eastern747
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Why No Winglets On 747-830?

Wed Aug 31, 2011 7:52 pm

I just saw a great picture of LH 747-830. I was surprised to see no winglets. Just wondering why(?)
 
PC12Fan
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RE: Why No Winglets On 747-830?

Wed Aug 31, 2011 7:53 pm

Wing efficiency basically. That and it is equipped with raked wingtips versus winglets.

[Edited 2011-08-31 12:58:42]
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fpetrutiu
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RE: Why No Winglets On 747-830?

Wed Aug 31, 2011 7:55 pm

it has raked wingtips ala 777, 787. They are supposedly more efficient than winglets but increases the lenght of the wing.
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Starlionblue
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RE: Why No Winglets On 747-830?

Thu Sep 01, 2011 2:14 am

Quoting fpetrutiu (Reply 2):
it has raked wingtips ala 777, 787. They are supposedly more efficient than winglets but increases the lenght of the wing.

There's the crux. Raked wingtips are more efficient than winglets. However on a plane that has to fit in narrow gates there may only be space for winglets. That's why the 380 has gates/winglets. Airbus would rather have made the wing longer but they had to fit in the 80x80 meter "box".


Also note that it is 747-8. The "30" is the Boeing customer code for Lufthansa/Condor.
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3rdGen
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RE: Why No Winglets On 747-830?

Thu Sep 01, 2011 6:40 am

There's plenty of info about raked wingtips out there but I wanted to clarify a logical thought I had about the actual path of the spanwise airflow, and whether I am right.

As we know the point of these wingtip devices is to stop or lessen the effects of wingtip vortices. with regard to the rake tip, is the spanwise flow from the main part of the wing, when it tries to come over the end of the wing forced then to travel over the rake, and therefore continue as laminar flow, with the resulting vortex off the rake tip being much smaller. Essentially what I'm saying is that does the rake act like a second wing which the low pressure air from the main part of wing is forced to travel over as opposed to mixing with the air above, with the resultant vortex much smaller than that which would be created without the rake.

And a second question, is the angle of incidence of the rake the same as that at the end of the main part of the wing.
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RE: Why No Winglets On 747-830?

Thu Sep 01, 2011 1:29 pm

Quoting Starlionblue (Reply 3):
Also note that it is 747-8. The "30" is the Boeing customer code for Lufthansa/Condor.

Both are equally correct. Much the same as a 737-7H4 can also be described as a 737-700, it all depends on how generic you want to be. I anticipate that 747-8s will be registered with the FAA as 747-8xxs (with a 3-digit suffix), as there's no other way to effectively denote the whole model number.

Quoting 3rdGen (Reply 4):
There's plenty of info about raked wingtips out there but I wanted to clarify a logical thought I had about the actual path of the spanwise airflow, and whether I am right.

A raked wingtip is effectively an extension of the wing. It serves the exact same purpose as a winglet, with an added benefit of also generating some additional lift due to its horizontal orientation. The concept isn't overly complicated; a normal wing will lose some of its lift-generating capability outboard due to spanwise flow. The closer to the wing tip, the greater the effects of spanwise flow. A raked wingtip extends the wingspan and allows more of the actual airfoil to function effectively in relatively free-stream air. Additionally, the taper of the wing tip lessens the intensity of the vortex formation at the tip.

As for the tip incidence, I have no idea. Airliner wings are highly optimized through experimentation, and may feature varying degrees of twist in the main airfoil section. I can't think of a reason to twist a wing tip device relative to the airfoil, but I can't back that up with an evidence. Not much has been published about raked wingtips, as they're pretty unique to Boeing.
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Starlionblue
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RE: Why No Winglets On 747-830?

Thu Sep 01, 2011 2:05 pm

Quoting KPWMSpotter (Reply 5):
Quoting Starlionblue (Reply 3):
Also note that it is 747-8. The "30" is the Boeing customer code for Lufthansa/Condor.

Both are equally correct. Much the same as a 737-7H4 can also be described as a 737-700, it all depends on how generic you want to be. I anticipate that 747-8s will be registered with the FAA as 747-8xxs (with a 3-digit suffix), as there's no other way to effectively denote the whole model number.

Generically speaking, none of the 747-8s will have winglets.  
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RE: Why No Winglets On 747-830?

Thu Sep 01, 2011 2:18 pm

Quoting KPWMSpotter (Reply 5):
As for the tip incidence, I have no idea. Airliner wings are highly optimized through experimentation, and may feature varying degrees of twist in the main airfoil section. I can't think of a reason to twist a wing tip device relative to the airfoil, but I can't back that up with an evidence. Not much has been published about raked wingtips, as they're pretty unique to Boeing.

Often the twist will decrease slightly (lower angle of attack) this helps with the bending stresses on the wing as its a long lever all the way out there.

Also one of the benefits of the raked wing tip is that when the wing loading increases the tendancy for the wing is to flex upwards which in a swept wing aircraft also means that the angle of attack reduces. This effect increases with a higher wing sweep and so if you increase the sweep towards the tip then as high loading is put on the wings they will flex but the spanwise loading of the wing will move inboard making the forces on the wing lower, this of course means that the wing structure can be lighter. This of course has to be weighed up and optimised with the twisting forces in the wing. (does that make sense?)

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tdscanuck
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RE: Why No Winglets On 747-830?

Thu Sep 01, 2011 4:12 pm

Quoting 3rdGen (Reply 4):
As we know the point of these wingtip devices is to stop or lessen the effects of wingtip vortices.

You cannot stop the vortices on a finite span wing, regardless of wingtip treatment. It's just there to lessen the effect that all the shed vorticity has on the rest of the wing. The tip vortex by itself is a relatively minor contributor...it's the vortex sheet shed off the whole trailing edge that's a much bigger factor.

Quoting 3rdGen (Reply 4):
with regard to the rake tip, is the spanwise flow from the main part of the wing, when it tries to come over the end of the wing forced then to travel over the rake, and therefore continue as laminar flow, with the resulting vortex off the rake tip being much smaller.

This is not a laminar vs. turbulent issue...the flow over the vast majority of an airliner wing will always be turbulent. Laminar vs. turbulent doesn't have anything to do with the size of the tip vortex.

Quoting 3rdGen (Reply 4):
Essentially what I'm saying is that does the rake act like a second wing which the low pressure air from the main part of wing is forced to travel over as opposed to mixing with the air above, with the resultant vortex much smaller than that which would be created without the rake.

The rake does act like an extension of the main wing. All the same aerodynamics apply. The raked tip doesn't change the size of the tip vortex much (it is smaller but not "much smaller"). It's major effect is to reduce vorticity shed by the rest of the wing.

Quoting 3rdGen (Reply 4):
And a second question, is the angle of incidence of the rake the same as that at the end of the main part of the wing.

It won't be exactly the same...typically it's a bit lower.

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RE: Why No Winglets On 747-830?

Thu Sep 01, 2011 8:44 pm

Quoting tdscanuck (Reply 8):
You cannot stop the vortices on a finite span wing, regardless of wingtip treatment. It's just there to lessen the effect that all the shed vorticity has on the rest of the wing. The tip vortex by itself is a relatively minor contributor...it's the vortex sheet shed off the whole trailing edge that's a much bigger factor.

Well now we're getting technical, this is fun.  

For the sake of discussion in this forum, it seems that most explanations boil down to the horseshoe-vortex model, where the wing tip vortex is the only source of circulation aft of the wing. The horseshoe model is complicated enough for most enthusiasts...

If you do take a look at the wing via the Prandtl Lifting Line theory, yes, the trailing vortex sheet does vary with position along the span, but dismissing the tip vortex is going a bit too far. The strongest of the trailing vorticity will always be at the wing tip, regardless of which theory you're looking at. The creation of the vortex sheet can also be traced to the same phenomenon which create the fictitious single tip vortex.

Not disagreeing with you, I just think your use of "vortex sheet" is a little misleading to those unfamiliar with Prandtl.
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RE: Why No Winglets On 747-830?

Thu Sep 01, 2011 11:50 pm

Quoting Starlionblue (Reply 3):
. That's why the 380 has gates/winglets

Here is a related question: Why does the A380 have A320-style wingtip fences, and not a more modern wingtip device, like a sharklet perhaps. It's hard to believe that significant engineering wasn't devoted to the A380's wingtips (being an ULH airliner and all), but if so, how does a normal wingtip fence suffice, when Airbus is promising such a significant fuel savings (3.5%) simply by adding sharklets to A320s?
 
tdscanuck
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RE: Why No Winglets On 747-830?

Fri Sep 02, 2011 12:28 am

Quoting KPWMSpotter (Reply 9):
If you do take a look at the wing via the Prandtl Lifting Line theory, yes, the trailing vortex sheet does vary with position along the span, but dismissing the tip vortex is going a bit too far.

The vortex shed from the tip itself is pretty tiny (i.e. if you're 0.5" behind the wingtip). It takes about a semispan (half the wingspan) for the vortex sheet to completely roll up and form the trailing vortex.

Quoting KPWMSpotter (Reply 9):
The strongest of the trailing vorticity will always be at the wing tip, regardless of which theory you're looking at. The creation of the vortex sheet can also be traced to the same phenomenon which create the fictitious single tip vortex.

Absolutely true. The difference between the single lifting line and the distirbuted lifting lines is where the vorticity actually physically is. The horseshoe model perpetuates the inaccurate idea that the entire vorticity is streaming from the wingtip, which has lead to a huge amount of really terrible ideas for vortex reduction because it causes people to think a relatively small device (about the size of the vortex) at the wingtip can make a big difference. It can't. That's why winglets are so big...you need to alter airflow over a significant portion of the wing to make a meaningful difference in the overall vortex strength.

Quoting KPWMSpotter (Reply 9):
I just think your use of "vortex sheet" is a little misleading to those unfamiliar with Prandtl.

Fair comment. The important thing is that the physical picture is much more like this:


A lot of textbooks present it like this, which is incorrect:


It's pictures like the last one that perpetuate the inaccurate idea that the winglet somehow blocks the vortex.

Quoting bonusonus (Reply 10):
Why does the A380 have A320-style wingtip fences, and not a more modern wingtip device, like a sharklet perhaps.

The A380 is span-restricted. They put in the largest span they could, then put in a fence to get what improvement they could without increasing the span.

Tom.
 
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RE: Why No Winglets On 747-830?

Fri Sep 02, 2011 1:45 am

Quoting bonusonus (Reply 10):
Here is a related question: Why does the A380 have A320-style wingtip fences, and not a more modern wingtip device, like a sharklet perhaps. It's hard to believe that significant engineering wasn't devoted to the A380's wingtips (being an ULH airliner and all), but if so, how does a normal wingtip fence suffice, when Airbus is promising such a significant fuel savings (3.5%) simply by adding sharklets to A320s?

It's a question about speed or cruise Mach numbers.

The winglets/sharklets, as we see them on 737, 757 and soon 320 planes, do not work well much beyond Mach 0.80, while the 380 is optimized to cruise efficiently at Mach 0.85. The combined speed of the vortex and the cruise speed will introduce local transonic airflow on the winglet/sharklet, increase drag, and that way reduce or eliminate the benefit.

737/757/320 style winglets/sharklets were not an option since they would add at least an hour to long haul flights.

We see no "fast" planes with large, blended winglets. The short and highly swept back winglets, which we see on 744 and MD11, are the best we can get when speed becomes 0.84 or 0.85-ish, and they don't deliver anything near 3-4%.

Airbus has plenty of experience with this sort of winglet on their 330 and 340 planes, as they have with the "old" 310/320 tip fences. The chose the fence for the 380, and sure they must have a good reason for that.

Twenty years ago there was a lot of hype about how much the MD11 winglets would improve the old DC-10 wing, and today we know how much they underdelivered. The Toulouse guys and gals know too, and we can be pretty sure that they knew what they were doing when designing the 380.

Raked wingtips are the way to go on fast long range planes. But that's impossible on the 380 as long as we have the 80x80 box.

What we see on the 350XWB is sort of hybrid between sharklets and raked wingtips. The 350XWB design was frozen in an environment of considerably higher fuel prices than the 380. Very likely it is optimized for an economic cruise speed which is slightly slower than the 380 and 787 with their fences and rakes respectively.
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RE: Why No Winglets On 747-830?

Fri Sep 02, 2011 2:53 am

Quoting bonusonus (Reply 10):
Why does the A380 have A320-style wingtip fences, and not a more modern wingtip device, like a sharklet perhaps. It's hard to believe that significant engineering wasn't devoted to the A380's wingtips (being an ULH airliner and all), but if so, how does a normal wingtip fence suffice, when Airbus is promising such a significant fuel savings (3.5%) simply by adding sharklets to A320s?

To expand on what Tom and Preben have explained, Airbus would ideally have wanted a wing with a more span and raked wingtips. But given the 80m restriction they went for the biggest span possible. Then they stuck a vertical device on there since that didn't increase span like a raked wingtips (777/787) or a diagonal winglet (330/340). Just one of those compromises.
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RE: Why No Winglets On 747-830?

Fri Sep 02, 2011 10:12 am

Thanks for the above.Most interesting.

Whilst I knew about the 80/80 "box" I still wondered why re No blended winglets.So it's about speed. Still if later developments as on 787 and 350 (similar speeds) is the way these days it would be nice (I think) if one day the 380 could have "tips" similar to the 787- would certainly improve her looks - perhaps with the 900?

As I recall the whole of the wingtip and Fence area is built (GRP) by Boeing in Australia!
 
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RE: Why No Winglets On 747-830?

Fri Sep 02, 2011 11:52 am

Quoting parapente (Reply 14):
Still if later developments as on 787 and 350 (similar speeds) is the way these days it would be nice (I think) if one day the 380 could have "tips" similar to the 787- would certainly improve her looks - perhaps with the 900?

Only if ICAO decides that an 80+ wingspan is ok!
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RE: Why No Winglets On 747-830?

Fri Sep 02, 2011 1:49 pm

Quoting parapente (Reply 14):
Whilst I knew about the 80/80 "box" I still wondered why re No blended winglets.

I'm not really following you here...they're filling the 80m width already. If you strap on a blended winglet, they bust the box.

If you shorten the wingspan to fit the blended winglet into the box, you lose more than you gain.

Keep in mind that an A380 wing sags quite a bit under its own weight so the wingspan gets larger on the ground. Couple that with the A380 needing a very large winglet (15'+ tall) and the impact on wingspan becomes pronounced.

Tom.
 
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RE: Why No Winglets On 747-830?

Fri Sep 02, 2011 3:00 pm

Quoting tdscanuck (Reply 11):
Quoting bonusonus (Reply 10):
Why does the A380 have A320-style wingtip fences, and not a more modern wingtip device, like a sharklet perhaps.

The A380 is span-restricted. They put in the largest span they could, then put in a fence to get what improvement they could without increasing the span.

Which is all the more reason to heap praise on that wing's efficiency given that it has a pudgy aspect ratio of around 7 when most modern long haul airliners are tending to 9-10. Just imagine how efficient it would have been at a higher aspect ratio like the 787's sleek wing design...

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Western727
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RE: Why No Winglets On 747-830?

Fri Sep 02, 2011 6:49 pm

Quoting prebennorholm (Reply 12):
The winglets/sharklets, as we see them on 737, 757 and soon 320 planes, do not work well much beyond Mach 0.80, while the 380 is optimized to cruise efficiently at Mach 0.85. The combined speed of the vortex and the cruise speed will introduce local transonic airflow on the winglet/sharklet, increase drag, and that way reduce or eliminate the benefit.

737/757/320 style winglets/sharklets were not an option since they would add at least an hour to long haul flights.

Intriguing. This brings to mind the 737MAX and, as I understand it, Boeing's choice to go raked intead of using BWs. Any insight on why Boeing is going raked, keeping in mind the inevitable increase in wingspan and possible gate spacing issues?
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RE: Why No Winglets On 747-830?

Fri Sep 02, 2011 11:10 pm

Quoting western727 (Reply 18):
Intriguing. This brings to mind the 737MAX and, as I understand it, Boeing's choice to go raked intead of using BWs. Any insight on why Boeing is going raked, keeping in mind the inevitable increase in wingspan and possible gate spacing issues?

In the renderings, the wingtip devices look more like blended winglets, or maybe like sharklets.

Quoting prebennorholm (Reply 12):

Thanks for the great answer!
 
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RE: Why No Winglets On 747-830?

Sat Sep 03, 2011 1:13 am

Quoting bonusonus (Reply 19):
In the renderings, the wingtip devices look more like blended winglets, or maybe like sharklets.

What's the matter with me...thanks for setting the record straight. They sure look like BWs. http://www.newairplane.com/737/737Max/
Jack @ AUS
 
parapente
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RE: Why No Winglets On 747-830?

Sat Sep 03, 2011 10:55 am

reply 16.

fair enough I was not explaining my thought well.And anyway it is probably wrong anyrate! It seems that the A380 wing - in it's ability to generate lift not only met but exceded expextations.We have seen Toulouse recently conducting some V heavy T/O's.However it also appears that the wingtip wake vortex was also greater than expexted (the 2 go hand in hand - sort of).OK Airbus disagrees with this and I believe discussions on seperation limits are still ongoing.

My thought was that if you took the whole of the tip (not just the fence) right back to the enf of the spar and replaced this with a 787 style tip (not exceding 80m and not a huge BW which would not work anyway as explained earlier on high mach numbers).

It may be possible to trade a very small amount of lift but gain vastly better control of the tip vortex.This (if possible) would have the advantage of both reducing drag in flight (sfc/range) it may also allow closer seperation on landings.

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