Dumb questions...

[Rami]

Hey guys,

Perhaps you can help me. Going to and coming from Vienna Austria, I flew in a Boeing 767-300ER on Austrian Airlines. The flight designations were (IAD-VIE) and (VIE-IAD).

Anyway, a couple of questions...

1) Why did the jet have winglets, and how do they affect performance?

2) Why did we only fly the great circle route on the way back?

Going to Vienna we flew on the "red eye," leaving about 6:00pm and arriving at 8:40am. We flew east over the Delmarva peninsula, then flew northeast, almost directly over Worcester, Massachusetts before turning more toward the east-northeast, passing over New Brunswick, Newfoundland, and into the Atlantic. We came ashore over Brittany near St. Malo, then flew over central France before skirting the Northern edge of the Alps on the way into Vienna.

Coming back, we flew up over Germany and the Netherlands, then out over the North Sea. Where we came ashore over Great Britain, I thought we'd fly over Leeds and Blackpool, but instead we made about a 20-25 degree right turn, and paralleled the coastline to Newcastle-on-Tyne before turning back on a west-northwesterly course over southwestern Scotland. This took us up to about the southern tip of Greenland before turning southwest for home. We came in over Labrador, then crossed the Gulf of St. Lawrence and the Champlain and Hudson valleys on the way back to Dulles.

Airspeed was about 900-ish km/h going to Vienna, and about 800-ish km/h on the way home, cruising altitude was between 10,000 and 11,000 meters.

The flight returning home was much rougher than the flight to Vienna.

Anything unusual here, or have I just not flown in a while?

[Fibber]

My guess would be a combination of weather and traffic. Also with a twin engine plane some pilots like to use the circle route that has them within plausible distance of a alternate field.

[Mick]

Winglets affect performance by setting up vortices opposite from the ones normally formed at the tips as high pressure air from below the wig rolls up to fill the low pressure region above the wing. Those vortexes involve span-wise flow; that reduces the efficiency of the outer part of the wing, which is designed to produce lift as air flows from the leading edge to the trailing edge. Tip vortices also create a lot of drag. So by counteracting tip vortices, winglets increase lift and reduce drag. This improves the plane's performance and improves fuel economy.

Incidentally, Whitcomb winglets were thought up by the same aerodynamicist who brought us the area rule for efficient supersonic performance.

[sandar]

When I flew to New Zealand from London, we went north to Scotland, then north west toward Greenland, over Canada, then down the west coast of the US. I asked the same question as you. Apparently west bound flights from Europe fly over the Arctic circle because the diameter of the Earth is narrower, therefore less time spent flying into prevailing winds. I was told later, that at high altitude over the Arctic Circle, there is far less turbulence.

Eastbound flights from US to Europe tend to use more southerly air lanes and make use of the Jet-stream.