Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!munnari.oz.au!uniwa!cc.curtin.edu.au!tcliftonr From: tcliftonr@cc.curtin.edu.au Newsgroups: rec.skydiving Subject: Graph of osc'n due to high windforce Message-ID: <1991Jun11.084111.8668@cc.curtin.edu.au> Date: 11 Jun 91 00:41:10 GMT Organization: Curtin University of Technology Lines: 82 RE: IMPACT WITH ATMOSPHERE: High speed exits The high altitude record jump from 120 000 ft will also achieve a record airspeed of 750 mph and then impact the atmosphere with 1.6 gees according to the simulation, nearby on the bulletin board. Once these jumpers have achieved the record airspeed (it will be a record regardless), this number will be something of a wow in itself, but a bigger achievement among skydivers will be the handling of sustained excess wind force. The violence of the forces affecting a jumper goes up as the square. Have you ever exited above terminal? You know all about it! There is a realisation of imminent hazard, particularly of the increased tendency to oscillate or rock. Beyond oscillation is the tendency to tumble. In the sustained wind force of the high altitude jump, the jumpers will have to ensure they do not tumble to the point of red- out. If anyone wants to train for excess wind force, they can get the required wind by exiting a plane at an airspeed v where- v2/Vt2 = no of gees so that v = Vt * sqrt( no of gees ) eg: if you are training for 1.21 gees, you can exit at v = Vt * sqrt(1.21) = 120 * 1.1 mph = 132 mph. (ie 120 knots). Similarly 1.44 gees requires another 10% of airspeed. That's if you exit at modest altitudes where Vt is 120 mph or so. Mind you, it wont last long, just a taste of the impact. Here is airspeed for an exit from a plane at 160 mph (142 knots) for an exit impact of 1.8 gees. The simulation assumes a normal posture of the jumper can be maintained against the wind and that the exit is made with the body inclined at 45 degrees to the wind. Since this means that the impact will lift this jumper above the exit point, there is a risk of hitting the tail of the plane. An assumption is made too, that the jumper is normally well-damped, that is, (s)he is a quite stable freefaller. Yet the simulation clearly shows oscillation: 0 v AIRSPEED, mph v 160 -90 a ANGLE OF TILT ON WIND a 90 0 f WIND FORCE, N/kg f 40 ................................................................. . . f . a v . jiggle in . f . a v. . wind force . f . a . v . . due to posture f . a . v . . changes . f a . . v . . . f a . oscillation . v . . . f a . . v . . . f a. . v . . . f a . v . . . f .a . v . .1 . f a . v . . . f a. . v . . .f a. flat . v . . .f a. on . v . . f one a. wind .v . . f gee a. v . . f. a. v 120 mph . . f. a. v. . . f. a. v . . . f . a. v . . .2 f . a. v . . If you want a copy of the simulator, just ask. Roger Clifton Kalgoorlie West Australia.