winglets - do they work...

[applehead]

Do winglets work? The age-old question in aviation that no one can seem to answer. I see that Boeing are now offering winglets to retrofit to the 737-300, yet they produce the 777, the longest-ranging aircraft on earth, without them!

Go figure...

[Kanga767]

The 777 ER has raked wingtips, which has similar effect.


K

[john_tullamarine]

.. winglets work fine .. but not as well as what they stand in for .. extra span. Problem is airport infrastructure.

[TAY 611]

Well they look real nice anyway..:}

[4SPOOLED]

if you understood how wake turbulance is produced and how this causes excess drag, the winglets are there to prevent some of the wake turbulance and gain some extra fuel economy. Not noticable on short haul, but long haul definatly.

The basic principle is because of lift, which is high pressure on the underside of the wing and low pressure on the top of the wing, the air naturally wants to flow to the top of the wing where the low pressure is. As it tries to do this it overlaps the outer edge of the wing causing it to spiral as the wing continues on the flight path.

To maintain level flight and level speed, thrust must equal drag, so more thrust (fuel) is required to compensate for more drag. With the winglets the theory is you will need less thrust to maintain the same speed because you have less drag. Although the cost of retrofitting and certification sometimes is more than the savings that will be recovered, which is why it is more viable on the long haul fleets

I believe the Winglets still are a option on most A/C aswell, so the carriers decide if its viable for the winglets for the route they are purchasing the A/C to fly.

Look at most of JAL 743's and 4's, alot of them are shorthaul only


Hope this helps

4s

[Going Boeing]

4spooled

As Kanga and JT said, winglets are only useful if you can't add extra length to the wings. The raked wingtips that Boeing developed for the B767-400 are a superior solution to winglets as they produce lift at the same time as reducing wingtip vortice drag. This is why Boeing is fitting them to the B773ER and B772LR. :ok:

[swh]

Going Boeing,

Adding extra wing span will increase the loads at the wing root, the overall aerodynamic compromise is not as simple as adding some more wing or a winglet.

Either way, it will require some form of structural modification to the wing.

The best looking ones I have seen are on the Continental Airlines 757-200..some 8 foot 2 inch tall...with a block fuel reduction of up to 5%.

:ok:

[DeBurcs]

Additional to the above, the 737-300 wing was designed decades before the 777 wing and the efficiency advantages of the newer creation are significant - Winglets, vortex generators, etc, are not as necessary these days due to modern wing technology improvements.

Span restrictions due to airport infrastructure are few and far between given most airports/aerobridges/tarmac areas easily cater for 707s, A320s, etc, etc also. I think that's what you meant??

Adding a winglet to an old design is a relatively cheap measure to lengthen the relevance of an old design, just like hush-kitting or re-engining. Also helps puts off the possibility of the operator (customer) buying a new machine from a competitor.

Whether the aerodynamic advantage greatly outweighs the physical weight penalty of the winglet, itself, on short-haul ops is for the bean-counters to wet themselves over, I sure wouldn't know.


As for looks, personally I believe having winglets of any shape or size, particularly the Airbus style, "spoils the look of the thing", as 'Moggy' Cattermaul once said.

Raked tips are definitely shnazzier.

While I'm at it, jet engines should always be at the back... :ok:

[Capt Stabbin]

Why the hell is this thread in D&G Reporting Points? There are far too many facts for this forum!

[Tankengine]

SWH,
Same goes for winglets, when 737 NGs are retrofitted with winlets there are some strutural mods done down the wing due to increased bending moments. Biggest decision is cost of mod v fuel savings v length of time depreciated.
NG winglets work , 744 winglets are close to a waste of time.

[Capn Bloggs]

Tank Engine,

Doesn't the 744 only have winglets so people can tell that it's a nice shiny new 747 instead of a crappy old 743?

And is it true that you can operate with one off? That'd cause a stir amoungst the journos...

[MarkD]

Capn Bloggs

The 330 can operate without one but with a extra burn to account for - see the 330 that sawed off a Dash 8's tail at YVR recently.

CO are pushing the 757 as a east coast US to British Isles/Western Europe option, thus the wingleting. Icelandair are also doing it (since Iceland to pretty much anywhere is medium haul at least) and apparently AA are looking at it too, as they also have 757s they can replace on SH on with 738s.

[Tankengine]

Capt Bloggs,
Thats about right, from memory [I don't have a 744 DDG with me] you can operate with one or none with no performance penalty!!:ooh:
I have heard that Boeing considered not continuing with them but airlines now wanted them for the purpose you said!;)

[404 Titan]

Tankengine & Capn Bloggs

That’s funny because Our MEL/CDL for the B744 states:
One may be missing provided the performance limited weights are reduced by the following:

Take-off: Input ACARS RTOW CDL/SP OPS code: 57-28-1 or reduce 9,435 KG
Landing: 9,435 KG
Enroute Climb: 4,536 KG

NOTE: If a winglet is removed, the affected winglet fairings except the leading edge wingtip fairing Part Number 118U0010 and the trailing edge wingtip fairing Part Number 118U0030 must be removed. The forward facing opening in the trailing edge wingtip fairing must be covered (e.g. speed tape).

NOTE: Fuel burn will increase by approximately 2.5%.

[Woomera]

This does belong in Questions

[Fly GBAirways]

I read a letter in Flyer magazine about winglets here is what it said, it is written in relation to GA aircraft but i think same concept of winglets is used on Jets.

Question: "Nowadays one sees more and more aircraft fitted with winglets. Some are small but others are several feet long. What aerodynamic effect do these winglets have?

Answer:
"The winglets fitted to aircraft have two functions. Their primary purpose is to reduce drag. There is lower pressure on the upper surface of the wing than there is on the underside - and as a result there is some span-wise flow towards outwards on the underside of the wing and inwards on the upper surface. When these two airflows meet they produce a vortex off the trailing edges and this is greatest at the wingtip: the air curls up from the underside producing a large vortex at the tip. This energy is all wasted, as it is almost all drag. Adding the winglets straightens out the airflow to a considerable degree and so reduces the aerodynamic drag a worthwhile amount in particular conditions - usually at cruise speeds. Some aircraft are fitted with fuel tanks at the tip, which have a very similar effect. In additional to the reduction of drag the winglets also produce a stabilising force in roll and so make the aircraft easier and more comfortable to fly - which is why some of them are so large."

[4SPOOLED]

backs up my views on them anyway.....

4s

[Arm out the window]

In addition to (or probably in the act of) reducing the tip vortices and so reducing induced drag that way, I remember reading somewhere that on some types the winglets are set at an angle to the aircraft centreline (in the yawing plane), and that this allows some thrust to be generated because of the angle at which the tip airflow strikes them - kind of like the sail on a boat.
Any aerodynamicists able to confirm or deny this?

[Zap Brannigan]

Yeah I have heard that is true. Apparently the MD-80 winglets are optimised to produce thrust, rather than reducing induced drag or increasing effective span.

I saw some bloke in a souped up Nissan the other day with what appeared to be winglets on his rear spoiler. Big ones too.

Looked rediculous.......:yuk:

[404 Titan]

I’ve heard the term thrust used as well and it is the wrong term guys. All they are doing is producing a component of lift in the horizontal plane that assists thrust. They DON’T, repeat DON’T produce thrust.

[Zap Brannigan]

Fair enough, but mere mortals such as myself it's probably the easiest way aircraft designers can explain it to us.

As far as aero engineers are concerned, for pilots, forward force = thrust or gravity.

[Arm out the window]

I'm with Zap - surely any component of any force that acts in the forward direction of the longitudinal axis is thrust?

[DeBurcs]

some bloke in a souped up Nissan Was it "fully sick", (mite)??

[404 Titan]

Arm out the window & Zap Brannigan

So when an aircraft is in a gliding decent what is producing the forward force keeping the aircraft moving through the air? It aint thrust gentlemen. It is the horizontal component of weight which is equal to drag. The same principle applies to the lift produced by some winglets.

[Ultralights]

Winglets, Do they work ??

judging by this image, i would say a resounding YES. note the vapour in the vorticies! there are NO vorticies from the wing at all, only from the tips of the winglets themselves. even the tips of the horizontal stabiliser has large vorticies, as do the outboard edge of the flaps.

http://home.exetel.com.au/pamuva/FLYING!!!/other%20aircraft/liftpattern.jpg

[DeBurcs]

There is no horizontal component of weight. Weight does not vary in a vector diagram.

Maybe you mean the horizontal component of lift?

Or have I forgotten more about aerodynamics than I ever knew...

[Arm out the window]

Fair enough Titan, I see where you're coming from; I guess it's really a drag reduction in any case. So are we saying that thrust is force produced by the powerplants?
As DeBurcs says though, it's not the horizontal plane you're talking about, it's the longitudinal axis of the aircraft in which the resolved component of weight does its sterling job of keeping us gliding.

[Ultralights]

any object that is either rising or descending but not in the vertical plane, be it an aircraft, or bushbike rider up or down a hill, will have a forward or rearward component of gravity! (weight) which is unchanging.

if the aircraft is level, then weight will be perpendicular, with no forward or rearward component, and have No effect on its forward speed. if the aircraft is at 10 deg nose down, then the weight will have a 10 deg forward component, its this percentage of it weight that will cause it to accelerate. the reverse is true if its is nose up. (assuming nose up or down is identical to the direction of travel)

[404 Titan]

DeBurcs

When I said Horizontal component of weight I was referring to the component of weight acting along the longitudinal axis of the aircraft. Bad choice of words on my part, sorry. All in all though it makes no difference to the point I was trying to make. Winglets don’t produce thrust. They produce lift.

[4SPOOLED]

404

Winglets reduce drag, so less thrust is required for the same IAS which equals $$ in the pocket for the operator..I doubt they provide much lift, especially since they are not postioned in a way that they could create much of it..

I think you will also find that Kinetic energy is the force which keeps the a/c in forward motion conducting a glide and as a result lift results accordingly. Interestingly enough if you go too fast in a glide, you create more drag, creating less distance, and if you go to slow, the weight takes advantage of you along with the drag.

[Arm out the window]

At risk of putting on the thick glasses and lab coat, kinetic energy isn't a force, it's 1/2 mass by the square of velocity - a measure of the energy of motion of an object.
Weight is the force that keeps us gliding; the component of it resolved in the direction of flight does that, counterbalanced by drag and the component of lift in that plane. These forces reach an equilibrium and a steady glide ensues.
As the aircraft glides, potential energy (mass x gravitational constant x height) is converted into kinetic energy.
Drag varies as the square of the velocity, so gliding faster than the best glide speed quickly increases the drag and wastes a lot of potential energy.
Take it away Professor Julius Sumner Miller!

[404 Titan]

4SPOOLED

I am very well aware that winglets reduce induced drag and the theory behind it. Please have a read of all my posts again. I was responding to a post that was saying that winglets produce thrust. I simply responded that they don’t, they produce a small component of lift in the direction of flight.
I think you will also find that Kinetic energy is the force which keeps the a/c in forward motion conducting a glide and as a result lift results accordingly.
Please tell me you are kidding with this statement??

Arm out the window

You are correct. Weight is the force. KE is not a force and doesn’t belong in a forces diagram.

[4SPOOLED]

Kinetic energy is the force describing an object in motion. Weight and lift may be componants of this, but the total energy is desribed as kinetic energy.

You are also correct in your interpretation AOOW......

[Arm out the window]

It all depends on how we commonly think about lift, I guess.
If you define it (correctly I think) as the component of an aerofoil's total reaction vector that is perpendicular to the relative airflow (and drag as the parallel component), then 404Titan's description of lift being produced by winglets is right.
Depending on where the relative airflow is coming from (could be anywhere depending on what you're doing) then lift can point anywhere too.
The tip vortices combined with the aircraft's velocity would cause the relative airflow striking the winglets to be from a forward, outboard direction, so the total reaction vector produced by the winglets should be able to be resolved with a forward-facing component.

4 Spooled, kinetic energy is definitely NOT a force, it's a property of a moving body that is a measure of how much work that body could do at a particular time.
A force is something that pushes or pulls something else; energy is, as I say, a measure of how much work something could do.

[404 Titan]

4SPOOLED

I guess I will have to through away all my aviation text books like Aerodynamics for Naval Aviators (NAVWEPS), The Advanced pilots Flight Manual, Handling the Big Jets, all my ATPL notes, CPL and PPL text books from Trevor Tom and my high school physics text books because they all must be wrong. What I don’t understand is how could all these people be so wrong?

PHYSICS LESSON 101.

For the record Kinetic energy is the energy of motion. An object which has motion - whether it be vertical or horizontal motion - has kinetic energy.

KE = ½ * m *v²

Where m = mass of object
v = speed of object

Potential Energy

An object can store energy as the result of its position. For example, the heavy heavy ball of a demolition machine is storing energy when it is held at an elevated position. This stored energy of position is referred to as potential energy. Similarly, a drawn bow is able to store energy as the result of its position.

PEgrav = mass * g * height
PEgrav = m * g * h

In the above equation, m represents the mass of the object, h represents the height of the object and g represents the acceleration of gravity (approximately 10 m/s/s on Earth).

Force and acceleration

F=ma

When an object changes speed (accelerates or decelerates),its shape or direction of motion, a force is acting on it. The formula for force is given below.

F=mass(kg) X acceleration(m/s/s)

The unit of force is called the newton.
A 100 kg person standing on wooden floor boards exerts a force of 1000 newtons on the floor.

In flight when the object stops accelerating the forces are in equilibrium.

[DeBurcs]

Correct.

Kinetic energy, as the name suggests, is an energy.

Weight is a force despite the fact it is usually measured in Kgs (a unit of mass) these days.

Since weight does not act perpendicular to the aircraft longitudinal and lateral axes in a descent, its sum is not reduced as it is for lift. But it does have a resolved component (as the guys said previously) in the same direction as the longitudinal axis which when added to the (reduced) thrust value, equals the drag value.

Thus the aircraft is descending and in equilibrium.

This is basic physics and the understanding of which is something airlines expect from pilots. It is surprising how many pilots have not learnt this at school.


As for winglets, they do not produce thrust. Some winglets produce lift with a forward vector, the orientation of which depends on the amount of toe (the angle of attack of the winglet in relation to the relative airflow) given to the winglet. This vector value adds to the thrust produced by the engines allowing a performance saving to be made, usually realised in a reduced fuel burn for the same speed.


I now see 404titan has also mentioned the force/mass comparison. I'll leave mine in as I don't want the fingertip and brain strain to have been for nothing.

[4SPOOLED]

Its easy to google these and get a result, but you still dont understand how they are applied.

Potential energy is in any object that is sationary, ie an aircraft on the crest of a hill about to roll down. The energy then becomes kinetic energy once the a/c begins to roll down the hill.

The same thing applies when an a/c is in a glide, it is basically gliding down a hill until it reaches the ground. Once it reaches the ground in in one peice, or in several, it then has potential energy once more.

There are other factors in the glide, lift weight drag and gravity, .... but these can all be desribed as kinetic energy and from the formula 1/2 M x v2 describes the amount of energy that is propelling the a/c forward. However drag will dissapate the energy as there is no thrust to maintain it. ie Thrust = Drag in straight and level, Thrust is greater then drag in climb or acceleration, thrust is less than drag in decent and while slowing down....

If im wrong ill admit it, but this is what i have read in my Bob Tait CPL aerodynamics text

[404 Titan]

4SPOOLED
Its easy to google these and get a result, but you still dont understand how they are applied.
WRONG. I have a very good grasp of KE and PE and how it applies in the real world. If you knew me and what I currently do you would be embarrassed by that statement.
There are other factors in the glide, lift weight drag and gravity,
Yep, these are all forces.
.... but these can all be described as kinetic energy
Bulls**t. They are all forces.
If im wrong ill admit it, but this is what i have read in my Bob Tait CPL aerodynamics text
Please tell me where in Bob Tait’s books it says that KE is a force because this is what you have previously said. I strongly doubt it does because Bob is much smarter than to say such things in his very fine books. I will say it again, KE and PE is energy, not a force. The energy is the resultant of the force.

From Wikipedia, the free encyclopedia.

Lift, an aerodynamic force.

Weight is the interaction of matter with a gravitational field. It is equal to the mass of the object multiplied by the magnitude of the gravitational field. "Weight" is often used as a synonym for mass. The weight of a kilogram of material on Earth is called a kilogram-force. The weight force that we sense is actually the normal force exerted by the surface we stand on, which prevents us from being pulled to the centre of the Earth

Drag is the sum of all the aerodynamic or hydrodynamic forces in the direction of the external fluid/gas flow.

Thrust is a reaction force described quantitatively by Newton's Second and Third Law of physics.

[Arm out the window]

4Spooled, maybe you're winding us up here...an object that has been sitting on top of a hill certainly does have an amount of potential energy; when it starts rolling down that potential is converted to kinetic energy, but when it comes to rest at the bottom it doesn't magically get that potential energy back again!
Imagine a frictionless rollercoaster; sitting still at the top of the track, it has no kinetic energy but a heap of potential. Given a tiny push to get going, it will accelerate down the track, converting that potential into kinetic energy.
As it goes up the next hill, it will convert kinetic back into potential, slowing down as it goes up.
In an ideal world, it would be able to just get up a hill of equal height to the start point as it came to a halt, but in the real case it won't ever make it back to the same height because of frictional losses of energy from the wheels rubbing on the track, bearings rubbing, air resistance and so on.
To clear things up, borrow a high school physics text from the library and start working through it; it'll certainly help with these concepts, particularly if you are thinking of instructing at any stage - at the moment, you're shooting from the hip, by the looks.

[4SPOOLED]

if im wrong im wrong, obviously i have no place to argue with an ATPL, however i think a few of the points i made were valid.

Just a quickie though, why is it then that we need to dissapate kinetic energy in the landing roll to reduce our landing distance?

Also why is kinetic energy defined as the ability to do work, and then defined as work is done when a force moves through a certain distance, and energy is the ability to produce motion.

Wouldnt then a A/C in flight under power/glide e.t.c have energy, and wouldnt this energy be called kinetic energy?

Sorry if i have hijacked this thread from "winglets" anyway

[404 Titan]

4SPOOLED
Wouldnt then a A/C in flight under power/glide e.t.c have energy, and wouldnt this energy be called kinetic energy?
I never said it didn’t have Kinetic Energy. It does. We just said Kinetic Energy isn’t a force.

I will leave it for you to make the relationship with Force, Momentum, Kinetic Energy and Work. I suggest you start with all their formulas. They speak a thousand words. Once you see how they are related you will finally grasp the concept we have been trying to explain to you.
:ok:

[Arm out the window]

Good on you, 4 Spooled; it's not about being right or wrong or whatever, we're all on a learning curve anyway so none of us know it all.
One problem with a discussion like this is that it includes terms like energy, force, potential and so on that we use in everyday language, but which also have clear and specific meanings in physics, so the obvious start point in clearing up misunderstandings is to make sure we're all talking about the same things.
As I said, a high school physics book will go through all this stuff and hopefully present it in a logical progression; it isn't rocket science (well I guess it is in a way!) but it needs to be worked through to be clearly understood.

Very briefly, forces (gravity, lift, magnetic forces, direct pushes and pulls etc) working on masses will accelerate them. A number of forces working in opposing directions (as for an aircraft in flight) will either add up to a resultant force (which will accelerate the object) or balance eachother out (leaving the object in a steady state, eg a steady climb say).
Force = Mass x Acceleration (F = mA)

The important things to note when figuring out a force diagram like the old lift/weight/drag/thrust aeroplane pictures is that forces are vectors (ie. they have a direction as well as a magnitude) so you can look at them in various directions and see how they balance out (fore and aft, up and down or whatever).

Energy is something that an object or system can have that is broadly energy of motion (kinetic energy, 1/2 x mass x velocity squared) or potential energy (eg gravitational potential, mass x gravitational constant x height, mgh). Potential energy can also be things like the energy stored in a stretched spring, or in the chemicals of a battery etc)
Energy can be converted between forms (eg. potential to kinetic and back, as for the roller coaster; or kinetic into heat, such as when your brakes slow you down by using friction, and get hot).

I could waffle on all day but the best thing is just to get hold of a book and work through it.

Cheers


:8

[tinpis]

:hmm: .....so....how do winglets work then?

[Arm out the window]

Well, glad you asked; firstly we must consider Bernoulli's theorem, the compressibility of a fluid, Reynolds numbers and of course the Heisenberg Uncertainty Principle, which leads us to the answer...I'm not certain!

[swh]

Tinni..

Think you were taking the pi.....anyway ...http://www.boeing.com/commercial/aeromagazine/aero_17/winglet_story.html will tell you some good info.

:ok:

[4SPOOLED]

cheers for the help then guys, i have reread CPL aerodynamics anyway and booked myself into a 2 week Physics course in October at YPPH

Best to have all the tools of the trade at my disposal i suppose.:ok: