Jetpacks currently suck. What are the flaws, and how can we overcome them?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Doggzilla, Nov 25, 2017.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Dec 5, 2017 #61

    markaeric

    markaeric

    markaeric

    Well-Known Member

    Joined:
    Aug 1, 2015
    Messages:
    346
    Likes Received:
    83
    Location:
    Wichita
    So I took the posted specs of a quality electric supercharger (http://www.aeristech.co.uk/electric-supercharger/) - specifically a PR of 2 and .07kg/s flow rate and ran it through a program called RPA (http://propulsion-analysis.com) combusting the air with kerosene at ~14:1 afr (much higher than a typical jet engine) and got an abysmal performance figure of <15lbs thrust. given that the compressor & electric motor combo itself weighs nearly 10lbs makes it untenable. Never mind that it would take around 50lbs of lithium ion cells to power the thing for 30 minutes. Taking just the compressor specs for Garrett's largest turbo (ignoring how it would even be powered) - PR of 5 and 2lbs/sec would produce ~330lbs of thrust, and that's a HUGE turbo. So I'm quite impressed by the performance of Zapata's rig of what I presume is 4 small turbojets (in the original video - looks like 6 in the latter ones). Unfortunately I was WAY off base with what I thought would be possible using electric turbocompressors and a rocket-like thrust chamber.
     
  2. Dec 5, 2017 #62

    Aesquire

    Aesquire

    Aesquire

    Well-Known Member

    Joined:
    Jul 29, 2014
    Messages:
    2,321
    Likes Received:
    935
    Location:
    Rochester, NY, USA
    Educational experience, check. Welcome to the world of science where being wrong teaches you more than being right, often.

    The flying hover board is impressive. Almost as impressive is the skill of the pilot. That's years of practice with water jets strapped to his legs.

    You don't learn how to hover one of those from Stick & Rudder, but the knowledge base from aviation gives you the language to describe your moves. Axis of motion & thrust. That is practiced kinesthetic skill.
     
  3. Dec 6, 2017 #63

    Aesquire

    Aesquire

    Aesquire

    Well-Known Member

    Joined:
    Jul 29, 2014
    Messages:
    2,321
    Likes Received:
    935
    Location:
    Rochester, NY, USA
    WASP platform

     
    Last edited by a moderator: Mar 20, 2019
  4. Dec 6, 2017 #64

    Aesquire

    Aesquire

    Aesquire

    Well-Known Member

    Joined:
    Jul 29, 2014
    Messages:
    2,321
    Likes Received:
    935
    Location:
    Rochester, NY, USA
    More WASP
     
    Last edited by a moderator: Mar 20, 2019
  5. Dec 6, 2017 #65

    Aesquire

    Aesquire

    Aesquire

    Well-Known Member

    Joined:
    Jul 29, 2014
    Messages:
    2,321
    Likes Received:
    935
    Location:
    Rochester, NY, USA
    And even more from a team that wants to make one.



    The Platform instead of Back Pack, solves the weight problem of legs carrying the load, and allows much more fuel.

    Still a limited design, but all designs have limits. You don't expect to fly to orbit in a Cessna 150 or land a Space Shuttle on a 700 ft runway.

    Computerized stabilization systems may make these kinds of flying machines easier to learn to fly, but I don't think they are really needed. The low level flying you see this kind of machine doing is too low for a ballistic 'chute to make a sure save, ( although I'd want one for commuting ) so you have to make your own risk assessment and choices. I'd take one if I could afford one.
     
    Last edited by a moderator: Mar 20, 2019
  6. Dec 7, 2017 #66

    BBerson

    BBerson

    BBerson

    Well-Known Member HBA Supporter

    Joined:
    Dec 16, 2007
    Messages:
    12,052
    Likes Received:
    2,349
    Location:
    Port Townsend WA
    It still needs a platform for takeoff and landing. So what would you do with it?
     
  7. Dec 7, 2017 #67

    Aesquire

    Aesquire

    Aesquire

    Well-Known Member

    Joined:
    Jul 29, 2014
    Messages:
    2,321
    Likes Received:
    935
    Location:
    Rochester, NY, USA
    The jet hover board uses a steel mesh raised platform.

    The Williams X-jet/ WASP takes off from asphalt or grass just fine. Sand would be an issue but that's true for helicopters and tilt rotors too.

    Range is marginal for weekend burger runs depending on location. Order of magnitude better than a backpack unit.
     
  8. Dec 7, 2017 #68

    bmcj

    bmcj

    bmcj

    Well-Known Member HBA Supporter

    Joined:
    Apr 10, 2007
    Messages:
    12,918
    Likes Received:
    4,867
    Location:
    Fresno, California
    The range is fine as long as the burger joint is on the same airport as your takeoff point.
     
    Topaz likes this.
  9. Dec 7, 2017 #69

    Aesquire

    Aesquire

    Aesquire

    Well-Known Member

    Joined:
    Jul 29, 2014
    Messages:
    2,321
    Likes Received:
    935
    Location:
    Rochester, NY, USA
    With a max speed of 60 mph, and 30 minutes flying time, if the next airport is in the next valley over...... Leave some safety margin and 20 miles range?
    https://en.wikipedia.org/wiki/Williams_X-Jet

    vs. original Bell Rocket belt. 21 seconds. https://en.wikipedia.org/wiki/Bell_Rocket_Belt 30 sec on the 1995 RB2000.

    vs. Bell/Williams Turbojet powered version, 5 minutes demonstrated. ( theoretically 25 minutes ? )

    vs. JetPack Aviation JB-9, 10 minutes.

    https://en.wikipedia.org/wiki/Jet_pack

    The problem with any fuel dependent system is simply the weight of the fuel. The Bell turbo jet model was marginal, at best, to walk around with. Landing in any VTOL aircraft is the hardest part, as far as precision flying goes. ( the power problem with transition isn't a skill issue ) Human landing gear is fragile. The Bell Jet pack used a "kickstand" frame to support the weight while the pilot strapped in, and he would then raise the stand, fly, land, and lower the stand to take the weight.

    Given a nuclear or antimatter powered jet that has no or little fuel mass, then you can beat the weight limitation.... But I can't order antimatter from Amazon, and I haven't figured out how to shield the hot nuclear core so the pilot survives without making it weigh more than 200 pounds. ( where is Tom Swift Jr. and his Tomasite? )
     
  10. Dec 22, 2017 #70

    REVAN

    REVAN

    REVAN

    Well-Known Member

    Joined:
    Dec 6, 2016
    Messages:
    181
    Likes Received:
    60
    Location:
    Tucson, Arizona USA
    "Jetpacks currently suck. What are the flaws, and how can we overcome them?"

    The primary flaw is the VTOL assumption. Eliminate VTOL and you can have a chance at making a viable "Jetpack". The current state-of-the-art in this category would be a paramotor. They have a lot of limitations, but they are WAY more viable than a Bell Rocket unit, or even the Bell/Williams Jet Belt. With some effort and money, I'm sure something much better could be done. One direction could be to add wheels to one of those jet powered parachute wings; eliminate the need for the jump plane and it could start to look viable (maybe with a few other modifications as well).
     
    jedi likes this.
  11. Dec 22, 2017 #71

    Aesquire

    Aesquire

    Aesquire

    Well-Known Member

    Joined:
    Jul 29, 2014
    Messages:
    2,321
    Likes Received:
    935
    Location:
    Rochester, NY, USA
    I can fly a powered paraglider out of a large hypothetical yard. Jet back off my driveway. A mini jet airplane? I'd need a real runway.

    And while it's a thrill ride rocketing along with my butt inches off the runway, it's a different critter than the VTOL.

    You're right that it's the VTOL aspects that are the most trouble. Especially the L part.

    While I like the WASP, it's a starting point not the end product. It really needs long stroke shock absorbing gear to be "practical".
    The flying garbage can Dick Tracy machines like the WASP aren't back packs either. And they are for most people just a stepping stone on the way to a mini Harrier. Niche market recursive.
     
  12. Dec 22, 2017 #72

    Vigilant1

    Vigilant1

    Vigilant1

    Well-Known Member Lifetime Supporter

    Joined:
    Jan 24, 2011
    Messages:
    4,062
    Likes Received:
    1,799
    Location:
    US
    It seems that the root problem is the inefficiency of developing thrust by accelerating a (relatively) small volume of air to high velocity. The compact, practical 1 person VTOL will need to await 1) development of non-aerodynamic lift capability (e.g antigravity) and/or 2) very small, high energy density power sources (antimatter reactions etc). Until then, small helicopters, small lifting platforms, etc will have to do.
     
  13. Dec 22, 2017 #73

    REVAN

    REVAN

    REVAN

    Well-Known Member

    Joined:
    Dec 6, 2016
    Messages:
    181
    Likes Received:
    60
    Location:
    Tucson, Arizona USA
    I think the best solution would be a machine that does what a paramotor does, but that does it much better and without all the paramotor limitations. Sacrifice a little of the paramotor's folded compactness for improved flying robustness and ability to handle turbulence and it could become a useful and fun "jetpack". IMO, it doesn't need to fly super fast to qualify as a jetpack. Without any structure around the pilot to protect him/her, I'm thinking that slow like an ultralight is going to be much prefered to fast.
     
    jedi likes this.
  14. Dec 23, 2017 #74

    jedi

    jedi

    jedi

    Well-Known Member

    Joined:
    Aug 8, 2009
    Messages:
    1,780
    Likes Received:
    402
    Location:
    Sahuarita Arizona, Renton Washington, USA
    I agree. The idea of VTOL is much overrated. The object of "flight" is by definition to go someplace. Going straight up and down is not a requirement.

    I watch helicopters at the local airport with all their VTOL capabilities that are used to raise or descend three feet so that they can taxi to the take off area where they make a conventional STOL takeoff or landing that generally takes an excessive amount of time as they make their high power slow motion landing or takeoff all while operating in the "danger zone".

    The paramotor without the limitations* of the paraglider is a practical jetpack. I want to keep it in my garage or the trunk of my car. If I need to walk out into the street to safely takeoff that is ok. If I need to walk to the stop sign I can do that. If I need to go further than that I want a wagon to carry the weight and I need to take the wagon with me for when I land.

    Now, somebody please design that. I have had several people approach me while setting up to fly (but before the wing was out of the bag) and say "Wow, that's a really neat helicopter, how does it work?"


    Paraglider limitations:

    1. Need to lay it out on the ground in preparation for takeoff.
    2. Blows away in the wind.
    3. Difficult to launch consistently.
    4. Excessive time required for pre and post flight activities. (Other than beer drinking.)
    5. Would be nice to go a little faster than some. There are "fast" paragliders.
     
  15. Dec 23, 2017 #75

    jedi

    jedi

    jedi

    Well-Known Member

    Joined:
    Aug 8, 2009
    Messages:
    1,780
    Likes Received:
    402
    Location:
    Sahuarita Arizona, Renton Washington, USA
    Deleted another double post. Cause is unknown. Site is reported to be very slow responding today.
     
    Last edited: Dec 23, 2017
  16. Dec 23, 2017 #76

    BJC

    BJC

    BJC

    Well-Known Member

    Joined:
    Oct 7, 2013
    Messages:
    9,550
    Likes Received:
    6,322
    Location:
    97FL, Florida, USA
    If that works for you, great. For me, going some place in a personal airplane is but one, of many, objectives of flight.

    I would bet that the vast majority of pilots, and an even higher percentage of HBAers, have dreamed of flying with a jet pack. Perhaps one day ...


    BJC
     
  17. Dec 23, 2017 #77

    jedi

    jedi

    jedi

    Well-Known Member

    Joined:
    Aug 8, 2009
    Messages:
    1,780
    Likes Received:
    402
    Location:
    Sahuarita Arizona, Renton Washington, USA
    Did it again, again. I have to use this software to sell my bit coins.
     
    Last edited: Dec 23, 2017
    BJC likes this.
  18. Dec 23, 2017 #78

    jedi

    jedi

    jedi

    Well-Known Member

    Joined:
    Aug 8, 2009
    Messages:
    1,780
    Likes Received:
    402
    Location:
    Sahuarita Arizona, Renton Washington, USA
    I suspect we may have differing concepts of "going someplace".

    To me going someplace is to not hanging out three feet above the ground in the same location where I take off or land. To go up 100 feet is to go someplace. To fly the Pits for an hour of loops and rolls and return to base is to go someplace even if it is to an aerobatic box over the field.

    I would love to have a balloon permanently moored in my back yard so as to be able to go up on a tether and have a look around each day. Three feet might be fun for a while but I want to be higher (with safety) than I care to fall, or jump without a parachute. Even the jet packs eventually go someplace. I am just saying I am willing to forgo the stationary flight and just go for it if that makes the engineering easier or reduces the power requirements. That is the way most birds do it and that is good enough for me. Jump or run and jump into the air for takeoff and fly low and nearly stop for landing. Skip the hover in place.

    BTW I switched jobs in 1973 to get a shot at the jet pack engineering and flight test but myself, the wife and kids only got to stand in the freezing cold for two hours while the two project employees prepared for and made the two minute or less demonstration hover flights. Total flight time less than two minutes split into one solo and one dual flight.
     
    Last edited: Dec 23, 2017
  19. Dec 23, 2017 #79

    jedi

    jedi

    jedi

    Well-Known Member

    Joined:
    Aug 8, 2009
    Messages:
    1,780
    Likes Received:
    402
    Location:
    Sahuarita Arizona, Renton Washington, USA
    Did it again.
     
  20. Jan 3, 2018 #80

    Sockmonkey

    Sockmonkey

    Sockmonkey

    Well-Known Member

    Joined:
    Apr 24, 2014
    Messages:
    1,657
    Likes Received:
    431
    Location:
    Flint, Mi, USA

Share This Page

arrow_white