Post History

Long thin wings aren't all that great for getting fast, but they are great for conserving energy.

The usual approach to efficient flight is to have hybrid wings that narrow down when you want to minimize air drag, and extend when you want more lift or maneuverability. Airplanes do that by sliding out an extra bit of wing from out of the main wing, birds do that by rotating their feathers parallel to the wing to get smaller wing area or parallel to the flight direction to get higher area instead. Bat-like wings might be able to achieve a similar effect by moving their fingers apart or keeping them closer together.

If you want two pairs of wings, you certainly can! Butterflies have two large wings that slide past each other to form one large very flexible area. Dragonflies are capable of controlling each pair of wings individually, which gives them twice as many opportunities to control their flight. But that's when they fly in place - from what I can gather, they do put their wings in one plane if they want to go fast. 

The way I'm imagining your four-winged humanoids, the wider arm-wings are _under_ the long thin back-wings, and in no good position to form one larger area with them. But the overlapping surfaces can be put to great use. And what I am proposing:

The shoulder wings are long and thin, with locking joints to offer effortless flight, while the arm wings are wider, shorter, and equiped with powerful muscles both on the upstroke and the downstroke. Fliers use their shoulder wings to generate lift, and push air against them with arm wings to squeeze it backwards and gain a lot of speed. When they want to glide, they slot their index fingers into specialized claws on the front underside of their shoulder wings. To slow down, they put their wing surfaces at a sharp angle to increase the drag significantly.

If fliers want even more maneuverability, they can put their shoulder wings at an angle or fold them completely to give more space to their much more maneuverable arm wings. Trained fliers may even be strong enough to use their shoulder wings more actively during flight, but the bulk of the work during active flight would certainly be done by the arm wings. 

One big tip for advanced maneuverability: You don't want to just push air. The best way to get hold of a fluid like air is to make it go spinning first. Fish use this to get up to speed really fast. One description I've seen of how they do it is, first they create a vortex (spinning mass of fluid), then they push it to the other side of their body while creating another vortex on that side. The final result is that they create vortexes that push them forward faster than just pushing off of still water would achieve. Your fliers would likely rely on this during take-off, and only extend their second pair of wings while they're already up to their gliding speed... unless their shoulder wings are strong enough for active flight, in which case they'd flutter all four wings independently in an X-wing formation.