"minimum" personal mobility device --ground and airmobile.

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Aircar, Apr 9, 2013.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Nov 9, 2014 #801

    Kingfisher

    Kingfisher

    Kingfisher

    Well-Known Member

    Joined:
    Aug 15, 2013
    Messages:
    448
    Likes Received:
    98
    Location:
    Perth, WA, Australia
    I guess you are right, I was looking at the pure force balance, directly using your arms like a bird, assuming the wing is a beam with a hinge, and the arms are all that hold it down. So is my statement wrong in that regard? Surely during the downstroke you would have to lift your own weight, in that case, like an athlete does on the rings, which would be the force at least temporarily applied in your equation.

    However, I suppose one would not design the machine like a bird, but like the Delfly drone, so the upstroke on one side assists the downstroke on the other side, and you would only need to expend the energy for level flight.

    Since birds are not build that way, I wonder how they manage to hold their wings out and soar for hours. Is it just their muscles holding their weight? I have seen some RC bird-like ornithopters fly, and they all were lacking a locking feature to stop the wing mid-stroke, so they could only glide poorly. To hold the wings out straight, wouldn't there be some power still required to overcome the static moment the wing generates at the "shoulder"?
     
    henryk likes this.
  2. Nov 9, 2014 #802

    henryk

    henryk

    henryk

    Well-Known Member

    Joined:
    Mar 8, 2010
    Messages:
    4,544
    Likes Received:
    417
    Location:
    krakow,poland
    https://www.youtube.com/watch?v=5HIq5y8lQgg

    =good solution=no static forces...
     
  3. Nov 9, 2014 #803

    Sockmonkey

    Sockmonkey

    Sockmonkey

    Well-Known Member

    Joined:
    Apr 24, 2014
    Messages:
    1,566
    Likes Received:
    402
    Location:
    Flint, Mi, USA
    Remember a wing produces lift along most of it's length, not just the very tips, so the 3m plank analogy isn't quite apt.

    Ornithopter efficiency could be improved with a spring mechanism at the "shoulder" joint by recycling the energy from each up and down stroke to "bounce" the wing. In the legless human example it also cuts way back on the energy needed to hold the wings out in the first place.
     
    henryk likes this.
  4. Nov 9, 2014 #804

    henryk

    henryk

    henryk

    Well-Known Member

    Joined:
    Mar 8, 2010
    Messages:
    4,544
    Likes Received:
    417
    Location:
    krakow,poland
    https://www.youtube.com/watch?v=26GIYxxg9aQ

    https://www.youtube.com/watch?v=CSKcG2Qo2o0
    =rubber compensators...
     
  5. Nov 18, 2014 #805

    WonderousMountain

    WonderousMountain

    WonderousMountain

    Well-Known Member

    Joined:
    Apr 10, 2010
    Messages:
    1,855
    Likes Received:
    192
    Location:
    Clatsop, Or
    Absolutely, glad you asked.

    For starters regulating the airflow by sectional position allows for perpendicular flow, realizing minimum airfoil drag, and aligning feathers, (turbulence regulators). Second by moving the vortex inward spanwise, the induced tip drag is reduced, though not necessarily zeroing out. This simply because less of it is "falling off the ends". Third by utilizing body-wing symmetry, separation drag can be nearly eliminated on body's boundary layer. Finally this structure allows for positive yaw, which greatly reduces tail losses.

    It's not a magic portal, there are still 3D imperfections even in birds. Compromises must b made, the challenge is to meet all objectives in a manner that doesn't have us moaning for more performance.

    Actually, laminar wings aren't all that far off, it's our bodies that we need more flexibility in.

    LuPi
     
  6. Nov 18, 2014 #806

    henryk

    henryk

    henryk

    Well-Known Member

    Joined:
    Mar 8, 2010
    Messages:
    4,544
    Likes Received:
    417
    Location:
    krakow,poland
  7. Nov 20, 2014 #807

    Kingfisher

    Kingfisher

    Kingfisher

    Well-Known Member

    Joined:
    Aug 15, 2013
    Messages:
    448
    Likes Received:
    98
    Location:
    Perth, WA, Australia
    Yes, that is like the Delfly drone in "full scale", with the difference that it doesn't fly. I think the "Falcon 12A" designer is right. One has to use a hinged wing with variable geometry to have more chance of success. Moreover, the stroke has to go through almost 180 degrees for each wing during take-off, where even the backstroke appears to generate some lift. If one watches geese taking off in slow motion, this appears to be what is happening. Once airborne, the birds ease off on the flapping and go to some more sustainable strokes. Even "Falcon" man admits that his ornithopter would likely not be able to lift off on even ground, despite the hydraulic actuators. However, it may sustain flight...
     
  8. Nov 20, 2014 #808

    Kingfisher

    Kingfisher

    Kingfisher

    Well-Known Member

    Joined:
    Aug 15, 2013
    Messages:
    448
    Likes Received:
    98
    Location:
    Perth, WA, Australia
    Well, read my #799 post, if you would, please. I assumed a 14m wingspan with centre of lift at 6m span, or 3m each side. Of course a 6m total wing span would not get you flying, and of course the lift does not act at the tip, then I would have used "7m planks".

    I suppose a spring would help, but you would have to fight it on the upstroke during early take-off. If you took off as a hang glider, it may be o.k. However, in your original post you said "just on arm's strength", so I assumed you meant without any other technical aids.

    How birds do it is still a mystery to me. Do they have a "spring tendon" of some sort to help their flight muscles?
     
    Last edited: Nov 20, 2014
  9. Nov 21, 2014 #809

    Sockmonkey

    Sockmonkey

    Sockmonkey

    Well-Known Member

    Joined:
    Apr 24, 2014
    Messages:
    1,566
    Likes Received:
    402
    Location:
    Flint, Mi, USA
    Ah, my misunderstanding. I know kangaroos have them in their legs but I'm not sure about birds.
    Anyhow, there would be springs for both the up and down stroke to recycle the momentum with muscle power being for overcoming drag and efficiency losses.
     
  10. Nov 21, 2014 #810

    jedi

    jedi

    jedi

    Well-Known Member

    Joined:
    Aug 8, 2009
    Messages:
    1,685
    Likes Received:
    374
    Location:
    Sahuarita Arizona, Renton Washington, USA
    Kingfisher "How birds do it is still a mystery to me. Do they have a "spring tendon" of some sort to help their flight muscles?"

    The spring to overcome 1 G flight load would be nice to have in soaring birds. In small birds that do not soar or glide much the spring would not be of much use. I do not think the spring to "overcome momentum" is of much use as the bird wings are very light (in comparison to aircraft wings, many of which are fuel tanks) and the aerodynamic damping due to the thrust production is the major force to overcome.

    I would like to know if the wish bone acts as a 1 G spring.

    I would also like to know why bird **** is both black and white. Sounds like a lot of work and effort to separate the good from the bad! Now there is the subject for a new thread.... There are just too many mysteries in life to be solved by one person.
     
  11. Nov 21, 2014 #811

    bmcj

    bmcj

    bmcj

    Well-Known Member HBA Supporter

    Joined:
    Apr 10, 2007
    Messages:
    12,558
    Likes Received:
    4,583
    Location:
    Fresno, California
    That's easy... it's so that you have to wash your car regardless of whether it is painted a dark or light color. :gig:
     
    Last edited: Nov 21, 2014
  12. Nov 22, 2014 #812

    Sockmonkey

    Sockmonkey

    Sockmonkey

    Well-Known Member

    Joined:
    Apr 24, 2014
    Messages:
    1,566
    Likes Received:
    402
    Location:
    Flint, Mi, USA
    Yep, it's on the big list of "why nature is a jerk" right under the bit where getting old involves losing the hair we like while growing new hair where we don't want it.
     
    bmcj likes this.
  13. Nov 25, 2014 #813

    Kingfisher

    Kingfisher

    Kingfisher

    Well-Known Member

    Joined:
    Aug 15, 2013
    Messages:
    448
    Likes Received:
    98
    Location:
    Perth, WA, Australia
    Ah, the wishbone, that sure is interesting! Although it snaps easily when cooked, and chickens are not known to be great fliers. Maybe it's more developed in eagles, have to check that out...

    Your second thought, though: Some mysteries do not need to be solved! Reminds me of my friends and I running after something we saw falling out of a glider when we were kids. When we finally reached it we realised it was a plastic bag full of wee....
     
    bmcj likes this.
  14. Nov 25, 2014 #814

    BJC

    BJC

    BJC

    Well-Known Member

    Joined:
    Oct 7, 2013
    Messages:
    8,879
    Likes Received:
    5,732
    Location:
    97FL, Florida, USA

    Snaps easily in cooked Eagles also.


    BJC
     
  15. Nov 25, 2014 #815

    jedi

    jedi

    jedi

    Well-Known Member

    Joined:
    Aug 8, 2009
    Messages:
    1,685
    Likes Received:
    374
    Location:
    Sahuarita Arizona, Renton Washington, USA
    I disagree about the wishbone snapping easily. I takes quite a pull considering the size of the bird and bone. It is a good spring.
     
  16. Nov 25, 2014 #816

    bmcj

    bmcj

    bmcj

    Well-Known Member HBA Supporter

    Joined:
    Apr 10, 2007
    Messages:
    12,558
    Likes Received:
    4,583
    Location:
    Fresno, California
    LOL... I think you missed the operative word in BJC's post... "cooked".
     
    BJC likes this.

Share This Page

arrow_white