"Wake Turbulence"

C

Chism G

Active member
When the commence fire command is given ,on the firing line, at a short range Becnhrest match. There is 7,10 sometimes 15 minutes of continuos rifle firing at targets positioned at 100,200,300yds.

This continuos firing creates what Gene Beggs describes as "Wake Turbulence"

This is his description of "Wake Turbulence"


Wake turbulence? Yep, and it's most dangerous in dead calm conditions.

There are actually three components to the wake turbulence we shooters are faced with;

1. Ring vortices created by the muzzle blast. (This has nothing to do with the projectile.)

2. The wake left behind the supersonic bullet.

3. The column of extremely hot gases that are blasted into the much cooler atmosphere.


Bear in mind that all this commotion is blasted right down the flight path of all succeeding shots, and if conditions are dead calm, it will hang there and rotate for a surprisingly long time.

"So,,, what can be done about it?" you ask.

Well, for one thing, you can wait; wait for a little breeze to come along and drift the stuff out of your way.

The other option is to wait longer between shots. (This is one time when you don't want to 'machine gun' your record shots.)



Dennis from Georgetown,Tx asked; Is there any consistency to the effects of these gun/bullet-induced turbulences or vortices? If I have an absolutely DEAD day, no wind at all, flags just sitting there, can I expect my bullets to be deflected one direction only, or is it random? If I wait long enough for the initial turbulence to go away, will my bullet deflection repeat in direction and magnitude?

Is any of the turbulence related to rate and direction of twist? I can imagine that the hot gases being ejected behind the bullet would corkscrew in alignment with the rifling - clockwise for a right hand twist for example - but have no proof. More for a fast twist, less for a slower twist?



Andy Cross says
These are the types of mysteries the interferometer would pick up and display. Being able to see the condition the flags probably don't respond to and find out how they affect a bullet will be a big learning curve. But you can't do that without the tools.
Andy.



Well..This subject may or may not be something that peaks your interest. Just thought I would put it out there for discussion.


Glenn
 
Glenn,

Thanks for starting this, and for saving me all that typing again!

I'm looking forward to comments and a good discussion on this.

Dennis
 
Before we get started,,

,,,with this discussion, please go to your favorite web browser and type in,

"Ring Vortices" After perusing that for a while then go to, "Vortex Cannons"

Fascinating; isn't it? And a real eye-opener.

Later,

Gene Beggs
 
The Dreaded Calm

Most very experienced benchrest shooters will tell you that the condition they are most wary of is the dead calm during the first match of the morning. :(

We've all been there; you go to the line and there is not a breath of air stirring, sight picture is crystal clear and not a ribbon is moving. You think to yourself, "Man, I can't wait, I'm gonna steal one this morning."

The range officer says "Commence firing" and you machine-gun your five shots downrange while the flags remain motionless and wind up with a .400. :mad: After whispering, "Aw shucks" or something of that nature, you ask youself, how in the world could that happen; nothing was moving. :mad:

Well let's take a look at the situation. :confused:

If you didn't fire a fouling shot and three or four sighters, how do you know the rifle was in tune? If you have ten minutes in which to complete your first group, take your time. Don't get suckered in to shooting in a dead calm without checking things out on the sighter.

But let's assume the rifle is shooting and you're doing a good job of rifle handling; what else could cause you to shoot a .400 group in a dead calm condition? :eek:

Could it have been wake turbulence? :eek:

To be continued.

BTW, did you take a look at 'Ring Vortices' and 'Vortex Cannons' ?

Later

Gene Beggs
 
Several years back, while looking down range at motionless everything, before the first match of the day, I was standing next to Eunice Berger and I said something about it looking like it was going to be a trigger pulling contest. She replied that I should not kid myself because there were things down there that could move a bullet, that could not be seen on the flags, and that there was no mirage, and that she shot mirage. If I remember correctly, she won that weekend, shooting a series of rather uniformly small groups, right in the centers of her targets. It was a real tour de class. The only way that I can think of to eliminate tune from the list of possible causes would be to come to the line with enough different loads so that after testing on the sighter, the best of the bunch could be used on the record. Wait a minute. I seem to remember watching a video of Mr. Boyer doing exactly that, although I believe that is was later in the day, and conditions were far from calm.
 
Ever tried smokers

Has anyone ever tried movie smokers on the range. Smokers are those flare like devices that are used on movie sets to create smoke in small amounts not like those machines where a battle field has to be simulated. The smoke is quite dense and it takes some wind to break it up.

At a friends private range about 5 years ago I set up 4 of them in almost dead calm wind conditions. We all fired a shot about 2 seconds apart and watched the smoke. The results were disturbing to say the least. The second and third shots went out of our groups. Some high some low and mine in opposition to the slight drift the flags were showing. Since then I have waited until some wind picks up. Perhaps the wind really is our friend although I doubt it.
Andy.
 
I have shot over smoke on my home range and while it did offer some useful things I decided to stop it because it's of no use at a public range.

al
 
"Dead Calm"

You don't have to be a HOF shooter or top shooter to be a victim of the phenomena being discussed here. 12/13 years ago when I first started shooting bench rest ,I mentioned to some fellow shooters that I felt there were some "Demons" lurking at the Range at Tom Ball,Tx. Back then,I dismissed it as being an unavoidable occurrence, common to the sport of Benchrest. Prior to coming to the Sport of Benchrest,I shot a lot of Pistol. I laughed when I saw a home made wind flag. Since then, I have come to love my wind flags. Me and my flags don't always communicate but I Wouldn't leave home without them.

When my wind flags aint moving,I get a little uneasy. When the top shooters are on the line,I figure it's going to be a trigger pull contest and I don't stand a chance. I've heard these concerns from other shooters. I've shot some big groups in dead calm conditions,that I can't explain. I know how to tune my rifle. An out of tune rifle will shoot big groups all weekend long. The "Demons" will get you in dead calm conditions. Whether your rifle is in tune or out.

Absent any other explanation,I'm on board with Gene and his suspicions about "Wake Turbulence"




Glenn
 
One time I happened to have a range to myself, on a weekday morning. There was a high bank of clouds, and narry a leaf or blade of grass moved for an hour and a half. During that time, I was able to shoot a number of small (for me) groups, and could see cause and effect so clearly that I learned a couple of things that I was doing wrong, that would have been lost in the noise in more ordinary conditions. My point is that calm conditions in an of themselves do not pose a problem. For those of you who have shot groups that were much larger than you should have, under calm conditions, did this always happen when others were shooting on the same range?
 
That's why

Chism G said:
You don't have to be a HOF shooter or top shooter to be a victim of the phenomena being discussed here. 12/13 years ago when I first started shooting bench rest ,I mentioned to some fellow shooters that I felt there were some "Demons" lurking at the Range at Tom Ball,Tx. Back then,I dismissed it as being an unavoidable occurrence, common to the sport of Benchrest. Prior to coming to the Sport of Benchrest,I shot a lot of Pistol. I laughed when I saw a home made wind flag. Since then, I have come to love my wind flags. Me and my flags don't always communicate but I Wouldn't leave home without them.

When my wind flags aint moving,I get a little uneasy. When the top shooters are on the line,I figure it's going to be a trigger pull contest and I don't stand a chance. I've heard these concerns from other shooters. I've shot some big groups in dead calm conditions,that I can't explain. I know how to tune my rifle. An out of tune rifle will shoot big groups all weekend long. The "Demons" will get you in dead calm conditions. Whether your rifle is in tune or out.

Absent any other explanation,I'm on board with Gene and his suspicions about "Wake Turbulence"




Glenn
Click to expand...

That's why I will continue with the interferometer project. You can make them as sensitive as needed. Any differences in air temperature and its movements could be visualized. Getting the units foot print small enough and at the same time cost effective are the main issues. Then I have to shoot enough with it to establish cause and effect patterns in order to make use of it. Don't expect to see them appearing at shoots very soon.
Andy.
 
The subject of wake turbulence is familiar to anyone who has flown a small aircraft from an airport where much larger aircraft operate.
 
Are sub-sonic, 50 yd RF BR rifles going to have wake turbulence issues ? I see the same issues in "no wind" conditions whether I am shooting my RF or CF rifles. When my props quit turning I stop shooting. Sad experience has shown me that the bullet flight is not predictable in these conditions.
 
"Calm Conditions"

Boyd Allen said:
My point is that calm conditions in an of themselves do not pose a problem. For those of you who have shot groups that were much larger than you should have, under calm conditions, did this always happen when others were shooting on the same range?
Click to expand...



A HOF shooter cautioned me one time about tuning my rifle in dead calm conditions. His reasoning was, when the wind starts blowing, your tune goes in the toilet. I have shot some small groups in dead calm conditions when nobody else was around. Those groups don't mean much because the only "wake turbulence" is created by your rifle and your groups don't get posted on the wailing wall.:D In a match where you got 30 rifles, all shooting, on both sides of you, in dead calm conditions, Its a whole different World out in front of the benches.

If you notice,I keep referring to the range at Tom Ball,Tx. For all I know, wake turbulence could be more prevalent at specific ranges. I seem to have more problems shooting in dead calm conditions at this range than any other range in the region.

We have competitors who have shot their way into the Benchrest Hall Of Fame. For some reason,they are reluctant to join these discussions. It would be interesting to hear what they have to say about this topic.




Glenn



Glenn
 
Boyd Allen said:
For those of you who have shot groups that were much larger than you should have, under calm conditions, did this always happen when others were shooting on the same range?
Click to expand...

Absolutely not...... while I'm not discounting wake turbulence, what I call "gremlins" are completely unrelated to others' shooting.





A story, from a match-type setup

I was at the ('99? 2000?) IBS Bench Rest School in Canastota shooting with Lee Euber as my instructor and we got one of those lulls. DEAD calm like the inside of a tomb, flags just hanging w/nary a tail twitch. The way we were set up was with seasoned Shooters, names like Kelbly, Sutton, White, Gammon etc as instructors each with 3-4 students and we shot as teams.

Now here's the problem, I'd picked up a brandy new Borden HV from Jim, gorgeous gun in metallic green from back in the day when their were still some stocks being painted, and Lee Euber had somehow gotten the (mistaken) impression that I had a clue......so while he was jabbering in everyone else's ears he was kinda' letting me have my head. And we were winning...... the word had just filtered down the line the he and Allie were neck and neck for first.... Those of you shooters who know the brothers will KNOW the dynamic, Lee was SERIOUS and we were feeling the heat.......This was my third or fourth group and the gun was shooting like a mo'chine.....and I was driving OK...... and then along comes MY CONDITION!!!!


I live in WA. The weather out here is as stable as a rack of anvils, glaciers move faster. I'd had a dedicated home range for 3-4yrs, carved out of a timber stand, just a 50ft wide trough through the trees, plagued with swirly-whirlies and nearly unshootable in windy conditions (I've since moved and set my range out in the open) so my favorite condition was dead calm.


Sooooo, long-story-short when the line went hot I was on that badboy like stink on cheese, gonna' RUN me one eh! Babbity-BABBity-bappity-BAPPP I laid down a group so fast I din't even have time to look.

And then I LOOKED......

And I slowly turned toward Lee and he was LOOKING too, at me, like I'd sprouted some sort of weird growth, completely speechless...flummoxed, stuttering....WHAT the??!!!!! He didn't have to look at the target,,,,,, in fact I think he just threw his head toward the range and rasped "well?"

It was a complete wreck, it wasn't a duck nor a turtle nor a wurm, it was a SPLATTER with paper gerrymandering through.

He couldn't really talk much but he did manage to articulate one more word, "WHY????"

I personally don't think it's localized blast turbulence for several reasons, one being that the wake turbulence is too SHORT and two having to do with what that bullet's doing as it hula's out from the immediate muzzle screwing down it's own blast tube but regardless, dead calm is deadly in many (most?) cases. I'm spoiled here at home. I keep a couple Borden's tuned up in the rack (GLACIAL weather, remember, and shooting from indoors :) ) and on any given day when I'm testing rifles I can grab up a known, tuned setup and SHOOT the range. Some days I wait for the wind to pick up. IMO the dispersion from a hot firing line is probably from the hot gases messing up the optics as Gene mentions in #3 above.... I'm guessing here...

FWIW

al
 
I wonder if slight differences in bullet shape and balance make a difference in the degree to which this is true. It almost seems as though the orientation of bullets in flight is stabilized by the addition of a small amount of cross wind. One thing that I do know is that mirage can be a lot worse when there is no wind, and I wonder if that is a contributing factor to what has been reported.
 
"Mirage"

Boyd Allen said:
I wonder if slight differences in bullet shape and balance make a difference in the degree to which this is true. It almost seems as though the orientation of bullets in flight is stabilized by the addition of a small amount of cross wind. One thing that I do know is that mirage can be a lot worse when there is no wind, and I wonder if that is a contributing factor to what has been reported.
Click to expand...

If you watch the video in post#12, you can see how vortices can travel pretty long distances, at least in this video. If these vortices are being produced by high velocity gasses,you can imagine how they would disturb the air in front of the bench.

As far as mirage(Image) being the culprit. I just bought a Rail Gun. When I shot it in dead calm conditions,I got the same results on many occasions. If your flags ain't moving,you can't see whats out in front of you. If you can't see it, you can't hold for it.

Hurry up with that project Andy.



Glenn
 
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Chism G said:
If you watch the video in post#12, you can see how vortices can travel pretty long distances, at least in this video. If these vortices are being produced by high velocity gasses,you can imagine how they would disturb the air in front of the bench.

As far as mirage(Image) being the culprit. I just bought a Rail Gun. When I shot it in dead calm conditions,I get the same results. If your flags ain't moving,you can't see whats out in front of you. If you can't see it, you can't hold for it.

Hurry up with that project Andy.



Glenn
Click to expand...


OK, on the distance thing, YES the air is disturbed for quite a long way out, almost exactly as far out as your shot is going to disturb (override?) it......

As far as mirage, I stand corrected, hadn't thought it through. I'm in agreement with you, in fact I've observed mirage and "slow mirage" as they move the image around in the scope of a stable setup and YES I'll agree that the gremlins affect rails just like baggers.....

In short, I have to agree with Glenn, it aint just optical!


BTW my term for this whole phenomena is "bumpy" air. But IMO it extends through the entire range, that it's not just disturbance near the muzzle, and that your own rifle shot punches a perty clean hole thru the immediate muzzle area.

al
 
Again, I hadn't thought this through..... "punching through" the disturbance is just wrong as the bullet passes the gasses while still in the disturbed area.

Soooo, I guess my ONLY support is anecdotal :) the fact that this effect is present whilst I'm shooting all alone and lonely at home....


ooops

al
 
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