Re: buoyant cannon balls

[brian whatcott <inet@intellisys.net>]

At 06:01 10/31/97 -0400, you wrote:

> >    It is a common-place of ballistics that a well-spun shell by holding 
> >    its attitude near to its initial elevation develops lift as it drops.
> >
> >    It is also well known that the general run of say - pistol bullets
nutate
> >    markedly about their flight axis and do not develop lift in the same
way.
> Would you expect the same thing to happen for a non-spinning cannon ball, a
> spherical shape projectile?

I am in danger of telling you more than I can support ( with most of my
reference material in temporary packing...)
 Balls have poor ballistic properties at sub-sonic speeds, but I recall
a stray comment that spheres looked more respectable at supersonic speeds.

 You can doubtless recall the cannon story about the Royal range trials.
By degrees more powder was added to a cannon charge to increase its range -
until a limiting charge, beyond which no more powder could induce an 
increase in range. And that of course was an early brush with the speed of
sound... 

> ... "a small vertical component" of v is probably essential 
> here. If this is true then a horizontally fired ball must have "initial 
> lift" equal to zero at any initial velocity. And the lift must increase
> in time, at least for a while.

This accords with what I remember.

> ... Is Leigh right that the quadratic F(v)
> dependence is not essential and that the same may be expected from the
> F=k*v? 
> ...
>                                                      ludwik kowalski

I already place a severe burden on the people whose academic reputations
should be carefully preserved. And so in an uncharacteristic surge 
of diplomacy (!) I assert I am not competent to generalize from the 
aerodynamic case.


Respectfully,

brian whatcott <inet@intellisys.net>
Altus OK