MauricioChung
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Possibility of adding raked wingtips to 737s?

Fri Oct 06, 2017 1:28 am

Hi Guys

Long time lurker, first time poster here

Forgive me if this is a stupid question, but what are your thoughts on adding raked wingtips as an option for the 737 MAX? Could it be possible to adapt the P-8 wing to civil use?

I ask this because, as far as I understand, raked wingtips are more efficient on longer flights whilst regular winglets(and the split scimitars) give better fuel savings on shorter flights(which is what the 737s were designed for). The thing is that nowadays we've been seeing 737s being used on rather long flights, especially with airlines such as Norwegian and Copa, which begs the question, do you think these operators would find the possibility of installing the raked wingtips interesting?
 
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BreninTW
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Re: Possibility of adding raked wingtips to 737s?

Fri Oct 06, 2017 1:47 am

Sure, it's possible (in theory you could slap a wing from a 787 onto a 737 fuselage if you wanted to).

Problem with adding the raked wingtips to a 737 is that it would make it too wide to fit into narrow-body gates, which would make it cost-prohibitive since all existing NB gates would have to be reconfigured to accept the new wingspan.

This topic has been discussed at length in the past, you can see past threads HERE.
 
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DocLightning
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Re: Possibility of adding raked wingtips to 737s?

Fri Oct 06, 2017 2:52 am

In fact, raked wingtips are standard on the Poseidon P-8 variant. Unless a folding variant was to be introduced, there would be clearance issues at gates. The same folding mechanism that makes sense on the 77X does not scale down to the 737 with its higher cycles per day and likely similar weight for a frame 1/3 the size.

The downward wing-like element on both the APB Split Scimitar and now the Boing Advanced Technology winglet serves a similar role. At the gate, the wing is relieved of upward force and the downward wing-like element does not extend beyond the upper wing-like element. When the airplane takes off, the wings flex upwards. This rotates that downward wing-like element outward, increasing the span and having a similar effect to a raked tip without the span extension at the gate.
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HAWK21M
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Re: Possibility of adding raked wingtips to 737s?

Sat Oct 07, 2017 7:07 pm

Would mounting a Raked wingtip on a Short haul B737 serve the purpose considering Fuel economy.
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Acey
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Re: Possibility of adding raked wingtips to 737s?

Sun Oct 08, 2017 2:53 pm

HAWK21M wrote:
Would mounting a Raked wingtip on a Short haul B737 serve the purpose considering Fuel economy.

Yes, especially for the aircraft flying longer sectors... but the wingspan cannot extend beyond the maximum for code C aircraft of 36 meters, so scimitars and now MAX winglets are the compromise.
If a man hasn't discovered something that he will die for, he isn't fit to live. -- Martin Luther King, Jr.
 
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Stitch
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Re: Possibility of adding raked wingtips to 737s?

Sun Oct 08, 2017 3:58 pm

MauricioChung wrote:
Forgive me if this is a stupid question, but what are your thoughts on adding raked wingtips as an option for the 737 MAX?


A bad idea - see below.


HAWK21M wrote:
Would mounting a Raked wingtip on a Short haul B737 serve the purpose considering Fuel economy.


The raked wingtip is optimized for long-duration cruise, which is what the P-8 mission is all about. For short-haul, it would be relatively useless. It would only make sense for 737-8(00)s dedicated to TATL services and having a small sub-fleet is likely uneconomical from a fleet-planning angle compared to being able to use a frame on any mission.

I will note that Boeing's 737-8ERX proposal for a long-range 737 to compete with the A321-200neoLR used the same scimitar wingtips of the MAX family. If any frame would have benefitted from raked wingtips, it would have been this one. Boeing also does not offer the option on the 737BBJ family, which are often employed on very long missions.
 
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DocLightning
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Re: Possibility of adding raked wingtips to 737s?

Sun Oct 08, 2017 4:02 pm

Stitch wrote:

The raked wingtip is optimized for long-duration cruise


I keep seeing this being repeated, but in my readings about the structural and aerodynamic characteristics of wingtip devices, I have never been able to justify this proposition.

The fact is that a raked tip offers the best improvement for the smallest amount of added wetted area and added structure at the tip. However, raked tips move the center of lift outboard, necessitating a stronger spar, which may lead to a weight disadvantage when they are added to an existing wing (rather than being designed into a clean sheet wing). They also extend the span at the gate. This is why nonplanar winglets are popular among shorter-haul airliners, while planar extensions are popular among long-haul airliners because the latter gets larger gates.

And Airbus doesn't use planar extensions at all, even on their A350, which is their longest-range airliner. Their wingtip devices are a strange planar/nonplanar hybrid.
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Stitch
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Re: Possibility of adding raked wingtips to 737s?

Sun Oct 08, 2017 4:33 pm

DocLightning wrote:
Stitch wrote:
The raked wingtip is optimized for long-duration cruise


I keep seeing this being repeated, but in my readings about the structural and aerodynamic characteristics of wingtip devices, I have never been able to justify this proposition.


The 767-400ER was the first frame to use them and I've read that the reason for it was performance on long-duration cruising so it seems reasonable to me that they would be on the P-8 for similar reasons, though I have also heard the P-8 also uses them because it does not obstruct the sensors views anywhere near to the level the standard 737NG winglets would.

Then again, they also were about 1000kg lighter than the longer winglets Boeing was originally considering (shades of the 787-9 using the 787-8's winglets rather than the longer and heavier ones originally planned), offered similar performance, and allowed the 767-400ER to still fit in the ICAO D gate (which the original winglets would not as they would have increased the span to 55m).
 
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DocLightning
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Re: Possibility of adding raked wingtips to 737s?

Mon Oct 09, 2017 12:07 am

Stitch wrote:
The 767-400ER was the first frame to use them and I've read that the reason for it was performance on long-duration cruising so it seems reasonable to me that they would be on the P-8 for similar reasons, though I have also heard the P-8 also uses them because it does not obstruct the sensors views anywhere near to the level the standard 737NG winglets would.


I don't know the specific reasoning for Boeing's choice of raked wingtips for the 764 vs winglets for the 763, but I can make some educated conjecture:

The 764's wing, while not "clean sheet," required a stronger structure than the 762/3 wing owing for the higher weights. Given that Boeing knew they were going to have to strengthen the spar anyway, it makes sense to add the planar wingtip, even though it increases the bending moment on the wing root more than nonplanar winglets would. But for the 763, the vast majority of the global fleet was already in service when the winglets were brought out. Boeing could have developed a planar wingtip for the 763 fleet, but it would have required more reinforcement of the wing root, and reinforcement weighs more than a redesigned wing spar built to a stronger spec. So the nonplanar winglet was a good compromise for this fleet. I don't believe a planar wingtip extension has ever been offered as a retrofit to an existing wing, probably for this reason. All Boeing models with planar tip extensions (764, 77W/L/X, 787, 748) have had them as standard factory-installed items from the first frame. The P-8 is the only exception, and it is not an airliner.
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flipdewaf
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Re: Possibility of adding raked wingtips to 737s?

Mon Oct 09, 2017 9:11 am

DocLightning wrote:
Stitch wrote:

The raked wingtip is optimized for long-duration cruise


I keep seeing this being repeated, but in my readings about the structural and aerodynamic characteristics of wingtip devices, I have never been able to justify this proposition.

The fact is that a raked tip offers the best improvement for the smallest amount of added wetted area and added structure at the tip. However, raked tips move the center of lift outboard, necessitating a stronger spar, which may lead to a weight disadvantage when they are added to an existing wing (rather than being designed into a clean sheet wing). They also extend the span at the gate. This is why nonplanar winglets are popular among shorter-haul airliners, while planar extensions are popular among long-haul airliners because the latter gets larger gates.

It was my understanding that while the center of lift is pushed outboard creating a more efficient lift distribution this is only the case during standard 1g ops. As the wing becomes loaded during a higher g maneuver the "raked" aspect of the wing tip acting in conjunction with swept wing means that the local angle of incidence is reduced relative to the wing creating an area of negative lift. It then acts as a 'non active aero-elastic load alleviation device' and effectively shifts the loads inboard but only in high load situations.

Fred
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DocLightning
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Re: Possibility of adding raked wingtips to 737s?

Mon Oct 09, 2017 10:43 pm

flipdewaf wrote:
It was my understanding that while the center of lift is pushed outboard creating a more efficient lift distribution this is only the case during standard 1g ops. As the wing becomes loaded during a higher g maneuver the "raked" aspect of the wing tip acting in conjunction with swept wing means that the local angle of incidence is reduced relative to the wing creating an area of negative lift. It then acts as a 'non active aero-elastic load alleviation device' and effectively shifts the loads inboard but only in high load situations.

Fred


As the center of lift on the raked wingtip is somewhat aft of the main wing, a gust will tend to cause the raked tip to twist towards a more negative AOA and unload the outboard wing through this mechanism, which is a pretty neat feature built in by design. But even still, the raked tips put more stress on the inboard spar than a winglet.
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