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DrPaul
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Winglets and Raked Wingtips — A Couple of Questions

Fri Aug 30, 2019 2:38 pm

Most airliners these days have either winglets or raked wingtips. I have a couple of questions. Why are they a relatively recent innovation, and why were the benefits of fitting them not realised earlier on, when jet airliners were first introduced in the 1950s?
 
GalaxyFlyer
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Re: Winglets and Raked Wingtips — A Couple of Questions

Fri Aug 30, 2019 3:04 pm

Aviation’s conservatism. The idea dates back to the earliest days of flight. Then, in the 70’s, Richard Whitcomb at NASA started experimenting with them. Fuel efficiency was a driver post-73.

https://en.m.wikipedia.org/wiki/Wingtip_device
 
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DocLightning
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Re: Winglets and Raked Wingtips — A Couple of Questions

Sat Aug 31, 2019 5:28 am

In addition to what GalaxyFlyer said, the benefits of these devices are relatively modest, in the range of 5%. So it took a fair amount of research (time) to develop wingtip devices that would maximize benefit while minimizing weight and additional drag. Keep in mind that these devices increase the lift on the outboard section of the wing, so spar strengthening (ads weight) is necessary. Sharp turns between the wing and a nonplanar winglet (like the 744 winglet) cause interference vortices (drag) and all of these devices increase overall wetted area. So careful design was necessary to minimize the added weight and drag while maximizing the additional lift.
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan
 
WIederling
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Re: Winglets and Raked Wingtips — A Couple of Questions

Sat Aug 31, 2019 11:49 am

GalaxyFlyer wrote:
Aviation’s conservatism. The idea dates back to the earliest days of flight. Then, in the 70’s, Richard Whitcomb at NASA started experimenting with them. Fuel efficiency was a driver post-73.

https://en.m.wikipedia.org/wiki/Wingtip_device


Henschelohren :-)
then you have the Let L-13 Blanik and PZL-101 Gawron
Wingtip tanks / shock bodies go in a comparable direction.

Hoerner Tips
Dr. Sighard F. Hoerner, his work straddles WWII and the post WWII time
Murphy is an optimist
 
GalaxyFlyer
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Re: Winglets and Raked Wingtips — A Couple of Questions

Sat Aug 31, 2019 1:56 pm

Yes, Hoerner wingtips were used in Part 23 planes long before winglets were tested and used on jets. The Lear 28 Longhorn was possibly the first Part 25 design.

GF
 
BravoOne
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Re: Winglets and Raked Wingtips — A Couple of Questions

Sat Aug 31, 2019 2:12 pm

It's interesting to note that Delta put winglets on one of their 727-200's and ran it for almost a year as I recall. They decided not to move forward and do the entire fleet as there were concern' that later in the life of the airplane there might be some structural issues passed on the downstream owners and thus legal exposure.
 
GalaxyFlyer
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Re: Winglets and Raked Wingtips — A Couple of Questions

Sat Aug 31, 2019 2:21 pm

Yes, the structure can be a factor. For example, the less vertical winglets on CL350 can’t be used on CL600 series for structure reasons.
 
WIederling
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Re: Winglets and Raked Wingtips — A Couple of Questions

Sat Aug 31, 2019 4:34 pm

GalaxyFlyer wrote:
Aviation’s conservatism.


no strong interest. Design was dominated by keeping the things in the air.
Fuel was a mass/volume limited resource, not money limited. :-)
Murphy is an optimist
 
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DrPaul
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Re: Winglets and Raked Wingtips — A Couple of Questions

Sun Sep 15, 2019 3:47 pm

Thanks for the replies.
 
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trpmb6
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Re: Winglets and Raked Wingtips — A Couple of Questions

Sun Sep 15, 2019 3:51 pm

DocLightning wrote:
In addition to what GalaxyFlyer said, the benefits of these devices are relatively modest, in the range of 5%. So it took a fair amount of research (time) to develop wingtip devices that would maximize benefit while minimizing weight and additional drag. Keep in mind that these devices increase the lift on the outboard section of the wing, so spar strengthening (ads weight) is necessary. Sharp turns between the wing and a nonplanar winglet (like the 744 winglet) cause interference vortices (drag) and all of these devices increase overall wetted area. So careful design was necessary to minimize the added weight and drag while maximizing the additional lift.


Actually, it's not so much maximizing additional lift but reducing induced drag (a function of lift). Induced drag is reduced by artificially increasing aspect ratio.
 
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DocLightning
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Re: Winglets and Raked Wingtips — A Couple of Questions

Tue Sep 17, 2019 2:25 am

trpmb6 wrote:

Actually, it's not so much maximizing additional lift but reducing induced drag (a function of lift). Induced drag is reduced by artificially increasing aspect ratio.


Both planar and nonplanar wingtip devices increase lift on the outboard span. A planar wingtip device, like the Boeing raked wingtip, adds lift outboard of the main span and distributes the overall lift over a larger span, which decreases the overall induced drag. A nonplanar wingtip device (a winglet) increases lift just inboard of the device and helps to move the axis of vorticity above and aft of the main span, which reduces induced drag.

A nonplanar device introduces less overall bending moment on the inboard spar, but it is less structurally efficient. As a rule of the thumb, a three-foot nonplanar winglet will offer the benefit of a two-foot planar wingtip extension, but will only add the bending moment of a one-foot span increase.
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan

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