tcliftonr@cc.curtin.edu.au (04/25/91)
GRAPH FOR PROPOSED 120 000 ft RECORD ATTEMPT Someone said a couple of days back that an attempt is being mounted on the altitude record without a drogue from 120 000 ft. You had said that 23 miles up is nearly space, I think. Yes, it is pretty close to it. I think I can show that freefall near 120 000 ft is effectively space walking. The air is too thin to offer effective drag at any ordinary speed. The jumpers [] mentioned as intending to exit from 120 000 ft will fall "weightless", perhaps rolling, for at least 30 seconds before the increasing airspeed and thickening air combine to make an impact with the atmosphere. The simulation shown below is correct in its skydiving physics and things like the standard atmosphere density. However, it extrapolates the drag coefficient and velocity-squared rule far from their proven performance in ordinary skydiving. In reality drag at the supersonic airspeeds probably has velocity-to-the-first- power which would provide a later and harder impact with the atmosphere. If you are inclined to follow the graph of the simulation, let's go on... 0 v AIRSPEED, mph v 160 0 f WIND FORCE, N/kg f 40 _________________________________________________________________ f . -exit- . . 120000. f v . . . . f . v . . . f . v . . . f . . v . . f . . v . . f No wind force yet . . v . f . . . v . f v . . . . f v. . . . f10 . v . . . f . .v . . f . . v . . f . . . v . f . . . v . f v . . . . f v . . . . f . v . . . f . v . . 115000. f . . v . . f20 . . Initially .v . .f . . velocity . v . vf . . increases at the v .f v . . acceleration due to gravity. .f .v . . . .f . v . . 110000. .f . .v . . .f . . v . . . f drag becomes significant .v . . f . . . v . v3f . . . v . f v . . . 105000. . f v. . . . . f . v . . . . f Sometime after v . . . . f 30 seconds, ordinary . v . . . f skydiving techniques . v . 100000. . f become effective . v . . . f . . . v . . f . . . v . .40 f . . . 9v000. . f . . . v. . v f . . . . . v f . . . . . v f . Airspeed peaks out when . 90000. . v f. wind drag reaches one gee . . v .f . . . . v . f -here, at 815 mph and 45 seconds . . v . f . . . . v . f . . 85000. .50 . f . . v. . . f . . v . . . f . . v . . . f . . v 80000. . . f . v . . . . f . v . . . . f v . . . . v f . . . . . v f . . 75000. . v . f . Impact with the atmosphere, . .60 v . f . appearing as a wind force . . . f . of 1.7 gees in this v . . . f . simulation . v . . . f . v 70000. . . f . v . . . . f . v . . . . f v . . . . . v f . . . . v f . . . . v . f . . 65000. .70 v . f .Impact lasting 30 seconds or so. v . f . . v . . f . . v . . . f . . v . . . f . . v . . . f . v . . . . f . v . 60000. . . f . v . . . . f . v . . . . f v. . . .80 . f v . . . . . f v .Accounting for supersonic . . . f .drag is expected to shorten . . . v f .and sharpen the impact . . v f . . . . v . f . . 55000. . v . f . . . . v . f . . . . v . f . . . . v . f . . . .9v . f Now at subsonic speed and . .v . f with a wind force near . . . . f normal of one gee, . v. . . f the aerodynamics are those of v . . . f an ordinary skydive. . v . . . f . . v . . . f . . v 50000. . . f . . v . . . f . . v . . . f . . v . .100 . f . . v . Well, that's at 50,000 ft altitude and the rest is straightforward. If you want the rest of the graph, I will mail it to you. Roger Clifton, Kalgoorlie, West Australia.