UFO- Useless Flying Object

Discussion in 'Hangar Flying' started by litespeed, Sep 27, 2016.

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  1. Sep 28, 2016 #41

    litespeed

    litespeed

    litespeed

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    Retractable gear is by hand cranking- 3 turns per side and yes is a simple wire mechanism.

    For you guys in the states- it may be possible to build a part 103 version as the original with a Rotax 503 and lots of paint and retractable gear is 145 kg.

    If you could figure a way to make it 115kg or 254lb then you would be golden.

    Possibly using light tube for the wing?

    Worth a thought.
     
  2. Sep 28, 2016 #42

    cluttonfred

    cluttonfred

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    I do agree that this is an excellent basis for a "21st century Volksplanes." Type fly-ins would be a hoot, call them "Roswells!" It would be interesting to see how this might work at microlight weight (300 kg/660 lb gross, a little more with a ballistic chute) with tricycle gear, a modest VW direct drive and folding or removable outer panels for trailering and storage. I suspect that you'd need a thinner airfoil due to the reduced thrust of the VW vs. Rotax 503 and maybe a smaller wing area?
     
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  3. Sep 28, 2016 #43

    litespeed

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    Microlight weight should be easy enough.

    That is the class it is here in Australia- sub 300kg.

    In current config. it is 145kg dry add 90kg for pilot and 40kg for fuel that gives a extra 25kg for more motor mass. So might be possible for a VW. Preferably with a redrive. Reduce fuel load until it works I guess.

    Not sure what a 503 weighs?
     
  4. Sep 28, 2016 #44

    cheapracer

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    Apparently it gets worse as you move towards 2:1 (whatever) and then very rapidly improves again beyond that.

    It's 2016 and reversing cameras are dirt cheap, problem solved.

    Some taildraggers have the same issue, and veritably having accidents killing people but don't seem to get a mention.
     
  5. Sep 28, 2016 #45

    cluttonfred

    cluttonfred

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    Yup, I saw that the UFO weights were right in the microlight range. The question would be how to optimize the design for the modest thrust of a direct drive VW. That second Zimmerman paper from 1935 (.pdf) shows a circular Clark Y with some dihedral (the tops of the main spar in a straight line) achieving a lift coefficient of 1.75 at 42 degrees, which is amazing but awfully nose high for practical use and would be massively draggy, essentially the "parachutal descent" of the Flying Flea with the stick back. Plugging in the CL from the Zimmerman paper (Figure 4), this is what I get for the speed required for level flight using 12' span (diameter), 113 sq ft/10.5 sq m area, Clark , single-seater, 300 kg/661 lb gross, sea level standard pressure/temperature:

    40 degree AOA, CL 1.72, 32 knots/59 kph
    30 degree AOA, CL 1.33, 36 knots/67 kph
    20 degree AOA, CL 0.9, 44 knots/81 kph
    10 degree AOA, CL 0.5, 59 knots/109 kph
    5 degree AOA, CL 0.3, 76 knots/140 kph

    So certainly no speed demon, but should be good for short fields. Now does anyone have a quick way to estimate the horsepower required for these conditions so we can have an idea what sort of engine makes sense?
     
  6. Sep 28, 2016 #46

    Winginit

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    Well it sounds as though my concerns are misplaced and he did indeed take into account solutions for safe egress if needed. Are there any more videos of his flight testing ? I'd love to see how it manuevers and deals with stall/spin inputs. What is the actual minimum flying speed for landing? I'm curious as to how the relatively large wing area works when flaps (apparently) aren't incorporated. You mention the aircrafts ability to" land short with a parachute like descent". So does he just cut the throttle back and it naturally begins to settle ? Again, I'm curious as to how that works.
     
  7. Sep 28, 2016 #47

    Autodidact

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    Is the familiar induced drag equation still valid for these wings?
     
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  8. Sep 28, 2016 #48

    BBerson

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    Zimmerman used a Clark Y which has a typical rounded leading edge. Did he test any sharp leading edge? (Other than flat plate) It isn't clear what the best leading edge radius is.

    It looks like the plan form was not a true circle either.
     
  9. Sep 28, 2016 #49

    bmcj

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    As some of you have already noted, a low aspect wing (disc, Hershey bar, or any number of low aspect planforms) might be ideal for an everyman's volksplane. Sure there is extra drag, but AOA tolerance is immense, making stall and stall-spin less likely. Also, the short wings are stouter and easier to design and build, and the extra drag means slower speeds with means less impact momentum in a crash. Add to that maybe a little bit of parachute tendencies if you get it into a high sink.
     
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  10. Sep 28, 2016 #50

    Himat

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    It depends.
    If you think about a slow cruise with the aeroplane (wing) working at a high lift coefficient you are right, the induced drag will be high to. On the other side, if the aeroplane is flown fast with the wing working at a low lift coefficient the induced drag will be low. Barnaby Wainfan’s NASA report on a future personal air vehicle makes for interesting reading on this.

    Trivia:
    The Concorde have lift to drag ratio as good as a Cessna 172. This when cruising at a speed close to the speed of sound.
     
  11. Sep 28, 2016 #51

    Himat

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    Probably not, at least how they are derived must be checked. Quite some of them are based on assumptions that are not strictly valid at these aspect ratios.
     
  12. Sep 29, 2016 #52

    Topaz

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    Below the angle of attack where vortex lift begins, yes. Vortex lift and the associated drag are a different animal, however.

    I'm going to take a wild guess and say that he didn't build his UFO series looking for any particular aerodynamic benefit. Much more like he just thought it would be neat and just built them for that reason. It's enough, for some people. Not everything has to be "better". Sometimes it can just be "fun".
     
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  13. Sep 29, 2016 #53

    litespeed

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    Here is a video of a earlier one he built.

    It is a very windy day.

    You can see he just plops it down and would have been able to stop very short- but just kept rolling.

    This one was flown for 12 or so years.

     
    Last edited by a moderator: Mar 20, 2019
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  14. Sep 29, 2016 #54

    FritzW

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    Too bad we missed the takeoff at ~0:14, it looked pretty "sporty".

    I'm playing with the idea of putting a round wing on one of the fuselages cluttering up my hangar (Nemeth parasol style). David Rowe obviously has the concept well in hand but it looks like he's going against the NACA reports: anhedral, sharp nosed airfoil, tapered airfoils in % chord, etc...

    I loose traction with the idea when I compare Rowe's successful idea with Nemeth's successful idea and the info in the NACA reports... (I'm trying to steal idea's, not sort them out for myself ;) )

    Any thoughts on why these three ideas seem to contradict themselves and all work so well?

    Disk stereo LO.jpg ...some "gee whiz" stuff for those who aren't stereo vision impaired :gig:
     
  15. Sep 29, 2016 #55

    cluttonfred

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    I'd say that the plethora of options is a good thing, it shows you that low aspect ratio wing design is not terribly finicky and lots of things can work. Personally, since the Zimmerman data in NACA TN-539 is pretty clear, I'd go with:

    1) The traditional round-nosed, flat-bottomed Clark Y because that's what Zimmerman's data describes and it's probably as good as anything else.

    2) The moderate dihedral shape (described as K=1 by Zimmerman, Figure 1) that corresponds to a dead straight to tho the tapered spar. The larger dihedral offers some advantages as low speeds but I'd be worried about Dutch roll or other bad behavior.

    3) A true circle rather than the Zimmerman or reverse Zimmerman planforms, since his own data shows that the circle keeps flying at a higher angle of attack and stalls more gently when it does let go. (Figure 8)

    4) For control surfaces, there does not seem to be any real consensus. Straight left-right aileron spars on the circular wing put most of the control surface area near the centerline where it is least effective for roll control and/or create low aspect ratio, almost triangular ailerons but would be simplest to build. Diagonal spars put the control surface area out where it will be more effective but will add substantial drag when deflected and may aggravate adverse yaw and will be harder to build. External control surfaces would be easier to modify to get just right but may have their own quirks.

    I wonder if a good solution might be to approximate the circle with something like a 12' chord x 2' span center section, straight-tapered 12'-8' x 4' span outer panels, and 8' x 1' elliptical tips. That would give straight trailing edge sections 4' span on each side for your ailerons.

    Cheers,

    Matthew
     
  16. Sep 29, 2016 #56

    WBNH

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    Getting closer, I imagine, to Milt Hatfield's Little Bird planform...which I also imagine, would be easier to build than circular. http://aviadejavu.ru/Site/Crafts/Craft34682.htm
     
  17. Sep 29, 2016 #57

    Winginit

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    Quite impressive, it does seem to do everything pretty well without the use of customary flaps and ailerons. I noticed that he went to a taildragger configuretion on the new version.
     
    Last edited by a moderator: Mar 20, 2019
  18. Sep 29, 2016 #58

    fly2kads

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    Can I just say how cool it would be to see some of our collective harebrained schemes, er, great ideas turned into flight articles? I like quirky flying machines. :)
     
  19. Sep 29, 2016 #59

    StarJar

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    I believe there are a few subtle things that can be done to the "pure" circle, if one is in pursuit of performance, and willing to give up the pure flying saucer circle shape, albeit not much.
    The vortex lift happens (planformwise) when the sweep angle on the circle reaches about 50° sweep. On the circle this appears to be at about 70% semi span.
    Inboard there is less than 50° sweep and outboard there is more than 50° sweep. (The vortex lift is available at angles of 50° or more.)
    So if one can slightly modify the circle to bring the 50° a little farther inboard, there would be more lift produced on takeoffs and landings.
    BUT you can't do it very much, because the vortex still needs a surface to 'act' on, which is why the non pointed or blunt wingtips shouldn't be changed.
    The l/d at cruise can be improved slightly by squaring off the trailing edge of the wingtip, instead of it's rounded shape.
    These are some things I observed by playing around with Xflr5 on a low aspect ratio experiment.

    The reason I abandoned my low aspect ratio experiment, is because it never occurred to me to put the vertical tail within the wing planform. This opens up some better performing possibilities.

    By the way it would be nice to know the span (or err diameter) of the UFO. Does anybody besides David Rowe know? (Or even better from David himself, if he were to privilege us goofballs with his presence.)
     
    Last edited: Sep 29, 2016
  20. Sep 29, 2016 #60

    cluttonfred

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    Those are very helpful comments, StarJar. I wonder if you have messed around with any other low AR shapes in Xflr5? Square, delta, Zimmerman, D, etc?
     

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