NACA 43012 for scale sailplane

[surfimp]

I've built a standoff 1/16 scale Waco CG-4A glider from EPP and it's great on the slope. The success of this project has inspired me to think of doing a built-up version in a larger scale, like 1/9 or so, that would be designed mainly for aerotow or mellow slopes like Los Banos and would be a lot stronger on scale details.

Towards that end, I was wondering what the experts think of using the fullscale Waco's NACA 43012 for a large scale model of the plane. At 1/9 scale the wingspan would be 112" with a chord of 14". The 43012 has an undercambered droop in the first 1/4 of the lower wing surface so I'm presuming that bigger will be better if I'm to use this airfoil. Here's a profile:

http://www.ds-cats.com/~kurisawa/aeronautics/Airfoils/OpenFiles.link/A2056/OS1085_A00.jpg

My EPP version used a thinned Clark Y and it flies great, though I did increase the chord slightly above true scale to aid in wing stiffness and light lift performance. However, it flies a bit too fast to really look scale in the air (not to mention it's too small, though it dwarfs nearly everything else at my local slope when it's in the air).

Anyways, feedback is much appreciated as always.

Steve

[Ollie]

The S4333 will give a wider useful speed range.

[surfimp]

Thanks Ollie! Any thought one whether there could/would be any severely negative consequences to using the NACA 43012, however? Mainly I would like to use it because the airfoil shape is very evident on the fullscale plane, but I'm just curious whether using it at this scale would be a really bad idea or not.

Steve

[Sparky Paul]

Since the Waco looks too much like a motorless Kadet, I doubt there's anything that can be done to "improve" the performance.
The scale airfoil would be a good talking point, and probably as good as anything for a flying box.

[Ollie]

If scale appearance is a very high priority then it trumps other competing values.

Paul makes a good point. The high drag of the fuselage, etc. dilutes any differences in the drag characteristics of the airfoil. Even the stall characteristics are less important because of the rectangular wing planform which has plenty of tip stall margin.

By all means use the scale airfoil. The full scale glider had a relatively poor glide and the model's glide will be scale like too with either airfoil.

It would look very nostalgic being towed behind a scale model of the C47.
An ex flying buddy of mine, Bill Moore, who passed away last year, built a scale model of the Waco troop carrying glider. His model is on display in the Waco museum in Ohio. Bill's model is of very scale quality. He didn't take pains to keep the weight down. He flew it just once and found it had a very high glide speed. Keeping the wing loading under control will compensate for any shortcomings in the scale airfoil, I think.

[surfimp]

Flying box? Hehehe, actually I think it's "flying cargo container", or more popularly, "flying coffin" :eek:

With the thinned out Clark Y my 1/16 version has, the performance is actually too "good"...it flies too fast. I need to slow it down some, so I figure when I build the larger version the fullsize airfoil might be interesting.

Video of my EPP CG-4A:
Waco CG-4A at Ellwood Bluffs (10.8MB, .MOV) (http://www.sbslopers.org/movies/ellwood/waco_ellwood.mov)

Thanks as always guys!

Steve

[Ollie]

The air speed varies as the square root of the wing loading. Light weight equals slow flier. There are serious limits on how much slower it can be made to fly by airfoil selection. You can achieve much slower flight by limiting weight.

[surfimp]

Thanks Ollie, the wingloading on the 1/16 version is about 14oz./sq.ft. If I remember correctly the airfoil is Clark Y thinned to about 8% with about 2% camber or so. I'm also thinking the built-up plane will have a lower relative airframe weight than the solid construction of the EPP, especially at the larger size I'm thinking of doing next.

The fullsize plane had 852 sq.ft. of wing area and a maximum gross weight of around 7000lb., though this was regularly exceeded by large margins. That puts the fullsize wingloading at about a minimum of 8.2lb./sq.ft., but I'm not sure how that should translate into a model for scale-like performance (that being a somewhat subjective notion, of course).

In any event, having a slightly too-high wingloading does make it more exciting to fly! Thanks for the clarification!

Steve

[Ollie]

The lift increases as the square of the airspeed. Because the airspeed of the full scale glider was so much higher and because the airfoil can reach a higher lift coefficient at full scale before stalling, the wing loading of the full scale glider could be much higher than the model.
A wing loading in the vicinity of 14 ounces per square foot for a model sounds reasonable to me.