Author Topic: Vertical Deflection due to a Crosswind aka Aerodynamic Jump  (Read 4733 times)

375CT

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Vertical Deflection due to a Crosswind aka Aerodynamic Jump
« on: April 13, 2014, 07:34:30 PM »
Hi there,

Just finished to read this paper by Mr. MacDonald (Sierra's ballistician) and it makes a lot of sense to me, indeed the formulation presented is much better than the usual "formula" by Mr. Litz (based on a curve fit and Sg)

Please check it out here

http://www.exteriorballistics.com/ebexplained/articles/article2.pdf

What do you think? ;)

mman

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Re: Vertical Deflection due to a Crosswind aka Aerodynamic Jump
« Reply #1 on: April 24, 2014, 06:26:41 AM »
I just finished reading the article for the first time. I have to read it again and compare with other books to come to any conclusion. Basis of the crosswind vertical drift seems to be bit different from what I have red before. Still this article doesn't give tools to solve the actual drift like Litz does. Not taking position at this point if Litz's formula is accurate or not. However the article states to answer three questions.

A) The total bullet drift in a crosswind blowing from left to right is toward 4 o’clock.
This is obvious and explained by other references like McCoy and Litz. Article still gives good input on this one.

B) As the crosswind speed increases, the vertical drift of the bullet does not increase as rapidly as the crossrange drift.
I didn't catch the explanation for this one at all. Did someone else? I still wonder if this is even true...

C) Crosswind blowing from right to left produces a little more vertical drift than a crosswind blowing from left to right.
Author doesn't explain this at all. Just couple of guesses. Same thing goes for this one; I don't know if it is true or not.

All in all those crosswind vertical drifts are so small compared to other deflections that it is really hard to achieve hard facts empirically. Some target shooters tend to jump into conclusions too easily based on what they see on the target. For example very small vertical wind components could lead to conclusions like B and C.

admin

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Re: Vertical Deflection due to a Crosswind aka Aerodynamic Jump
« Reply #2 on: April 30, 2014, 07:29:53 PM »
The problem with these matters is that assumptions are made "e.g bullet flies in the direction of the wind" and presented as facts.

Even they are somewhere along the trajectory true, there is a period they are not valid. What happens then.

Nevertheless, I have time to spare I will read better the article.

Robert

375CT

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Re: Vertical Deflection due to a Crosswind aka Aerodynamic Jump
« Reply #3 on: May 05, 2014, 05:51:19 AM »
Nice replie, thanks for them.

Now, I agree there are some holes in the paper, but compared to what Litz is offering in terms of addressing the AJ, I think the outline is way better in many aspects. Will take a new in depth read to see if I can understand it better.

In my opinion, AJ due to crosswind alone is a tricky one, and this formulation makes more sense to me than the one presented by Litz.

Further comments are welcome of course. ;)