How to chose the right airfoil

[Joe Yap]

Yes Rookieone,

Thicker airfoil does produce more lift. To be fair, if you compare E374 and Clark-Y with same thickness, the Clark-Y will produce more lift.
Thicker airfoil does produce more drag but not necessary requires more power to fly the plane. You can simply play around with M-dot(mass flow) and V-dot (velocity). Higher mass flow means higher static thrust, and higher velocity means higher top speed. If you have thicker airfoil (higher drag), change the prop to a larger diameter and less pitch to overcome it (more mass flow),or change the gear ratio. If you have thin airfoil (less drag), use a small prop with higer pitch to achieve more velocity as thin airfoil needs to fly fast to create lift. The good examples are WW1 Biplanes/triplanes and pylon racers driven by a Speed 400.
There aren't much airfoil that can totally satisfy all flight envelope and that why most aircraft uses flaps to change its airfoil(camber).You can have a ultra thin airfoil to fly supersonic and use flaps to increase camber for TO/landing.

[EZ-Bee]

I like Paul's answer.

You see the 205 used a lot in both e-power an sailplanes, it was in its time a moderately agressive choice for a foil with a bit of penetration.

I saw an article once that plotted the history of hot sailplane aerofoils.

Over time camber has lowered along with thickness ( apart from a series of very thick aerofoils to survive Gorrilla Winches ).

Hand Launch movement bought back more camber for a while , but thin caught on here too.

Thin foils give more penetration, it was found better to be able to cover lots of ground efficently to find the next thermal.

Thin foils do put the emphais on designing good structures and perhaps exotic materials.

Older foils like 205 give not too thin and hard a structre to build but still a bit of penetration. They may also play nicer.

Indeed the Clark Y may have a good following for its ability to Play nice and support strong easy to build structure.

GYROGEARLOOSE idea is a great one, find a plane that flies and behaves the way you would like yours to ( Fits your Flying Style ), use that areofoil with similar wing loading.

Copy something that works:

For the Right Aerofoil, Copy the Left :-)

Always worked for me .....

Peter

[fregon45]

I propose we change the name of this board to "Modeling Technology" since hardly anyone wants to discuss the real science of flight. One thing that I always disliked about the Mag "Popular Science" is that it never discusses anything scientific. It's just a review of current gadgets and technology.

Anyway, now that I'm done with my rant I'll go on to say that all of the opinions here on copying other designs is really the best advice. It will get you to where you want to go the quickest and with the least amount of headache. Let's not discourage anyone from actually learning something about the theory of flight, though.

Nathan

***Flame shield engaged****

[markrduckworth]

What is the definition of a Clark-Y airfoil? From one's I've seen that claim to be Clark-Y, it looks like flat bottom from spar to trailing edge, but curved up to the leading edge. Is there a more precise definition?

I have plans for a biplane with symmetrical airfoil wings. But I was thinking of changing it to something else that would fly better with less power. I would intend to spend much less time inverted than not. It sounds like the Eppler 374 would be good?

Mark.

[EZ-Bee]

Will the real Clark Y stand up !

There is probably a lot of 'Clarks' that have been thinned and otherwise manipulated.

There is also the age old system of using the edge of your shoe for the main curve and filling in the rest by memory.

An excellent site to see all the Aerofoils you could ever want is:

http://amber.aae.uiuc.edu/~m-selig/ads.html

In the Aerofoils section is a list of more than 1000, with .dat files of co-ordinates to import into your Aerofoil Plotting progam.

There are also .gif file images so you can preview and see what they look like.

Links to free analysis software are also provide if you want to get into the technical suff and see the physical efffect you aerofoil has in the air around it.

Picture of Clark Y according to UIUC attached.

Peter...

[RookieOne]

Would you use a thinned Clark-Y on a sailplane?

[EZ-Bee]

The Clark Y is better suited for the B25 .

Something like the SD7037 , may fit the bill for a glider.

Floaty type, that always flies right side up.

Wing loading really effects the Floaty bit.

Peter...

[Joe Yap]

IMHO, it doesn't mean Clark-Y is useless on sailplanes whether altered or not. You mentioned sailplane but did not say what type. It all depends on the condition of the slope lift, if it's slope soarer and the flying characteristic desired. If you are flying over small slope where lift is concentrated in a small area, a standard Clark-Y should work well since it tends to fly slower and can stay in the same lift zone longer. If the place you are flying has lift zones all over, you'll need a newer or thinner airfoil to move around and hunt for the lift. Standard Clark-Y can also tolerate higher wing loading. My DAW TG-3 uses a altered Clark-Y which flies very well on small slope ( 2m high and about 10m wide ) since it can stay around it and stay in the small lift zone.

[Joe Yap]

This a pic of my DAW TG-3.

[Humbug]

Hi Guys,

I'm just starting in r/c and an interested rookie in aerodynamics. I just had found Martin Hepperle's great site for airfoils and modeling aerodynamics (link below). His page which discusses the effects of rib and spar construction on wing aerodynamics was quite interesting and explained Paul's point above that a wing like this has "10 different airfoils for every few inches of wingspan"; i.e., because of "droop" of the covering between the ribs along the span.


http://beadec1.ea.bs.dlr.de/Airfoils/theory.htm

This site should also satisfy Nathan's desire for a little theory!

Steve

[Sparky Paul]

Here's four common and good shapes..
Clark-Y
Eppler 205
NACA 2411
Selig 2032
Within usual construction standards the shapes are the same.

[RookieOne]

All in one wing!

[Spam]

Originally posted by Humbug
Hi Guys,

I'm just starting in r/c and an interested rookie in aerodynamics. I just had found Martin Hepperle's great site for airfoils and modeling aerodynamics (link below). His page which discusses the effects of rib and spar construction on wing aerodynamics was quite interesting and explained Paul's point above that a wing like this has "10 different airfoils for every few inches of wingspan"; i.e., because of "droop" of the covering between the ribs along the span.
Steve

That's a small part of why I like building foam wings! There are other advantages to foam: you can build them as cheap or as nice as you want. Most of my prototypes are tape covered, while finished birds are either glassed or sheeted with balsa. Once you build your templates for cutting the wing, you can make new wing cores in a matter of minutes.

re: selection of glider airfoil: Everybody here has posted good advice: it's just a matter of how technical you want to get. I agree on the SD7037 airfoil for a thermal-hunter, good lift, low drag and a good speed-range at light wing loadings. I used Clark-Y airfoils almost exclusively at first, and was always very happy with them on a powered plane. The only reason I don't use them much anymore is I like to fly inverted. You can fly inverted with a clark-Y, just not very well. For fully symmetrical airfoils, the NACA series are great, you can adjust the thickness to your flying style.

The one thing that nobody mentioned is the effect of thickness on AOA (Angle of Attack). A thinner airfoil will stall at a lower AOA than a thicker one. (take a look at a gas-fun-fly type plane, or a 3-d plane--very thick airfoils). There is always a tradeoff, though: the thicker an airfoil, the higher the coefficient of friction. Since friction is a function of the speed squared (If I remember my physics right), you can have a huge speed difference between the same airfoil with differing thicknesses...

Best of luck

[Joe Yap]

I have also use the S3021 and S4083 on my gliders and have good results. However, you don't need to go crazy about choosing airfoil since theory and practical are sometime quite far apart. What I mean is that it also depends on your worksmanship. Sometime, a stroke of the sanding block can effectively change the airfoil. If you shrink the bottom covering of an undercamber wing too tight, you may ended up a flat bottomed wing. It's quite difficult to produce a 100% accurate wing. Choose one which has the desired characteristic and within your building capability.

[EZ-Bee]

Joe....

The 2m high slope... Interesting...

In Auckland if you want to find the slope flyers you go to the top of one of our many 'Extinct ?' volcanic cones.
Though they can lack a nice flat landing spot.

Lucky hardly anyone looks up otherwise it would be regulated out of existance.

Apart from one , I think you have to travel some distance for flat feild flying.

Where are the flying spots in Singapore ?

No problems with fines ?

Peter