Wing Airfoil Design.

[Donnie Bee]

I'm building the FT Simple Cub speed build kit. I know it flies because I seen you tube videos of it flying. This is the 1st foam board plane I ever built. The wing seems to have a strange airfoil design to me. Most of the wing all the way to the root has a Flat-bottom/Clark-Y- airfoil with about 1/4
(1 and 7/8"/ 4 1/2cm) of a strange looking trailing edge. 4 and 3/4"/ 12cm of the wing tips are a under-cambered design. Which is even more slower ( more drag ) then a flat-bottom airfoil. Seems to me, this would make it more prone to wing tip stalls. Most, if not all real planes & some RC planes have some type of washout in the wings making the wing tips faster then the rest of the wing to help prevent wing tip stalls.
I just can't wrap my head around the Simple Cub's wing design.

 

[Matthewdupreez]

I'm building the FT Simple Cub speed build kit. I know it flies because I seen you tube videos of it flying. This is the 1st foam board plane I ever built. The wing seems to have a strange airfoil design to me. Most of the wing all the way to the root has a Flat-bottom/Clark-Y- airfoil with about 1/4
(1 and 7/8"/ 4 1/2cm) of a strange looking trailing edge. 4 and 3/4"/ 12cm of the wing tips are a under-cambered design. Which is even more slower ( more drag ) then a flat-bottom airfoil. Seems to me, this would make it more prone to wing tip stalls. Most, if not all real planes & some RC planes have some type of washout in the wings making the wing tips faster then the rest of the wing to help prevent wing tip stalls.
I just can't wrap my head around the Simple Cub's wing design.

from what i have heard.... the under camber wingtip actually helps to prevent tip stalls... i could be wrong but they have mentioned that in the ft spitfire, and a couple of other vids

 

[The Fopster]

At the scale we build the shape of the airfoil doesn’t matter too much. A flat plate wing will fly. Best thing is not to worry about it - as you said, you know it flies. Get out there and give it a go!

 

[Hondo76251]

It flies, dont overthink it! 😂

The scale, speed, and wing loading have a lot to with what a model plane can get away with.

That being said, after having built a few ive found i like to modify the design a bit. I like to remove the inner layer of paper and hand roll the shape off the edge of a table or a with a dowel rather than using the FT's crease method. Also like to bevel the lower piece so that it makes a nicer trailing edge. Just a cleaner shape, not sure how much it helps really for all the extra work.

 

[Merv]

I'm building the FT Simple Cub speed build kit. .....

Id build the kit according to the plan. It will fly well. I've seen a few kits that had the CG mark too far aft. If you moved the CG 1/4 inch forward, it flew much better.

When you start cutting out your own planes, not a kit. then make them the way you want.

 

[Tench745]

The first thing to understand about a stall is that it is angle of attack, not airspeed, which causes a wing to stall. As the plane slows down it loses lift and starts to sink more, moving the relative wind lower and lower until it reaches the critical angle of attack and the wing stalls. This is why you can also get something called an "accelerated stall" when you pitch up sharply at high speeds; you're pitching up and pushing the wing past the critical angle of attack.

Washout simply lowers the angle of attack of the wingtip so it isn't quite to the critical angle of attack when the rest of the wing is. The wingtips don't fly any faster than the rest of the wing.

Undercambered wingtips naturally stall at a higher angle of attack than a flat-bottomed airfoil of the same relative shape. This keeps the wingtips flying even when the rest of the wing is starting to stall out, preventing tip-stalls without the need for washout.

Edited to add:
A constant chord wing (big rectangle, same airfoil the whole way) like on a Cub, RV, Piper Cherokee, etc. will naturally start to stall at the root anyway, so even without washout or undercambered tips the stall behavior will be pretty tame.

All the technical mumbo-jumbo aside, the Simple Cub will fly if built to plans. For a first build, it's probably best to build it as designed.