Is there an aerodynamic reason for this design?

[mcmoyer]

I’m starting up a new build of a simple stick. It got me wondering why the bottom of the wing doesn’t extend out as far as the top of the wing. Is there some aerodynamic advantage to this design or is it just a simpler way of making the wing?

 

[luvmy40]

I'm as ignorant as they come from an aerodynamics point. I would assume there is some "under camber" effect but it is probably more to do with simplicity of making it look good.

 

[Merv]

...Is there some aerodynamic advantage to this design...

If I recall, a video a long time ago, Josh mentioned that the step in the wing that you are referring to helped reduce wing stall.
I don't care for the step, I bevel the training edge of my wings to eliminate the step. I feel this gives me a better glide slope. I did keep the single foam thickness control surface, that is just easier to build. Some day, I will try building the control surface into the airfoil to see if it improves glide performance.

 

[Ketchup]

I think that the under cambered wingtips are supposed to stop the plane from tip stalling, but honestly I don't buy it.

Wings stall because they reach a certain angle of attack at which the airflow over the top of the wing separates from the surface of the wing. The tip of the wing is at the same angle of attack as the rest of it, so it should also stall at the same time as the rest of the wing. Now yes, different airfoils stall at different angles (and the wing tip is effectively a different airfoil), but in this case the top of the airfoil is the important bit, and the top of the airfoil stays consistent across the span of the wing. Therefore the airflow over the top of the airfoil should separate at the same time all across the span of the wing.
Maybe the under cambered tips produce more lift beyond a stall than the flat bottomed part? That would make stalls gentler and I would assume tip stalls would be more forgiving in that case.

Either way, I'd bet that FT does this mostly because it makes wingtips easier to shape, and whatever positive flight characteristics they gain from this seem like a side effect.

 

[Tench745]

I’m starting up a new build of a simple stick. It got me wondering why the bottom of the wing doesn’t extend out as far as the top of the wing. Is there some aerodynamic advantage to this design or is it just a simpler way of making the wing?

I am aware of two reasons.
1) When the leading edge of the wing stops being a straight line, it's harder to make top and bottom surfaces fold together into a pretty airfoil. Easier to just lop off the bottom surface.

2) Under-cambered airfoils tend to stall at higher angles of attack than their flat-bottomed counterparts. If the root of the wing starts to stall first, it's easier to maintain roll control through the stall.
I built a Simple Soarer wing without the under-camber and when it got slow it would always drop a wingtip pretty dramatically. With just rudder control it was nearly unrecoverable. As soon as I cut out the lower skin on the wingtips it was a different animal. Very docile and predictable even when flirting with a stall.