rob@ireta.cynic.wimsey.bc.ca (Rob Prior) (02/06/91)
ds4a@dalton.acc.Virginia.EDU (Dale Southard) writes: > >> I can imagine ... not much. (note that the length of cord has no effect > >> on the torque as it is not rigid) > > >Where did you learn physics? Pilot loses one jumper as he leaves, conpensat > >accordingly, and suddenly has to compensate the other way as the cord tighte > >when the lost jumper reaches the end of his line and the torque increases. > > Well, sorry to point it out, but the length of the cord has no effect. > Velocity does. > Effective force constant does. > Distance from CG does. > Length doesn't. I didn't say length had _any_ effect, did I? What I said was that the pilot would compensate for the loss of 1 200lb person and then have to deal with regaining it 3 or more seconds later when he/she gets to the end of the line. Length would affect how long the pilot has to wait for this, though. Another thing, the whole rope isn't bungee. It (if I recall correctly) (someone here did an analysis of it once :) is about 80% rope, 20% rubber (or bungee cord, or whatever). This may have an effect. > 1) Can the jumper really bounce back up and hit the plane? (I think this > violates some enery conversion law somewhere) I don't think so... I would think that (wind resistance+energy loss) would be sufficient to keep the jumper far enough from the plane. Maybe after the jumper cuts away? Could the cord snap back far enough? > 2) Are static lines safe? (It may indeed be that all pilots are just one > student in tow away from tumbling out of the sky) Sure, static lines are safe. BUT... I'm sure that when a student goes out and gets stopped at the end of the line because of something jamming, the pilot gets a _very_ sudden shock that he has to compensate for... I have never jumed SL, and have never seen videos of SL hangups (apart from Wally's :) so I don't know if this is true or not. > 3) Why the hell am I defending an idea that I really don't care all that much > to try? (Couldn't we discuss the best way to do a triple dragplane diamond > instead?) Possibly hoping someone will come up with a completely safe method for implementing the idea? :) I don't know why i'm defending the other side of it either, but debates like this are fun... :) > But at any rate, thanks for the deversions -- I really hate to do productive > work :-) Who doesn't? :) +------------ | rob@ireta.cynic.wimsey.bc.ca | Rob Prior, President, Still Animation Logo Design +------------------------------------------------------------
rob@ireta.cynic.wimsey.bc.ca (Rob Prior) (02/06/91)
msb@hosmsb.ATT.COM (Mike Balenger) writes: > >>>>> On 6 Feb 91 01:50:02 GMT, rob@ireta.cynic.wimsey.bc.ca (Rob Prior) said > > rob> But, how about doing this from a _baloon_ at about 10,000 AGL? > rob> (can baloons go this high? I know nothing about them). > > I've heard that some bungee jumpers are using baloons to avoid laws > prohibiting bridge jumps. No need to get 10K AGL -- 200-300 feet > tethered in no- to light-winds is fine. Instead of reeling the > bungeer back into the balloon, you can just (softly?) let the baloon > down. The bunggeer has plenty of time to get out of the baloon's way. Yes, but to drop off the end of the rope and parachute to the ground below is the idea... :) +------------ | rob@ireta.cynic.wimsey.bc.ca | Rob Prior, President, Still Animation Logo Design +------------------------------------------------------------
rob@ireta.cynic.wimsey.bc.ca (Rob Prior) (02/06/91)
ds4a@dalton.acc.Virginia.EDU (Dale Southard) writes: > First off -- I am NOT saying that bungee jumping from aircraft is a possible > or good idea, but... Agreed. > >First off, connecting the bungee cord to any point other than > >the center of gravity is going to cause the plane to be unstable > >at best, or tumble out of the sky at worst. > > Why Dave? I seem to remember hanging off the far tail of a skyvan with > seveal others -- [text deleted] Not the same thing. A bungee jump imparts a sudden torque on the CG, while hanging off the tail of the aircraft requires edging out to it. The pilot compensates as the CG shifts when you guys get out there. > >SECOND, as each person leaves the plane, the center of gravity > >changes. Thus the connecting point is going to move. > > Yea so? I don't move the connecting point for the static line in-between > students, and I haven't lost any yet. The static line has a very low force applied to it (unless the pin jams :) and hence has a very low effect on the flight characteristics of the jump plane. > >THIRD, it would be impossible to connect the bungee to the > >"true" CG, but it would have to be connected to the frame > >or fuselage at the nearest point. Thus, when a force is > >applied on the connecting point, it will cause the plane > >to rotate. Initially in a direction perpendicular to the > >line segment between the connecting point and the true CG. > > Again, SO WHAT??? Bungee jumpers regularly connect the bungee to their > ankles. The rate of deceleration that a bungee causes is obviously within > that which the human knee can handle (or there are a lot of spare lower leg > parts hanging around connected to a lot of used bungees :-) ). Actually, Bungee Jumping started as Bridge Jumping, at the end of a _rope_, not a rubber band... The human knee can take quite a jolt and still hold up. > So, you > are saying that the torque caused by this much force on a lever arm 1 meter > long (we will assume that a sutable hardpoint can be found that close to > the CG) is going to be more than the pilot can counter. No, but the sudden effect of a torque applied unexpectedly to the CG could cause the pilot to lose control. > Before you respond, > remember that the force is not really perpindicular to the lever arm--if > it does displace the plane via rotation, the lever arm is shortened and the > torque reduced -- assuming that the attachment is located behind and below > the actual CG, I would probably term the torque negligible. Only negligible if the aircraft is HUGE and the jumper SMALL. Also, what if the jumper catches his pilot chute on the way out? Suddenly jumper is supporting the weight of an aircraft over the length of his body. (providing nothing gives... :( > >FOURTH, the pendulum effect of a mass hanging at the end > >of a long elastic cord is going to cause it to bounce around. > >What effect do you think this will have on the pilot's efforts > >to keep the plane stable? > > Well Dave, last I checked, the period of a harmonic oscilator becomes greater > when the force constant is decreased (aka the less "stiff" the elastic > band is, the slower the mass at the end will bounce up and down). It doesn't matter. The force applied to the lever arm is the same no matter _how_ 'stiff' the rubber band is. When it is stretched fully, you have the same force. > Since the > effective force constant of elastic is increased with its length, a body at t > end of a long piece of elastic will bounce up and down more slowly than one > on a short piece. For the proposed 100 meter elastics, the bounces would be > very slow, probably on the order of one bounce every ten sec (but I am really > guessing here) And how close will the jumper bounce to the plane? > >How big a plane did you plan to do this from? I've noticed that > >even when a skydiver shifts his position from sitting on his > >(or her, excuse me) butt to a kneeling position in the back of > >a Twin Beech, that the pilot immediately feels it and has > >to make small adjustments. Now imagine the torque applied > >by a 200 pound object at the end of a 300 foot elastic cord. > > I can imagine ... not much. (note that the length of cord has no effect > on the torque as it is not rigid) Where did you learn physics? Pilot loses one jumper as he leaves, conpensates accordingly, and suddenly has to compensate the other way as the cord tightens when the lost jumper reaches the end of his line and the torque increases. > >Maybe, just MAYBE, such a stunt would be possible from a C-130 > >hercules, where the weight of one jumper would make only > >a very small difference in the CG. But anything the size > >of a DC-3 or smaller would be courting disaster. > > Well, I will be sure to keep that in mind the next time someone suggests > square-dancing in the Mr. Douglas. I have to agree with you on this... :) > Seriously, I don't mean to flame Mr. Apple... Then why did you? > ...for anything other that a failure > to understand physics. Seems as though he's not too far off... maybe _you_ should give _us_ some facts/figures? > There are lots of reasons not to bungee from a plane, > amoung them is the severe spacial disorientation casued by spinning at the > end of a bungee (you can't fly your body as well with your feet tied together > and they can't cut you away from the plane without risking a bungee/chute > entanglement). Or how about getting tangled/hung in the bungee when you > bounce back up into its slack? Or how about how stupid/trivial it makes > skydiving look? But I would be of the opinion that aircraft stability/CG > concerns would not preclude bungee jumping from something as small as even > a 182. The potential for accident is too great to bother with this kind of silliness. But, how about doing this from a _baloon_ at about 10,000 AGL? (can baloons go this high? I know nothing about them). This I could see as being possible. After all, the baloon would only bounce up and down... possibly creating seasick occupants... barfing overboard right down on top of... 'oh! I thought you had cut away already!'... :) > Flame away -- but don't bother unless you have HARD FIGURES, or at least a > couple of equations to back you up. I don't think equations are really necessary here... Most people, I think, have a gut feeling about this form of physics (if they've studied it at the post-secondary level). Perhaps you would like to supply your own equations? +------------ | rob@ireta.cynic.wimsey.bc.ca | Rob Prior, President, Still Animation Logo Design +------------------------------------------------------------
dappel@grafted.UUCP (Dave Appel) (02/09/91)
to: the genius who wants to bungee jump from a plane. Uh, excuse me, but where did you leave your BRAIN? Do you have any idea of the effects that vector forces have on an airplane? Lift, drag, thrust, etc? Have you ever noticed the pilot trying his darnedest to maintain straight and level flight with 4 or more skydivers hanging on the outside? Usually causing the CG (center of gravity) to be outside of normal limits? First off, connecting the bungee cord to any point other than the center of gravity is going to cause the plane to be unstable at best, or tumble out of the sky at worst. SECOND, as each person leaves the plane, the center of gravity changes. Thus the connecting point is going to move. THIRD, it would be impossible to connect the bungee to the "true" CG, but it would have to be connected to the frame or fuselage at the nearest point. Thus, when a force is applied on the connecting point, it will cause the plane to rotate. Initially in a direction perpendicular to the line segment between the connecting point and the true CG. FOURTH, the pendulum effect of a mass hanging at the end of a long elastic cord is going to cause it to bounce around. What effect do you think this will have on the pilot's efforts to keep the plane stable? How big a plane did you plan to do this from? I've noticed that even when a skydiver shifts his position from sitting on his (or her, excuse me) butt to a kneeling position in the back of a Twin Beech, that the pilot immediately feels it and has to make small adjustments. Now imagine the torque applied by a 200 pound object at the end of a 300 foot elastic cord. Maybe, just MAYBE, such a stunt would be possible from a C-130 hercules, where the weight of one jumper would make only a very small difference in the CG. But anything the size of a DC-3 or smaller would be courting disaster.
ds4a@dalton.acc.Virginia.EDU (Dale Southard) (02/12/91)
to: Dave Appel Gee Dave, do a little research already... First off -- I am NOT saying that bungee jumping from aircraft is a possible or good idea, but... >First off, connecting the bungee cord to any point other than >the center of gravity is going to cause the plane to be unstable >at best, or tumble out of the sky at worst. Why Dave? I seem to remember hanging off the far tail of a skyvan with seveal others -- that's about as far from the CG as you can get. I assume that only one person is going to bungee about at a time. If you had a little experience in the sport, you would have seen pictures of people hanging beneath aircraft practicing the "slide down the static line and cut the student free" method of "saving" a student who is in tow after a failed static line jump. >SECOND, as each person leaves the plane, the center of gravity >changes. Thus the connecting point is going to move. Yea so? I don't move the connecting point for the static line in-between students, and I haven't lost any yet. >THIRD, it would be impossible to connect the bungee to the >"true" CG, but it would have to be connected to the frame >or fuselage at the nearest point. Thus, when a force is >applied on the connecting point, it will cause the plane >to rotate. Initially in a direction perpendicular to the >line segment between the connecting point and the true CG. Again, SO WHAT??? Bungee jumpers regularly connect the bungee to their ankles. The rate of deceleration that a bungee causes is obviously within that which the human knee can handle (or there are a lot of spare lower leg parts hanging around connected to a lot of used bungees :-) ). So, you are saying that the torque caused by this much force on a lever arm 1 meter long (we will assume that a sutable hardpoint can be found that close to the CG) is going to be more than the pilot can counter. Before you respond, remember that the force is not really perpindicular to the lever arm--if it does displace the plane via rotation, the lever arm is shortened and the torque reduced -- assuming that the attachment is located behind and below the actual CG, I would probably term the torque negligible. >FOURTH, the pendulum effect of a mass hanging at the end >of a long elastic cord is going to cause it to bounce around. >What effect do you think this will have on the pilot's efforts >to keep the plane stable? Well Dave, last I checked, the period of a harmonic oscilator becomes greater when the force constant is decreased (aka the less "stiff" the elastic band is, the slower the mass at the end will bounce up and down). Since the effective force constant of elastic is increased with its length, a body at the end of a long piece of elastic will bounce up and down more slowly than one on a short piece. For the proposed 100 meter elastics, the bounces would be very slow, probably on the order of one bounce every ten sec (but I am really guessing here) >How big a plane did you plan to do this from? I've noticed that >even when a skydiver shifts his position from sitting on his >(or her, excuse me) butt to a kneeling position in the back of >a Twin Beech, that the pilot immediately feels it and has >to make small adjustments. Now imagine the torque applied >by a 200 pound object at the end of a 300 foot elastic cord. I can imagine ... not much. (note that the length of cord has no effect on the torque as it is not rigid) >Maybe, just MAYBE, such a stunt would be possible from a C-130 >hercules, where the weight of one jumper would make only >a very small difference in the CG. But anything the size >of a DC-3 or smaller would be courting disaster. Well, I will be sure to keep that in mind the next time someone suggests square-dancing in the Mr. Douglas. Seriously, I don't mean to flame Mr. Apple for anything other that a failure to understand physics. There are lots of reasons not to bungee from a plane, amoung them is the sever spacial disorientation casued by spinning at the end of a bungee (you can't fly your body as well with your feet tied together, and they can't cut you away from the plane without risking a bungee/chute entanglement). Or how about getting tangled/hung in the bungee when you bounce back up into its slack? Or how about how stupid/trivial it makes skydiving look? But I would be of the opinion that aircraft stability/CG concerns would not preclude bungee jumping from something as small as even a 182. Flame away -- but don't bother unless you have HARD FIGURES, or at least a couple of equations to back you up. --> --> Dale UVa (ds4a@virginia.edu)
bruce@logic.dsg.ti.com (Bruce Florman (BFLM)) (02/12/91)
In article <38P3w3w161w@grafted.UUCP> dappel@grafted.UUCP (Dave Appel) writes: >to: the genius who wants to bungee jump from a plane. > >Uh, excuse me, but where did you leave your BRAIN? > >Do you have any idea of the effects that vector forces have >on an airplane? Lift, drag, thrust, etc? Have you ever >noticed the pilot trying his darnedest to maintain straight >and level flight with 4 or more skydivers hanging on the >outside? Usually causing the CG (center of gravity) to >be outside of normal limits? > >First off, connecting the bungee cord to any point other than >the center of gravity is going to cause the plane to be unstable >at best, or tumble out of the sky at worst. Uh, I don't think so. I suppose that in these modern times it may be that nobody remembers them, but have you ever heard of a "jumper in tow?" It is a situation which arises when a static-line (remember those?) fails to release a jumper due to entanglement or mis-rigging. Although it is (was) something to be avoided, it is not generally considered to be catastrophic to the airplane. A bungee, because of its elasticity would probably be even less stressful to the airplane than a jumper in tow. > [other complaints deleted] > >Maybe, just MAYBE, such a stunt would be possible from a C-130 >hercules, where the weight of one jumper would make only >a very small difference in the CG. But anything the size >of a DC-3 or smaller would be courting disaster. Well, I do know of one static-line jumper who managed to get his main entangled with the tail wheel of a DC-3 (don't ask me how, I didn't see the event itself, I just saw the plane landing with the main trailing off the wheel). Even with a whole slew of floaters, the CG on a DC-3 is well ahead of the tail wheel, but the plane didn't crash or have any other severe control problems. I'm not the one who proposed bungee jumping from a plane, and I'm not sufficiently impressed with the idea to expend much energy trying to organize such a jump, but I think that your objections are largely without basis. --Bruce Florman D9019 (ret.) Blue Skies!
ryoder@en.ecn.purdue.edu (Robert W Yoder) (02/13/91)
In article <40BXw1w163w@ireta.cynic.wimsey.bc.ca>, rob@ireta.cynic.wimsey.bc.ca (Rob Prior) writes: > ds4a@dalton.acc.Virginia.EDU (Dale Southard) writes: [text deleted] > After all, the baloon would only bounce up and down... possibly creating Yeah, throwing the burner right into the envelope.8-) -- Robert Yoder "It's 10 o'clock. Do you know where your child processes are?" 306 Hawkins Graduate House Internet: ryoder@ecn.purdue.edu West Lafayette, IN 47906 Bitnet: ryoder%ecn.purdue.edu@purccvm (317)495-6845 N9CON UUCP: {purdue, pur-ee}!ecn.purdue.edu!ryoder
ds4a@dalton.acc.Virginia.EDU (Dale Southard) (02/14/91)
Rob -- good post (I like to see lively discussions without the use of the word Idiot, etc) Now, to really beat this thing to death... OK hanging off the tail of the skyvan is NOT the same thing, but Mr. Appel's original post maintained the the CG would be moved too far foreard/aft. My point is that this is not going to happen. In days of old (when men were bold??) the "student in tow" malfunction was not unknown. People really did hang below aricraft on the end of a static line. My point (though I didn't word it very well) was that the force being generated is not all that great. We are not talking about a rope, but an elastic cord. The longer the cord, the slower the mass at the end will be decelerated. The pilot would not recieve a sharp jerk, but a gradual tug. I would maintain that this should be controlable -- The lever arm is/would be far shorter than the lever arm on which the control surfaces of the plane are located. Rob: >> Well Dave, last I checked, the period of a harmonic oscilator becomes greater >> when the force constant is decreased (aka the less "stiff" the elastic >> band is, the slower the mass at the end will bounce up and down). >It doesn't matter. The force applied to the lever arm is the same no matter >_how_ 'stiff' the rubber band is. When it is stretched fully, you have the >same force. That isn't what I said -- I was talking about the PERIOD of the oscilations. The jumper would bounce up and down slowly, not rapidly. Not to mention that the force constant of the rubber band would be of great importance -- If the rubber band is too stiff, the force will be transmitted to the plane much more quickly, and the pilot would have to correct for it in a much shorter (possibly too quick) time frame. The important criteria in this example is the rate at which the jumper's momentum is "absorbed" by the bungee/aircraft that rate is determined by the force constant of the elastic. --------- >> I can imagine ... not much. (note that the length of cord has no effect >> on the torque as it is not rigid) >Where did you learn physics? Pilot loses one jumper as he leaves, conpensates >accordingly, and suddenly has to compensate the other way as the cord tightens >when the lost jumper reaches the end of his line and the torque increases. Well, sorry to point it out, but the length of the cord has no effect. Velocity does. Effective force constant does. Distance from CG does. Length doesn't. To sum up: We are all making educated guesses here, let's not call each other idiots. Some questions to ponder: 1) Can the jumper really bounce back up and hit the plane? (I think this violates some enery conversion law somewhere) 2) Are static lines safe? (It may indeed be that all pilots are just one student in tow away from tumbling out of the sky) 3) Why the hell am I defending an idea that I really don't care all that much to try? (Couldn't we discuss the best way to do a triple dragplane diamond instead?) But at any rate, thanks for the deversions -- I really hate to do productive work :-) --> --> Dale UVa (ds4a@virginia.edu)
msb@hosmsb.ATT.COM (Mike Balenger) (02/14/91)
>>>>> On 6 Feb 91 01:50:02 GMT, rob@ireta.cynic.wimsey.bc.ca (Rob Prior) said:
rob> But, how about doing this from a _baloon_ at about 10,000 AGL?
rob> (can baloons go this high? I know nothing about them).
I've heard that some bungee jumpers are using baloons to avoid laws
prohibiting bridge jumps. No need to get 10K AGL -- 200-300 feet
tethered in no- to light-winds is fine. Instead of reeling the
bungeer back into the balloon, you can just (softly?) let the baloon
down. The bunggeer has plenty of time to get out of the baloon's way.
--
----------------------------------------------------------------------
<cute quote> Michael S. Balenger (908) 949-8789
<cute disclaimer> AT&T Bell Labs FAX: (908) 949-7512
M_Balenger@att.com Room 1L-405
msb@hos1cad.att.com Crawfords Corner Road
att!hos1cad!msb Holmdel, NJ 07733-1988msb@hosmsb.ATT.COM (Mike Balenger) (02/14/91)
>>>>> 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.
--
----------------------------------------------------------------------
<cute quote> Michael S. Balenger (908) 949-8789
<cute disclaimer> AT&T Bell Labs FAX: (908) 949-7512
M_Balenger@att.com Room 1L-405
msb@hos1cad.att.com Crawfords Corner Road
att!hos1cad!msb Holmdel, NJ 07733-1988pvf@ESD.3Com.COM (Paul Fries) (02/14/91)
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
ds4a@dalton.acc.Virginia.EDU (Dale Southard) (02/14/91)
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)
evan@plxsun.uucp (Evan Bigall) (02/15/91)
In article <1991Feb13.191314.13568@cbnewsh.att.com> msb@hosmsb.ATT.COM (Mike Balenger) writes:
Bungee jumpers never make it back to the jump altitude!!!
Except for the twits* who carry rocks and/or other jumpers with them on the
way down, and then drop them at the bottom.
/Evan
*substitute a word based on your own personal stupidity to coolness ratio.ds4a@dalton.acc.Virginia.EDU (Dale Southard) (02/18/91)
Reply to SKYDIVE@f15.n233.z1.fidonet.org (SKYDIVE) > You probably have never flown an airplane. Vector >forces and CG calculations are a basic part of ground school. Yes, but I seriously doubt they knew where those vector/CG equations came from (I know the guy I had for ground school was clueless). They are teaching applications, not derivations, which is what is needed to solve problems other than those few that fit in to the conditions for which the working equation was generated (i.e. you can learn physics without learning calculus, but don't count on being able to use it for anything). But no, I ain't no pilot. > For a 7,000 pound airplane (a Twin Beech fully loaded), that >puts the CG 5 to 6 feet BELOW and OUTSIDE the frigging airplane! >And, not fully loaded, or with a smaller plane, it makes it even >FARTHER below. Pilots usually calculate moment in pound-INCHES, >from the datum line, and here we have 60,000 pound-FEET! >so where is that going to put the CG for your C-182? >About 12 feet below it! Case in point. The plane and the jumper are connected by a bungee/static line -- not a rigid steel rod. They are NOT part of the same inertial body and calculation of moment is meaningless. The above calculation would suggest that the jumper would move in relation to the planes pitch. Sorry, won't happen. The system you describe above cannot move the aircraft's CG outside of the aircraft. > Again, not the same thing. Here you have 200 pounds hanging only >6 to 8 feet below the craft. And yes, I have TALKED to pilots >who have had student-in-tow. And the student swings wildly from >side to side of the plane, causing the pilot a HELL of a time to >maintain control. Have you actually TALKED to >a pilot who had a student-in-tow? Its damn hard to fly a >Cessna, even the larger 206, in such a condition. The jumpmaster >is so worried about the student, he is not paying attention >to the bricks that the pilot is excreting from his rectum. >(See, I am keeping my sense of humor here.:) Ah...had not thought much about side to side motion...might be important.... I would imagine the bricks would be pretty big (one of my buddies just had a 182 shoot out a piston -- jump doors are nice -- they let you open the door so the smoke clears out enough to see were you are going). > You are still not looking at it from the pilot's viewpoint. >Regardless of the PERIOD of oscilations, the pilot is going >to have to make severe adjustments in an unpredictable >direction, as a result of the "bouncing". The fact that the >plane "absorbs" it over a longer "period" is of little >comfort to the pilot. The only way to overcome this is >the relative MASS of the plane to the jumper, as Rob Prior >pointed out. Well, the PERIOD effects the severity in haw often the pilot has to reverse the direction of correction. Longer cord --> slower (less frequent) oscilation. But I can see your point. > Its obvious to me that little thought has been given >to the wonderful pilots who transport us skydivers >to altitude and dump us out. As a student pilot, I have I think about them all the time -- didn't we spend a couple K of bandwidth the last week or so making sure that they didn't get asked to do something stupid and unsafe?? Please don't insult me like this (or I won't play anymore :-( ). Closing remark: The problem with modeling a situation like this is that it has too many contributing factors. Dave made the mistake when he tried to make it simple weight and balance. I err'd trying to make it simple kinetic energy & projectile motion (but I do have a nifty set of mathematica definitions that would only require about 30 hours more work to better resemble reality -- there is a reason why they have cray y-mp programed to model the effect of impact on a dropped beer (pop?) can -- I kid you not). The basic problem is that we are trying to determine what the PILOT can handle. Obviously, that is impossible! NEXT TOPIC PLEASE. --> --> Dale UVa (ds4a@virginia.edu)
dmason@ecs.umass.edu (02/19/91)
In article <38P3w3w161w@grafted.UUCP>, dappel@grafted.UUCP (Dave Appel) writes: > to: the genius who wants to bungee jump from a plane. > > Uh, excuse me, but where did you leave your BRAIN? Really, not to mention.... > > Do you have any idea of the effects that vector forces have > on an airplane? Lift, drag, thrust, etc? Have you ever > noticed the pilot trying his darnedest to maintain straight > and level flight with 4 or more skydivers hanging on the > outside? Usually causing the CG (center of gravity) to > be outside of normal limits? > what about the..... > First off, connecting the bungee cord to any point other than > the center of gravity is going to cause the plane to be unstable > at best, or tumble out of the sky at worst. > when the, you know........ > SECOND, as each person leaves the plane, the center of gravity > changes. Thus the connecting point is going to move. > It would...you would..... > THIRD, it would be impossible to connect the bungee to the > "true" CG, but it would have to be connected to the frame > or fuselage at the nearest point. Thus, when a force is > applied on the connecting point, it will cause the plane > to rotate. Initially in a direction perpendicular to the > line segment between the connecting point and the true CG. > ....really messed up...... > FOURTH, the pendulum effect of a mass hanging at the end > of a long elastic cord is going to cause it to bounce around. > What effect do you think this will have on the pilot's efforts > to keep the plane stable? > WOW is that dumb!! > How big a plane did you plan to do this from? I've noticed that > even when a skydiver shifts his position from sitting on his > (or her, excuse me) butt to a kneeling position in the back of > a Twin Beech, that the pilot immediately feels it and has > to make small adjustments. Now imagine the torque applied > by a 200 pound object at the end of a 300 foot elastic cord. > > Maybe, just MAYBE, such a stunt would be possible from a C-130 > hercules, where the weight of one jumper would make only > a very small difference in the CG. But anything the size > of a DC-3 or smaller would be courting disaster. O.k., now say this person does get ahold of a C-130, maybe at Fort Benning,Ga AIRBORNE school, and you do get to jump with the cord attached. I can tell you right now, when the cord recoils, and you get slapped across the underside of a C-130, you will be hurtin' 4 certain. One particular jump I made at AIRBORNE School, I jumped from the door, and a strap got snagged on a piece of metal, I was left dangling on the outside of the plane, getting bumped around against the fusilage about a dozen times before the trainer got me loose. I had bruises for months. Sheeeeeeesh, a bungee cord. -------------------------------------------------------------------------------- Don Mason \ Send all replys and comments to me College of eNGinEeRiNg / all .sigs on vacation University of Massachusetts \ Amherst / --------------------------------------------------------------------------------
rob@ireta.cynic.wimsey.bc.ca (Rob Prior) (02/19/91)
lonhyn@nas.nasa.gov (Lonhyn T. Jasinskyj) writes: > Dave Appel writes: > > Sorry, a rubber band is hardly capable of generating torque on the > object to which it is attached [text deleted] Yes, it is. It's not just a 'rubber band', either. This is a _bungee cord_. These are a fair bit stronger than the rubber bands you fling at each other in boring lectures. Have you ever tried to stretch a bungee like the ones used for bungee jumping? Bet you have to put your weight into it. Bungee jumpers use a composite cord. Mostly rope, with a length of bungee on the end of it. This keeps the bungee from snapping up too quickly when the jumper is released. > I see no reason why a smoothly increasing and decreasing force (the > bouncing jumper) coming from a direction that is barely changing (varying > over only a few degrees) should be such a great concern. What is keeping the abruptly increasing and decreasing force 'coming from a direction that is barely changing'? The jumper might be bounced all over the sky. > -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- > Email to: lonhyn@gulag.nas.nasa.gov Human at: 415-604-3989 > -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +------------ | rob@ireta.cynic.wimsey.bc.ca | Rob Prior, President, Still Animation Logo Design +------------------------------------------------------------
rob@ireta.cynic.wimsey.bc.ca (Rob Prior) (02/22/91)
dmason@ecs.umass.edu writes: > In article <38P3w3w161w@grafted.UUCP>, dappel@grafted.UUCP (Dave Appel) write > O.k., now say this person does get ahold of a C-130, > maybe at Fort Benning,Ga AIRBORNE school, and you do get to jump with > the cord attached. I can tell you right now, when the cord recoils, and you > get slapped across the underside of a C-130, you will be hurtin' 4 certain. > One particular jump I made at AIRBORNE School, I jumped from the door, and a > strap got snagged on a piece of metal, I was left dangling on the outside of > plane, getting bumped around against the fusilage about a dozen times before > the trainer got me loose. I had bruises for months. Sheeeeeeesh, a bungee cor Please read the rest of the postings before replying.... (1) You can't bounce back far enough to _get_ to the C-130 after exiting. There is too much wind resistance, and too much potential energy is lost. (2) Once you are not bouncing at the end of the cord, but rather just hanging there, you would be a _long_ way away from the airplane. You would not be swinging into the side of the plane and getting bruised. (3) It would be _much_ different than being 'snagged' on one of your straps at the doorway. Is this not obvious? +------------ | rob@ireta.cynic.wimsey.bc.ca | Rob Prior, President, Still Animation Logo Design +------------------------------------------------------------
ds4a@dalton.acc.Virginia.EDU (Dale Southard) (03/04/91)
Reply to message <2642.27D18611@ehsnet.fidonet.org> (Dave Appel): >Wait a minute. Why don't we write to a stuntman like >BJ Worth and ask him what his gut-feel would be for the >forces involved? Yeh, but a REAL skydiver would have jumped the "pit 'o' death" from a C-182, only a wimp would use a chopper. (I can see it now -- "Just one more go-around -- I'll leave this time for sure.") ;-) (If you have never watched what passes as entertainment on the Fox network, you won't get it). --> --> Dale UVa (ds4a@virginia.edu)