Winglets

[uwochris]

Hey guys,

Apart from cost, can anyone think of a reason why an a/c manufacturer would decide not toincorporate winglets into the design? If they are so beneficial, why do not all airliners use them?

I have heard that this Q comes up on interviews with some airlines. The only pitfalls I can think of are cost and added weight, but there must be some better reasons.

Thanks in advance,

Chris.

 

[Pugh]

Well, I think one reason is that some aircraft don't fly high enough for them to be beneficial. Like the ERJ-145 regional configured plane doesnt have them, but the Legacy biz jet does, because it flies longer and higher. As with nearly everything in aviation there is a trade off.

 

[enigma]

Hey guys,

Apart from cost, can anyone think of a reason why an a/c manufacturer would decide not toincorporate winglets into the design?

Chris, I'm going to try and answer this specific question. Manufacturers don't always incorporate winglets because winglets are not always the best way to accomplish the design goals. That's the answer. I suspect that you really are asking about winglets in a more general sense. More at the end.

If they are so beneficial, why do not all airliners use them?

I'll answer the first question (if they are so beneficial?) and that should answer the others. Winglets are not beneficial in all situations. You must first realize that all aircraft design is a series of compromises. If the designer is able to ignore all outside factors, he will be able to design a wing that doesn't need winglets. The Falcon series of business jets, and the Citation X are good examples.

Here's the secret to understanding winglets. A winglet gives the effect of increased span but it doesn't increase the wing root bending moment. In other words, a winglet can allow a short wing to act like a long wing, without modifying/strengthening the original wing structure.

With that understanding, let's look at one of the compromises that might allow/rule-out winglets from an airliner designers standpoint. One of the most obvious examples would be ramp space. If you're designing a new airliner, you may well have to work around the customers requirement that your new bird must be able to park at the existing gates. That limits your wingspan, and in that case, winglets might be your answer. If the designer was able to design the wing without regard to ramp space, he would most likely just make it longer to begin with.

I have heard that this Q comes up on interviews with some airlines. The only pitfalls I can think of are cost and added weight, but there must be some better reasons.

Thanks in advance,

Chris.

I would guess that the question is asked in an attempt to determine the applicant understanding of aero structures and aerodynamics. I'd answer it like this: "Winglets do a good job of making an existing wing more efficient without increasing it's span and taking up more ramp space.
Some airplanes come from the factory with winglets because they are outgrowth designs (like the 747-400) where the original wing is being asked to be more efficient without a complete redesign; and some like the 777 come without winglets. Those that come without winglets do so because a properly designed, no-compromise, wing is more efficient without a big add-on winglet. "

regards,
enigma

 

[mzaharis]

Also consider that winglets have two effects - they decrease induced drag (drag generated by generating lift), but increase skin friction, by increasing surface area. Depending on a number of factors, including wing aspect ratio, wing loading, airfoil characteristics, etc., it could be that the increase in skin friction outweighs the decrease in induced drag.

Just a slight adjustment to Enigma's excellent post. Winglets SLIGHTLY increase the bending moment on the wing, as the lift is distributed slightly to the outer sections of the wing. Still, he's correct that it doesn't increase the bending moment nearly as much as a span increase. It's a much more pronounced phenomenon on sailplanes, and why some sailplane manufacturers recommend against installing aftermarket winglets if they haven't performed a new structural analysis on the wing. In general, though, I would imagine, most business aircraft have sufficient design margin to accommodate the minimal increase in bending moment by adding a winglet, as opposed to the greater increase in bending moment imposed by a span increase.

 

[SkyWestCRJPilot]

Here's another example of not using winglets. When Boeing designed the 767-400 they decided upon a raked wing tip instead of winglets. Here is a quote from the data section of airliners.net.
"Compared to the 767-300, the 767-400ER's wing features 2.34m (7ft 8in) long raked wingtips which improve aerodynamic efficiency. Winglets were originally considered but the wingtip extensions proved more efficient."

 

[stingray]

If you look into it in Japan, 2 of the airlines Japan Air, and Nippon, both have 747-400's (that don't have winglets) that serve domestic routes. Its to their advantage to not have them installed on the high density shorter domestic routes. there may be others.

 

[ProLine4]

Regarding the NH and JL -400Ds, Boeing calculated that the weight penalty for the winglets plus 6 ft wing extensions exceeded any increased performance numbers on such short stage lengths (<3 hrs). Basically, the -400 has to fly far for the winglets to be cost effective. The -400Ds can be converted back to 400s if needed.

Also, another consideration is ground handling. I read that AirTran opted to not get the 737-700s with winglets because the increased wingspan would not fit in the standard DC-9/717 gatebox "footprint" in ATL. Maybe some FL pilots can help out and verify if this is true...

 

[The Boss]

Like the ERJ-145 regional configured plane doesnt have them, but the Legacy biz jet does

You obviously haven't seen any of ExpressJet's EMB145XR's.

 

[Propsfullfwd]

I second the Xjet 145xr

 

[mzaharis]

Here's a link that discusses the decision to add winglets. Of course, it's focused on a Piper Navajo (see near the bottom of the page).

Basically, if an aircraft is operating "in the drag bucket" (on the bottom or to the left of the u-shaped curve that represents the sum of induced and parasite/skin friction drag), there is an advantage to adding winglets. If it's to the right of that point, as would be the case at lower altitudes or higher speeds, where parasite drag dominates, winglets make less sense. I'd also suspect that those short-range ANA 747-400s don't climb to FL370, either, which would make winglets less useful.

http://142.26.194.131/aerodynamics1/drag/page8.html

 

[GVFlyer]

... If the designer is able to ignore all outside factors, he will be able to design a wing that doesn't need winglets. The Falcon series of business jets, and the Citation X are good examples...

...I would guess that the question is asked in an attempt to determine the applicant understanding of aero structures and aerodynamics. I'd answer it like this: "Winglets do a good job of making an existing wing more efficient without increasing it's span and taking up more ramp space.
Some airplanes come from the factory with winglets because they are outgrowth designs (like the 747-400) where the original wing is being asked to be more efficient without a complete redesign; and some like the 777 come without winglets. Those that come without winglets do so because a properly designed, no-compromise, wing is more efficient without a big add-on winglet. "

regards,
enigma

You are spectacularly misinformed.

The 93.47 foot GV wing was developed with winglets by Gulfstream scientists on the same Boeing computers that had been used for 777 development. Final development was accomplished at the NASA Langley wind tunnel where the wing was idealized for it's operating environment. It is a beautiful design unmatched by any T-category aircraft wing in the industry. The entire top surface is a single bonded piece of extruded aluminum. It is an all lifting design including the radius going into the winglet, there are no washed-in or washed-out areas and no stalled regions. The winglets provide a forward thrust vector. There are no leading edge devices required to provide a min. Vref of 110 knots or any canoes needed to hide flap gear. The wing develops even more lift than the computers had predicted necessitating the addition of vortices generators to the horizontal stabilizer.

The GV was flown to Mach 1.07 during developmental test with no buffet or adverse Mach effects. Aerodynamic center of pressure moved to 50% MAC and a shock wave formed ahead of the aileron trim tab rendering aileron trim inoperative. Another shock wave formed ahead of the elevators with the same effect, but the all moving tail remained effective for pitch control.

In my book, the true proof of a wing design is in how the aircraft performs. The G550 at maximum gross weight, 91,000 lbs., will always initially climb to at least 41,000 feet. 51,000 feet is available for up to the last 3 hours of flight. With 8 passengers, the G550 will fly 6750 nm at M.80, 6500 nm at M.83, 6000 nm at M.85 and 5,000 nm at M.87.

The Citation X is such an aeronautical blunder that with 8 passengers on board range is reduced by two-thirds at max speed. Low speed controlability has been such an issue that a series of aerodynamic patchs have been applied to improve safety.

There is no existing Falcon, nor one in development or on the drawing boards that will fly either as fast or as far as the Gulfstream.

Is it simply the absence of a winglet that, in your mind, constitutes "a properly designed, no-compromise, wing" or is performance a factor in your equation?


GV

 

[Uncle Sparky]

You are spectacularly misinformed.

The 93.47 foot GV wing was developed with winglets by Gulfstream scientists on the same Boeing computers that had been used for 777 development.


The Citation X is such an aeronautical blunder that with 8 passengers on board range is reduced by two-thirds at max speed. Low speed controlability has been such an issue that a series of aerodynamic patchs have been applied to improve safety.


Is it simply the absence of a winglet that, in your mind, constitutes "a properly designed, no-compromise, wing" or is performance a factor in your equation?


GV

Cessna makes the same "computers that Boeing used on the 777" claim about the Citation X wing design. ....last time I checked, the 777 didn't have any winglets?!

 

[NJA Capt]

You are spectacularly misinformed.
The Citation X is such an aeronautical blunder that with 8 passengers on board range is reduced by two-thirds at max speed.

...and it won the same beloved Collier Trophy that your GV won.

Give it a rest already. We know....we know...."all hail the magnificent, stupendous, colossal, unparalleled GV." All aircraft manufacturers in the world should just surrender defeat to Gulfstream and shut their doors, because the MIGHTY (not) Gulfstream has the most perfectly designed aircraft on the planet and will never be beaten.

Give us a break and quit sounding like a 3rd rate used car salesman. You come across like a middle-aged man with low virility bragging about his new Porsche.

Why did you compare a CX and GV with 8 pax? Gee, go figure.....a CX with seats full compared to a GV at 57% pax load. Not to mention they aren't even competing designs. Maybe I should brag by comparing the CX to the Beechjet.
Using your logic, I could say the GV is junk because it burns more gas than a CX.
Can a GV run .88+ at less than 1000# per side???

 

[mzaharis]

Aircraft design is a maddeningly iterative process, leading to structural/weight/aerodynamic tradeoffs, and winglets impact each of these areas. Winglets themselves add weight, but may reduce structural weight at the wing root spar, by reducing the bending moment compared to span extensions, and they decrease induced drag (in fact, generating thrust if they have a proper angle of incidence, as GVflyer said), but increase parasite drag. Then, you have to consider what the aircraft is being used for - is it flying in a regime conducive to the benefits that winglets provide? Without going to the engineers and looking at their analyses element-by-element, it would be pretty difficult to determine conclusively why one aircraft has winglets and another one in a similar mission/weight/performance class doesn't.

Back to uwochris's original question, my guess is that, if you are asked this question in an airline interview, they may want to see if you can riff on these topics knowledgably. Otherwise, I can't understand why an airline would ask you this question. Maybe if they're hiring you as an evaluator for a new type, or joining their strategy group that decides what types would be most appropriate for purchase/lease, but I'd guess that this wouldn't be an entry-level position.

 

[NJA Capt]

The 93.47 foot GV wing...

Couldn't find a few more decimal places? Come on, don't hold out.

The entire top surface is a single bonded piece of extruded aluminum.

Just like the CX.

There are no...canoes needed to hide flap gear.

Just like the CX.

...necessitating the addition of vortices generators to the horizontal stabilizer.

none on the CX

The GV was flown to Mach 1.07
Aerodynamic center of pressure moved to...
Another shock wave formed ahead of the elevators...
In my book...
The G550 at maximum gross weight...
With 8 passengers...

So much for his question about winglets.

 

[enigma]

You are spectacularly misinformed.

The 93.47 foot GV wing was developed with winglets ..........................

Is it simply the absence of a winglet that, in your mind, constitutes "a properly designed, no-compromise, wing" or is performance a factor in your equation?


GV

Wow dude, Did I step on your toes at some point in the past?

Thanks for the info on the Gulfstream, you obviously posses a great deal of info on this subject.

I'm not an aero engineer, but I do read a lot. I gathered my info on winglets from various sources. I've read the same gouge on winglets from the technical columns in Flying Magazine, in aeronautical texts and even pouring through boxes of old Sport Aviation magazines. BTW, Sport Aviations published in the sixties and seventies are a treasure trove of technical info.
Being that my training is less than formal, I'll be glad to bow to superior knowledge and training. But I don't conceed just because someone with a chip on their shoulder posts a manufacturers propaganda list. Please show me proof. Was the GV wing a clean sheet design in which the engineers were given a goal without restrictions, or were they restricted in any way?

I was just a lowly Lear35 driver when the big gulfstream was designed, but I seem to remember that the GV design was constrained by the need to fit into the existing corportate aircraft infrastructure. Meaning that the designer had to limit wingspan so that the aircraft would fit the ramp. The buyers needed an airplane that would fit into the existing system, otherwise for the same money, they could just buy a Boeing BJ or Airbus BJ.

I do salute your knowledge and devotion to the Gulfstream, I'd be danged devoted as well.

Sincerely,
enigma

 

[mzaharis]

Another interesting winglet design article, from Boeing:

http://www.boeing.com/commercial/aeromagazine/aero_17/winglet_story.html
http://www.boeing.com/commercial/aeromagazine/aero_17/wingtip_devices.html

 

[GVFlyer]

Good links...

 

[GVFlyer]

...But I don't conceed just because someone with a chip on their shoulder posts a manufacturers propaganda list.

I don't have a chip on my shoulder - I merely resent misinformation or opinion represented as fact. By the way, please try to find "a manufacturers (sic) propaganda list" providing a technical description of the GV wing. It doesn't exist, Marketing doesn't work that way.

Please show me proof. Was the GV wing a clean sheet design in which the engineers were given a goal without restrictions, or were they restricted in any way?

The goal was a wing optimized for high speed, high altitude flight for an ultra long range business jet. Gulfstream scientist Ed Flynn and his team of engineers did the initial design at Gulfstream and subsequent mid-development at Boeing and NASA Langley. In May 1993 they took their work to Vought Aircraft Industries in Dallas, then working in concert with Japan's ShinMaywa launched a 25 month wing final development program using advanced Computer Aided Design and NASA developed Computational Fluid Dynamics. Vought delivered the first GV wing July 18, 1995.

I was just a lowly Lear35 driver when the big gulfstream was designed, but I seem to remember that the GV design was constrained by the need to fit into the existing corportate aircraft infrastructure. Meaning that the designer had to limit wingspan so that the aircraft would fit the ramp. The buyers needed an airplane that would fit into the existing system, otherwise for the same money, they could just buy a Boeing BJ or Airbus BJ.
enigma

The 93.47 foot wing combined with the GV's 90,500 pound weight presented some initial problems for airport access. All previous Gulfstreams had been Airplane Design Group II aircraft with a wing span "up to but not exceeeding 79 feet" (AC 150/5300-13). The GV was a Design Group III airplane ruling out such airports as Santa Monica and Scottsdale. Prior to conceiving of the GV, Gulfstream had lobbied hard to get aircraft of less than 75,000 pounds (read the G-IV and previous) classified as non-transport aircraft so that we could go into airports where the community didn't want scheduled air carriers. Subsequently, many reliever airports have a 75,000 pound limit. As a result Gulfstream had to develop Aircraft Service Change 64A which limited the GV to a 75,000 pound operating weight when dispatched as such.

There are many compelling reasons to buy the G550 over the BBJ and the A319CJ, but wing dimensions are not among them. The BBJ wing is only 23.9 feet longer than the GV wing; the A319CJ 19.25 feet, placing all three aircraft in the same Design Group for airports. Weight and ACN are more important in determining airport access. Due to the dual tandem wheel design of the GV which counts as a single wheel when determing loads, the GV Aircraft Classification Number will never be greater than 25, the Boeing /Airbus numbers will never be less than 45. Combine this with the weight differential: G550- 91,000 lbs, BBJ -171,000 lbs, A319CJ - 166,450 lbs, and you find that the GV/G550 is able to operate out of 75% more airports than either of the converted airliners.

GV








.

 

[bigD]

What's funny is that yesterday when I read this in enigma's post:

Those that come without winglets do so because a properly designed, no-compromise, wing is more efficient without a big add-on winglet.

...I immediately thought of GVFlyer coming in here with guns blazing! I like to harrass him a bit about his devotion to Gulfstream, but I gotta say, I've learned more about those jets from his posts on the corporate boards than I ever thought I'd know!

 

[enigma]

I don't have a chip on my shoulder -
.

Ya coulda fooled me.

I congratulate you on your devotion to and knowledge of the GV. Did you have some part in the design?

regards,
enigma

 

[USAFftrplt]

Also, another consideration is ground handling. I read that AirTran opted to not get the 737-700s with winglets because the increased wingspan would not fit in the standard DC-9/717 gatebox "footprint" in ATL. Maybe some FL pilots can help out and verify if this is true...

I asked CEO Joe Leonard when he visted our university about this and he told me it was simply because they couldnt get a good deal on them. They wanted to get the same deal 1million per pair that SWA was getting and they simply werent able to, so they said screw it. However they said the keep revisiting the idea of updating the fleet at a later time but as of now the economics are very minimal to have them.

 

[GVFlyer]

Ya coulda fooled me.

I congratulate you on your devotion to and knowledge of the GV. Did you have some part in the design?

regards,
enigma

I was one of the original engineering test pilots on the design.

GV

 

[Uncle Sparky]

I was one of the original engineering test pilots on the design.

GV

WOW.!!.....impressive, yet arrogant!

I don't suppose, in all of your infinite wisdom and omnipotence, your highness, you posess the ability to shelf your ego for a moment and answer the very basic question that was originally posed....

 

[mzaharis]

WOW.!!.....impressive, yet arrogant!

I don't suppose, in all of your infinite wisdom and omnipotence, your highness, you posess the ability to shelf your ego for a moment and answer the very basic question that was originally posed....

He did.

ENIGMA: - . . . Did you have some part in the design? (in reference to the GV)
GVFLYER: - I was one of the original engineering test pilots on the design.

Looks like a pretty direct response to me.

 

[Uncle Sparky]

He did.

ENIGMA: - . . . Did you have some part in the design? (in reference to the GV)
GVFLYER: - I was one of the original engineering test pilots on the design.

Looks like a pretty direct response to me.

...answer the question that was posed by the originator of the thread!! ...you mental midget!!

 

[mzaharis]

...answer the question that was posed by the originator of the thread!! ...you mental midget!!

Where did he say that he addressed the original question? He addressed someone's response that he felt was an incorrect characterization of why winglets are added to a wing (as an aftermarket addition or a kluge). Of course, it was very Gulfstream-specific, and he seemed to take offense at a post that wasn't specifically in regard to Gulfstream, but he has provided some insight into the original question, which is what is the design decision to add a winglet. He indicated that some aircraft designers didn't do it as a kluge for a problematic wing or an add-on, but as part of an original design.

As for the response you're talking about - you're the one who qouted it, not me. Sorry if I took you at your word.

 

[Uncle Sparky]

Sorry, I typed a long response but I deleted it in exasperation.........I think I'm going to try something more practical than trying to communicate with you.....like, maybe, teaching my dog trigonometry.

 

[GVFlyer]

Where did he say that he addressed the original question? He addressed someone's response that he felt was an incorrect characterization of why winglets are added to a wing (as an aftermarket addition or a kluge). Of course, it was very Gulfstream-specific, and he seemed to take offense at a post that wasn't specifically in regard to Gulfstream, but he has provided some insight into the original question, which is what is the design decision to add a winglet. He indicated that some aircraft designers didn't do it as a kluge for a problematic wing or an add-on, but as part of an original design.

I guess I was a lttle harsh in my response to Enigma, but you have to understand, it's a lot like someone calling your kid ugly. We invested a lot of our lives in the certification of the GV, each of us sometimes flying over 30 days in a row in one of the four test articles before getting a day off and we made the best no compromises jet we could.

We had a lot of talent in Flight Test during GV development - the Chief Test pilot for the B-1 Program, the Chief Test Pilot for the B-2 Program, test pilots from the F-14 and F-16 programs and we all came away feeling that on balance the GV was the best jet we had ever flown.

You'll have to forgive Uncle Spanky for his comments; he was just turned down for Gender Reassignment Surgery and he's been taking it out on everybody.

GV

 

[TonyC]

WOW.!!.....impressive, yet arrogant!

I don't suppose, in all of your infinite wisdom and omnipotence, your highness, you posess the ability to shelf your ego for a moment and answer the very basic question that was originally posed....

He did.

ENIGMA: - . . . Did you have some part in the design? (in reference to the GV)
GVFLYER: - I was one of the original engineering test pilots on the design.

Looks like a pretty direct response to me.

He didn't.

If I may . . .


Original question, from Post #1:

"Apart from cost, can anyone think of a reason why an a/c manufacturer would decide not toincorporate winglets into the design? If they are so beneficial, why do not all airliners use them?"

GVFLYER offered tremendous insight into the desgin considerations and superiority of the GV wing, with winglets, but he failed to answer the question as to why a wing would be designed without winglets.

enigma's question received a direct answer, but uwochris's question (the original question of the thread) did not.

Maybe I missed it, but I haven't read anything about "spanwise flow" on this thread.