From: firstname.lastname@example.org (Terrell D. Drinkard) Organization: Boeing Commercial Airplane Group Date: 20 Mar 94 22:30:00 PST References: 1 2 3
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In article <airliners.1994.980@orchard.Chicago.COM>, email@example.com (Steve Derry) writes: > > On many flights on jet airliners, I have noticed that during cruise the > aircraft appears to maintain a nose-up pitch angle. > > I thought that for efficiency, airliners were designed with the > appropriate angle of incidence between wings and fuselage so that at > cruise angle of attack, the fuselage would be "level" with the oncoming > airstream to minimize drag. > > Why then do I notice this "uphill" effect? Is the fuselage actually > pitched up slightly? I love the questions that come off this group. I always end up learning quite a bit myself. Keep them coming! I cornered one of the senior aero guys and sure enough, the aero fraternity is responsible for the deck angle you've noticed. The body, as a surface of revolution, develops a moment when flown through the air at a positive angle of attack (nose up). Inviscid effect. If too much angle of attack in used, the body begins to develop lift along with the moment. Viscous effect. The body is incredibly inefficient at making lift, so the angle of attack must be kept quite small. Also, the cabin crew has a heck of a time moving those serving carts uphill if the deck angle is too large. What does this moment buy us? Reduction in trim drag through reduction in the amount of moment (lift times tail arm) generated by the horizontal tail. Less lift/moment generated by the tail, less induced drag generated by the tail. Terry -- Terry firstname.lastname@example.org "Anyone who thinks they can hold the company responsible for what I say has more lawyers than sense."