From: firstname.lastname@example.org (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 <email@example.com>, Richard Shevell <firstname.lastname@example.org> wrote: >In article <airliners.1994.1738@ohare.Chicago.COM>, David Lednicer ><email@example.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 firstname.lastname@example.org "Anyone who thinks they can hold the company responsible for what I say has more lawyers than sense."