Winglets
- Thread starter B767
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PGT
Well-Known Member
made me wonder so i hit up google and found this
also discussion here http://www.airliners.net/discussions/tech_ops/read.main/134164/
also discussion here http://www.airliners.net/discussions/tech_ops/read.main/134164/
Maximilian_Jenius
Super User
PGT said:
Which makes you wonder why the 787 comes with winglets? It is the newest Boeing plane...why not make it with with a wing similar or better to the 777's if the 777 doesn't need winglets.
seagull
Well-Known Member
It's a mission thing. The 767 and 777 were marketed to be both long and short haul. Winglets aren't that useful for stage lengths under a certain value, as the gain is not offset enough by the weight and drag when in less than optimum speeds.
The key to this is in understanding how winglets work in the first place. They essentially act as sails, developing a forward thrust vector in almost the same way as a sail boat tacks into the wind. The inboard flow vector at the tip combined with the forward motion, yield the L/Dmax for the winglet at only one combination of AoA.
Contrary to what was written above, the 777 could benefit from them, if you were going to only use them for a very specific operation, but, as has been stated, due to the wing design and efficiency, you would lose performance over too much of the rest of the type of operations.
I do not know for certain, but I would venture the RJs have winglets more due to requirements for shorter wingspan to fit into tight gates, so they are trying to find some way to make up for it. The MD-11 would not have had them had MD been willing to put the money into a new wing, instead of just trying to get more efficiency out of a DC-10-30 wing. In spite of that, the MD-11 is close enough to the 777 numbers (considering more engines and higher payload capability) that it is clear that, had the MD management been a little more forward thinking, we might not have much of a 777 market today.
The key to this is in understanding how winglets work in the first place. They essentially act as sails, developing a forward thrust vector in almost the same way as a sail boat tacks into the wind. The inboard flow vector at the tip combined with the forward motion, yield the L/Dmax for the winglet at only one combination of AoA.
Contrary to what was written above, the 777 could benefit from them, if you were going to only use them for a very specific operation, but, as has been stated, due to the wing design and efficiency, you would lose performance over too much of the rest of the type of operations.
I do not know for certain, but I would venture the RJs have winglets more due to requirements for shorter wingspan to fit into tight gates, so they are trying to find some way to make up for it. The MD-11 would not have had them had MD been willing to put the money into a new wing, instead of just trying to get more efficiency out of a DC-10-30 wing. In spite of that, the MD-11 is close enough to the 777 numbers (considering more engines and higher payload capability) that it is clear that, had the MD management been a little more forward thinking, we might not have much of a 777 market today.
Minuteman
I HAVE STRONG OPINIONS ABOUT AUTOMOTIVE LIGHTING!
I was about to say that the lack of winglets on the 777 might have something to do with how "flexy" the wings are ... that the amount of tip deflection (and corresponding changes to the relative wind on the winglet) throughout the normal range of operating weights is too significant to "average out" to any appreciable savings.
Or, it could also be due to some kind of decreased flutter margin (a la VMO varying depending how much gas you have in your tip tanks) ... hit some significant turbulence or the pressure distribution changes as you push into transsonic speeds and the response could be more dramatic when you have a less-rigid structure.
But, the 737NG wings are also pretty bendy compared to the older planes, so maybe I'm full of it. The only thing I can think of is that minimum-to-maximum weight operating range of the 737 is small enough, and the wings are still sufficiently rigid to constrain the operating condintions into something that allows a net gain from winglets.
Case in point (maybe?
if you assume there won't be much variation in ZFW). The 787-8 and 787-9 have MTOWs of 476000 lb and 540000 lb, both with 224600 lb usable. That's a potential weight variation from takeoff to landing of 41% and 47% of the MTOW and neither of these planes has winglets (interestingly, they have different wingspans of 197 ft and 203 ft). The short-range 787-3 has a max gross takeoff of 361000 lb with 74200 lb usable. That's a potential variation of 21% MTOW and it does have winglets (and a horizontal wing span of 170 ft.)
Just for numbers:
a high gross weight 777-200 can be up to 52% fuel (couldn't find numbers for the -200LR),
a 737-700 up to 35% (30% with winglets if I read Boeing's table correctly),
a 737-900ER up to 32% (28% with winglets),
BBJ up to 42% and BBJ2 up to 40% ... that's a little high to exactly support the theory unless someone can tell me the SFC of a BBJ isn't as good as its -700 and -800 equivalents,
an MD-11 up to 42%,
and a CRJ-700 up to 30%.
So, who's working on those variable-geometry winglets? :yar: That's the best solution, isn't itsarcasm?
Or, it could also be due to some kind of decreased flutter margin (a la VMO varying depending how much gas you have in your tip tanks) ... hit some significant turbulence or the pressure distribution changes as you push into transsonic speeds and the response could be more dramatic when you have a less-rigid structure.
But, the 737NG wings are also pretty bendy compared to the older planes, so maybe I'm full of it. The only thing I can think of is that minimum-to-maximum weight operating range of the 737 is small enough, and the wings are still sufficiently rigid to constrain the operating condintions into something that allows a net gain from winglets.
Case in point (maybe?
if you assume there won't be much variation in ZFW). The 787-8 and 787-9 have MTOWs of 476000 lb and 540000 lb, both with 224600 lb usable. That's a potential weight variation from takeoff to landing of 41% and 47% of the MTOW and neither of these planes has winglets (interestingly, they have different wingspans of 197 ft and 203 ft). The short-range 787-3 has a max gross takeoff of 361000 lb with 74200 lb usable. That's a potential variation of 21% MTOW and it does have winglets (and a horizontal wing span of 170 ft.)Just for numbers:
a high gross weight 777-200 can be up to 52% fuel (couldn't find numbers for the -200LR),
a 737-700 up to 35% (30% with winglets if I read Boeing's table correctly),
a 737-900ER up to 32% (28% with winglets),
BBJ up to 42% and BBJ2 up to 40% ... that's a little high to exactly support the theory unless someone can tell me the SFC of a BBJ isn't as good as its -700 and -800 equivalents,
an MD-11 up to 42%,
and a CRJ-700 up to 30%.
So, who's working on those variable-geometry winglets? :yar: That's the best solution, isn't it
sarcasm?
Maximilian_Jenius
Super User
Would putting winglets on the horizontal stabs produce any benefits or negatives in terms of performance? Always wanted to know!
seagull
Well-Known Member
I do not think it's an issue of the weight change so much as AoA.
As for the horiz stab, not much to be gained there. If you had a significant tail-down force, then it might be possible, but the idea is to NOT have that by loading the aircraft fairly aft, towards neutral stability with FBW enhancements.
As for the horiz stab, not much to be gained there. If you had a significant tail-down force, then it might be possible, but the idea is to NOT have that by loading the aircraft fairly aft, towards neutral stability with FBW enhancements.
caliginousface
Frank N. Beans
http://www.boeing.com/commercial/aeromagazine/aero_17/winglet_story.html#1
Talks about why the put winglets on certain models and why they didn't.
Talks about why the put winglets on certain models and why they didn't.