Airfoil for 200 Inch Span Sailplane

[DT56]

Am considering building a 200" span thermal sailplane with a planform similar to the Olympic II. Wing would be of wooden construction and employ flaps and ailerons, with a root chord of 18-20 inches and tip chord of 10-12 inches.

Any opinions on what airfoils to use for the wing?

[jtlsf5]

Am considering building a 200" span thermal sailplane with a planform similar to the Olympic II. Wing would be of wooden construction and employ flaps and ailerons, with a root chord of 18-20 inches and tip chord of 10-12 inches.

Any opinions on what airfoils to use for the wing?


At that chord almost any airfoil will work well. You are designing to a higher Reynolds number than most models fly at, which is good for airfoils. Keep FAI limits in mind if you intend to use this plane in any competition. The total wing-stab projected surface area must be no more than 2100 sq in. The wing you describe has a minimum area of 2800 sq in. A 15% stab takes you to 3220 sq in.

JT

[StevenatorLTFO]

Do the FAI limits apply to AMA contests, or just FAI contests?

[StevenatorLTFO]

Nevermind, found my answer. :D

[DT56]

At that chord almost any airfoil will work well. You are designing to a higher Reynolds number than most models fly at, which is good for airfoils. Keep FAI limits in mind if you intend to use this plane in any competition. The total wing-stab projected surface area must be no more than 2100 sq in. The wing you describe has a minimum area of 2800 sq in. A 15% stab takes you to 3220 sq in.

JT


Thanks JT, I forgot to mention the intended use was for sport only.

[DT56]

Any other airfoil suggestions?

[atjurhs]

I'd use a Drela AG35-38 series. They're optimized for open-bay ease of construction type things.

BUT, where you gonna find a winch big enough to take that thing up? Or are you gonna build that too?

Wouldn't the AMA insurance be void if that thing hits something (given that you're well over 2100sq.inch) and takes out a barn or whatever?

[Hossfly72]

Winch? He don't need no stinking winches... LOL

Hook it to a jeep and gas it and go!! I'd pay to see that!

[rdeis]

Probably need a giant scale waiver or somesuch..

[Spekd'out]

Probably need a giant scale waiver or somesuch..

I believe its by weight whatever that is with the AMA. FAI was mentioned for competition eligibility only.

You might consider the HQW series as they are available in many thickness and camber variants. I've heard that they are more forgiving to inaccuracy than many newer foils. They are used on many built up scalies.

http://www.hq-modellflug.de/koordinatenframe.htm

[Phoebusflyer]

I wouldn't use any of the model airfoils, I'ld look at the ones the new glass full scale ships are using. Those are really good for a high L/D at higher speeds. However, if you just want to fly and dink around, the old Clark Y would be hard to beat.

[scaflock]

At 200" span it's also going to be important to have a very good spar and wing joiner system. All that wing isn't going to do you any good if it folds up on you. You'd just end up with a larger pile of scrap wood and covering materials.

As far as airfoils go... I'd use something like a S3014 so it's got good lift but not be a total gasbag in the air. The S3014 is one of the best all around airfoils for soaring and scaled up to the size you want it should work even better.

Jeff

[ozmo01]

Hi
I would second the 3014 or AG series and also would second the spar advice.
take a look at the spars on the Bubble Dancer on the Charlesriverrc.org site.
The 5 section wing planform might not be a bad way to go either.

[DT56]

Thanks for the comments!!!

[seanpcola]

I don't see where the Ws should be a consideration other than for contest rules. There is no AMA waiver needed in regards to that size. Weight is a different matter and right off the top of my head I don't know what it is, maybe 50+ lbs. or so. I have several sailplanes over 200" WS and at the shop we have scale sailplanes up to 30' (360") WS. The model in my Avatar is 217".

[lincoln]

I have seen a 24 footer flown at the Nats. It didn't weigh 50 lbs, though. I don't think the Reynolds number is high enough to allow a fancy laminar airfoil to work well.

If the aspect ratio is going to be low, there's no need to use a high lift airfoil. That will just make you mush. So pick a fast one. You can probably get away with a thicker airfoil too.

I was just poking around on Profili. According to Profili, at your Reynolds numbers (250k at Cl of 1, higher for lower CL), a Clark Y that has been thinned out to 10% and decambered to 1.5% does about the same as an AG37, and better at the very highest speeds. Plus it's still a lot thicker. Probably some other airfoil would be even better.

[fnev]

5 meter span gliders are pretty common these days; but, not built with an open structure… All the modern wing sections (including ALL the HQ series) request a certain accuracy not achievable with an open structure.

Choose from a selection of “older” sections as mentioned before: you won’t go wrong. Just be careful with the thickness as you will need a pretty good strength at the root and a well designed wing joiner. For this reason a 3 pieces wing is the way to go.

When you start designing gliders this size, the criticality of the wing section is less (Re number higher), the wing plan form and general geometry start to play an important role. You would be surprised how much performances you can squeeze out of a “stupid” Clark Y or better Gottingen wing section…

[lincoln]

I think if you're willing to make a d tube, you can get a fair amount of precision on the front part of the wing. I think probably the section is less critical only in the sense that the bigger it gets, the better the performance, so you can probably afford to give away more. But if you build precisely you can gain more, too.

Planform, etc. matter on any model, large or small. I suppose the structural weight implications become more important. But snap roll and pitch sensitivity are going to be affected by planform even on smaller models.

[DT56]

I don't see where the Ws should be a consideration other than for contest rules. There is no AMA waiver needed in regards to that size. Weight is a different matter and right off the top of my head I don't know what it is, maybe 50+ lbs. or so. I have several sailplanes over 200" WS and at the shop we have scale sailplanes up to 30' (360") WS. The model in my Avatar is 217".


Sean, what airfoil is used on your 217" span sailplane? How about the 30' model?

The 200" span is an approximate 200% version of the Oly 2 planform, sort of a stretch Merlyn. Since I want to build in wood, I'm leaning toward a thickened version (12%) of the E205 for the root foil for structural purposes. Airfoil would transition to the standard E205 at the tip. The HQ foils look good, but I'm not sure I could build them in wood to the degree of accuracy required to see any performance gain over the E205. I think the S3014 that has been mentioned would be far too thin at standard thickness for wooden construction of this size. An interesting thing I've noticed in Compufoil comparisons of the E205 and S3014, is that when compared at the same thickness and camber, the 2 foils are within perhaps building tolerance of looking identical.

The center section at a minimum will be fully sheeted, perhaps with thin ply. The outer panels will have D-tube construction or perhaps full sheeting like the center section. A built-up wood main spar for the center section is planned, though I've minimal objections to employing carbon caps with perhaps kevlar wrapping.

In keeping with the sport theme of this model, I'll be cheating, as it will have an outrunner for launching.

Thanks again for all the comments! Any other suggestions are welcome!!!

[jbeanelliott]

What is an "outrunner" for launching?
Sound like something useful.

-John Elliott

<snip>
In keeping with the sport theme of this model, I'll be cheating, as it will have an outrunner for launching.

[Nico Peursum]

What is an "outrunner" for launching?
Sound like something useful.


Looks like a guy running flat out to launch an airplane F3J style

http://www.torreypinesgulls.org/images/HandTow.jpg


;)

[steelhead]

From what I've seen and tested, the larger you go, the less requiring of the airfoil, especially for sport use.

The E205 is a step up from the CY, but most of the common Selig 30 series airfoils seem to be a good choice for a larger plane. The plane will fly the way it wants to, your job is finding hout how it wants to fly and then guiding it to do what you'd like!

I'm not sure I'd go with a fullscale airfoil, but as has been said on this thread, just about anything will work.

Dean