THEN when the target comes up on normal f6 view..its off often by 15-20 degrees--the zoom on the cal. crosshairs and the ACTUAL crosshairs dont agree.. (this is like 18k or so..above the wind elev. whish is always at 14k) Ya CANT
change course that close to target or ya hopelessly miss...THEN ya have to fluff'n go around again. Can SOMEone explain why this is so?
Welcome to the wonderful world of vector mathematics. Fortunately, you won't have to learn all the dirty parts inside.
Let's say you are at 20K due north of your target about 5 minutes flight time at a speed of 250 mph true (not IAS) from drop, your compass reading showing you on a heading of 180°. You calibrate your sight, and you're lined up
perfectly with your target, and continue flying south, waiting for your target to appear.
Well, during those 5 minutes, while you fly about 21 miles south, that wind layer is pushing you east; in five minutes, that wind will have pushed you 2.5 miles east of your target. Now, of course, you'll notice that you aren't lined up any more well before you reach the actual drop point, which is why you see your target at an angle off your crosshair lineup.
In order to fly due south with that 30-mph crosswind, you have to steer into the crosswind, so that the drift from the wind and the drift from your pointing your plane at an angle to your intended line of flight cancel out. In this case, you would have to hold a course of about 187° in order to have a ground track (the course your plane follows along the ground) be a course of 180°.
There are various tools you can use to figure out what your drift correction should be. The E-6B Flight Computer (which is actually more of an aviation slide rule) will let you compute drift correction angles from your flight data -- true airspeed, wind speed, wind angle, etc..
You can also ballpark it, which is easier to work out and just as good for AH purposes. First, you compare the angle between your course and the wind and look up the wind speed in this table:
If you were flying a course of, say, 150°, the wind would have an angle of 60° to your plane. Looking at the table above, at 30 mph, a crosswind at 60° will have a 15-mph component along your flight path, and a 26-mph component across your flight path.
Then you apply the wind component along your flight path to your true airspeed, and compare that against the crosswind to find your drift correction angle:
Going back to our example, let's assum you were flying at 180 mph true. Since a course of 150° is
away from the wind, you
add the wind component along your flight path -- 180 + 15 gives you a speed of 195 mph, with a 26 mph crosswind. Looking up at the table above, we'll use 200 mph and 25 mph crosswind, and get a 7° correction, so for your ground path to be a course of 150°, you would have to
fly a course of 15
7°.
Once you've got your drift killed, you can calibrate your bombsight. Minor course corrections at the last minute -- 5° either way, for example -- won't make enough of a change in your course triangle to throw your bombsight calibration off much -- a 10° course change with a 30-mph crosswind would only move the actual impact point about 5 feet, well within the bomb scatter distance. You'd get wider errors with a larger course correction, but if you see large miss distances if you drop right after a sudden course change, what you are actually seeing is aiming slop that is caused by the sight being pulled out of line by the course change and taking some time after you stop the turn for the sight to settle back down. If you make a sharp right turn, you'll drop left of where you're aiming, and the reverse for left turns.
