Wing/paint protection film???

Discussion in 'General Experimental Aviation Questions' started by Rik-, Oct 13, 2019.

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  1. Oct 13, 2019 #1

    Rik-

    Rik-

    Rik-

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    Just wondering how to prevent rock chips in the paint and I thought the 3M film that new cars use on the front of the hood or lower body panels.

    https://www.3m.com/3M/en_US/post-fa...KqvOPND1XmHtCho9lkt1BePVXF_t4rZBoCZEMQAvD_BwE

    My concern is, let’s say the film is long enough to reach end to end of the wing, but it’s only going to be for/aft a certain amount of inches. Would the transition point of where the tape ends cause any air disturbances to the wing that would cause any problems??
     
  2. Oct 13, 2019 #2

    TFF

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    3m has essentially the same stuff in a roll of tape various thicknesses used on airplanes. Not cheap stuff.
     
  3. Oct 13, 2019 #3

    Rik-

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    Just found the answer. They already use this as leading edge tape, guess there are no air disturbances with it.

    https://www.aerotect.net/
     
  4. Oct 13, 2019 #4

    BJC

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    The answer is, “It depends.” You would not want to use it on an open class class sailplane; it probably would help the aerodynamics of a J-3.

    BJC
     
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  5. Oct 13, 2019 #5

    Rik-

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    Thanks, the reason I was pondering this is that the GU wing design has issues with bugs, water, etc. and I was thinking would the abrupt ending, even though it’s thin, of the film create an issues with air separation on a wing?
     
  6. Oct 13, 2019 #6

    pfarber

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    You could add the wrap to about 1/2 to 2/3rds the camber where natural separation occurs. Few E/AB wings take advantage of laminar flow (they are usually to thick).

    Another option would be make the strip as thin on the nose as possible. In essence it would be a very, very thin stall strip, mostly invisible until a high AOA is reached. And even then its at best a few mill thick.
     
  7. Oct 14, 2019 #7

    Rik-

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    Thanks
     
  8. Oct 14, 2019 #8

    Marc Zeitlin

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    Yes. Your concern is warranted, and you should not use ANYTHING, including a paint stripe, that causes a chordwise discontinuity in the laminar flow wing's surface. Particularly the GU canard on a Q2 type aircraft. NO chordwise discontinuities from the LE to at LEAST the thickest part of the airfoil, if not further aft, and preferably not anywhere.
     
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  9. Oct 14, 2019 #9

    Rik-

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    T

    thanks. I looked at a Q200 that had the LS1 canard but I was thinking the design is really prone to rock chips being on the ground.
     
  10. Oct 14, 2019 #10

    Victor Bravo

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    What Marc Z is pointing out is that some of the canard airfoils have had serious issues because of just this issue you brought up. Much much more so than even other smooth composite fast airplanes (Lancair, Glasair). By screwing up the airflow on the canard, it disrupts the pitch stability or pitch balance of the whole airplane. So definitely don't screw around with that stuff on a Q or EZ type airplane IMHO.
     
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  11. Oct 14, 2019 #11

    pfarber

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    From looking at many Q2 photos (not sure what variant) it seems that vortex generators are a popular mod on the rear of the canard... so goodbye laminar flow.

    As for a paint stripe/sub 1mm sheet of adhesive causing flow seperation on a high aspect wing at low speeds? I'm not going to super concerned. That wing will delaminate for 1000 other reasons.
     
  12. Oct 14, 2019 #12

    Rik-

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    Yes that’s the GU wing design. The later LS1 does not suffer these same problems
     
  13. Oct 14, 2019 #13

    wsimpso1

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    Exactly. The 3M protective stuff will trip the boundary layer from laminar to turbulent flow. If the wing is a turbulent flow foil, it will be almost immeasurable, or as BJC pointed out for fabric covered wings, maybe even improve things. On a laminar flow foil executed with adequate smoothness, it will spoil all that careful work.

    Some folks have applied the tapes prior to painting, masked the tapes, then painted the wings leaving the paint and film butted to each other with no step in an attempt at maintaining the low drag laminar flow. You would have to be mighty good to make it work, but it is supposed to work fine until you need to replace the tape.

    Billski
     
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  14. Oct 14, 2019 #14

    wsimpso1

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    Not quite.

    If VG's are applied forward of the thickest part of the wing, you will spoil laminar flow aft of that line. Forward of that line you will get whatever flow the foil would have without the VG's. VG's forward are usually applied to maintain attached flow on the whole wing as AOA gets large, which can lower landing speeds.

    The flow will usually trip from laminar to turbulent somewhere around or aft of the thickest part of the wing. If the VG's are applied aft of the trip line, they will not spoil the laminar flow as the flow has already transitioned to turbulent. VG's applied after the thickest part of the wing are usually an attempt at keeping a lowered flap or aileron working further into the stall.

    Additionally, if you deliberately trip the flow to turbulent around the point where it does so naturally, you can achieve further drag reductions. Turbulator tapes are used extensively by sailplane racers and is even reputed to work for propellors.

    VG's are usually used to "fix" a wing that either was a poor choice for the intended mission or to make an airplane work better in a regime it was not intended for. Better solutions are appropriate airfoils and flaps for the mission, appropriate twist (either physical or aerodynamic washout), planform to suit, and other choices. Once it is flying and it has a behavior you can not allow, you start playing with fixes rather than design/build a new wing... You should not design a wing intending to apply VG's or other fixes from the beginning - if you end up with bad behavior and VG's are already there, well, you are out of moves.

    Billski
     
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  15. Oct 14, 2019 #15

    Victor Bravo

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    One of our race prep and repair guys used to do that on the wings of our sailplanes all with paint instead of tape. We had pretty big "contest numbers" and/or letters (24 inch tall) painted on the bottoms of the glider wings, so the timers on the ground at the start line could identify which glider was starting the race (Mine was VB, hence my screen name on this and other forums). On reeaally smooth laminar flow wings, that paint would indeed make a measurable difference, and by gum we were racers through and through. So this genius-caliber composite guru we had, Rick Wagner, would sand off the gel coat and paint, down to the fiberglass, mask off the contest numbers, paint the numbers in dark gray right onto the fiberglass, and let the paint cure hard (this was real lacquer paint, now considered a third-degree death penalty felony hazmat in California). Then he'd paint a thick coat over everything with the white gel coat or white lacquer. Then he'd sand it all carefully down to match the contour of the original airfoil, leaving perfectly flush smooth painted letters that the eye can see but the air can't. I'm talking days worth of sanding, by hand, with a three foot long sanding board. The edges of the letters were often just a little faded instead of sharp lines, but the real racers knew this was a badge of honor instead of sloppy work.

    Sorry, pathetic sniveling over my long-gone youth again.
     
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  16. Oct 14, 2019 #16

    Marc Zeitlin

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    Bill Simpson has already corrected this erroneous statement, but I'll elaborate.

    There are two versions of VG's that get installed on laminar flow airfoil canards. One is positioned aft of the thickest point of the airfoil, generally at 50 - 55% chord, and is used to mitigate separation when contaminated - it mostly alleviates the pitch trim change in rain. The second is positioned at about the 25% chord point, and MUST also be accompanied by VG's on the main wing. Since positioning the VG's this far forward allows for a higher max. Cl, it increases the danger of deep stall unless the main wing is treated equally. Since this trips the boundary layer to turbulent earlier than it otherwise would, it leads to a drag increase and a decrease in max. IAS by a couple of knots. Jim Price used this technique to set an FAI altitude record in a Long-EZ - about 35K ft.

    While you may not be super concerned, or even a bit concerned, your lack of concern would be exceedingly misplaced. GU canards on EZ type aircraft have demonstrated issues with contamination (and a span-wise strip of ANY height over a couple of thousandths of an inch is considered contamination) causing moderate to severe pitch trim changes.

    And even more tolerant canard airfoils, such as the Roncz on my COZY MKIV, or the LS1 on later Q-birds, can demonstrate problems. A story for elucidation:

    In the 2003 Airventure Cup race, there were a number of canard flying (mine included), some with GU's and some with Roncz canard airfoils. At the mid-race gate on the second day, we flew down the runway at Aurora, IL at 500 ft. AGL. There were a cloud of gnats hanging out there, and everyones plane got coated with black goo on the leading edge of every **** thing, including the canopy. In any case, in my plane with the Roncz canard, I did not notice much in the way of trim change, but I DID note, before landing, that I got a canard bob (canard stall) about 10 KIAS higher than when the canard was clean. Those folks with the GU canards, however, had SUBSTANTIAL trim change, requiring a LOT of back pressure on the stick (and elevator TE down deflection) to maintain altitude/speed. Some Variezes had to land at OSH at 110 - 120 KIAS, rather than the usual 75 KIAS, because THAT'S the minimum they could maintain with full aft stick. Emergencies were declared.

    So if you think that a small chordwise discontinuity won't have any effect on some laminar flow airfoils, think again.
     
  17. Oct 14, 2019 #17

    Hephaestus

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    Now... Assuming you're fully wrapping the canard back to the control surface - that 3M film would actually be a better finished surface than one would likely ever get with typical fiberglass finishing.

    However if you ever got a ding - strip and replace because you can't patch it.
     
  18. Oct 14, 2019 #18

    Rik-

    Rik-

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    Thanks, so I'm not as stupid as one might believe me to be. I was concerned exactly for the reasons you have outlined!!

    Thanks again.
     
  19. Oct 14, 2019 #19

    Rik-

    Rik-

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    I was looking at the "common" supply of the 3M film and it seems to come in like 3" increments, 3, 6, 9" so I was just wanting to avoid the rock chips in the paint and add a 9" section of the 3M film (hell I don't even have a plane yet) to avoid this scenario if possible. Just thinking forward. Don't know how hard it is to remove, nor how good of a quality the paint adhesion is on the plane either for that matter.
     
  20. Oct 14, 2019 #20

    Hephaestus

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    They vinyl wrap 737s every day...

    All of it comes off larger rolls, usually 50" wide(?)

    But go run your hand across a high mileage 2-3yr old wrapped car. Anything but perfectly smooth will trip the boundary layer. That's where the problem lies.
     
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