Re: Back to the F-22's cannon question.

Message posted by Argo on January 20, 2007 at 12:30:12 PST:

>> Does the speed of the bullet, relative to the speed of the vehicle, remain constant regardless of the ballistic speed? ie bullet at 1000fps, vehicle at 60mph...When the bullet loses all it's ballistic energy from the gun, is it still traveling at 60mph? Surely air resistance (at least) would cause it to slow to less than 60 mph.

And none of that takes into account the movement of the
bullet due to gravity which may or may not take it in or out of the vector of the vehicle.

We should mount phasers on those F-22's. Then we wouldn't have to worry about bullet <<

Well, offcourse, there are several factors to include into equation, but that was a simplified answer based on simple Gallilean transformations of speeds and movement(since speeds of the bullet and plane is not a big percentage of c). That is, if the bullet is fired and it's speed is, say, 1000 meters/sec, and the plane itself flies at 600 meters/sec(close to M2.0), that the bullet would have a starting speed of no less than 1600 meters/secund,relative to the ground, but 1000 meters/secund relative to the plane. That means that it would probably be very far from the plane after only few secunds of its flight. Though, at those speeds the friction of the air becomes very high and intense and would cause rapid deceleration of the bullet, but few things should be considered here... First is the mass of the bullet, secund is the drag which is dependant on the shape of the bullet. Higher mass would cause higher kinetical energy and probably more range of the bullet.

You asked about gravity. Let's take a look at a simple
example. If the plane is travelling horizontally, or purpendicular to the vector of the gravitational force, then the speed of the bullet would not change, but altitude would offcourse(both due to the gravitation and airresistance), because forces which act in the right angle to the forces which create motion make no effect, that is, no work is done by such forces. It's different offcourse when a plane is shooting at some angle.
But maybe the best example is when a freefall bomb is dropped from a plane. Here we have an example of same starting speeds for both the plane and the bomb. If the bomb doesn't have a high drag, and the plane doesn't accelerate, than their speeds would be quite similar, but the bomb would loose altitude and hit the ground right beneath the plane(remember those shots from WW2 when they would show the bombs falling and then later on, exploding right beneath the planes, the best example)... I could explain it even better if my skills of teaching physics in english would be better( I am a physics student), ... or, if you speek croatian, even better :-))))

<< When the bullet loses all it's ballistic energy from the gun, is it still traveling at 60mph? Surely air resistance (at least) would cause it to slow to less than 60 mph. >>

Depends on the mass of the bullet and air ressistance.

But I think we can say with large degree of certainty that no plane cannot catch its bullet. Just maybe if the plane would go to a vertical climb and fired its guns, but that is also largely dependant on alot of factors(maximum ceiling for one :-) ).
And offcourse if those bullets are very slow.

In Reply to: Re: Back to the F-22's cannon question. posted by Lumpy on January 20, 2007 at 2:19:48 PST:


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