Recently in Aviation Category

A friend and I were chatting this morning. It started with "how was your weekend?"

I said we went out on one of the Newport Marina's skiffs and did some fishing while the Eco-Wife sunbathed, yada yada, which migrated to us talking about the advantages of sailing vs powerboats, which wandered into a discussion about sail efficiency, and somehow we ended up talking about aircraft wings and winglets.

LOL - couple Navy aviation buffs, obviously.

Anywho, we wondered aloud about how long winglets have been around and why they weren't on every plane since they apparently save aircraft fuel.

So here's the deal:

Commercial airplanes have to overcome two types of drag: (1) skin friction and (2) induced drag. Ride a bike down a hill or stick your hands out a moving car's window and you already know what the first feels like.

The second is caused when air flows over the wings and lifts the plane. You can't do much about induced drag, since you wouldn't have "lift" without it. It's the same force that pulls against your string to lift a kite it into the air. Near the end of the wings this lifting force wraps around the wingtip in little tornados ("vortices"). Here's an awesome picture! Putting winglets on the ends cuts these vortices down, almost eliminating this kind of induced drag.

Wingtip vortices are the most pronounced when the wings are doing the most lifting, which is usually when the plane is flying slowly and during takeoff and landing. So that's when winglets help the most.

But surprisingly, they can also hurt a plane's fuel economy. Once the plane has leveled off and is zooming along the extra friction from the winglets cancels out (or even subtracts) the benefits they provide at other times.

The Air Force recently completed a complex study that found some larger aircraft (cargo, aerial refueling) benefited from them and some didn't depending on the shape of the wing and the type of flying (lots of takeoff/landings vs hours of long cruise).

Then there's the cost of installing them. It's comparatively cheap to build them as part of a new wing, which the Air Force did with the C-17 cargo plane. But the Air Force found the cost of adding them to existing planes quickly out-paced any fuel savings costs, at least for now. As fuel costs rise that will probably change.

Oh - and the USAF study on winglets is already 15% over budget. LOL!

Here's a wiki with lots of good info.