about jet engine
 

Hi all, i am new to this forum, i just want to ask a question, may be it is quite silly, but still hope someone can answer.

As we know that the lifting force is provided by pressure difference, and by bernoulli equation, the faster the air will decrease the pressure. AND the jet engine is used to accelerate the ambient air to provide thrust. So, will it deteriorate the lifting ability and why not building it above the wing? thank you

Boeing YC-14. There will be many others more qualified to give you more detailed answers.

The VFW614 had jet engines above the wing. I believe reduced exposure of the engines to foreign object damage was the motivation for that unusual configuration.

Go look up "Coanda" effect.

It's called Upper Surface Blowing. (Fnaar, fnaar;))

http://www.globalsecurity.org/milita...amst-flaps.gif

Or a simpler version (which I used at a job interview by the way:O)

http://www.ysjournal.com/articles/20..._107612_u4.jpg

Or the complete article..

http://piyasara.com/images/content/c...p_image083.jpg

The new HondaJet has overwing engines too.

You also need very reliable fuel pumps! No gravity feed here!

...and the wheel is still round. :ok:

Hondajet story
 

Honda's justification for overwing engines


http://hondajet.honda.com/pdf/tech_p...Drag_OTWEM.pdf

YC-14 exhaust over wing
 

Check out this article on YC-14 and YC-15



1975 | 0193 | Flight Archive

see page 152 also for more details on upper surface blowing on the YC-14.

... and, of course, just about every business jet ever made along with 90% of tail mount engines on airliners have the engines mounted above the wing.

Yes, but usually not to produce a "Blown" wing.

To address the OP, as you can see, it jet efflux CAN be used to produce lift- but producing that lift also produces drag.

Thus it can help in STOL applications, but is less useful when a high cruising speed is desired.

The upper part of the wing is more important than the lower part in providing lift. Most of the lift is generated by the "sucking" force.
So aerodynamically it's better to leave the upper part of the wing undisturbed, except if you really need it for e.g. STOL designs.

I wonder what Bernoulli would have to say about this?

I think that Mr. Bernoulli would be totally speechless on hearing that we have flying machines.