Why weren't wingtip devices used on airliners since day 1?

I know the 747-400 was the first jumbo jet model to feature the winglets from what I recall. It's the only way I can tell the difference between the -300 and -400 most times.

The new 787 doesn't really have them...the entire wing has a bend in it that mimics it, but is even more efficient (excluding the inefficiencies of computers blowing up ).

 

The Wright brothers played around with a design after their first flight, they knew about it back then. I think it just came down to getting the momentum going of applying the idea into into general aviation, breaking out of that "If it ain't broke, why fix it?" mentality as fuel savings started becoming a higher priority. Once the Learjet 28 came out in the 1970's, I guess you can say, that's when airframe designers started taking note.
Image Unavailable, Please Login

 

The gains from the winglets on the 747 aren't as great as people are led to believe (.5%?), that's why the 777 doesn't have them but went to a horizontally raked tip which produced the same effects/ gains with less added weight. The 747 Freighters don't use them either. IIRC the new 747-8 doesn't use the winglets.

The vortices that the following aircraft experience are created from the bulk of the plane itself going through the air. The 747 puches and huge hole in the air, especially when flying "dirty". The winglets would have virtually zero affect in reducing this.

The tall tips on the 737 were an evolution of the first concept. I really don't know if they are that much better than the shorter ones. You'll have to ask an engineer. I think they are more of a marketing gimmick than anything else, although, they do offer a retro fit to add the tall tips to the 767 so some gains must be there.

They didn't have the knowledge of refined aerodynamics back at day one of the modern jet airliner, ( in the 50's and early 60's). They were just finding out about the advantages and reduced drag of the "Coke Bottle" shape on jet fighters in the 50's. ( The 787 uses a very pronounced Coke Bottle shape in it's wing-to-body fairing)
Fuel was relatively cheap in the 60's so why add build cost and weight to the airplane?
Until the advent of composites the added weight would have negated the advantage anyway.

The 787 uses a combination of both, a blended, upturned, raked tip that changes configuration with load and speed.

 

I dont know where you got those numbers? Winglet fuel savings on the MD-11 is 3.5% to 5% based on weight and CG. We had winglets available for Airlines in 1980 for the DC-10. Airline MGMT chose not to save 3-5% of fuel. The cost/benefit analysis indicates different.

Douglas was involved in flightesting in a joint NASA/Air Force team, using a KC-135 and DC-10. This design was directly implemented on the MD-11, which was rolled out in 1990.

The wingtip vortex, which rotates around from below the wing, strikes the cambered surface of the winglet, generating a force that angles inward and slightly forward, analogous to a sailboat sailing close hauled for the sailors out there. The winglet converts some of the otherwise-wasted energy in the wingtip vortex to an apparent thrust. Another benefit of winglets is that they reduce the strength of wingtip vortices!

In contrast, the tip of a raked wing has a higher degree of sweep than the rest of the wing. This improves fuel efficiency and climb performance, and to shorten takeoff field length. It does this in much the same way that winglets do, by increasing the effective aspect ratio of the wing and interrupting harmful wingtip vortices. This decreases the amount of lift-induced drag experienced by the aircraft.

In testing by Boeing and NASA, raked wingtips have been shown to reduce drag by as much as 5.5%, as opposed to improvements of 3.5% to 4.5% from conventional winglets.

So winglests do save alot of fuel, raked wingtips save more.

more reading here on the topic.

http://www.sti.nasa.gov/tto/Spinoff2010/t_5.html


Cheers

 

The winglets for the 737 were first done for the BBJ(1)/737-700IGW. It was controversial at the time for Boeing and the in-house engineers talked of how they would do nothing for the performance and overstress the wings. When the winglets were flown these same engineers were embarrassed by the improvement. Aviation Partners was not allowed claim the full percentage improvement. They achieved a 5+% improvement at cruise and eliminated one step in climb to altitude.

Jeff

 

I fly around the Canyon Blue jets.....kinda purpley . It's not fuel savings, but cost savings. With Jet fuel at 50 cents a gallon, it took too long to get your money back out of the cost of winglets. With fuel at $2 a gallon, the amortization period is much shorter, therefore cost effective. We are in the business to make the most $ out of each flight.

One bad side effect, is flying around another 1000 pounds of aluminum means that weight comes off the "payload", ie paying passengers, cargo or fuel. My max takeoff weight still has to be same for safety reasons.

As for the coke bottle shape...the cost of "coke bottling" a fuselage for an airliner made out of 2 dimensional aluminum cost too much to realize the fuel savings. I would think that molded carbon is much easier to "coke bottle" and still be able to be pressurized a couple of thousand times with out failure. Still comes down to cost......imho.

Dogdish
Image Unavailable, Please Login

 

I have to add a bit of history here regarding wing tips. I admit that I go a ways back but not as far as the Wright Brothers. When I was working on the 707-300 series i got into a discussion with an aero guy and project chief about the raked wing tips, new on this airplane. he said, " We really don't know why these work but we think that it kids the wing into thinking that it's thinner."
Then on the 727 he raked the tips further with the same curved planform, increasing the aspect ratio.It also allowed the high energy flow under the wings to roll up and flow over a longer leading edge and form a smaller vortex at the tip thus producing less drag.
Then the tip winglets entered the scene by virtue of the aero wonky's thinking and messing around. I did some of the geometrical layouts on the 747-400 tiplets and the aero people told us that it lowered the drag by .1 % to 1.1 %. Not a big improvement but it looks high tech and it will be a good logo display item.
Then the big winglets came and produced a fair improvement in drag reduction but they are heavy and expensive...lots of strong hardware to attach them. Again, the lower surface flow does a little more good worh by rolling onto the upper surface of the winglet and providing some lift and leaves the winglet on a smaller tip thus producing a smaller vortex.
Then to make things less expensive and lighter, the extreme raked tip came back and does the same job only better...and looks much nicer. The 787 makes the most use out of all the previous devises by curved entry to the tip instead of a sharp break and the curved dihedral in the wing helps to add a sexy high tech look to it.
In summary, the raked tip does a better job , cheaper, and lighter.

 

I was told the original numbers on the early 747-400 winglets yielded one half of one percent.(By somebody in the Engineering department at Boeing)

I am sure with the advances in design and research that number went up but until the cost fuel went up the business model leaned away from adding the winglets.

 

Here is the Douglas Study. I think that "somebody" was grossly minsinformed.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19850002628_1985002628.pdf

 

If anyone wants to read the information on the 737 blended winglet go to Aviation Partners Boeing http://www.aviationpartnersboeing.com/ They have versions for the 737, 757 and 767.

Then go to http://www.aviationpartners.com/ to see what they do for corporate jets.

Jeff

 

Funny thing about the Southwest winglets, the average pax on SW would probably be thinking to themselves....."geez........what a smart airline........they built little advertising flaps on the edge of the wings with their website so we could see who we were flying with"..........

 

That was almost the exact comment made by a Boeing aerodynamic guru with whom I worked when he discussed the value of the wing tip devices then. They have improved greatly over the last twenty years but the raked tips are even better.

 

The questions about building a coke bottle fuselage on airliners should have a comment. To do that to the fuselage tube of a passenger jet would negate the purpose of building a people hauler. Imagine the loss of seats and abruptly going from a 10 abreast to three abreast and back to 10 abreast as you walked down the aisle. The coke bottling of the fuselage was a fix to get rid of the spike in frontal area and resultant drag where the wing and fuselage get together. The other way that this was accomplished was discovered by Douglas on the DC-8 by simply inverting the airfoil at the wing/body joint and diverting the upper surface flow to below the wing so that it wouldn't mix with the body flow at that point. Every single passenger jet from the DC-8 on uses this process. I did a sketch on this and posted it earlier in the year.
I am also reminded of a question posed by a 747 freighter customer years ago who asked us why we didn't build square fuselages like the trucks. One of our guys answered, " Have you ever tried to blow up a square ballon?"

 

Richard Whitcomb (RIP) was responsible for three important aerodynamics breakthroughs of the 20th century. Those are the area rule (coke bottle), winglets and the supercritical airfoil that he designed and tested in the NASA wind tunnels. The area rule is a design concept in which the cross-sectional area distribution along the aircraft is more even, which causes the fuselage to be necked in at the sections joined to the wing so the overall area is more even in relation to the rest of the aircraft. That is the coke bottle effect that you can see most visibly in the T-38, F-106, etc. It is all designed to reduce the wave drag at transonic and supersonic speeds.
Airliners don't have it (except the Concorde did) or need it because we have not solved the shock wave (sonic boom) problem yet so they now cruise at transonic speeds, about .90 Mach. If we could reduce the strength of the shock wave so that it did not rattle your house, then airliners could fly supersonic over land. Even then, the business case may not be strong enough to design supersonic airliners, as we saw with the Concorde.

 

The first one that comes to mind is the F-102, then the B-58, and the F-105 to a degree. The Boeing SST proposal That's all I can think of right now.

 

Winglets are an ad-hoc design to avoid the cost of designing a new wing. Reason the 747-400 has it and all the other aircrafy have them retrofitted is because its cheaper than redesigning the wing. The 787, 777, and 747-8 don't have them is because those are brand new wing designs.

The 767-400, 777-200LR, and 777-300er have their own version of "winglets" but in the form of raked wingtips instead.

 

Richard Whitcomb "Area Rule" (pinched waist)

http://www.youtube.com/watch?v=xZWBVgL8I54

 

Whitcomb is also responsible for "Whitcomb Bodies", that were used on the Convair 990 wings. Those teardrop shapes were supposed to act as conduits to bleed off mid chord drag waves.
I have never heard that winglets were a way to redesign the wing on the 747-400. It was an attempt to lower the tip drag. The 747 wing is still the fastest in the commercial field. The 747-8 has a new wing section that makes use of newer aero technology and is supposed to have better figures. Don't know how much better but I'm told that it is a good improvement.

 

http://www.boeing.com/videos/video.html?fr_chl=&fr_story=12123ea05604f09f35f6fc25f96a97a6c8b59c1f&rf=cs

"787 conducts fatigue testing"

Around 30 seconds into the video it shows static testing of the 787. The wing has quite the range of motion in the vertical direction. How that represents different points in flight is beyond me, but pretty interesting.

 

Jedi,

Most modern fighters are "coke bottled". It is more subtle on the modern fighters. The F-16/18 have thin wings. Our old F/A-18's did "neck down" on the turtleback and underneath the wing behind the engine intakes. With those thin wings, it needs less necking down to control the frontal area spike. The flight control computers will run the leading and trailing edge flaps (down and sometimes up) to produce camber (lift) when flight conditions dictate....to replicate a fat wing at high AOA's or low speeds.

Also, back to the airliners. If you look at the trailing edge of the wing....you'll see the flap tracks. These are those pods or "canoes". They start out thin, at about the fattest point on the chord of the wing, and get increasing larger in cross section as you move rearward, to their largest cross section at the trailing edge of the wing....exactly where the wing cross section ends. So with those "canoes", I increase total cross sectional area, but smooth out the frontal area spikes, and reduce drag. A swept wing will also smooth out the cross sectional area changes.

Pull up a picture of Soviet TU-95 Bear bomber, and look at the inner pods on those wings. Silcone or Saline is all I ask

http://www.fas.org/nuke/guide/russia/bomber/tu-95.htm

 

Jedi- To give you some idea of the area rule efficiency, Convair's delta wing interceptor prototype was the YF-102, based loosely on the earlier XF-92 . The YF-102 refused to penetrate the sonic barrier set up by transonic and supersonic airflow over various parts of the airframe and came up against a solid wall at mach 0.98. The aircraft was extensively redesigned to incorporate Whitcomb's newly proven area rule and the resulting YF-102A easily penetrated the mach due to much lower transonic (~mach 0.92-1.05) drag. The follow-on F-106 with the much larger J-75 turbo-jet engine (F-102 used the J-57 also fitted to the F-100) reached mach 2.5 and held the world's speed record at 1525 mph for a while. A look at Lockheed's F-104 also demonstrates an obvious use of the area rule.

Taz
Terry Phillips