The Jetpack thread

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Doggzilla, Jul 26, 2019.

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  1. Aug 8, 2019 #41

    Doggzilla

    Doggzilla

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    Im actually surprised they havent had an accident yet. The Harrier Jump jets were extremely dangerous because the exhaust would hit the ground and roll back into the intake and suffocate the engine. Pilots had to develop a special landing technique that was very rough on the aircraft. Basically a belly flop. Which is clearly not good for their frame life.

    So far the jetpacks seem surprisingly immune to this effect. But it would not surprise me if an accident were to occur eventually.
     
  2. Aug 8, 2019 #42

    BBerson

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    They only land on deflector grills, from what I've seen. Sort of limits the usefulness.
     
  3. Aug 10, 2019 #43

    Doggzilla

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    It’s surprisingly difficult to find video of takeoffs and landings that don’t look scripted.

    I don’t see any videos with grates, but I sure don’t see any that appear to be genuine unplanned footage.

    That is either very bad or very good. They are either trying to cover instability or it performs good enough that they don’t even bother to include it.

    There is video of a training school without any special ground modifications, but they also have tethers from a tower. So that also can’t be used to make assumptions from.

    I guess we will just have to wait and see. The spray from the ocean didn’t look too bad, but they almost always film videos over water or clean concrete. So the performance on real life ground surfaces is unknown as well.

    But common sense says real life operations will be plagued with dust, just as real life harrier operations were.
     
  4. Aug 10, 2019 #44

    Aesquire

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    The "hover board" type is IMHO a dead end for any "practical" use.

    The use of a raised steel grid for takeoff and landing ( except for promo films ) is only part of my reasoning, it's the balance and leg strength that limits it to very fit and board sport conditioned types. Even the original test pilot stands very, very still to keep it from looping on him. He also designed and is expert on the water jet boards, so a board style was in his comfort zone.

    Moving the hot exhaust from foot level to outside of the shoulders eliminates most ground effect & FOD issues. I can see they varied from the known functional configuration to use multiple hobby jets.

    I don't want to say the Bell rocket belt configuration is the only viable one. The flying garbage can works too, as the WASP shows. ( and is the answer to most issues, IMHO. )

    There may be superior answers that I haven't imagined. But I know the 2 "work".

    And they have ample history.

    https://dicktracy.fandom.com/wiki/Air_Car
    https://www.damninteresting.com/hovering-in-history/

    For someone's next project?
    https://dicktracy.fandom.com/wiki/Space_Coupe
    https://www.hobbytalk.com/bbs1/99-s...ld-dick-tracy-fanastic-space-coupe-build.html
     
  5. Aug 10, 2019 #45

    Doggzilla

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    Very good points.

    It would be suitable as a powered harness for hang gliders or cliff jumpers, but it’s just not stable enough for practical use in its intended function.

    Although adding a gimbal and lowering the pilot’s feet under the center of thrust would greatly improve stability.

    Think of a small bucket on an axle with a ring of engines holding it up. The weight on the fliers feet is at a point under the center of thrust and under the axle connecting the bucket to the engines.

    The ring of engines would require a control rod that can be used to angle it while the “bucket” stays mostly upright simply from the weight of gravity and it hanging slightly under the engines.
     
  6. Aug 10, 2019 #46

    MadRocketScientist

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    Takeoff and landing in this video, does this help?

    Pity the takeoff is slowed down
     
  7. Aug 10, 2019 #47

    Doggzilla

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    Thanks. I take back what I said about the sea spray, it’s much worse than the Brit jet pack.

    I still think it would make a good powered harness for hang gliders, but you guys were right about the rest.
     
  8. Aug 10, 2019 #48

    Aesquire

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    A Doodlebug ( seated/supine) or Mosquito powered hang glider harness with 3? of those jet engines would be short ranged, but very fun. What's the fuel consumption at full throttle, each? I wonder?
    It
    How much altitude could I gain with the U.S. Pt 103 five gallon tank? A more complicated question.
     
  9. Aug 10, 2019 #49

    Doggzilla

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    At full thrust they last about 15 minutes.

    It only takes 70lbs of thrust to keep a wingsuit flying, and hang gliders have almost 10 times the glide ratio. So it would very likely take far less than 35lbs of trust.

    35lbs of thrust would be 11gph. And the fuel tank is almost exactly 11 gallons. So it would definitely be an hour or more in the worst case scenario.

    But honestly it’s probably twice that because hang gliders take nearly no thrust to stay airborne.
     
  10. Aug 10, 2019 #50

    Doggzilla

    Doggzilla

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    And that’s with Jetcat engines. The Kingtech engines have significantly better fuel consumption.
     
  11. Aug 10, 2019 #51

    bmcj

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    Range extender wings?

    5A2EB6D3-FCC6-41A2-8395-CBB6C75A8C52.jpeg CE5C2380-2C23-47B1-BFC3-E2CE5DAF279B.jpeg 6FA7127B-F313-4ABA-B2E9-BCFC1474B25B.jpeg
     
  12. Aug 10, 2019 #52

    Doggzilla

    Doggzilla

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    Yesss. Where did you get that from? Even all knowing google shows nothing in reverse search haha

    Was looking at some other winged models and simply using a wing suit TRIPLED the range and cut thrust requirements by 70%.

    Only 70lbs of thrust required.

    Increase wing size 50% and add another 11 gallons and it would probably have close to a 2 hour endurance and 200+ mile range.

    Not exactly efficient, but the use of cheap fuel would make it far less than half the operating cost of most entry level aircraft.
     
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  13. Aug 10, 2019 #53

    Doggzilla

    Doggzilla

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    Found it on the unilad site but no details. Wonder how well it works. Really impressive reduction in AoA.
     

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