Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!elroy.jpl.nasa.gov!decwrl!mcnc!uvaarpa!murdoch!dalton.acc.Virginia.EDU!ds4a From: ds4a@dalton.acc.Virginia.EDU (Dale Southard) Newsgroups: rec.skydiving Subject: Re: bungee jump from plane Message-ID: <1991Feb14.051830.16843@murdoch.acc.Virginia.EDU> Date: 14 Feb 91 05:18:30 GMT References: <1991Feb13.172511.6896@murdoch.acc.Virginia.EDU> <1991Feb13.191314.13568@cbnewsh.att.com> <3044@bridge2.ESD.3Com.COM> Sender: usenet@murdoch.acc.Virginia.EDU Organization: University of Virginia Lines: 85 Ireallyam: ds4a In article <3044@bridge2.ESD.3Com.COM> +------------------ |In article <1991Feb13.191314.13568@cbnewsh.att.com> msb@hos1cad.ATT.COM |(Mike Balenger) writes: |> |>>>>>> On 13 Feb 91 17:25:11 GMT, ds4a@dalton.acc.Virginia.EDU |(Dale Southard) said: |> |>ds4a> 1) Can the jumper really bounce back up and hit the plane? (I |>ds4a> think this violates some enery conversion law somewhere) |> |>Finally, a good question!!! |> |>Bungee jumpers never make it back to the jump altitude!!! (I think |>they make it back to about 70%, but I'd rather hear the real number |>from a real jumper.) Energy is lost in stretching the cord and |>overcoming air drag. My guess is that the air drag on a plane bungee |>jumper would so dominate the equations that there'd be little or no |>rebound. Boo hiss!!! I'd like lots of rebounds. | |I can't comment on this particular thing. In a very early reply |to the original post, I asked what was going to happen to the bungee |when the jumper released. It would, I think, be able to get back to |the plane. Could it get into the prop? control surfaces? what else? | |Re: the magnitude of the force acting on the plane when you have a |jumper in tow vs the bungee jumper: | |Nobody seems to account for the different relative velocities of the |two situations. A jumper in tow hits the end of the static line in |about 10 feet or so. His relative velocity with respect to the plane |is not great. The bungee jumper on a 300 foot elastic is going to |have a lot more relative velocity. Is this going to be distributed |adequately by the elastic, or is it going to be transmitted as a jolt |to the airframe? If a jolt is involved, I fear it would be well in |excess of the jolt presented by the jumper in tow situation, even |though the jumper in tow does not have an elastic static line. | |Comments? | |pvf +----------------- In my original Re post, that was the point I was trying to make. Namely, that the shock felt by the aircraft due to a body being slowly decelerated is less than the shock felt by an aircraft decelerating a body (let's use jumper,body don't sound so good) at the end of inelastic (non-elastic??)static line. YES, of course the bungee jumper has more kinetic energy, he is moving faster. BUT the jumper on the bungee is decelerated slowly, over say ten seconds. I ran the equations through mathematica over lunch today. The peak force felt by the aircraft was on the order of 5900 N. Yes, that is a lot of force, but it is built up in a linear fashion from a starting value of 0 N to its peak of 5900 N at the 10 sec mark. Lets compare that to a jumper coming to an ABRUPT stop at the end of a static line. Neglecting friction, after a 4 m drop, the body is moving 8.85 m/s. Assuming a 60 kg jumper, you now have to dissipate 2350 J of energy nearly intantanously. Yeh, right. Assuming that the deceleration takes 0.5 seconds (which is a BIG assumption) you have comparable forces (5700 N to decelerate th/L jumper) and the jumper pulls about 9.5 Gs. But even if this is the case, the pilot still feels 0 N one second, and 5700 N the next. I am not sure which is the worse situation, but I would guess the gradual increase of the bungee is easier to counter. Of course these are thumbnail calcs, not good enough for government work, but try it and you'll get the general idea. Anyone with a better model is welcome to correct me, I have already spent _way_ too much time defending bungee jumpers who really should get there own newsgroup. But at least the traffic will move rec.skydiving a couple places closer to alt.sex.pictures (perhaps if I posted some digitized skydiving shots ... nah) As for the bungee getting to the plane ... good point (ever play with icky-poo??)! --> --> Dale UVa (ds4a@virginia.edu) --> --> Dale UVa (ds4a@virginia.edu)