Re: Rear Engined Aircraft

From:         jjm@swl.msd.ray.com (James Murphy {75881})
Organization: Raytheon Company
Date:         07 Dec 94 01:15:46 
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In article <airliners.1994.1751@ohare.Chicago.COM>, shevell@leland.stanford.edu (Richard Shevell) writes:
|I think we said this earlier but here it is again.  In addition to the
|above, an upward inclination of the thrust line provides a little free
|lift.  The loss of thrust is trivial since the cosine of 3 degrees is
|.99863, and lift is increasd by 5% of the thrust since sine of 3 degrees is
|.05234.  

I would be interested in knowing if this is really true... because:

Aircraft are design nose-heavy to allow for stall recovery, hence the
tail is already trying to go "up".  The role of the horizontal
stabilizer is push DOWN on the tail and balance this tendancy, hence
level flight.  Adding "up thrust" will in fact require more angle-of-attack
in the horizontal stab to maintain level flight attitude, hence more 
induced drag.  Now, I have to assume that the added efficiency of canting the
nacelles up to align with downwash more than overcomes the added drag
from the stab, howvever, I can't see where vertical vectors that far from the
CG, on that long a moment arm do much to the CG in terms of vertical
components.  Sort of like trying to carry a see-saw by lifting one end. :-)


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