RE: 747 Vs 777

[mikusiaa]

I was wondering if anyone could kindly explain to me why the 747 has winglets and say, for example, 777 does not? Also if asked on an interview what brakes get hotter than the other in a tandem bogey aircraft, what the correct response would be. Thanks alot and feel free to PM...Cheers

[Notso Fantastic]

The 777 is supposed to have a better designed wing which reduces the effectiveness and need for winglets.
Tandem bogy undercarriage- we talking B52/Harrier here? I would imagine the answer is 'whichever absorbs most energy'. Decelerating, the weight is thrown forward so probably the front gear absorbs more weight hence better traction hence more energy (less skidding)?

[typhoonpilot]

Looks like someone is studying for a Cathay interview.

The hot brake question can't be answered with certainty. There are too many variables to make it the same brake every time. Factors to consider would be brake wear, crosswind, assymetrical braking, etc.

There was an answer for the winglet question couple of days ago either here or over on flightinfo. Not sure that I agreed with it since it basically comes down to looks. A 777 with winglets would look ugly :)

Good luck with the interview,


Typhoonpilot

[gas path]

Not forgetting of course that the 747 wing was designed back in the early 60's. It was just tarted up a bit for the 744 (grew a bit of span and a winglet!). The triple seven wing design probably got set in stone in the late 80's and being of a better design (supercritical?) there was no need for a winglet. Having said that, the next incarnation (read, falling sales!!) it will probably sprout a 'blended' winglet.:hmm:

[mutt]

The B777 was a victim of the NIH syndrome (Not invented here). At the time of its conception, winglets were common on Airbus aircraft. Boeing didnt want to be seen to be using Airbus ideas so they spent more time developing the wing without winglets. :):):)

That answer should see you through any interview :)


Mutt.

[Phil Squares]

I can't tell you why the 777 does not have winglets, but I can tell you why the -400 does.

One of the goals Boeing had for the -400 was an increase in TOW. But one of the constraints was to keep the footprint the same. One method would have been to redesign the wing. This was given up as too expensive (20/20 hindsight maybe that was the best option). So another 12' had to be added to the wing span to accomodate the 20 tonne increase in weight. That's where the winglets came from. It gave the-400 the ability to increase it's TOW and yet have the same footprint as the 200/300.

[Lu Zuckerman]

To: Mutt

The B777 was a victim of the NIH syndrome (Not invented here). At the time of its conception, winglets were common on Airbus aircraft. Boeing didnt want to be seen to be using Airbus ideas so they spent more time developing the wing without winglets.

Airbus Industrie did not design the small winglets used on the A-310 and the A-320. Boeing designed them under a NASA contract. When the design was completed it was given (free) to Airbus but if Boeing wanted to use the design on their own aircraft they would have to pay a large licensing fee to cover the design costs. They opted not to use them and save a few bucks.

:E :E

[747FOCAL]

The 777 wing was designed to be super efficient in cruise using latest wing technology and understanding.

The 747 winglet is there to increase span length without having to change gate size requirements. It is not as efficient as a blended winglet, but that is part of the "Not invented here" ego issues within Boeing. Aviation Partners has a blended winglet design that is 14 Ft tall and has been flight tested, but they were strangled by Boeing Senior Management when they started marketing it without permission. :E :E

Now the new 777-300ER has winglets, the raked kind. Harder to see unless your standing underneath the wing. They were designed a long time ago(I have 707 marketing photos with Raked wingtips :E ).

But..........one has to be careful when you grow an airplane many thousand pounds beyond its original intended design MAX weight. If you don't redesign certain things, winglets can cause you much headache and frustration. :E :{ :uhoh:

[dusk2dawn]

...and ANA and JAL have 747 without winglets - 747-446D and 747-481D...

[747FOCAL]

Winglets are of most benefit in cruise. These airplanes only fly about 1.5 hours avg per leg and usually less the extra wing and winglet of a 747-400 international version really don't fit well in the picture. But, if one decides to change the purpose or sell their 747-400D, one can purchase the Domestic to International mod from Boeing. :cool:

[swh]

Lu Zuckerman,

Dont quite agree with your statement of history, from memory British Aerospace did the wing design for airbus, including winglet technology.

There is a good historical report about the place "The A320 Wing: Designing for Commercial Success" seen it once before scanned in as a PDF file on the internet.

The winglets on the 320 were not original equipment on the 320-100 when it was first rolled out, was on the 320-200. Cannot speak about the 310, before my time.

Quote from this (http://airtransportbiz.free.fr/Technique/Thewinglet.html) site :

However, although a newer airplane, the 777 was not designed with winglets. At the time Boeing chose to increase the span of the wing rather than add winglets. As increased span also increases wing aspect ratio [another measure of efficiency] Boeing outlined the addition of winglets did not overcome the weight penalty of carrying winglets. Sources have since shown that increasing the span of the wing by 4/5 of the height of the winglet will have a similar effect on induced drag as a winglet, though without the added complexities of extra outboard structure, extra weight and extra cost.


:ok:

[mikusiaa]

Thanks alot to all who took the time to post a reply to my Q. I think that by putting all the points offered together, I'll be able to convince any interviewer the nuaces of the Boeing wings. Thanks alot again folks!