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Thread: Olibuilt 's New Cub project

  1. #481

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    Been using Herc for years now, good stuff!

    I like the lightening holes in the gussets of the fuselage sides, never seen gussets there before! Sure can't hurt.

  2. #482
    RVBottomly's Avatar
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    Quote Originally Posted by courierguy View Post
    Been using Herc for years now, good stuff!

    I like the lightening holes in the gussets of the fuselage sides, never seen gussets there before! Sure can't hurt.
    I forgot to comment on the Herculiner because I was taken by the flying. I've used it on drift boat bottoms. It is good stuff.

  3. #483
    Dave Calkins's Avatar
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    Courier Guy and RV Bottomly.........!Herculiner on drift boat bottom? wow. I am impressed.

    aluminum, fiberglass, or glassed-wood boat hull?

    any special prep?

    how does it fail/scrape? does it come off locally at scrape or big sheets/chips?

    have a skiff project I was planning on West System barrier coating in epoxy, but maybe there is a better way.
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  4. #484
    RVBottomly's Avatar
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    Quote Originally Posted by Dave Calkins View Post
    Courier Guy and RV Bottomly.........!Herculiner on drift boat bottom? wow. I am impressed.

    aluminum, fiberglass, or glassed-wood boat hull?

    any special prep?

    how does it fail/scrape? does it come off locally at scrape or big sheets/chips?

    have a skiff project I was planning on West System barrier coating in epoxy, but maybe there is a better way.
    Plywood bottom epoxy-fiberglass coated. It was an old 'scrap wood dory' I built from scrap wood 20 years ago. The bottom rotted out so I cut it out and put a new marine ply bottom on it and sealed it up with epoxy fiberglass. After a few years of gouges in it from sharp rocks, I tried Herculiner as a coating. It stuck with no particular prep.

    It's heavy, and not quite as streamlined, but it slid over rocks pretty well. No failure point except gouges in the material. It does not seem like it would ever come off.

    The boat met its end because of a different problem. It got stove in by a log while tied to a bulkhead in a storm.
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  5. #485
    RVBottomly's Avatar
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    I should add a reply to your last sentence. I do not recommend it as a better way than epoxy and fiberglass for most boats. It is heavy. For most skiffs a single layer of fiberglass ought to be enough. If you are dragging it around, two layers would be better. Some have tried carbon fiber with mixed results. Others have added graphite powder as a filler in their epoxy. I think the verdict is out on that, too.

  6. #486

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    I've never used it on boats, only on my Airstreaks. It wears off, but I've never had it come off in large pieces. I get about 75 to 125 hours out of a coat (actually 2 or 3 thin coats, between letting it setup, better then goobering it on super thick all at once) using the (I believe) qt size can, about 30 bucks. I take that back, I had my rocker panels on my Dodge pickup looking pretty shabby from road rash, and darned if the stuff didn't stick like glue there also. No prep other then soap and water wash.
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  7. #487
    Olibuilt's Avatar
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    Something happened yesterday. For the first time in my Super Cub flying experience, I'm convinced I could land where I won't be able to takeoff. A weird feeling.


  8. #488
    Olibuilt's Avatar
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    Always looking to improve the airplane.

    Those wings were built with "aileron coves" shaped ribs all the way. The wings have a concave shape just in front of the flaps. Now that I see all those slot and slat mods, I think it could be improve.


    So I added an inch to my flap hangers. I now have a little more room to fabricate some flap gap seal, thing that never went on those wings...



    Flap gap seal questions:

    - Main purpose of those seal is to close the gap for cruise speed OR redirect the air in the slot between the flap and the wing ???
    - What size slot should I be looking for when full flaps ??

    Thanks
    Hoping for help.





    IMG_0030.jpg


    IMG_0033.jpg

    IMG_0034.jpg

    IMG_0036.jpg

  9. #489
    www.SkupTech.com mike mcs repair's Avatar
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    not a direct answer, but i use a scotch brite pad as my filler/gap setter when installing gap seals..... with flaps partially down, so i can drill bottom holes and install screws

  10. #490
    skywagon8a's Avatar
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    [QUOTE=Olibuilt;749120]Always looking to improve the airplane.

    Flap gap seal questions:

    - Main purpose of those seal is to close the gap for cruise speed OR redirect the air in the slot between the flap and the wing ??? Both
    - What size slot should I be looking for when full flaps ?? 1/2"
    [QUOTE]

    Start by extending the top surface of the wing to where it almost touches the top of the flap. That will be between the 3" & 3-1/4" location on your tape measure.



    The angle from the lower surface of the wing up into the flap cove area looks to be a fairly sharp 90 degree bend. This wants to have a large radius in the 1-2" range to minimize turbulence. Then it wants to slope back in a lazy S shape clearing the leading edge of the flap and following the flap up until it meets the extension which you placed on the top surface at 3-1/4".




    I made mine from balsa wood gluing it on and covering it with fabric. It was shaped by placing sandpaper on the flap using the flap as a sanding block running it back and forth until there was clearance for the entire length. When the flaps are up there is a strip of tephlon attached to the underside of this seal used as a rubbing strip for the entire length of the flap.
    Piper uses soft aluminum bent at a sharp angle where it almost touches the flap. This is screwed to the top trailing edge of the wing and the flap cove.

    When the flaps are down this will give you a slot gap of about 1/2" at the top of the flap. When the flaps are moving down and back this gap will open.

    The purpose of the gap seal is to prevent up flow of the air when the flaps are up improving lift in cruise. It also serves the same function as the leading edge slats when the flaps are down by accelerating the higher pressure air from below the wing and redirecting it over the top of the flap thus improving the boundary layer flow over the flap reducing the speed that the flaps stall, improving lift at lower speeds and smoothing the airflow over the tail. This reduces or eliminates tail shaking.
    N1PA
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  11. #491
    Olibuilt's Avatar
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    IMG_0038.jpg

    IMG_0039.jpg

    IMG_0040.jpg

    IMG_0041.jpg

    What about a "lazy Z" ?
    It leaves about 1/2 inch gap at full flaps

  12. #492
    skywagon8a's Avatar
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    Quote Originally Posted by Olibuilt View Post
    IMG_0041.jpg

    What about a "lazy Z" ?
    It leaves about 1/2 inch gap at full flaps
    It would be better if that bend was not there. Make it a smooth curved section instead. The abrupt change in cross section disturbs the smooth air flow. If you have a long piece of 4" or 6" plastic pipe, use that to bend the shape. Then bend your tight bend afterwards.

    It will work as you have done it but will be better if it is curved. Curved = smooth. Abrupt angle = turbulence.
    N1PA
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  13. #493
    Olibuilt's Avatar
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    Done with a curved prototype.


    Before I go into mass production, is a 3/8 inch gap at full 65 degrees flaps enough ??




    IMG_0042.jpg


    IMG_0043.jpg

  14. #494

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    Looking at the side view of your curved section, it would perform the best if the closest gap is at the very aft end of the filler and it opens fairly consistently from there forwards. This will induce the maximum flow energy at partial flaps as in your upper photo as well as offering a high energy at the maximum extension.
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  15. #495
    BC12D-4-85's Avatar
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    After you perfect your flap fairing try installing end plates on the flaps for added lift.
    Attached Images Attached Images
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  16. #496
    Olibuilt's Avatar
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    Quote Originally Posted by CharlieN View Post
    Looking at the side view of your curved section, it would perform the best if the closest gap is at the very aft end of the filler and it opens fairly consistently from there forwards. This will induce the maximum flow energy at partial flaps as in your upper photo as well as offering a high energy at the maximum extension.
    If I understand good, you are telling to add another + or - 1/2 inch in horizontal lenght.

    I'v tried, but then there is no more gap. The fairing touches the flaps, even full flap down.

  17. #497
    www.SkupTech.com mike mcs repair's Avatar
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    Olibuilt 's New Cub project

    More than enough. Probably too much at outlet


    Sent from my iPhone using SuperCub.Org

  18. #498

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    Quote Originally Posted by Olibuilt View Post
    If I understand good, you are telling to add another + or - 1/2 inch in horizontal lenght.

    I'v tried, but then there is no more gap. The fairing touches the flaps, even full flap down.
    You do not want to open the outlet from where it is, you want the cross section from that closest point to open evenly going forwards. The goal is that as air moves from the lower surface it is accelerated into the highest energy stream till it goes out of the gap onto the upper surface of the flap.
    This will draw air aft from the upper wing surface delaying or reducing flow separation as much as possible.
    Looking at the two pictures, the full down position will only see small improvement. The partial flap will see the greatest gain since it has a fair amount of distance for the airflow to gain energy.
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  19. #499
    skywagon8a's Avatar
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    Quote Originally Posted by Olibuilt View Post
    Done with a curved prototype.

    Before I go into mass production, is a 3/8 inch gap at full 65 degrees flaps enough ??
    That should work Oli.
    65 degrees is a lot, your airplane will almost hover when you are done.
    When you finish, tape some yarn to the trailing edge of the flap and notice how it trails with the full 65 degrees of flaps. If it streams back at a fairly steady almost straight line you have cracked the code. It will likely twirl around in the prop wash area.

    Charlie, he moved his hinge point aft an inch which is giving him that extra distance forward.
    N1PA

  20. #500
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    Quote Originally Posted by BC12D-4-85 View Post
    After you perfect your flap fairing try installing end plates on the flaps for added lift.
    Gary, I tried that on my 185 by installing a plate on the outboard end of one flap. It made no difference whatsoever. I did a series of stalls with each flap position expecting that the extra lift from the plate would cause the other wing to stall first. NOPE....Nothing.
    N1PA

  21. #501

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    Quote Originally Posted by skywagon8a View Post
    That should work Oli.
    65 degrees is a lot, your airplane will almost hover when you are done.

    Charlie, he moved his hinge point aft an inch which is giving him that extra distance forward.
    The trick as you are already addressing is to prevent the flap from stalling at high angles, I think you are going at it right.
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  22. #502
    BC12D-4-85's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Gary, I tried that on my 185 by installing a plate on the outboard end of one flap. It made no difference whatsoever. I did a series of stalls with each flap position expecting that the extra lift from the plate would cause the other wing to stall first. NOPE....Nothing.
    Cessnas? Who knows and there's no warranty. The Citabria and Cub I had liked it and rolled away from the spill plated flap but again it's all an experiment.

    Gary

  23. #503
    Olibuilt's Avatar
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    Almost done. Thanks again!!

    I really hope to notice an improvement in slow flight.

    IMG_0048.jpg

    IMG_0049.jpg
    Last edited by Olibuilt; 06-16-2019 at 04:41 PM.

  24. #504
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    Oli, Be sure to give us a flight test report.
    N1PA

  25. #505
    Southern Aero's Avatar
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    Oli

    From what I have been able to gather from others research, the gap, slot or nozzle (different terms in different researches) created by the flap should be about 1.5% - 1.75% of chord.......... but that would probly depend on how much air you had available from the entry area........... The engineer types in here could be more accurate I'm sure .......... And the aft edge of the piece you are adding should align about the center of the radius of the leading edge of your flap. It would be better to have a radiused entry from the false spar area aft of the rear spar to get more and smoother air into the "gap"......... maybe address that if you ever had to go into the wing. More air from below may be needed to keep flaps from a stall at 65 degrees. I believe CharlieN would be correct that you would have the most gain at a partial flap setting. More air and double slots for 65 degrees? I have mine designed for double slots and 55 degrees but will be end of year or so before I will be able to do any testing. Good luck with your testing and let us know how it goes........ really like your airplane!
    ......... It doesn't cost any more to go first class! You just can't stay as long.

  26. #506
    skywagon8a's Avatar
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    Quote Originally Posted by Southern Aero View Post
    ...More air and double slots for 65 degrees? I have mine designed for double slots and 55 degrees but will be end of year or so before I will be able to do any testing.
    The slot that Oli has is about the same as the one on my Cub. My long flaps are single slotted stock Cub airfoil, deflect to 56 degrees and are very efficient which was noted through tuft testing. So, I'm optimistic that Oli's 65 degrees being only 9 degrees more may also work well.
    N1PA
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  27. #507
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    Might be that I don’t know what I don’t know, which is probably the case. But would the trade-off for the amount of lift You might get by allowing the air to go through the pressurized slot opening to gain increments of lift that the flap may produce, be more than made up for it if you close the slot and deflect it ALL downward as ground effect vehicles do. Seems to me the only time the flaps are at full deflection is close to ground affect anyhow.
    Remember reading when some of the back country Cubs had a problem with blow back and not being able to get full deflection, and when the problem was resolved and they were able to get them to fully deploy it made a tremendous difference in the performance and the ability to get much slower approach speeds.

  28. #508
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    Quote Originally Posted by flyrite View Post
    Might be that I don’t know what I don’t know, which is probably the case. But would the trade-off for the amount of lift You might get by allowing the air to go through the pressurized slot opening to gain increments of lift that the flap may produce, be more than made up for it if you close the slot and deflect it ALL downward as ground effect vehicles do. Seems to me the only time the flaps are at full deflection is close to ground affect anyhow.
    Remember reading when some of the back country Cubs had a problem with blow back and not being able to get full deflection, and when the problem was resolved and they were able to get them to fully deploy it made a tremendous difference in the performance and the ability to get much slower approach speeds.
    That high-pressure, high-energy air from under the wing is directed through the slot. The slot accelerates that air as it joins the boundary layer on the flap, which re-energizes that boundary layer and delays the boundary layer's separation (stall).

    Short version - stealing some of the air from under the wing can help the flap resist stall longer.
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  29. #509
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    Quote Originally Posted by skywagon8a View Post
    The slot that Oli has is about the same as the one on my Cub. My long flaps are single slotted stock Cub airfoil, deflect to 56 degrees and are very efficient which was noted through tuft testing. So, I'm optimistic that Oli's 65 degrees being only 9 degrees more may also work well.
    sky

    Is your false spar at the flap as in Piper drawing 11670? That is what I was referring to by "more air". ................. more air from the high pressure side to get accelerated thru the slot. Oli's appears to have the "square edge" at the moment that might hinder flow.
    ......... It doesn't cost any more to go first class! You just can't stay as long.

  30. #510
    skywagon8a's Avatar
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    Quote Originally Posted by Southern Aero View Post
    sky

    Is your false spar at the flap as in Piper drawing 11670? That is what I was referring to by "more air". ................. more air from the high pressure side to get accelerated thru the slot. Oli's appears to have the "square edge" at the moment that might hinder flow.
    Yes mine is as per Piper's. We addressed Oli's square edge at the beginning of this discussion. Also he moved his flaps 1" further back from the wing so that his new fairing shape should take care of that issue which was also addressed. He has not yet shown a picture of that lower section of how he bent his fairing to compensate for that tight radius which was also a concern of mine. Even if he doesn't change that radius, just bringing the fairing down low and sloping back at an angle should help though not as much as the large radius as you have noted.
    N1PA

  31. #511
    Olibuilt's Avatar
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    Had the time to do a little flight test today. It still fly, that is the good thing.. Hahah ...

    First impressions may be wrong:

    -less tail shake a 45mph, with 45 flaps
    -less sink rate at 45mph with 45 flaps

    Did only one landing. Will report feedback when I have the chance to test it more.




    Pics bellow are at 65 flaps:

    IMG_0053.jpg

    IMG_0054.jpg

    IMG_0055.jpg

  32. #512

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    The wings I am slowly building are similar to yours Oli. Thanks for your testing and posting. I don't fully understand everything that is going on here, but I know how to copy something that remedies something bad. Tail shake sounds bad. Pacers and Tri-Pacers appear to have the same cove as what you and I have. Do they/did they have a tail shake without the gap seals? Sounded like Christian from SuperCub project had the same deal. Lurking, Learning...

    Thanks,

    Jim

  33. #513
    skywagon8a's Avatar
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    Quote Originally Posted by Jim A. View Post
    . I don't fully understand everything that is going on here, but I know how to copy something that remedies something bad. Tail shake sounds bad.. Lurking, Learning...

    Thanks,

    Jim
    Jim, Think about this. Drag comes from behind where something is holding the plane back. In this picture those arrows which are turned around facing the airflow are drag. The idea is to reduce the amount of the drag which is done by making a suitable shape which minimizes the reverse flow. That flat trailing edge which Oli has on his wing is a large drag generator. Drag = Turbulence. Turbulence creates Drag. The part which he made in this discussion serves to reduce this reverse flow as well as directing the flow in an efficient manner over the flap. Once the air flows efficiently over the flap, it will not be turned into as much turbulence/reverse flow which in turn would start shaking the tail.


    The swirling circular white lines to the upper right of the airfoil in the second picture is drag. Those white lines which are close together have a higher pressure than those which are further apart. If you are good at meteorology compare this to the isobars on the pressure gradient map. The whole idea is to minimize this swirling effect. Notice the far right swirling, that is causing the tail shake. What Oli has done will guide the air flow over the flap in order to reduce the amount of this swirling.
    Placing a slat on the wing leading edge reduces these swirling circular white lines. What Oli is doing converts the wing into a slat for the flap.

    Hope this helps.
    N1PA
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  34. #514
    skywagon8a's Avatar
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    Quote Originally Posted by Olibuilt View Post
    When you take these off to paint them, try to iron out those two small bends in the lower forward part of the piece turning them into a smooth radius. This will make the part more aerodynamically efficient. It will make a small improvement, though likely so small that you will not see it.

    Another thought. Those gaps in the flaps are allowing air to spill through rendering that small section of flap behind them unusable. If you could make a fairing which wraps around the hinge and up into that opening area blocking air flow, this could block some of the turbulence which is generated by the air flowing through the opening. Also, because you moved the flaps back 1" perhaps the opening doesn't need to be as large and you could make a small cover plate for the top of the flap which would also smooth the air flow.

    Both ideas are just thoughts and may or may not make a noticeable difference. Small details can sometimes have big results. I can give examples.
    N1PA
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  35. #515
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    Quote Originally Posted by CamTom12 View Post
    That high-pressure, high-energy air from under the wing is directed through the slot. The slot accelerates that air as it joins the boundary layer on the flap, which re-energizes that boundary layer and delays the boundary layer's separation (stall).

    Short version - stealing some of the air from under the wing can help the flap resist stall longer.
    No argument here Tom on what makes slotted flaps work, Same aerodynamics at play as my Slats. My point was , Is the miniscule lift gained by slotting it [not considering the tail buffet help], outweighed by the Benefit of smoothly directing it all down. Seems there's one of the planes that sets records at Valdez that is setup more as a "ground effect vehicle" without the slots. Once you get close to landing {which is what most are concerned with} It would seem to make more sense to use the GEV's setups,and play off ground effect, Than something trying to maximize lift away from the ground. Not trying to talk nobody outta their slotted flaps, Or rewrite the aerodynamic rules. Just seems to me If the slowest touch down speed is what were after, As well as a good nose down approach, Might be worth considering a different way of looking at it. They's a reason we tape our control surface gaps closed, I know its slightly "apples and oranges" to the flaps but, It Makes them more efficient at deflection By not allowing any air to escape.
    Would be a simple experiment for giggles, for someone with a set to tape the slots closed and shoot a few approaches.

  36. #516
    skywagon8a's Avatar
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    Quote Originally Posted by flyrite View Post
    My point was , Is the miniscule lift gained by slotting it [not considering the tail buffet help], outweighed by the Benefit of smoothly directing it all down. Seems there's one of the planes that sets records at Valdez that is setup more as a "ground effect vehicle" without the slots. Once you get close to landing {which is what most are concerned with} It would seem to make more sense to use the GEV's setups,and play off ground effect, Than something trying to maximize lift away from the ground. Not trying to talk nobody outta their slotted flaps, Or rewrite the aerodynamic rules. Just seems to me If the slowest touch down speed is what were after, As well as a good nose down approach, Might be worth considering a different way of looking at it. They's a reason we tape our control surface gaps closed, I know its slightly "apples and oranges" to the flaps but, It Makes them more efficient at deflection By not allowing any air to escape.
    Would be a simple experiment for giggles, for someone with a set to tape the slots closed and shoot a few approaches.
    Let me try to explain it as I understand what you are saying. You are suggesting that the slot be closed. This will give you what is called a hinged flap. Oli's goes down 65 degrees which exceeds the angle of attack at which most all airfoils stall. This means that the flap would be producing mostly drag with minimal lift.
    A slotted flap of the same size and deflection has the advantage of the higher pressure air below the wing causing an accelerated flow over the top of the flap thus "blowing" down the turbulent air on the top of the flap. This creates lift as well as the drag from the deflected flap.
    SO, if the hinged flap is producing little or no lift that means that the wing has to carry more weight per square foot of area.
    The slotted flap will still be producing lift. Thus more wing area producing lift means less weight per square foot. Less weight per square foot means lower stall speeds, slower landing speeds and shorter landing distances.

    Your observations at Valdez only demonstrates that the pilot with the hinged flap was a better pilot than the one with the slotted flaps on that particular day.
    N1PA
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  37. #517
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    Quote Originally Posted by flyrite View Post
    No argument here Tom on what makes slotted flaps work, Same aerodynamics at play as my Slats. My point was , Is the miniscule lift gained by slotting it [not considering the tail buffet help], outweighed by the Benefit of smoothly directing it all down. Seems there's one of the planes that sets records at Valdez that is setup more as a "ground effect vehicle" without the slots. Once you get close to landing {which is what most are concerned with} It would seem to make more sense to use the GEV's setups,and play off ground effect, Than something trying to maximize lift away from the ground. Not trying to talk nobody outta their slotted flaps, Or rewrite the aerodynamic rules. Just seems to me If the slowest touch down speed is what were after, As well as a good nose down approach, Might be worth considering a different way of looking at it. They's a reason we tape our control surface gaps closed, I know its slightly "apples and oranges" to the flaps but, It Makes them more efficient at deflection By not allowing any air to escape.
    Would be a simple experiment for giggles, for someone with a set to tape the slots closed and shoot a few approaches.
    A lot of the "directing air down" happens after the airfoil. It needs to be in a non-stalled configuration in order to direct the air downward and create lift to keep the vehicle from falling. Once the airfoil stalls, it just leaves an ugly series of vortices above it and no effective deflection on the flow underneath and behind the airfoil.

    Once the wing stalls, it is unable to effectively direct air downwards and we don't create lift. Keeping the boundary layer attached delays the stall, allowing for slower flying speeds. Adding the slot will help delay the stall on Oli's flaps.

    Nose-down attitudes associated with flaps have more to do with the wing's effective camber change when the flaps are deployed. Because of the change in camber, the wing's AoA will change when the flaps go down. This requires a more nose down attitude of the airplane to keep from climbing when flying at the same airspeed as before the flaps were deployed. It's more of a geometry problem than one involving slots/slats.
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  38. #518

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    I think Flyrite is on to something. Couldn't tell you where I saw it, but somewhere there is thread where Frank Knapp talked of the process where he sealed off the slots on lil cub. He said the slot made a wing drop, sealing the slots fixed the problem.
    Not an aeronautical engineer, but I think there is a velocity threshold at which a slot helps.
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  39. #519

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    STOL contests wins are more dependent on getting a lucky gust of wind on takeoff and steady wind on landing than anything else. Having said that I know Frank does a lot of testing and I do respect his opinion. He did trade out his Keller flaps, BUT, his cub is a single mission plane. Not your basic daily flyer.
    DENNY

  40. #520
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    On my PA-18A I attached small metal covers/seals fitted to the curve on top of the flaps over the hinge and pushrod locations. Seemed to help and would slowly roll away from the sealed flap when they were deflected.

    Tuft testing on other controls like ailerons can show disturbed flow downstream from any openings like noted in #514 as shown here: https://ntrs.nasa.gov/archive/nasa/c...9930083935.pdf

    One enigma though is we tend to slot flaps and seal ailerons. That may be simply due to the cove design in front of each. Citabrias are like that for their ailerons and partially sealed flaps. Unless it flows well to help then a seal simply reduces any loss of pressure air from below or above and makes the control more effective (like the aileron).

    Crossinds STOL used to seal the flaps and ailerons on Cubs with fabric and still may. I'm sure there was a reason Cal and Gordon Mandell did that. I flew one with the flaps sealed then with them removed. I don't recall a marked change but it was the '80's.

    An older summary of high lift techniques by Cornish and Tanner is available here: https://www.jstor.org/stable/4456500...n_tab_contents For example they examined the flap slot and nearby boundary layer flow then sealed the flaps on a Cessna L-19 to restore elevator authority. The flaps and horizontal stabilizer were end plated.

    Gary
    Last edited by BC12D-4-85; 06-18-2019 at 10:16 PM.

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