Newsgroups: sci.aeronautics
From: shevell@leland.stanford.edu (Richard Shevell)
Subject: Re: High vs Low wing Commercial jets
Date: Thu, 16 Nov 1995 13:36:46 GMT

>[Moderator's note:  The great flying public doesn't like high-winged
>aircraft.  They don't look like real airplanes and the gfp won't fly
>in them.  Same thing for engines mounted over the wing rather than
>under it.  MFS]


There are good reasons why low wing configurations are generally used in
commercial airplanes, reasons other than public bias. Once the passengers
load, most of them don't know where the wing is anyway.
 1) The major structure of the wing does provide some crash protection. 
 2) The wing shields much of the cabin from the acoustic waves (noise)
produced by the jet exhaust.  With high wings the passenger is looking
right at the engine nozzles.
 3) Accessibility to the nacelles for engine maintenance.  In a small
airplane like the HS-146, this is less important.  
 4) A swept high wing has excessive dihedral stability provided both by the
high wing arrangement and by the sweep effect.  The faster the airplane,
the more the sweep angle and the worse this problem gets.  A lot of
negative dihedral is required to counteract it.  (The HS-146 does not have
a high sweep angle. only 15 degrees)

	I do not have the detailed cost comparisons but the HS-146 probably
suffers cost penalties because it is a four engine airplane.  Service
checks require more time when there are more engines.  Also engine first
cost and overhaul is less for the same total power in a smaller number of
units.  That is why the 757, 767, and 777 are two engine configurations.  I
believe somebody mentioned the cost of the HS-145 is lower than a 737. 
That may be true per mile but it has fewer seats. The cost per seat mile is
probably higher. 

For military cargo aircraft, the loading advantages of a low floor is
predominant.  Furthermore the cargo does not care about noise so the high
wing is used.  Troops may not like the noise but their choices of airplane
are very limited,

Another point, if I remember correctly, it is more difficult to minimize
fuselage-wing interference drag at cruise condititons with a high wing
arrangement. The filleting is tricky and I think a drag penalty usually
results.  A significant piece of the upper surface wing area has to face
the fuselage boundary layer.  In the low wing case, the corresponding
problem is faced by the lower surface which has a pressure distribution
much better able to tolerate the boundary layer.  Of course, the low wing
wing-fuselage fillet must be properly done but means for this are well
established.
-- 
Richard Shevell
Email: shevell@leland.stanford.edu