No runways on Mars, so takeoff could be difficult. Maybe we could do that once we have well prepared surfaces.
Helicopters can also hover and are much more manoeuvrable than fixed-wing.
Lift is proportional to density.
L = Cl x .5 x rho x v^2 x S
(L is lift, Cl a non-dimensional coefficient which depends on wing shape, rho is density, v is speed and S is surface area of the wing).
For fixed wing aircraft, v is speed of aircraft. For helicopters its the speed of the blade (when its in hover. When its moving forward its a bit more complex).
Haven't done the math but the aircraft has to be going pretty fast ('v' in the equation) to generate the required lift. This also means longer runway lengths.
Quad/hex would be less efficient and heavier for the same performance (range, speed, service ceiling), but yes, more stable. In this mission, I suspect minimizing weight (as a rocket payload to be sent through space) and maximizing range (hop flights on Mars on a limited power source) were a priority. This is also why full size helicopters are almost all single main rotors with a TR.
The propellers are huge in order to get this tiny helicopter to fly. A quadcopter would be larger than Perseverance, unless you devise some zero-mass hinges to make the entire thing fold into the same space that was available for Ingenuity.
My guess is that takeoff would be too difficult for a traditional winged aircraft and VTOL was way too complicated.
But given the thin nature of the atmosphere, a helicopter seems even more difficult to get lift than a winged aircraft.
Can someone explain or link to the science between lift and air density and it's relation to helicopters and winged aircraft? Thanks!