Top Mounted Engines?


Vice President of Awesome
I was looking at a picture of the Antonov AN-74 and it got me wondering what the advantage of having the engines mounted on top of the wing were. I know it will help to reduce FOD but other than that, I can't think of any reasons. Anyone care to shed some light on this?


Here is a picture of an AN74...
According to a website I found about the YC-14 (a very similar plane):

"To this wing Boeing added an advanced wing upper-surface blowing concept, mounting the twin turbofan engines forward and above the wing so that their efflux was exhausted over the wing (this location also gave the airplane a quieter noise footprint.). With the wing's leading-edge flaps and Coanda-type trailing-edge flaps extended, the high-speed airflow from the engines tended to cling to the upper surface of the wing/flap system and was thus directed downward to provide powered lift. It was the most efficient powered-lift system ever developed. "
A multi-engine prop aircraft has a big advantage if you want stol performance. As soon as the engines increase rpm, they create not only instant thrust, but instant lift as well. This is due to the 'induced airflow' over the wings. You already know that the amount of lift a wing can create increases with airspeed. In a prop aircraft you can use the engines to blow air over the wings and create lift instead of having to go faster.

Jet aircraft are at a disadvantage in this regard. If you throttle up, you just get more thrust. You must then accelerate the aircraft to get more airflow over the wings to increase lift. Or, you can mount the engines on the top of the wings. This gives more airflow over the tops of the wings to create more lift at slow speeds. Through the use of slats and flaps you can get acceptable stol performance and still cruise at a higher speed than a prop aircraft. If you use special systems like 'blown flaps' you can get still more low speed performance. These tap bleed air from the engine and use it to energize the boundary layer on the upper surface of the wing at high angles of attack, to delay airflow separation and stall.