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Old 22nd August 2001 | 10:59
  #34 (permalink)  
A7E Driver
 
Joined: Apr 2001
Posts: 68
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From: San Diego - now Paris
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Let's do a little math guys. Will you grant me a 3000 foot distance abeam. I know -- a little wide --- but if you first climb to 400-500 before turning --- you still have another 400-500 feet to go to pattern altitude = 1 minute of flying crosswind. So assume 3000 feet abeam on downwind. If you turn when the threshold is 45 degrees behind you (a little late in my opinion -- but OK). That puts the start of the turn to base (using 45/45/90 trig) at 3000 feet past the threshold. Assume 10 knots of wind down the runway = 17 feet per second drift. Assume one minute time from start of turn to base to start of turn to final = 60x17 =another 1020 feet from the threshold due to wind drift (and probably more because that would be a rather quick base). Assume 80 knot indicated during the turn to base = 133 feet/sec (I fly my Arrow 100/90/80 kts --- so would be a little more). OK the 90 degree turn to base takes 20-25 seconds --- so let's just take half of that as direct downwind distance at 133 feet/sec = another 1600 feet downwind to complete the turn to base. OK let's add it up:

3000 feet past threshold start turn
1020 feet for 10 knot wind
1600 feet for aircraft turn radius at 80 kts
500-700 feet from threshold to touch down point

Total distance = 6320 feet = 1.2 miles

OK you micro light guys can do it much tighter --- but I maintain my case that 1.25 - 1.5 mile final at 500 foot glideslope intercept is about right. +/- 0.5 miles to allow speed difference in Cessnas/Pipers.

BTW, in fighters we didn't fly a base leg. 1.1 nm abeam at 800 feet -- continuous spiral to final at 27 degrees angle of bank --- aiming for about 600 feet at the 90 and rolling wings level at 450 feet.
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