I'm looking to build a larger wing for my "foam" Mini Super Cub.
http://www.amazon.com/Hobbyzone-HBZ4...uct/B001IF3XVY
The purpose is to improve it's glide properties. I would like to have a spare wing that I could put on when I'm in the mood to do a little slow flying and chase a few thermals.
Is there a formula to calculate a maximum wing size for a specific fuse size? Rib/Spar size and length?

Thanks,
Curtis

You can typically make the wing about another 25% bigger and not run into issues. But that's it. The model's stability and other flight factors is affected by the wing and tail size and the distance between the wing and tail. If you alter these things by too much on a given design then the resulting model will either be a bear to fly or won't fly at all due to stability issues.

This is why power models look like they do and sailplanes look like they do and why you can't just mix and match stuff around willy nilly.

Originally Posted by BMatthews

You can typically make the wing about another 25% bigger and not run into issues. But that's it. The model's stability and other flight factors is affected by the wing and tail size and the distance between the wing and tail. If you alter these things by too much on a given design then the resulting model will either be a bear to fly or won't fly at all due to stability issues.

This is why power models look like they do and sailplanes look like they do and why you can't just mix and match stuff around willy nilly.

That makes total sense. I knew there had to be a maximum length and width that could be used without running into problems. I'm sure the standard wing size on the model is more a matter of keeping the model to scale as much as anything. And the original wing size for the full-size Super Cub was designed to give the best overall performance. I am just trying to push the wing towards maximum lift rather than maximum engine powered performance and forward speed. The stock Mini Super Cub is a real floater in stock form. I'm looking at designing a wing with a flat bottom.

Curtis

At the size of the Mini Cub the best low speed option is the simple arc wing that it came with. I know that sounds odd but it's related to the airspeed and wing chord size. The term used to describe this size scaling effect is given as the Reynolds number that the wing operates at. For the sort of very low Reynolds number range of operation of this sort and size of model for the slowest flight speed the simple arc shape is actually the optimum shape.

If you want to make the model fly slower the trick would be to build a new model of around the same size but lighter. And the best low speed flying would come from using a fairly highly cambered airfoil such as those used on free flight P-30 or Coupe d'Hiver rubber powered models.

It would be really hard to make a lighter airframe. The Mini Super Cub doesn't weight much. So, I think wing design is about my only option. I always thought a wing with a flat lower surface created the most lift.

Curtis

All else being equal the one with the greater % of camber (the mid line between the upper and lower surfaces) will achieve a higher lift coefficient before stalling. This is why undercamberd airfoils are used for slow flying models in free flight.

BMatthews,

Please a few words on your expression "arc shape".

Thanks

Zor

Zor asked about the term "arc shaped". Not speaking for BMatthews, but it is probably the rounded wingtips shown on Hobyzone's webpage for this Cub looks like what most people call 'an arc shape". It's not exactly an arc because it is not 'an exact arc' —a section of a perfect circle— but other Hobbyzone Cubs all have a rounded wingtip.

I don't think so. I think BMatthews was discussing airfoil cross section.

Now we can see why I asked.

Zor

It WAS the airfoil shape that I was referring to.

By "arc shaped" I mean that the airfoil resembles a sheet of balsa that has been curved across the grain into an arc. A popular example of such a wing section are the molded "meat try" foam wings of the GWS Lite Stik, Beaver, Cub and other GWS models that share that same wing style. Another example would be the single covering on a typical indoor rubber duration model that is supported in an arc shaped or at least single surface camber shape by the ribs of the wing. The Steven's Aero Doodlebug is another example of such a basic shape. It basically describes any "airfoil" that is formed from very thin sheet that is less than about 1% thick or uses a single sided covering where that covering is basically both the top and bottom surface shapes.