I'd love to join, and I'm sure Cat Shooter wouldn't be opposed to joining our ragtag bunch of miscreant math dudes!

hehehehe

AJ

AJ Peacock said:

Catshooter, well said.

And thanks for the great explanation of what REALLY happens to a bullet. It's been too long for me since physics class, but you 're-ignited' some synapses that hadn't fired since my BS in Mathematics was fresh.

Thanks,
AJ

Click to expand...

AJ...

There are a LOT of myths in shooting - and those myths cripple shooters, because it keeps them from pushing the envelope (though I guess many don't want to).

Like the one about bullets tumbling when they go subsonic.

Lots of guys believe that one.

But (it's an easy test) get a bunch or '06 tracer, a spotting scope, and a good friend.

Have your friend shoot the tracers in a place where you can shoot them up at about 10 degrees... and watch them in the scope.

They do NOT tumble, or change direction, or do anything else, except gently fly over the horizon - and most of that flight is under 900 fps.

I have done this with a 50BMG, using brown tipped "VLT" (very long trace), that stays lit for about three weeks .

They do NOT tumble or change direction.

Guys that believe this one, never fired a round of tracer in their lives.

-

There was an article in "Precision Shooting Magazine" about 4 years ago, that said that when a bullet goes below 1,050 fps, it immediately turns 45 degrees DOWN and hits the earth under it.

There were about 10,000 SAW gunners that fell off of their chairs at that one.

Most of this crap can be killed with a simple test, and some digging in the dark recesses of the mind (assuming that it is still working).


.

AJ Peacock said:

CatShooter,

The comments in ()'s and CAPS are mine.

------------------------

Action of the Air

The air not only tries to hold the bullet back, but also causes it to drift in the direction of the spin. The action is as follows: as the bullet starts to fall from the action of gravity after it has started its flight, the air pressure under its point causes the point to deviate in the direction of rotation, because of the fact that the rapidly rotating bullet acts as a gyroscope, and any pressure causes the axis of rotation to swing at right angles to the direction of the pressure. Thus if the bullet is rotating to the right, the upward pressure on the nose causes it to swing very slightly toward the right, and as the bullet presents its elongated surface to the air resistance (BECAUSE THE POINT DOES NOT FOLLOW THE ARC OF TRAJECTORY!!),

Click to expand...

Aaagh! I'm going to give up. What's being described in that passage is the mechanism by which the yaw of repose is established.



To spin stabilise statically unstable projectiles they must be spun sufficiently rapidly to ensure their angular momentum is capable of gyroscopically neutralising the aerodynamic overturning moment acting on them.

The actual mechanism by which this is achieved is as follows: when the projectile is yawed in one plane it experiences an overturning moment in that plane, the gyroscopic reaction to this moment then yaws the projectile in a plane normal to the original one and thus creates a 'negative feedback' situation which causes the yaw in the original plane to decrease (although there will be some residual yaw in the other plane).

For a gyroscopically stabilised projectile following a normal trajectory, the zero yaw position will 'fall away' from the projectile axis as the trajectory curves downwards due to gravity. This causes the projectile to be effectively yawed upwards and the gyroscopic response to this creates a residual equilibrium yaw in the horizontal plane.

AJ Peacock said:

Most excellent, the founding members can be Sir Isaac Newton and Julian Hatcher. I'd love to join, and I'm sure Cat Shooter wouldn't be opposed to joining our ragtag bunch of miscreant math dudes!

hehehehe

AJ

Click to expand...

No! Sir Isaac's 1st law is being misapplied here by Catshooter, a direction changing force IS being applied to the projectile to cause it's nose to broadly (ie less the yaw of repose) follow the trajectory...but confusingly (to some!!) it is the overturning (ie nose lifting) moment.

...which is why all his "it turns left" nonsense is back to front....nothing's trying to push the nose down (which would indeed have a leftwards reaction) the nose is going down ultimately as the result of gyroscopic stablisation.



Anyway, I give up. I'll not waste anymore time trying to re-educate Flat Earth 'the rest of the world is wrong' self taught ballisticians




Got to get back to recalling all those point detonating fuzes.

Brown Dog said:

No! Sir Isaac's 1st law is being misapplied here by Catshooter, a direction changing force IS being applied to the projectile to cause it's nose to broadly (ie less the yaw of repose) follow the trajectory...but confusingly (to some!!) it is the overturning (ie nose lifting) moment.

...which is why all his "it turns left" nonsense is back to front....nothing's trying to push the nose down (which would indeed have a leftwards reaction) the nose is going down as the result of gyroscopic stablisation reacting to the UPWARD moment on the CP.

Click to expand...

What force are you talking about that causes the nose to follow the trajectory? I don't recall you enlightening us about it.

CatShooter didn't say "it turns left" he said that if a force were applied (as you suggest), it 'would turn left', which it doesn't, therefore there is NO force applied as you surmise.

Please enlighten us, Isaac, Julian and I await your explanation of this mythical force that pushes up on the tail of the bullet exactly in line with the arc of trajectory (or is it pushing down on the nose). And please explain to us, how it doesn't push the bullet to the left (assuming a CW rotation), as I would have assumed that the right hand rule and conservation of momentum (rotational in this case) should still apply.

I'm also curious, why those long passes that Peyton Manning throws, don't all come down nose first? Or does this law only apply to bullets? What about evil kneivel, why didn't his motorcycle follow the arc of trajectory? If I remember correctly, his motorcycle tended to stay in pretty much the same attitude it left the ramp?

I humbly await your explanations.

AJ

AJ Peacock said:

What about evil kneivel, why didn't his motorcycle follow the arc of trajectory? If I remember correctly, his motorcycle tended to stay in pretty much the same attitude it left the ramp?

Click to expand...

Bloody Hell!

Was Evil Kneivel's motorbike spin stabilised?!!


What RPM?





and those long passes, are they gyroscopically stabilised too??







So to answer your question

AJ Peacock said:

Or does this law only apply to bullets?

Click to expand...

change 'bullet' to 'spin stabilised projectile' and YES



I've already explained what's going on, and where the force comes from (the OVERTURNING MOMENT) but you fellows don't want to understand.




....and meanwhile properly stabilised shells just keep on landing point first.



The firing table elevation for an L15 155mm shell Charge 8 at 24.7km is 834mils (approx 47degrees).

Your theories state that the shell will retain that angle throughout its flight and land still pointing up at 47degrees.

But they don't.

Weird isn't it?


Still, from your Flat Earth perspective, at least you don't have to worry about Coriolis !




Abandon Ship!

No, evil's bike wasn't spin stabilized. So please for my benefit, what causes the point of a bullet to EXACTLY follow the trajectory. To tell you the truth, your explanation of 'overturning moment' didn't completely clear this all up for me.

You said, that a "gyroscopically stabilised projectile following a normal trajectory", which I think we all agree with.

But you lost me in explaining how/if the nose of the bullet follows that path (normal trajectory). You said:

"the zero yaw position will 'fall away' from the projectile axis as the trajectory curves downwards due to gravity. This causes the projectile to be effectively yawed upwards and the gyroscopic response to this creates a residual equilibrium yaw in the horizontal plane."

Wouldn't this essentially mean that a gyroscopically stable projectile would tend to hold its attitude, even though it would (as a whole) be following a normal trajectory?

I'm really trying to follow you here and not trying to inflame etc. Just trying to figure out and understand how the nose follows the trajectory exactly.

Thanks,

AJ

Brown Dog said:

Bloody Hell!

Was Evil Kneivel's motorbike spin stabilised?!!


What RPM?





and those long passes, are they gyroscopically stabilised too??



So to answer your question change 'bullet' to 'spin stabilised projectile' and YES



I've already explained what's going on, and where the force comes from (the OVERTURNING MOMENT) but you fellows don't want to understand.

....and meanwhile properly stabilised shells just keep on landing point first.

Weird isn't it, the firing table elevation for an L15 155mm shell Charge 8 at 24.7km is 834mils (approx 47degrees). Your theories state that it will retain that angle throughout its flight and land still pointing up at 47degrees. But they don't.

..and the other fellow seems to have started chewing backy and waffling on about the last time he watched tracer burnout

Click to expand...

Brown Dog said:

Bloody Hell!

Was Evil Kneivel's motorbike spin stabilised?!!

Click to expand...

It had tail fins - a dopey remark!

]"and those long passes, are they gyroscopically stabilised too??

Click to expand...

Another dopey remark. Read Kerby's comments on footballs.

If you had any real knowledge, you could answer with an explanation, instead of childish remarks.

I've already explained what's going on, and where the force comes from (the OVERTURNING MOMENT) but you fellows don't want to understand.

Click to expand...

And just where does the energy of this "overturning moment" come from - where is it generated, and how does it work, without envolking the other laws of physics.

You run your mouth, but you explain nothing.

On "Overturning Moment":

"The point of the longitudinal axis, at which the resulting wind force appears to attack is called the centre of pressure CPW of the wind force, which, for spin-stabilized bullets is located ahead of the CG. As the flow field varies, the location of the CPW varies as a function of the Mach number. Due to the non-coincidence of the CG and the CPW, a moment is associated with the wind force. This moment MWis called overturning moment or yawing moment. For spin-stabilized projectiles MWtends to increase the yaw angle and destabilizes the bullet. In the absence of spin, the moment would cause the bullet to tumble.

Click to expand...

So... for a (what did you call yourself)... " and a military trained gunnery expert (me)". you don't know crapola about the words you throw around.

The "Overturning moment" is NOT a moment that causes a bullet to track the tangent of the arc... it is a motion, or tendency to change, from a wind force, and NOT a force you claiom it is.

I think a "...and a military trained gunnery expert (me)"... you are not.

That leaves one other possibility - a typical BS artist - gun shops here in the states are full of them... they were ALL snipers, or artillery specialistas, or Seals, or UDT, and they throw around words to impress the kids, but eventually get busted as "Posers".

....and meanwhile properly stabilised shells just keep on landing point first.

Click to expand...

Not hardly.

The firing table elevation for an L15 155mm shell Charge 8 at 24.7km is 834mils (approx 47degrees).

Your theories state that the shell will retain that angle throughout its flight and land still pointing up at 47degrees.

But they don't.

Weird isn't it?[/quote]

And so I guess they don't have rotational (spin) drift either, and there is no need to compensate for it... I guess things are different over there.

Abandon Ship!

Click to expand...

It's about time - you wanted an e-fight, you got it - Workie for me


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CatShooter,

I found a nice couple of diagrams that helped me understand a little bit more. The "Yaw of Repose" that our friend was talking about is interesting.

In the following diagram (from a site that quoted by BWaites early in the thread)
http://www.nennstiel-ruprecht.de/bullfly/fig25.htm

Am I reading that chart correct, in that the axis of a bullet doesn't follow the trajectory exactly? At 3000m the difference between the bullet axis and the trajectory is up to 1/2 degree?

Am I reading that right?


AJ

CatShooter said:

It had tail fins - a dopey remark!


Another dopey remark. Read Kerby's comments on footballs.

If you had any real knowledge, you could answer with an explanation, instead of childish remarks.
.

Click to expand...

And to top it all, you don't even understand ironic humo(u)r.



Catshooter,

In your simple "I once saw tracer burn out" understanding of ballistics;

enlighten me as to how point detonating impact fuzes function.


Base your answer on a shell fired at a 47 degree elevation.




AJ,

What a relief that one of you does humour!

I'll extend what I wrote earlier:

"The actual mechanism by which this is achieved is as follows: when the projectile is yawed in one plane it experiences an overturning moment in that plane, the gyroscopic reaction to this moment then yaws the projectile in a plane normal to the original one and thus creates a 'negative feedback' situation which causes the yaw in the original plane to decrease (although there will be some residual yaw in the other plane)."

This mechanism operates satisfactorily whether a projectile is statically stable or unstable...but a problem arises if the projectile is neutrally stable....because then there is no aerodynamic overturning moment (the upward pressure being applied to the nose due to the nose attitude caused by the 'falling' trajectory) and gyroscopic stabilisation will not work correctly and the projectile will tend to retain its initial attitude. Thus, if the projectile is nearly neutrally stable, or the spin rate is excessive, there WILL be a tendency for the projectile to retain its firing attitude, but such a projectile would be described as 'overstable'.

Thus there is an upper and lower bound on the spin rate used for gyroscopically stabilising statically unstable projectiles. If the spin is too low then the projectile will not have enough angular momentum to counteract gyroscopically the aerodynamic overturning moment, if it has too much spin it will be overstable (and yes, it would then land at its firing attitude).

So, appropriately spun, it is the gyroscopic reaction and its 'negative feedback' loop as it responds to off axis airflow that causes the nose to follow the trajectory.




Just popped back to edit, you posted whist I was typing. The yaw of repose is usually a few fractions of a degree. Don't ask Catshooter, he doesn't believe it exists.....which, if he were correct, would rather render 6DOF ballistic modelling irrelevant!

Just popped back again, Your link actually states "Although, for the example shown in the drawing, the yaw of repose never exceeds half a degree" under the graph