Why don't more jets have wings mounted above the fuselage?

Vince

Jets being fighter jets or passenger jets?

Here you go:

http://blackandwhitetravel.is/wp-conten ... 00x460.png
http://media.defenceindustrydaily.com/i ... CC2_lg.jpg
http://www.sme.sk/cdata/1862592/2004121 ... 48_big.jpg
http://www.polarflight90.com/pageImages ... _7321.jpeg
http://www.combatreform.org/A3Dskywarriorinflight.jpg
http://inktank.fi/wp-content/uploads/20 ... e-Wing.jpg

I'm going to guess because high wing anything does not look sexy.

Or aerodynamics and cabin intrusion.

It's a matter of mechanical, structural & packaging design trade-offs for the
intended mission.

Example: If optimizing a design for cargo and/or ops from unimproved runways, you
bias the design for:

- Long, flat floors
- Minimize FOD risks by getting the engines higher

The trade-off is increased airframe structure (weight) because the critical structure loads
are at multiple points.

Where do you want to put the landing gear if you have a high wing? Long gangly legs from the wings for a wide, stable stance or short legs from the fuselage for a narrow, tippy stance? Which do you prefer as a pilot or as an operator?

Choices and compromises.

I think it comes down mostly to weight. The low wing allows for short light landing gear where the wing structure serves the dual role of supporting the airplane in the air and on the ground.

High wing jet either has fuselage body gear (which means fuselage needs extra structure and it requires pods or encroaches on the fuselage volume), or it has long gear to the higher wing (which makes it heavier, weaker). With fuselage body gear, landing impacts can cause high negative G loading on the wing spar if the airplane has a lot of fuel.

Low wing allows a wide stance landing gear, less likely to sway or wobble down the runway.

Low wing keeps the wing wake away from the engine intakes (on the traditional rear engine planform for business jets). This way, wing airflow doesn't disturb jet intake flow, and wing ice shedding doesn't go into the intake either. The low wing tends to isolate the main landing gear from kicking up debris that could FOD the engines as well. High wing jets tend to be wing mounted engine pylons instead of on the tail partly to avoid landing gear FOD.

Low wing is easier to fuel if not single point.

High wing, all other things being equal, is probably a bit better aerodynamically. The CG range will be slightly larger due to pendulum effect, and the low pressure top of the wing extends across the center section yielding effectively more wing area. That turns out to be more important than the high pressure area under the low wing for some reason (which is why wing pylon engines are hung under the wing generally, don't mess with the top surface of the wing).

Generally speaking, the fuselage floor structure is stronger than the roof structure, so having the main spar attach to the floor is lighter weight. In legacy Citations, the spar penetrates the fuselage section, in the 525 series, the spar bends under the fuselage.

For a GA jet, you really can't do much better than the traditional planform, two engines in back, low wing, mid or T tail. That is why almost all of them look that way. The Honda jet with top mounted pylons is a bit different, but not really that far from the same thing. The Westwind is a mid wing, but otherwise is mostly like a low wing in terms of gear. Smallest high wing jet I know of is the Dornier 328, two wing pylon engines, about 35,000 lbs MGTOW.

Mike C.

Beauty is in the eye of the beholder.

Classic Single Engine Fighter (F-8):

https://upload.wikimedia.org/wikipedia/ ... c1978.jpeg

and the

A-7

https://youtu.be/HKDNyYSFB3I

Finally Here it IS:
http://media.defense.gov/2010/Jun/24/20 ... 5B-001.JPG

In my part of the country where hangar space is really a major constraint the high wing model is ideal. Lets me park my toys under the wing and really multiplies the available space. I wish...

Here's on more:

https://www.youtube.com/watch?v=BHOF4eXC2o4

And there is always the RJ85s and BAC146s

https://www.youtube.com/watch?v=6njrbkC ... detailpage

Well... sort of... but a lot of big swept wing jets with underslung nacelles extend some of the pylon over the wing to behave like a vortilon (which messes with the top surface of the wing and sort of does the jobs of a stall fence and a stall strip... sort of...).



You picked a good example of an outlier to contrast your explanation of why the traditional layout, as you described, is most common. The Dornier Jet is high wing because it is derived from a commuter turboprop that was itself a high wing for propeller clearance. (A lot of commuter turboprops in the 80s and 90s had big propellers with a low fuselage and cabin floor.)

Fueling high wings isn't much fun (sorry MU-2 owners). Of course if you own the jet you probably don't fuel your own plane....

Wing travel (sag at rest and lift at altitude and speed) is probably less disconcerting to the passengers of low wing planes - its not nearly as obvious....

Peace,
Don

Fueling an MU2 is no fun. I hardly ever do it myself, maybe once a year.

Note that many times, though, you only require fueling the tips, which isn't too bad.


It seems pretty obvious to airline passengers, the wing tip bouncing all around in turbulence.

I can tell if my MU2 has been fueled as I drive up to the airport just from the wing sag. It is about 8 inches from empty to full. No need to dip the tip tanks!

Mike C.

An MU-2 with a pylon mounted turbofan on each side A single point fuel system would make the fueling easier.