Pober Pixie Airfoil

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Soliex, Mar 29, 2019.

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  1. Mar 29, 2019 #1

    Soliex

    Soliex

    Soliex

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    Hi all

    I've been working on a Pober Pixie 2" stretch in length and height of the cockpit, I call it the Dixie Parasol. I haven't made any calculations yet of the airframe, but plan on it and may have questions for those in the know. The Pegasus O-100 is the engine of choice and the modifications are in CAD, no tube has been cut as yet and may not ever, we'll see.

    While admitting that I haven't spent more time than a quick search on this topic I have a question:

    What changes would you make (if any) to the wing construction or airfoil? Stay with the wood or could this be an opportunity for a new metal wing... it was designed with the Clark Y, my plans are from '91 or so and have a flat bottom, maybe there is something better.

    Comments and suggestions welcomed...

    Thanks
     

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  2. Mar 29, 2019 #2

    Little Scrapper

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    GA 30-612 from Harry Riblett would be a cool experiment on that airplane. I think the Kitfox uses it.

    I knew a guy who buult this airfoil on a Pietenpole and loved it. He died of old age and said it was a incredible change and we'll worth it.
     
  3. Mar 29, 2019 #3

    TFF

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    Better is relative. I would be putting an Taylorcraft airfoil so I could go faster. Don’t care about the last mph of stall. You have to know more on what you want and is it really worth it. It’s a pretty big airplane. O-100 is going to be marginal. Most people ditche the VW for a A-65. Ps& Qs on weight.
     
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  4. Mar 29, 2019 #4

    pictsidhe

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    I've been playing around with Riblett type airfoils in XFLR5. His thickness distribution change on the NACA 4 digit is not liked by XFLR5. However, it does like the Riblett combination of the 6 series 'a' camber lines with the original NACA 4 digit thickness. I personally believe that his choice of camber line is all of the magic in the Riblett airfoils. I'll be using those in my project. That would make Scrapper's suggested foil a GA30A-612.
    But, 12% isn't really optimum at the speeds Pixies fly at, moving up to 14-15% will increase Clmax a little more and soften stall without hurting cruise drag. I'd therefore suggest a GA30A-614 or 615
    Cruise drag between the GA30A Ribletts and the Y is a wash. Moment is slightly more negative on the Ribletts. Clmax has a healthy increase.

    I have a spreadsheet that generates Riblett type airfoils using up to three combined a=0-1 camber lines and whatever thickness you want. Multiple camber lines allow altering the pressure distribution and Cm. I believe that Riblett used the a=0.5 camber line on all his airfoils.
     
  5. Mar 29, 2019 #5

    don january

    don january

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    My comment is Paul was real good at building and designing airplanes and TFF is right on about the power plant. I never got to say hello so glad to see your getting ready to build.
     
  6. Mar 30, 2019 #6

    Soliex

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    Thanks for the comments, all are being taken into consideration and appreciate the fine work that has been done by Mr. Poberezny. This is basically a new airplane because of all the modifications, weight saving is part of the goal, plus I like the what ifs. Like Scrapper, I want to participate somehow and this is how I can for now, and if time allows I'm going to open a new thread on the structural analysis... one calculation at a time.

    As mentioned in post #1, 'No materials have been harmed in this stage of the project'.
     
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  7. Mar 30, 2019 #7

    Little Scrapper

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    I like your attitude. Similar to you I'm participating and just having fun.

    A changed up Pixie sounds like a fun way to spend time
     
  8. Mar 30, 2019 #8

    GeeZee

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    Have been fan of the Pixie for a long time. Actually have a 8 1/2 x11 framed cutaway drawing of a Pixie on my garage wall. What would be really cool is an aluminum tube and gusset fuselage and a “clipped” wing with a metal spar (maybe a tube) with metal ribs. The O-100 would then be a fine choice....
     
  9. Mar 30, 2019 #9

    Pops

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    Friend of my in NC has a Pixie with a Cont C-85- 12F and likes it.
     
  10. Mar 31, 2019 #10

    lr27

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    Don't count on some fancy airfoil to make a big change in performance unless the wing is at least mostly sheathed. Fabric will only give you an approximate airfoil. You may be able to have some affect on pitching moment, max lift, etc.
     
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  11. Apr 1, 2019 #11

    Soliex

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    The Pixie has some sexy lines for sure, I'm going to try to maintain the looks with the Dixie Parasol.

    I will open it's own thread in the near future.
     
  12. Apr 2, 2019 #12

    lr27

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    Sheeted, not sheathed. Not sure if that was the spellchecker or my own idiocy.
     
  13. Apr 2, 2019 #13

    Victor Bravo

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    The O-100 weighs a fair amount less than the VW and A-65, and then you are stretching the fuselage. So make sure you calculate the probable CG using the O-100's lighter weight AND considering where you are stretching th fuselage. Keeping it light should be the number one prority by far. Every pound sthat is not there will make the airplane perform better, use less fuel, and handle better.
     
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  14. Apr 2, 2019 #14

    Little Scrapper

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    Are you sure you want to build a airolair around a engine that isn't 100% available and completely proven?
     
  15. Apr 2, 2019 #15

    Soliex

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    VB, the stretch is the result of reclining the seat back to 10°from 4°and all the changes from the domino effect.
    Scrapper, I'm confident that the O-100 will be available if this ever gets built. From what I understand it's just finding a supplier for the crank machining that's holding things up.
     
  16. Apr 2, 2019 #16

    Victor Bravo

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    Reclining the pilot will move the CG back, plus you are moving all the weightof the tail secton 2 inches further back, then you are lightening thenose by 40-60 pounds compared to the VW. So I would still be looking at movig the wing rearward on the fuselage by a small amount? We do have some highly trained people here who are capable of looking at your proposed plans and verifying that you are on the roght track.
     
  17. Apr 2, 2019 #17

    TFF

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    More likely the nose needs to be extended. The wing is right on the edge of the hole. The Crackerjack that they are using to test the O-100 would be a good indication of general dimensions the engine will pull well.
     
  18. Apr 3, 2019 #18

    lr27

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    Do you mean flat bottom, or Clark Y? The Clark Y isn't completely flat bottomed. Only the aft 75 percent or so.
     
  19. Apr 3, 2019 #19

    TFF

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    Most people consider the Clark y as the definitive flat bottom. It may be lay termed but what is accepted. Straight front to back flat is not what most think of, but like you say a section is flat.
     
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  20. Apr 3, 2019 #20

    Turd Ferguson

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    I don't think the Pixie goes fast enough for a different airfoil to make it faster. The straight seat back could certainly use some ergonomic attention.
     

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