757 Winglets

[haughtney1]

As a keen 757 driver, I look on with interest at the various operators about who have fitted winglets to their 757 fleets. My understanding is that there is a trade-off between fuel burn and initial capital outlay.
My questions are as follows.
1. What approximate reduction in fuel-burn is realised, with a corresponding increase in useful payload/range?
2. An approximate cost, or increase in lease rates based on present market values?
3. Is there a certain sector length that the fuel burn reduction just isnt economical enough to cover the additional costs. i.e a break-even point
4. Are there any changes in the handling characteristics of the aircraft ala increased float during the flare/crosswind sensitivity?
Thanks in advance
H:ok:

[Flight Safety]

This may help to answer some of your questions.

http://www.flug-revue.rotor.com/FRTypen/FRErstfl/FR05Erst/PR757BW.htm

[haughtney1]

Thanks Flight Safety....theres always someone on here that knows the answer:ok: ;)

[XPMorten]

I heard that if you compare two 757's one with and one without winglets,
you will see that the one with winglets burns 3% less fuel for the same weight.
However, the one without has to plan more trip fuel, and will
be heavier for the same flight, burning more. So, a total average of 5% saved.

Cheers,

M

[enicalyth]

These claims are always interesting. Boeing tell me that the 757-200 winglets will increase wingspan from 38 metres to 41 metres in round figures.

If I take the view that all they will do is reduce absolute induced drag and keep compressible drag to the same overall percentage I might as well assume that the span efficiency is the same as well, say e = 85%, and the wing area is the same.

Thus the baseline aspect ratio is 7.8 and the wingletted version is 9.2 again in round figures.

So if induced drag is ((CL)^2)/(Pi.AR.e) and I do a little guess manipulation the baseline tripartite drag equation is
CDtot = 0.0143 + (((CL)^2)/20.9) + 0.00152 so when CL = 0.5 then L/D = 18

How much better could the winglets possibly make it? Well assume parasite drag is the same. Assume span efficiency is the same at 85% (not quite true but what the heck?). And in my guesstimation I went for compressibility drag being 5.5% of the whole in the baseline situation. So redo the sums.

CDtot = 0.0143 +(((CL)^2/24.3) + 0.00142 so when CL = 0.5 the L/D now is 19.2 instead of 18 in the baseline version, an improvement of 6% and the inventors are talking about 5% so I hope my guesses are not too unintelligent.

Why do I therefore remain so hard to convince? I'm not a Luddite nor yet an embittered disbeliever. But did I sniff the teensiest bit of snake-oil in the claimants pitch?

The "e"

[Engine overtemp]

If they are that good, why doesn't Boeing install them as standard fit?

[Algy]

American Airlines is taking these on 20 aircraft at a time when it is probably performing more rigorous cost/benefit analysis than at any time in its history (since getting it wrong could mean Chapter 11 not long afterwards).

One effect is that they can use 757s on some current 767 routes, freeing 767 for greater things.

But I think you can take it that if the kit can survive the American CBA process then it definitely works.

(American also looking at 737 and MD-80 winglets BTW)

[hawk37]

Enicalyth,
I’m wondering if the induced drag component coefficient Cl^2/pi*e*AR can be manipulated in the manner you’ve shown. For example, consider the case where an aircraft’s fuselage is, say, doubled in width, from 10 to 20 feet, but made of a lighter material, resulting in a wider shape but of the SAME WEIGHT. The wingspan is increased by 10 feet, producing an increased Aspect ratio AR and thus smaller Cdi.

Does it make sense then that the aircraft has a lower Cdi and Drag induced, just by increasing the fuselage width?

Hawk

[FLCH]

Haughtney, personally I couldn't tell the handling difference between a wingletted plane and not. I heard during certification for winglets, the airplane couldn't be certified for Cat3, as the lift generated by the wings and winglets, wouldn't put the airplane on the ground in the proper place.... but this is an unsubstantiated story .(makes for a good tale anyways)

[Monde]

H
A figure of about £500k for winglets on the 738 is what i have heard being banded around with a total saving of 5% on fuel per trip.
As for landing , my firm arrivals on a non-winglet a/c suddenly become ok on a winglet one , must try and open my eyes a bit more when i do this though!!

[paperdragon]

Good Day fellow airmen!
As for flight characteristics I find the 737-800W (yes I know it´s not a 757), much more direct in roll and pitch, I think it´s easier to controll and make smooth approches and landings in :cool: , however there are some who wil say the aircraft is more unstable and trickier to fly :confused:
Boeing landings, is only invented by men who just can´t make nice landings ;)

[oceancrosser]

Now having flown the 757 both with and without winglets, I can tell you the following:

1. No apparent handling difference.
2. Maybe a little bit of float on landing if you are above your bug speed
3. Manufacturers guarantee is not based on a fixed percentage of total fuel burn, but a margin of +/- 5% OF CRUIZE FUEL BURN. That makes it difficult to calculate a linear reduction, as the block fuel reduction is fairly big on a 3000 nm sector, but hardly worth it on a 700 nm sector. Little difference in climb or decent fuel burn.
4. Price for the mods is in the +/- $800K excluding downtime.
5. Payback time for an operator w/ the average sector in excess of 1000 nm is probably less than 2 years.
6. There is also an impressive, but as yet unquantified improvement in take-off performance. Boeing/APB have not yet issued the numbers to operators, but it is significant.
7. Looks good too.

All the best.

Oceancrosser

[barit1]

Enicalyth,
I’m wondering if the induced drag component coefficient Cl^2/pi*e*AR can be manipulated in the manner you’ve shown. For example, consider the case where an aircraft’s fuselage is, say, doubled in width, from 10 to 20 feet, but made of a lighter material, resulting in a wider shape but of the SAME WEIGHT. The wingspan is increased by 10 feet, producing an increased Aspect ratio AR and thus smaller Cdi.
Does it make sense then that the aircraft has a lower Cdi and Drag induced, just by increasing the fuselage width?
Hawk

This academic problem has many similarities to a private aircraft 66 years ago. The earlier model of the ship (Howard DGA) had a 38' wingspan and advertised 185 sq. ft. area. A later model had the same span and chord (in fact identical outboard of the root), but a 6" wider fuselage at the aft spar. Yet the advertised area was 210 sq ft!

The 25 sq. ft. difference is the same as the "dotted line" projected chord x the fuselage width. It is evident the earlier ship did not count this area, and the later model did.

What is the current standard for quoting wing area - is it with or without the center section? :confused:

[hawk37]

Barit,
Further on wing area, I found this via google
“There exists no unique, universally accepted definition of wing area. Brochure numbers are often quoted without explanation or consistency, leading to misinterpretation and gross errors. It's therefore important to be aware of any treatment of wing area:
The basic reference area used in Piano is wing-area , the trapezoidal area. All relevant input parameters and coefficients are based on it. Internal aerodynamic calculations also use this reference area, making suitable corrections for any planform break.
Starting from the trapezoidal wing plus an optional planform break as outlined in the previous sections, Piano also calculates the following alternative area definitions:
Airbus (or 'Airbus Gross') definition: = exposed wing area + (area of rectangle inside the fuselage between the leading and trailing edges at the root).
Boeing (or 'Wimpress') definition: = trapezoidal area + (exposed 'yehudi' break area) + (covered 'yehudi' break area) * (fraction of exposed span at the break).
ESDU definition: = the area of a notional trapezoid having the same exposed area as the actual exposed wing, and with the same tip chord and span. (This notional trapezoid is intended as a rough aerodynamic equivalent to the entire wing. It differs from the basic trapezoidal wing).
Piano Gross definition: = the total area encompassed when extending the leading and trailing edge lines through the fuselage to the centerline”
The image below, if I’ve linked it correctly, helps to understand.
http://www.lissys.demon.co.uk/pug/fig05.jpg
http://www.lissys.demon.co.uk/pug/fig05.jpg
Basically it seems it you take distance from tip to tip, and multiply the average chord, that gives fairly close to the area. The different methods above only slightly change that. But it is very interesting that one counts the wing area as if it continues right through the fuselage. In other words, it’s the exposed wing area, plus an amount equal to the fuselage width times the root chord.
Which seems to be agreement with the definition of wingspan, which is wingtip to wingtip distance, regardless of the fuselage width.
This “may” explain the apparent decrease in induced drag coefficient, Cdi due to a larger value of aspect ratio in the denominator, in the example I previously posted. Should Cdi be less, then perhaps total induced drag may work out to be the same, since we now have a higher wing area value to use in the formula D = .5 * rho V^2 * Cd * S
Or maybe Enicalyth is just too busy to enlighten us.

[pstaney]

But wing area is a bogus number, can be anything you wish. For use in equations for lift, drag. Thats why can be used in the equation for total drag, not wetted area. Results always the same.

What's the normal bug speed reduction, you call it, for a winglet 57 over a non winglet version. Oceancrosser, can you give me AUW and speeds?

Stan