NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/sci/military/12692

Text File | 1993-01-21 | 3.4 KB | 75 lines

Newsgroups: sci.military
Path: sparky!uunet!gatech!hubcap!ncrcae!ncrhub2!ciss!law7!military
From: Gary Coffman <[e-mail]>
Subject: Re: Anti-aircraft
Message-ID: <[e-mail]>
Sender: [e-mail] (Sci.Military Login)
Organization: Destructive Testing Systems
References: <[e-mail]> <[e-mail]>
Date: Thu, 21 Jan 1993 18:34:32 GMT
Approved: [e-mail]
Lines: 62


From Gary Coffman <[e-mail]>

In article <[e-mail]> [e-mail] (Stephen A. Creps) writes:
>In article <[e-mail]> "John M. Wu" <[e-mail]> writes:
>>1)  When anti-aircraft shells go up, they have to eventually come
>>back down.  With a gun shooting 90 deg., the bullet will go up to
>>around 9000 ft. and then start coming down up to terminal
>>velocity (300 fps?).  At terminal velocity, the bullet can still kill a
>>person.  Do anti-aircraft weapons like those in Iraq cause large
>>ground damage and numerous casualties due to what eventually
>>happens to fired shells (eg. the Baghdad hotel damage)?  Seems
>>like a terribly inefficient way to defend a city from damage.
>>Wouldn't not firing anything cause less damage to Baghdad?

Most AAA is of the explosive shell variety, so terminal velocity
is a rather unimportant part of the damage caused by falling
shells. The shells that are fuzed for air burst only rain down
shrapnel, which is subject to terminal velocity calculations,
but is not a major source of damage to property. But contact
fuzed shells can cause major damage when they strike the ground
at *any* velocity.

>   However, while terminal velocity affects the Y-vector (vertical) of
>an object's velocity, it should not affect its X-vector (horizontal).
>Simple physics tells us (if I'm not screwing this up), that the higher
>the angle at which the projectile is fired, the larger its Y-vector,
>and the lower angle it is fired, the higher its X-vector.
>
>   Therefore, is it valid to assume that this kind of damage is not
>caused so much by the projectile _coming down_, but by it _continuing
>in the same horizontal direction_, where terminal velocity does not
>come into play?

Sorry, you're screwing it up after a fashion. Let's look at three
cases and use the 30-06 data of Hatcher.

1) The bullet is fired straight up. It will reach an altitude of
   about 9,000 feet and fall back at a terminal velocity of about
   300 fps. Flight time is 30-40 seconds.

2) The bullet is fired horizonally. It has a flight time of about
   0.625 seconds and reaches a distance of about 500 yards. Remaining
   velocity is about 1800 fps. Note the bullet falls the height from
   the shoulder to ground level in 0.625 seconds. It's stopped by
   impact with the ground.

3) The bullet is fired at an angle of 45 degrees above the horizon.
   Flight time is 30-40 seconds, range is about 8 miles. Impact
   velocity is nearly nil, <<200 fps. Essentially all the forward
   speed is lost to air resistance during the flight and insufficient
   altitude is gained to achieve terminal velocity during the
   descent.

Gary
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