On Mon, 13 Mar 2017 07:30:37 -0500, Pete Keillor
wrote:

On Mon, 13 Mar 2017 08:33:42 +0700, John B.
wrote:

On Sun, 12 Mar 2017 11:18:28 -0400, "Jim Wilkins"
wrote:

"Volker Borchert" wrote in message
news wrote:
On Thursday, March 9, 2017 at 9:52:34 PM UTC-5, David R Brooks
wrote:

A howitzer fires, with elevation 45 degs. So the shell exits,
pointing
upward at 45 degs., spinning. When it hits the target, it is (to
1st
approximation) falling at 45 degs., but the spin should have kept
it
pointing upward. This means it would be flying sideways-on.
This sounds wrong to me, but where is the error?\\

The shell flies with its axis in line with the direction that the
shell is moving.
So the shell starts out pointed up by 45 degrees , it flight path
changes and its orientation also changes. Since the shell is
spinning , changing the orientation causes it to precess. And the
shell changes from not only the angle up but also changes sideways.
So a shell with a clockwise rotation fired due west, will turn so
it is going south west.

And it gets worse. A shell fired due North in the Northern
hemisphere will go somewhat East because of the Coriolis effect.

Well, it seems the people who designed the Rheinmetall Rh120 knew
what they were doing.

Joseph Whitworth knew what he was doing in 1860.
http://civilwarwiki.net/wiki/12_pdr....hloading_Rifle
"At 1600 yards the Whitworth gun fired 10 shots with a lateral
deviation of only 5 inches."

I think I would take that figure with a grain of salt. After all, at
1,000 yards with a muzzle velocity of 1,300 fps ( probably similar to
the Whitworth ) with a .45-90 rifle, wind drift is approximately 15"
per mph of wind speed, at 90 degrees to the line of sight. Even air
temperature and humidity has a measurable effect at these kind of
ranges.

snip

I think he was referring to the Whitworth rifled cannon, 2.75" bore,
hexagonal rifling with a matching twisted "long bolt" projectile.
Don't know the velocity, but it probably had a very high ballistic
coefficient due to mass as much as shape.

Pete

Yes, I was aware of that. But one of the determining factors in wind
drift is the amount of time the projectile is exposed to the wind,
i.e., distance and muzzle velocity. From all I could find on the net
the Whitworth 12 pound had a muzzle velocity of 1,500 fps thus wind
drift might have been in the neighborhood of 1300/1500 of the .45 cal
rifle I mentioned. Perhaps 13"/mph.

My point was that the figure given (the Whitworth gun fired 10 shots
with a lateral deviation of only 5 inches.), which seems to a
quotation from one magazine article, is very highly unlikely.

--
Cheers,

John B.