Re: Jet Engines above the wing: why not used?

From:         gcaron@mack.Rt66.com (Terra Corp.)
Organization: Rt66.COM, Public Internet Access in New Mexico
Date:         21 May 96 11:10:53 
References:   1 2
View raw article
  or MIME structure

Tony Maddern (tmaddern@cse.unsw.edu.au) wrote:
: Tom Speer wrote:
: >

: > I doubt that causing a pitch up with the application of power is a major
: > design driver in the positioning of engines.  I know of no flying
: > qualities requirement for this.  Even if were required, the aircraft
: > speed stability may result in a pitch up even for engines mounted
: > some distance above the c.g.

: I believe there is a certification design requirement for an increase
: in thrust/power to cause a pitch up in order to cover the go-around
: from low altitude case. A nose down pitching moment close to the
: ground would be most undesireable whereas a nose up pitching moment
: will assist in rotating the aircraft to the go around attitude. Speed
: stability will only come into effect once airspeed has been increased.
: TM

No such requirement.  The only real requirement is that the a/c remain
stable and controllable at all throttle settings and in all normal
configurations.

The fact is high mounted engines have been demonstrated in the YC-14. The
upper surface blowing (Coanda effect) had many benefits related to the
STOL requirements for this a/c. Real nice plane, but it (and the more
conventional YC-15) lost out in budget battles to the good old reliable
C-130.

Airliners, on the other hand, have one all-purpose goal -- to make money.
The high mounted engines cost more to operate (maintain) due to the more
difficult access, and have no significant cost benefits. If it isn't cost
effective, airlines won't buy it.

OTOH, engines *are* mounted forward of the wing for sound engineering
reasons.  It has to do with torsional and flutter modes.

Gerry

--
  Gerry Caron               "Opinions are mine, not my employer's."
  gcaron@rt66.com            PH: 800-328-1995 or 505-884-2321
  Terra Corp.  ABQ           FAX: 505-884-2384