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Thread: Leading edge slats and Keller Flaps

  1. #1

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    Leading edge slats and Keller Flaps

    I have a Javron wing and a set of leading edge slats to fit. My wings also have Keller flaps. I知 planning on initial flying without the slats fitted, so I have some base line performance figures to compare. I intend to try maybe fitting some platenuts as the attach for the slats rather than screws. So they are removable if I decide to when on floats. I知 concerned on chaffing the fabric leading edge at the attach points any ideas on mounting options for this leading edge system.

  2. #2

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    Looking forward to report on how much top speed you use with the slats. I would like to have them but don't want to loose a lot of speed on long trips.
    DENNY

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    I used nut plates for my slat hangers. I thought it would be better than PK screws into the leading edge metal. Of all the slat guys I know or have talked to I知 the only one with nut plates. I thought I may remove my slats, too, but once I flew them? I don稚 have any motivation to remove them. As for nut plates? Are they better than PK screws? Yes, but the only thing that might stress the attachments and make PK screws work loose would be parking in a tailwind, and frankly anyone with slats that plans to park outdoors occasionally needs to make slat locks to prevent them from hammering in a tail breeze.

    Lowlevel, send me a PM and we can swap emails so I can send photos of the gust locks. Nut plates are pretty self-explanitory. Trust me when I say to put the slats on. Enjoy the benefits from flight #1. You値l never want to remove them.

  4. #4

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    Quote Originally Posted by DENNY View Post
    Looking forward to report on how much top speed you use with the slats. I would like to have them but don't want to loose a lot of speed on long trips.
    DENNY
    Denny, with Catto 84x37 prop without slats, 92/93...With Slats 87...
    Running a 84/36 Catto now...82 with slats...

    As for nut plates, I used PK Screws...no issues yet...I do take mine off once in a while, however I only take off the Slats and leave the hangers...seems it takes 10 min...I have a buddy who used Riv Nuts...

    Slats are fun...think they would be better with the Fowler Flap...
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  5. #5

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    I'm curious how much lifting force is exerted on the slats themselves? They seem to have proven themselves with PK screws, though it seems under kill. The designer of the Helio Courier states that the slats when deployed on that airplane carry 64 percent of the aircraft's weight (12:45 mark on the video). That must not be the case for a slatted cub or I've underestimated the holding power of PK screws. Just something I found interesting whether it crosses over to the cub slats or not.
    https://youtu.be/GRmLtRVfcGk

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    I figure I’m slow anyway , I would have built another RV if I was worried about 5 knots , or 5 kilos

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    Thanks that’s exactly why I was thinking plate nuts. All food for thought thank you for your input.

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    Thanks Ron for your input, I have purchased an IO 360 and a constant speed Whirlwind 84inch Stol prop hoping the performance will be good

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    skywagon8a's Avatar
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    Quote Originally Posted by Lowleveldevil View Post
    I’m concerned on chaffing the fabric leading edge at the attach points any ideas on mounting options for this leading edge system.
    You could stick some teflon tape to each slat bracket. I used this on the bottom of the wing trailing edge to prevent chafing of the fabric on the top of the flaps. It works. Stick it on before you drill the holes since the thickness could effect the accuracy of the holes in the curved leading edge.
    https://www.aircraftspruce.com/catal...?clickkey=6458
    N1PA
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  10. #10

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    The only way the slat brackets would abrade the leading edges would be if there was motion. If you have movement there you need to eliminate it. Teflon tape is unnecessary and is probably a bad idea. There’s no benefit to reducing friction there.

    The idea that slats carry load is interesting. Helio slats are different. I doubt mine carry much if any. They direct airflow. They energize the VGs. I think nut plates are a better attachment than sheet metal screws but it doesn’t appear slats stress the attachment so better isn’t important from a structural standpoint. That said, I’d probably do the same thing if I built another one.

    You’ll need to fully install the leading edges, position the slats to mark positions, then release the edges to install nut plates. Mine are fitted so the slat nose is flush with the bottom of the wing. Some guys lower the slats. I can make new hangers if I want to try it but I don’t see that happening. FWIW, I do have square fabric reinforcement patches at the slat hanger attachment locations.
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    Last edited by stewartb; 04-05-2021 at 08:29 AM.
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  11. #11

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    Re: slat gust locks. Post #296 on page 8 of the Wildcat Cub thread shows them. Mike added a longer stop screw so I can attach a UHMW disc with a wing nut to block the slat in the closed position. Simple and effective, but with 35s and 6” gear it makes me stand on my toes to reach. https://www.supercub.org/forum/showt...dcat-Cub/page8

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    tedwaltman1's Avatar
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    I riveted my hangars to the leading edge. PK screws does indeed seem too “lite.” I wish I had used nut plates. Good job in that regard Stewart!
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    In regard to placing the leading edge flush or 1/8” lower than the bottom of the wing...to my knowledge there is a lot of “I tried this placement” out there but no definitive aerodynamic study. I’d would love to see some well defined analysis with accurately measured results on slat leading edge placement. Mine are about 1/4” lower—seems to work very well.

    A friend and I continue to discuss varying ways to test different mount placements without making Swiss cheese out of the leading edge. No answer yet.
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    skywagon8a's Avatar
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    Quote Originally Posted by eskimo77 View Post
    The designer of the Helio Courier states that the slats when deployed on that airplane carry 64 percent of the aircraft's weight (12:45 mark on the video).
    That is an interesting comment. I think he misspoke. I can understand the slats enabling the wing to be able to provide 64% more lift in a certain situation. I can not see the structural strength in the slat attachment hardware being able to provide the strength to carry 64% more.

    I used to work for the two engineers who did the stress analysis on the wing of the Helio. Unfortunately, they are both not with us anymore for verification of Mr Koppen's statement.
    N1PA
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    I’ve heard Wayne Mackey has tried his slats lowered one inch and went back to 1/2”, but that’s second hand info. One long time slat pilot I know has tried flush and 5/8” down and he thinks 5/8” is probably better but the difference is subtle. Given his description I doubt I’d recognize the difference. I know I’m leaving a bit of slat capability unused but I do enjoy the part I’m familiar with.

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    Quote Originally Posted by stewartb View Post
    I’ve heard Wayne Mackey has tried his slats lowered one inch and went back to 1/2”, but that’s second hand info. One long time slat pilot I know has tried flush and 5/8” down and he thinks 5/8” is probably better but the difference is subtle. Given his description I doubt I’d recognize the difference. I know I’m leaving a bit of slat capability unused but I do enjoy the part I’m familiar with.
    Stewart -- How did you set the size of the exit area on your slat? Does your generation slat use the single through hole in the slat hanger with a bolt and nylon bump washer to limit the travel?

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    Excellent info Stewart, I might even rivet a small skin doubler to the back of the leading edge before platenuts

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    Another excellent post thanks again.

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    One must not forget the" holding power" of a good screw.
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    Original question of slat and flap. The one cub I know that is a basic piper design but added slats and fowler flaps... I think you would be beat to a pulp if you tried to take either from his plane, he likes them that well!
    I don't know where you've been me lad, but I see you won first Prize!

  21. #21

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    I think Keller Flaps improve the slat....with that said I have original style flaps, extended inboard and added three inches cord wise...when doing real world, back country landings in rougher terrain, I do NOT utilize the Slats to their full potential...I’ll typically land around a solid 35 in those conditions...which allows for some forward visibility and still a short landing...when I slow her down in the twenties, I am really nose high, making seeing touchdown spots more challenging...I think with the Keller flaps you can fly a bit slower but with a better deck angle...
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