Bullet lift, does it exist?

[AJ Peacock]

Brown dog,

What about the diagram? Doesn't it show that the axis of the bullet varies from the trajectory (up to 25 degrees from the chart)?

Unless I'm reading this incorrectly, it shows that the nose DOESN'T follow the trajectory.

Also, just curious what 'appropriately stabilized' is? In the real world, would you say a 300gr SMK spun at 1 revolution in 10" is Over, Under or appropriately stabilized for 3300fps? That's about 240,000 rpm. If it is in your definition Over Stabilized, then according to your last post
"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'."

And we all agree.

from BRown Dog:
"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

I didn't see that, and was reading the label on the right as the angle of Yoaw of repose.

AJ

 

[Brown Dog]

Catshooter,

Since my last post, I notice you've reworked your earlier post rather substantially.


Can't say I like the ad hominem stuff, but sadly that appears to be your style.

I won't degrade myself to match.




As regards the discussion; the piece you've added in about the overturning moment is spot on.


What you don't understand

is

the

effect

the

moment

has

on

a

gyroscopically

stabilised

projectile



I typed that slowly for you


Read my answer to AJ above. I doubt you'll understand, but the least you can do is try...isn't it?


Meanwhile please have a go at my earlier question:


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.

 

[Buffalobob]

Smooth bore mortars are fin stabilized much like an arrow. If you put the drag force far behind the CG then you will achieve a slightly different result than with spin staiblized projectiles. As stated a 4.2 mortar is spin staiblized.

Fin stabilized projectiles have a whistle from the holes in the fins and you will know when to make your peace with your maker from the sound of the whistle, except sometimes you are just lucky and there is a lot of humus and it buries far into it before it detonates.

Unstable spin stabilized projectiles (known as "short rounds") actually tumble and you will also hear them coming and they make a "whoop, whoop, whoop" sound that gets louder as it comes closer. Your ears can actually calculate whether you are fixing to be meeting St Peter in the next few nanoseconds. Because they are tumbling they come at you pretty slow so you can jump right or left or just grit your teeth and pray. Once again, if you have been living right and eating your brocoli it may land badly and not detonate immediately, at which time you run like a sumbitch and wait a while and carefully ease back and get your rifle and ammo and gear. You do not go close to that round because St Peter might change his mind and decide he wants to see you.

 

[Brown Dog]

AJ,

Another quote from your link (well, the page preceding the one linked)


"In other words, the maximum yaw angle, which occurs close to the muzzle, is damped out as the bullet moves on. After a traveling distance of a few thousand calibers, depending on the damping rate, the transient yaw angle practically approaches zero."


If you're happy with the concept described (of bullets being rather unstable at launch, but stabilising as they get further downrange).......Simply apply it to the apparent yaw angle produced by the trajectory falling away from the bullet....all that's happening is that that yaw is being gyroscopically damped out to match the changing airflow....in just the same way that transient yaw is damped.

Hope that makes it a little clearer!

 

[daveosok]

Wow all this typing on such a mute subject must be at best for all involved an "exercise in futility".

So we have the mathematical equations, theory, and test data to make a 3500 yard first shot cold bore on a p-dog sized target with 1000% accuracy.

I think not it still takes a few shots to hit the dog despite whatever amount of spin drifting yaw dropping gravity pushing drag defying bullets we use lol.

Yall have fun, active lasers solve all this if you can afford them!!

 

[goodgrouper]

Wow all this typing on such a mute subject must be at best for all involved an "exercise in futility".

Yes. I don't even know what we're debating anymore or who is saying what. I thought this was a thread about bullet's rise above LOS in atmosphere as opposed to a bullet fired in a vacuum?

 

[Stormrider]

...and my head hurts from reading all this.

 

[bwaites]

Since I apparently (according to CatShooter anyway) don't understand any of this, will someone please let me know just when we determine if bullets actually have lift? I'm sure a few others would appreciate knowing as well.

I'm sorry Catshooter, my very first comment in the original thread was intended as a satirical comment, but evidently that was completely missed. I then followed up with a few more smart *** comments, also all missed. Now I understand that you just take everything literally, so I can make appropriate comments in the future.

As for the lift issue, none of my reading has yet confirmed anything one way or the other.

AJ, I've spent years coaching quarterbacks, (2 sons with scholarship offers as college QB's will do that to you!). I've attended workshops, I've coached mechanics. (Including attending Peytons Manning Passing Academy with my son) Any well thrown pass thrown with an arc will come down on the front half of the football, most passes qualify at the NFL level. You can throw a pass that doesn't, but it won't be a well thrown pass. (I left the original "sailing pass" quote alone, but a pass that "sails" is released a little early, causing it to be nose up, and the pass balloons. It balloons because the weight of the ball in relation to the air pressure isn't high enough to overcome the "balloon effect". Lots of surface area in relation to weight will do that. Try throwing a balloon with a spiral, it exaggerates the effect.)

I watched Peytons game tonite, every deep pass was nose down. Passes are spin stabilized, although the velocity isn't in the same ball park as a rifle, obviously. Well punted balls also do the same, "turning over" is the phrase often used to describe them.

I'm not sure, however, that footballs react the same as bullets, because the air pressure on the surface area of the ball is so much higher in respect to the weight. I do know that footballs do not exhibit "lift" on their own, after having used a throwing machine for thousands of passes!

As for the above arguments, I'm still unsure of the correct answer, since no one seems capable of putting it into language that is comprehensible by someone like me with so little apparent education!

The Sierra stuff never seems to directly address the question, and the only other scientific discussions I can find say that they don't. CatShooter points out that DOE physicists can't possibly know what they are talking about, and maybe he is correct. But, then again, initially he insisted this was all just simple high school physics, and I guess those guys, and the high school physics teachers asking the question must all have forgotten THEIR basic high school physics!

As for picking a fight, not hardly, I was trying to be funny, but quite obviously, I missed the mark!!

Bill

 

[Brown Dog]

Goodgrouper,

Yes the thread has wandered a little, my fault. Trouble is, that before you can consider the lift question, you have to establish the bullet's orientation in flight. A misleading bunch of aggressively stated twaddle was posted stating that all bullets maintain their firing orientation throughout their flight. That had to be clarified correctly (well, it didn't have to be, I just chose to ).

Bill,

I believe most here would accept that bullets are 'wobbly' on shot exit and stabilise over their first 100m or so of flight.

And would therefore accept that 'something' is happening to them that causes them to stabilise to point, broadly, into the airflow.

The mechanism by which that happens, is the same mechanism by which they are caused to keep themselves broadly pointing on the line of the trajectory through their whole flight.

(Obviously the above must be caveated with 'approriately spun' bullets)

I thought this one I posted earlier explained in easy terms why a properly spun projectile's nose broadly follows the trajectory :

If you're happy with the concept described (of bullets being rather unstable at launch, but stabilising as they get further downrange).......Simply apply it to the apparent yaw angle produced by the trajectory falling away from the bullet....all that's happening is that that yaw is being gyroscopically damped out to match the changing airflow....in just the same way that transient yaw is damped.

So,

As regards 'lift'.

Appropriately spun: One of your opening quotes mentioned that Magnus forces arising from the bullet moving into the airflow at a yaw of repose would generate some lift. This is correct. But wildly insignificant...remember that the yaw of repose is a few fractions of a degree.

Overstabilised: The projectile will retain its firing attitude. As it begins to fly 'side on' to the airflow, its drag massively increases (obviously they are design optimised to fly nose on). The effect is rather like a space shuttle nose-up re-entry to the atmosphere. The nose-up attitude in that case is clearly to provide a braking effect. I'm not sure I would describe that effect as 'lift'. ...and rather than increasing range, it's always been my understanding that it drastically decreases it.

...and to confuse it further...if fully 'side on' and very highly spun, the magnus forces will become far more significant...diverting the round laterally. In extreme examples this can even cause a massively overstabilised projectile to (on a 'plan view' doppler trace) execute a wide slow j-turn.

 

[AJ Peacock]

...
Any well thrown pass thrown with an arc will come down on the front half of the football, most passes qualify at the NFL level. You can throw a pass that doesn't, but it won't be a well thrown pass. (I left the original "sailing pass" quote alone, but a pass that "sails" is released a little early, causing it to be nose up, and the pass balloons....

Actually, that's what I was trying (poorly) to get at. A pass that is not released perfectly won't 'magically' straighten out and follow the arc. I was just asking why that wouldn't happen. I assumed its because the spin wasn't enough, or the surface area was too much etc. At that point in the 'conversation', I was curious why some projectiles tended to have their nose follow the arc and others didn't.

Cool on your sons, I know how much you can learn being associated with kids. Ask me how I've learned what I know about girls softball ;-)

Later,
AJ

 

[Buffalobob]

I left the original "sailing pass" quote alone, but a pass that "sails" is released a little early, causing it to be nose up, and the pass balloons.

I made that post to be tactful because Catshooter was in a bad mood. If you took it to be argumentative I am sorry. If you took it to be wrong, then just keep it in mind and as time passes along you may wish to revisit that thought or you may not.

 

[bwaites]

AJ and BB, no offense taken. I had to learn the football stuff since I was coaching at the middle school level and then with my sons progressing I had to keep a little ahead. I have been watching Elway and Montana, with vastly more knowledge than I started with, also deal with the same situation. It's one of the reasons that I believe having kids makes us better people, we MUST learn or fall behind, because our kids don't wait for us!!

BB, I was going from memory on the sailing pass thing, I haven't had time to go back and reread it yet.

Bill

 

[Brown Dog]

Well, this thread seems to have gone to sleep!

..Although I've certainly learnt something about American Football (must be such a gentle game with all that padding )



....I was rather hoping that Catshooter (who I note was on the site earlier today) was going to come back with his explanation as to how point detonating impact fuzes function in his side-landing shells theory.

...whether that's possible or not (and it isn't!)....some sort of mumbled apology for the ad hominem stuff would be rather nice.


(clearly, although I treat this as a chat over a pint with similar hobbyists, and not some sort of online keyboard duel......fessing up that his (extremely strongly presented) theory was utter b*ll*cks would be equally impressive. )

 

[bwaites]

Well,

I'm don't understand that the original question was answered unambiguosly, although I am sure that CatShooter feels HE has answered the question.

My definition of lift is that the bullet rises above a direct line between the muzzle and the target caused solely by the airflow created around the bullet shape.

Does that shape and/or that associated spin cause the bullet to rise?

Bill