Airfoils with nominal Clmax > 2.3 ?

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I understand that by modifying the camber of a good profile, very high Cl can be reached.
Usually this means unusable drag and large moments.
And very rarely there is any actual wind tunnel data (and then only for truly minor mods).

So, what are the tested airfoil above 2.3 Clmax (say at Re 2M) ?

The Selig family (S1223) comes to mind, but are there other (less exotic, "thick", non laminar et c.) airfoils in this class ?
 

Aircar

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The airfoil selected by Rutan for the canard of the 'production' Vari eze was the Glasgow University GU 25 -x-x section developed for a man powered aircraft by Prof. Nonweiler --that was the nominally highest Cl airfoil for low Re Nos until improved upon by John Roncz --can't recall the exact numbers off the top of my head but it was over 2.0 at the ReNo applying to the Vari eze at min speed . The Wortmann Fx 67 K MS 170 is another with increased camber to get a higher Cl max and Cl cubed/Cd squared value. Both should be on the airfoil database on the Illinois University 'catalogue' --someone else might be able to link to it, that airfoil with slotted and double slotted flaps was used on Formula One car rear airfoils in the mid eighties also.

On the Oshkosh videos posted by Karoliina last year John Roncz mentions his developing an airfoil with Cl max over 4 for a Scaled project --don't know if that was with VGs or any other details . Liebeck and Lissaman have both developed very high Cl low ReNo airfoils which have very unusual shapes --the Boeing 787 flap uses a Liebeck section (they are very much one point designs but that is OK for a flap that is retracted in cruise. )
 
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topspeed100

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Good point.I think the Vari-eze profile is this: UNIVERSITY OF GLASGOW GU25-5(11)8 AIRFOIL (gu255118-il) but Xfoil has a pretty low prediction for it.For the FX 72 MS 150 at WORTMANN FX 72-MS-150B AIRFOIL (fx72150b-il)Xfoil predicts about 2.1, not bad at all.I guess the 170 could outperform that, but I could not find it. May someone with Xfoil check its numbers ? Not an easy airfoil to build a wing, though, even if thicker than the S1223.
It depends what you are after..if you want to score high Cl at low drag. This foil has 190 best LD at Cl 1.8. I figure this is cool for very low hp output engine.

The Glasgow GU25 does not really shine in this respect ( low Cm ). Mach number for both is 0.01 ( albeit latter seems to miss it ). Increasing the Mach number to 0.1 at Cl 2.0 made the LD drop to 142. No affect on the other foil ( ? ).
 

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Topaz

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If you're simply trying to make a smaller wing, then you're being caught in a trap most of us fall into during the beginnings of our journey as aircraft designers. Small wing = high cruise for a given power (all else being equal), so we strive mightily for a small wing. Complicated flaps seem like too much, so we try to find the highest lift-coefficient airfoil we can.

Here's why that's a bad idea, and it's two-fold, and the two sides are related to each other: Climb and Glide.

Your climb rate (or angle) for a given installed power and takeoff weight is going to be influenced by a number of factors, but one of the largest is wing loading. In short, if you find your high-lift airfoil and build your small wing, you may well end up with an aircraft that can't climb very well (or at all), especially under high density altitude conditions (Read: "Hot and high"). Your easiest bet is to lower your wing loading with a larger wing area (adding span helps, too), which also means your wing doesn't need to work as hard at stall. Yes, cruise suffers.

Gliding???
"Hey," you say, "I'm not building a glider here!" Fact is, yes you are. Because one day, some day, sooner or later, the big greasy towplane you bolted to the nose of your airplane is going to go silent in-flight. Fly long enough, far enough, and it's going to happen. That's a fact. It's also a fact that you can't always have a suitable landing site directly underneath you. Which means you're going to have to glide to someplace suitable. An airplane that glides like a brick is terribly unsafe. The better your airplane can glide, the more options you have. Double the glide radius and the total area opened up for you to find a suitable landing site goes up by a lot more than double. Again, the solutions to this are lower wing loading and more span.

Span is generally limited by weight and aeroelastic effects (largely flutter in our part of flying).

It isn't sexy and it cuts back on the high-speed-for-power that you want, but the fact is that putting ultra-high-lift airfoil on your design will create more problems than it solves. If you want speed, it's better to find a low drag airfoil and spend your design time on cleaning up other areas of high drag on the airframe: engine cooling, landing gear, interference drag between components, carefully matching the pressure fields of the wing and fuselage, etc.
 

topspeed100

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If you're simply trying to make a smaller wing, then you're being caught in a trap most of us fall into during the beginnings of our journey as aircraft designers. Small wing = high cruise for a given power (all else being equal), so we strive mightily for a small wing. Complicated flaps seem like too much, so we try to find the highest lift-coefficient airfoil we can.

Here's why that's a bad idea, and it's two-fold, and the two sides are related to each other: Climb and Glide.

Your climb rate (or angle) for a given installed power and takeoff weight is going to be influenced by a number of factors, but one of the largest is wing loading. In short, if you find your high-lift airfoil and build your small wing, you may well end up with an aircraft that can't climb very well (or at all), especially under high density altitude conditions (Read: "Hot and high"). Your easiest bet is to lower your wing loading with a larger wing area (adding span helps, too), which also means your wing doesn't need to work as hard at stall. Yes, cruise suffers.
I did put some effort to think a solar/muscle powered plane and there my small AC foil seems to excel...214+ L/D...at 1.4 Cl..this was my 200 ft + spanning kite with minimum hp:s...like Wright's Flyer....still at 2.0 CL it has 170 L/D. For the fuselage part ( lifting body ) the L/D hits 230-240 in 2D.
 

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clanon

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IMHO the Selig 1223 is unbeatable (for lift that is)' the price Cd and horrific Cm close to that my own and the similar FX 73-CL1-152 ; just stepping on the 2.x CL max...i'll recommend fiddling with the Worthmann (but remember you'll need Laminar stuff):ermm:
 

Aircar

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Fly scared!- that is the right GU airfoil but I am sceptical to say the least of the extraordinary degradation of Cl/Cd at low ReNos --particularly since this airfoil was designed for man powered aircraft --a 30 to one variation of L/D from 50 000 to 1 million seems incorrect --the question was about tested performance so the X foil calculations might be somehow predicting massive separation that isn't there. Any tested figures for that airfoil or any others for Man powered aircraft @ their working ReNos ? (there must be published figures --Man Powered Flight by Keith Sherwin gives some MPA airfoil section curves to 300,000 from 700.000 showing at most a 50% increase inCd --the Gu25 -5(11)8 is actually the last thing in the book with a polar @ re 630 000 and Cl max 1.8 --maybe vortex generators are needed at lower Re No .
 

topspeed100

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Fly scared!- that is the right GU airfoil but I am sceptical to say the least of the extraordinary degradation of Cl/Cd at low ReNos --particularly since this airfoil was designed for man powered aircraft --a 30 to one variation of L/D from 50 000 to 1 million seems incorrect --the question was about tested performance so the X foil calculations might be somehow predicting massive separation that isn't there. Any tested figures for that airfoil or any others for Man powered aircraft @ their working ReNos ? (there must be published figures --Man Powered Flight by Keith Sherwin gives some MPA airfoil section curves to 300,000 from 700.000 showing at most a 50% increase inCd --the Gu25 -5(11)8 is actually the last thing in the book with a polar @ re 630 000 and Cl max 1.8 --maybe vortex generators are needed at lower Re No .
I think the 20% thickness like the in Cri Cri ( even thicker ) may contribute in smaller structural weight..I was able to get CL 2.1 ( with just 61 digits ) with 15% thick foil..this 17% gives just a tad over 2.0. Glasgow foil seem to deliver 123 L/D somewhere 5-7 degs AoA in 2D at reno 2 mio.
 
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Thank you for your comments, but please don't focus on L/D in this thread.
I'm just curious about the highest CLmax range actually reached by "normal" airfoils at Re 2M.
(btw "normal" airfoils always have a design point with workable L/D, usually the problem is more Cm)
 
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If you're simply trying to make a smaller wing, then you're being caught in a trap most of us fall into during the beginnings of our journey as aircraft designers. Small wing = high cruise for a given power (all else being equal), so we strive mightily for a small wing. Complicated flaps seem like too much, so we try to find the highest lift-coefficient airfoil we can.
I understand your point, but as you know wing loading is only loosely coupled with CLmax. Theorically you could design a large wing with a high (potential) lift airfoil and always fly it at a very low (or negative) aoa (L/D would be horrible, that's for sure).
As for high density and glide ratio, I guess it depends on the real world application.
For an ULM aircraft flying at 500 ft, those features are pretty useless.
For an executive jet they could make the difference to reach the strip or not.
 

topspeed100

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Thank you for your comments, but please don't focus on L/D in this thread.
I'm just curious about the highest CLmax range actually reached by "normal" airfoils at Re 2M.
(btw "normal" airfoils always have a design point with workable L/D, usually the problem is more Cm)
I hope you are correct.

I seem to hit the roof at 2.15 ClMAX at 12 degs AoA..in ReNo2mio..in 2D using 61 digits. I did get a 200+ L/D also at 5 degs AoA with 1.4 CL..in 2mio reno at 2D.

I intepolated several foil more in XFRL5.

I am also able to get super 4/180..it has thickness 18%, L/D180 and CL max 1.8 ( even ), Cm <-0.180...in 2 D 2 mio reno ( Cd 0.01 ).

...CL 2.0 at LD 150...only with flaps can I go 2.34 and beyond in CL max ( LD drops to 33 in 2D ).
 
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autoreply

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Thank you for your comments, but please don't focus on L/D in this thread.
I'm just curious about the highest CLmax range actually reached by "normal" airfoils at Re 2M.
(btw "normal" airfoils always have a design point with workable L/D, usually the problem is more Cm)
That's like asking "how high is high"?

The highest lift airfoil looks similar to an airliner with deployed flaps, relatively thin and very high camber. And yes, a very low L/D. Much like the first generation of aircraft in fact. A Liebeck airfoil can get close to Clmax=3 and yes, those are windtunnel tested.

I guess (mulling over) airfoils is the pet toy for many modern-day Nihilarians. That's not aimed at anybody in particular by the way, just an observation of the approach of many. Take a good, popular airfoil, apply flaps (or not) and spend the time on interference drag for example or a good slotted flap system. Having a wing that doesn't fall out of the sky with a few bugs on it would be a good start.
 
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That's like asking "how high is high"?

The highest lift airfoil looks similar to an airliner with deployed flaps, relatively thin and very high camber. And yes, a very low L/D. Much like the first generation of aircraft in fact. A Liebeck airfoil can get close to Clmax=3 and yes, those are windtunnel tested.

I guess (mulling over) airfoils is the pet toy for many modern-day Nihilarians. That's not aimed at anybody in particular by the way, just an observation of the approach of many. Take a good, popular airfoil, apply flaps (or not) and spend the time on interference drag for example or a good slotted flap system. Having a wing that doesn't fall out of the sky with a few bugs on it would be a good start.
Maybe more like "how high is high, considering there's a roof above ?"

I didn't know the Liebeck airfoils were actually tested, out of "maximum" theory, thank you !

Liebeck.jpg

Doesn't seem an extreme shape too, even if I guess it is way more sensitive to defects than the typical laminar sections.
 

topspeed100

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topspeed100

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That's like asking "how high is high"?

The highest lift airfoil looks similar to an airliner with deployed flaps, relatively thin and very high camber. And yes, a very low L/D. Much like the first generation of aircraft in fact. A Liebeck airfoil can get close to Clmax=3 and yes, those are windtunnel tested.

I guess (mulling over) airfoils is the pet toy for many modern-day Nihilarians. That's not aimed at anybody in particular by the way, just an observation of the approach of many. Take a good, popular airfoil, apply flaps (or not) and spend the time on interference drag for example or a good slotted flap system. Having a wing that doesn't fall out of the sky with a few bugs on it would be a good start.
Which one ? LNV109A doesn't come anywhere near 3.

LNV109A (lnv109a-il)
 

WonderousMountain

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Surprised nobody mentioned Gaw 1 or 2, but they've not had too much usage. The Leibeck airfoils are made off sound theory, but some of the more extreme seem to do better in laboratories. Most of the really high single element airfoils are very curved at the trailing edge, which does cause a price in drag. After around 2 it's better to employ a flap if you can. Thickness is your friend, a +20 percent foil can be a good compromise between drag and large lift.

Blessings,
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clanon

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Don't forget to check the Volmer Jensen's ~18% tapered to ~15 ; softest stall ;drooped LE ; VJ 23 alike and the ultralight from it : CFM shadow
The problem will be that it has to be re-engineered for lighter materials...
 

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Topspeed et al -- that link involves a model contest with ReNos in the in the low 100 000's at best -- I thought that the specified figure was about 2 million in a later post . It is true enough that most airfoils fall off a cliff edge below 500 000 or so but not all and the ReNo on the outer wings of modern sailplanes or tailsurfaces is often lower than this in climb -- using untapered wings and staying just above a critical Re limit is theoretically better (and the 'buggy' wing or behaviour with deflected control surfaces can invalidate a lot of the predictions as well . "Nihilarians" ? --must google that one --meaning pessimists or something?

This whole thread shows the value of variable geometry -in both wing size and section , to match the shape and size to the requirements -- in gliding the implementation of variable geometry has not been too successful because of things that are somewhat peculiar to soaring (no power operation allowed, disturbance of attention in transitioning and the feel of the aircraft , structural difficulties and the need for very low drag at high lift ) --the NEEDED wing at high speed is certainly very small compared to what we are stuck with to meet stall speed limits and the high Cl airfoils are also high Cm and high Cd which as Topaz notes are not suited to good cruise performance . Some type of retractable leading edge slat might be a worthwhile innovation ( say ,thinking of something in the nature of a tape measure ribbon as the slat and running along a tiny slot in the leading edge --rolling up in the fuselage .
Something to change the leading edge radius and camber might be most effective and surely should be possible without affecting laminar flow with modern materials .
 

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Doesn't seem an extreme shape too, even if I guess it is way more sensitive to defects than the typical laminar sections.
That's why all those "fantastic" airfoils aren't so fantastic at all. The above basically means that it'll drop as a brick after a few bugs have kissed your LE. Been there, done that (in rain). Bad idea.
This whole thread shows the value of variable geometry -in both wing size and section , to match the shape and size to the requirements -- in gliding the implementation of variable geometry has not been too successful because of things that are somewhat peculiar to soaring (no power operation allowed, disturbance of attention in transitioning and the feel of the aircraft , structural difficulties and the need for very low drag at high lift ) --the NEEDED wing at high speed is certainly very small compared to what we are stuck with to meet stall speed limits and the high Cl airfoils are also high Cm and high Cd which as Topaz notes are not suited to good cruise performance . Some type of retractable leading edge slat might be a worthwhile innovation ( say ,thinking of something in the nature of a tape measure ribbon as the slat and running along a tiny slot in the leading edge --rolling up in the fuselage .
Something to change the leading edge radius and camber might be most effective and surely should be possible without affecting laminar flow with modern materials .
So why not start a separate thread about it? I never saw much use for it except for the traditional applications, but the more I think about it, the more sense it makes for sailplanes.
 
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