Why aren't winglets fitted to all 737s?

[dot]

Before you say - they were developed for the 737NGs, I know that.

What I am asking is if winglets improve fuel consumption by as much as is claimed (between 3 and 5% depending on the aircraft in question), why havent all the operators of 737-originals (-100 and -200) and classics (-300, -400 and -500) retrofitted their aircraft with winglets (either from Boeing or aftermarket) to improve the efficiency of their fleet?

With most commercial airliners spending most of their days working hard, I would have thought the commercial justification would have been easy to make.

Along these lines, I noticed that Aviation Partners have test flown their winglets on a B767 and have got (or just about got) FAA approval - they claim to have orders from 10 separate airlines for those winglets. Why not the 737s?

I am hoping some of you (especially those in the industry) may be able to share some wisdom.

 

[Mal]

I believed they were only an aftermarket option from Boeing for the 73G and as a factory fitted option for the 73H.

Not sure of the list price, but doubt they would be cheap. If you have a leased plane, then the economics may not work out.

 

[oz_mark]

I understand that the cost of retrofitting was over $1 million per aircraft.

 

[NM]

Also note that adding winglets adds weight to the aircraft. This means the added fuel efficiency only becomes viable for flights with enough cruise time to overcome the extra fuel needed to lift the extra weight of the wingets to the cruise segment of the mission.

This is why the 747-400D (the short-hail version specially built for the Japanese domestic market) does not have the winrlets that are installed on all other 747-400 models. They are simply not in the air long enough for the cruise benefits to overcome the extra weight carriage. The same stands for most missions operated by early model 737s.

Note also that not all 737NG models have the winglets. For example, the original delivery 737-800s for AA did not have winglets. Later delivers have them and they have been added to the older one.

 

[codash1099]

As I understand it, the wing needs strengthening in order to take winglets. This adds to the cost and to the weight.

As NM pointed out, this makes the economics borderline in many cases.

 

[nlagalle]

Here is a really good link about the winglets.

Boeing 737 Advanced Blended Winglets

bascially any flight over 1 hour would benefit, but how long to recoup the costs I'm not sure on.

 

[albatross710]

With the rise of fuel costs you would have to think that the original "marginal" business cases would now be in the money.

 

[simongr]

Just watched some of the Richard Hammond A380 show and the winglets are a key factor in that aircraft being able to have short enough wings to fit in most major airports.

 

[albatross710]

Slightly OT, but relevant now that you mention A380. I'm distracted by Qantas use of a doctored ground picture of the A380 in its promotional posters to make it look like it is flying.

The wings are illustrated drooped but if the aircraft was inflight, the winglets and wings would have flexed up.

inflight wings: http://farm2.static.flickr.com/1344/889258657_a4976ddec4.jpg?v=0

 

[ColinP]

Slightly OT, but relevant now that you mention A380. I'm distracted by Qantas use of a doctored ground picture of the A380 in its promotional posters to make it look like it is flying.

The wings are illustrated drooped but if the aircraft was inflight, the winglets and wings would have flexed up.

inflight wings: http://farm2.static.flickr.com/1344/889258657_a4976ddec4.jpg?v=0

I love looking out the window and watching the wings flex upwards on rotation.

I'm easily amused

 

[Flying Fox]

As I understand it, the wing needs strengthening in order to take winglets. This adds to the cost and to the weight.

As NM pointed out, this makes the economics borderline in many cases.

I also believe that installation time is also > 1 week so there is also a loss of revenue whilst the aircraft is out of service.

The overall economics may lead the business case closer to replacement of 737 Classics with 737-800 new or used.

 

[UP4014]

I understand that the cost of retrofitting was over $1 million per aircraft.

Don't quote me, but I think I read somewhere the cost was nearly $5M per aircraft for a Boeing. I guess there is a lot of pull a part and rebuild and they are a decent size.

 

[medhead]

Also note that adding winglets adds weight to the aircraft. This means the added fuel efficiency only becomes viable for flights with enough cruise time to overcome the extra fuel needed to lift the extra weight of the wingets to the cruise segment of the mission.

Could they compensate for the extra weight by removing/reducing some of the counter weight in the wing?

The wings are illustrated drooped but if the aircraft was inflight, the winglets and wings would have flexed up.

Do the wings flex up? Or does the body sag?

 

[serfty]

... Do the wings flex up? Or does the body sag?

They flex upward relative to the fuselage as the aircraft accelerates and the wings commence to take over supporting the load from the wheels.

 

[medhead]

They flex upward relative to the fuselage as the aircraft accelerates and the wings commence to take over supporting the load from the wheels.

While the wing appear to flex up relative to the frame of reference of an observer in the fuselage.

It absolute terms the wings are moving along and then flying in their normal position and the fuselage is sagging in relation to the wings because the fuselage doesn't support it's own weight (useless it's one of those flying coffins that qantas used to have) in flight. i.e. the fuselage doesn't keep up and hence flexs down.

Who says I didn't learn something in those relativity lectures - but only frames of reference.

 

[v8Statesman]

While the wing appear to flex up relative to the frame of reference of an observer in the fuselage.

It absolute terms the wings are moving along and then flying in their normal position and the fuselage is sagging in relation to the wings because the fuselage doesn't support it's own weight (useless it's one of those flying coffins that qantas used to have) in flight. i.e. the fuselage doesn't keep up and hence flexs down.

Who says I didn't learn something in those relativity lectures - but only frames of reference.

I think this is 50/50. If you look at a cross section. You will see both happening. The fuselage saging under its own weight, and the wingtips lifted due to the lift created. (All this is in flight). But at takeoff speed (but still on the ground) the fuselage is not saging, so the wings are lifted.

 

[serfty]

Nothing really "Sags" - the wings flex (a lot more than the Fuselage).

When stationary on the ground, the fuselage is supporting the wings; gravity pull the wings down, points on the wings further from the fuselage flex lower.

At airspeed the wings are quite rigid as the force to counter the immense weight being lifted is pushing the wings into the sky (along with the attached fuselage).

 

[medhead]

SNIP

Maybe....

(damn forgot gravity)

 

[straitman]

While the wing appear to flex up relative to the frame of reference of an observer in the fuselage.

It absolute terms the wings are moving along and then flying in their normal position and the fuselage is sagging in relation to the wings because the fuselage doesn't support it's own weight (useless it's one of those flying coffins that qantas used to have) in flight. i.e. the fuselage doesn't keep up and hence flexs down.

Who says I didn't learn something in those relativity lectures - but only frames of reference.

medhead,

Close but sorry no banana!

What is defined as the normal position? You could say the flight position or you could say the static position. Aerodynamically speaking the terminology is that the wings flex upward from a static position.

When the aircraft is stationary the wings are static. When the aircraft accelerates the wings generate lift and flex upward toward their flying position BUT the aircraft is in the same position relative to the ground. When the aircraft reaches flying speed there is no more sagging down or flexing upward, just the lift vectors changed by elevator control and the aircraft leaves the ground. You may also be surprised to know that the fuselage does provide some lift on its own (30% is the highest I’m aware of) so the wings and tail usually don’t have to do all the work.

There's actually a lot more to it but that's a really simplifies version. Flaps, Slats & Slots all have a big roll to play as well.

 

[medhead]

What is defined as the normal position? You could say the flight position or you could say the static position. Aerodynamically speaking the terminology is that the wings flex upward from a static position.

Ok,ok,ok, I forgot gravity! Honest mistake, could happen to anyone.

Normal position - that's a subject of a book. I was however, only making a statement of the frame of reference of judging what is moving and in what direction. Perhaps aerodynamicists are too practical and straight forward for such esoteric ideas.

Seriously, on the fuselage lift thing, there might have been a few words missing and I didn't understand. Are you saying that all fuselage contribute to the lift or only only some fuselage? If the later, I did realise that hence my reference to the BAe aircraft that qantas used to operate that looks like a coffin. If the first thanks for the info.