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787 Winglets?  
User currently offlineFlightmedic72 From United States of America, joined Oct 2009, 27 posts, RR: 0
Posted (4 years 7 months 1 week 1 day 16 hours ago) and read 7756 times:

I noticed yesterday during the first flight of the 787 that the wings lack the winglets common to nearly all next generation aircraft to improve efficency and performence. Is this because the new wing design eliminates the need or will they be added later?

32 replies: All unread, showing first 25:
 
User currently offlineAcey From Canada, joined Jun 2007, 1029 posts, RR: 0
Reply 1, posted (4 years 7 months 1 week 1 day 15 hours ago) and read 7764 times:



Quoting Flightmedic72 (Thread starter):
Is this because the new wing design eliminates the need

Correct. As is the case with the raked wingtips on the 777-200LR, 777-300ER, and 767-400ER. Having said that, on renderings of the 787-3 that I have seen, there are winglets.



If a man hasn't discovered something that he will die for, he isn't fit to live. -- Martin Luther King, Jr.
User currently offlineBMI727 From United States of America, joined Feb 2009, 15707 posts, RR: 26
Reply 2, posted (4 years 7 months 1 week 1 day 15 hours ago) and read 7750 times:

Boeing has been somewhat ambiguous as far as winglets vs. raked wingtips. The 767-400 and 777 along with the P-8 have raked wintips while the 737, 757, and 767 have gone the winglet routes. I suspect that at least part of it has to do with gate space. After all, gate spacing isn't really an issue for the P-8. The 787-8 and -9 (and most likely the -10 as well) will have the raked wingtips while the -3 will have winglets, assuming that it ever gets built.


Why do Aerospace Engineering students have to turn things in on time?
User currently offlineStitch From United States of America, joined Jul 2005, 30522 posts, RR: 84
Reply 3, posted (4 years 7 months 1 week 1 day 9 hours ago) and read 7594 times:
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The 787-8 and 787-9 used raked wingtips, while the 787-3 is expected to use winglets to keep the span shorter to fit in 767-sized gates at Japanese airports.

User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 4, posted (4 years 7 months 1 week 1 day 8 hours ago) and read 7586 times:



Quoting BMI727 (Reply 2):
Boeing has been somewhat ambiguous as far as winglets vs. raked wingtips. The 767-400 and 777 along with the P-8 have raked wintips while the 737, 757, and 767 have gone the winglet routes.

It's not really ambiguous, it just depends which requirements path you had to follow.

Span restriction > winglet

No span restriction >
Retrofit? > winglet
No retrofit > raked wingtip

Tom.


User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 5, posted (4 years 7 months 1 week 1 day 3 hours ago) and read 7519 times:

Partially related....The Wings looked very highly tapered upwards at the tip.Is this normal or was minimum fuel being carried.
regds
MEL.



Think of the brighter side!
User currently offlineStitch From United States of America, joined Jul 2005, 30522 posts, RR: 84
Reply 6, posted (4 years 7 months 1 week 22 hours ago) and read 7444 times:
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Quoting HAWK21M (Reply 5):
Partially related....The Wings looked very highly tapered upwards at the tip.Is this normal or was minimum fuel being carried.

The Seattle Times reported TOW was 195t, which is 25t less than the original spec MTOW. She was intended to fly for over five hours, so I expect her tanks were reasonably full.


User currently offlineBMI727 From United States of America, joined Feb 2009, 15707 posts, RR: 26
Reply 7, posted (4 years 7 months 1 week 14 hours ago) and read 7325 times:



Quoting Tdscanuck (Reply 4):
Span restriction > winglet

So would there be the possibility that the BBJ2 would be offered with raked wingtips at some point?

Quoting Tdscanuck (Reply 4):
Retrofit? > winglet
No retrofit > raked wingtip

Just out of curiosity, why can't raked wingtips be retrofitted? Is it because they require more structural mods than the winglets?



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 8, posted (4 years 7 months 1 week 11 hours ago) and read 7270 times:



Quoting HAWK21M (Reply 5):
The Wings looked very highly tapered upwards at the tip.Is this normal or was minimum fuel being carried.

That's normal...if you look at the empty 787's in the factory when you're on the tour, or headed for paint before they're fueled, they've got a pronounced upward deflection at the tips. It's probably more pronounced with certain fuel loads, but it's in there right from the wing jigs.

Quoting Stitch (Reply 6):
She was intended to fly for over five hours, so I expect her tanks were reasonably full.

Probably full mains, but max endurance on a 787 has got to be 18 hours, so not very close to full fuel load.

Quoting BMI727 (Reply 7):
So would there be the possibility that the BBJ2 would be offered with raked wingtips at some point?

In theory, I guess so, although I've never seen it offered up. I've never found hard proof, but I've been told many times that the original driver to put winglets on the 737 at all was to make it look better for the biz jet customers.

Quoting BMI727 (Reply 7):
Just out of curiosity, why can't raked wingtips be retrofitted? Is it because they require more structural mods than the winglets?

You got it. A winglet shifts the lift distribution of the wing outboard, which cases higher stress in the wing, but the winglet itself contributes very little lift since it's mostly vertical. The raked tip shifts the lift outboard in a similar fashion, but also increases wing area and generates lift in its own right. As a result, the stress change is bigger and you need more excess margin to retrofit a raked wingtip than an equivalent winglet.

Tom.


User currently offlineNomadd22 From United States of America, joined Feb 2008, 1826 posts, RR: 0
Reply 9, posted (4 years 7 months 1 week 10 hours ago) and read 7250 times:

Wouldn't a raked wingtip also generate something of a twisting force to the end of the wing, which would seem to require a wing desinged to take that tp in the first place?
I got the idea that the efficiency of raked wingtips compared to winglets got more favorable the higher the airspeed, so longer range planes, whch spent a higher percentage of time at cruise, would be more likely to have raked tips where shorter range would do better with winglets.



Andy Goetsch
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 10, posted (4 years 7 months 1 week 10 hours ago) and read 7245 times:



Quoting Nomadd22 (Reply 9):
Wouldn't a raked wingtip also generate something of a twisting force to the end of the wing, which would seem to require a wing desinged to take that tp in the first place?

That sounds right to me but, of all the possible forces, a wing is best suited to withstand twisting because it's a closed torque box. I'd be kind of surprised if there were wings out there that are critical in torsion.

Quoting Nomadd22 (Reply 9):
I got the idea that the efficiency of raked wingtips compared to winglets got more favorable the higher the airspeed, so longer range planes, whch spent a higher percentage of time at cruise, would be more likely to have raked tips where shorter range would do better with winglets.

I can't really picture the aerodynamics behind that, but it certainly could be true. It's definitely true that a properly design raked tip will give you better performance than a properly designed winglet on the same wing, so I suspect it's simply a default to raked tips unless something (span restriction, retrofit, etc.) forces you another way.

Tom.


User currently offlineJetMech From Australia, joined Mar 2006, 2684 posts, RR: 53
Reply 11, posted (4 years 7 months 1 week 8 hours ago) and read 7227 times:



Quoting Tdscanuck (Reply 4):
winglet



Quoting Tdscanuck (Reply 4):
raked wingtip

One of the intuitive explanations given for the function of winglets is that they form a physical barrier at the wing tip, which reduces the ability of the air under the bottom of the wing - which tends to flow towards the tip - from interacting with the air over the top of the wing, which tends to flow toward the root. Reducing the interaction of these two streams near the wing tip then reduces the magnitude of the wing tip vortice. However, this explanation is harder to apply to raked wingtips.

Thus, I suppose a better explanation that would apply to both cases is that one wants to reduce the difference between the span wise components of flow at the wing tip. This would require that the pressure difference between the top and bottom surfaces at the wing tip are minimised, which also has the effect of reduce the lift produce at the tip.

Is this a good explanation for the basic desired function of winglets and raked wingtips? In lieu of any other penalties one may need to pay, would the ideal case be one where the lift distribution tapers to zero at the wingtip?

Low aspect ratio wings and one without tip devices produce strong vortices at the tip, which implies that the pressure difference is high. Does this mean that the lift coefficient is non zero at the tip with these configurations? Is a non zero wingtip lift coefficient observable and / or producible in reality?

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 12, posted (4 years 7 months 1 week 7 hours ago) and read 7205 times:



Quoting JetMech (Reply 11):
Is this a good explanation for the basic desired function of winglets and raked wingtips?

Not particularly, unfortunately. This is one of those cases where the intuitive explanation is nice, but not all that physically accurate. Both winglets and raked tips work the same way; they decrease vortex-induced downwash across the wing, which lowers induced drag. A winglet is just a raked tip that's been bent up.

Quoting JetMech (Reply 11):
In lieu of any other penalties one may need to pay, would the ideal case be one where the lift distribution tapers to zero at the wingtip?

The lift always drops to zero at the tip, because there's nothing to maintain pressure differential. The ideal (aerodynamic) case for non-transonic lift distribution is an elliptical distribution, but for a variety of reasons in real transonic aircraft you want closer to a triangular distribution. Either way, it will go to zero at the tip.

Quoting JetMech (Reply 11):
Low aspect ratio wings and one without tip devices produce strong vortices at the tip, which implies that the pressure difference is high.

Not exactly...you can build two wings with the same pressure difference and the same lift (i.e. same area) but the high aspect ratio one will have lower induced drag and weaker vortices. The major contributor is that, in a high aspect ratio wing, most of the flow is far from the tip, so most of it isn't influenced much by the ability to "sneak" around the end of the wing. In a low aspect ratio wing, much more of the wing is close to the tip, so it feels the effect more.

Quoting JetMech (Reply 11):
Does this mean that the lift coefficient is non zero at the tip with these configurations?

No. Even with a winglet or raked tip, the lift still has to drop to zero at the tip.

Quoting JetMech (Reply 11):
Is a non zero wingtip lift coefficient observable and / or producible in reality?

The only way I think you might be able to do that is some kind of powered lift (suction or blowing in the right places) but I'm not sure anybody's ever done that explicitely as a tip treatment.

Tom.


User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 13, posted (4 years 7 months 1 week 5 hours ago) and read 7173 times:



Quoting Stitch (Reply 3):
The 787-8 and 787-9 used raked wingtips, while the 787-3 is expected to use winglets to keep the span shorter to fit in 767-sized gates at Japanese airports.

What would be the approx comparative performance of a Raked v/s blended wingtip on the type.
regds
MEL.



Think of the brighter side!
User currently offlineMSNDC9 From , joined Dec 1969, posts, RR:
Reply 14, posted (4 years 7 months 6 days 20 hours ago) and read 7114 times:



Quoting Stitch (Reply 6):
The Seattle Times reported TOW was 195t, which is 25t less than the original spec MTOW. She was intended to fly for over five hours, so I expect her tanks were reasonably full.

The Seattle times reported the TOW was 430,000 lbs, which is 72,500 lbs less than its current design max takeoff weight of 502,500lbs, so yes, it probably had a substantial fuel load.

Welcome to the US. This is a US aircraft, and yes we still use pounds.


User currently offlineNomadd22 From United States of America, joined Feb 2008, 1826 posts, RR: 0
Reply 15, posted (4 years 7 months 6 days 19 hours ago) and read 7094 times:



Quoting Tdscanuck (Reply 10):
Quoting Nomadd22 (Reply 9):
I got the idea that the efficiency of raked wingtips compared to winglets got more favorable the higher the airspeed, so longer range planes, whch spent a higher percentage of time at cruise, would be more likely to have raked tips where shorter range would do better with winglets.

I can't really picture the aerodynamics behind that, but it certainly could be true. It's definitely true that a properly design raked tip will give you better performance than a properly designed winglet on the same wing, so I suspect it's simply a default to raked tips unless something (span restriction, retrofit, etc.) forces you another way.

I was picturing Rutan's explanation of the winglet when he came up with the Vari-eze. He explained how it decreased drag and increased lift by preventing the turbulence on upper and lower tip surfaces from the low and high pressure areas meeting. I just get the feel that that area of turbulence would move further back as you got closer to mach speeds, so the aft rake would help more than a vertical winglet at those speeds.



Andy Goetsch
User currently offlineDocLightning From United States of America, joined Nov 2005, 19361 posts, RR: 58
Reply 16, posted (4 years 7 months 6 days 18 hours ago) and read 7072 times:



Quoting Acey (Reply 1):

Correct. As is the case with the raked wingtips on the 777-200LR, 777-300ER, and 767-400ER. Having said that, on renderings of the 787-3 that I have seen, there are winglets.

Raked wingtips offer the benefit of a winglet twice as high as the wingtip is long. The disadvantage is that you can make winglets as tall as you want, but the wingtips increase the span.

What I've never understood is why no Airbus has raked wingtips.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 17, posted (4 years 7 months 6 days 8 hours ago) and read 6967 times:



Quoting DocLightning (Reply 16):
What I've never understood is why no Airbus has raked wingtips.

The A350XWB appears to have them, although the rake is much more gradual than the sharp kink seen on the 777 and 767-400ER. The A380 is span restricted, so I don't think it was an option for them. The A330/340 appear to share the same aerodynamic heritage as the 747-400 tips and, as previously discussed, probably aren't good candidates for a retrofit raked tip.

Tom.


User currently offlineGST From United Kingdom, joined Jun 2008, 930 posts, RR: 0
Reply 18, posted (4 years 7 months 5 days 21 hours ago) and read 6894 times:



Quoting Tdscanuck (Reply 10):
Quoting Nomadd22 (Reply 9):
Wouldn't a raked wingtip also generate something of a twisting force to the end of the wing, which would seem to require a wing desinged to take that tp in the first place?

That sounds right to me but, of all the possible forces, a wing is best suited to withstand twisting because it's a closed torque box. I'd be kind of surprised if there were wings out there that are critical in torsion.

As lift decreases towards the tip, similarly your applied bending moment also decreases, so that it is zero at the tip. If you put a wingtip divide onto the wing, you generate a massive point bending moment at your wing tip, that tries to twist the wingtip upwards and towards the fuselage.

If you assume that your typical wing spar is the shape of a square bracket, like this [, the vertical part takes all of the shear loads, and the horizontal parts take all of the bending moment loads (in reality each takes a little of the other, but this is a good approximation). Your shear force will still go to zero towards the tip, so the vertical part of the beam can become very small, but by putting a large point moment on your wingtip,l your horizontal booms must remain thick (read: heavy) right to the tip, you you need to be sure that your wingtip device will give you enough performance to pay for itself.


User currently offlineDynamicsguy From Australia, joined Jul 2008, 868 posts, RR: 9
Reply 19, posted (4 years 7 months 5 days 15 hours ago) and read 6824 times:



Quoting GST (Reply 18):
but by putting a large point moment on your wingtip,l your horizontal booms must remain thick (read: heavy) right to the tip,

The spar doesn't act on it's own. It is the skin which resists most of that moment. The job of the spar flange is mostly to transfer loads between the skins and spar web.


User currently offlineWestern727 From United States of America, joined Jan 2007, 740 posts, RR: 4
Reply 20, posted (4 years 7 months 4 days 22 hours ago) and read 6679 times:



Quoting MSNDC9 (Reply 14):
The Seattle times reported the TOW was 430,000 lbs, which is 72,500 lbs less than its current design max takeoff weight of 502,500lbs, so yes, it probably had a substantial fuel load.

On the very first flight of an experimental, uncertified and unproven aircraft? Sounds irresponsible to me.

Quoting Tdscanuck (Reply 8):
Probably full mains, but max endurance on a 787 has got to be 18 hours, so not very close to full fuel load.

This sounds more logical. I'm confident in assuming much of the bulk of the payload was made up of the testing equipment, and possibly some ballast water (if the aircraft at the time had the testing ballast tanks fitted around the inside of the fuselage, that is)...and not fuel.



Jack @ AUS
User currently offlineStitch From United States of America, joined Jul 2005, 30522 posts, RR: 84
Reply 21, posted (4 years 7 months 4 days 21 hours ago) and read 6662 times:
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Quoting Western727 (Reply 20):
On the very first flight of an experimental, uncertified and unproven aircraft? Sounds irresponsible to me.

Some of the critical initial tests (like flutter) probably need to be performed with a decent fuel load in the tanks to accurately reflect how they will respond when loaded for a long-distance customer revenue flight.

Since she only flew three of her scheduled five hours, I wonder how close to MLW she was when she touched down at BFI?


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 22, posted (4 years 7 months 4 days 19 hours ago) and read 6637 times:



Quoting Western727 (Reply 20):
On the very first flight of an experimental, uncertified and unproven aircraft? Sounds irresponsible to me.

Irresponsible how? "Experimental" is a big of red herring...in this context, it just means it's not certified under the transport category FAR's (yet). The plane is certified (just as an Experimental). "Unproven" is also a little complicated; although you should never underestimate the complexity of systems integration, all of the systems and structures on the plane have already been validated individual, and most of them validated in concert via things like the gauntlet testing.

It's obviously not zero risk, but given the gap between the known limits and the first flight limits (no big load factors, no high speeds, no radical maneuvers) I don't really see how a slightly lower weight would really provide much risk reduction.

Quoting Stitch (Reply 21):
Since she only flew three of her scheduled five hours, I wonder how close to MLW she was when she touched down at BFI?

Flight test aircraft can land above MLW (well, any aircraft can, but the paperwork is easier when you're on an Experimental ticket). I have no idea if they actually did or not but, provided you control sink rate, it's not a big deal.

Tom.


User currently offlineWestern727 From United States of America, joined Jan 2007, 740 posts, RR: 4
Reply 23, posted (4 years 7 months 4 days 18 hours ago) and read 6621 times:



Quoting Tdscanuck (Reply 22):
Irresponsible how? "Experimental" is a big of red herring...in this context, it just means it's not certified under the transport category FAR's (yet). The plane is certified (just as an Experimental). "Unproven" is also a little complicated; although you should never underestimate the complexity of systems integration, all of the systems and structures on the plane have already been validated individual, and most of them validated in concert via things like the gauntlet testing.

Irresponsible in that I'd assume one would want to minimize risk on the very first flight by not maxing out on fuel and instead putting on only, say, half its fuel capacity - and that is only a broad, uneducated guess for I am not qualified to give precise numbers. I mean, why push the envelope that early if there are no intentions to fly a long first flight? Likewise, one would not have wanted to take the 787 out on its very first flight at MTOW.

On the second (or third) flight - sure, fill 'er up, if the flight test team feels the data from the first flight (flutter characteristics, for example, as stated in another post above) justify doing so at that point.

Quoting Tdscanuck (Reply 22):
I don't really see how a slightly lower weight would really provide much risk reduction.

What I meant was only not to have the bulk portion of whatever the total payload weight might be - in fuel as in a max-fuel-capacity set-up. My apologies for not being clear on that.



Jack @ AUS
User currently onlineRoseflyer From United States of America, joined Feb 2004, 9478 posts, RR: 52
Reply 24, posted (4 years 7 months 4 days 16 hours ago) and read 6591 times:



Quoting BMI727 (Reply 2):
I suspect that at least part of it has to do with gate space. After all, gate spacing isn't really an issue for the P-8.

The P-8A does not have winglets because they did not handle icing conditions very well in analysis. The P-8A has to be able to operate in a much different environment than a commercial 737. It has to be able to operate at extremely low altitudes (as low as 50ft) for hours at a time in icing conditions. The raked wingtip handles those conditions better. While fuel efficiency is important, the P-8A is designed more about performance and capabilities since it has a different mission.



If you have never designed an airplane part before, let the real designers do the work!
25 JetMech : Fair enough. But what could be an easy to grasp yet robust explanation into the physics of reducing the vortex strength at the wing tip? IIRC, an ell
26 Tdscanuck : Ah, gotcha. Yeah, that makes sense...I don't see why you'd pack more fuel than you really needed, unless it was part of some flutter condition for th
27 BMI727 : So is lift. A wing works entirely by creating a pressure differential with higher pressure below and lower pressure above. As in any pressure differe
28 Tdscanuck : The strength of the vortex is basically a measure of how hard the work is working. Since the wingtip device lowers induced drag, the wing doesn't hav
29 JetMech : Fair enough. The down wash produced by the vortex system tilts the lift vector backward causing induced drag. However, I suspect that this phenomenon
30 Tdscanuck : Very much so. If you have a true 2D airfoil (equivalent to an infinite wing or a wind tunnel with a full-span wing) you get zero shed vortices precis
31 Faro : I imagine this is especially relevant to swept wings. If your wing is straight, spanwise flow will be minimal and caused mainly by the lateral airflo
32 Tdscanuck : Assuming that the wing is roughly at the fuselage midpoint, the spanwise flow due to fuselage displacement should be pretty minimal (since it needs t
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