Why do big commercial airplanes have wings on the bottom and big (US) military airplanes have their wings on top?
In: Engineering
High wings allow the fuselage to sit closer to the ground, which aids in ease of loading. You can drive a tank into a C-17, but it would be hard to do it in a Dreamlifter.
The secondary benefit is the engines sit higher, lowering the risk of debris ingestion during take-off. There is a danger during landing, but if the engine fails after you hit the ground it’s not as dangerous.
For low wing aircraft, placing the engines close to the ground for ease of maintenance is important. Also, usually placing the wing structure (spar) through the bottom of the fuselage avoids having to strengthen a high wing design. The landing gear can also be placed on the wings in a low wing design.
There are some commenters who speak to the differences in flight characteristics, but I don’t really think that’s a major consideration when deciding, in these particular classes of aircraft, where to place the wings. There are tradeoffs when it comes to rolling stability and whatnot but I don’t think those are the main design objectives.
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