Are there advantages or disadvantages to a mid wing design for a monoplane? If so, how would this design compare to a high wing or a low wing monoplane design?
What might be the aerodynamic advantages or disadvantages?
What might be the design or structural advantages or disadvantages?
What might be the control or flight characteristic advantages or disadvantages?
The mid wing is mostly used in combat aircraft and rarely in passenger jets. The reasons are mostly structural.
Aerodynamically, the mid wing is the best option as it is much more streamlined and has less interference drag compared to the high and low wings.
The mid-wing also has neutral roll stability, which is good from the prespective of combat and aerobatic aircraft as it allows for the performance of rapid roll maneuvers with minimum yaw coupling.
The mid wing has certain disadvantages when it comes to structural design as far as passenger and cargo aircraft are concerned- the wing will have to either pass through the fuselage, eating into usable volume or the structure has to be strengthened around the fuselage to carry the loads. This is the main reason this type of wing is rarely found in commercial airliners.
There are some aircraft which do have mid mountedwings, like the Piaggio Avanti, which has the wings passing behind the cabin and canards and the Hansa jat, which solved the problem by sweeping the wings forward and thus passing it through the rear fuselage. These types are rare, however.
Image from hansajet.de
This type of wings are used by a number of combat aircraft, however, for example, the Dassault Rafale.
Image from http://indiandefence.com
For combat aircraft, the adoption of mid wings means that the landing gear have to retract into the fuselage for keeping the length under check. The mid wing allows for the carriage of weapons and fuel tanks in underwing pylons however. Also, the pilot's visibility is not affected during turns as in the case of high wing.
A mid wing design is mostly used on aerobatic and combat aircraft. The wing spar carry-through would be where the payload needs to be in transport and passenger aircraft, so a mid wing is the worst choice for these types of aircraft. When Boeing turned the B-29 into an airliner (the 377 Stratocruiser), they needed to add a second tube on top of the original fuselage, turning a mid-wing design into a low-wing.
Boeing 377 Stratocruiser (picture source)
Patty Wagstaff's Extra 300 over Florida (picture source).
They have a main structural advantage:
Mid mounted wings have the advantage of being structurally efficient when aerospace engineers desire to incorporate a swept or tapered wing design on the aircraft. This increase in structural integrity is essential for aircraft that perform extreme maneuvers or aerobatics
Source: Student Pilot News
They also leave the aircraft free of spars on the belly and room for cargo. And they reduce the induced drag The main disadvantage is the speed. The fastest planes use low-wings. Also many of this aircraft use spars in the middle of the fuselage, so you have to have a bigger fuselage and thus more weight.
It is aerodynamically the cleanest and most balanced, but the carry-through spar can reduce the useful fuselage volume near its centre of gravity, where space is often in most demand. It is common on high-performance types such as sailplanes.
A low wing allows the pilot to have a good visibility and a lighter structure because as it is below fuselage, it doesn't have to carry more weight. But there's also a main disadvantage which occurs when landing; it produces a strong ground effect compared to the high and mid-wing. In case of an emergency you can step out and can be used as overwing exits. And finally, they have better flexibility.
A high wing provides also good visibility and lateral stability. Also increases ground clearance for the engines and cargo. More info can be found here and here.
