Wind drift anomalies?

Tim....

You proved my point. Shooters are picking ammo that travels all the way to the target in the transonic region. Why would they pick this velocity ammo if it wasn't performing just fine. Obviously it wasn't affected by some strange effect or some "transonic shock wave".
 
Goodgrouper, in point of fact ELEY and others used to make more of the match stuff supersonic years ago. Now wether they researched on a parrallel path or were influenced by Tirrell's efforts I never heard, but I do have some solid info that because of the recognition of the stability issue we began to see a lot of subsonic offerings in ammo.
I would also add that the research at the time i believe, included a fair amount of down range chrono matched with high speed camera work to show rather directly what was going on under certain circumstances.
I know for a fact that there are a lot of match .22 barrels that will stabilize slugs to a higher or lower degree under a wide number of variables and always believed that some guns that put slugs right on that hairy edge of stability would get bit by this.
 
To Goodgrouper....

I tried to make this point but I guess it just didn't get through. A bullet traveling at or just below the speed of sound doesn't instantly change over to subsonic flight. It takes a drop of about 200 f/s before it is completely subsonic. While it is traveling through that 200 f/s it is considered to be in the transonic region. If you want to put this in terms of mach number it would start out at mach 1 and would not go subsonic until about mach .8. The entire transonic region is from about mach 1.2 down to roughly mach .8. You can work out the math and decide if the ammo you are shooting stays in the transonic region or not.

Now your comment that Eley ammo can't be moving at transonic velocity because it was never supersonic is just not correct. "Transonic" means it's velocity is between mach 1.2 and .8, period. It has nothing to do with what it was traveling at before or after this velocity.

I shoot at 1000 yards and I'm well aware of the common knowledge that you need to stay supersonic out at the target. However I've never found out what it is that is really affecting the bullets flight during transonic velocity. Shooters talk about a "shock wave effect" or they compare it to what happens to a plane's control in this region, but this is just not a full explanation. Maybe it has something to do rotation speed but I can't pin this down. All I find when velocity is transonic is a rapid drop in drag force. If anything it seems to me this would make for greater accuracy during this period, not poorer accuracy.
 
Problem is Big Daddy Cece....... it looks suspiciously as though your "interpreting" (making up as you go along?) just doesn't fall in with established fact.

A sonic boom is a BOOM! my man..... it's a threshhold.

The precursor 'trans' comes from transfer or passage. You keep saying "there's no wall, only a "region."" So please explain the BOOM!????

You state as understood fact that "The entire transonic region is from about mach 1.2 down to roughly mach .8."

Sez WHO?

you??


Transonic simply means crossing the barrier.... yes, the "sound barrier" is a term that's been used (correctly) for lo these many years. Yes we DID kill people crossing this gentle threshhold. Yeager's deal was truly gutsy regardless all the PC types try to downplay it as hype. And, no it's not a "wall" as you've correctly stated..... but flight characteristics, airflow characteristics above and below the speed of sound are unrelated.


Here's a definition...." being or relating to speeds near that of sound in air or about 741 miles (1185 kilometers) per hour at sea level and especially to speeds slightly below the speed of sound at which the speed of airflow varies from subsonic to supersonic at different points along the surface of a body in motion relative to the surrounding air."

The key is to be found in the last sentence.

Under a given set of conditions the "speed" or required velocity is fixed but the airflow speed VARIES AT DIFFERENT POINTS ALONG THE BODY OF THE PROJECTILE. So, some parts are SUPERsonic while other parts are SUBsonic.

Hence "transonic."

It's not at all as if the entire "region" is mushy..... in fact a surface 1mph over the threshhold is SUPERsonic while an area maybe only a foot away is SUBsonic. During a slow transition the air on top of the wing is crackling while that below is still subsonic.

buffeting

turbulent

ROUGH

"get through FAST...."

or lose stability.

Show me wrong?

al
 
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To Alwina....

No, I'm not making up anything here. My info comes from just about all the science on this subject. It comes from Sierra, Wikipedia, Nennstiel, McCoy, NASA, just to name a few that come to mind. In any case I probably should have made it clear I just have to say I don't quite understand what really happens to a bullet at transonic velocity so I have to take explanations given by others with a grain of salt. I know whats going on with the shock wave but it's some of the other things I haven't grasped yet.

Now as to some of your comments; I see you have the same viewpoint as some others. You think a shock wave is a sudden thing that happens in an instant - you think it is a "boom" - you also think it is a "threshold" - both concepts are wrong. You are thinking just like a lot of others - you hear a loud noise so you think, wow, something must have happened very suddenly. or hit something. The shock wave is basically an area, or volume in shape of a cone. in which the pressure is higher than what's all around the wave. The angle , or shape, of the cone changes as bullet velocity changes.

What happens is that as a bullet traveling at supersonic velocity enters the transonic velocity range, at about Mach 1.2 the shock wave angle begins to decrease. It keeps decreasing so that as the velocity falls to about Mach .8 the wave angle is down to essentially zero.

I've said it before but I'll repeat it again......The transonic region is velocity between Mach 1.2 and .8. It covers a velocity from about 1300 f/s down to roughly 900 f/s. This is about where match 22 rim fire is in it's travel from gun to target. Kind of makes you think- why would they load ammo so it's in the most unstable range? Maybe that's why rim fire is bad compared to center fire!

Here's what Wikipedia says about the transonic region:
When the velocity of a rifle bullet fired at supersonic muzzle velocity approaches the speed of sound it enters the transonic region (about Mach 1.2–0.8). In the transonic region, the centre of pressure (CP) of most bullets shifts forward as the bullet decelerates. That CP shift affects the (dynamic) stability of the bullet. If the bullet is not well stabilized, it can not remain pointing forward through the transonic region (the bullets starts to exhibit an unwanted precession or coning motion that, if not dampened out, can eventually end in uncontrollable tumbling along the length axis). However, even if the bullet has sufficient stability (static and dynamic) to be able to fly through the transonic region and stays pointing forward, it is still affected. The erratic and sudden CP shift and (temporary) decrease of dynamic stability can cause significant dispersion (and hence significant accuracy decay), even if the bullet's flight becomes well behaved again when it enters the subsonic region.

It's that CP shift I'm having trouble with. I donknow maybe some crazy benchrester fed that info into Wiki!
 
So pa, what you're saying is that a projectile carries a boom while traveling anywhere from .8 to 1.2 mach?

al
 
Allow me to clarify what I have said. In a .22 reference the older, larger amount of faster .22 ammo, it was found, went subsonic just prior to target impact. It may very well remain less stable for a time after target range. That's academic[ i.e. Cecil]. The point is you don't want it unstable just prior to impact. I don't care what happens the other side of the target. This is why we now increasingly shoot slower .22 match ammo IMHO. Cecil, as usual, is now off on a tangent[ 1000 yard] forgetting what the original point was.......again. If you read carefully his first post [nothing happens] and his last post [something happens] you will see why he usually has to sit in the corner with the pointy hat on.
P.S. Cecil get the Tirrell material, relative to rimfire, educate yourself, don't argue it until you've read it. He is way smarter than both of us.....especially you.
 
HuskerP7M8 said:
Boyd,

I read that report a long time ago and have studied it extensively. I've also searched for and studied everything I can find dealing with transonic ballistics for many years, but like my friend Gene Beggs said "I'm staying out of this discussion". LOL

Try this link and you can view or save this BRL Document as a PDF file.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA229713&Location=U2&doc=GetTRDoc.pdf

Landy
Click to expand...

Landy,
Most of the shadowgraphs are so dark as to be useless in this report. Is your copy any better, or is it just my computer?

Thanks,
Keith
 
mks said:
Landy,
Most of the shadowgraphs are so dark as to be useless in this report. Is your copy any better, or is it just my computer?

Thanks,
Keith
Click to expand...

Keith,

It's not your computer. Almost all of the BRL reports have very poor quality photos and I'm assuming they copied or scanned them for the best contrast of the printed material before they were released to the public.
You can use Google and find a few better shadowgraphs of blunt nose projectiles in the transonic range, but they're pretty rare.

I guess you'll just have to use your imagination to fill in the blanks. LOL

Landy
 
To Aliwna.....

The "boom" you are talking about I assume is a shock wave. A shock exists from about Mach .8 and above. In other words as velocity increases from about Mach .8, (roughly 900 f/s) on up through the transonic region and into supersonic there will be a shock wave. At low velocity, 900 f/s, the wave has an angle in the cone that is near zero. As the velocity goes higher the cone angle will keep getting larger.

It's this changing of the cone angle that I think is what is supposed to cause the center of pressure to shift and tip the bullet. As I've said this is phenomena that I don't understand. This may be one of those things that only the math explains
 
To l'ipecac

I THINK that your contention is that the plane, train or automobile doesn't "pass through" anything, that it only encounters a gradually increasing pressure which begins climbing steeply at 8mach and stabilizes as velocity increases beyond mach 1.2.....

Also that the "boom" is simply a compression phenomena which the plane carries with it like the sonic "crack" of a bullet's passage.

Here are a couple vid's which seem to show a threshhold.

http://www.youtube.com/watch?v=-d9A2oq1N38

http://www.youtube.com/watch?v=gWGLAAYdbbc

Is it your contention that the visual phenomena are produced only by viewing angle? That the "clouds" and "rings" and "waves" and other annuli aren't temporary but are present during supersonic flight?

Is it your contention that a passing supersonic plane "booms" just the same as a plane "breaking the sound barrier?" That the boom is carried around by the plane?

(sorry to be so imprecise but it seemed to work for you last post...... I've spent many yrs honing my communication methods but sometimes I still miss)

al
 
To Aliwna.....

Right, I don't consider that the plane passes through anything - except air at normal pressure and temperature. If below .8 Mach then the nose of the plane will build up pressure and cause air to move out ahead and to the sides of the nose at the speed of sound. When you get above Mach .8 then air can't get out ahead (it can't travel faster than the speed of sound) so pressure begins to build and more air goes out the sides starting a shock wave, When you get to Mach1 no air moves ahead of the plane and pressure builds high enough to push all air out the sides into a shock wave. When you get to Mach 1.2 the pressure builds even higher and you are compressing more air such that a stronger higher pressure shock wave is produced - and this stays with the plane. I don't think it's right to say the air ahead of the nose "stabilizes" - it's always changing as the speed of the plane changes. And if it flies by you the pressure wave will hit your ears and you will hear a boom. Yes the plane flying above Mach .8 is carrying the boom around with it - it doesn't just occur as the plane passes through Mach 1. (That brings up a question - if you fire a rifle in the forest and no one is around to hear it does it make a sound?)

Depending on how you define "threshold" you can consider the plane will pass through it. Most people probably consider Mach 1 is a threshold.

The "visual phenomena" occurs when the air conditions are such moisture forms in the air. It has nothing to do with "viewing angle". The plane is carrying with it the pressure and temperature conditions that will cause moisture to form in the air if the air conditions the plane is passing through are right.
 
OK, here's what I think.....

BELOW mach 1 a jet flies on it's surfaces, laminar flow, stable. The plane is "pushed" upward by the ambient. It floats.

AROUND mach 1 a jet can't make up it's mind, unstable. The biggest problem in this region is that while some surfaces are subsonic (laminar flow), others are experiencing supersonic flow (shockwave). This inconsistency produces "buffeting" differentials. It's like getting a boat up on step in choppy water.

ABOVE mach 1 a jet flies on shock wave surfaces and jets, it's skin surfaces are useless, but it's stable. As long as it stays above mach 1.2 it's stable because it's pinned against the wall by pure muscle. It's no longer floating.

I think you absolutely need to get your aircraft through the transonic zone quickly or risk losing it. And with bullets it's best to avoid dropping through it.

al
 
Bent and rebent...........

In the Atlas rocket part of the video, you can see how the pressure wave makes the 'sun dog' (in the upper right) disappear. Sun dogs themselves being a visible example of bent light waves due to ice crystals in the atmosphere, of course.
 
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To Aliwna.....

Almost everything you think is right. You can say planes "float", However when you say .....
ABOVE mach 1 a jet flies on shock wave surfaces
You are not quite right. Planes at supersonic speed get lift pretty much like planes at subsonic speed, that is with higher pressure below the wing as compared to lower pressure above wing. However this pressure difference is achieved with angle of attack rather than shape of the wing. The difference in pressure is due to higher pressure behind the shock wave off the lower leading edge as compared to a lower pressure behind the shock wave off the upper leading edge.
 
pacecil said:
Almost everything you think is right. You can say planes "float", However when you say .....
ABOVE mach 1 a jet flies on shock wave surfaces
You are not quite right. Planes at supersonic speed get lift pretty much like planes at subsonic speed, that is with higher pressure below the wing as compared to lower pressure above wing. However this pressure difference is achieved with angle of attack rather than shape of the wing. The difference in pressure is due to higher pressure behind the shock wave off the lower leading edge as compared to a lower pressure behind the shock wave off the upper leading edge.
Click to expand...

If this is completely true then a supersonic plane still "floats" as opposed to slipping.

al
 
Yes, the wall changes with conditions but "the speed of sound" under a given set of conditions is fixed. "Speed of sound" must be defined as XXX velocity @ XXX temp/hum/alt/barom etc.

al
 
To Aliwna.....

Would I say something that wasn't completely true???
 
To goodgrouper....
The shock wave is coming from the bullet so it's traveling at the same speed as the bullet. You couldn't have the bullet traveling slower.

The definition of the transonic range is somewhat arbitrary so in fact it does "change - probably by about 500 f/s one way or the other.

As to how long bullets stay in the transonic region; you would have to say it's interesting that good match ammo probably spends it's entire time from gun to target in this region. Makes you think doesn't it?
 
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