Pál_K
Cameras. I has it.
Sorry, there is some confusion in the above statement.Guns don't work on an SR-71, because the plane at really high altitude is faster than the bullet. Let that sink in...
First, it is true that the speed or velocity of the SR-71 is faster than the muzzle velocity of a typical bullet (e.g. 3000 fps). So, for an observer on the ground, if a bullet was fired at a distant target at the same moment an SR-71 passed overhead, yes, the SR-71 would be faster: it would reach a point downrange faster than the bullet did.
Second, except for velocities approaching the speed of light, we can reasonably consider velocities to add. For example, if an aircraft is traveling at 682 mph (~1000fps) relative to the ground and that plane fired a bullet at 3000 fps, that bullet would be traveling at 4000fps relative to the ground. So, the same is true for the SR-71: its velocity would add to the bullet’s velocity. Statements written in other forums on this very topic, claiming the bullet wouldn’t leave the barrel or the plane would fly into the bullet are incorrect (due to gravity, the bullet will start falling as soon as it’s fired - as is always the case). So a gun, or cannon, would work on the SR-71.
Third, the SR-71 (previously named RS-71) was designed for reconnaissance, not combat.
Fun photography-related fact: if the focal plane shutter on your 35mm camera has a sync speed of 1/60, the shutter curtain travels at 4.83 mph.
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