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RAT 5
6th Sep 2007, 22:21
I've been flying the B73NG with winglets for a while. We are still using non-winglet fuel burn calculations. I do not know why short haul a/c are fitted with winglets; is it fuel burn or takeoff/landing performance plus time to CRZ? I saw that Air France had Airbus's without winglets and was told that they were not necessary for short sectors.
Anyway, I have not noticed any fuel saving with winglets over the non-winglet expected fuel burn. So, what is their use on short-haul ops? If it allows better takeoff performance it might allow great assumed temp reductions, thus better engine maintenance. If it allows greater RTOW's then there is a benefit in payload; sector fuel saving does not seem to be the case. Does anyone know the real reason some airlines fit them; and does anyone know what sector length is necessary to see a fuel saving?

Ivanbogus
6th Sep 2007, 22:59
The first AF airbuses had no winglets. BA have a few of them too.

Airbus38
6th Sep 2007, 23:10
As I understand it (not the most well informed person though - that's my disclaimer) the decrease in induced drag is fairly well balanced by the increase in profile drag created by fitting them.

Seems it's an issue of pure cosmetics.

easymoney
7th Sep 2007, 09:23
On our fleet all the aircraft are now fitted with winglets. Reckon they managed to get them for next to nothing, so already have increased the value of the fleet and the resale price tag.

Quite alot of our trips are for example 4 sectors, made up of three hours there and back followed by a short sector of one hour there and back. So it would be very difficult to juggle aircraft if it was mixed fleet of non and winglet ac.

On the longer trips the fuel burn is often half a ton less than planned, with maybe only 0.1 of a ton saved on the shorter trips.

RAT 5
7th Sep 2007, 14:24
Fuel less than planned is often accounted for by shorter than planned SID's & STARS + short cuts enroute. On a few trips, I have flown optimum uninterupted climb, CRZ at optimum, idle descent to straight in approach, spool up <1500'. Flight time was exact the plan to the minute. Sector flight time +/-1.45. Thus about 1.00 in CRZ. Taxi time at each end insignificant. The taxi out fuel was less than allowed and thus the taxi in fuel was already in the numbers. The fuel burnt was exactly the non-winglet plan. Thus no savings for the winglets.

Any other sector fuel savings I have made could be accounted for by shorter flight times. They balanced. The inflight winglet CRZ F.F. seems the same, within gauge error.

I assume that the long-haul heavies show some savings, otherwise what's the point, but for us.....? Hence my thoughts about takeoff performance.

Algy
7th Sep 2007, 15:25
The 737 winglets business case has been pretty thoroughly tested and I don't think there's any fundamental question over it anymore. Some pretty demanding customers have accepted the vendor's numbers after substantial in-flight trials - the North German tour operators, Ryanair of course (no pushover), and American and Delta (ditto). But clearly stage-length is pretty crucial.

JAL declined them for the 747-400 on domestic routes after deciding the weight penalty was never overcome on those routes.

Oh, and I just had the pleasure of watching the A380 fly without its tip fences on the Hong Kong flypasts this week. I don't know what it does to the economics, but in my view it looked better without.

Checkboard
7th Sep 2007, 22:30
Generally accepted that the winglet's increased weight outweighed the drag benefits in sectors less than 3 hours. After that the drag benefits outweighed the weight issue.

Operators that ran short sectors and looked at the numbers chose not to order them.

Competitors who ran short sectors, and knew that passengers were normally loaded via the tarmac (as opposed to a jetway/aerobridge) specified them because it made the aircraft look newer, and the efficiency difference was negligible.

CaptainSandL
7th Sep 2007, 22:37
Checkboard,

It depends upon the fuel price. The break-even sector length can be as low as 1.5 hours if fuel price is v high. It also varies with 737 series.

S&L

archae86
7th Sep 2007, 23:41
There is a quick listing of 737 winglet claimed benefits at:

737 winglet summary (http://www.b737.org.uk/winglets.htm)

My impression is that the 737 NG winglets break even on fuel use at a very much shorter sector length than do the 747-400 ones.

Algy
10th Sep 2007, 08:57
...the other issue that American looked at was the effect on gate utilisation, because 737 winglets meant they could no longer be parked with widebody wings overlapping them. Eventually concluded that the advantages outweighed any downside.