Slot in wing for pusher prop???

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Aerowerx, Jul 16, 2019.

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  1. Jul 17, 2019 #21

    blane.c

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  2. Jul 18, 2019 #22

    deskpilot

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  3. Jul 18, 2019 #23

    Speedboat100

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    Does Saab J-21 count ?
     

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  4. Jul 18, 2019 #24

    Aerowerx

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    No. That is not slot-in-wing tailless. It is a "normal" tailled aircraft with the tail mounted on twin booms.
     
  5. Jul 18, 2019 #25

    Aerowerx

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    Ok, I guess I remembered wrong.

    The Archon comes close to what I was thinking, but it still is not a tailless flying wing. It has typical rudder and elevator controls surfaces.
     
  6. Jul 18, 2019 #26

    Aerowerx

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    This isn't the best example, but should give you an idea of what I meant.
    [​IMG]

    And a YouTube of one under construction. A better example since the prop is more towards the trailing edge.

     
  7. Jul 18, 2019 #27

    BBerson

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    RC doesn't need a fuselage like a Homebuilt. So you want to put a single prop where the fuselage is?
    The reality is, on a Homebuilt that is going to be two props in each of the wings. So that's like two spoilers open at all times. So we don't see it.
     
  8. Jul 18, 2019 #28

    bmcj

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    Did you miss my post #9 about the Sawyer Skyjacker? It’s a tailless wing with the prop in a slot. The last time I saw it, it was sitting in plain view just inside the chainlink fence at the Mojave Airport.
     
  9. Jul 18, 2019 #29

    Vigilant1

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    It's probably misleading to even think of the part in front of the prop and the part behind the prop as a single airfoil. With the large open area and a prop blade (and wake) whooshing through, there just won't be much continuous flow along the top or bottom surfaces. It is probably more accurate and useful to think of the situation as two separate entities. If a prop must go in that spot, maybe there should be a trailing edge in front of the prop and a leading edge behind the prop.
    But the siren analogy is very appropriate.
     
    Last edited: Jul 18, 2019
  10. Jul 18, 2019 #30

    Aerowerx

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    No, I did not miss it. I just did not have any comment on it at the time, but it is what I was thinking about.

    The Skyjacker and the Saab are quite different, though[​IMG]

    [​IMG]

    I would not classify the Saab as "Tailless".
     
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  11. Jul 18, 2019 #31

    plncraze

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    I wonder why the Skyjacker got parked? Interesting design and a good way to have the pusher prop with out cg issues.
     
  12. Jul 18, 2019 #32

    Aerowerx

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    And note that the part behind the prop is NOT and airfoil, but a flat plate!

    Also, if you look carefully at the picture, there appears to be control horns such that the flat central plate is some kind of control surface.
     
  13. Jul 19, 2019 #33

    Riggerrob

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    Yes,
    Skyjacker blurs the distinction between short-coupled and slotted.
    I suspect that Skyjacker suffered the same in-efficiency as most low aspect-ratio wings: high induced drag at high angles of attack ... limiting climb performance. Delta jet fighters get around that problem with massive amounts of thrust.

    I wonder how far aft of the trailing edge you need to install a propeller to reduce vibration??
    Similarly, how far above or below a wing’s trailing edge do you need to install a propeller to to reduce vibration/noise???
    My question is more related to pusher propellers on Seabee-style flying boats.
     
  14. Jul 19, 2019 #34

    bmcj

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    The thing about the Skyjacker is that it DOES meet the definition of prop in a slot because the surface aft of the prop line up with the rest of the wing chord (unlike the Saab that has a trait surface independent of the wing and wing chord. You can’t remove the Skyjacker’s aftnof prop surface or else there would be no slot to speak of.
     
  15. Jul 19, 2019 #35

    plncraze

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    I found a little more info on the Skyjacker. It reportedly needed more power. One of the joys of high span loading.
     
  16. Jul 19, 2019 #36

    TFF

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    For noise, My thought on the slot is that it should be airfoiled to accept the spin of air the prop makes. In front of prop, the trailing edge would taper down for the down blade and up for the up blade; feeding the air in a spin. Trailing edge behind prop would keep the spin going. Prop tip area would have a bell shape, widening toward the tip. Expansion for the vortices.
     
  17. Jul 19, 2019 #37

    Aerowerx

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    I have that information around here somewhere, it would probably take me all day to find it.

    You can try to google "pusher prop wing clearance".
     
  18. Jul 19, 2019 #38

    poormansairforce

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  19. Jul 19, 2019 #39

    bmcj

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    Not surprising. Low aspect ratio has its detriments as well as its benefits, and I can really see no benefit in having a prop running in a slot (only losses).

    I’m surprised at the high empty weight of the Skyjacker... it seems like that platform would lend itself to a much lighter structure without sacrificing strength.
     
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  20. Jul 19, 2019 #40

    Speedboat100

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    I agree 100%.
     

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