B777winglets

[Peover Prop]

Hi hopefully the correct forum to ask this question:

Given the facts and figures for stability and fuel consumption why are the Boeing 777 manufactured without winglets.
Also it would appear that the degree the winglets are set from the main body of the wing differs I would have guessed that the angle would be pretty constant or does it depend on surface areas of the wings and distance from fuselage
Thanks PP

[AircraftOperations]

Most newer build 777 models have raked wingtips instead, which serve a similar purpose.

[ARNTU]

winglets are also heavier than the raked tips and therefore designed for shorter sectors. the tips such as 737-800 provide improvements in climb performance in particular the second segment whereas the raked tips have greater emphasis on cruise performance.

[Mr @ Spotty M]

I remember back into my distant past that they did have an option to fit folding winglets on the B777, but nobody took them up on it because of the increase in weight and l guess complexity.
The folding idea was for easy access to gates and stands.

[Gas Bags]

737-800 or any series NG for that matter have the winglets fited to improve performance in CRUISE.

That is the reason operaters of the NG who operate shorter sectors sometimes choose not to have them fitted.

GB

[PEOPLESX]

Raked wings is another possibility to solve the "problem" with the induced drag. AFAIK are raked wings the better solution for long range aircraft -> the pressure difference between bottom and top wing in cruise is low compared to the landing configuration (with higher angle of attack and flaps set), so winglets working for start and landing but also producing some drag in cruise. Raked wings are less effective during start/landing but better for cruise flight.

But why are A380 and A340-5/600 equipped with common winglets oder wingtip fences -> i don't know, but i'm sure a lot of construction engineers at AI will know it.
All in all the performance for the whole flight counts.

mike

[Peover Prop]

Thanks to all, most informative

PP

[Callsign Kilo]

In terms of the 737NG winglets are most beneficial whilst at cruising altitude. This is when most fuel saving is noted. However as suggested it is only really of any true benefit for long sectors. The increased efficiency of the wing allows for reduced cruise power settings. However the saving is negligible if the flight is around 1 to 1.5 hrs. Believe it or not, the added weight of the winglets create a fuel penalty at certain parts of the flight!

The wings efficiency (with winglets) allows for increased climb rates which improves performance from restricted airfields (think AeroMexico and the 737-700 for 'hot and high' destinations). There is also the added de-rate and assumed temperature reduction possibility as the efficiency allows greater lift at lower thrust settings therefore reducing engine maintenance costs.

There is also the added benefit of the wingleted aircraft to reach it's optimum or indeed maximum service ceiling quicker. Step climbs are still required, especially with high payloads, however the average time to required to reach a higher level becomes reduced. A higher level equals fuel savings in terms of shortened routes due to less traffic density and turbofan efficiency. I suppose this is back to the initial concept of the main fuel saving being in the cruise.

Finally, winglets are said to add resale value to the aircraft. One of Ryanair's reasons to install them across the fleet. Plus when you are talking about a fleet of 250+ aircraft, average fuel burn with winglets is greater than without due to average sector lengths.