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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’m 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’m concerned on chaffing the fabric leading edge at the attach points any ideas on mounting options for this leading edge system.
 
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
 
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’m the only one with nut plates. I thought I may remove my slats, too, but once I flew them? I don’t 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’ll never want to remove them.
 
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...
 
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
 
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
 
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/catalog/cspages/teflonantichafetape.php?clickkey=6458
 
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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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!
 
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.
 
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.
 
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.
 
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?
 
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 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...
 
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.
 
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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 it’s going as the airspeed drops out at 30 but as soon as the tail touchs the plane plops down on the mains and it’s 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
 
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 “pick a spot” and land on it.
So I added “fences” 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.
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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.
 
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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.”

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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