From: email@example.com (Ed Hahn) Organization: The MITRE Corporation, McLean, Va. Date: 22 Jun 94 16:57:49 References: 1 Followups: 1
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In article <airliners.1994.1334@ohare.Chicago.COM> "Fred Christiansen" <firstname.lastname@example.org> writes: Seeing the amount of thrust that the PW4084's can put out on the 777 prompts me to ask about wake turbulence. It is my understanding that wake turbulence has been a problem with the "heavies" -- DC-10, MD-11, 747, 767, TriStar. My guess was that this was due to the large amount of thrust put out by the engines of these aircraft. I heard on the radio that it is now known that the 757 has significant wake turbulence, just like a "heavy". The report did not say, as I recall, but I again guessed it was due to engine thrust. If that's the case, what sort of wake turbulence will a 777 put out? The thrust on those engines is amazing! Are there high-engine-thrust airplanes w/o wake turbulence problems? Why did the 757 problem come as a surprise? ------ Wake Turbulence is primarily caused by wingtip vortex shedding, not engine thrust. The wingtip vortex strength is proportional to the amount of lift the wing must generate to stay in the air (to the first order). The reason that the B757 was somewhat of a surprise is that the particular wing design chosen for that aircraft turns out to have very high intensity wake vortex for its weight, probably as an outgrowth of the wing's aerodynamic efficiency. In fact, I recall reports that the tangential velocities of the air in the vortex exceeded any previous measurement done on any airliner. However, the total energy of the vortex is smaller than that of a B747, say, because the vortex itself occurs in a smaller volume. However, if you happen to fly into that small area, it appears that you are in for one heck of a ride! ed //////// Ed Hahn | email@example.com | (703) 883-5988 \\\\\\\\ The above comment reflects the opinions of the author, and does not constitute endorsement or implied warranty by the MITRE Corporation. Really, I wouldn't kid you about a thing like this.