Low vs. High Wings?

Date:         31 Jul 97 12:30:28 
From:         hmt@cygnus.co.ukx (Hugo Tyson)
Organization: Cygnus Solutions, Cambridge, UK
Followups:    1
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Apologies if it's in the FAQ, a question, and suggested answer:

Why do commercial airliners have low wings and military transports have
high wings?

We figured:

Commercial passenger airliners want (all of these for passenger
 o clear, uniform cross section full length of (upper part of) body
   = with high wings, the spar &c intrudes
   = low wings, it's in the hold, no worries, can contain fuel tank
 o straight body for as long as possible
   = implies long undercarriage to let you land it without tailscrape
     - high wings get reduced ground effect and awkward maintenance
     - low wings get good ground effect and easier maintenance
     - can get along with long, weak undercarriage, runways are good, and
       landing weights are low
 o engines away from the body for reduced noise
   = and for less interference from fuselage airflow

Military transports want:
 o low body for driving stuff on & off
   = high wings needed for ground clearance and reduced FOD
     - spar is in the roof, above round, low payload bay
 o strong, so short, undercarriage needed, runways may be bad
   = see above
   = need raked up tail to let you land it without tailscrape
   = landing weight may be high, no refuel available at destination?
 o don't care about shape in tail
   = so you can have banana shaped 'plane with short legs
     - even if it's troop transport it can be banana shaped
 o don't care about noise for the payload

I know some transports have low wings & some small airliners have high
wings (usually with props on), so it ain't a complete generalisation.  But
are there any obvious, simple reasons beyond those above in combination?

	- Huge