ikramerica
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"737" Raked Wingtips Better Than Blended Winglets?

Sun Jun 05, 2005 5:38 am

http://www.boeing.com/news/releases/...05/photorelease/q2/pr_050602s.html

http://www.boeing.com/news/releases/2005/q2/nr_050602s.html

Now I know this isn't civil, (being a special purpose long range 737 derivative) but it begs the question...

Boeing has moved to raked wingtips on the 777 longer range, the 764, and the longer range 787, but still has the blended winglets on the 783 design and the 737 products (including the long range BBJs).

Considering they had soured on winglet technology due to less than impressive performance on the 744, even when they proved to be effective on 737 testing, have Boeing determined the raked wingtip works better on longer range?

The winglet manufactur says no way, blended winglets are always best. (what would they say?)

And of coure A doesn't use either on most products at this point, opting for the triangular vortex disruptor technology of the A320, A380 etc. over the angled winglet design on the 340 (and preliminary 350 sketches).

[Edited 2005-06-04 22:46:03]
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swadispatcher
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Sun Jun 05, 2005 5:58 am

I would think that the winglets do a better job of stopping the span-wise flow of air inflight, reducing drag, and subsequently increasing fuel efficiency.
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gigneil
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Sun Jun 05, 2005 6:01 am

Gate space is the issue. Blended Winglets optimize gate space much better than the backswept wingtip.

This is why the 787-3 and 737 feature Blended Winglets, but longer range widebody products feature the backswept wingtip.

N
 
ikramerica
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Sun Jun 05, 2005 8:54 am

Quoting Gigneil (Reply 2):
Gate space is the issue

Makes sense, assuming that's the only reason.

Quoting Swadispatcher (Reply 1):
I would think that the winglets do a better job of stopping the span-wise flow of air inflight, reducing drag, and subsequently increasing fuel efficiency.

so does the raked wingtip. it's also lighter and requires no structural reinforcement of existing wings to install a raked tip.
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swadispatcher
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Sun Jun 05, 2005 11:14 am

Quoting Ikramerica (Reply 3):
so does the raked wingtip. it's also lighter and requires no structural reinforcement of existing wings to install a raked tip.

I might have to break out the Aero/Astro engineering books from college and do a few calculations...
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srbmod
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Sun Jun 05, 2005 11:55 am

The reasoning behind Boeing using the raked wingtips as opposed to the blended winglets on the 764 was that they offered greater aerodynamic efficiency than the winglets.
 
ikramerica
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Sun Jun 05, 2005 12:02 pm

Right, and on the 777 and the 788/9 (but not the 783).

But this plane is a 737 derivative, and they are using raked tips, not winglets for it. I am honestly asking if anyone knows why. I am very familiar with both concepts, including the physics, and they both seem to accomplish the same thing, so I am wondering why Boeing is using one vs. other.

The wingspan argument makes the most sense so far. A 73X or 783 needs to fit in tighter spaces than does a LR type jet, and the military recon 738 does not have the space constraints either. Which might lead one to believe, that all things being equal, the raked tip is more efficient than the blended winglet.
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N1120A
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Sun Jun 05, 2005 3:14 pm

Quoting Gigneil (Reply 2):
Gate space is the issue. Blended Winglets optimize gate space much better than the backswept wingtip.

This is why the 787-3 and 737 feature Blended Winglets, but longer range widebody products feature the backswept wingtip.

What Neil says is right. The RWD improves aerodynamics better than the BWL, but it needs a full wingspan to do it. The winglets add wing surface area without adding a massive amount to the span. As it is, some 737 operators have trouble fitting ones with winglets into gates (see FL), so to get the same add in lift, you would really have a problem. Also, it would require a redesign of the wing
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CXA340
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Mon Jun 06, 2005 3:10 am

IKRAmerica - first off, thanks for starting a really good thread here, I have been wondering this same question (a friend of mine actually asked me the difference between these two systems the other day, knowing I have a passion for aviation, and I was at a loss to give him a definitive answer), also I appreciate a well reasoned conversation on fluid dynamics and structural engineering anyday. It reminds me of all those cool, but hard as hell engineering classes I took in college at Carnegie, and now never use any of it.

Here's my theory/understanding:
I thought the BW had an advantage over the RW on smaller to medium range routes, whereas the RW were more advantageous on medium to long range routes. The higher degree of lift crated by the BW was more efficient on the shorter routes, where the BW's higher coefficient of friction (drag) did not have enough flying time/distance to become as significant as the fuel expenditure needed in lift. As opposed to the RW, which create less lift, but greatly reduce the effects of drag which had a larger impact on longer routes.

Think of an analogy of two types of cars: one burns less fuel during the process of starting the engine, but has greater fuel economy when driven, while the other burns less fuel in starting the engine, but has less fuel economy when being driven. Obviously car A would be the car to take on a long distance, less frequent route, where as car B would be the car for shorter and more frequent trips (this is actually very similar to hybrid vs tradition engine cars - hybrids have notoriously bad fuel efficiency for highway/long distance driving - around 15-20mpg, but are better at in city drving 40mpg - so depending on the type of driving you do, a hybrid may be worse off at saving you fuel - the NHTSA recently tested all three hybrids, the toyota, honda, and ford, and found the ford to be the only one tp deliver on the promised fuel savings under both conditions.

So basically one set of winglettes perform better for long distance routes, the other on shorter routes, the increased drag of the BW was offset by the higher lift they generate, thus saving fuel, where on longer routes the cost of that increaed drag becomes significant and the necessity of higher lift generating winglets becomes less important - I hope this is making sense - I was in the back of the fluid dynamics class, certainly not up at the front.

Anyway, does this seem plausible/probable? This was my understanding of what the differences betwen BW and RW are, but I am making a lot of operational assumptions here so I could be totally wrong, if so I apologize.
 
ikramerica
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Mon Jun 06, 2005 3:21 am

CXA-

That's always been my understanding to, but Aviation Partners (the winglet maker) says otherwise. The CEO says the BWt always performs better. But again, what's he going to say? He doesn't make the composit RWt.

Also, I believe that both technologies as currently applied create a similar 'effective length' to the wing, but the RWt does it with much less weight. The added weight of the BWt would take away from the added lift on short haul, would it not?

I'm still leaning toward the idea that the RWt is actually a better technology, but it requires more parking space and a longer wingtip to start. The BWt can be retrofitted more easily (albeit at cost and expense of weight), while the raked tip wing is lighter and more effecient but needs to be designed for it (the new 764 wing, the new 777 wing, the all new 787, the new 747Adv wing...).

Unfortunately, getting an expert to be unbiased about such things is like an A vs B debate. Each one has a preference and defends it over the other, it seems, since most have either a financial or personal interest in one over the other.
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Lemurs
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Mon Jun 06, 2005 4:23 am

Everything I have read says that the differences between the two is lift vs not. Asuming equally optimal designs, both devices will reduce induced drag, but the raked device will add a lift component, while the blended one will not. (Or at least, far less). Assuming the wing can handle the extra load from the lift, more lift is usually going to give you better all-around performance than simply reducing drag.

Really, you should check out a lot of the recent threads in Tech Ops...there are some real aero engineers there who know their stuff.
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tinpusher007
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Mon Jun 06, 2005 5:04 am

Quoting Lemurs (Reply 10):
more lift is usually going to give you better all-around performance than simply reducing drag.

No claims of being an expert on aerodynamics, but doesn't more lift produce more induced drag?
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Lemurs
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Mon Jun 06, 2005 5:24 am

Quoting TinPusher007 (Reply 11):
No claims of being an expert on aerodynamics, but doesn't more lift produce more induced drag?

Just a disclaimer, I'm no expert either, but I do have an above-and-beyond curiosity that has led me to read a lot about aerodynamic designs. Since this is coming from a lay-understanding, I could be missing big points or oversimplifying.

It depends on the design of the wing and device, AoA, max cruise and a host of other factors. From the way I understand it, the RWd's delay and offset the spillover of air from the underside of the wing to the point where the vortices are drastically reduced, or at least offset to where they can't interfere with the flow of air over the top of the wing , which causes a fair ammt of induced drag. (which of course increases lift as well)

The BWt's on the other hand simply use the air coming up over the edge of wing to induce lift, and at the same time block that air from spilling over the upper surface of the wing and creating more induced drag.

So they both reduce induced drag, and both create lift, but the BWt pays a weight penalty and produces less lift. Anyone wants to correct me, feel free.
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tinpusher007
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Mon Jun 06, 2005 10:39 am

Good explaination...so it would seem that the RWT's are a more efficient design but have a longer lateral wing span which can be a problem with gate space for some operators?
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Lemurs
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Mon Jun 06, 2005 11:07 am

Quoting TinPusher007 (Reply 13):
Good explaination...so it would seem that the RWT's are a more efficient design but have a longer lateral wing span which can be a problem with gate space for some operators?

On smaller aircraft, definitely. From the way I understand it, to have the same kind of overall effect and improvement, a RWd would have to be as long or slightly longer than the same BWt on the aircraft. That's a pretty significant 12-16+ ft on an a 737 that's designed to fit into small gates. Considering the wingspan is ~112ft normal, 117ft w/BWt, that's more or less a 10% growth in span...big!

I doubt this is a problem for the Navy, so they're more interested in the gains offered than the space restrictions.
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ikramerica
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Mon Jun 06, 2005 11:23 am

and again, i assume that you need to redesign the wing to get the length of a RWt, but the winglet can be retrofitted more easily. Since the 737, 757, 767(x400), 777(xLR) etc. were not designed for either, so a retrofit could only be possible with the BWt.

Can't wait to see those 772s and 743s with BWt in a few years. 15' tall or more, so I understand...
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Mon Jun 06, 2005 3:02 pm

Quoting Ikramerica (Reply 6):
But this plane is a 737 derivative, and they are using raked tips, not winglets for it. I am honestly asking if anyone knows why. I am very familiar with both concepts, including the physics, and they both seem to accomplish the same thing, so I am wondering why Boeing is using one vs. other.

Winglets do have one major disadvantage. The reduce the take-off and landing cross wind componet by a significant amount. Depending on the airplane lenght, weight, and configueration, the cross wind componet can be reduced as much as 12 knots. This is why some airlines do not and will not buy airplanes with winglets, or they will have them removed.

Quoting N1120A (Reply 7):
What Neil says is right. The RWD improves aerodynamics better than the BWL, but it needs a full wingspan to do it. The winglets add wing surface area without adding a massive amount to the span. As it is, some 737 operators have trouble fitting ones with winglets into gates (see FL), so to get the same add in lift, you would really have a problem. Also, it would require a redesign of the wing

That is correct.
 
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Tue Jun 07, 2005 1:59 am

Quoting N1120A (Reply 7):
The RWD improves aerodynamics better than the BWL,

Nonsense! Both the raked wingtip and the blended winglet are span extension devices. The raked wingtip is planar, while the winglet is non-planar. Testing has shown that the blended winglets produce more benefit for a given amount of span extension (measured up the trailing edge of the winglet). The blended winglets also produce less bending moment. Its just that The Empire doesn't like being upstaged by the upstart API company.
 
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Tue Jun 07, 2005 2:14 am

Boeing is using the raked wingtip on their P-8/737-800/MMA aircraft design now instead of the blended winglet. Reason being that the raked wingtips perform better in icing conditions, where a P-8 might expect to loiter for longer periods than a commercial airliner. They didn't explain, however, if the icing performance is related tot eh ability of the structure to shed ice, or if it is just how the structure performs when ice is accumulating.

Perhaps this will opent he door to a commercially available raked wingtip for the 737 family.
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Wed Jun 08, 2005 12:59 pm

I'd expect that it's easier to build the heating elements for a raked wingtip, instead of a complex curve up a blended winglet.
 
aeroweanie
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Wed Jun 08, 2005 4:48 pm

I think the icing issue is BS. The blended winglets are not anti-iced and don't need to be. This has been demonstrated in certification testing. Are the 767-400ER or 777-300ER raked wing tips anti-iced? (I don't think so, but I don't know for certain).

Quoting Spacepope (Reply 18):
Perhaps this will opent he door to a commercially available raked wingtip for the 737 family.

And the US Navy will pay the development costs! As I said in another thread - The Empire Strikes Back!
 
CX Flyboy
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Wed Jun 08, 2005 5:21 pm

The current issue of Flight mentions that the leading edge of the raked wingtip will be anti-iced as an extension to the wing. I assume it would have been difficult to anti-ice the 'normal 737' winglets?
 
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Wed Jun 08, 2005 11:46 pm

Quoting CX flyboy (Reply 21):
I assume it would have been difficult to anti-ice the 'normal 737' winglets?

You don't have to! They are certified to FAR 25 without the need for anti-icing.
 
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Thu Jun 09, 2005 9:57 am

Quoting AeroWeanie (Reply 22):
You don't have to! They are certified to FAR 25 without the need for anti-icing.

I assume that is for the normal operating altitudes of the 737, and not for the new MMA 737 which will be significantly lower, hence the whole reason for the winglet design change?
 
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Thu Jun 09, 2005 10:00 am

Quoting AeroWeanie (Reply 20):
I think the icing issue is BS. The blended winglets are not anti-iced and don't need to be

it may be BS for airlines but not for the navy who are likely to have those planes loitering for hours in the spray from those waves above those subs! of course since they probably will be operating in the Gulf in the MidEast and not the Berings sea, it may well all be BS!
 
CX Flyboy
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Thu Jun 09, 2005 11:21 am

Well, the Navy wants 108 of them, so they can't all be operating in the Gulf!!.....or can they?
 
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Thu Jun 09, 2005 2:41 pm

Quoting Trex8 (Reply 24):
t may be BS for airlines but not for the navy who are likely to have those planes loitering for hours in the spray from those waves above those subs! of course since they probably will be operating in the Gulf in the MidEast and not the Berings sea, it may well all be BS!

As temperature falls with altitude, the worst icing is usually well above sea level. Typically, 10,000 feet is about the worst altitude (see the FAR 25 Appendix C Maximum Continuous Icing envelope). Airliners must be able to hold for 45 minutes in these conditions.
 
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Thu Jun 09, 2005 10:42 pm

Quoting AeroWeanie (Reply 20):
Are the 767-400ER or 777-300ER raked wing tips anti-iced? (I don't think so, but I don't know for certain).

The outboard slats are not de-iced on any 777. Ditto for the -300ER raked wing tips.
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F14D4ever
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RE: "737" Raked Wingtips Better Than Blended Wingl

Sat Jun 11, 2005 5:04 am

Quoting Lemurs (Reply 12):
So they both reduce induced drag, and both create lift, but the BWt pays a weight penalty and produces less lift. Anyone wants to correct me, feel free.

Okay, here goes. Yes, the both reduce induced drag. No, they don't both create lift. The RWt, as a horizontal extension of the wing produces lift (if cambered); the BWl does not.

Finally, according to AvWeek (June 6), the RWt is slightly heavier than the BWl. I'm struggling to understand and believe that. I suppose that, for a given span length, the RWtis subject to a heavier load (again, if cambered), thus requiring a stronger and heavier spar.

Sound reasonable?
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aeroweanie
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Sat Jun 11, 2005 7:31 am

Quoting F14D4ever (Reply 28):

Finally, according to AvWeek (June 6), the RWt is slightly heavier than the BWl. I'm struggling to understand and believe that. I suppose that, for a given span length, the RWtis subject to a heavier load (again, if cambered), thus requiring a stronger and heavier spar.

The raked wing tip increases wing bending loads more than the blended winglet. Hence, the raked wing tip will require more wing reinforcement, which will be heavier.
 
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Sat Jun 11, 2005 12:36 pm

Quoting AeroWeanie (Reply 20):
I think the icing issue is BS. The blended winglets are not anti-iced and don't need to be. This has been demonstrated in certification testing. Are the 767-400ER or 777-300ER raked wing tips anti-iced?

As mentioned Boeing has altered the wing design form the P-8 Maritime Aircraft to use raked wingtips. According to article in the June 6th edition of Aviation Week the design change was required as the blended wing does not allow for built in deicing components. The raked wing will provide easier insertion of the deice gear. It is felt the P-8 will be quite susceptible to icing conditions as it will spend hours on patrol in clouding and bad weather at low levels of 15,000ft. Commercial B737 are not considered subject to similar icing as they climb thru rapidly these low levels and cruise at much higher altitudes.
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Sun Jun 12, 2005 12:45 pm

How high are these Raked Wingtips in Ft.
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Sun Jun 12, 2005 2:27 pm



well, it definately look scool. don't forget, the raked wingtip is just basically a winglet mounted sideways.
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mrocktor
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Mon Jun 13, 2005 1:46 am

DISCLAIMER: I am an aeronautical systems engineer, this discussion is based on my understanding of the issue from explanations by my aerodynamicist colleagues.

One important issue not addressed is the design parameters for winglet/wingtip design.

A conventional winglet (vertical or near vertical surface) has to be "tuned" so to speak. It will be designed to work at a specific wing lift coeficient (and speed, to a lesser degree). The induced drag reduction is very large in the design condition but drops off significantly with variations in these design parameters.

A raked wigtip (or "shark" tip as was proposed for the Do 728) on the other hand is much less sensitive to small variations in lift coeficient and speed.

The consequence is that short haul aircraft can get great savings from winglets tuned specifically to the climb flight phase (high weight, climb speed). Since this is when the highest lift coeficients (and consequently induced drag) occur and a lot of fuel is spent it makes sense.

On the other hand, long range (or loitering) aircraft burn most of their fuel during cruise (or loitering). This means large variations in aircraft weight and consequently lift coeficient. The raked wingtip would be the better solution for these aircraft.

At least thats how I understand it...

mrocktor
 
lehpron
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Thu Jun 30, 2005 5:54 am

I describe better with pictures so I made these, hope you like it. To simplify: wing tip devices act like little kites, pulling the plane along.

The first explains traditional winglets, basically they are angled away from the airplane so that the freestream airflow can for the most part counter the induced flow coming from under the wing that wants to flow over the wing. The pressure vectors are shown below, where the induced pressure vector pushes inwards and forwards and the freestrean trys to balance it outwards. But it is uneven on purpose, the idea is the have a small resultant vector inwards so that we have a tiny vector forwards. This tiny vector is what reduces the overall drag.


Raked wingtips are different only functionally. The fact is that when wings lift they don't just bend upwards, with greater sweep back they bend up and forward to the point where the wingtip has a negative pitch to the rest of the wing. In fact the plane of reference looks like it is angled downwards. The black lines represent a non-lifting wing, the green would be only upward bend and the red represents the total bend and twist due to lift pressure.

And here is a picture of a 744 taking off to show the real world example:
http://www.airliners.net/open.file/868656/M/

Since 747 has a wing with a high sweep angle, the twist is more pronounced beyond natural wing twist. Ironically, the purpose wing twist was to reduce the lift pressure spike at the tip due to the flow spooling-up there, to make the overall lift pressure more distributed along the wing. A raked wing tip takes advantage of what naturally goes on.

Anyway, from a flow/pressure perspective, a raked tip is just like a winglet. There is the freestream flow wanting to bend the tip downwards while the induced flow wants to bend the tip upwards. But this time the forces are even, the difference is that the induced flow also end up creating a vortex on top of the tip, something like Concorde's wing. The resulting vortex pressure vector is now pointing upwards and forwards, the forward vector pulls the plane. Then there is the free lift...  

I say 'free lift' because had there been a span extention there, there would be another induced and parasite drag component. The raked tip supercedes these drags by the forward pressure vector enough to drop the total drag of the airplane by around 5% (depending on overall design). That could be how they would be better than winglets that pull sideways and forwards. The actual drag (reverse vector) from a raked tip is small compared to the forward vector developed by the main wing's spanwise induced flow. Free lift with an increase in aspect ratio by a slight increase in span, yay! 

Those wing tip fence devices on A320/A380 function like a cross between both types mentioned above. The sweep angle on them are high like the raked tips spooling a vortex both on the outboard side of the lower fin and the inboard side of the upper fin. The result are two pressure vectors, the top fin has one going inwards and forwards and the lower fin has one going outwards and forwards, and the freestream tries to counter them both but the tiny vectors forward take over to reduce drag.

For the record, as of now I am entering my senior year (finally) @ Embry-Riddle Aeronautical University, but none of the info I have just posted have been from there. The above was self-taught stuff, just like my knowledge on sonics (super and hyper).

[Edited 2005-06-29 23:19:21]
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aeroweanie
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Thu Jun 30, 2005 9:39 am

Quoting Lehpron (Reply 34):
I describe better with pictures so I made these, hope you like it. To simplify: wing tip devices act like little kites, pulling the plane along.

No, wing tip devices are simply planar or non-planar span extensions that decrease induce drag. End of story.
 
lehpron
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RE: "737" Raked Wingtips Better Than Blended Winglets?

Fri Jul 01, 2005 6:37 am

Quoting AeroWeanie (Reply 35):
No, wing tip devices are simply planar or non-planar span extensions that decrease induce drag. End of story.

No? Mathematically we're are the same even though you speak of a result while I speak of how it works.

A drag reduction from a wingtip device and how it uses winglift to induced a pull forward (which is what it actually DOES) can be calculated as numerically the same in this case. What part have you not agreed with?
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aeroweanie
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RE: "737" Raked Wingtips Better Than Blended Wingl

Fri Jul 01, 2005 10:37 am

Lehpron,

You make it sound like the winglet is a thrust producing device. Only engines produce thrust, by burning fuel under pressure and expanding the exhaust. A winglet by itself produces drag. It has the effect of moving the wing load outboard, which is seen as more span, which reduces induce drag.

Don't believe me? I've been involved in the aero design of all of these winglets:

Beech Duke

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lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

RE: "737" Raked Wingtips Better Than Blended Winglets?

Wed Jul 06, 2005 4:30 pm

Quoting AeroWeanie (Reply 37):
You make it sound like the winglet is a thrust producing device.

AeroWeanie, I do not know what you were assuming to come to this conclusion. Of course I wonder if you read my reply #34 and not just the 'kites' comment...

As I have stated before, a wingtip device uses induced flow to create low pressure on its surface that result in a vector component forward. The 'planar' wingtip device produces an induced lift vector due to induced flow spinning over the top of it that happens to point somewhat forward due to the surface normal. This is not a thrust production. But I don't call that a drag reduction unless I look at the big picture comparing the total drag to what it was before attaching the device, that which you insist for one. In that respect you are so correct and I am not arguing against that. In fact, I do not know what you are arguing about, except that you went off on the 'kites' comment. I look at the fact that there is a upward and forward pointing low pressure vector that is DEPENDENT on motion. I get the impression that you are either oversimplifying or ignoring that fact.

How would you describe leading-edge vortex flaps (LEVF) on proposed modern SST concepts? This is how I see it, a 60-degree sweeping delta would have large vortices goin over the leading edge as part of its lowspeed performance. A LEVF would extend down with its surface normal pointing up, away and forward. As the vortices go over the flap, it forms more low pressure on the flap than the overall wing, hence a low pressure vector component FORWARD increase the (L/D) max by 20%. Are they simply planar devices that reduce the effect of what?  irked  The way SST wings and Raked wingtips function is exactly the same but you think differently, how?

Quoting AeroWeanie (Reply 37):
Only engines produce thrust, by burning fuel under pressure and expanding the exhaust.

Thank you for clairifing that.  expressionless 

Quoting AeroWeanie (Reply 37):
A winglet by itself produces drag.

This was achknowledged above.

Quoting AeroWeanie (Reply 37):
It has the effect of moving the wing load outboard, which is seen as more span, which reduces induce drag.

An "effect" of moving wing load? Why are you refusing to go into details? If you get to be vague, then my 'kites' simplification still flies, no pun intended.  Yeah sure

Quoting AeroWeanie (Reply 37):
Don't believe me? I've been involved in the aero design of all of these winglets:

Off topic question: what aspect were you involved in, specifically?

This is not a matter of belief, dude. I simply concentrated on the tip device, while you go on about what thrust is and the 'effect' of moving wingload. While the latter can be calculated as true, regular people are not going to do the calculation. If they take your word for it, then they didn't learn anything. They can become ignorant because you were vague enough for them, that they do not need to know everything.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
aeroweanie
Posts: 1577
Joined: Fri Dec 03, 2004 9:33 pm

RE: "737" Raked Wingtips Better Than Blended Winglets?

Fri Jul 08, 2005 2:35 am

Lehpron:

I've discussed this a bit with the other folks here. It really all boils down to your argument being a near-field measurement of what's going on and mine being a far-field measurement. In the near-field, the lift force on the winglet is tilted forward sufficiently far in some flight conditions as to provide a forward force in the wind axes system, which is bookkeeped as a drag reduction. However, this isn't the full story. The presence of the winglet changes the wing load distribution and this also changes the overall drag. Hence, you are looking at just one detail of what's going on.

In the near-field, a raked wingtip will also probably see a forward orientation of its lift vector at the same flight conditions. And like a winglet, it too changes the wing load distribution, so by looking at the tip, you are missing part of the story.

A fuller view can be found by examining the far-field, at the Trefftz plane. Here, the wing wake is spread out over a greater apparent span and if the winglet is designed correctly, the downwash will still be fairly uniform, producing an induced drag reduction. A raked wingtip will have the same effect in the far-field.

When considering induced drag, you are always much better off looking at the far-field, as this is where induced drag is fundamentally defined.

The leading edge vortex flaps you talk about are completely different. These are circulation increasing devices, not induced drag reduction devices.

As to my role, as I said, I have been involved in the aerodynamic design of all the winglets cited. If you want more details, you'll have to contact me directly (via my profile).
 
LeanOfPeak
Posts: 496
Joined: Thu Oct 21, 2004 2:18 am

RE: "737" Raked Wingtips Better Than Blended Winglets?

Fri Jul 08, 2005 8:24 am

I may not have the experience you have, but it certainly seems to me that FAR certification is dependent upon the aircraft's assumed mission profile. Once you change altitudes, airspeeds, humidities, exposure times, thrust settings, etc., the problem has changed, and the solution to the problem very well might as well.

You might be right that it's a case of NIH, but I am not certain the official explanation should so readily be dismissed out of hand.
 
F14D4ever
Posts: 306
Joined: Sat May 07, 2005 3:20 am

RE: "737" Raked Wingtips Better Than Blended Winglets?

Wed Aug 31, 2005 2:08 am

Quoting AeroWeanie (Reply 37):
You make it sound like the winglet is a thrust producing device.

Yes, I got the same impression.

Quoting Lehpron (Reply 38):

As I have stated before, a wingtip device uses induced flow to create low pressure on its surface that result in a vector component forward.

Lehpron, "vector component forward" is synonymous with thrust, irrespective of what device is generating said vector. When you say a winglet is producing a "forward vector", you're saying it's producing thrust.

Looking at your first vector diagram, if the winglet sees free stream velocity, then the net vector is not inward and forward but outward (left) and back, creating drag. Maybe showing the local velocity vector of air over the winglet would more clearly state your case.
"He is risen, as He said."
 
777wt
Posts: 828
Joined: Wed Jan 19, 2005 7:45 am

RE: "737" Raked Wingtips Better Than Blended Winglets?

Wed Aug 31, 2005 2:30 am

Quoting AeroWeanie (Reply 37):
Boeing 747-200


Those are some huge winglets!
 
looneytoon
Posts: 438
Joined: Thu Mar 10, 2005 9:33 am

RE: "737" Raked Wingtips Better Than Blended Winglets?

Wed Aug 31, 2005 5:26 am

Quoting 777WT (Reply 42):
Those are some huge winglets!

Holy smokes! Those things are huge!
LooneyToon
 
amtrosie
Posts: 273
Joined: Thu Jan 06, 2005 6:44 am

RE: "737" Raked Wingtips Better Than Blended Winglets?

Wed Aug 31, 2005 7:12 am

GOOD LORD!! throw a fuselage on those winglets.
 
Molykote
Posts: 1239
Joined: Tue Aug 23, 2005 8:21 pm

RE: "737" Raked Wingtips Better Than Blended Winglets?

Wed Aug 31, 2005 1:25 pm

Although most of the aerodynamics have already been covered here I would humbly caution those who haven't been involved in aerodynamics to not look for universal truths on this topic. I am not an aerodynamics expert.

Much of the confusion over the winglet "thrust" component boils down to book keeping and perspective - However, the consequence of airflow over a winglet will have a forward "thrust" force component when viewed at the local winglet level - basically neglecting power input required to force airflow over the winglet. Of course this is not thrust in the usual context but simply a component of forward force stemming from flow over the winglet.

This force component may be appreciated if one looks at the progression of winglet design over time... Some of the early and less effective winglets were basically planar fences attached to the wing tip at a 90 degree angle. The intent and idea at this time was to inhibit the tendency of flow to progress spanwise by isolating high and low pressure regions. Many of the early winglet concepts did not pan out in practice as the friction drag imposed by a large wing tip fence (needed to effectively reduce induced drag effects) was greater than the reduction in induced drag. As time progressed and knowledge was gained we can observe some more elegant winglet designs that blend cleanly with the wing and do a more effective job of "massaging" the airflow rather than taking a brute force approach to preventing spanwise flow. It is from the "massaging" of this flow that the "thrust" term begins to be thrown about - understandably to the confusion of many.

On a similar note, the whole notion of induced drag (being the force winglets are meant to counter in the first place) can also be viewed as a rearward tilt of the wing's resultant lift vector.
However, since this slight rearward tilt of the large lift force resultant will work adversely to the forward movement of the aircraft the effect is tabulated as drag for book keeping purposes. This is similar in concept to winglet "thrust".
Speedtape - The aspirin of aviation!
 
Molykote
Posts: 1239
Joined: Tue Aug 23, 2005 8:21 pm

RE: "737" Raked Wingtips Better Than Blended Winglets?

Wed Aug 31, 2005 1:28 pm

One disadvantage of the blended winglet compared to the raked wingtip is that the 737 blended winglet is a pretty effective lighting rod!

A major 737 operator told me that they see almost one of these per day in need of off-wing repair.

[Edited 2005-08-31 06:28:42]
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