It just occurred to me that it might be possible to mount Fowler-like flaps in a much simpler way as the common guided rails or an offset hinge, which have both a lot of drag and are structurally and mechanically rather complex. Let's say we connect the flaps to a simple tube that's hinged on the upper rear wing spar and on the upper flap LE. And we use a triangular plate that's hinged vertical at the wing spar and has a single joint on the lower part of the flap LE. Both the triangle and the tube are (with the flap up) parallel to the span. If we now extend the flap it will move rearwards (and sideways) and dependent on the position of the upper tube will also extend downwards. Canting the axis to which the "triangle" hinges to the wing aft will result in the flap extending both downwards and aft (and, dependent on the upper tube) also deflect downwards. I know some airliners use a similar, but vertical mechanism. The above strikes me as easier in almost any way. You can bolt/screw/glue the joints for "tube and triangle" directly to the spar and since you're not limited by the airfoils thickness and length, you can have much deeper flaps. I can see 2 clear disadvantages. *Flap rotation is intrinsically coupled to how much you extend them rearwards, like in the slotted flaps with a hinge point below the wing. You can notably reduce this by moving the "tube's" hinge point not only spanwise, but also chordwise. It isn't as discrete as a total Fowler flap, but you can get close to full rearwards deflection with only a minor flap deflection (circular instead of a straight trajectory if you plot rearwards deflection against change in flap pitch) *The spanwise movement, though this might actually be an advantage, in a low-winged aircraft you could also employ flaps under the fuselage. Anything else? It occurred to me as a neat solution, but since it's nowhere (I'm aware of) used in actual designs, I wonder what's wrong with this setup?