Feb 09, 2011, 12:32 PM Curtis Nampa, Idaho Joined Apr 2010 950 Posts Discussion How to determine maximum wing size? 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
 Feb 09, 2011, 12:56 PM B for Bruce The 'Wack, BC, Canada Joined Oct 2002 12,204 Posts 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.
Feb 09, 2011, 02:25 PM
Curtis
Nampa, Idaho
Joined Apr 2010
950 Posts
Quote:
 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
 Feb 10, 2011, 12:55 PM B for Bruce The 'Wack, BC, Canada Joined Oct 2002 12,204 Posts 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.
 Feb 10, 2011, 04:00 PM Curtis Nampa, Idaho Joined Apr 2010 950 Posts 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
 Feb 10, 2011, 10:09 PM B for Bruce The 'Wack, BC, Canada Joined Oct 2002 12,204 Posts 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.
 Feb 11, 2011, 09:52 AM Suspended Account Ontario,Canada Joined Feb 2007 9,742 Posts BMatthews, Please a few words on your expression "arc shape". Thanks Zor
Feb 11, 2011, 10:55 AM
Jim C Patrick
Shenandoah County
Joined Jan 2008
897 Posts
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.