wings and structures
I've just completed and flown a Mark Drela design, the E_Allegro_Lite.. Speed 400 direct drive, itty-bitty 6x3 Graupner prop.
Seriously difficult construction, and I even simplified that!
I was surprised to see that this plane is slipperier than the usual glider in its class. It flies faster, but doesn't come down any faster.
Thermals well, turning very tightly without tip stalls.
The airfoil is very skinny, relative to say my Mini-Challenger which is the same general size, but needs a gear-box and 1 more cell to fly well.
And a giant prop.