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  1. Norman

    Plotting Aerofoils for Ribs

    He didn't leave that 1/8" on the plane. To profile a wing you can either mix your micro in Dixi cups and fill each surface imperfection or mix it in a salad bowl and skim coat the whole thing. You'll save a couple hundred hours by using the big bowl. Either way most of your micro ends up on...
  2. Norman

    Pushers...way to go ?

    Possibly true, especially if your engine mount was designed by a moron.
  3. Norman

    Plotting Aerofoils for Ribs

    The technique illustrated in post #60 simply can not produced a finished wing. I know a lot of pilots think it's finished when the laminates are cured but it's not FINISHED until it's filled and sanded at least once. That final overlap you're concerned about should be sanded down to a feather...
  4. Norman

    Plotting Aerofoils for Ribs

    Well that's just... that's...
  5. Norman

    Plotting Aerofoils for Ribs

    It's unfortunate that Mike Arnold didn't show the process of smoothing the wing because he did it by hand, without a gauge to check his work. I seem to recall that he said the gauge that Bruce brought was the first one that touched his wing. Block sanding is not a sophisticated process...
  6. Norman

    Plotting Aerofoils for Ribs

    Well there is the nominal profile and waviness and surface finish. I'd say that the leading and trailing edges could be 1/4' inch out of position without having a major effect as long as the nominal curve of the surface was smooth but a 1/4 inch high wave would be unacceptable on any wing...
  7. Norman

    Pushers...way to go ?

    Ya mean like this?
  8. Norman

    Pushers...way to go ?

    Yes, specifically cutting through the trailing edge shear layer. The RCG thread I linked to in post #14 included more information than I want to wright. If you don't want to read the whole 2 page thread just scroll down to the comment from, Don Stackhouse, he used to do this stuff for a living.
  9. Norman

    Pushers...way to go ?

    Acording to Wikipedia the Avanti cruises at 318 knots with a maximum speed of 400. The page for the Beech Super King air just says "maximum cruise 310 kt". So I guess if you feed the engines through a fire-hose the Avanti is a lot faster.
  10. Norman

    Pushers...way to go ?

    Piaggio spent 2000 hours in the wind tunnel developing the nacelles for the Avanti and it's still a flying siren because the trailing edge wake is still a well defined sheet 2 chord lengths behind the wing.
  11. Norman

    Pushers...way to go ?

    I'm saying you pick your compromises and do the best you can to mitigate to down side of those compromises.
  12. Norman

    Pushers...way to go ?

    During takeoff and climb the prop accelerates the air a lot but at cruise the air isn't really accelerated very much as it passes through the prop disk so the excess drag on the fuselage of a tractor isn't all that much when it really matters. There are a couple of good reasons to put the prop...
  13. Norman

    Pushers...way to go ?

    Anything in front of the propeller will decrease its efficiency, turning some of your horsepower into noise and vibration. The bigger the obstruction the higher the losses so a pod like the Lake amphibian isn't as bad as a Cessna Skymaster. Wings are far worse than axisymmetric bodies though...
  14. Norman

    Plotting Aerofoils for Ribs

    Someone dredged up an old zombie thread. The OP was in 2005.
  15. Norman

    Aerofoil layout

    I did the illustrations for this post a few days ago then thought better of it because it's not a response to the OP and I really hate writing but it looks like he's back in the conversation and going with the flow so I'll muddy the water some more. I started by typing in coordinates from my...
  16. Norman

    Aerofoil layout

    Yep. Fluids don't like flat spots or corners.
  17. Norman

    Aerofoil layout

    Are you sure about that? Looks like it would require some stretching to force lines drawn on the sheet metal to hit points of equal slope as Raymer defines "flat-wrap". To avoid stretching just cut a trapezoid with the ends equal to the wrap length of the airfoils and attache it wherever it fits.
  18. Norman

    Plotting Aerofoils for Ribs

    I agree that the published coordinates are too coarse but it's what the old measuring processes produced and those old airfoils weren't very sensitive to small geometric errors. Unless the original wind tunnel model was made of metal and still around there's no way to find the original shape of...
  19. Norman

    Aerofoil layout

    Here's a source of those NACA airfoil plotting programs. They're in Fortran90.
  20. Norman

    Aerofoil layout

    There's a Python API for xflr5 under development. Fortran is out of the picture. XFoil was written in Fortran77 but it was ported to C for xflr5. Since development of xflr5 ended a few years ago this looks like the only way new features can be added. Sadly it looks like it only runs on Linux for...
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