Vtol design: 1 vs 6 engines

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by leviterande, Oct 14, 2008.

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  1. Nov 13, 2010 #101

    Dan Thomas

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  2. Nov 13, 2010 #102

    BBerson

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    The counter-rotation neutralizes the precession.
    Forward speed is limited because the inflow tends to tilt the disc backward opposing forward flight. This limits forward speed.
     
  3. Nov 14, 2010 #103

    Dana

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    Looks like fun though... I'm surprised nobody's duplicated it since then.

    -Dana

    Lottery: a tax on the mathematically challenged.
     
  4. Nov 14, 2010 #104

    autoreply

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    I don't understand all the fail-safe modes. If an engine quits, you can always throw a parachute (BRS), or make a gliding landing (with small wings). A couple of big airbags on the underside might also help. I'm sure all those redundant engines, props and such are way more complex.
    And just a sidenote, virtually every helicopter also has a no-go zone, where an engine failure is likely to seriously hurt you:
    [​IMG]

    Precession isn't canceled by contra-rotating rotors; rather the contrary. If your left top rotor goes down and your left bottom rotor goes up, they'll touch. There's a reason the discs on the Kamov are so far apart.
     
  5. Nov 14, 2010 #105

    BBerson

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    The Hiller platform had rigid counter-rotating propellers, not rotors. I chose the word "neutralize" carefully. I did not say canceled. Precession is not cancelled, but it is neutral with respect to the pilot in that he can tilt the machine forward to get a forward tilt.

    If the machine had only a single propeller, in this case, the pilot would need to tilt the machine 90 degrees ahead to allow for precession, I think. (lean right to go forward)

    In any case, precession does not seem to be an issue with the counter-rotating Hiller platform. So Dan's comment about precession killing the platform is incorrect, as far as I know.

    My VTOL book says the platforms had some advantages over helicopters, such as flying close to obstacles, but suffered from high fuel consumption.
     
  6. Nov 14, 2010 #106

    Starman

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    That Hiller platform sounds like a very good idea to persue, and easy! To increase fuel economy and use a smaller engine make the prop diameter bigger, like just going from five to ten feet would make a huge difference. Something like an 8 ft diameter seems practical, and evidently it's pretty easy to make as far as the control system works, there isn't one, only the throttle. For safety all you need is a ballistic parachute on your back :)
     
  7. Nov 14, 2010 #107

    Dana

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    Neither would help you if you're hovering at 100'

    They made a helicopter of similar configuration (pilot standing on top) around the same time.

    -Dana

    Never weed wack poison ivy in the nude.
     
  8. Nov 14, 2010 #108

    Dan Thomas

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    Any system that uses a rotor or prop so close to the ground will be limited in its choice of surfaces. The wind created would kick vast quantities of any loose materials like dust or sand or leaves or grass; some of those would obscure vision and/or incapacitate a pilot, and others could clog the fan or its cage. Ordinary helicopters have a time of it already, even with rotors eight feet or more off the ground.

    We have a Cirrus with the ballistic 'chute. Below 1000' it's pretty much useless, as it does take some time to rocket out, expand and fill before it can contribute to any deceleration, and that's after the pilot's reaction and deployment times are figured in. On anything with open fans or rotors it would probably get tangled up in the machinery.

    Dan
     
  9. Nov 15, 2010 #109

    Starman

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    What I meant instead of a ballistic chute, actually, was a rocket powered escape pod ... plus a parachute. A Gemini type rocket on top as used in the first space capsules. You would be wanting to be sitting down for that part :) Something like that wouldn't help much though if you were sideways when you triggered it :D

    You could make this platform using a seated position and just lean the upper body, or stand if you wanted to.
     
  10. Nov 15, 2010 #110

    Starman

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    And for the important part ... to make the power source fail safe use at least two engines, fuel supplies, etc, each one of which can lift the machine by itself. In that case the engines would normally be running at bellow 50% unless you were climbing fast.
     
  11. Nov 15, 2010 #111

    autoreply

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    Sorry, then I misunderstood you.
    Nope, not at zero knots. but neither would a helicopter (see the above graph). That was my point; it's unrealistic to except a "totally" safe design. No aircraft is and neither is a helo, since both have "dead zones" where escape isn't always possible.
    I like the Russian approach (just blow the rotor head off)

    Apart from that; there's a big difference between a fast Cirrus and a much slower aircraft/helo; the latter don't drop that fast and parachute forces are much lower.
    [video=youtube;sLY7LghTeB8]http://www.youtube.com/watch?v=sLY7LghTeB8&feature=player_embedded[/video]

    3-4 seconds to stationary descent? That'd be 250 ft of freefall.

    As for the wings; helo's come in with forward speed as well, mainly to make an autorotation possible. Who not do the same with a VTOL design?

    @ Starman; you're referring to something like the Russians used for their tanks? They dropped a complete tank, hung it on parachutes and a 100 ft long line, hanging beneath it, ignited a rocket motor above the tank, slowing it down. Yes, the crew remained inside during the drop :gig:

    Here's a long vid, action around 31:15:
    http://video.yandex.ru/users/arni-raj/view/564/
     
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  12. Nov 15, 2010 #112

    leviterande

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    Considering curing the issue of precession, has anybody considered using the simplest rotor head there is for control... Why not usea small 10 ft teetering prop/rotor for a small VTOL.

    How about a ligth one manned 200kg VTOL with a 10 ft teetering rotor for control? I know some helicopters used direct tilt hubs like gyrocopters.(B.J Schramm Scorpion helicopter for instance). Sure they are not as good as true swashplates but teetering hinges are way simpler and we are not looking for best performance here in a first prototype VTOL. Seriously, why hasn't anyone thought about using the mechanism of a gyrocopter head to both neutralize and control a small 10ft rotor VTOL?


    Kalle
     
  13. Nov 15, 2010 #113

    Dan Thomas

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    I believe the Scorpion had a true rotor head. The link rods from the swash plate were hidden inside the mast instead of along the outside, but they're there.

    Dan
     
  14. Nov 15, 2010 #114

    leviterande

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    Dan, I know some versions of this helicopter had an ordinary swashplate and some hade direct hub tilt control. It is very confusing to know the exact name but yes some B.J helicopter had direct control. One can see the collective-wire indicating that the collective is seperate from the direct control. Early helicopters used direct hub tilt. heck, even the advanced V-22 uses direct hub tilt control!

    The helicopter is either shramm scorpion I or II. You can see the picture here. It is a fixed swashplate with a seperate collective mechanism. A closeup:


    Rotorway "Scorpion Too" helicopter - development history, photos, technical data
    Rotorway "Scorpion" helicopter - development history, photos, technical data

    My point is, what about having a teetering 10ft propeller/ rotor for control and elimination of the precession
     

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  15. Nov 15, 2010 #115

    Dan Thomas

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    OK. I can see that direct-tilt control there. Thanks

    If one goes to a ten-foot prop he might as well build a helicopter, I'd think. The power requirements for small, highly-loaded disks might make it a heavy, poorly-performing machine. But it sure would be fun.

    My idea of a fun machine would be a really light fixed-wing ultralight, electric motor driving a big, slow, quiet propeller for cruising over the countryside at low level at something like 30 mph.

    Dan
     
  16. Nov 15, 2010 #116

    leviterande

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    I can definitely see the low level cruising, what a joy. A fixed wing ultralite may be the last resort to any vtol. By keeping the wing loading low and the prop big and engine power small, a low slow level flight on a quiet calm day isnt too wrong for sure:)
     
  17. Dec 13, 2010 #117

    copter

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    Hi guys, i'm currently building a flying platform (similar to hillers but not exactly the same) 5 foot duct, 1 set of ivoprops (three blades) with 50hp engine and im getting enough lift for a 10 and a half stone person but i'm not 10 and a half stone, so, what do i do? do i 1; go on a diet, 2; get another set of blades on there spinning the opposite direction, 3; use a bigger engine, 4; use 2 engines, each turning its own set of blades? or use fan blades instead of ivoprops? any suggestions most welcome.

    thanks
     
  18. Dec 13, 2010 #118

    copter

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    Hi again

    Someone had a look at the hillers blade tip clearence from the duct and its 1cm or so which i thought was too much of a gap, everywere i'm reading that it has to be really close, i mean, really really close without touching when spinning, i read elsewere that they glued a peace of carpet to the duct to close the gap and it made a great difference, i know the one in the museum hasn't got carpet glued to it but the bigger gap is there so i made mine with the gap, if i close this gap will it really make that much of a difference to lift?

    thanks
     
  19. Dec 18, 2010 #119

    leviterande

    leviterande

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    the efficiency of a ducted propeller is lower than "slightly larger free propeller"
     

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