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Slots -if it works, why not more?

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Slots -if it works, why not more?

Post  wha-tah-hey on Thu Oct 20, 2016 11:05 am

Rummaging through the internet, I ran across an article about the 1/2A Dancer.
The pic below is captioned: "The slot makes the flat wing act like a proper airfoil. Simple."
If so, why isn't a slot on every plate wing?

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Slots?

Post  RK Flyer on Thu Oct 20, 2016 12:55 pm

Hard to think that something that small would act like a second wing!

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Re: Slots -if it works, why not more?

Post  KariFS on Thu Oct 20, 2016 1:10 pm

Maybe because building or making an ordinary airfoil is simpler and it's also more durable? That is an interesting piece of engineering though.
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Re: Slots -if it works, why not more?

Post  wha-tah-hey on Thu Oct 20, 2016 1:56 pm

I dunno - plate wings are quick, simple and pretty durable.
If it were an essentially simple thing to add slots to the profusion of barely manuverable profile plans available (or easily drawn up from 3-views, rubber model plans, etc.) it'd be a real boon to someone (me!  Very Happy ) who'd like to build a fleet of worthwhile 1/2As quickly.
Maybe it takes engineering knowledge to design, maybe each wing might need different specs, maybe only works on 1-piece wings - who knows? Huh...
I'll bet someone on the forum could tell us.
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Re: Slots -if it works, why not more?

Post  KariFS on Thu Oct 20, 2016 2:15 pm

Yes, plate wings are durable but I can imagine that slot thing will break easily.  

Not sure what is the science behind it... The little strip probably creates turbulence and it in turn will help to create a better vacuum above the wing. This in turn would cause better lift with a smaller angle of attack, just like a "proper" airfoil. Maybe Smile

But on the other hand, sanding an airfoil into a 1/4" slab wing is quick and easy to do and almost guaranteed to work, so not many people are looking for alternatives.

It would be interesting to see this type of wing in action. Maybe even on a free flight model Huh...
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Re: Slots -if it works, why not more?

Post  wha-tah-hey on Thu Oct 20, 2016 2:50 pm

I know nothing of aero-engineering but the AoA on Dancer is considerable with the slots.

As for fragility, on a low or midwing (as most profiles are) there wouldn't be the crash risk seen here.
MOF, maybe the slot wing (?) could tie to the fuselage to lessen inertial damage to the slot assy in a crash.
As I said, I dunno.
And as you said, interesting to see.
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Re: Slots -if it works, why not more?

Post  roddie on Thu Oct 20, 2016 4:33 pm

I agree with Kari's thinking, on how it works. It's a bit fugly though.. and would need to be sealed/painted before assembly. Lift is good.. but for stunt; the wing should be symmetrical. "Flat" is at least symmetrical. If there were top "and" bottom L/E slots.. well, that would be interesting.. but no less complicated than say; a diamond-airfoil and covering would be to construct. Considering a constant-chord wing; how about gluing L/E stock O/C to a sheet-wings' leading-edge? There'd be a lot of turbulence with the blunt 90-degree rear-edges.. but might that be advantageous? Maybe back-up that L/E top/bottom with T/E stock; feathered-down smooth with the sheet-wing? Then if you're really curious... build some same-span sheet-wings having shorter chords.. but keeping the as-per-plan CG unchanged.. which can be measured from the L/E.

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Re: Slots -if it works, why not more?

Post  wha-tah-hey on Thu Oct 20, 2016 4:50 pm

The point prompting my question is the statement that the slot, apparently to some significant degree, allows a flat plate wing (the easiest thing to build) to emulate a full airfoil.
Sheet wing, profile 1/2A is about the simplest thing going but few are what one would call capable stunters.
Looks like here's a simple solution if slotted wing design IS simple.
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Re: Slots -if it works, why not more?

Post  Mark Boesen on Thu Oct 20, 2016 5:00 pm

At that point, i'd consider a 'built-up' wing, as the time to build wouldn't be that much more and performance would be significantly better.

Years ago i designed a 1/2a Nobler with flaps in an attempt to pick up an extra 20-25 points flying a flat wing plane in 1/2a stunt contest.

Lol, it was a big waste of time, i could of built a constant cord wing without flaps in a lot less time and fly circles (?) around the flat wing!
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Re: Slots -if it works, why not more?

Post  Mark Boesen on Thu Oct 20, 2016 5:09 pm

wha-tah-hey wrote:I know nothing of aero-engineering but the AoA on Dancer is considerable with the slots.

As for fragility, on a low or midwing (as most profiles are) there wouldn't be the crash risk seen here.
MOF, maybe the slot wing (?) could tie to the fuselage to lessen inertial damage to the slot assy in a crash.
As I said, I dunno.
And as you said, interesting to see.


I see where this would generate lift, but what about outside maneuvers?
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Re: Slots -if it works, why not more?

Post  pkrankow on Thu Oct 20, 2016 5:45 pm

Why do I want to make that into RC .049?

Slots work well, but must be carefully engineered and evenly constructed. In stunt it has been determined that elimination of slots makes for more stable flight.

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Re: Slots -if it works, why not more?

Post  wha-tah-hey on Thu Oct 20, 2016 7:30 pm

The caption notes only "acting like a proper airfoil" and the article says "A unique feature of the Dancer is use of a leading edge slot to enhance lift and stall characteristics of the flat airfoil of the wing."
Which I thought, since it also works inverted, to imply some useful "stuntability".
But remember, I don't know. Popcorn


Last edited by wha-tah-hey on Sat Oct 22, 2016 9:55 am; edited 1 time in total
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Re: Slots -if it works, why not more?

Post  JPvelo on Thu Oct 20, 2016 8:14 pm

A KFM airfoil acts like  traditional airfoil and is a cinch to build. I have one on my carrier plane and it's almost impossible to stall.
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Re: Slots -if it works, why not more?

Post  PeterJGregory on Fri Oct 21, 2016 2:01 pm

It's like a jib's effect on the sailboat's main - creates a slot between the sails, speeds air over the main.
https://www.youtube.com/watch?v=xivue7RrbGw
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Re: Slots -if it works, why not more?

Post  fredvon4 on Fri Oct 21, 2016 2:10 pm

With the first photo I assumed the "slot" was same angle as flat wing

But looking at the side view I see 2/3 things

The Angle of attack (AOA) of the wing is very positive relative to the thrust line, and the stabilator/elevator is at zero AOA

The included "slot" appears to have a very negative AOA relative to the main wing AND the thrust line

I have a few slab wing ideas and may replicate this to see what it does for aerobatic maneuverability for a plain jane slab NARROW chord wing

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Re: Slots -if it works, why not more?

Post  wha-tah-hey on Fri Oct 21, 2016 2:23 pm

Fantastic, Fred - I suspect others have tried a slot, but I didn't find anything about it's use on a more common sheet wing.
Possible variations in slot height, relative AoA, slot chord and who knows what (not me) are too daunting for me to experiment with. I don't have a clue whether there's math and engineering that allows direct design.
I've been hoping some industrious fellow would take the bit in his mouth and run with it.
Please let us know what you discover!
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Re: Slots -if it works, why not more?

Post  roddie on Fri Oct 21, 2016 4:02 pm

wha-tah-hey wrote:Fantastic, Fred - I suspect others have tried a slot, but I didn't find anything about it's use on a more common sheet wing.
Possible variations in slot height, relative AoA, slot chord and who knows what (not me) are too daunting for me to experiment with. I don't have a clue whether there's math and engineering that allows direct design.
I've been hoping some industrious fellow would take the bit in his mouth and run with it.
Please let us know what you discover!

I second that Terry. Jim's "KFm-airfoil" example is the first I've ever seen. It's a wild concept! I'd still like to find-out whether it could be simply-applied to a zero-incidence sheet-wing, to produce symmetrical turbulence above and below.

When you think about it.. flat/sheet-wing models fly fast.. even with a mild engine. There's little turbulence to grab air and slow them down. The elevator is sensitive.. because it's doing double-time. That leaves less time and space for maneuvers.. in my way of thinking. The elevator-inputs are actually stabilizing the CG.. Huh... .. from a point furthest from it.

I think that's why most sheet-wing C/L designs are difficult to fly a pattern with.

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Re: Slots -if it works, why not more?

Post  pkrankow on Fri Oct 21, 2016 4:22 pm

KFm airfoils work pretty good in foam on 'lectric rc.

Phil
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Re: Slots -if it works, why not more?

Post  getback on Sat Oct 22, 2016 9:50 am

It says FOR THE TINDERFOOT , MAN ck. out that off set in the rudder 3/4" affraid that should keep some tension on the lines . Interesting but i think i will pass have enough not built planes and things now Airplane
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Re: Slots -if it works, why not more?

Post  wha-tah-hey on Sat Oct 22, 2016 10:08 am

I've seen plasticor stunt trainer wings with one or more staggered layers which I guess work as a KFm-type airfoil.
But I'm still hoping someone with technical knowledge of slot design will pop in and explain the black arts involved.
It seems a simple matter to add a slot during a build or even to an existing sheet wing if the aerodynamic principles don't require a supercomputer to design.
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Re: Slots -if it works, why not more?

Post  bamboozler on Sun Oct 23, 2016 11:46 pm

fredvon4 wrote:

...
The Angle of attack (AOA) of the wing is very positive relative to the thrust line,  and the stabilator/elevator is at zero AOA

The included "slot" appears to have a very negative AOA relative to the main wing AND the thrust line

...


+1
I noticed these things too right away, seems like the plane would have counteracting forces.
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Re: Slots -if it works, why not more?

Post  wha-tah-hey on Tue Oct 25, 2016 7:47 pm

Looking over the article, I realized the author's remark about acting like a proper airfoil most likely refer to only a flat-bottom airfoil.
Still, if true, a slot on the bottom should also work similarly.
Question is: does the slot's AoA as shown depend on the wing's AoA or would it be the same for a flat wing?
Any designers out there who can help?
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Re: Slots -if it works, why not more?

Post  crankbndr on Tue Oct 25, 2016 9:48 pm

Not to be too snippety but your talking about angle of incidence, angle of attack is related to airflow.
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Re: Slots -if it works, why not more?

Post  wha-tah-hey on Tue Oct 25, 2016 10:02 pm

Not to be argumentative, crank, but they seem to be pretty much the same:
http://www.dictionary.com/browse/angle-of-incidence
angle of incidence
noun
1.
the angle that a line or beam of radiation makes with the normal to the surface at the point of incidence
2.
another name for angle of attack
3.
Also called rigging angle of incidence. the angle between the chord line of an aircraft wing or tailplane and the aircraft's longitudinal axis



Last edited by wha-tah-hey on Wed Oct 26, 2016 9:06 am; edited 1 time in total
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Re: Slots -if it works, why not more?

Post  crankbndr on Tue Oct 25, 2016 10:47 pm

Angle of incidence is set in design and build and not changeable, attack is controlled by the pilot in flight.
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