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Leading edge slats and Keller Flaps

More chord, better hinge geometry, and leading edge vents.

Sorry for the pic layout. I took snapshots of a video Bruce sent me in 2018.
 

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He runs out of fuel using them to climb, doesn’t have the aoa at take off to use them, and 15mph slower. He’s comfortable with the airplane for sure. I have heard a lot of the legend guys took the slats off. I would imagine you can get in much shorter than you can get out? He did say it was safer horsing around, that was the upside. Just passing along what he told me.


Sent from my iPhone using Tapatalk

If you are going to do high AOA climbs you are going to need a fuel pump or header tank higher than the carb. 1/4 Right tank on a stock cub can be a issue if you climb long and hard enough. I know more than one pilot that is avoiding slats, just depends on how you fly.
DENNY
 
There's a couple of those BCSC's in Fairbanks. One's got the double flaps, the other the later single with LE slots. Haven't seen the second one in action yet. Very unique and well built aircraft. None on floats as that's my interest.

Gary
 
More chord, better hinge geometry, and leading edge vents.

Sorry for the pic layout. I took snapshots of a video Bruce sent me in 2018.

Rev%203g.jpg
 
Nice! First one could have done a bit better not dragging the heels until speed reached. Second did good. He says 320'. In a regular Cub I'd have churned up the water with a few circles first but he didn't need to do much. My PA-12-180 consistently took 450-500' with 82/43, 25 gallons, 50# dog, 50# gear and me at 200 no wind. So that plane in the vids does real good.

Gary
 
Has anyone done a direct comparison between the "screw-on" exposed LE slats and the Dakota built-in slot? Performance and cruise drag in particular?
We compared same airplane with stock wing and Dakota Cub slotted wing and saw no difference in cruise. Installed Mackey slats on a Smith Cub many years ago and it slowed the airplane down in cruise a noticeable amount.
 
We compared same airplane with stock wing and Dakota Cub slotted wing and saw no difference in cruise. Installed Mackey slats on a Smith Cub many years ago and it slowed the airplane down in cruise a noticeable amount.
Thanks Steve, that is what I suspected the results would be.
 
Has anyone experimented with pinning down the current variant of slats for cruise flights to see if speeds can be increased?
 
If you are going to do high AOA climbs you are going to need a fuel pump or header tank higher than the carb. 1/4 Right tank on a stock cub can be a issue if you climb long and hard enough. I know more than one pilot that is avoiding slats, just depends on how you fly.
DENNY

Good observation. I would add if adding a header tank make sure it has provisions for drainage and/or is installed where it always feeds. A header installed with the feeds rearward is what caused my crash in a Thrush. It started and was fine on my self checkout runs, but when I put it into the takeoff attitude it was sucking water from the header (which had no sump drain). Ran fine to 300 ft. with predictable results afterwards.

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I absolutely agree with a header/pump for high AOA ops.
 

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Has anyone experimented with pinning down the current variant of slats for cruise flights to see if speeds can be increased?
During the days when leading edge cuffs were all the rage, some had more droop than others. Those with the bigger droop had higher drag, losing cruise speed. From what I've seen, most of these current screw onto the leading edge slats would resemble those high drag cuffs even if they were fastened closed. This because their leading edges project well below the lower surface of the wing regardless of the opening of the upper slot.

Since your construction hasn't yet started, why don't you discuss "in the leading edge" slats similar to Dakota's with the Legend people?
 
I have asked the speed loss question for several years whenever I find someone with a slatted cub. Many have not flown without them but those that have flown the same wing with and with out say it is a 7-10 mph difference even with the top closed. Skywagon8a comment is correct the lower the front of the slat the more drag. But even mounted flush with the bottom they still had a lot of drag. DENNY
 
Johnny,

The slats are open maybe 1/16" in cruise. Not a lot to gain by pinning them closed but it wouldn't be hard to do. My Cub can cruise 26/2600 at 100MPH. I don't do it now that it's broken in well. Too loud, the prop pulses on the wind screen are unnerving, and honestly the plane just isn't very comfortable to fly at that power setting. And it burns too much gas. I dial it back top 65% and enjoy the view. If I want to go fast I take the 180, but it has big tires so only does 145-150 mph. If I really wanted to go fast I'd put littles on it. It used to do 180 with those. Speed isn't my priority.

SB
 
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Johnny, are your wings standard Cub chord and length? Flaps standard or extended?
Standard length, square tips. I’m recalling flaps are extended about one bay, so about 15”, but I may be wrong on number.

EDIT: Standard chord. Legend’s competition Cub reportedly has modified/deeper chords and control surfaces
 
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To be fair, when discussing slats, you probably should factor in how modified from stock the wings are aside from slats. My wings are extended nearly 2’ each way, have a deeper chord, and the control surfaces have deeper chord. One of my neighbors has what appears to be a standard wing with slats. I’ll ask him how it compares to the Mackey SQ-18 he flies with regularly. I’m sure the SQ has the advantage because it has more than just slats, including 12’ flaps, but I don’t think those are Kellers. Plotting slat performance from the Mackey planes to the standard wings would define limits and variants in between those would establish a curve. Probably a predictable curve if anyone had the ability to test different planes in a useful way. Then you could consider Carbon Concepts slats, which I’m told are also different. There are too many variables that are reported anecdotally by different owners with different expectations, and essentially no factual data. While Tom tells of a standard wing owner installing and removing and says some Legend owners have done the same, I haven’t heard of anyone with an SQ-Rev variant wanting to do that. All those with planes like mine are smiling, or buying/building another one. That’s something to factor into your decision.

To the slat-slot comments earlier, I talked to a neighbor last night that has Dakota Cub slots. Those wings are standard Cub dimensions with standard Cub leading edge. To compare them to even an otherwise standard wing with slats added is apples to oranges. The slats enlarge the wing area and relocate the leading edge forward. The CG changes. Added drag is expected. Improved low speed performance is also expected. He confirmed that and made a comment that the slats he’s seen run at a high AOA to the point the rudder becomes ineffective. I’d never heard that, and it doesn’t happen on my plane, but again, my plane has several other mods. More food for thought.
 
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He confirmed that and made a comment that the slats he’s seen run at a high AOA to the point the rudder becomes ineffective. I’d never heard that, and it doesn’t happen on my plane, but again, my plane has several other mods. More food for thought.
Isn't your fuselage longer than a stock -18? If so, a stock sized rudder would have more authority due to the longer leverage arm. That could be the difference between what you've observed and what your friend observed.
 
Longer, yes, and that goes to what I said about more mods than just slats.

I was told the primary reason for lengthening the airframe was to provide better trim and elevator control when slow, so that likely is about the leverage. Subsequently my control surfaces are also enlarged. It may also be related to the size of the wing, or maybe those two things are one and the same. I don’t have an AOA problem or a weak controls problem. My plane is very comfortable to land within the 3-point AOA with 6” gear. I may be giving up some performance at that but it isn’t something I’m missing. But I don’t wring it out like some Instagram guys do.
 
I doubt that was a driving factor. We all balance nose heaviness with weight. Added length doesn't solve it. Even with my long airframe I have 40-50# shoved in back behind where the CG instructions suggest a 10# maximum placard. My engine mount is as short as it can be without modifying the firewall. Slats move the aft CG limit back an inch. I believe they should move the forward limit back as well. My plane's a handful to fly near the forward limit.

My nephew's Mackey SQ-12 airframe is extended further than mine. These things keep evolving.
 
Maybe for the guys who fill their tail posts with lead shot. I prefer to change my ballast seasonally and use the baggage compartment. What I really notice with the extended airframe is the tail weight. Empty tail weigh in level position is pretty typical Cub. Add fuel and the survival gear? My hangar scale only goes to 150#. My zero cargo/no passenger tail weight in three point exceeds that.
 
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There's a couple of those BCSC's in Fairbanks. One's got the double flaps, the other the later single with LE slots. Haven't seen the second one in action yet. Very unique and well built aircraft. None on floats as that's my interest.

Gary

Saw the 2nd one with the LE slots in the flaps tonight doing T&G's. Very conservative flying with 2 souls. Lots of slow flight in pattern but landings appeared to use only one notch of flaps - not much deflection. Maybe I missed something. No real STOL so might be just learning the aircraft's moves. Takeoff impressive for the amount of dirt blown back and noise. Tail low the gear lightens and folds in quick like a Helio Courier, but takeoff lingered somehow. Big tires - 35's I believe so AOA is max. It will improve as the pilot gains experience.

Gary
 
I believe the Rev 3 vented flaps only go to 30°. They make less drag and more lift than other flaps. I’m told there’s a learning curve. It sounds like that plane must have used Porter style gear? The airframes are built to use either Cub or Porter gear.
 
The plane I saw last eve had a odd gear - maybe these. Wanted to rock the wings some on the ground. I'll look closer today while it's parked to confirm style. Still a great performer and nice to see one locally.

Gary
 

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That's Porter style gear.

Anyone interested in the slats-Keller flaps combo should go to Instagram and search for xploringalaska. The blue and silver plane that's the star of the channel is a Mackey SQ-12 and the guy driving it knows how to fly it. I don't watch many airplane videos but that channel is one I follow.
 
Pics of the exciting new airplane here in Post #115 and 118. Hope the owner doesn't mind. If so I'll delete. Sure would be fun to learn to fly that. Edit: This aircraft at the factory> https://www.supercub.com/our-planes

Gary
 

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