Physics question

("Rich S." wrote)
In your illustration, the gunner fires straight back
before the Me-109 is directly behind the B17. He can hit
if he fires at precisely the moment his gun crosses the
flight path of the Me-109.

Not so. The bullet simply falls to Earth and the ME-109 passes safely 50
yards (or so) behind the B-17.


Agreed.

(For those who don't agree)
Think of a pickup truck driving along at 40 mph. I'm standing in the bed
with a baseball.

When we reach the manhole cover in the middle of the street I let fly out
the back of the truck with my best stuff, which just happens to be a 40 mph
fastball g. That ball will not go past the manhole cover.

If you're a batter (or an ME-109) standing at the manhole cover - which
every kid knows is home plate - you won't get hit by my fastball ...or be
able to hit it. (I'm unhittable!!)

Now, if I flip the ball into the air, but a little to the left, and you are
standing in the street when the truck drives by, you will be hit by a 40 mph
ball. Just thought I'd toss that one out there :-)

So long as the ME-109 is not moving (at all) in the same direction as the
"magic" B-17, when it crosses behind the Flying Fortress, it will be safe
from the bullet.. I would think wind drift would not be an issue (with
perpendicular plane paths) since it will drift the B-17 too ... away from
the ME-109.


Montblack ..."car"

"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.

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?

But just imagine, as the bullet falls to earth, it will remain horizontal for a while due to the gyroscopic spin caused
by the rifling...


"Montblack" wrote in message ...
("Rich S." wrote)
In your illustration, the gunner fires straight back
before the Me-109 is directly behind the B17. He can hit
if he fires at precisely the moment his gun crosses the
flight path of the Me-109.

Not so. The bullet simply falls to Earth and the ME-109 passes safely 50 yards (or so) behind the B-17.


Agreed.

(For those who don't agree)
Think of a pickup truck driving along at 40 mph. I'm standing in the bed with a baseball.

When we reach the manhole cover in the middle of the street I let fly out the back of the truck with my best stuff,
which just happens to be a 40 mph fastball g. That ball will not go past the manhole cover.

If you're a batter (or an ME-109) standing at the manhole cover - which every kid knows is home plate - you won't get
hit by my fastball ...or be able to hit it. (I'm unhittable!!)

Now, if I flip the ball into the air, but a little to the left, and you are standing in the street when the truck
drives by, you will be hit by a 40 mph ball. Just thought I'd toss that one out there :-)

So long as the ME-109 is not moving (at all) in the same direction as the "magic" B-17, when it crosses behind the
Flying Fortress, it will be safe from the bullet.. I would think wind drift would not be an issue (with perpendicular
plane paths) since it will drift the B-17 too ... away from the ME-109.


Montblack ..."car"

"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.

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?


This would only work if the 109 was ahead of the 17 when the shot was fired.

(Dan_Thomas_nospam wrote)
He misses the ME-109 because the recoil of firing the bullet
accelerates the B-17 just a bit, so that the bullet, travelling at a
little less than the bomber's speed actually briefly follows the bomber
as it falls.

Plus there is a constant speed with the B-17. The bullet needs to accelerate
to reach that same speed. g


A related question: Haven't there been cases of supersonic
fighters shooting themselves down when they caught up to the shells
they'd fired forward?

'If I drive the speed of light, and turn on the headlights - would anything
happen?' Steven Wright ...and maybe also "The Lazlo Letters" (1977) by Don
Novello.


Montblack

"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.

This would only work if the 109 was ahead of the 17 when the shot was fired.

It will work fine as long as the two maintain the relative 50 yards
distance between them. - one following the other. Or is Rich S.
description of the motion muddled? I took "crossing behind the B-17" as
simply crossing the line of sight slightly and not a perpendicular
ground path. Normally a 109 would follow a B-17 to attack.

Montblack wrote:
("Rich S." wrote)
In your illustration, the gunner fires straight back
before the Me-109 is directly behind the B17. He can hit
if he fires at precisely the moment his gun crosses the
flight path of the Me-109.

Not so. The bullet simply falls to Earth and the ME-109 passes safely 50
yards (or so) behind the B-17.


Agreed.

(For those who don't agree)
Think of a pickup truck driving along at 40 mph. I'm standing in the bed
with a baseball.

When we reach the manhole cover in the middle of the street I let fly out
the back of the truck with my best stuff, which just happens to be a 40 mph
fastball g. That ball will not go past the manhole cover.

Won't it drop stairght down toward the manhole cover? (Yes it will.)


If you're a batter (or an ME-109) standing at the manhole cover - which
every kid knows is home plate - you won't get hit by my fastball ...or be
able to hit it. (I'm unhittable!!)


Evidently you have seen me at bat. But someone else could hit it.

And if I'm running toward the manhole cover at a right angle to
the direction the truck is driving I can catch the ball as I
step accross the manhole cover, right?

(Well, maybe you've seen me field too.)

--

FF

Rich S. wrote:
"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 =3D 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 =3D 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.

Half a foot at 50 yards? I misrememeberd that a 45 drops half an
inch at 50 yards. How embarassing.


Nope. You are assuming "the other plane reaches the bullet position . . .=
"=2E
It never reaches the bullet's position because it is traveling at 90=B0 t=
o 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=2E
coriolis force & wind velocity.)


You're still assuming he's leading the ME-109 as if the gunner
were in a fixed location. He's assuming the gunner is actually
trying to hit the plane, and smart enough to figure out how
so that he times his shot *correctly*. You're both assuming
he fires straight back. He can hit the Me-109 by firing straight
back, but ONLY if he fires exactly as B-17 crosses the flight
path of the Me-109, and only if the Me-109 is fast enough or
close enough to get there before the bullet drops out of the
flight path of the Me-109. If the Me-109 is at a range of 50
yards, and no slower than the bullet the bullet will be no
more than 7 inches lower than the muzzle of the gun and will
still hit the Me-109 assuming the two planes are at the same
altitude.

Here is an example:

Both planes are at the same altitude.
The gunner fires straight back and level when the B-17
crosses the flight path ahead of the ME-109. At that
moment, the Me-109 is at a range of 50 yards, e.g. it
is 50 yards directly to the right of the gunner and
flying from right to left, and also flying at 820 ft/s.
If you think that bullet misses, calculate by how much.
Now do that again, assuming the Me-109 is a bit faster,
say, 900 ft/s.

There is a range of realistic speeds and altitudes
for the Me 109 for which it will be hit, and a larger range
of speeds an altitudes for which it can be hit if the gunner
is allowed to aim up or down, larger still if he can aim from
left to right even though in all cases the ME-109 is flying
at 90 degrees to the flight path of the B-17.

--=20

FF

Rich S. wrote:

Aiming
point
. ----- ME-109

B-17
|
V


The gunner cannot hit the ME-109 given those relative positions
and trajectories no matter where he aims.

If the gunner fires straight back when he is at the aiming point
(e.g. re-lable 'aiming point' to be 'firing point' then the bullet
will drop straight down from that point, right?

Then if the ME-109 is close enough and fast enough the bullet
will be just below the aiming/firing point when the ME-109
gets there and will hit the bullet. Your specified range
of 50 yards (50 yards to the right in this case) is close
enough for normal ME=109 speeds.

If the Me-109 is slower or farther it will pass over the
bullet unless it is also at sufficiently lower altitude.

--

FF