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Sky harpoon

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This may be spectacularly inefficient, or then again it may not. Frankly, I have no idea.

So.

Imagine a sleek titanium cylinder sitting upright on the ground. Its base is flat; the top is funnel-shaped, funneling down to a tube within the cylinder. This tube is a gun.

Upon activation, a charge fires a projectile out of the large cylinder. As it rises up some thousand feet or so, this projectile trails behind it a light, strong cable, harpoonesquely.

When the projectile reaches the limits of the tether, two things happen. First, the projectile itself springs open, releasing a large but simple round parachute. Second, a winch in the cylinder is activated, and starts to wind the cable in as fast as it can go. Quickly, the parachute inflates, affording considerable air resistance. In response, the cylinder starts to rise upward, winching itself toward the parachute. Although the chute is descending slowly, the cylinder is climbing faster, and the two meet eachother at about 800 feet.

The winch continues to wind the parachute in, drawing it back into the funnel and collapsing it in the process. As it does so, a deftly ingenious mechanism swiftly concertinas the parachute and its lines and re-stows them in the shell of the projectile. All this time, of course, the contraption will be falling but, in the second or so that it takes to re-pack the chute, it only falls a few tens of feed.

As soon as the chute is re-packed in the projectile, another charge fires it skyward again, and the cycle re-commences. Of course, firing the projectile upwards propels the launcher downwards but, thanks to their relative masses, the recoil is not too violent and little height is lost.

At each cycle, then, the launcher winches itself up 800ft, then falls back maybe 100ft. The result is a noisy but impressive reciprocating walk up to any chosen altitude.

MaxwellBuchanan, Jun 25 2008

Paddle Wheel Helicopters http://rotoplan.narod.ru/history_e.htm
Well how about that. [mylodon, Jun 25 2008]

Parachute and Cable http://homepage.ntl...iepurnell/dems.html
Near bottom of page [8th of 7, Jun 26 2008]

[link]






       I have no idea either so I will bun till this is proved to be rubbish.
MisterQED, Jun 25 2008
  

       I was pondering shooting guns in the air, as I often do. With shame, I realized that my math was inadequate to determine how high a bullet would go given a muzzle velocity. I thought perhaps it would involve calculus, applying gravitational acceleration (here slowing) to a projectile with an initial velocity. The shame, the shame. My face is as red as my bikini briefs.   

       But here Max has opened the door to an honest question. Given a projectile with a desired apogee of 1000 feet, and disregarding drag from air or any dangly appurtenances, what must the initial muzzle velocity be? Show your math.
bungston, Jun 25 2008
  

       The maths is easy, and doesn't involve calculus if you ignore drag. As always, there is a shortcut.   

       As it leaves the muzzle, the bullet has velocity V and mass M; it has kinetic energy of M.V.V/2 . At its peak, it has zero velocity but has converted its kinetic energy into gravitational potential energy, given by MGH (where G = acceleration due to gravity, and H = height).   

       Since we are looking at the complete conversion of kinetic energy into gravitational potential energy, we have:   

       M.V.V/2 = MGH   

       and hence:   

       V.V/2 = GH   

       and, since G = 10m/s/s:   

       V.V = 20H   

       or:   

       V = Sqrt (20H)   

       or roughly   

       V = 4.5.SqrtH   

       So, if you want an altitude of 1000 metres, then:   

       V = 4.5 x Sqrt(1000) or   

       V = 4.5 x 31 or   

       V =140m/s   

       Note that the square root relationship means that extra velocity buys you *lots* of extra height. This makes sense, because a faster bullet not only travels further during the initial, fast part of its flight, but also takes longer to slow to a standstill, so you get a double bonus.
MaxwellBuchanan, Jun 25 2008
  

       [+] though you're still gonna be weighed down by the winching.
FlyingToaster, Jun 25 2008
  

       I was going to suggest you could probably do this with levers and a rotary engine, but then the whole suggestion devolved into a paddle-wheel helicopter, and from there, to a regular helicopter, getting less impressive as I went.
mylodon, Jun 25 2008
  

       //As soon as the chute is re-packed in the projectile, another charge fires it skyward again// and the launcher is shot towards the ground at a high rate of speed...?
Klaatu, Jun 25 2008
  

       Bun for inventiveness.
simonj, Jun 25 2008
  

       two legs, i mean wings, for the vertical flap walk .
wjt, Jun 25 2008
  

       The other interesting thing about this idea is that the main body of the device will (unlike a conventional rocket) be subject to relatively low rates of acceleration, which could make it a more comfortable ride. If the harpoony bit can take very high rates of acceleration you can take advantage of high explosives to launch it.
hippo, Jun 26 2008
  

       You need added drag enhancers that deploy at the second stage firing, to minimise the recoil.
simonj, Jun 26 2008
  

       You are going to need a succession of ever larger parachutes to gain the same drag in the rarified upper atmosphere. Unless your mechanism is becoming lighter.   

       Your projectile is dragging weed.   

       You are going to need to keep your firing cylinder pointing up, once the parachute is winched into position.
4whom, Jun 26 2008
  

       This is similar in many ways to the Schermuly PAC (Parachute and cable) low level air defence system developed in conjunction with D.M.W.D. in the early 1940's. That used a vertically launched rocket and parachute, trailing a cable, to provide an alternative to barrage balloons. <link>   

       A quick calculation indicates that the mass of the system will be too great for "flight". But [+] for a HalfBaked idea.
8th of 7, Jun 26 2008
  

       //and the launcher is shot towards the ground at a high rate of speed...?// and   

       //drag enhancers that deploy at the second stage firing, to minimise the recoil//   

       Both true, but not excessively. If the launcher weighs 50x the projectile, then the recoil velocity (and hence distance lost) will be only 1/50th that of the projectile.   

       //You are going to need to keep your firing cylinder pointing up// Good point.   

       //two legs, i mean wings, for the vertical flap walk // Undoubtedly more appealing.   

       //the mass of the system will be too great for "flight"//   

       I'm not so sure. Consider a typical round parachute as a reference point. When carrying a human (say 100kg) it has a descent rate on the order of a couple of metres per second.   

       So, we need a system which weighs about 100kg all in, can fire the chute ballistically to (say) 1000ft, and then winch itself up the wire fairly swiftly. I don't think this would be impossible.   

       Of course, you could scale the whole thing, and larger versions may be more efficient (?), but at least for a 100kg system it should work.
MaxwellBuchanan, Jun 26 2008
  

       //The maths is easy, and doesn't involve calculus if you ignore drag//
I had to do some calculations a while back on 40mm AA rounds.
Although at firing, they underwent something like 25000g, as soon as they were out of the barrel, they started decellerating at something like 10g, even in near-horizontal flight.
Ignore drag at you peril.
coprocephalous, Jun 26 2008
  

       //Ignore drag at you peril.// There's a lesson for us all there.
MaxwellBuchanan, Jun 26 2008
  

       ////Ignore drag at you peril.// There's a lesson for us all there.// Cut to that scene from that movie...
4whom, Jun 26 2008
  

       I would say ignore calculus at your peril.   

       Several other problems. As the parachute is reeled in you will lose "purchase" as it loses surface area.   

       Calculations of this and the limit to which this idea will achieve a service ceiling will undoubtedly involve calculus.   

       It has sparked off an idea though. Is there a time limit from launch to orbit completeion on the N-Prize?
4whom, Jun 26 2008
  

       //will undoubtedly involve calculus// "If you need calculus to tell if it's going to work, it's not going to work." (John 'Shorty' Bahrnfharter).   

       [4whom] no, no limit except the final deadline for completing the 9th orbit.
MaxwellBuchanan, Jun 26 2008
  

       Calculus is my middle name. Physics is my first, and witty repartee is a distant third.   

       Ignoring the effects of drag when dealing with velocities of around 140m/s is like ignoring the effects of heat when mining the sun.   

       Taking an assumed projectile of 2kg mass (gleened from numbers bandied around here) and about the size of a metric pot roast, with a somewhat streamlined drag coeffecient of 0.5, and a muzzle velocity of 140m/s, we get an apogee of 461.5m.   

       As this is considerably less than the 1000m predicted when ignoring drag, we can see the perils of such an assumption.   

       Any request for alternate shapes, sizes and muzzle velocities?
Texticle, Jun 26 2008
  

       I think this idea is worth a try because if it works, great, and if it doesn't, well, 'chute harpoons.
imaginality, Jun 26 2008
  

       One could dispose of the chute after the cylinder was maximally reeled in. It will never deploy propoerly a second time anyway. Chutes have to be packed just so.   

       The cylinder would contain a stacked series of chutes, made of thin film. On maximal reeling in, fire the new chute through the first. When I say dispose of the chute, of course I mean make it explode. The chute film is highly flammable and will ignite from the exhaust of the next fired chute, burning in a harmless cloud of flame as the projectile passes through it.
bungston, Jun 26 2008
  

       Or use the old chute to hold up the launcher while the new chute is coasting upwards.
baconbrain, Jun 26 2008
  

       why the emphasis on a normal parachute?... picture a large brolly on a rope.
FlyingToaster, Jun 27 2008
  

       [Texticle], there is also the *small* matter of dragging a cable behind the projectile
4whom, Jun 27 2008
  

       //well, 'chute harpoons// {{{claps}}} [imaginality]
coprocephalous, Jun 27 2008
  

       An advancement to humanity is making something new - making a repacking multi-deployable parachute would be the cutting edge of science and art .
wjt, Jun 29 2008
  

       {looking for a hat to put on, so that I can take it off to [MaxwellBuchanan]}[+]
pertinax, Jun 29 2008
  

       Use a power-cord tether and a winch at the top. Add climbing monkeys and you have an Indian rope trick to beat all.
ldischler, Jun 29 2008
  
      
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