"abripl" wrote in message
oups.com...
With bullet/plane(s) relative horizontal speed of 820ft/s, the other
plane reaches the bullet position in (50x3)/820 = 0.183 sec (pretty
slow bullet). In that time the bullet falls a vertical distance of 0.5
x 32 x 0.183 x 0.183 ft = 0.536 ft. If the messer plane bottom was at
least 0.537 ft (about 7 inches) below bullet firing vertical position
its gona hit the other plane.

Nope. You are assuming "the other plane reaches the bullet position . . .".
It never reaches the bullet's position because it is traveling at 90° to the
flight path of the B-17. If it was following the B-17, it could possibly run
into the bullet, but only at its foward velocity. The bullet has only a
downward component relative to the Earth. (Ignoring minor variations, i. e.
coriolis force & wind velocity.)

Ignoring air friction, whether the planes are moving or parked on the
ground with same separation it does not matter. It is only the relative
velocity of the bullet to the planes that counts. But with backward
airstream and downward friction the bullet will fall slower down than
in vacuum - so better chance of hitting the plane behind.

Is this your night school physics home assignment and you are cheating
here?

Nope. Last physics course I took was at the U of Wash., 47 years ago. I
brought this subject up because I was reading an article in the May 1942
issue of "Flying and Popular Aviation". It was titled "Speedy" and tells the
story of a quiet young fellow named Andy McDonough who dove a new Army
fighter to 620 mph a "few weeks ago". He'd like to try for 700.

The airplane was a new P-39 Airacobra. "After his test, McDonough said he
thought of that now-famous problem: 'I wondered what would have happened if
I could have fired a pistol back over the tail. At that speed would the
bullet have rolled out of the barrel and then fallen back?'".

Well, perhaps that was a famous problem in the spring of 1942. I don't know,
having entered this vale of tears late in 1941. But I thought it would be
fun to toss it up here among all these reasonable, logical, polite folks.

Rich S.