Aerofoils -

[mitchamus]

I trying to design a wing and I've used profili before, but the one thing that stumps me is how aerofoils are categorised,

I mean you building a glider wing, how do you know what is a good profile is to start with?

Does anyone know where there is a list of aerofoils with a corresponding description or review of how the aerofoil performs, it's applications etc etc....

such as
Eppler 212
category: thermal or slope
- a good all round thermal aerofoil for competition or semi competitive slope soring. Good low speed characteristics with the ability to produce a generous amount of lift in low speed or low updraft environments....

I mean where do you start??? :confused:

cheers,
Mitch.

[hul]

try this for flying wings (tailless):
http://www.aerodesign.de/english/profile/profile_s.htm

or this for conventional gliders (this page is in german)
http://www.aerodesign.de/profile/profile_n.htm

Hans

[Antonsoarer]

Mitch, if you get to know about a few and then use Profili to find similar foils and have a look at the polars, also 'suck-it & see' works well :rolleyes: Been messing with foils for 30 years and still learning. Also asking what foil and loading a given model you are watching is using is useful especially when you check out the finish and planform. I have a mental :rolleyes: database of many foils and foil types that are always being updated.

Plenty of people on these forums who can describe foil characteristics. Stating what you looking for will usually get some good responses.

Tony.

[Ollie]

http://www.charlesriverrc.org/articles/drela-airfoilshop/markdrela-ag-ht-airfoils.htm
Better a custom 3 or 4 airfoil set to match a wing for Re's and structures.

[mitchamus]

Stating what you looking for will usually get some good responses.
Tony.

The application is basically a 2-2.5m span polyhedral glider wing, tapered to the tip on both the L & T edges with a root chord of somewhere between 200 - 300mm and a tip chord length of about 100mm.

I'm building it for an AP platform, where i want to be able to climb quickly to height, soar around an amount of time and take a few photos with the engine off, and then glide back down for a slow landing or catch. (I will be incorporating flaps and crow brakes into the design.)

cheers,
Mitch

[Ollie]

http://www.rcgroups.com/forums/showthread.php?t=191234

[Antonsoarer]

QUOTE=mitchamus]The application is basically a 2-2.5m span polyhedral glider wing, tapered to the tip on both the L & T edges with a root chord of somewhere between 200 - 300mm and a tip chord length of about 100mm.

I'm building it for an AP platform, where i want to be able to climb quickly to height, soar around an amount of time and take a few photos with the engine off, and then glide back down for a slow landing or catch. (I will be incorporating flaps and crow brakes into the design.)

cheers,
Mitch[/QUOTE]


Mitch, plenty of great threads on AP designs, like the one Ollie posted.

Low flying speed seems to be the main aim combined with a load (camera) carrying capability.

Your design ‘2.5m span x average 150mm chord’ gives a high AR for this type of work and payload. The small tips at 50-30% of root will need careful design (washout and or foil blending) to avoid tip stalling.

To carry the load and get candidate foils working well consider lowering your AR to 11-14. Consider camber changing flaps and have a look at the following; S7012, MH32, SD7037. If you operate in windy conditions the S7012 will probably do better and the SD7037 will load carry well. They should all respond well to larger chords.

Polyhedral makes span-wide camber changing more complex. You don't mention target wing-loading, this could help when picking the best chord/span/foil combination.

Tony.

[HankF]

Pick any one that pleases you.

The only real difference between 90% of all airfoils is the zero lift angle of attack so choose one that gives you the right decalage to hold your fuselage at the pitch angle you want at cruise.

Hank

[Antonsoarer]

Pick any one that pleases you.

The only real difference between 90% of all airfoils is the zero lift angle of attack so choose one that gives you the right decalage to hold your fuselage at the pitch angle you want at cruise.

Hank

Wow! the world just got real simple :rolleyes: Helpfull stuff!!... I like the ones that look like bananas.. they really please me! :) ;)

[HankF]

You may sneer, but if you take a book of airfoil Cl/Cd graphs and reproduce them into transparencies and lay the transparencies on top of each other, between -8 degrees and 12 degrees angle of attack the graphs will be the same if you match the zero lift points (assuming the graphs are to the same scale).

Hank

[Ollie]

Hank,

What do you know beyond:
"You may sneer, but if you take a book of airfoil Cl/Cd graphs and reproduce them into transparencies and lay the transparencies on top of each other, between -8 degrees and 12 degrees angle of attack the graphs will be the same if you match the zero lift points (assuming the graphs are to the same scale)."

?????

[HankF]

Ollie, What's your point? Or is this just a putdown? I'm just saying that except for zero lift angle of attack, most airfoils are within 10% of each other in terms of lift and drag over the usual range of attack angles.

Of course there are exceptions but there aren't many and the comparison doesn't hold passed stall.

Hank

[Ollie]

Hank,
I think maybe only importart some parts for you. There are more things for other ways like for gliders for low drag, but not low drag for power planes with lots of power. There ways that stall (not on some graphs) like airfoil mushy stalls vs. other airfoil sharp stalls.

[HankF]

As I said, there are exceptions and you noted two, one of which I mentioned.

Stall can be a consideration but since we tend to use thick and relatively blunt airfoils (compared to what the Wrights used) there isn't much difference.

Laminar flow for low drag I suspect is not often achieved at the size of our models and it would probably require surface preparation most would not be willing to do.

But at the cutting edge of performance all bets are off. Like I said, there are exceptions.

Hank

[Ollie]

Hank,
You did not reason to your conclusion. You rationalized to your conclusion. I don't believe your conclusion.

[markdrela]

One of the most important characteristics of a glider airfoil is "speed range". This means that the Cd must be very low near the bottom of the operating Cl range. The Cl can go as low as 0.1 in a fast upwind glide, and this is where airfoils differ a great deal.

Compared to a modern thin low camber section, something thicker like a Clark Y will have roughly 100% more drag at this Cl. A flat-bottom Gentle Lady airfoil might have a 200% or more drag. In practice, this means that gliders with these airfoils cannot fly fast at a reasonable glide angle, and hence do not have wind penetration ability. The thicker airfoils can have narrower chords and proportionately higher wing loadings which will help to overcome this drawback, but only partially.

Another important characteristic is "float". This means that the Cd must stay reasonably low near the top of the Cl range. Here the low-camber airfoil is at a disadvantage, but not if the thicker airfoils had to be narrowed and more highly loaded for the sake of adequate high-speed performance.

When all the tradeoffs are made, the low-camber light-loading approach seems to give the best balance between float and speed range. Gliders have trended that way in the last decade.

[HankF]

I don't believe your conclusion

That the zero lift angle of attack is the primary measure that distingushes airfoils from each other?

Hank

[Cebola]

try this for flying wings (tailless):
http://www.aerodesign.de/english/profile/profile_s.htm

or this for conventional gliders (this page is in german)
http://www.aerodesign.de/profile/profile_n.htm

Hans

Well!!! :confused:

Its written on Deutshgramophonen language, its impossible for a Brazilian guy like me ready this!!!
Is there any other choice????

Cebola
brazil

[DLC]

HANKF,

I agree with Ollie that your statement is a bit of an over-simplification. Since my 73-year old reflexes are not what they once were, the first thing I look for when selecting an airfoil is a gentle stall. Also, it is not clear to me what sliding drag polars around on paper means in the real world. For example, look at the drag polars for the Clark Y and WASP airfoils in Profili. To me, they show that for a relatively wide range of Cl (and alpha), the WASP has substantially less drag than the Clark Y. It is not clear to me how matching zero lift alpha (which really isn't that much different for the two airfols) can change that conclusion.