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Problems with Jetpacks ?

  1. Apr 6, 2013 #1
    I see the jetpacks ( or any kind of thrusters ) in movies like James Bond, Iron man, MIB are impractical but they aren't impractical in correct sense, I mean they can be made. But there are problems like -

    - Less flight time
    - Complex design of efficient packs
    - Added weight of the fuel
    - No advanced research in the field
    - Hazardous working
    - Not cost effective

    But these all points have been going on from decades, doesn't the modern research have any answers to these. Less flight time, hazardous working, complexity in design, almost all kinds of problems are due to carrying fuel along with the packs.

    Instead of fuels can't we design a motor which just creates enough thrust to lift an average person powered by car batteries ( or any other batteries of course !! )
     
  2. jcsd
  3. Apr 6, 2013 #2

    mfb

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    Car batteries have a worse energy to mass ratio than fuel. And you cannot use car batteries as exhaust. You would need a large propeller, which gives other issues.
     
  4. Apr 6, 2013 #3

    Danger

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    Car batteries would be a worst-case scenario. That's lead-acid technology, and the power to weight ratio is hideous. They're great for sudden blasts of intense amperage, but sustained output isn't a priority for them. (In cold weather, my Roadrunner draws 945 amps to start. I have a 350 amp regular battery up front, parallel wired to a 690 amp tractor battery in the trunk, using 00 welding cable. At -30° or lower, if it hasn't fired up within 45 seconds the pack is dead. The first time that I sparked it up after the engine rebuild, it fused the windings in the starter. Had to get a custom unit built with an extra 30 turns in the field windings.)
    The best current jet belt technology uses peroxide rockets. There are a few reasons for that, and safety is not the least of those. The output is steam. While that could potentially scald the pilot, it won't set him on fire. It's also a high-density blast for your buck. Very few fuels work as efficiently, and the best that you can get out of a totable peroxide tank is 30 seconds of flight.
    If you investigate the Iron Man situation, you'll note that his electric fan boots (that's the original version; the repulsors were strictly weapons in his gauntlets) relied upon the same non-existent energy generation technology that the rest of the suit used. It doesn't exist in reality.

    edit: Oh, hi mfb. You sneaked in while I was composing. I'll return now to just decomposing.
     
  5. Apr 6, 2013 #4
    Thats funny! Whats a road runner? Sounds like a big machine :-)
     
  6. Apr 8, 2013 #5
    You could also build a jetpack out of smaller jet engines, assuming your budget is almost unlimited. For a little over five grand per motor, you can get a 5 lb motor with a little over 50 lbs of thrust. Assuming a light pilot, you could use four to six of these for flight, but you're eating 24 oz of kerosene for each engine, each minute... and the fuel isn't all that light, so you need to either add more engines or accept that you aren't flying all day with one of these. Noise level is also considerable, and the exhaust temperatures are enough to set the pilot on fire, while he's carrying a significant amount of kerosene. There are good reasons why jetpacks remain largely a feature of science fiction...
     
  7. Apr 8, 2013 #6

    berkeman

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  8. Apr 8, 2013 #7

    Borg

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    As long as you're willing to stay over water, flight times can be hours on a JetLev.
     
  9. Apr 9, 2013 #8

    Danger

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    Thanks, Berkeman. Mine is the '72 GTX. If that page displays the same on all monitors (4-wide), it's the 2nd model in the 3rd row. That's the yellow one, but mine is green. The engine is a 446 (.030 over-bored 440) with 12 1/2:1 compression. Of course, you gotta know that my dream machine is the Hemi Superbird (the one with the fins, shown in the 3rd picture of the first row). I think that there might still be a couple available in the $200,000 range.
    Borg, I never thought of this until I read your post, but you wouldn't actually have to stay over water. You could get several minutes of flight time and some moderately useful distance by tethering the JetLev to a tanker truck and having it follow you around. The practicality would be nil, of course, but it could be fun. I'm sure that it would be frowned upon in an urban environment.
     
  10. Apr 9, 2013 #9

    Borg

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    It would give a new meaning to the the term jet wash. :tongue:
     
  11. Apr 9, 2013 #10

    Danger

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  12. Apr 19, 2013 #11

    Danger

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    I just looked back at at this thread and realized that those Roadrunner pictures keep changing places. To simplify it, mine is the one that is slime green and shown with a middle-aged couple standing behind it, in front of a barn and a garden shed. The differences are that mine is dark pine green and has a vinyl roof.
     
  13. Apr 19, 2013 #12
    The biggest problem is that there is no buisness type incentive to build jet packs. The military explored them in the past but found them to be very costly in terms of...cost and fuel, with poor performance.
     
  14. Apr 19, 2013 #13

    berkeman

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    Maybe you could call in a few quadcopter drones to do a group lift... :smile:
     
  15. Apr 20, 2013 #14

    Danger

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    If you can attach a vibrator to that, I sense a business opportunity...
     
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