Winglets - Benefit?
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ASI, sorry, shouldn't have made the blanket statement that only Cuban's posts were correct. I was referring to the posts that implied that winglets would eliminate vorticy.
As to the mention that the BBj "only gets about 4.5% to 5.5%" more efficiency out of winglets, obviously someone has missed the fact that manufacturers will do what they can to tweak 0.5% improvement, let alone those numbers!
As to the 777, I stand by my original reasons for it not having winglets...so far.
As to the mention that the BBj "only gets about 4.5% to 5.5%" more efficiency out of winglets, obviously someone has missed the fact that manufacturers will do what they can to tweak 0.5% improvement, let alone those numbers!
As to the 777, I stand by my original reasons for it not having winglets...so far.
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Sorry for the length of this reply...hope you find it interesting...
I have been hitting this subject quite hard over the last while...for the -400 the figures quoted are a 3% increase in cruise efficiency. "Winglets provide a theoretical straightening of the wing vorticies" My understanding is that winglets are a compromise...the same benifits would come from a re-designed wing (777, 767-400) or by an increased span. The 747-400, A340 & 330 all have large wings and are reduced in design philosophy to the size of airports and there gate design...if the wing is too big it will not fit into the available gates which would make it useless...no sense in savings by the wing if it cant fit into an airport. The 747-400 used winglets to save in cruise so they would not need to grossly increase the span. Each wing is increased in span by 6 ft and then has the addition of the 6 ft winglets, though this is generally for cruise the winglets actually increase the a/c's wingspan for takeoff with a full load of fuel. The wing bends or flexes with a full fuel load and will increase the span from 211.5ft to 213ft, a small but effective increase in wing for t/o.
The 777 wing and I am sure the 767 wing are obviously unique. They are very new and have been completely re-designed. Boeing took the 757 and 767 wing and made more improvements on it for the 777 which is the most efficient wing ever designed. The 777 wing is fatter than most conventional designs and was able to take advantage of stronger materials for its build...which I am sure is where the difference comes from now that I think about it...the 777 and generally boeings a/c philosophy seems to be that they will use the more expensive, modern materials that are stronger and would allow for differing designs...the B 777 has a very hight "taper ratio", chord length from the root to the tip. This was and still is not normally used as it requires a very strong wing, and use of very expensive materials to create a stable wing tip...that wont move and flex beyond an optimum range. (all wings will flex and are supposed to but too much would bend and twist the wing, disruppting airflow.)....so without going on for too long, the 777 and 767 are using a different disign which requires more money to build and a higher a/c cost, I am sure that Airbus is using winglets to get similar results at a lower cost for competition reasons. Also just for interest sake the 777 was designed with an optional folding wing. The a/c was designed initially to fit into gates that were used by the DC-10, L1011 and the like...so to fit the a/c into smaller gate sizes or to allow the company some flexibility in its routes and use of gates the 777 was given this folding design like a carrier a/c...that I know of as of yet none have been ordered with it.
I have been hitting this subject quite hard over the last while...for the -400 the figures quoted are a 3% increase in cruise efficiency. "Winglets provide a theoretical straightening of the wing vorticies" My understanding is that winglets are a compromise...the same benifits would come from a re-designed wing (777, 767-400) or by an increased span. The 747-400, A340 & 330 all have large wings and are reduced in design philosophy to the size of airports and there gate design...if the wing is too big it will not fit into the available gates which would make it useless...no sense in savings by the wing if it cant fit into an airport. The 747-400 used winglets to save in cruise so they would not need to grossly increase the span. Each wing is increased in span by 6 ft and then has the addition of the 6 ft winglets, though this is generally for cruise the winglets actually increase the a/c's wingspan for takeoff with a full load of fuel. The wing bends or flexes with a full fuel load and will increase the span from 211.5ft to 213ft, a small but effective increase in wing for t/o.
The 777 wing and I am sure the 767 wing are obviously unique. They are very new and have been completely re-designed. Boeing took the 757 and 767 wing and made more improvements on it for the 777 which is the most efficient wing ever designed. The 777 wing is fatter than most conventional designs and was able to take advantage of stronger materials for its build...which I am sure is where the difference comes from now that I think about it...the 777 and generally boeings a/c philosophy seems to be that they will use the more expensive, modern materials that are stronger and would allow for differing designs...the B 777 has a very hight "taper ratio", chord length from the root to the tip. This was and still is not normally used as it requires a very strong wing, and use of very expensive materials to create a stable wing tip...that wont move and flex beyond an optimum range. (all wings will flex and are supposed to but too much would bend and twist the wing, disruppting airflow.)....so without going on for too long, the 777 and 767 are using a different disign which requires more money to build and a higher a/c cost, I am sure that Airbus is using winglets to get similar results at a lower cost for competition reasons. Also just for interest sake the 777 was designed with an optional folding wing. The a/c was designed initially to fit into gates that were used by the DC-10, L1011 and the like...so to fit the a/c into smaller gate sizes or to allow the company some flexibility in its routes and use of gates the 777 was given this folding design like a carrier a/c...that I know of as of yet none have been ordered with it.
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I see no point why winglets should be most efficient in cruise; as I remember my aerodynamics lessons winglets are best at reducing induced drag which is increasing with decreasing speeds and increasing angles of attack.
Also, winglets are not only useful for long-range airliners; just look at the canadair regionaljet.
A look at my Airbus 320 operating manual shows that with ONE wingtip fence (small winglet) missing, the fuelflow increases by 1.4%, and the take-off weight as well as the approach climb limiting weight has to be adjusted by 4 %.
Quite a change at the low-speed range, I think
Also, winglets are not only useful for long-range airliners; just look at the canadair regionaljet.
A look at my Airbus 320 operating manual shows that with ONE wingtip fence (small winglet) missing, the fuelflow increases by 1.4%, and the take-off weight as well as the approach climb limiting weight has to be adjusted by 4 %.
Quite a change at the low-speed range, I think
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In addition to the above, rumours say that Boeing 777 will be available with winglet retrofits for increased efficiency, just like the Boeing Business Jet.
www.aviationpartners.com has more information about performance benefits with winglets
www.aviationpartners.com has more information about performance benefits with winglets
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Max,
Winglets don't _have_ to be more efficient in cruise, but as they are fixed, they are set so that they are creating forward thrust most efficiently under just one flight regime. The manufacturer can choose what flight regime that is. In the flight regime that is not optimized you can actually lose performance.
The RJ obviously has been been optimized for some flight regime, or maybe a bit inbetween (sort of like a fixed pitch prop, it is ok for climb and cruise, but not best for either). Perhaps they figure a small amount in both regimes will net more in that airplane. However, a 777 does either short haul or long haul on any given flight, and you would have to choose which one to optimize. Since the same airframe might alternate from day to day, the other solution is to increase the span with the super-critical wing, as they have done.
Winglets don't _have_ to be more efficient in cruise, but as they are fixed, they are set so that they are creating forward thrust most efficiently under just one flight regime. The manufacturer can choose what flight regime that is. In the flight regime that is not optimized you can actually lose performance.
The RJ obviously has been been optimized for some flight regime, or maybe a bit inbetween (sort of like a fixed pitch prop, it is ok for climb and cruise, but not best for either). Perhaps they figure a small amount in both regimes will net more in that airplane. However, a 777 does either short haul or long haul on any given flight, and you would have to choose which one to optimize. Since the same airframe might alternate from day to day, the other solution is to increase the span with the super-critical wing, as they have done.
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Prof2MDA,
I wanted to stress that in my opinion winglets are of most use at low speed, not in high-speed, as some earlier postings indicated. Somebody also stated that Airbus uses them merely for proper looks; if that's the case, I wonder why Boeing's 737's are now available with aviation partner's winglets, they sure are of some use...
Jambo Buana,
by the 4% penalty I was not referring to the climb GRADIENT, but to a calculatory adjustment of the approach climb limiting WEIGHT, which is with G/A thrust, landing flaps and gear still down.
When You mention Salzburg Airport I hope You already had a chance to enjoy the view onto Salzburg Castle...
I wanted to stress that in my opinion winglets are of most use at low speed, not in high-speed, as some earlier postings indicated. Somebody also stated that Airbus uses them merely for proper looks; if that's the case, I wonder why Boeing's 737's are now available with aviation partner's winglets, they sure are of some use...
Jambo Buana,
by the 4% penalty I was not referring to the climb GRADIENT, but to a calculatory adjustment of the approach climb limiting WEIGHT, which is with G/A thrust, landing flaps and gear still down.
When You mention Salzburg Airport I hope You already had a chance to enjoy the view onto Salzburg Castle...
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Cuban,
Yes, the downwash does give the aircraft lift however too much whilst the aircraft is travelling forward at 500+ mph isn't particularly good.
Draw a picture...The effective angle of attack (AoA) increases with downwash meaning that the lift is not perpendicular to the direction of flight but is actually pushing the aircraft upward and backward. (I only wrote that because it says on your profile that you're a student so you'll know what i'm going on about)
Also, winglets reduce the effect wingtip vortices have if nothing else but again this would be mainly at low speeds where the induced drag is at iits greatest.
Yes, the downwash does give the aircraft lift however too much whilst the aircraft is travelling forward at 500+ mph isn't particularly good.
Draw a picture...The effective angle of attack (AoA) increases with downwash meaning that the lift is not perpendicular to the direction of flight but is actually pushing the aircraft upward and backward. (I only wrote that because it says on your profile that you're a student so you'll know what i'm going on about)
Also, winglets reduce the effect wingtip vortices have if nothing else but again this would be mainly at low speeds where the induced drag is at iits greatest.
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Not a one of you got it totally right. Putting winglets on the 777 will do nothing for the airplane regardless of what Joe Clark says at aviation partners.
Their are no performance benefits with Raked tips over conventional winglets. LIKE I SAID IT IS JUST THE TWEAK OF THE WEAK AT BOEING.
Their are no performance benefits with Raked tips over conventional winglets. LIKE I SAID IT IS JUST THE TWEAK OF THE WEAK AT BOEING.
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MAX,
If winglets are optimized for low speed flight they will produce the most benefits at that time. However, if they are set at an angle to gain the most forward lift vector ("thrust") at normal cruise, then at low speeds the angle will likely be such that the winglets have a neutral contribution, possibly worse.
Rather than debate endlessly here, I point you to page 339 of Flightwise, Principles of Aircraft Flight by Chris Carpenter (available at http://www.amazon.co.uk but not on the U.S. site for some reason). Chris is head of Aerodynamics at the RAF College, Cranwell.
It is also discussed in "The Illustrated Guide to Aerodynamics" by H.C. Smith, 1992 Tab Books, ISBN 0-8306-3901-2, pages 286-288.
Also, to those who make the very silly assertions that Boeing adds winglets for marketing purposes, I ask you one question: If that were true, why are they NOT on the B-777? Surely they wouldn't want to give the A-330 the advantage, would they?
The answer is as I have previously stated. Expect to see them on some future "long range only" 777 if there is demand for such a beast.
The 747-400 gains a 2.5% drag reduction on average with winglets.
If winglets are optimized for low speed flight they will produce the most benefits at that time. However, if they are set at an angle to gain the most forward lift vector ("thrust") at normal cruise, then at low speeds the angle will likely be such that the winglets have a neutral contribution, possibly worse.
Rather than debate endlessly here, I point you to page 339 of Flightwise, Principles of Aircraft Flight by Chris Carpenter (available at http://www.amazon.co.uk but not on the U.S. site for some reason). Chris is head of Aerodynamics at the RAF College, Cranwell.
It is also discussed in "The Illustrated Guide to Aerodynamics" by H.C. Smith, 1992 Tab Books, ISBN 0-8306-3901-2, pages 286-288.
Also, to those who make the very silly assertions that Boeing adds winglets for marketing purposes, I ask you one question: If that were true, why are they NOT on the B-777? Surely they wouldn't want to give the A-330 the advantage, would they?
The answer is as I have previously stated. Expect to see them on some future "long range only" 777 if there is demand for such a beast.
The 747-400 gains a 2.5% drag reduction on average with winglets.
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Those speeds are just a few knots higher than MD-11 speeds, but I have to wonder why the need for such high speeds? The A-380 lists surprisingly low speeds.
As to how pilots feel about it, as long as the performance numbers show adequate margin for the runway, I have no problem with it.
As to how pilots feel about it, as long as the performance numbers show adequate margin for the runway, I have no problem with it.
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Prof2MDA,
Thanks for a number of good and technically accurate posts. It is nice to see that some people still believe in having a firm technical understanding of a concept before attempting to preach about them!
I would suggest that posts like 747FOCAL's are made with a certian degree of ignorance. Do you have and particular merit on which to state you claim that winglets are useless, or are you merely providing us with your well informed opinion?
Cheers,
Cuban_8
Thanks for a number of good and technically accurate posts. It is nice to see that some people still believe in having a firm technical understanding of a concept before attempting to preach about them!
I would suggest that posts like 747FOCAL's are made with a certian degree of ignorance. Do you have and particular merit on which to state you claim that winglets are useless, or are you merely providing us with your well informed opinion?
Cheers,
Cuban_8
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As the B777 is a completely new design, the addition of winglets may have no additional benefit especially with a new wing design? I'm not a designer and havent looked into the design of the B777 wing compared to the B747 so will take a backseat on the technical merits of this discussion however I would like to respond to the marketing side of things.
My comments about marketing were to highlight that although something might not be a great idea technically, it might be incorporated because of other reasons. Perhaps a design is a retrofit on something that has gone through a design freeze or the customer wanted a specific cruise perfomance or penalties would apply and the manufacturer could achieve this through a certain addition in design. Or perhaps other tangible benefits of a component may be sufficient enough to include it in a design even though it may not have a significant technical benefit - ie it makes it look different or adds and aesthetic value? No decision to include a component is done in isolation - everything that goes into or on an aircraft is a compromise.
As this thread has developed it is apparent that the inclusion of winglets for different phases of flight is debatable and very much related to the mission of the aircraft and the benefit - 'percieved' by the manufacturer and the operator.
Perhaps someone from Boeing can comment why winglets weren't included?
scuffle, scuffle - returns to backbench to after putting two pence in.
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Its life Jim, but not as we know it!!
My comments about marketing were to highlight that although something might not be a great idea technically, it might be incorporated because of other reasons. Perhaps a design is a retrofit on something that has gone through a design freeze or the customer wanted a specific cruise perfomance or penalties would apply and the manufacturer could achieve this through a certain addition in design. Or perhaps other tangible benefits of a component may be sufficient enough to include it in a design even though it may not have a significant technical benefit - ie it makes it look different or adds and aesthetic value? No decision to include a component is done in isolation - everything that goes into or on an aircraft is a compromise.
As this thread has developed it is apparent that the inclusion of winglets for different phases of flight is debatable and very much related to the mission of the aircraft and the benefit - 'percieved' by the manufacturer and the operator.
Perhaps someone from Boeing can comment why winglets weren't included?
scuffle, scuffle - returns to backbench to after putting two pence in.
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Its life Jim, but not as we know it!!
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200kt rotation? 175 landing speed....Wow...that'll leave the 747X up a certain creek without a paddle against the A380
It seems for some of you die hard fanatics that 'if it ain't boeing...you're not going?' then you might start having to enjoy cruises from soon onwards
It seems for some of you die hard fanatics that 'if it ain't boeing...you're not going?' then you might start having to enjoy cruises from soon onwards
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CEPO-You obviously do not understand aircraft performance. Some of the older duffers around here are forgetting that things advance. The new supersonic airplanes they are designing all have rotate speeds in excess of 350 kts. Think of how afraid a worldwar 1 pilot would feel if you took him for a scare ride in an F18... He would think it was crazy. You must think that aircraft are always going to perform the same way and never look beyond that which you have seen for years???? We wouldn't even have airplanes if nobody reached beyond what they had been taught was impossible. Those people that think of themselves as experts close their eyes to all that MAY be possible. That fatb*tch A380 is going to make one hell of a frieghter, but it will never pass safety tests for passenger evac. Okay, here we go, jump down that 6 story safety slide and we can all break our legs together.
As for the rest of you that are reaching for why the 777 does not have winglets. That is one of the most advanced wing designs ever constructed. It was optimized so much that putting winglets on would realize you undetectable amounts of climb performance and very small benefits in cruise. There would be more in looking at drag reduction elsewhere on the bird.
As for the rest of you that are reaching for why the 777 does not have winglets. That is one of the most advanced wing designs ever constructed. It was optimized so much that putting winglets on would realize you undetectable amounts of climb performance and very small benefits in cruise. There would be more in looking at drag reduction elsewhere on the bird.