jamesjoneill

Hi,

I'm trying to track down the coordinates for the aerofoil used on the wing of the Extra 300 S. The sections are as follows:

root - "MA 15 S"
tip - "MA 12 S"

If anyone knows where I can find this information I would be most grateful.

Many thanks,

James

jamesjoneill

Any one have any ideas? If not of this particular aerofoil then maybe of a good source for this kind of information?

thanks,

James

Ben Lanterman

I found some drawings, crude and small and useless, when I went searching on the net. I also looked in Profili and found nothing. I do remember seeing the sections somewhere but am drawing a blank.

I find the section interesting and wonder how in the world the designer ever came up with it. No doubt that it works but it is not a finesse kind of thing. I would like to see some data on it compared to a "normal" type of airfoil.

Rotaryphile

What appears to be virtually the same airfoil is used on the Sukoi 26, and all of the Extras and Edges. I understand that John Roncz designed the airfoil used on the Edge, but I don't know the pedigree of the others. I, too, have searched, fruitlessly, for the Roncz Edge airfoil coordinates, and have been forced to approximate it from small scale drawings of Extras and Edges for a rotary powered 30% scale carbon composite Edge 540 that I am designing and building.

jamesjoneill

Sounds like I am not going to be successful in my search then. I guess I will have to just use an appropriate-looking section!

Thanks for the help though.

James

AdrianM

Look at the planesplus.com section on the Fiberclassics Extra 40%. They tested the scale airfoil and the plane didn't fly right. They switched to a pattern airfoil and then the plane was perfect.

Rotaryphile

I am proceeding with the molds to make carbon composite wings with the scale section. Nothing ventured, nothing gained, I figure. I used a very similar section on a competition fun-fly model that I designed and built a few years ago, and it works well, even with 60% wing taper, which tends to worsen tip-stall. According to theory, such a section should produce considerably higher lift (and higher profile drag) than a conventional NACA 0015 Pattern-type section.

One thing that I noticed was that the model tracked better than usual through very tight turns, close to stall. I think that the reason for the better tracking may have been that incipient stall burbles that seem to start hurting tracking at around one-half peak lift coefficient were delayed. Any section that produces higher lift also tends to have a more abrupt stall. The wing seemed to just hang in there until all hell broke loose, but this also tends to produce cleaner entry to, and recovery from, snap rolls and spins. Even so, I found the model quite easy to get along with in low and slow tight maneuvers, but its wing loading was very low, and a model with a considerably higher wing loading might be a bit trickier to fly. My fun-fly model also has 33% chord full span ailerons, which remained very effective right into deep stall. I would definitely hesitate to use the blunt section with partial span ailerons, which tend to produce a lot more adverse yaw, particularly when the wing is close to stall.

Montague

When using the same airfoil as a full scale plane, it pays to take in account the Re values of the model vs the full scale. Some airfoils don't translate down to model values of Re at all well, so if you looking for flight performance, a scaled down airfoil might not be the way to go. I'm guessing that's what the Fiberclassics guys mentioned above ran in to.

If you are looking for a perfect scale model though, that's a different story.

AirWolfRC

I don't remember who I was talking to quite a while back, but the EXTRA airfoil was described as a "Snow Cone" airfoil.

That means an eliptical front end with straight tangent lines to the trailing edge. The "15" and "12" used in the airfoil designation is the percent thickness. I can not say how far back the maximum thickness is but it looks to be about 25%.

After seeing (and flying) the real thing first hand, I tend to believe the above description.

Wolfgang

shonny

Try Eppler 169 or S8035.
They are both around 14 %, symmetrical, and the Selig one made for model aerobatics.
Reason for suggestion is that there seems little joy with the MAs in the numbers suggested.

Roberto B.

Have a look here:

http://www.eng-tips.com/viewthread.cfm?qid=183605

What they say is right: it's just a geometric shape without any aerodynamic driven parameter.
I've traced them and compared with the full size, they are pretty the same.

I'm wondering about the carbon composite wings job.... Has it been accomplished?

frequent flyer

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na

Roberto B.

Sorry, but you are wrong. Completely. Such airfoils don't resemble the Extra ones at all.

BMatthews

Roberto, I trust you realize that this thread last ended back in 2003? With such things it's more normal to PM the original poster to ask such questions.

Roberto B.

Yes I did, I did also scroll all the topics of the user, and I've seen he is actually active in the forum, but I didn't find anything related to such job anymore. So...

Rotaryphile

As Cludwig mentioned previously in this thread, I think that the subject airfoil may have originated with the Eppler 242 series. Coordinates are in the URL below, for 12.1 percent thickness, which could easily be translated to any desired thickness.

http://rg65.iq-web.net/foils_index.p...rofil=e472.txt

I suspect that the airfoil used on the Extras, Edges, and Sukoi could be very closely approximated simply by using a elliptical nose, with maximum thickness located somewhere between around the 14 to 17 percent chord, spliced onto tangent chord lines that run perfectly straight to nearly the trailing edge. A small amount of reflex (inverse) camber, maybe 1/2 percent, might have been used. Recent NASA low reynolds number airfoils frequently use reflex camber, evidently for better L/D ratio at high lift coefficients.

Roberto B.

The reflex camber on the Sukhoi arise from its wing structure: elliptical leading edge, then straigth to the rear spar. Then again straigth to the trailing edge.
No complicated calculations here too....

I confirm too the geometrical driven airfoil of the Extra . Nothing to compare to "calculated" or previously known airfoils.

frequent flyer

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n

cutaway

Hard to go wrong with any of the NACA 00xx series.

speedracerntrixie

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I'm curious what it is you want to accomplish by using the scale airfoil?

Roberto B.

A scale look and a realistic way of flying.

da Rock

You'll get a scale look, but the realistic flying doesn't come from a model's airfoil. Our model's can do much, much more than full scale simply from out wing loading and power loading. It's up to the guy with the TX to do "realistic", not the airfoil.

speedracerntrixie

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I agree. I have flown a Sukhoi with the scale airfoil and was quite dissapointed. It did have great slow speed manners but it was difficult to get any consistancy in snaps and spin entries. The airfoil was just too stable. For model use just about any symmetrical airfoil with 12% thickness and high point at 35% at the root and 8%thickness and high point 30% at the tip is going to perform well and have a good stall. In R/C aerobatics we need to find that balance between stability and the ability to stall predictably.

rmh

The size and wing loading will greatly affect how that shape responds-

Rotaryphile

As I mentioned previously, I used a similar section, (15 percent thickness, max. thickness at about 14 percent chord), and it worked just fine, on a very low wing loading competition fun fly bird, although I had to use quite a bit of wing washout to avoid sudden tip stalls at low airspeed, probably because the wing had 60 percent taper. It also has large chord coupled flaperons, which may have made the stall more abrupt.