wing length and winglets
Discussion
I guess a certain amount of wing length is determined by the weight the aircraft is going to be fully laden, but how much over size is needed ? also if the winglets are a good thing then how come they don't feature on the tail section ?
the other half and I were looking at the A380 in front of us at Heathrow and its a mighty thing, but it looks out of proportion which lead me to seek out answers from the wise folk on here. . .
the other half and I were looking at the A380 in front of us at Heathrow and its a mighty thing, but it looks out of proportion which lead me to seek out answers from the wise folk on here. . .
I assume you mean wing span when you say 'length' (i.e. wing tip to wing tip distance)? Winglets or sharklets are normally used to reduce induced drag, which is the drag caused as a result of lift generation and the associated vortices (generated at the wing tip because of the pressure difference between the lower and upper wing surfaces). I can only assume they're not used on the horizontal stabiliser because this isn't a main generator of lift. It may infact produce a downforce depending on the aircraft and the centre of gravity, which would maybe mean that a wingtip device would not be beneficial.
Wing design is influenced by a lot of things, such as efficiency, handling characteristics, required performance etc. Large wing span doesn't always mean great performance, but a measurement called aspect ratio (wing span divided by wing chord (i.e. leading edge to trailing edge breadth)) can influence efficiency. Look at a glider for example, and it will have a high aspect ratio, so a really large span relative to the chord. Small powered aircraft generally have a 'Hershey bar' style wing planform, so that they have good performance for their weight and predictable handling.
Wing design is influenced by a lot of things, such as efficiency, handling characteristics, required performance etc. Large wing span doesn't always mean great performance, but a measurement called aspect ratio (wing span divided by wing chord (i.e. leading edge to trailing edge breadth)) can influence efficiency. Look at a glider for example, and it will have a high aspect ratio, so a really large span relative to the chord. Small powered aircraft generally have a 'Hershey bar' style wing planform, so that they have good performance for their weight and predictable handling.
Edited by Prawo Jazdy on Thursday 27th August 11:39
benters said:
I guess a certain amount of wing length is determined by the weight the aircraft is going to be fully laden, but how much over size is needed ? also if the winglets are a good thing then how come they don't feature on the tail section ?
the other half and I were looking at the A380 in front of us at Heathrow and its a mighty thing, but it looks out of proportion which lead me to seek out answers from the wise folk on here. . .
Some aircraft have them the other half and I were looking at the A380 in front of us at Heathrow and its a mighty thing, but it looks out of proportion which lead me to seek out answers from the wise folk on here. . .
Collectingbrass said:
As I understand it (Civil Engineer, if my stuff flys we've really got problems etc) the winglet also enables the aircraft to be larger without requiring entire airports to be rebuilt.
Airports are designed to allow aircraft of various sizes to navigate around, via the Code system. The largest aircraft are Code F and have a wingspan >65m but <80m. Anything bigger than that, and you end of with an aircraft that wont fit into an airports taxiway/stand infrastructure..And therein lies a problem!
I thought winglets or call them what you like were there to reduce drag, nothing to do with fitting an aircraft in an airport.
Having spoken to an A320 Captain about this very subject he suggested that an A320 with winglets is far more slippery through the air and slows down a lot slower than one with normal wings.
I remember reading somewhere that to add these to an A320 retrospectively for example cost around £500,000 but the fuel saving was around 5% which is a fair amount of dosh over a few years I guess.
However if you look at the 747-8 it doesn't have the winglets the 747-400 has whihc are about 1m tall it simply has a turned up wing tip at the end of the wing. Obviously the wing chord and shape etc. has changed massively since those early 747's and I guess these aircraft manufacturers are always finding new was to make aircraft more cost effective to run.
Having spoken to an A320 Captain about this very subject he suggested that an A320 with winglets is far more slippery through the air and slows down a lot slower than one with normal wings.
I remember reading somewhere that to add these to an A320 retrospectively for example cost around £500,000 but the fuel saving was around 5% which is a fair amount of dosh over a few years I guess.
However if you look at the 747-8 it doesn't have the winglets the 747-400 has whihc are about 1m tall it simply has a turned up wing tip at the end of the wing. Obviously the wing chord and shape etc. has changed massively since those early 747's and I guess these aircraft manufacturers are always finding new was to make aircraft more cost effective to run.
Passive winglets need to be built in to the wing structure from the start. They add a significant amount of extra load on the wing and when this is scaled up for the max load calculations for gusts etc then the wing needs to be much stronger to cope.
There are some active systems around that use flaps that trigger at set g loadings that then reduce the wing tip load, but these aren't fitted on commercial aircraft as a rule. It's an old trick to do this sort of load alleviation, but it's been ignorned by commercial aircraft builders.
Winglets work by making it seem that a wing is longer an it actually is, so you get a bigger aspect ratio (think gliders) and this reduces drag.
They can make the aircraft more susceptible to cross winds on approach and on the ground, so they aren't perfect and need to be handled with a bit of care, but the fuel savings are massive and so if you can fit them or buy an aircraft with them, then you do. They pay for themselves many times over in service.
There are some active systems around that use flaps that trigger at set g loadings that then reduce the wing tip load, but these aren't fitted on commercial aircraft as a rule. It's an old trick to do this sort of load alleviation, but it's been ignorned by commercial aircraft builders.
Winglets work by making it seem that a wing is longer an it actually is, so you get a bigger aspect ratio (think gliders) and this reduces drag.
They can make the aircraft more susceptible to cross winds on approach and on the ground, so they aren't perfect and need to be handled with a bit of care, but the fuel savings are massive and so if you can fit them or buy an aircraft with them, then you do. They pay for themselves many times over in service.
First reply was my favourite.
I'll add that some basic principles should be understood
1) High aspect ratios (long wings with narrow chord (horizontal width front to back)) usually generate most lift for least drag at subsonic speeds.
2) The vast proportion of induced drag (as above, drag generated by virtue of creating lift) is caused by airflow moving span-wise. It moves inboards on top of the wing and outboards beneath the wing when flying normally. Where the spanwise flow spills over the wingtips and then finds the wing has gone it swirls into the tip vortices which is where the drag is.
3) Mathematically efficient wings would be infinitely long with no tips to cause tip vortices. Lifting bodies are the opposite - they're just two wingtips with no wing inbetween and very inefficient for cruising.
4) Winglets can only really be optimised for a fairly narrow operating envelope of cruising speeds etc. Hence they suit airliners well which fly in a straight line at a steady speed for most of their time. Fighter jets, not so much.
5) For an aeroplane that's flying along with a good CofG etc, the tail surfaces should be doing very little in terms of imparting any aerodynamic loads. No aerodynamic loads = no induced drag = no benefit in winglets.
6) Winglets make the wings effectively longer for the spanwise flow and reduces the intensity of the tip vortices. They do not add extra effective span for lifting purposes, because they are close to vertical - how does a vertical aerofoil lift perpendicular to itself? Ok, it alters the shape of the spanwise lift distribution a little - but you don't lift a bigger aeroplane by pointing the wings upwards. The winglets are there for drag reduction and therefore improved fuel economy.
I'll add that some basic principles should be understood
1) High aspect ratios (long wings with narrow chord (horizontal width front to back)) usually generate most lift for least drag at subsonic speeds.
2) The vast proportion of induced drag (as above, drag generated by virtue of creating lift) is caused by airflow moving span-wise. It moves inboards on top of the wing and outboards beneath the wing when flying normally. Where the spanwise flow spills over the wingtips and then finds the wing has gone it swirls into the tip vortices which is where the drag is.
3) Mathematically efficient wings would be infinitely long with no tips to cause tip vortices. Lifting bodies are the opposite - they're just two wingtips with no wing inbetween and very inefficient for cruising.
4) Winglets can only really be optimised for a fairly narrow operating envelope of cruising speeds etc. Hence they suit airliners well which fly in a straight line at a steady speed for most of their time. Fighter jets, not so much.
5) For an aeroplane that's flying along with a good CofG etc, the tail surfaces should be doing very little in terms of imparting any aerodynamic loads. No aerodynamic loads = no induced drag = no benefit in winglets.
6) Winglets make the wings effectively longer for the spanwise flow and reduces the intensity of the tip vortices. They do not add extra effective span for lifting purposes, because they are close to vertical - how does a vertical aerofoil lift perpendicular to itself? Ok, it alters the shape of the spanwise lift distribution a little - but you don't lift a bigger aeroplane by pointing the wings upwards. The winglets are there for drag reduction and therefore improved fuel economy.
jamieduff1981 said:
I'll add that some basic principles should be understood
2) The vast proportion of induced drag (as above, drag generated by virtue of creating lift) is caused by airflow moving span-wise. It moves inboards on top of the wing and outboards beneath the wing when flying normally...
Hmmm, so for the swept wing of, say, an airliner, the upper surface spanwise flow is inboard? Really?2) The vast proportion of induced drag (as above, drag generated by virtue of creating lift) is caused by airflow moving span-wise. It moves inboards on top of the wing and outboards beneath the wing when flying normally...
I thought wing fences were sometimes fitted on the upper surfaces of swept wings partly to prevent the opposite: outboard spanwise flow deflecting air along rather than over the wing thereby reducing lift at the tips and mkaing them more prone - among other things - to tip stalls?
As far as I'm aware, upswept winglets improve efficiency primarily becasue they increase effective aspect ratio without proportionally increasing span.
benters said:
Thanks for the info guys. . . .
G-PEEK is an interesting looking bird
Diamonds DA42 or whatever they call it these days G-PEEK is an interesting looking bird
It's a rich mans toy or a flying schools training twin, ivenot had the pleasure to fly one yet but the engines run on diesel and the avionics are G1000 glass
dr_gn said:
jamieduff1981 said:
I'll add that some basic principles should be understood
2) The vast proportion of induced drag (as above, drag generated by virtue of creating lift) is caused by airflow moving span-wise. It moves inboards on top of the wing and outboards beneath the wing when flying normally...
Hmmm, so for the swept wing of, say, an airliner, the upper surface spanwise flow is inboard? Really?2) The vast proportion of induced drag (as above, drag generated by virtue of creating lift) is caused by airflow moving span-wise. It moves inboards on top of the wing and outboards beneath the wing when flying normally...
I thought wing fences were sometimes fitted on the upper surfaces of swept wings partly to prevent the opposite: outboard spanwise flow deflecting air along rather than over the wing thereby reducing lift at the tips and mkaing them more prone - among other things - to tip stalls?
As far as I'm aware, upswept winglets improve efficiency primarily becasue they increase effective aspect ratio without proportionally increasing span.
The tip vortex is still caused by an up-and-over flow from under the tip though
r1flyguy1 said:
benters said:
Thanks for the info guys. . . .
G-PEEK is an interesting looking bird
Diamonds DA42 or whatever they call it these days G-PEEK is an interesting looking bird
It's a rich mans toy or a flying schools training twin, ivenot had the pleasure to fly one yet but the engines run on diesel and the avionics are G1000 glass
benters said:
the other half and I were looking at the A380 in front of us at Heathrow and its a mighty thing, but it looks out of proportion which lead me to seek out answers from the wise folk on here. . .
The A380-800 looks awkward because Airbus sized the wing (and tail?) to allow for stretched versions in the future. The proposed A380-900 looks more in proportion.
jamieduff1981 said:
First reply was my favourite.
Thanks to the limitations of written communication, I can't work out if that's something to be proud of, or whether it means it's full of inaccuracies! If I'm telling people nonsense, I apologise. It's also good to know if I've understood this wrong, as it will be important to my future. jamieduff1981 said:
First reply was my favourite.
...would be infinitely long with no tips to cause tip vortices. Lifting bodies are the opposite - they're just two wingtips with no wing inbetween and very inefficient for cruising.
Not really because lifting bodies are used for high-speed flight where the lift coefficient (and therefore induced drag) is heading for zero....would be infinitely long with no tips to cause tip vortices. Lifting bodies are the opposite - they're just two wingtips with no wing inbetween and very inefficient for cruising.
dr_gn said:
I thought wing fences were sometimes fitted on the upper surfaces of swept wings partly to prevent the opposite: outboard spanwise flow deflecting air along rather than over the wing thereby reducing lift at the tips and mkaing them more prone - among other things - to tip stalls?
Wing fences are really only functional at high-alpha. Of course, if you can increase CLmax with them then you can use a smaller wing, so I guess they do have a secondary drag-reducing function in high-speed flight. Gassing Station | Boats, Planes & Trains | Top of Page | What's New | My Stuff