Delta wing airfoil

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Monty, Mar 8, 2019.

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  1. Mar 8, 2019 #1

    Monty

    Monty

    Monty

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    Or perhaps lack thereof.

    Thinking about the FacetMobile and the tail design on the Sonex series of aircraft.....

    Suppose you use all the vortex tricks, and simply make the center portion of the wing flat with the ability to droop the leading edge and trailing edge like so:

    wing1.jpg

    Very easy to build in aluminum.....How much performance will be lost from a lack of airfoil?? The wing is thin.... It is an "airfoil"-just a really bad one. But the primary lift mechanism is from vortex flow at "high" CL. I figure if a Regallo wing can fly...so can this. As long as the area is large enough. Obviously a smaller optimized airfoil wing will outperform...though at lowish Reynolds number bad things start to happen with that type of wing and it's much harder to build.

    Monty
     
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  2. Mar 8, 2019 #2

    jedi

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    Interesting. Paul Weston's latest proposal is to use a flat plate wing as you suggest. His concept is a follow on to the Sea Era and considerable model tests.

    I can not vouch for it and I think there are scale effects that mask results based on model work. He is proposing a full scale Ultralight single seat and light sport two seat and is wanting to work with others who would like to progress towards the build. His proposal does not incorporate the drooped LE and TE of your diagram but does include simple breakdown for roadable transport. Confirm you are showing a negative dihedral.

    I have some drawings of his proposal but there is little to no active work. My question at this time is the airfoil thickness and LE/TE metrics. I assume it would have a tube for LE and TE and have some required dia. and wall thickness but those numbers have not been determined. Wing interior would likely be foam or honeycomb ribs and fabric cover. Overly basic? Perhaps? Would it fly, yes. How well? only one way to tell.
     
  3. Mar 8, 2019 #3

    Monty

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    This idea is the result of realizing that pilots of overpowered sport aircraft only care about high-speed, low-drag, and low-speed, high-drag configurations. I started thinking about the easiest construction method to meet those two requirements. This wing is literally flat. No dihedral or twist at all. The CG of the aircraft would be below the wing. The configuration would have a conventional tail. In high speed flight the leading and trailing edge would not be drooped. The thickness is mostly a trade off between spar wt and form drag. It has to be relatively thin for vortex lift to work. The dogtooth leading edge at the tip is drooped, so there is some aerodynamic twist, and the constant thickness means the tip is a much thicker airfoil on a percentage basis. The leading edge is simply an ellipse, trailing edge/control surface a triangle.
     
  4. Mar 8, 2019 #4

    daveklingler

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    I think the proliferation of MakerSpaces all over the world is going to have a huge effect on experimental aircraft over the next few years. The majority of them have CNC routers, mills and laser cutters. Combine that with the availabiity of SolidWorks at low cost to EAA members, and you can have one person publish a design and a hundred people start making it the next day. (I notice that the Fab Lab in Fayetteville is offering training on a new CNC router they just purchased).

    A lot of construction obstacles disappear with access to CAD design tools + CNC equipment, and it remains to be seen whether efforts like this one benefit from the ability to draw something up one night, cut it the next day, and start gluing. Maybe people will see this delta wing as an opportunity to experiment, or maybe they'll just see it as unnecessary and not bother. Certainly it seems like it would benefit from a scale model.
     
  5. Mar 8, 2019 #5

    Topaz

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    As noted in another recent vortex lift discussion, it's great for increasing CL for landing, but not so much for takeoff because of the attendant high drag. Driving those big vortices sucks a lot of energy out of the airframe, all of it coming from the engine. So, if you're going to use vortex lift for takeoff, you're going to need a relatively big engine to keep the airplane moving forward against all that drag. The situation becomes worse for climb - no you not only have to keep the airplane moving forward, you have to lift it higher as well. This makes the engine power required that much more.

    Big engines are anathema to "low cost" airplane projects, since they're usually the single most-expensive item on the bill of materials to begin with.

    However, there's nothing wrong with your basic idea - that of a flat box forming not only the spar, but the entire central portion of the wing and airfoil. If you're willing to build curved leading and trailing edges - and, from your drawing, you are - then there's no reason this can't be applied to a more conventional wing that doesn't use vortex lift. No, it's not going to be the world's greatest airfoil. But it'll fly.
     
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  6. Mar 8, 2019 #6

    Vigilant1

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    It would be a natural for solid-core foam construction. If the flat area could be built up to the proper thickness using off-the-shelf XPS sheets, then no hot wiring would even be required (it's not hard, but it is "another step", and it is a step where ridges and dips in the core are often introduced, which need to be addressed sooner (light) or later (heavy)). The flat surface skins could be made using infusion or vac bag against a flat smooth surface "mold" to avoid filling/sanding, though getting the excess resin out out would require some tricks. Go with a thick enough skin and no true separate spar might be required, though the front and back of the center sheet would need to be beefed up for the LE/TE attachments.

    I don't know about the aerodynamics.
     
    Last edited: Mar 8, 2019
  7. Mar 8, 2019 #7

    BoKu

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    The RIFPIB principle says that an airfoil doesn't have to be very refined in order to be a lot better than a flat plane. Just leave the bottom flat, give the top some sort of curve, make the whole thing sort of smooth, and you'll probably get higher Cl and way better Cl/Cd that a flat plane.
     
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  8. Mar 8, 2019 #8

    henryk

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  9. Mar 8, 2019 #9

    Monty

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    I agree, and I thought of that....but that still complicates the construction where the wing meets the fuselage and means the spars can no longer be straight 90 degree extrusions,the stringers that interface them can no longer be 90 degree extrusions, and the ribs can't just be made on the sheet metal brake.....etc. I know i'm giving up some performance. The question is...how much. The cruise CL is VERY low....
     
  10. Mar 8, 2019 #10

    Monty

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    "low cost" airplane....:roll:

    Takeoff CL is not a problem....way over-powered by conventional standards.

    The gust response of a delta wing is interesting too....much better ride in turbulence and lower gust loading.
     
  11. Mar 8, 2019 #11

    Monty

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    Yes, only one way to tell.

    Models are useful, but not sure how much due to the low Reynolds #.

    Monty
     
  12. Mar 8, 2019 #12

    Himat

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    I can’t remember what book, but one aerodynamic book had a story from the development of the A4 Skyhawk. One of the aerodynamic engineers had done a lot of testing of different airfoils and could not decide. One of the seniors told him to cut a plywood sheet to the same outline and thickness as the wing tested. All in all, the plywood sheet did not perform that much worse.
     
    Last edited: Mar 8, 2019
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  13. Mar 8, 2019 #13

    rotax618

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    If you choose the planform carefully you probably wont need the drooped LE/TE to avoid sudden loss of lift at normal stall AOA, read NACA report 431.
     
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  14. Mar 8, 2019 #14

    Topaz

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    Okay, I'll bite. If you're not trying to cut airframe costs, why are you doing this, instead of a more-efficient "regular" airfoil? Perhaps I misunderstood your intent.
     
  15. Mar 9, 2019 #15

    deskpilot

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    For what it's worth, here's my wing for a Double Delta I designed way back when.

    Delta wing top.jpg

    Delta wing bottom.jpg

    The under-cut leading edge was (hopefully) a vortex generator.
     
  16. Mar 9, 2019 #16

    Monty

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    I have read that same book at some point....and I agree that way too much emphasis is placed on airfoils.
     
  17. Mar 9, 2019 #17

    Monty

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    Because metal does not like to bend in more than one direction.
     
  18. Mar 9, 2019 #18

    Monty

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    This is all true, but I am only interested in aluminum. It's recyclable, and I want to save the planet :gig:

    It's also a fuel tank, and I don't like working with composites very much. Personal preference.
     
  19. Mar 9, 2019 #19

    Monty

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    Thanks for the info. I knew there had to be some data somewhere....
     
  20. Mar 9, 2019 #20

    Topaz

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    >squints< Most wings are flat-wrap conic projections until you get to the tip, which is the same for this delta as a "regular" wing. What am I not following here?
     
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