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Simple Slats....Maybe

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StarJar

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Mulling over an ultralight I want to design, I really wanted to use full span slots, or even better, slats. The slots were attractive, because they are so much more do-able than slats. Right? But like a spoiled brat, I kept thinking about slats.

Then, one day, I had an idea. I did some research, and some testing on JavaFoil (once I figured out to enter in slats/slots).

So, the idea is that the cruise-angle air closes the slot (at the top), and the slow- flight air opens the slat, by blowing up through it, and pushing at a more direct angle below the pivot.

There would be a single pivot-point positioned where the differences in pressure, acting on the LE slot-element or curved plate, would change the position of the plate when the angle of attack reached the desired angle, (about 10 degrees AOA)

The bottom would always have a gap, but at least the top will block the flow of air, up through the slot.

An aditional possibility, is that that the element could be shaped to create a leading edge droop (not shown), when the slat is open, but go back to normal when the slot is closed. You could have about a 10degree droop, although it would be for a small portion of the leading edge.

When i first started writing this post, I thought a pivot at the bottom would work, but in reading my own writing, I realized that the pivot would have to be farther up, because there still will be air acting on the front of the plate, even at higher AOA's. But the air trying to push up through the slot, and the relative wind hitting more directly on the lower shape of the plate, should allow it to work, as described.

Opinions, questions, ideas for improvement, or changes, or things I am not seeing, are welcome.

All I've done so far, is tested a few shapes on Java Foil, basically to see what kind of Max CL is possible, for slots in general. I found that with 10 degrees of full span flaps (flaperons) I could get about a 2.3 Max Cl, at 15 deg. AOA. At 22 deg. it started to peak out at 2.5 Cl. This was a full-wing run with an AR of 5.

I would love to get slat cruise-performance without all the difficulty normally MMMM.JPGinvolved with them.

If anyone is interested trying the idea also, let's get together and share notes. I'm not interested in a patent at this time.

PS I had some better drawings, with longer slats, that contoured with the wing better, but somehow they didn't get saved on my Turbo Cad:depressed.
 
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Birdman100

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the question is how much drag would you save in that closed configuration compared to open? The edge of the slat would ruin laminar flow.
I wonder if that would function as you proposed... above the plate is high velocity and low pressure region-actually right there is the lowest p. around the airfoil, I think it would make it opened all the time.

I found that with 10 degrees of full span flaps (flaperons) I could get about a 2.3 Max Cl, at 15 deg. AOA. At 22 deg. it started to peak out at 2.5 Cl. This was a full-wing run with an AR of 5.
Note that JavaFoil often overestimate CL max!

I'm not interested in a patent at this time.
As for the patent it may be late for that once you show your idea publicly. We had some discussion here.
 

Dewey

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the question is how much drag would you save in that closed configuration compared to open? The edge of the slat would ruin laminar flow.
I wonder if that would function as you proposed... above the plate is high velocity and low pressure region-actually right there is the lowest p. around the airfoil, I think it would make it opened all the time.



Note that JavaFoil often overestimate CL max!
I don't know of many ultralights that use laminar airfoils.
 

Birdman100

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I don't know of many ultralights that use laminar airfoils.
Nobody mentioned that. But so called turbulent airfoils still have some laminar flow, that extend to roughly 35-40% chord. Reducing that BL to 3% where the edge of the plate is would increase drag for up to 50%! Slightly?

its not important how we call these airfoils it matters what happens and what consequences are
 

StarJar

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the question is how much drag would you save in that closed configuration compared to open? The edge of the slat would ruin laminar flow.
I wonder if that would function as you proposed... above the plate is high velocity and low pressure region-actually right there is the lowest p. around the airfoil, I think it would make it opened all the time.
Note that JavaFoil often overestimate CL max!
As for the patent it may be late for that once you show your idea publicly. We had some discussion here.
The closing would be aided by the all the pressure, on the LE, similar to normal slats. But I will agree that it is not exaclty the same force as on a current slat. Also the bottom should be designed so a vaccum develops in the gap by bernoulli principle.

The edge could be very thin or bevelled to match the wing, to minimize flow disturbance, hopefully.

On JavaFoil I was using a healthilly cambered airfoil, and my figures are kind of abstract without knowing the original CL max of the airfoil, but IIRC it was about 1.7 for the AR=5 wing annalization.
 

Birdman100

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StarJar, seemingly someone invented it already:

cub-slat.jpg cub-unstallable.jpg

"A closer look at Backcountry's castering slat, which changes position with the angle of attack of the wing to achieve impressively low minimum speeds. This is standard on the Mackey SQ2 and optional on its standard Super Cub. These slatted wings are also available for installation on certificated Super Cubs."
 

StarJar

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@Birdman100- Ok thanks for pointing that out. I am going to see if I can learn more about them. Hope they are not patented. Anyway I don't want to sell them, i want to make them,keep them, and use them......and then burn the airplane when I'm done. :grin: (maddness)
 

Dan Thomas

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I wonder if they're using any means of damping to prevent flutter. Or would flutter be an issue?

Dan
 

StarJar

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I wonder if they're using any means of damping to prevent flutter. Or would flutter be an issue?
Dan
I think at the higher speeds, they would always be pushed back solid against the wing.
Edit, hmm. i see your point, they are so light, free,and 'unbalanced', it seems like it could occur at low speed. Maybe they are pushed back solid in the open position? Transition, may be the place to look out for.
 
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SpainCub

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Hi all, looking that the thread and the ideas and solutions already in practice, I was wondering if anyone has a reference in comparing the differences in performance in an airfoil designed around Slats or and airfoil which Slats are added on to it.
 

revkev6

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aside from the flutter issues, unless the two slats are connected I would be very scared of individual blown slats. I can remember all the early incidents that corsairs had with blown flaps coming up/down asymmetrically causing crashes.
 

StarJar

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aside from the flutter issues, unless the two slats are connected I would be very scared of individual blown slats. I can remember all the early incidents that corsairs had with blown flaps coming up/down asymmetrically causing crashes.
As far as flutter, don't forget that the faster the aircraft goes, the more solidly they will be be held shut against the wing.

Are talking about assynetrical flaps, or slats on the Corsair? If a flap deploys unevenly, you've got an instant nightmare. But the slats do no not change the lift of wing a whole lot. The high lift comes only when the nose starts going way up.
I believe the Helio Couriour's slats pop out individually, and even when not simultaneous, is apparently no big deal. (However, the original test pilot probably does deserve the Golden Underwear award.:gig:)
 

revkev6

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As far as flutter, don't forget that the faster the aircraft goes, the more solidly they will be be held shut against the wing.

Are talking about assynetrical flaps, or slats on the Corsair? If a flap deploys unevenly, you've got an instant nightmare. But the slats do no not change the lift of wing a whole lot. The high lift comes only when the nose starts going way up.
I believe the Helio Couriour's slats pop out individually, and even when not simultaneous, is apparently no big deal. (However, the original test pilot probably does deserve the Golden Underwear award.:gig:)
vought corsair has a blown flap.

lets just imagine worst possible failure mode I can come up with off the top of my head..... wing ices a bit and the slat sticks or they wear and stick or they corrode and stick.... you are landing, the slats do not deploy. just before flare one deploys... you try to pick up the wing with aileron and you stall the dropped wing sending you cartwheeling into the runway....
 

StarJar

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vought corsair has a blown flap.

lets just imagine worst possible failure mode I can come up with off the top of my head..... wing ices a bit and the slat sticks or they wear and stick or they corrode and stick.... you are landing, the slats do not deploy. just before flare one deploys... you try to pick up the wing with aileron and you stall the dropped wing sending you cartwheeling into the runway....
Ya, I can see how you are saying if one was held shut, that could be a problem. You might not realize it on a high wing, untill one wing stalled. Something to think about and overcome, perhaps mechanically as you said.
I am interested in using them on a low wing ultralight design, so I should be able to see them well. I'm mostly thingking of very small slow planes, trying to get the wing area down a bit.
 

revkev6

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This is why we do a preflight before every flight.
hence my "icing" scenario..... not exactly that common in the type of planes we are discussing but relevant.

this is why you need to design for failure modes that don't kill you. all you need to do is connect the two slats together so they either both blow or both stay shut... problem solved
 

akwrencher

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This is probably a stupid question, so don't laugh, but what a bout controling them manually? Flaps are manual, and work fine. would negate the worry of the failure modes mentioned I would think.......
 

StarJar

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This is probably a stupid question, so don't laugh, but what a bout controling them manually? Flaps are manual, and work fine. would negate the worry of the failure modes mentioned I would think.......
I ain't laughin. Wouldn't be much harder than cross linking them. But on my low-wing UL design, I'm inclined to try letting them blow in the wind, but (extra) cautiously at first.

There was a slat called a Maxwell slat (1940's), that looked similar to these but was manually deployed. It also had a bottom plate that unfolded to fill the bottom gap. A torque-tube, manual deployment, like this, may be simpler, than the ones that use internal rails, and springs IMO. (Helio and perhaps Rallye)
 
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