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Vertical Wind

Started by 375CT, February 11, 2014, 07:30:08 PM

375CT

Hi there, since I've been reading about vertical winds, I'd like to know if somebody does know what formula is applied to compute the vertical drift.

Is it the same as for an horizontal wind? If not, please any help is welcomed!

Thanks in advance.

mman

#1
My ballistic calculator estimates vertical drift due to crosswind. But I guess you meant vertical drift from actual vertical wind component. For that you can use the same formula as for crosswind.

For example

Wd = Ws * Tlag

Wd = vertical wind drift
Ws = velocity of vertical wind component
Tlag = lag time

and

Tlag =  Tf - R/V0

R = shooting range
V0 = muzzle velocity
Tf = actual time of flight (you can use any ballistic calculator to solve this)

375CT

#2
Quote from: mman on February 13, 2014, 09:19:29 PM
My ballistic calculator estimates vertical drift due to crosswind. But I guess you meant vertical drift from actual vertical wind component. For that you can use the same formula as for crosswind.

For example

Wd = Ws * Tlag

Wd = vertical wind drift
Ws = velocity of vertical wind component
Tlag = lag time

and

Tlag =  Tf - R/V0

R = shooting range
V0 = muzzle velocity
Tf = actual time of flight (you can use any ballistic calculator to solve this)

Mman, thanks for your kind reply. I mean wind from an air stream coming from above the LOS, like the one you can encounter on a hillside. So it's a vertical air current, normal to the ground and not parallel. So, it's not what I meant a component of the "usual" wind.

Does this change your answer or does it remains the same?

Thanks!

mman

#3
Quote from: 375CT on February 15, 2014, 04:39:31 AM
Does this change your answer or does it remains the same?
Thanks!
Basicly it doesn't. In downhill shooting the easiest approach would be to divide wind into 3 components. Parallel to bullet path (aka. range wind), side component (crosswind) and vertical component. Then you can separately calculate all these components. Most ballistic calculators are capable of calculating range wind and cross wind and there you have it.

For example if your downhill shooting angle is 30 deg and you are shooting directly against 10 m/s wind:

Range wind component is cos(30) * 10 m/s = 8,7 m/s
Vertical component is sin(30) * 10 m/s = 5,0 m/s

To be exact bullet path curves along the trajectory so this 30 deg angle is not exactly constant but it is close enough remembering that in practice wind velocity is always only an estimate.
And then of course there would be a sideway aerodynamic jump due to vertical wind when bullet aligns against incoming air flow. If vertical wind comes from upwards then aerodynamic jump drifts left (right hand twist).

This down/uphill shooting is actually something I could include my ballistics calculator. I haven't thought about it since it's so flat where I live.

375CT

#4
Quote from: mman on February 15, 2014, 07:10:48 AM
Quote from: 375CT on February 15, 2014, 04:39:31 AM
Does this change your answer or does it remains the same?
Thanks!
Basicly it doesn't. In downhill shooting the easiest approach would be to divide wind into 3 components. Parallel to bullet path (aka. range wind), side component (crosswind) and vertical component. Then you can separately calculate all these components. Most ballistic calculators are capable of calculating range wind and cross wind and there you have it.

For example if your downhill shooting angle is 30 deg and you are shooting directly against 10 m/s wind:

Range wind component is cos(30) * 10 m/s = 8,7 m/s
Vertical component is sin(30) * 10 m/s = 5,0 m/s

To be exact bullet path curves along the trajectory so this 30 deg angle is not exactly constant but it is close enough remembering that in practice wind velocity is always only an estimate.
And then of course there would be a sideway aerodynamic jump due to vertical wind when bullet aligns against incoming air flow. If vertical wind comes from upwards then aerodynamic jump drifts left (right hand twist).

This down/uphill shooting is actually something I could include my ballistics calculator. I haven't thought about it since it's so flat where I live.

Mman, thanks again for your help. Certainly it makes a lot of sense now. Well, if you can add it to your calculator, just will make it a better one, and certainly it will not hurt...so why not?

mman

#5
I looked into it and I think it actually doesn't make sense to add vertical wind due to up/downhill shooting. That's because flat fire approximation in bfx doesn't allow shooting angles larger than 15 degrees or so. But I did it anyway.

You can play with following input values and see the results for vertical wind on horizontal and vertical plane:
Shooting angle [deg]
Wind velocity [m/s]
Incoming wind direction [deg]

admin

In the Netherlands there is nothing a shooter can shoot at that requires an elevation of more than a degree...

375CT

Quote from: mman on February 21, 2014, 05:03:51 PM
I looked into it and I think it actually doesn't make sense to add vertical wind due to up/downhill shooting. That's because flat fire approximation in bfx doesn't allow shooting angles larger than 15 degrees or so. But I did it anyway.

You can play with following input values and see the results for vertical wind on horizontal and vertical plane:
Shooting angle [deg]
Wind velocity [m/s]
Incoming wind direction [deg]

Mman, thanks for updating the calculator, much appreciated

I have a question, if you don't mind. Why did you care about the slope angle? I mean, I assume that a vertical wind is always normal to the LOS.

mman

Quote from: 375CT on February 25, 2014, 07:44:04 PM
I have a question, if you don't mind. Why did you care about the slope angle? I mean, I assume that a vertical wind is always normal to the LOS.
I'm not quite sure if I understand your question. Do you mean why I mentioned flat fire approximation in bFX?

375CT

Quote from: mman on February 25, 2014, 08:10:03 PM
Quote from: 375CT on February 25, 2014, 07:44:04 PM
I have a question, if you don't mind. Why did you care about the slope angle? I mean, I assume that a vertical wind is always normal to the LOS.
I'm not quite sure if I understand your question. Do you mean why I mentioned flat fire approximation in bFX?

Yes, that's correct, otherwise I'm somewhat confused about the slope in your post.

mman

That's because due to slope angle there is vertical wind component even when wind direction is parallel to ground level. I thought it was something you wanted but now I understand that you would like to input the actual vertical wind component.

Okay let's assume that wind direction is so that there is an actual vertical component, how can you measure it in practise?

375CT

Quote from: mman on February 26, 2014, 08:38:18 AM
That's because due to slope angle there is vertical wind component even when wind direction is parallel to ground level. I thought it was something you wanted but now I understand that you would like to input the actual vertical wind component.

Okay let's assume that wind direction is so that there is an actual vertical component, how can you measure it in practise?

In practice, very hard or next to impossible for sure. But for "what if" calcs that would be nice.

Sorry, but I'm not getting what you said about the wind along a slope, any chance to elaborate that a little further?

Thanks!

mman

#12

Wind vector = Vertical wind vector + Range wind vector

375CT

Mman, thanks again, Crystal clear