candidate for magic airfoil section?

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topspeed100

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Funny FX-73 ( reflexed ) is closest to the foil that I drew intuitively for the small plane I have on avatar.

or FX 84 http://www.worldofkrauss.com/foils/765

Thickest point is not 50% but less tha 40%..this could be maneuverable in short plane ?

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Could GOE 425 like foil be better in aerobatics ? Better spin recovery ?

http://www.worldofkrauss.com/foils/245

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Any comment on foils like JPM3-07 where the thickness and camber are the same point ( 42.1 % of the chord ). Easy pitch moment ?
 
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Topaz

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...If you take a look at those attachment you will notice difference between XFLR5 and DesignFoil, I'm wondering which one is closer to the true results. I've read somewhere that DesignFoil is better for drag bucket estimation, it generally also has lower Cl for particular foils than XFLR5, and even Orion wrote that Xfoil isn't very good at predicting Cl max. http://www.homebuiltairplanes.com/forums/aircraft-design-aerodynamics-new-technology/4154-maximum-lift-values.html
Hi Seb,

Just want to throw in the point that simulating the performance of an airfoil out to the "nth" degree is largely a fruitless exercise. Remember that the construction tolerances on almost any wing we might build as homebuilders is roughly of the same magnitude as the errors in the various codes such as XFoil, which is why those codes weren't developed to a higher degree of accuracy. There simply is little point in determining the exact performance of a given airfoil, when what will be on your airplane will not be that airfoil, to that same degree of "exactness". None of our aircraft are so performance-critical that we need to nail performance numbers exactly.

At some point you have to say "good enough" and accept that the real article will differ in performance from your calculations to some slight degree. When someone says XFoil is no longer accurate enough, they've probably passed that point, IMHO.
 

HumanPoweredDesigner

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If you want a thick airfoil with good L/D, how about this one:

Airfoil Investigation Database - Showing SIKORSKY DBLN-526

It is 26% thick with L/D = 53 at a high Cl. Only problem is I don't know how you'd attach ailerons or flaps. The Cl max is over 2. The lack of a low drag bucket is probably not good for a speedster, though.

Do you believe that wind tunnel data? Even more interesting is with the same front half and a pointier back, the performance drops dramatically:

http://www.worldofkrauss.com/foils/show_compare/?id[]=1244&id[]=1950&chord=6.5

I suspect this airfoil gets laminar flow over most of its surface, which makes up for the blunt trailing edge. Funny looking airfoil though.

Here is a 22% thick one that has less high speed drag and more aileron potential:
http://www.worldofkrauss.com/foils/show_compare/?id[]=1244&id[]=1566&chord=6.5


Another tool to play with. Some results are really strange, hmm
Kevin's Online Panel Code - Version 2.0

Seb
I use that site extensively for estimating the Cm at non 25% cord locations. But the Coefficient of drag is so unbelievably low, unless that is hydraulically smooth and Re well above a million.
 
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Mac790

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That's probably because both programs use Xfoil for 2D analysis:lex::computer:
Norman,

Yes I knew that, I was expecting that your version is improved because it's payable and mine is free, but it seems that there is no difference between them. I was looking also at Airfoil, but I found a suggestion about using xfoil instead, because it's better, hmmm, there are some differences between mine charts and Harry's. It seems that also John Roncz was offering a free software, I found this (I like this guy style:))
John Roncz said:
FINAL NOTES
I'm giving you these programs for free, because I believe that the EAA ought to be an organization in which people freely share their knowledge with others. I do not think of you as a way to make money. This program is, to the best of my knowledge, the same or better than the program Airfoil II which someone sells for nearly $400. My opinion of that is unprintable! Please feel free to copy these files and give them to your friends. YOU MAY NOT, UNDER ANY CIRCUMSTANCES, CHARGE ANYONE FOR THESE PROGRAMS! If you do, first I will have you killed, and then I will come and personally piss on your grave!
John Roncz
Granger, Indiana
August, 1990
But because it was 20 years ago, I bet it was DOS based or even worse.

Topaz,

I agree with most what you wrote, but also have a slightly different opinion about a few things, well about quality of your wing, there is also CNC stuff (for wing you don't need fancy 5-Axis stuff, 3-axis is more than you need for it), but even without it it's still possible to make your wing quite accurately, I don't think that all those gliders in the 70/80's were built with a CNC precision, and most of them used FX style airfoils, instead of old NACA 66 series, if they were able to gain some improvements over NACA, why we shouldn't be able too. Of course I'm not seeing here that those foils will work for airplanes, I only giving a example.

Someone could also say, if you have two different airfoils, one is better over other, about let's say generally 10%, even if you lose 8% in performance due to improper wings quality, isn't it better to lose those 8% in performance in better airfoil. Of course some airfoils mighty be more prone for poor build quality, and lose in performance might be bigger for them.

Besides I treat this thread more theoretically at the moment, even a title for it "magic airfoils" isn't very serious, there is nothing like magic airfoil, some are better than others, that's true, but there is no magic. But if you take a look at this attachment, you will see, that both modified sailplanes airfoils FX73, and HQ17, wins contest over Harry's 40 series with ease at 4x10^6 Re.

Seb
 

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Mac790

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Norman, last question:) what do you think about DesignFoil, have you tried it? you can download demo for free, I tend to have more faith in DesignFoils results than in XFLR5, just compare NACA 66-2-215, charts from DesignFoil seems to be closer to Abbott results (cl is almost identical) than XFLR5, unless I messed with some settings.

Seb
 

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Mac790

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I must said that when Jarno wrote in "Lancair 414F" thread about new sailplanes airfoils with Cd around 0.002 I didn't have much faith in it, besides I was expecting very high Cm for those foils which might turn those airfoils into useless for GA application, today I found some time, and decided to try that HQ-35 (which is relatively new airfoil, pic4), the problem was that coordinates which are available, aren't extremely useful, in short you can't generate an airfoil directly with them, because lack of coordinates, plus I have also a feeling that at least few of them are incorrect. But like I said found some time today and decided to give it a try, first I created an airfoil based on those coordinates, next I used Direct Foil Design tool available in XLFR5 and created a new airfoil around it.

Despite I didn't make it extremely accurately (lack of time, plus that was only a test, you can see it form charts, I bet that the drag curve should be more vertical), still I must say that I'm extremely surprised, I got following specifications for Re 5x10^6.

For .5 AOA
Cl 0.280
Cm -0.33
Cd 0.003
L/D 93

For 2.5 AOA
Cl 0.516
Cm -0.35
Cd 0.03
L/D 194

For 5 AOA
Cl 0.777
Cm -0.35
Cd 0.008
L/D 95

If you take a look at charts you will notice that the lowest Cd is around 0.0026.

Because like I said I didn't put much care in it, I can bet that original airfoil has even better parameters, of course I'm aware of difference between 2D and 3D effect, and I know limitations of the XFOIL, but it's still the best airfoil I've ever played with, I would love to see those newest ones.

btw, when I find time I try to see what I can do about kl002 (pic 1,2), there are no coordinates, but I should be able to get some of them wit CAD software.

Ok now back to the reality :gig:.

Seb
 

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Norman

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Yes I knew that, I was expecting that your version is improved because it's payable and mine is free, but it seems that there is no difference between them.
As far as I know The Xfoil code behind profili has not been altered. What you pay for when you send your "donation" is a user friendly shell that also dose some nice things like draw ribs for arbitrary planforms with spar slots and leading edge blocks. It also does templates for hot wire cutting and aparently there's even some CNC output capability. All in all a good deal for modelers
 

topspeed100

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How about low reynolds number E201 ( tip ) and E210 ( root ) and E374...I love the looks of those. Good for a 1 metre spanning R/C model ?
 

Mac790

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As far as I know The Xfoil code behind profili has not been altered. What you pay for when you send your "donation" is a user friendly shell that also dose some nice things like draw ribs for arbitrary planforms with spar slots and leading edge blocks. It also does templates for hot wire cutting and aparently there's even some CNC output capability. All in all a good deal for modelers
Norman I'll take a look at it, but it's a pity that their demo version isn't very useful, I would like to test it first (of course it's cheap so the risk isn't big), I wondering which version of Xfoil was used in Profili, so far I noticed that DesignFoil is good for NACA 6- series but it's terrible for some sailplane airfoils, XFLR5 seems to work fine with sailplane airfoils (some charts were at least similar to those from windtunnel), but on the other hand it doesn't work very well with NACA 6- series, I'm wondering about Profili. I read discussion about Profili a few days ago, (didn't bookmark it so can't give a link for it) anyway someone was claiming that there is a difference in charts between Base and Pro version of Profili, he was talking something about simplified approach which was used for calculations in base version, I don't have personal opinion about it just writing what I've read. But it seems that price may vary because Pro version has more tools in it, not because it's more accurate.

Seb
 

autoreply

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I must said that when Jarno wrote in "Lancair 414F" thread about new sailplanes airfoils with Cd around 0.002 I didn't have much faith in it, besides I was expecting very high Cm for those foils which might turn those airfoils into useless for GA application, today I found some time, and decided to try that HQ-35 (which is relatively new airfoil, pic4), the problem was that coordinates which are available, aren't extremely useful, in short you can't generate an airfoil directly with them, because lack of coordinates, plus I have also a feeling that at least few of them are incorrect. But like I said found some time today and decided to give it a try, first I created an airfoil based on those coordinates, next I used Direct Foil Design tool available in XLFR5 and created a new airfoil around it.
A quick lookup shows only the DG-600 as a user of this airfoil. It's an excellent performer, but has a bad reputation as being very aggressive in the stall. Whether it's because of the very thin airfoils (and a bit thicker might help) or the airfoil itself, I don't know, but more than one remains high in the Alps, shattered in pieces after a stall/spin..
 

Norman

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Norman I'll take a look at it, but it's a pity that their demo version isn't very useful, I would like to test it first (of course it's cheap so the risk isn't big), I wondering which version of Xfoil was used in Profili,
I think the version of Xfoil behind Profili is not the latest version so if you're comfortable with XFLR5 and don't need the rib design functions there's not much reason to buy Profili. Profili also limits your access to the airfoil design functions and some output types in the basic version (and alpha is limited to 13 degrees). So if you realy want to use all of Xfoil's potential the $15 version ain't gona satisfy you, you'll have to shell out a bit more money for Profili Pro. I don't even know what he's asking for that because at the Re I'm usualy looking at most airfoils stall at prety low AoA
 

Mac790

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Jarno, you are right this HQ35 is very thin, leading edge it's extremely thin, but on the other hand it doesn't look bad at charts, of course without proper coordinates it's hard to compare, that chart which I did with original foil.

But I must say that it doesn't matter :), I found something much more interesting, it has slightly higher Cd but overall it's a real killer :), you probably heard about it before it's AH 93-K-132/15, I know you probably say, I've never heard about a glider with that foil... of course but keep in mind that it's a relatively new airfoil, and take into account that all modern sailplanes (besides Diana:)) use Boermans airfoils so who is gonna to try something else (besides one crazy Dutch and one mad Pole:roll:), besides I found something http://www.icas-proceedings.net/ICAS2008/PAPERS/319.PDF

NACA 6-digit airfoils and the more recent NASA Natural Laminar Flow (NLF) sections show relatively low drag when compared to widely used turbulent airfoils. However, it appears to be difficult to combine a large laminar bucket with low drag in the laminar region with the NACA and NLF airfoils.

After a consultation with L.M.M. Boermans (a lecturer in aerodynamics at the TU Delft), the decision was made to use a laminar airfoil developed by the University of Stuttgart, the AH 93-K- 131/15. It is a 13% thick airfoil, with maximal t/c at 50% chord, and a design lift coefficient of 0.2 at Re = 2.5e6.

This airfoil exhibits a large laminar bucket combined with a low drag count. Compared to NACA 6-digit and NLF airfoils at similar Reynolds number, the AH airfoil shows at least 1 drag count less at the same Cl, combined with a more extensive laminar bucket.

A GREEN ALTERNATIVE FOR PILOT TRAINING reaches its maximum lift coefficient in fully turbulent flow ensuring the aircraft will not stall catastrophically if the wing surface happens to become contaminated by rain or bugs. This, combined with very gradual stall characteristics, made it a good airfoil choice for a trainer aircraft. The original airfoil camber is tailored using XFoil to reach a cruise lift coefficient of 0.38 while remaining at the lowest drag point.
Of course he recommended it for different purposes, I did comparison between AH 93-K-131/15 (which he recommended) and AH 93-K-132/15, and it seems that 132 is even better.

Take a look at those charts: Re 5x10^6, Mach 0.28, NCrit 9

black AH-93K-132/15 (mod)
violet AH-93K-132/15 (mod)
light green NACA 671-215
navy blue NLS 414F
orange I tried KL-002, but as you can see with little success (without proper coordinates).

Second chart (pix1) for Cl/Cd at cruise.

I was going also to include FX 79 in those charts, but it's a piece of %&^% compared to those.


Norman,

I think I'll stay with XFLR5, I think I solved all problems, the key is to use at least 290 panels, previously I was using around 100, NCrit 9 instead of 12, and calculate every 0.5 ideally 0.1 AOA, setting like that works fine even with NACA 66-serries foils :).

Seb
 

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Navy guy

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I am still looking for that magic airfoil that has low pitching motion, high lift, a slow stall and easy to build. So far i have tried GEO387 and GEO384 airfoils with a full length Junkers flap of an eleven inch cord. Lots of rear airfoil chamber when the flap is deployed (too much pitching motion I should think) which would likely result in a first flight crash. Not good.
 

flat6

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Of course he recommended it for different purposes, I did comparison between AH 93-K-131/15 (which he recommended) and AH 93-K-132/15, and it seems that 132 is even better.

Seb
this is very interesting. where can we get data for this airfoil?
 

Mac790

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You can find it here Airfoil Investigation Database - Showing AH 93-K-132/15 or here http://www.ae.illinois.edu/m-selig/ads/coord_database.html#A to get decent performance in cruise, you have two choices, first lower camber to around 2.3 (if I remember correctly), second use flaps at around -3 deg.

You will also find coordinates and graphs in Stuttgarter Profilkatalog II: Niedriggeschwindigkeitsprofile, you can order copy here http://www.iag.uni-stuttgart.de/laminarwindkanal/profcat1.html

Seb
 
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