Dissimilar Wind Drift Question for Bryan

[dcali]

What I mean is drag is not a force that acts sideways on the bullet. It acts in line with the bullet's velocity. The only forces that are acting sideways are not due to the wind - gravity and the lift force from the yaw of repose. What dissimilar wind deflection implies is that there is another force involved that is somehow dependent on the wind and the spin. If this effect is real, that force has to be present. Nobody has come up with an explanation for that force.

 

[jrm850]

I'm like a billy goat watching a television; i'm thinking 2d.

So travelling through the soup with a yaw in effect creates a series of different lift profiles from tip to base? In other words, if you sectioned the bullet in flight attitude to reveal chord profiles with the direction of travel as your cut plane, each profile would be unique with different drag and lift? It seems like that would cause some kind of resonant cycling with the drag being greater at the base trying to counter the tip wanting to point where it needs to point.

exaggerated example:

 

[jrm850]

I hope I'm not asking really dumb questions. The only background I have in fluid dynamics is getting about halfway through the book Aero-Hydrodynamics of Sailing while trying to cram for a project at work dealing with Traction kites.

 

[dcali]

I think a simpler way of saying that is that both lift and drag are dependent on yaw.

Drag by definition is opposite the motion of the bullet, even if it's crooked. Lift is at 90 degrees to the motion of the bullet, even if the bullet is crooked. Note that "lift" is sort of a confusing term - it does not mean "up". It means at 90 degrees to the trajectory, and can be up, down, sideways or any other direction.

Think about sticking your hand out the window of your car palm down but perfectly straight. You will feel the wind trying to push your hand back to the rear of the car, but only a little since your hand is flat, fingertips to the wind. You won't feel any tendency for your hand to rise or fall due to the wind.

But if you angle your hand up a little, you will realize two things. First, that the wind is now pushing your hand backwards more forcefully - in other words, increasing the yaw of your hand has increased drag. Second, there is now wind pushing your hand up. This is lift. The more you angle your hand, the more lift - to a point. When your hand is pointed straight up, there is no lift, but a lot of drag.

The force pushing your hand back toward the rear of the car is drag. The force pushing your hand up or down is lift. Both change with the angle of your hand (yaw). It's the same thing with bullets.

The conventional wisdom is that wind deflection is entirely drag based. It is the result of the net air flow (velocity + wind) being at an angle to the line of fire. This is why wind deflection is determined by BC, and not some other number (say, a wind coefficient).

Spin drift is lift based. It is the result of the yaw of the bullet being on average pointed in the direction of the spin (which is due to gravity pulling the back end of the bullet down - the gyroscopic effect of the spin causes the tip to point right instead of up. This is a bit of an oversimplification.).

A dissimilar wind effect would be something else according to Mr. Tubb's explanation, which isn't entirely clear to me.

As to the cycling you describe, it's not quite that simple, but you do in fact see cyclic motion in the motion of the bullet's tip.

 

[Berger.Fan222]

I think the scientific method properly applied reasons from observed effects back to possible causes.

Saying the observed effect (dissimilar wind drift) cannot exist until the theoretical cause (force) is understood and articulated seems silly.

Claiming the possibility of an effect has been disproven by the absence of observed dissimilar wind drift in spin stabilized rockets also seems silly. Have any rocket experiments been performed with opposite spins that would recognize an effect of the expected magnitude?

I think we should be open to the idea that the effect may not have been widely observed because most observers have not been looking with sufficient care.

 

[dcali]

I would agree, except that great care has been taken to look at these effects. There are several forces that have been looked into that were too small to be measured, but that did not stop the folks at the BRL and elsewhere from trying! This is an effect that is reported to be not only measurable, but obviously measurable. The fact that it was never measured, observed or theorized in the past 100 years of military research is not a small thing. Good science means taking in ALL of the available information. There is currently far more evidence to refute dissimilar wind drift than to support it.

That doesn't mean that the observations of Mr. Tubb aren't real. It just means his explanation is lacking.

 

[DTubb]

No one to my knowledge has ever shot these dissimilar wind drift tests with stellar ammo/scope/ rifle combinations.
I have done this same test over and over and over again with multiple shooters in multiple classes over multiple years (I am not always one of the shooters) so this indicates several hundred virtual simultaneous volley firings for reference criteria and conclusion is that this phenomenon exists...

It is equatable to being approx. 100 yards closer to the target with the optimum barrel twist direction for the prevailing conditions.
DTubb

Shot this test 4 days ago and it hasn't changed...

 

[DTubb]

If one is exploring other bullet flight phenomenon how about the concept that a full value right hand wind isn't from 3 oclock....

 

[Scott Harris]

David, thanks for your info and all the great contributions you have given the sport over the years. I don't doubt your claim, but it is considered a best practice in science to have an independent third party review your results and conduct separate experiments to validate them. That is the gist of my questioning. Have you considered asking someone reputable to do this for you.....like Bryan? Of course, Bryan will have to come out West where we actually have some wind.

Thanks,
Scott Harris

PS. Thanks much for those CS-Duo springs....they rock. and the chapter in your book explaining how you set up your Dillon 550. You saved me many hours of work!

 

[DTubb]

Scott,
Bryan was invited a couple of years ago to come by when he is working/visiting his friends in Canadian.
Dtubb

 

[Bryan Litz Ballistics]

Consider the following hypothesis:

What's being described as dissimilar wind drift is actually spin drift.

Here's why I support this hypothesis:

1. Spin drift is a known mechanism in ballistics which explains the observed effects of dissimilar wind drift.
2. None of the accounts of observed 'dissimilar wind' describe how spin drift was accounted for in the test.
3. Hundreds of years of ballistic research have failed to identify this effect. Coriolis, a much subtler effect was identified and is well understood. How could the world have missed a bigger effect?

Suppose you zero a rifle at 100 yards, install a level and verify pure vertical tracking of your turret or reticle hold. Now go out and shoot in different winds. If your barrel is a right twist barrel, of course you will see less total deflection in a right-to-left wind, and more total deflection in a left-to-right wind at long range. You're seeing spin drift.

The actual wind deflection is the same, but the reason you see more or less total deflection is because spin drift is either adding or subtracting to the wind deflection. Of course it works the opposite for left twist barrels.

You don't need to invent a new name for spin drift. Unless you can't patent spin drift in a scope reticle.

-Bryan

 

[Berger.Fan222]

Someone correct me if I am wrong, but I think it is simple to conduct an experiment to distinguish between the two hypotheses (dissimilar wind drift vs. spin drift).

If two rifles (otherwise identical left and right twist barrels) are sighted in for a given range under windless conditions, then experience dissimilar wind drift when the wind starts to blow, this would support the dissimilar wind drift hypothesis.

If the two rifles only exhibit drift differences when sighted in a shorter range and then moved to longer range, but do not exhibit drift differences in the earlier test (sighted in at long range with no wind), then the spin drift only hypothesis is supported.

Did I miss something, or does this make sense?

 

[jrm850]

If your barrel is a right twist barrel, of course you will see less total deflection in a right-to-left wind, and more total deflection in a left-to-right wind at long range. You're seeing spin drift.

-Bryan

I think the confusing part is that he says a right wind will deflect more to the left than right.


From the linked paper:
Right twist — Wind from the right moves the bullet further left than a left wind moves the bullet to the
right.
It’s just the opposite for a left twist — Right wind will move the bullet less and a left wind moves the
bullet more. Remember, this phenomenon is totally independent of spin drift.

 

[Marksman63]

Still confusing?

What Bryan said seems quite clear and is what I learnt at my university engineering classes

 

[DTubb]

Shot a lot of different distances in the (800- 1300yds) past. Always shot at the 1000 yard targets with someone in the pits marking each shot for immediate feedback. Different distances allowed for high right and left wind feedback by moving laterally on the range.
Rifles were rechecked for zero each time at 200 yards preceding each test time. Still do same technique.

The spin drift is accounted for in the testing. I have used Bryan's spin drift recommended numbers with the leupold mildot scopes.
Even if his calculations are off 1 click either way it is still too large a difference to ignore and the more spin drift dialed for each rifle the larger the ERROR becomes.
Since we all know there is some spin drift involved. You want 6 inches or 9 inches of spin drift doesn't matter the dissimilar windrift distance between the two rifles indicates a larger effect occurring.

Both of the current R&L twist rifles use the same Mark 8- 3x25 Leupold mildot reticle (used to use 5x25 Premiers with mirror imaged DTR reticles- installed left twist with a reticle in reverse - also one does not touch the DTR's knobs after 200yd zeroing) with same results. All the rifles have 2 sets of bubblevels (one on the scope and one on the barrel). Every effort for controlled experiment has been accounted for herein. Same ammo - almost the same velocity.

Shot the test with 284's and 180's at 2850fps for a few years and switched to 6XC and 115's and 3050fps last year. Same results with either.

Dtubb

 

[jrm850]

Still confusing?

Confusing as in-
A very well respected member of the competitive shooting community has demonstrated a repeatable unexplained phenomenon with results that are exactly opposite of what another very well respected member of the competitive shooting community says we should expect according the to laws of physics. I know neither personally, although I do know of their accomplishments, and I am neither learned nor experienced enough to refute either.

 

[dcali]

I think it's worth saying that spin drift is in itself difficult to calculate precisely. We approximate it pretty well, but it wouldn't surprise me to see variations due to a simple lack of data.

The trouble is that the only known force that can cause this effect would be lift. For that to be true (and not simple spin drift), we have to have a way for the wind to increase or decrease the yaw of repose that we expect from spin drift. I just can't see how that could happen. Remember, the yaw of repose is caused by gravity, which acts vertically. How is a left to right wind going to induce a vertical tipping of a stable bullet? You can't prove a negative, but this is a pretty tricky thing to explain around.

The alternative is a yet unknown mystery force of a magnitude that is much greater than other known forces but was yet overlooked for centuries, and that is something that's a bit too far for me to reach for.

 

[Bryan Litz Ballistics]

I clicked on the link earlier in this thread and it didn't bring anything up.

However, dissimilar wind drift is mentioned 18 times in the patent for the DTR reticle: http://www.google.com/patents/US20130047485

jrm850,
When experts disagree it's common to consider how their credentials compare on the topic at hand. As you observed, David and I are both successful competitors. However, the issue at hand has nothing to do with competition. It's ballistics. It's science. In this area, my credentials include an aerospace engineering degree from Penn State. My first job after college was with the US Air Force where I worked on air-to-air missile design for 6 years. David can correct me if I'm wrong, but I believe his formal education is in business. Not sure what his work experience is prior to working in the shooting industry.

I don't intend any negativity or ill will toward David, nor is the matter of credentials decisive when experts disagree. It's just something to consider. For example, I would expect someone formally educated in business to get patents on things they can profit from that aren't necessarily scientifically proven. That happens all the time. Likewise no-one should expect a scientist to believe something just because a businessman has patented it and makes money from it.

-Bryan

 

[JRS]

I clicked on the link earlier in this thread and it didn't bring anything up.

However, dissimilar wind drift is mentioned 18 times in the patent for the DTR reticle: http://www.google.com/patents/US20130047485

jrm850,
When experts disagree it's common to consider how their credentials compare on the topic at hand. As you observed, David and I are both successful competitors. However, the issue at hand has nothing to do with competition. It's ballistics. It's science. In this area, my credentials include an aerospace engineering degree from Penn State. My first job after college was with the US Air Force where I worked on air-to-air missile design for 6 years. David can correct me if I'm wrong, but I believe his formal education is in business. Not sure what his work experience is prior to working in the shooting industry.

I don't intend any negativity or ill will toward David, nor is the matter of credentials decisive when experts disagree. It's just something to consider. For example, I would expect someone formally educated in business to get patents on things they can profit from that aren't necessarily scientifically proven. That happens all the time. Likewise no-one should expect a scientist to believe something just because a businessman has patented it and makes money from it.

-Bryan

Well said Bryan

 

[lawman29]

Sophistry = Dissimilar Wind Drift