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Transportation Technology

The Ephemerality and Reality of the Jetpack 127

Posted by samzenpus
from the up-up-and-away dept.
First time accepted submitter Recaply writes "Here's a look back at the 1960's Bell Aerosystems Rocket Belt. 'Born out of sci-fi cinema, pulp literature and a general lust for launching ourselves into the wild blue yonder, the real-world Rocket Belt began to truly unfold once the military industrial complex opened up its wallet. In the late 1950s, the US Army's Transportation Research Command (TRECOM) was looking at ways to augment the mobility of foot soldiers and enable them to bypass minefields and other obstacles on the battleground by making long-range jumps. It put out a call to various aerospace companies looking for prototypes of a Small Rocket Lift Device (SRLD). Bell Aerospace, which had built the sound-barrier-breaking X-1 aircraft for the Army Air Forces, managed to get the contract and Wendell Moore, a propulsion engineer at Bell became the technical lead.'"
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The Ephemerality and Reality of the Jetpack

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  • by Deadstick (535032) on Sunday March 02, 2014 @06:51PM (#46384347)

    ...as opposed to the rocket belt, which was merely eardrum-breaking...

  • by Anonymous Coward

    I know it's offtopic and all, but is it just me, or has this not changed in like a week or more?

    • by Soulskill (1459) Works for Slashdot

      We had to disable updates to most of the Slashboxes, including 'This Day on Slashdot' in order to fix an underlying issue in the code. The work should be completed soon, at which point we'll re-enable everything. Apologies for the inconvenience!

      • I am detecting a significantly elevated level of story quality and of course, beta changes, in the last week or so. I guess you guys really did listen...eventually.

  • Chuck Taylor's weren't responsible for the gain in vertical leap?
    • by rts008 (812749)

      No.

      Kids these days...*sigh.

      Chuck Taylor's couldn't hold one of the PF Flyers shoestrings!

      PF Flyers even came with a 'Magic Ring' that done encoding and decoding...Johnny Quest would never lie to me.

  • by Animats (122034) on Sunday March 02, 2014 @07:04PM (#46384401) Homepage

    A big problem with jetpacks is that human ankles are weak landing gear. You can't do a parachute landing fall while wearing a jetpack; you have to do a standing landing. With all the mass of the gear on your back.

    The other big problem is that rocket systems have a short flight time, and jet engine systems are too expensive. The jet engine powered backpack [youtube.com] worked well, but cost too much. That used a small Williams jet engine. Williams International has tried and tried to make small jet engines cheaper. So have many others. Unfortunately, that's a very hard problem, which is why general aviation is still piston-powered. Below small-bizjet size, jet engines don't seem to get much cheaper as they get smaller. There was a big effort about a decade ago to develop "very light jets", but they ended up costing well over $1 million, most of that being engine cost.

    So it can be done, and it has been done, but it just doesn't work very well.

    • That's a great video
    • by Recaply (3554641)
      Great video thanks for sharing. Added it into the post..
    • That and stabilization.

      It is easy to launch someone into the air with just a moderate amount of explosives, or a jet engine strapped to your back, doing so in a slow controlled manner when we are talking at least 300 pounds of human, their gear, and the jetpack itself is a whole lot harder. Add to that this engine or rocket has to be in direct contact with a living human being for an extended period.

      Practically, you are not going to create a solution light enough to carry around just in-case it is needed. M

      • by plover (150551)

        I think they could solve stabilization with modern electronics. Kid's toy quadcopters are already self leveling, and as they weigh much less thank a kilogram, they're far more "twitchy" than 150kg of inertia carried about by the humans and their gear.

        As you mentioned, it's the soldier who has to carry the additional 60kg pack that is the real limit.

      • by Anonymous Coward

        Practically, you are not going to create a solution light enough to carry around just in-case it is needed. Maybe you could create something that is usable, but it will be so heavy that, best case scenario, it would just be carry-able by a single man without too much extra gear, and more likely it would be a very limited range vehicle that needed to be transported to where it was to be used by plane or truck

        Which is why we still use helicopters. We haven't really figured a way to scale that type of mobility down to a single person. And frankly speaking, unless we get moving on actual mechanized battle-suit technology, we won't. The ultimate problem is your power source, getting it small and light enough while maintaining enough power to be useful.

    • by jafac (1449)

      Based on the prices of some programs, I don't think that "too expensive" is an issue.

      When killing people is concerned, I think that no price is too high for our military.

      • by pepty (1976012)
        The goal isn't to kill people; the goal is to distribute the project to as many congressional districts as possible. More moving parts, more better.
  • Williams WASP X-Jet (Score:5, Interesting)

    by OzPeter (195038) on Sunday March 02, 2014 @07:08PM (#46384423)

    This is the reality of how to make a single man fly.

    Williams WASP X-Jet [youtube.com]

    It worked, it flew, there was no military justification for it, it disappeared.

    • It worked, it flew, there was no military justification for it, it disappeared.

      Specifically, with fuel lasting only 30 minutes, it didn't have much practical application.

    • by aliquis (678370)

      As I understood it the designer behind that one is a one which worked with Moore until he died (at age 54?) and later continued with the work.

      I'm not all that surprised there wasn't much interest for that can though. Then again maybe it was awesome to avoid branches, offer some protection, let you carry gear / rifle, .. Maybe it just looked worse :)

      They all controlled great :)

    • I saw that when I was a kid in the 80's on some TV program and as I grew up I was pretty sure that I had either watched something fictional, or I was too young and misunderstood. I mean, if they had that working in the 70s, they would have something even better in the 90s, 00s etc, instead of, ehm, pretty much nothing. Thanks for that! You verified my childhood memory and solved what was a "mystery" to me!!
      • AFAIK power density hasnt really changed that much. You have a pretty fundamental limit on how long flight lasts given a fuel density and a payload.

      • by twosat (1414337)

        I remember seeing this on a TV science program in the 1980's when I was at university in New Zealand. I'm pretty sure that it would have been mentioned in science magazines like "Popular Science" and "Popular Mechanics" - it was well-known at the time.

    • To be fair, it could be defeated completely by wearing the crocodile mask.

  • 1950s (Score:4, Insightful)

    by djupedal (584558) on Sunday March 02, 2014 @08:01PM (#46384669)
    I suspect they ran the numbers and decided that rather than making medicore-range quasi-flyers out of ground soldiers, the smart money was on just getting it over with and develop better helicopters, instead. Better speed; longer flights; bigger payloads - all much cheaper than adding limited flight capabilities to the individual.
    • by delt0r (999393)
      Jet packs are like flying cars. Everyone thinks they are awesome and would make like better, but no one knows how or why it would be better. Logic is hardly going to work with these fans.

      Also the way things scale means its easier and cheaper to make some of these things bigger. So its cheaper to make a 2 man-4 man helicopter than a one man jet pack. Range is always a problem with smaller things because of the cube law.
      • by Wolfrider (856)

        --Jet packs will likely be much more feasible if/when we start colonizing other planets. If you can get to 60-70% of Earth's gravity or lower, it will be much easier to fly.

  • Like the problem with a functional 5 megawatt laser, it is about a power source
  • by joe_frisch (1366229) on Sunday March 02, 2014 @11:27PM (#46385527)

    We don't see jetpacks or flying cars for the very same physics reason. In order to hover against gravity you need to produce thrust > weight. Since thrust is proportional to (mass/second) X velocity, and power is proportional to (mass/second) X velocity^2, an efficient source of thrust you want to move a lot of material slowly (assuming you have unlimited reaction mass -> the atmosphere).

    So, things that hover need to move lots of air, and have great big propellers. That is why helicopters work, and jet-reaction cars are too inefficient to be practical. It is why airplanes have big wings, not stubby lifting bodies. There may be a few spacial cases where you are willing to tolerate inefficiency, but they are rare.

    Planes look like planes for a reason. Helicopters look like helicopters for a reason.

    • Stubby lifting bodies can be practical at interesting cruise speeds, but you wouldn't want to take off or land at such speeds. Adding VTOL capability would solve that problem, but then we are back to the big and slow propellers issue you explained so well. I believe it is possible to convert a small, low thrust, high speed jet to a high thrust, low speed one with no moving parts. Air amplifiers actually increase thrust below 5cm in diameter but reduce it for larger sizes, so you have to figure out why it do

      • I didn't know that air amplifiers didn't scale, but also didn't know how efficient they were. Turbulent systems can be very non-intuitive - some airplanes have small vortex generators (tabs on the to of the wing that stick into the air flow) because they decrease drag. (they prevent boundary layer separation, but it still feels like exactly the wrong thing to do.....

        • Fluids "love" to twist, so laminar flows (such as the curtain of air along the inner surface of air amplifiers) don't always get the best results. The laminar flows seem so quiet and smooth so it is hard for our intuition not to consider them to be the way to move mass with the least energy.

          Vortices can scale very well. I always point to the Red Spot on Jupiter as an example. Can one be generated on a scale that could keep a car or a person suspended in mid air while using less fuel than a helicopter? I thi

  • by Anonymous Coward

    Wisdom from http://www.schlockmercenary.com/2011-05-28
    corporal: "Do you know what we call flying soldiers on the battlefield?"
    private: "Air support?"
    corporal: "skeet"

  • I wonder how things would have been different if multiple identical R&D contracts were awarded to several companies so as to set up competition for the best technology. Basically, set aside R&D money to be given to a company so there is disincentive to risk their own money. I would also throw in there that R&D awards be given to startups rather than huge public companies.

    • Because contract competition in the early 1960s would have circumvented the fundamental limits of engineering and materials and produced something that cannot be made in 2014?

      Note that there have been dozens of small "flying man" devices from the late 1950s to the present day, none of them practical for any important application. The limits of fuels and propulsion systems constrain everyone and even modern computers and composite materials aren't making flying belts practical today.

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