Re: Rear Engined Aircraft

From:         drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Organization: Boeing Commercial Aircraft Group
Date:         15 Dec 94 05:17:37 
References:   1 2 3
Followups:    1 2
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In article <airliners.1994.1751@ohare.chicago.com>,
Richard Shevell <shevell@leland.stanford.edu> wrote:
>In article <airliners.1994.1738@ohare.Chicago.COM>, David Lednicer
><dave@amiwest.com> wrote:
>
>> 	The nacelles on 727s, DC-9s, etc. are canted nose up because of 
>> the downwash created by the wing.  You want the inlet highlight plane to 
>> be at right angles to the local flowfield, which behind the wing is 
>> deflected downwards.  DC-9 nacelles are canted up 3 degrees and I believe 
>> that the 727 nacelles are canted 3.5 degrees nose up.  The nacelles also 
>> have a toe angle.  On the DC-9, the highlight plane is toed 2 degrees in, 
>> but the engine thrust line is toed 2 degrees out.  Wing mounted engines 
>> also have non-zero cant and toe, to match the local flow field.
>
>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.  

Actually, it isn't the thrust line change that gives the increase in lift.
It is the fact that the body is flying at a 3 degree angle of attack (about
the most you can get without incurring an offsetting drag penalty).  The
thrust line is then correctly positioned for an efficient cruise attitude.
A small difference, I know, but I think it is important.

Terry

-- 
Terry
drinkard@bcstec.ca.boeing.com
"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."