On 2007-04-18 12:02:54 -0700, Erik said:

Maxwell wrote:
"Mxsmanic" wrote in message
...

How do you know when you are exactly overflying a specific spot on the ground?
It's it just a matter of knowing your particular aircraft, or are there tricks
that can help to determine this? I know you can look off the tip of your wing
to see if you're abeam something (such as a runway), but how can you tell when
you're right over something? I presume there's no way to look straight down
from most aircraft, and it seems like the view over the nose is often several
miles away.



Why would a pilot care?


You don't want to pelt noncombatants with errant golf balls!

A golf ball (or anything else) doesn't drop straight down. You have to
release it before you reach your target as it continues to move forward
at the speed of the aircraft.

Best if you can get a wind report from the ground just before you
arrive in the area. Then you can use your E6B (You knew that thing had
to be good for something, right?) to compute how far forward the ball
will travel before hitting the ground, assuming you know the rate of
fall and the altitude of the aircraft. You then use the E6B to compute
the amount of wind drift for that period of time and you also have to
allow for the fact that the ball will decelerate its forward movement
due to wind resistance as it falls. But the hard part is figuring out
the rate of fall, which has to be determined experimentally. After that
the rest is easy.

Using a scale diagram of the target area with prominent features
marked on it (or, heck, an aerial photo works, too), you can then
quickly plot the forward distance to the target, mark that on the map,
plot the wind vector, mark that on the map, and use landmarks to put
you directly over the drop point. Best to use a point in front of you
that you will always be able to see during the bomb run, and a side
point that can be seen from the plane anywhere in the DZ.

Best to work in a team of two. One guy flies the plane and the other
plots the drop and actually drops the ball. As you approach the target
area you run through the drop checklist -- 10 minutes to drop, descend
to final drop altitude, 5 minutes to drop, flaps, gear, winds, plot,
line up the aircraft on the aiming reference (or offset by the amount
calculated by the bombardier), open the window, start time from lateral
visual reference (note that you do not choose a lateral visual
reference for the actual drop point -- too hard -- but instead you have
a fixed reference about a minute before the drop and time from that),
30 seconds to drop, 15 seconds to drop, 10 seconds to drop, 5, 4, 3, 2,
1, PICKLE (or GREEN LIGHT, if you have one, for DROP) or NO DROP (you
don't want these two commands to sound the same), time to the end of
the drop zone (assuming you are dropping a bunch of golf balls), STOP
DROP (or RED LIGHT, if you have one), clean, climb, turn, take evasive
action, etc.

There are some safety considerations. You don't want the golf ball
hitting your tail or denting a strut, so you have to lower the ball out
the window or door as much as possible and then drop it straight down.
Don't throw it forward; you might hit the prop. If you can mark the
target with a bright orange piece of plastic and have people on the
ground to keep innocent bystanders away, that is also good, but
military necessity must rule. You generally do not want to drop from
lower than 500' AGL. You don't want to go hitting any trees.

Not that I have done this or given it much thought. :-)
Okay, I was a navigator/bombardier on C-130 Hercules planes, and had
one of the most consistently accurate drop records in our wing. But
aside from that....

So, bottom line, the only reason you need to know you are over an exact
point is indeed if you are going to drop something (or photograph
something straight down) and the way you tell you are there is to line
up on two objects in front -- so that they are line with each other --
and two objects in line with each other to the side. Roads work well.
So do utility lines, fences, buildings, and rows of crops or trees. Man
likes straight lines, and that makes it easier for other men to drop
things on him.
--
Waddling Eagle
World Famous Flight Instructor