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jlmurphy
10-26-2010, 05:20 PM
While discussing the ballistics of .45-70 long range silhouette bullets, my friend mentioned the importance of staying below the speed of sound. I assumed it was for stability, but he said wind drift was his main concern. I thought time of flight was the major component, but after playing with an online ballistics program, it it was obvious he was right, the faster the projectile traveled, the greater the wind drift, with a large bump at the speed of sound. My guess is that a shock wave forms in front of the object, causing greater drag, although the time of flight remains proportional. Any thoughts?

tim
10-26-2010, 06:38 PM
Your bud is commenting on the issue of sub sonic/wind issues but it relates to rimfire not center fire. I can't imagine anybody shoots subsonic big bore silhouette.

Larry Elliott
10-26-2010, 06:47 PM
They do in Black Powder Cartridge Rifle silhouette. It's like rimfire, but at longer range and a lot smokier.

alinwa
10-26-2010, 09:57 PM
While discussing the ballistics of ....................................


Any thoughts?

Yup,

your friend is right.

And there are no "anomolies," it's a well understood subject.

re your 'guesses'........ ;) ................ if you're really interested you'd maybe enjoy some books on the subject.

Time of flight has little or nothing to do with it.

al

Gene Beggs
10-26-2010, 10:19 PM
Alinwa is certainly right; it has little or nothing to do with time of flight.

Wind and how it affects bullets in flight is far more complex than it first appears to be.

I have studied the subject for many years and each year I learn something new.

Al and I and many others have had some very enlightening and lively discussions here on the forum about wind drift. I encourage you to search the archives and review those posts. It's fascinating! :)

Gene Beggs

tim
10-27-2010, 12:03 AM
Alwina,Really? You might wander over to BPCR.net, there's literally 100's of loads listed over there, most of them seem to average about 1200 fps or so. The rimfire assertion has more to do with the issue of slugs that start out supersonic and tend to destabilize as they pass back to subsonic, usually just before 50yds where most .22 BR targets are.

WSnyder
10-27-2010, 12:51 AM
Here's an explanation from the NRA Firearms Fact book. The same info was published in an article in Precision Shooting or one of their specials or annuals years ago.

"Those unfamiliar with smallbore rifle competition are often surprised to learn that target shooters almost universally use standard velocity ammunition in preference to the many varieties of high and hyper-velocity rounds available. The reason given is the low-velocity ammunitions resistance to wind deflection.

Despite what might seem at first to be the case, wind deflection is not proportional to the time of flight. Instead, it is proportional to the amount of delay in the flight caused by air resistance. The 1145 f.p.s. standard velocity .22 long rifle round takes .287 seconds to go 100 yds., but would take only .262 seconds to cover the same distance in a vacuum. The latter figure is easily found by dividing 300 ft. by the speed of the bullet (1145 f.p.s.), which would remain the same throughout its flight if it were in a vacuum. Thus the delay caused by air resistance is .025 second with the standard velocity ammunition.

The 1335 f.p.s. high velocity ammunition, which will take .259 second to cover 100 yds., would take only .225 second in a vacuum. Thus, the delay for this bullet is .035 second or 37% greater than that of the standard velocity round .22.

The high speed round, then, suffers about 37% more wind deflection than the standard velocity.

This remarkable result is due to the very rapid rate at which air resistance increases with increase in bullet speed in the region near the speed of sound. The .22 rimfires rimfires are the only important rifle cartridges that occupy this speed range, and they are the only ones that show more wind deflection as velocity is increased.

While air resistance always increases when the bullet is shot faster, the rate of this increase is less steep at supersonic velocities. Rifle bullets in general, contrary to the case of rimfires, are made less sensitive to the wind by raising their velocities."

NRA Firearms Fact Book

alinwa
10-27-2010, 03:26 AM
Alwina,Really? You might wander over to BPCR.net, there's literally 100's of loads listed over there, most of them seem to average about 1200 fps or so. The rimfire assertion has more to do with the issue of slugs that start out supersonic and tend to destabilize as they pass back to subsonic, usually just before 50yds where most .22 BR targets are.

mit, Really? I could "learn" something there?

You're 'wayyy over my head here man. I have no idea what you're trying to tell me. I'm guessing it's sarcasm? I don't even know what you're referring to....

Maybe just spit it out instead of asking me to read between the lines?? I'm really not good at that whole "interpretation" thing (as my wife well knows!)

al

Vern
10-27-2010, 06:29 AM
Since I dont know,... this means this is a real question.
If subsonic speeds are more accurate then we should be loading down the 6ppc?

John Kielly
10-27-2010, 06:48 AM
It's just the window round sonic velocities where it hits the fan.

Why not run a few velocity ranges thru the ballistics table of your choice & see what the relative gains & losses there are?

jo191145
10-27-2010, 11:17 AM
Now you guys got me thinkin bout using the ol 1911 for F-Class

Charles E
10-27-2010, 08:06 PM
Grouper,

Drag is drag,at whatever speed. That we cannot predict, but only empirically measure it in the transonic region is not a physical property, just a human one. You will not be "all right" just by ignoring it.

For fun sometime, read the Lyman book on pistol reloading. Some bullets "pick up BC" in the transonic region, some lose it. AFAIK, no one yet has been able to model just which shapes go one way, which the other. Modeling (predicting) does work pretty well as you get above 1400 fps.

tim
10-27-2010, 09:40 PM
mit, Really? I could "learn" something there?

You're 'wayyy over my head here man. I have no idea what you're trying to tell me. I'm guessing it's sarcasm? I don't even know what you're referring to....

Maybe just spit it out instead of asking me to read between the lines?? I'm really not good at that whole "interpretation" thing (as my wife well knows!)

al

Well, let me try again. First, as to BP cartridge rifles it would seem that since the BPCR site lists so many loads well above the speed of sound, that most in fact, do not load subsonic. [ I also happen to cast/shoot a 32-40 and an 8.15x46 and most loads seem to be between 1200-1300fps].
Second, it seems the biggest incidence of subsonic in recent years has been rimfire. A lot of the faster match ammo used to be slightly supersonic and it was proven that when it passed back to subsonic it would breifly destabilize...usually just before it hit the target. I'm guessing the whole deal gets translated into "subsonic for everything" except most loads for heavier cast slugs would seem not to be, silhouette, scheutzen, BR or otherwise, you gave me an opinion, I gave you a fairly widely used source...even the lightest loads for some of these guns are supersonic.
The wind drift issue I'd suspect, impacts a slug only more so in it's pass back to subsonic, given it's blowing, etc. If one was inherintdly less wind sensitive I'd be shooting my 6PPC @ 1050fps.

alinwa
10-28-2010, 03:28 AM
Well, let me try again. First, as to BP cartridge rifles it would seem that since the BPCR site lists so many loads well above the speed of sound, that most in fact, do not load subsonic. [ I also happen to cast/shoot a 32-40 and an 8.15x46 and most loads seem to be between 1200-1300fps].
Second, it seems the biggest incidence of subsonic in recent years has been rimfire. A lot of the faster match ammo used to be slightly supersonic and it was proven that when it passed back to subsonic it would breifly destabilize...usually just before it hit the target. I'm guessing the whole deal gets translated into "subsonic for everything" except most loads for heavier cast slugs would seem not to be, silhouette, scheutzen, BR or otherwise, you gave me an opinion, I gave you a fairly widely used source...even the lightest loads for some of these guns are supersonic.
The wind drift issue I'd suspect, impacts a slug only more so in it's pass back to subsonic, given it's blowing, etc. If one was inherintdly less wind sensitive I'd be shooting my 6PPC @ 1050fps.

hmmmm

Well, I'm no expert on subsonic flight characteristics but I do shoot over a chronograph, a lot. A while back I lined up three of my chrony's on a board and noted that at 10ft off the muzzle I was losing about 2-4fps/ft with supersonic projectiles. (empirical, an estimate, rough) But they shed vel very quickly.

I submit that IF a projectile is shedding even 2fps/ft then these projectiles that're loaded to 1200-1300 may well be going subsonic in 50-100ft. That they stabilize from blast effects, lateral jump and inbore cant effects AS they are going subsonic, not clear out by the target board. And that this combination, this lumping together of several effects into the same frame of flight is advantageous....

Threads like this illustrate for me why the REAL ballisticians (HBC et al) refrain from trying to illustrate/explain such a broad subject here on the board.


al

Greg Culpepper
10-28-2010, 09:34 AM
While discussing the ballistics of .45-70 long range silhouette bullets, my friend mentioned the importance of staying below the speed of sound. I assumed it was for stability, but he said wind drift was his main concern.

Mornin' Mr. Murphy,

Out of my experience and observation, staying below the speed of sound is not a crucial issue for being competitive. As in most pursuits, a balanced program that embraces the best set of compromises wins. The least wind drift alone doesn't guarantee a win.


I thought time of flight was the major component,

Time of flight has nothing to do with drift. "Wind drift" is the product of time lag only. How fast a projectile slows down is the predictor of its drift. How fast it slows down is determined by its bc and air density.



but after playing with an online ballistics program, it it was obvious he was right, the faster the projectile traveled, the greater the wind drift, with a large bump at the speed of sound.
My guess is that a shock wave forms in front of the object, causing greater drag,

Right.



although the time of flight remains proportional.

I'm not following you here. Proportional to what?



Any thoughts?

When shot with black powder, big old roomy cartridges shoot with the least velocity extreme spread with some compression of the powder charge. The lowest velocity extreme spread will give the least vertical shot variation at the long range target. Vertical is one important issue in field and at target. To a large extent, achieving that optimum powder compression for velocity consistency influences the resulting bullet velocity. Long, heavy for diameter, high bc bullets that drift less than shorter, lighter bullets help suppress velocity but most frequently not to below the speed of sound in the cartridges that we shoot. So there is, as always, a compromise involving trade offs between vertical spread at the target and drift at the target. The compromise that typically appears seems to be a little less than 1200 fps which as you note is a faster than the speed of sound where drag (and drift) take a big jump. Maybe the best performance is available just sub-sonic. I don't know. My BPCR experience is with 40-90 (about 1500 fps) and 40-65 (about 1200 fps), both with the same 416 gr 0.410 bullet at about 0.50 bc. Predictably, the slower 40-65 cartridge drifts much less and (edit here) the 40-90 is not at all competitive for its greater velocity.

I shoot them both exclusively with black powder. I get chronographed velocity consistency with black powder that will break the needle off most folk's BS meter so I'll leave it at that. I expect much better results on target than if I used smokeless. As Steve Garbe is given to say, "Smokeless powder is a passing fad".

Books have been and will be written on this subject. A great one is by Bryan Litz who also also walks the walk. One (sort of) them developed on this board a few years back and contains the work of many authors. Gene references it above. It's a beautiful thing to see Al come to lose his miss-perceptions about "wind blowing bullets over" and come to a full appreciation that they are actually "backing down the wind" along their own axis due to vectoring into the apparent wind and moving across the ground due to drag alone. Al is a great student, experimenter (and teacher) and shares voluminously to the gratitude of many, myself included. Gene is a fantastic teacher of many subjects. Like Al, he is a Renaissance man. I hope you will take the time to do as Gene suggested and search "What exactly does a bullet do in the wind?" or something like that. It's a good (although long) read.

Greg

pacecil
10-29-2010, 05:37 PM
I put this in another thread - I'll try it here and see what happens.

Nothing happens to a bullet when it's velocity changes from sonic to subsonic, or subsonic to sonic. There is no "shock wave" effect. All that takes place is a change in the slope of the curve that describes the effect of wind. It's like you were climbing a hill, when you come to a place that the hill becomes steeper, or less steep, it simply becomes harder ,or easier to climb the hill. I'll go out on a limb here and say bullets might be described as "going very gently" into or out of the transonic region!

I'm sure there will be many who think they could almost hear their bullet hitting a wall in this terrible region called "transonic". Truth is it's difficult to pin point exactly where this region is. Probably it can only be done mathematically and somewhat arbitrarily.

alinwa
10-30-2010, 01:04 AM
I put this in another thread - I'll try it here and see what happens.

Nothing happens to a bullet when it's velocity changes from sonic to subsonic, or subsonic to sonic. There is no "shock wave" effect. All that takes place is a change in the slope of the curve that describes the effect of wind. It's like you were climbing a hill, when you come to a place that the hill becomes steeper, or less steep, it simply becomes harder ,or easier to climb the hill. I'll go out on a limb here and say bullets might be described as "going very gently" into or out of the transonic region!

I'm sure there will be many who think they could almost hear their bullet hitting a wall in this terrible region called "transonic". Truth is it's difficult to pin point exactly where this region is. Probably it can only be done mathematically and somewhat arbitrarily.

OK pacecil..... I'm only conversant with supersonic flight phenomena but I CAN read, and I DO have real books written by real ballisticians at my disposal so's I refuse to just let'cher allegation lie :p

As you no doubt know, it's more than just a "steeper slope," the transonic area. And why you're presenting it a "gentle" I dunno but tests agree with theory here, it's not.

Quote for me ONE real ballistics text, show me ONE opinion other than your own or otherwise substantiate your position :p else'twise I'll have to give it the same credence as your last exposition wherein you asserted that "smoke rings don't exist because you pointed your airhose around the shop and nothing untoward happened."

According to (Rinker/McCoy/Litz/Vaughn et al) there most certainly IS a shockwave, this shockwave is illustrated/described (verbally/dramatically/photographically) in EVERY ballistics text with which I'm conversant. And all texts agree that in that region where the bullet is "crossing over" it's strongly "buffeted" (this is the most common descriptor) due to the fact that as it ascends/descends through this region there's a period of "back-and-forth" action where parts of the system are protruding or mixing between the two states of flight.

To quote Robt Rinker, 'Understanding Firearm Ballistics, Basic To Advanced Ballistics Simplified & Explained,' "a lot of phenomena occur during this transonic range. Most of the difficulties are associated with shock wave induced flow and pressure changes."

He goes on for pages (with pixtures) explaining/showing how airflow transitions from laminar to "behind the shock wave" with a little "NOTE: Shock waves are different than airflow" accompanying the pixtures.......

In fact Rinker goes so far as to say that "for the study of aerodynamics and airflow at velocities below the speed of sound, air is termed incompressible. At the higher speeds there are large and important changes in air density and compressibility."

Much reference to "turbulence" and "pressure changes moving in all directions...."


sooooo, more input? Something more than just "nothing!"

I've got no answers, no real understanding of laminar airflow flight characteristics, but I hesitate to let your assertion go unchallenged. Wouldn't be prudent. :D

Good luck

al

(BTW, the (nonexistent) "shock wave effect" as you so indelicately put it is rawther well and easily explained in ALL of the ballistic tomes on my bookshelf....)

Boyd Allen
10-30-2010, 02:11 AM
I have gotten to the point that I am amused by the various statements that come from discussions of wind drift. For example, I have never heard a less apt description than the contention that bullets "back up". Find another way of saying what you mean. I have never seen a fired bullet "back up", and neither has anyone else. They are positioned by the sum of the forces acting on them. None of this involves reversing direction. which is the common understanding of "back up". As to the need for a bullet to tilt if it is to be caused to drift by it interaction with the wind, round balls drift the most, and they cannot turn into the wind. Correlation does not prove causation. Also, owning and reading a number of books on a subject does not guarantee mastery of a subject, it makes it more likely, but there is no guarantee. Understand, I am not trying to contradict ballistic theory that has proven reliable in predicting how a bullet will behave, it is just that some of the "explanations" do more to obscure than illuminate. One of my favorites is the one where the author comments that if there was no lag, there would be no wind drift. Please, the only way that there would be no lag, would be in a vacuum , where there can be no wind...so what is the point, yet this nonsense has developed a life of its own, being repeated over and over, as if it meant something.

MilGunsmith
10-30-2010, 09:09 AM
As was explained to me by Chuck Yeager; ''The bullets at subsonic are like being in a boat moving along with the throttle just cracked open a little, the boat moves along displacing the water and is very controlable. The supersonic stage is the same as the boat wide open up on plane, controlable. The trans-sonic range is the stage were the throttle is partialy open and the boat is trying to get up on plane, there is water built up in front of the bow trying to get around and the boat is uncontrolable"" Most of us ave been in a boat so we can understand tis example.
At work we have tracked bullets out to 2000 meters using Weible Radar and the .300Win Mag with 190gr SMK bullets, we watched a normal ballistic curve until the bullets went trans-sonic at around 1200 to 1400 meters depending on the tempratures. In the trans-sonic range, nothing was predictable until the bullets went subsonic and then stabled out sometimes.

Charles E
10-30-2010, 09:55 AM
In the trans-sonic range, nothing was predictable until the bullets went subsonic and then stabled out sometimes. I like that. It shows -- to me anyway -- that what Lyman found by the empirical testing of their pistol bullets in the 1200 to 1500 fps region -- is still valid. They found that you couldn't predict what would happen. Apparently, all the variables still aren't known, only empirical testing of each bullet gives useful information.

Happens a lot in shooting. We don't know all the causes of in-bore yaw, and the resulting shot dispersion, but from the dispersion, we can calculate what the in-bore yaw was -- we just don't know all the causes. Or didn't at the time of McCoys book . . .

We don't know the exact cause of dynamic instability. We know the result -- don't use Sierra 168 MKs if you can't stay above the transsonic region. But not all bullets behave that way. Is it the boattail angle of the 168? Maybe, but not yet proven.

As an aside, what is all this talk of a vacuum? The difference between a vacuum and life on Earth is air. The primary effect of air on projectiles is "drag." There are a few others, but they can be ignored like anything else down in the <1% effect region. The complexities of drag are best covered in books on exterior ballistics. The descriptive/predictive model is mathematically complex.

People try to find shortcuts to avoid the math. Me too. At the level of an individual bullet, that's called empirical testing, and is valid if done properly. If extending the result of that test to a general rule proves false because another (say bullet) doesn't behave that way, you don't have a good model. So use the test for what it is worth-- applicable to one situation.

Greg Culpepper
10-30-2010, 12:41 PM
Morning Boyd,


I have gotten to the point that I am amused by the various statements that come from discussions of wind drift. For example, I have never heard a less apt description than the contention that bullets "back up". Find another way of saying what you mean. I have never seen a fired bullet "back up", and neither has anyone else. They are positioned by the sum of the forces acting on them. None of this involves reversing direction. which is the common understanding of "back up".




With acknowledgment that there is nothing new under the sun, I may have coined the phrase on this board "backing down the wind".as a descriptive paradigm to illustrate a somewhat counter-intuitive phenomena of bullet behavior. If I didn't, apologies to he who did. If I did, I'll continue to own the phase happily and extend its use with or without demand of attribution to any and all who might choose its shorthand to some lengthier and more exhausting description of "what exactly the wind does to a bullet".

Depending on one's perspective, bullets can be said to back up. For example, suppose you were piloting an airplane vertically, either up or down to eliminate non-axial gravity effects. Suppose you shot a bullet straight out the front of the plane. Now wait a moment or two. As the plane continues on at a constant air speed with thrust and drag exactly equal you will catch up to and pass (or run into) the bullet you just fired. Air creates drag on the bullet but the bullet has no thrust so it slows as drag absorbs its inertial energy is changed into heat. Without a reference to the ground but only the airplane you're in the bullet would appear to fly away, slow to a stop, reverse and then accelerate back at you. Is the bullet backing up? If your frame of reference is your location in the moving plane then you might say the bullet has "backed up".

Now I'll ask that you imagine that you are in space. In space what is motion? Can you tell if you are moving? If an object that you see is changing position relative to you is it moving or are you? Maybe you're both in motion relative to some third object. Is the third object moving? Is it backing up? It's relative, isn't it.

Now lets come back to shooters, targets and bullets. Shooters and targets are typically earthbound. (An exception would two airplanes whose pilots are attempting to shoot one another.) Bullets, by contrast, are not earthbound. They are in flight in air and are unaffected by the earth (other than by gravity). Bullets in flight behave separately from the earth, just influenced by air. Once fired, the air is their whole world. Understanding and accepting this fact is necessary to understand wind drift of bullets.




As to the need for a bullet to tilt if it is to be caused to drift by it interaction with the wind, round balls drift the most, and they cannot turn into the wind.

Were this true rifling round ball guns might not produce any effect different from smooth bore musket.






Correlation does not prove causation. Also, owning and reading a number of books on a subject does not guarantee mastery of a subject, it makes it more likely, but there is no guarantee. Understand, I am not trying to contradict ballistic theory that has proven reliable in predicting how a bullet will behave, it is just that some of the "explanations" do more to obscure than illuminate.

Your incorrect statement concerning round ball flight might fall into this category.

One of my favorites is the one where the author comments that if there was no lag, there would be no wind drift. Please, the only way that there would be no lag, would be in a vacuum , where there can be no wind...

There is a situation where there would be no lag and it applies directly to understanding wind drift of bullets and the utility of the phrase "backing down the wind" as an aid to that understanding. That would be for a rocket or airplane flying at a constant speed through the air when thrust and drag are exactly equal. I'll use the example of the rocket only as it, as fin stabilized projectile, more closely resembles a spin stabilized bullet than does an airplane with its movable flight control surfaces.

A rocket in steady state flight does not exhibit wind drift. It will fly on a straight line, point-on into the air. If the air is moving relative to the earth (wind) the rocket will turn relative to the earth (but not in the air) and will proceed on vector. To an observer on earth the rocket will appear to fly slightly sideways but on an absolutely straight path. Now if that rocket has more thrust than drag and is accelerating, it will still point straight into the air but if the air is moving across the earth the rocket will travel upwind relative to the earth. If the rocket has less thrust than drag it will decelerate and travel downwind.

Why am I talking about rockets? I'm talking about rockets to provide a frame of reference that is not earthbound. To more easily understand bullet wind drift it helps to get one's frame of reference up in the air with the bullet. Keeping you feet and frame of reference firmly planted on the ground does "more to obscure than illuminate".

Climb on the rocket with me Boyd and look over your shoulder at where we have been. Let go of some object, maybe one that resembles a spin stabilized bullet. Would you expect it to slow as drag overcomes its inertia? Sure. Would you expect it to curve left or right as it "backs up" accelerating away from and behind us? Why would it? OK. We're on the rocket and the bullet we dropped is slowing down from drag and trailing straight behind us (and down from gravity of course).

What is someone on the ground going to observe? We're in the air going straight in the wind and the bullet is dropping away from us straight behind and down. But the person on the ground sees us flying slightly sideways to the ground (although straight in the air whose motion as not directly observable as air is transparent). The dropped bullet remains exactly on the horizontal vector of our travel, but increasingly behind us from the moment of its release from our rocket. But the earthbound observer sees the bullet from his earthbound reference. For him the bullet isn't traveling straight at all but arcing downwind and the faster it slows due to drag, the more it arcs. When we on the rocket look back it is still straight behind us, increasing farther away and below as drag and gravity exert their influence. Wind doesn't blow bullets over. Drag pulls them back along their own axis from where they would be without drag. This difference between a no drag bullet and a real bullet is time lag. Time lag (time delay produced by drag) is the only mechanism that causes air movement to alter bullet travel in flight relative to the earth.

so what is the point, Well, it allows science to model and predict the path of projectiles.
yet this nonsense has developed a life of its own, being repeated over and over, as if it meant something.

Think expansively. Let your mind soar. Don't be bound to the earth. Maybe some day "backing up", relatively speaking, will mean something to you. I can hope. And you can hope that I buy wind flags for LR Benchrest and LR Prone.

All the best to you Boyd,

Greg

IndianaJames
10-30-2010, 01:10 PM
Greg,

Thank you for taking the time to compose and type this. I hope it is appreciated by others. It works for me.

Jim

alinwa
10-30-2010, 01:30 PM
Interesting illustration re the shock wave.

I found this mind-pic to be illuminating.

(others will find it annoying!:p)

A boat sets in a pond. As one rocks or bobs the boat, ripples spread out (propagate) in all directions. These ripples move at a certain speed.

The boat starts to move. In moving it begins to catch up to the ripples in the direction it's moving. When describing sound propagation this is called "the Doppler Effect."

Get the boat moving fast enough and it catches up with ALL the waves, it's moving faster than the waves can propogate ahead. When describing sound this is "the sound barrier" or "the speed of sound."

Push the nose of the boat THROUGH this barrier....... and, well you can take it from there......

hth

al

BTW, unlike some, I LIKE the "backing up" descriptor. In fact I used it a recently as........ oh, lasterday evening. I had a young engineering student over using the range and the subject came up. He's shooting a 300WSM and intrigued by the idea of pushing 110gr bullets to 4200fps.....wondering how they'd do in the wind. I was able to tell him "terrible," and explain why. He related well to the idea that the bullets "backed off-line" as opposed to the flawed idea that the wind "blows the bullet over" since it had already become apparent to the fellow that bullets didn't slide.

"Backing down the wind" or "backing up" has always worked for me but then I've never considered my views to be bound by convention.

Gene Beggs
10-30-2010, 01:54 PM
Greg, you understand this stuff perfectly and I commend you for your well written post #22.

You're a brave man my friend, a brave man.

I guess you noticed, I'm staying out of this discussion.

Best regards

Gene Beggs

Greg Culpepper
10-30-2010, 02:20 PM
Not brave Gene. Foolish? Probably. Lazy? For sure. I'm supposed to be painting the house.

Fred J
10-30-2010, 03:20 PM
My wife while driving down the road, passes an old man in his pick-up truck. She later comes to a stop at a Red light, and the old man in the truck hits her. His explanation for the accident, was, "She backed-up into me". Cop didn't believe him either.

Greg Culpepper
10-30-2010, 03:32 PM
Fred,

That's his story and he's stickin' to it.

Me to.

Greg

Fred J
10-31-2010, 12:01 AM
He still got the ticket.

pacecil
10-31-2010, 01:09 AM
Wow a lot has been said since your post but anyway I'll just answer to you. First lets consider when we talk about bullets and the transonic region we are only talking about going from sonic to subsonic. It does go the other way while the bullet is in the barrel, and there is a shock wave ahead of the bullet but I believe we can ignore the shock wave effect on bullets movement in the bore. Incidentally I didn't mean to imply shock waves don't exist - you inferred it.

So what happens when the bullet slows down and the shock wave gradually moves from a wave expanded out from the bullets nose to a pressure "wave" that lies back along the bullet? "Gradually" could also be taken as "gentle" since the pressures do change relatively slowly, but really these terms don't carry much meaning in what we are talking about here. Now all along the bullet's surface air is being compressed at different rates and in different directions so exactly when the transonic region is reached is hard to define exactly. In any case all that is happening are changes in pressure conditions that exist over the surface of the bullet.

Now. You, and others, are probably going to insist that it's this pressure, or the different pressures, that might exist all around the bullet that cause a "bump" when in the transonic region. However the possibility exists that yaw, and even bullet shape, can cause similar pressure conditions. My point is there is nothing in the science that describes a particular "shock effect" as velocity drops down through the speed of sound. I think this is just an impression people have when they hear a sonic boom from a plane, and assume there was a corresponding boom right at the plane. Some people also assume the "crack" of a bullet in flight means the bullet must have hit something (they call it a shock wave) in the air that disrupts it's flight. You and I both know, you don't "hit" a shock wave.

You asked if I could cite other opinions that agree with mine. I wasn't giving an opinion. I was just telling how I interpret the science. I'm sure there's things happening during the bullets velocity change that I don't understand. I welcome your explanation for what is going on. and what might jar a bullet out of it's flight path while it's in the transonic region

tim
11-01-2010, 10:49 PM
I put this in another thread - I'll try it here and see what happens.

Nothing happens to a bullet when it's velocity changes from sonic to subsonic, or subsonic to sonic. There is no "shock wave" effect. All that takes place is a change in the slope of the curve that describes the effect of wind. It's like you were climbing a hill, when you come to a place that the hill becomes steeper, or less steep, it simply becomes harder ,or easier to climb the hill. I'll go out on a limb here and say bullets might be described as "going very gently" into or out of the transonic region!

I'm sure there will be many who think they could almost hear their bullet hitting a wall in this terrible region called "transonic". Truth is it's difficult to pin point exactly where this region is. Probably it can only be done mathematically and somewhat arbitrarily.

Once again you, friend Cecil, are in the deep end of the pool with your lead bloomers on. As it relates to .22 slugs, Frank Tirrell, in an extensive series of articles, published in Small Caliber News, showed a tremendous amount of data as to his tests on the subject. They showed that the center of pressure surrounding a .22 slug in flight moves along the axis of said slug and will with regularity cause said slug to slightly destabilize as it becomes subsonic down range. Said effects became somewhat altered by the flattening of the slug at it's mid-ogive. This was some time before ELEY released the now commonly utilized EPS bullet. These tests were done, I believe, both outside and in his tunnel. I should be charging you for these lessons. Copy Al in since my response to this thread initially started out as a rimfire statement, that is to those that do some shooting other than on the 'ol keyboard.

Boyd Allen
11-02-2010, 03:04 AM
OK all you guys with really fast computers, who have more savvy than I, I found a 75 page report by Robert McCoy, that was published in 1990. I am trying to download as I write this. The report was scanned, so the file will probably turn out to be gynormus. The report is about .22 rimfire ammunition tested in Olympic quality rifles. It is chock full of test data, and ballistic formulas. In scanning the contents I came across one part that said that the wind sensitivity of one particular lot of RWS ammunition that chronographed at 1090 would be reduced if its velocity was reduced to 950. In any case, here is the link. Perhaps someone with a more modern computer will have an easier time with the download. I will keep trying. http://www.scribd.com/doc/19076172/Aerodynamic-Characteristics-of-22LR-Match-Ammunition
I found this by Googling "nonlinear bullet wind drift in sub sonic region" I believe this was government funded research that was done at a government facility.

HuskerP7M8
11-02-2010, 06:33 AM
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

tim
11-02-2010, 09:02 AM
Boyd, that report brings up the effect without going past there. Franks research goes far deeper.

pacecil
11-02-2010, 03:47 PM
I like to respond to you cause you like to respond to me! (I resist dealing with you personally, only with what you say.) This is what you said:
As it relates to .22 slugs, Frank Tirrell, in an extensive series of articles, published in Small Caliber News, showed a tremendous amount of data as to his tests on the subject. They showed that the center of pressure surrounding a .22 slug in flight moves along the axis of said slug and will with regularity cause said slug to slightly destabilize as it becomes subsonic down range
That's interesting and I'm sure it's true but it has no relation to what was being discussed in the posts. What was discussed was whether or not there is some unusual or unexpected effect on a bullets flight in the transonic region. Something you (and others) may not realize is that the ammo you are probably shooting starts out and stays in this region for their entire flight out to about 100 yards. All I've been saying is I can't find anything in the science - or for that matter in my shooting - that indicates anything other than a drop in drag forces and less change in drag as the bullet moves subsonic. If there is in fact some intense disruption of flight in the transonic region then we rimfire shooters probably have it with every round we shoot in competition.

tim
11-02-2010, 05:58 PM
I like to respond to you cause you like to respond to me! (I resist dealing with you personally, only with what you say.) This is what you said:
As it relates to .22 slugs, Frank Tirrell, in an extensive series of articles, published in Small Caliber News, showed a tremendous amount of data as to his tests on the subject. They showed that the center of pressure surrounding a .22 slug in flight moves along the axis of said slug and will with regularity cause said slug to slightly destabilize as it becomes subsonic down range
That's interesting and I'm sure it's true but it has no relation to what was being discussed in the posts. What was discussed was whether or not there is some unusual or unexpected effect on a bullets flight in the transonic region. Something you (and others) may not realize is that the ammo you are probably shooting starts out and stays in this region for their entire flight out to about 100 yards. All I've been saying is I can't find anything in the science - or for that matter in my shooting - that indicates anything other than a drop in drag forces and less change in drag as the bullet moves subsonic. If there is in fact some intense disruption of flight in the transonic region then we rimfire shooters probably have it with every round we shoot in competition.

OK Cec, throw the updated "reading for understanding" refreasher course in there. In the .22 world when more match ammo was actually made at supersonic velocities it was found that lots of it in the particular barrels it was being pushed through, was only slightly so and it would pass back to subsonic, often just in front of a 50 yard target, become destabilized and print at that state, thereby developing the entire question of avoiding the whole[ hole] issue be starting out lower than the speed of sound. Note I made a funny. I know you can't find that in science also but I'm assuming at some point Mom let you outside to play with the big kids.

Larry Elliott
11-02-2010, 06:43 PM
Geez Tim, ya beat me to it! Most modern rimfire match ammo is subsonic so doesn't have to go transonic. Another reason that HV .22 LR ammo isn't usually as accurate as standard velocity or subsonic ammo.

alinwa
11-02-2010, 10:28 PM
tim made a funny!!

pacecil
11-03-2010, 12:19 PM
Ok, I think I see the problem. (other than the mental abilities of Tim!) Sorry Tim I couldn't resist! My mom let me out to play with the other kids but she warned me to stay away from that Tim kid - he's not quite right!

Bullet flight doesn't just switch from supersonic over to subsonic instantly. It actually occurs over about a 400 ft/sec range. That Eley ammo you are shooting will be in the transonic range from roughly 1100 f/s down to about 900 f/s. So if it is going to be unusually disturbed when traveling in the transonic range it's probably being disturbed all the way to the target. It doesn't just pop over to a stabilized condition an instance before it enters the 50 yard target. In the real world, of which you are apparently not a part, nothing happens instantly. Eley ammo then is loaded so it exits your gun in the worst condition for combating the wind according to the beliefs of a great many shooters. This is what the McCoy report, pointed out by Boyd Allen, was trying to tell you when he recommended ammo be loaded down to 950 for best wind resistance. It is around 950 that you are coming out of the transonic region.

The point of my whole argument is that contrary to what a great many shooters think I don't believe there is any amplified effect to a bullets flight in the transonic region. All that I know happens is a rapid fall off in the drag force and also a reduction in how fast the drag force is changing. It's kinda like you were braking in your auto and you begin to let up on the brake. This just slows you at a lesser rate but it's nothing violent.

tim
11-03-2010, 09:18 PM
Cecil, the McCoy report is old and there is a fair bit it does not delve into, this being one major piece. I understand that your argument goes against what a great many shooters believe. That's because they actually shoot. But hell nobody has it over you on the keyboard, I'll grant you that. If you actually shot you'd probably know several shooters that pick ammo that chrono's about 950fps just in front of the target, go figure.
Rather than just winging this as you go, read the Tirrell research.

Boyd Allen
11-04-2010, 12:11 AM
goodgrouper,
You know you just mucked up a perfectly good discussion, that had the potential of going on pretty much forever, by polluting it with real reproducible experience. Shame on you!;)
Boyd

pacecil
11-04-2010, 01:26 AM
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".

tim
11-04-2010, 09:29 PM
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.

pacecil
11-04-2010, 11:14 PM
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.

alinwa
11-05-2010, 01:05 AM
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

pacecil
11-05-2010, 01:01 PM
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 1.20.8). 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!

alinwa
11-05-2010, 01:32 PM
So pa, what you're saying is that a projectile carries a boom while traveling anywhere from .8 to 1.2 mach?

al

tim
11-05-2010, 03:09 PM
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.

mks
11-05-2010, 06:17 PM
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

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

HuskerP7M8
11-05-2010, 07:04 PM
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

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

pacecil
11-06-2010, 12:21 PM
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

alinwa
11-06-2010, 02:00 PM
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

pacecil
11-06-2010, 11:18 PM
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.

alinwa
11-07-2010, 03:15 AM
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

alinwa
11-07-2010, 03:17 AM
To answer your rifle in the forest question....... NO

:)

al

Al Nyhus
11-07-2010, 07:52 AM
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.

pacecil
11-07-2010, 12:24 PM
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.

alinwa
11-07-2010, 11:11 PM
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.

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

al

alinwa
11-07-2010, 11:27 PM
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

pacecil
11-08-2010, 08:54 AM
Would I say something that wasn't completely true???

pacecil
11-08-2010, 09:12 AM
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?

Greg Culpepper
11-08-2010, 10:04 AM
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

Al,

Speed of sound in air is directly dependent on temperature with minor influence from humidity. SoS is not influenced by air density. I had thought that SoS increased with air density since we know that it's faster in water and steel but this is wrong. Yeager's team chased the sound barrier at high altitude because of high speed/low drag (low density at altitude) with the side benefit of lower speed of sound because of much lower temperature at high altitude.

I had thought that Federal UM 1 rimfire ammo that was slightly supersonic lost its crack with dropping temperature because the speed of sound increased with the resultant increase in air density. Henry got me past this misunderstanding of the physics of it. Actually, the speed of the ammo drops faster with decreasing temperature than the speed of sound drops and the two cross at about 50 degree F.

It helps to remember that the speed of sound at a temp of absolute zero is also zero.

Greg

pacecil
11-08-2010, 10:44 AM
The speed of sound in air is equal to the sq. rt of P/r where P=pressure and r=density. There are approximate formulas that involve only temperature for SOS in air but density is in there. Believe me the SOS depends on density in all materials.

Greg Culpepper
11-08-2010, 12:03 PM
The speed of sound in air is equal to the sq. rt of P/r where P=pressure and r=density. There are approximate formulas that involve only temperature for SOS in air but density is in there. Believe me the SOS depends on density in all materials.

Cecil,

True as far as you go but since pressure and density of air change together in lockstep with each other (ideal gas law) and one is divided by the other in your formula, when applied to earth atmosphere and not some other gas or combination of gasses, the resulting value is a constant and may be ignored as a source of change. Water vapor as a variable does have a minor effect on SoS as its molecular weight is different than the average for nitrogen/oxygen-air. Temperature derived SoS values in earth atmosphere are far better than mere approximations for our purposes, even over very large changes in pressure and attendant density.

Greg

Gene Beggs
11-08-2010, 02:58 PM
I believe it was Hemingway who said, and I'm paraphrasing,

"Better to remain silent and appear dumb than to open one's mouth and remove all doubt."

Boy, I'm sure glad I stayed outta' this one!

Gene Beggs

pacecil
11-08-2010, 07:10 PM
The equation you use for calculating SOS, which involves only temperature assumes pressure and density are constant. This is why it is only approximate, It's perfectly fine for standard conditions or near standard conditions. It assumes some standard density and is probably accurate enough for everything we're doing here. You must know density and pressure to determine true SOS. You CANNOT do it with temperature alone. Your statement that P/r is a constant is true only if these are the only air properties that were changing.

Greg Culpepper
11-08-2010, 10:06 PM
The equation you use for calculating SOS, which involves only temperature assumes pressure and density are constant. Wrong. I assume nothing of the kind. But pressure and density always change together and proportionately to each other, always. If pressure doubles, so does density, always. So the ratio between them is constant and changes nothing.
This is why it is only approximate, It's perfectly fine for standard conditions or near standard conditions. It assumes some standard density and is probably accurate enough for everything we're doing here. You must know density and pressure to determine true SOS.
Standard air pressure is 14.7 psi at sea level. Standard air density is 0.075 lb/cubic ft at sea level. Travel up until pressure is 14.7/2 or 7.35 psi and density will also be haved to exactly 0.0375 lb/cubic ft.

14.7/0.075=7.35/0.0375

It's the same value, the same ratio, exactly, always, everytime and has no effect on SoS because a change in pressure indicates a change, the same change, in density. Go up or down in the atmosphere and the pressure changes exactly the same percentage as density and exactly inversely to volume.

You CANNOT do it with temperature alone. Temperature is the only thing that changes SoS in air (ignoring minor changes from water vapor)
Your statement that P/r is a constant is true only if these are the only air properties that were changing. What other air properties are you talking about?

Greg

alinwa
11-08-2010, 10:07 PM
I believe it was Hemingway who said, and I'm paraphrasing,

"Better to remain silent and appear dumb than to open one's mouth and remove all doubt."

Boy, I'm sure glad I stayed outta' this one!

Gene Beggs

Smart Feller!

;)

al

Gene Beggs
11-08-2010, 10:15 PM
Smart Feller!

;)

al



This thread has certainly been lively and interesting. Some great minds at work here.

Pacecil has probably put me on his ignore list but I enjoy reading his posts and must say he has proven himself to be very smart and very well educated.

Greg and Al, you guys have been doing your homework. Keep up the good work. I love you all and look forward to visiting with you face to face; including you, Pacecil.

Gene Beggs

alinwa
11-08-2010, 10:34 PM
Al,

Yeager's team chased the sound barrier at high altitude because of high speed/low drag (low density at altitude) with the side benefit of lower speed of sound because of much lower temperature at high altitude.




AND...... let's not forget the added benefit of several more minutes and miles before you smoke a hole!

al

Greg Culpepper
11-08-2010, 10:44 PM
I'm looking forward to that visit as well, Gene. Maybe we can get Al to Odessa at the same time.

Greg

alinwa
11-08-2010, 10:54 PM
Well, I think I've learned some things......

I've always wondered why you even need wing surfaces on a swept-wing SS jet (other that to support the leading edge!) and pacecil has given me impetus to look into it more. I'm still tempted to argue that the only function of the wing is to change the plane of the shockwave but I'd best shut up and lissen a liddle, aeronautics not being my bailiwick. I'm working on theory alone in this arena.

And Greg...... Temp only huhh..... it's easy to see that pressure and density are in lockstep but ??? Temp only???

So pressure and density effects cancel in a gas but not in a liquid where of course they're ALSO lockstepped...


hmmmmm, fun.


al

alinwa
11-08-2010, 10:58 PM
I'd love the face-to-face...... pacecil too...... but I've learned that TIME is a killer!

Need days not hours

:)

Odessa sounds like the logical place!
al

Greg Culpepper
11-08-2010, 11:45 PM
Well, I think I've learned some things......

I've always wondered why you even need wing surfaces on a swept-wing SS jet (other that to support the leading edge!) and pacecil has given me impetus to look into it more. Supersonic landings are tough on the equipment and the pilot. Take offs to. Not to mention rate of turn which is what kills in a dog fight. SS is just for getting to the fight. You need a wing to hold you up the rest of the time.


And Greg...... Temp only huhh..... it's easy to see that pressure and density are in lockstep but ??? Temp only??? If you take away pressure/density what else is there? Phase of the moon?


So pressure and density effects cancel in a gas but not in a liquid where of course they're ALSO lockstepped...Air is elastic so pressure and density change together. Not so for liquids. A quart of water at the depths of the ocean weighs the same as at the surface. But the pressure.....



hmmmmm, fun.You betcha!


Greg

alinwa
11-09-2010, 01:30 AM
A quart of water at the depths of the ocean weighs the same as at the surface. But the pressure.....You betcha!


Greg

hey...... duhhh! :)

that makes sense even to me

al

pacecil
11-09-2010, 10:17 AM
Nope you are wrong. A quart of water at the bottom of the ocean is more dense, thus weights more. All substances are compressible, some just more that others. In most cases you don't have to deal with compressibility of liquids and solids but there are instances in engineering, and for that matter in practical every day applications, where you do.

Greg Culpepper
11-09-2010, 01:56 PM
Nope you are wrong. A quart of water at the bottom of the ocean is more dense, thus weights more. All substances are compressible, some just more that others. In most cases you don't have to deal with compressibility of liquids and solids but there are instances in engineering, and for that matter in practical every day applications, where you do.

Really. Can you give us an example in practical everyday life where the compressibility of fluids needs to be dealt with?

pacecil
11-09-2010, 05:19 PM
If you use silicone based brake fluid you will have a mushy pedal because of the greater compressibility of the silicone fluid. That's about the only instance I can think of at moment for "everyday" life. However compressibility can give problems when engineering high pressure devices such as pumps, compressors, and hydraulic systems. It also has to be considered in lubrication, metal forming, and actually chemical processing, - any place where liquid at high pressure is involved.

Greg Culpepper
11-10-2010, 07:32 AM
Well, there you go!

Charles E
11-10-2010, 07:38 AM
So, practically speaking, I shouldn't use silicon fluid in the (muzzle) brake of a .22 rimfire?

Geez. And bowling balls in the gunsmith forum?