Starman's plane

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Starman, Aug 27, 2009.

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  1. Sep 13, 2009 #61

    BBerson

    BBerson

    BBerson

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    One error, in my opinion, is Raymer's comment that a steel tube is 80% heavier than a sheet metal fuselage.
     
  2. Sep 13, 2009 #62

    Starman

    Starman

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    Yes, I wouldn't think it would be much heavier. I guess you could say that my design is basically going to be a steel tube fuselage, but with very few tubes, a couple of aluminum tubes, and an aluminum fuselage front end.
     
    Last edited: Sep 13, 2009
  3. Sep 13, 2009 #63

    BDD

    BDD

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    The fabric leading edge would not be stable, even with wire reinforcement. It would "luff" something like the sail on a sailboat when the sail is parallel to the wind. With a lot of tension on the wire I suppose that the entire wire might vibrate up and down between the endpoints. With a bit less tension, or at greater speeds, I suppose that the wire could have more up and down vibrations along it's length. I would have a metal tube spar for a leading edge.

    The fabric version is a powered kite. This would produce lift about on the order of a flat plate, maybe a bit more when the fabric flexes upwards. You will need a large area to produce enough lift. An exposed box spar under the wing, if that's what you propose, would have a lot of drag. This would tend to act against the small amount of lift that this kite-wing would create.

    You should consider the turbulence behind a flat plate at high angle of attack when you are thinking about blanketing of the tail, rudder, elevator, etc.

    I remember seeing an early prototype plane (before anyone but the Wright Brothers were actually flying) that did some short hops from water that had an exposed truss type spar under the wing. If your hypothetical spar (or spars) were cylindrical, I'd enclose them with some fabric at the bottom.

    This "fabric version" would behave very differently from the other versions.

    I would say that the "Quickie" is a tandem wing configuration.

    The way you now describe it (in your last post withe the sketch), I would say that moment and shear forces would be at a maximum at the centerline of the plane and spar or spars.
     
  4. Sep 13, 2009 #64

    Starman

    Starman

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    I’m glad you like that, I do too. I’ve added a drawing to better illustrate what my current idea is for the spar center section.

    As you can see in the drawing I made while I was in the mountains, I’ve optimised the shape and included details that weren’t in the original computer drawing.

    I made the web wider at the top of the curve, where there is the most concentrated compression stress, and I’ve put some ‘reverse’ curves into the center area so it will align better with the steel tube outer section.

    I prefer the idaea of just one spar but with high strength torsion resistance built in, this way I can vary the sweep and not need to be concerned about it ... too much =)

    In the drawing detail #1 is the point where the spar attaches to the rear end of the aluminum fuselage front section. It will be made out of a steel ‘T’ bar carved to shape.

    Details #2 are round steel tubes that go forward to a point so they are triangulated, to anchor to the fuselage tub about three feet ahead. This provides the torsional resistance for the spar and these same steel tubes go back in another triangle to serve as the engine mount and anti torsion anchors for the aluminum tail tubes.

    Detail #3 is a square tube steel truss. I guess you guys use gussets for this kind of thing? so I’ll have to study those a bit.

    Detail #4 is a strong aluminum tube that anchors to the front torsion point that the #2 tubes anchor to. It provides the torsional resistance to the outer ends of the spar center section and these aluminum tubes continue back to provide mounting points to the horizontal and vertical tails.

    The front torsion points that anchor the engine mounts and tail tubes are actually going to provide all the vertical support for the aluminum cockpit tub and pilot, the weight of which is centered at this point. Where the rear of the cockpit attaches to the spar there will be almost no force but it will be very strong anyway. The same forward hard points will also provide additional anti torsion connections for the front of the wing.

    The vertical lines are one foot markers.

    Let me know what you think.

    As you can see, this is only one half of the spar, so it will only hold one wing. I don't know what I'll do about the other wing
     

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    Last edited: Oct 2, 2009
  5. Sep 13, 2009 #65

    bmcj

    bmcj

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    In the way I look at it... and this may not align with conventional thinking... is that the one is a subset of the other. Both have dual lifting surfaces, but different area ratios.
     
  6. Sep 13, 2009 #66

    Starman

    Starman

    Starman

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    I think you might have talked me out of using a fabric leading edge.

    I wouldn't stretch the fabric tight enough, front to back, to make it flat, but allow it to flex upwards a fair amount for a good curve, I definitely do not want a flat plate or a kite like wing. I like the idea of using a round tube for a leading edge but I guess using a D cell is the ideal way to go and it was my 'dominant' idea for this.

    Concerning the exposed box spar, the idea is/was to put the leading edge below that, but I shouldn't even have written about that because it falls under the category of 'crazy' idea.

    However, take a real good look at the cross section of a flight feather from a big bird. It's a thing of supreme beauty and engineering excellence. It has an exposed 'spar' underneath a single surface airfoil with the lower edges of the spar curved, and a drooped leading edge to blanket it's spar, the flow reattaches to the trailing edge behind the spar due to it's camber; so it gives up nothing to a standard airfoil (for slower flight) (in my opinion, which unfortunately, isn't usually too humble =) someday I'm going to make a wing like that, and I might do it for version #2 to replace the fabric, or add them to the fabric as wing extensions for an extra long wing span. I reeeally don't like the idea of making wing ribs, at least not more than four of them.

    Referring you back to the bird feather idea :)

    edit ... but it wouldn't be too hard to enclose the spar with fabric that goes back from the leading edge. I just always gravitate to the simplest methods first and if that isn't good enough then make it more complex.

    Yes it would, but it will be slow, which I want. I might also make horizontal tails separate from the, and below the wing, that sounds better, doesn't it?

    I really appreciate your feedback.
     
    Last edited: Sep 13, 2009
  7. Sep 13, 2009 #67

    Starman

    Starman

    Starman

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    By the way, as a fall back scenario I can always put the horizontal tail across the top of the two vertical tails but I'll work on avoiding that.
     
  8. Sep 13, 2009 #68

    BDD

    BDD

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    On closer inspection, you will also note that nearly 1/2 of the engine is missing.
     
    Last edited: Sep 14, 2009
  9. Sep 14, 2009 #69

    BDD

    BDD

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    You could think in terms of a sailwing with a streamlined d-section that also has a fairing at the back. This would have more lift and less drag than a kite-wing or a kite-wing with loose fabric at the top.

    The slack fabric at the top could also flutter around and the high point could move around with the center of pressure. Without any ribs or formers or curved battens I don't see it creating much of an airfoil. Good sails for boats are pieced together in sections to allow a curved shape when the wind hits them. At the wrong angle of attack this stops working and the sail "luffs".

    The structural quill of a bird feather doesn't project that much from the feather and operates at a very low Reynolds number. It probably doesn't add much drag and may even help lift by adding some turbulence at that point. My speculation.

    I imagine that it is also probably placed at the feather's aerodynamic center or at some favorable point to minimize torsion.

    Feathers also always have a built in camber for much of their length and aren't really flat. The fuzziness of the fibers that make up the feather when you look really close also probably create useful turbulence for lift, making a very thin section seem thicker, etc.
     
    Last edited: Sep 14, 2009
  10. Sep 14, 2009 #70

    Starman

    Starman

    Starman

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    I was hoping that if I got the slack adjusted correctly that it should fill in pretty well but I suppose that was wishful thinking. Curved battens sounds like a good idea. I really don't know much about how they make hang gliders so I think I'll go snoop around the hang glider forum here and see what I can learn. All I can say is I've seen the Rogallo wings and the modified, longer span, Rogallo type wings, and they don't have any ribs or battens, well maybe some of the longer wing span ones do. I agree I could make a more streamlined spar/D section, but keep in mind I don't really care much about the L/D ratio on this fabric wing. If it looks like it's going to be too much work and I can't slap something together fast and easy I might skip the fabric and go ahead and make fiberglass wings for it from the start. I guess I could start with longer fiberglass wings and then shorten them in steps :)

    Does anyone have any ideas about the proportional non twitchy control system I wrote about? I guess I should write about that in a different thread.

    Dang! No wonder this sucker won't fly, good eye there.

    edit, hey I just learned something new, this forum aint got no hang glider info.
     
    Last edited: Sep 14, 2009
  11. Sep 14, 2009 #71

    BBerson

    BBerson

    BBerson

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    A normal control stick that moves the same angle as the elevator is proportional. A control stick that moves the elevator much more at the end is called "exponential" ( an RC model word). I am not aware of this for full scale aviation.
     
  12. Sep 14, 2009 #72

    bmcj

    bmcj

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    The term "nonlinear" is often used in full sized airplanes. It just indicates a changing ratio across the range of travel, but it does not indicate whether the surface throw ratio increases or decreases with stick displacement, just that the ratio is not linear.

    Also, on a minor point, an linear (or "proportional") system does not necessarily match the angle of the stick to the angle of the elevator... it just matches the percentage of stick displacement to the percentage of elevator displacement. I know that is what you meant, but I wanted to restate it for those that might interpret it differently.

    Bruce :)
     
  13. Sep 14, 2009 #73

    Birdmanzak

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    Rogallo hang gliders had a L/D ratio of about 4. That's pretty terrible - about the same as a parachute.
     
  14. Sep 14, 2009 #74

    bmcj

    bmcj

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    The newer (higher aspect ratio) flexwing hangliders that grew out of the old Rogallo design have wing rib battens.
     
  15. Sep 14, 2009 #75

    BBerson

    BBerson

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    Good point Bruce, nonlinear is a better word to use.

    Model airplanes also sometimes have "dual rates". Flip a switch and control throw is doubled for extreme maneuvers but more "twitchy". I doubt that dual rates are used in full scale, but who knows?
     
  16. Sep 15, 2009 #76

    Starman

    Starman

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    Hey, a hang glider guy, thanks for visiting hang glider guy.

    Yes they did, but then the higher aspect ratio ones came out and everyone started line dancin', high kickin', and singin' "Ooh Ah, I lost my bra, I left it in my boyfriend's car". That's about when I took a last good look at hang gliders. It seems the line dancing, high kicking thing happens every four years and goes along with price and complexity increases.

    if you saw the sketch I posted earlier you would see I'm trying to apply the same fabric principle to a low aspect ratio rectangular or plank wing.

    The Rogalos had a horizontal center tube running front to back, I don't know what you call it so I'll call it a center rib. When they went to higher aspect ratios they added wing tip 'ribs' that were straight tubes. These seemed to fly pretty well but I don't recall if they had battens at first, do you?

    I know they installed battens later and that's a good idea that seems to be not too much work.
     
  17. Sep 15, 2009 #77

    bmcj

    bmcj

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    The center spine is usually referred to as the "keel". The very earliest Rogallo style hangglider designs had the keel, the wing spars (leading edge tubes), the crossmember (that held the span open), the kingpost (mostly for supporting the landing wires which held the wings in landing load), and the trapeze bar & downtubes (which made up the triangle structure at the bottom that is used for handhold and to mount the flying wires). No battens.
     
  18. Sep 15, 2009 #78

    Starman

    Starman

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    What about having the fairing behind the spar be made out of the fabric. I see that is a common solution for hang gliders. In other words, make the spar/d-section out of wood, with a flat back, and use a sleeve type wing fabric to cover it? I envision the bottom wing fabric being sewed to the upper wing fabric at about the 70% chord point. This is then going to a double surface covering, which you suggested. If it was a sleeve type covering that should keep it pretty simple. That way you could pull it pretty tight but it seems that would create a sharp angle at the bottom rear of the spar and negate the streamlining effect.

    It looks like there are no plans sold for modern hang gliders now but I'll Goggle for some cross section pictures.
     
  19. Sep 15, 2009 #79

    bmcj

    bmcj

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    Seems sort of unnecessary. The purpose of the D-section is to provide torsional rigidity. If you make the aft section of the wing flex style like you are saying, there is nothing for the D-section to support... it would be wasted stucture.
     
  20. Sep 15, 2009 #80

    Starman

    Starman

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    Thanks Bruce, I remember 'keel' now. when they went to the higher aspect ration they added the wing tip 'ribs', were those called ribs?

    So far I'm thinking: make the D-section and wrap the fabric around starting at the back of the spar and going under, around the front, over the top, and then pulling it tight in back with wire. In order to transition smoothly from the back of the spar to the nature made airfoil rear section it would need to be able to lift off the back of the spar (not be glued on) to avoid a sharp angle there, and not be pulled too tightly to the back.
     

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