Wind correction in long range gunnery

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marcelo_malara
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Wind correction in long range gunnery

Post by marcelo_malara » Sat Apr 04, 2020 11:08 pm

Hi guys, a question related to wind. What was the effectiveness of putting the wind in the long range gunnery calculation? The firer can only measure the wind direction and speed at sea level, on firing the shell will climb many thousand meters, passing by atmospheric layers with different wind directions, speed and densities than those used in the calculations. Wouldn´t it be the same than discarding the data at all?

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Byron Angel
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Re: Wind correction in long range gunnery

Post by Byron Angel » Sun Apr 05, 2020 4:06 pm

Hi Marcelo,
What you say is quite true for very long ranges.
Here are some (simplified) data for USN 14in/45 (1500lb AP @ 2700 f/s) -

RANGE - - - - - MAX ORDINATE - - - TIME OF FLIGHT
10,000 yds - - - - 700 ft - - - - - - - - - - 13 sec
15,000 yds - - - - 1,900 ft - - - - - - - - - 18 sec
20,000 yds - - - - 3,900 ft - - - - - - - - - 31 sec
30,000 yds - - - - 12,000 ft - - - - - - - - 55 sec
36,000 yds - - - - 22,000 ft - - - - - - - - 73 sec


Byron

dunmunro
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Re: Wind correction in long range gunnery

Post by dunmunro » Tue Apr 07, 2020 12:15 am

marcelo_malara wrote:
Sat Apr 04, 2020 11:08 pm
Hi guys, a question related to wind. What was the effectiveness of putting the wind in the long range gunnery calculation? The firer can only measure the wind direction and speed at sea level, on firing the shell will climb many thousand meters, passing by atmospheric layers with different wind directions, speed and densities than those used in the calculations. Wouldn´t it be the same than discarding the data at all?

Regards
Yes, Wind Velocity will vary considerably with altitude. One thing that I haven't read about, but which seems logically true, is that the effect of WV will vary due to air pressure. At sea level air pressure is highest and will have the largest effect on trajectory, especially for low angle/short range firing. However, correcting for WV can only be approximate, hence the need for spotting corrections.

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marcelo_malara
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Re: Wind correction in long range gunnery

Post by marcelo_malara » Tue Apr 07, 2020 12:37 am

I think that the variation responds to the dynamic pressure formula:

Q = 0.5 * rho * V^2 * S * C

rho = air density
V = velocity
S = surface exposed to the flow
C = a non dimensional coefficient related to the form

Air density decreases with altitude, approximately linearly for the lower atmosphere, but as the dynamic pressure depends on the square of the velocity, and the velocity increases with height, the influence of the wind in the apex would not be slight.

Regards

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