Rick767 From United Kingdom, joined Jan 2000, 2662 posts, RR: 51
Reply 1, posted (12 years 3 months 2 weeks 4 days 16 hours ago) and read 916 times:
Winglets reduce "Induced Drag" which is created by all wings when they create lift. It is simply an indesireable, but inevitable by-product of lift.
Induced drag basically creates a rearward component of the lift vector at the wing tip, where the airflows from the upper and lower surface of the wing interact (they are forced to interact by tha abrupt ending of the wing!).
This rearward component acts like all rearward forces on an aircraft, as drag.
Now winglets are small vertical aerofoils which form part of the wingtip. They are usually specifically shaped and angled to the induced airflow to generate a small forward force (a negative drag, or "thrust"). They partly block the air from flowing from the bottom to the top surface of the wing, reducing the strength of the tip vortex which is the cause of induced drag.
Also, the small vortex caused by the winglet itself can be designed to interact with and further reduce the strength of the main tip vortex... clever stuff.
All in all this reduction in drag means less thrust means less fuel means less cost per-seat-mile and so on...
I know of no disadvantages of having winglets, though I recall a 747-400 (BA I think) which had the winglet bashed by something and it had to be removed. The aircraft continued to fly in revenue service for a week or so with only one winglet whilst a replacement was shipped over. The fuel penalty for having just one winglet was 4% or so.
There are pictures on the net somewhere of the "single winglet 747"!
I hope this helped you out.
I used to love the smell of Jet-A in the morning...
Jetguy From , joined Dec 1969, posts, RR:
Reply 3, posted (12 years 3 months 2 weeks 3 days 15 hours ago) and read 884 times:
For what it's worth, I believe that it was Marcel Dassault, the famous French aircraft designer, who said that properly designed wings don't need winglets. I'm not an aeronautical engineer by any means, but I've flown thousands of hours in turbojet aircraft that were essencially identical except some had winglets and some didn't. My personal observation is that what ever small performance gains they provide often is usurped by the handling penalties they impose. Additionally, from what I've heard and read, their design is still somewhat of a "black art" and claims for increased efficiencies can often be tenious at best. It seems to me that few new aircraft with "clean sheet" wing designs, such as the Boeing 777, incorporate them, while airframe manufacturers will use them on "old technology" designs (B747-400) that they've tried to fix with minimal redesign costs.
EssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 4, posted (12 years 3 months 2 weeks 3 days 14 hours ago) and read 874 times:
Winglets add form drag and weight to a design. The reduction of induced drag typically occurs at low angles of attack for winglet equipped a/c; ie cruise flight.
The Domestic version of the 747-400 spends little time at cruise; winglets are not optimal for that application. Therefore, the -400 domestic is not winglet equipped as the climb, descent, and weight penalties are not offset by ample time at cruise.
There is no design aspect in a/c design that doesn't have disadvantages...if winglets had no disadvantages, every design would utilize them.
Broke From United States of America, joined Apr 2002, 1322 posts, RR: 3
Reply 5, posted (12 years 3 months 2 weeks 2 days 3 hours ago) and read 829 times:
One disadvantage of modifying an airplane to include winglets is that the load distribution across the wing generated by areodynamic forces changes greatly. The result is that the outboard portion of the wing is carrying higher loads and is subject to more bending. Since there is a considerable amount of wing flex, this would most likely exhibit problems in the fatigue life of that portion of the wing, than ultimate load structural problems.