Newsgroups: sci.aeronautics.airliners Path: news From: raveling@Unify.com (Paul Raveling) Subject: Re: objects on wing tips X-Submission-Date: Fri, 11 Dec 92 20:58:52 GMT References: Message-ID: Approved: kls@ohare.Chicago.COM Organization: Unify Corporation (Sacramento) Sender: kls@ohare.Chicago.COM X-Submission-Message-Id: Date: 11 Dec 92 17:42:33 PST In article , dowlatir@cu1.crl.aecl.ca.crl.aecl.ca (Ramin Dowlati) writes: > I have a few questions for any of you passenger airplane gurus. > Several years ago, the aeropspace industry introduced vertical > flap-like things on the ends of their airplane wings. I've > only noticed these on 'larger' planes such Airbus, 747-400 and > MD-11. > Q1. What is the technical name for these flap-like things? Winglets. The most common name usage was "Whitcomb winglets" until they became fairly common. Many would say that Whitcomb was their inventor, but watching the tip feathers of large soaring birds suggests that Mother Nature should get some credit. > Q2. Are they mobile or fixed? Fixed > Q3. Do they only serve to stabilize the flight? No. Their purpose is to reduce induced drag, which they do by reducing circulation in wingtip vortices. > Q4. Why haven't they appeared on smaller aircraft? They have. In fact recent times have brought some controversy to competitive soaring, about whether winglets should count for measuring sailplane wingspan. This application uses winglets on airframes that weigh a few hundred pounds and carry one person, sometimes with about 1/4 inch of headroom for a pilot who's already laid out almost flat on his [or her] back. > Q5. The ones I saw on the Airbus were shaped like a 'V' > and symmetric with the wing tip, ie. one leg of the 'V' > was above the wing and the other pointed below the wing. > Whereas the ones on the 747-400 looked like extensions > of the actually wing, but bent 90 degrees upwards. > Why the difference? The 'V' form sounds like the classic Whitcomb design. Sailplanes don't use the downward-pointing winglet because ground clearance at the wingtips won't allow it. The same might be true of many airliners, with variations. This is just a guess: Many need clearance under the wings for servicing vehicles, such as fuel trucks. Having "hanging" winglets would increase the rate of ground damage. Some might also have a ground clearance problem for landing with an engine out, where designers usually plan for the certification limit of 5 degrees of bank (plus rudder of course) to compensate for asymmetric thrust. Finally, the extra winglet might require enough extra structure to negate most of the aerodynamic benefit it would produce. ------------------ Paul Raveling Raveling@Unify.com