okay, here's rough calculation for 18 knots. you can do same for 20 knots if you want. pulling data from my other post:
go to page 60 (manual not pdf#) of that link. look at the chart for gross weight 13100 lb for takeoff on a hard surface. notice that you need 380 feet with a 30 knot headwind or 680 feet with a 15 knot headwind.
So for 18 knot, to figure required distance from the chart data:
680 ft-380ft=300 ft (distance differential)
30 knot-15 knot=15 knot (headwind differential)
300 ft /15knot = 20 ft/knot (relate the two differential)
18 knot-15 knot = 3 knot (18 knots is what we knot, not 15 knots...he, he another one)
3knot*20ft/knot = 60 ft
680 ft-60ft ~ 620 feet needed at 18 knots.
Casablanca is 512 ft, so too short at 18 knots.
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