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Thread: Leading edge slats and Keller Flaps

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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. Iím 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. Iím concerned on chaffing the fabric leading edge at the attach points any ideas on mounting options for this leading edge system.

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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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    stewartb's Avatar
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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 Iím the only one with nut plates. I thought I may remove my slats, too, but once I flew them? I donít 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. Youíll never want to remove them.
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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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    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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    stewartb's Avatar
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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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    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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    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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    stewartb's Avatar
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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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    TurboBeaver's Avatar
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    One must not forget the" holding power" of a good screw.
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    aktango58's Avatar
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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!
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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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    aktango58's Avatar
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    I just got done ferrying a cub with Keller Flaps and Slats. I have never flown a plane with either flaps or slats. My comparison are squared off wings and stock wings, so please understand my experience with the mods is limited.

    First thing I noticed was the feel of the flaps at the handle was slightly different. No big deal, but just an interesting aside.

    The plane flies incredibly slow, lands short and takes off in almost nothing. We had a whole six or eight knots of wind, and with 30 gallons of fuel and me, hundred pounds of gear in the plane I was off in 100' or less. Landing is about 150' without heavy breaking or trying to drop it in in a stall.

    I finally got comfortable enough that I could look at the airspeed. I was on final at 30 mph. The plane was flying well, but at that speed the controls are mushy- wishing for deeper chord ailerons for sure. A little puff of wind, 3 KTS even, and the plane would balloon 10' in the air- but it never wanted to stall out or quit flying.

    The trim really needs to be limber, as you slow down you need to keep rolling forward trim in, lots of trip.

    My touchdowns were gentle and docile. It never felt like I had pushed the wing over the edge to a stall. I think I was down to 25 mph and she just stayed flying.

    I got eight take offs and landings in the plane. The last one I got to go out totally light with lower fuel, (180 lbs), and that was the chance I could measure take-off distance. The previous take offs were longer, but had heavy fuel, never did it feel like I was using lots of runway.

    My airspeed suffered with the mods this plane had. She was slow as a J-3. That said, if I wanted to go into little bitty places with a cub, I would be investing in slats and Keller flaps!!


    After a night's sleep I remembered some other things to mention: First let the plane slow down before putting on the flaps, lots of stress on the wing with that much flap hanging down... I waited until under 60, and tried for under 50. Leave the last notch until short final- when ever I pulled the last notch the plane would tend to drift left, this was especially apparent on take off. With the amount of lift that wing was producing, and the very slow speed, all the left forces just sucked the plane sideways- not a quick turn the Maule will do to me. Takes lots of right rudder, and I mean way more than I am used to.

    Again, none of it was bad, but just different, and worth practicing before you depart for a super short narrow place.
    Last edited by aktango58; 05-07-2021 at 09:26 AM. Reason: added more information
    I don't know where you've been me lad, but I see you won first Prize!
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    After a night's sleep I remembered some other things to mention: First let the plane slow down before putting on the flaps, lots of stress on the wing with that much flap hanging down... I waited until under 60, and tried for under 50. Leave the last notch until short final- when ever I pulled the last notch the plane would tend to drift left, this was especially apparent on take off. With the amount of lift that wing was producing, and the very slow speed, all the left forces just sucked the plane sideways- not a quick turn the Maule will do to me. Takes lots of right rudder, and I mean way more than I am used to.

    Again, none of it was bad, but just different, and worth practicing before you depart for a super short narrow place.[/QUOTE]

    I have about 65 hours now in the Monster Cub with 20 on wheels and have noticed the drift as well at slow speeds when below 30 mph just before touch down. Not sure how slow below 30 itís going as the airspeed drops out at 30 but as soon as the tail touchs the plane plops down on the mains and itís done flying. To get the plane this slow you are well behind the power curve carrying moderate power and there is no float once you chop the power, it mushes in with directional control only effective with strong rudder input. Very different than my stock Cub with P STOL flaps which will still float a little with power off and tail wheel touching first landings.
    LiteCub

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    Hang it out there...

    *Not a cub*
    With full flaps, and very slow (20-25) hanging on the slats, I was seeing drift as well.
    it was enough that I couldnt ďpick a spotĒ and land on it.
    So I added ďfencesĒ to the ends of the flaps and added VGs to the flap cove.
    No more drift, now I can pick a spot and be accurate.
    Click image for larger version. 

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    Had to install rear view mirrors on my plane. Backs up to land!
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    Best. Combo. Ever.
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    aktango58's Avatar
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    Quote Originally Posted by stewartb View Post
    Best. Combo. Ever.
    How is she on skis?? If it moves it flies?
    I don't know where you've been me lad, but I see you won first Prize!

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    stewartb's Avatar
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    No ski flying until late February-ish. I still need to figure how to attach to TK-1 gear but I think welding Trick Air brackets can be done, especially if I scallop the fixture bases to keep welds away from bolts/nuts.

    I bought Cubpilot2’s 2250s knowing they’re on the small side for exploring, but with two new hips I have no business looking for places to get stuck so these will be good for cabin trips, lake landings, etc, and the now that’s all I want. I still have 3600s on the Cessna if I need more. For me, Cub skis are toys, not tools. I think I’ll have adequate power to overcome penetration ski drag and if I like these I’ll probably spring for 2500s in the future. It’s all about having some fun.
    Last edited by stewartb; 11-27-2021 at 03:59 PM.
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  29. #29

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    Darin Hart @ Legend Cub reported to me this week that they cut back the slats approximately 24” from wing roots (removed from the propwash area) on their MOAC builds and found effectiveness of slats about the same but picked up “about 4-5 mph in cruise.”

    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
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  30. #30
    stewartb's Avatar
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    My slats begin 16” from each wing root. It makes fueling a non issue.
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    stewartb's Avatar
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    Are they using electric trim on the MOAC? If you can add it? It's worth doing. Especially when used with a 2-speed trim controller.
    Last edited by stewartb; 01-14-2022 at 12:28 PM.
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    Also, Darin reported they install slats solely via nut plates.
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    Am starting to question the wisdom of both slats & PStol flaps for our MOAC build. I have some time to think about it, as we don't start working on the wing until August. My landings are done in a largely flat deck angle, and the plane will also be on skis and floats. I don't hang on the prop. The PStol flaps make sense to me for my flying style, but the slats? Wouldn't they largely be dormant unless my deck angle was higher or I was in a turn (moose stalls)?
    J

  34. #34
    skywagon8a's Avatar
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    Quote Originally Posted by JohnnyR View Post
    Am starting to question the wisdom of both slats & PStol flaps for our MOAC build. I have some time to think about it, as we don't start working on the wing until August. My landings are done in a largely flat deck angle, and the plane will also be on skis and floats. I don't hang on the prop. The PStol flaps make sense to me for my flying style, but the slats? Wouldn't they largely be dormant unless my deck angle was higher or I was in a turn (moose stalls)?
    J
    My 2 cents ........ skip the slats, but do install the nut plates since they go under the LE skin. That way you'll not feel any pressure to do it now, particularly since your description of use doesn't appear to call for them.

    Remember the purpose of slats is to control the boundary layer separation at the trailing edge of the wing at high angles of attack while improving the lift characteristics at low speeds. This is also what the PStol flaps do without the high angle of attack.

    If you have the option of installing longer than stock Cub flaps ....... do it. The longer the better. You'll not be disappointed. I love my double length flaps. If they were PStols I would like them even better.
    N1PA
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  35. #35
    BC12D-4-85's Avatar
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    I'd like to hear from anyone that's flown Helio Couriers on floats. They do well on conventional gear with LE slats and log flaps at high AOA. Do the slats significantly add to performance on floats? Not sure how to really tell w/o tying them up and testing. Floats can limit AOA on the water.

    Gary

  36. #36
    skywagon8a's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    I'd like to hear from anyone that's flown Helio Couriers on floats. They do well on conventional gear with LE slats and log flaps at high AOA. Do the slats significantly add to performance on floats? Not sure how to really tell w/o tying them up and testing. Floats can limit AOA on the water.

    Gary
    I haven't flown a Helio on floats. But, I did have a side by side competition with one flown by a long time Helio owner. I was flying the Twin Bee. We did side by side take offs on land and water as well as landing over an obstacle to a stop on water. And a standing start race to 1000 feet. In all cases the Helio came in second to the Twin Bee. In the race to 1000 feet, the Twin Bee was climbing so fast, I went to 1200 feet and back down to 1000 where I was waiting for the Helio to arrive. There were two people in the Twin Bee and one in the Helio.
    N1PA
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  37. #37
    mvivion's Avatar
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    Quote Originally Posted by eskimo77 View Post
    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
    Years ago, I asked Wayne Mackey, who created these slats and did all the original flight test about attach methods. He laughed and said his first set were very solidly attached, but he discovered that these slats exert very little force to the attach points. If I recall, he somewhat jokingly said you could almost attach them with tape.

    Pretty amazing devices. The Helio slats are a very different device, since they retract to form the LE of the wing, unlike these. So, speed penalty is considerably reduced/eliminated. But, that means structure….

    MTV

  38. #38
    Steve Pierce's Avatar
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    All the MOACs I have seen have the slats and I would think if they didn't work they wouldn't install them. Also per conversations with Randy Goza who worked with Mackey and is a pilot who's opinion I trust, he said the slats compliment that P-STOL flaps and vice versa. My experience with slats and slots, they are fun to hang on and play with in constant wind but they really shine when loaded. The airplane is rock solid even when slow and doesn't feel like it is about to come out from under you.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
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  39. #39
    skywagon8a's Avatar
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    Quote Originally Posted by eskimo77 View Post
    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
    It's always interesting to listen to aviation pioneers speak. I do have to respectively disagree with Otto Koppen on his premise that differential ailerons do not improve aileron performance. I looked up the Helio TC and found the ailerons have equal 20 degrees up and down travel. It was also mentioned that there are two sets of interceptors on the wing, of which I was unaware. I thought there was only one. One person in the audience mentioned that he had disabled one set of interceptors and found no difference in roll control. There is also a picture of the two sets of interceptors in the up position. The inboard interceptor is in front of the flap and the outboard one is in front of the aileron. The purpose of the interceptor is to dump lift over that portion of the wing. Thus when operating in conjunction with the aileron it improves the down authority of that aileron by dumping lift over that portion of the wing. The interceptor which is not in front of the aileron has no effect whatsoever on that aileron's authority. It is well known that differential aileron control has positive effects on roll control along with the reduction of adverse yaw. Perhaps had he used differential ailerons, he would have been able to eliminate the interceptors altogether?

    I also believe that he misspoke when he stated the slats carry 64% of the aircraft's weight. It is more likely the slats improved the lifting capacity of the wing by 64% at certain angles of attack. Even that number seems high, but I can't speak to that.

    He used to have his Yankee maintained here at the Plymouth airport. I used to work for the two engineers who did the engineering stress analysis on the Helio's wing before they designed the Twin Bee at the airport where the original Helio factory was located in Canton Mass. http://www.airfields-freeman.com/MA/...tm#bostonmetro The Twin Bee was built in that back left hangar in the photograph.
    Last edited by skywagon8a; 06-24-2022 at 07:09 AM.
    N1PA

  40. #40
    skywagon8a's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    All the MOACs I have seen have the slats and I would think if they didn't work they wouldn't install them.
    How many of those have been installed due to the actual performance improvements having been proven to the owners? OR have they been installed just because "every one installs them" and/or "I spent the money, so of course they are an improvement"?

    Many alterations are done "just because". I'm not saying the slats do nothing, because they do. But are they needed in all applications?
    N1PA
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    Replies: 86
    Last Post: 03-30-2014, 04:05 PM
  4. Leading edge slats ?
    By knucles in forum Cafe Supercub
    Replies: 26
    Last Post: 10-30-2012, 05:01 PM

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