737 - 800, why the upswept wings?
Discussion
Ari said:
Just that really, they look like they've been lowered into a box that was slightly too small.
Why haven't other planes got them if they're worth having?
There you go:Why haven't other planes got them if they're worth having?
http://en.wikipedia.org/wiki/Wingtip_device
I remember seeing a documentary about it...I think it goes along the lines of 'disrupted airflow at the tips of the wings'. So technically small wings lose a lot of lift as a certain % of the wing tips are not efficient as the airflow from top and bottom join up.
The upswept wing tips move that turbulence away from lift generating wing and allow 100% of the wing to be efficient.
The upswept wing tips move that turbulence away from lift generating wing and allow 100% of the wing to be efficient.
Simpo Two said:
Wingtip vortices have been known about for a long time and so have wind tunnels, so I'm surprised they didn't appear sooner.
Fuel efficiency was not as big a drive previously, as it is now. Might have had something to do with materials available for the kind of construction now seen.In the late 50s and early 60, jet travel was all about speed. Some of these earlier designs such as the Convair 880/990 and the de Havilland Trident all had fairly high subsonic cruise speeds.
By the mid to late 70s, it was obvious that cheap fuel was gone forever so newer designs were more about fuel economy rather than speed.
The first aircrft I'm aware of that featured low drag winglets was a version of Learjet. In the 80s winglets began to appear on Airbus A310s and A320s and were offered as a retrofit on older aircraft such as the 727 and the 757. The latest version of the 737 also now have them. The original 737 first flew in 1967 so it is quite an elderly design from an aerodynamic point of view.
By the mid to late 70s, it was obvious that cheap fuel was gone forever so newer designs were more about fuel economy rather than speed.
The first aircrft I'm aware of that featured low drag winglets was a version of Learjet. In the 80s winglets began to appear on Airbus A310s and A320s and were offered as a retrofit on older aircraft such as the 727 and the 757. The latest version of the 737 also now have them. The original 737 first flew in 1967 so it is quite an elderly design from an aerodynamic point of view.
The next technology for drag reduction that might make it on a commercial plane are riblets. Little V-shaped ridges on the fuselage or wings that prevent vortices (micro-vortices ?) from attaching onto surfaces.
Problem is they are fairly fine structures and would interfere with paint jobs and would require more regular cleaning. But I could see them being 'painted' on to a wing surface.
These have been around for some time as well.
links
http://www.stanford.edu/group/ctr/articles/tackle....
http://adsabs.harvard.edu/abs/1982aiaa.meetT....W
http://tinyurl.com/c3d2e9b
Problem is they are fairly fine structures and would interfere with paint jobs and would require more regular cleaning. But I could see them being 'painted' on to a wing surface.
These have been around for some time as well.
links
http://www.stanford.edu/group/ctr/articles/tackle....
http://adsabs.harvard.edu/abs/1982aiaa.meetT....W
http://tinyurl.com/c3d2e9b
Eric Mc said:
Aircraft like the Buccaneer and Javelin had vortex generators on their wings - and they were designed in the 1950s.
So there are good vortices and bad vortices?dr_gn said:
I think it might be laminar flow surfaces...
I thought it was going to be nanotechnology paint with molecule-sized wheels in it...Simpo Two said:
So there are good vortices and bad vortices?
Indeed. Vortex generators are used to 'Re-Energise' the Boundary Layer which aids in drag reduction (because it keeps the Boundary layer thin) as well as to prevent flow separation (which can have ramifications in things like stall characteristics).
On Transonic wings they can assist with flow stagnation and how the shock-wave(s) forms (which affects Transonic handling).
Simpo Two said:
Ta! Yes, I can see that every case is different.
Indeed. Such devices can also be used to assist how an a/c handles and how it 'feels'.For eg. When the Jet provost Mk5 entered service, the redesign of the cockpit and canopy had ramifications as to how the a/c stalled (viciously with no warning) because of the airflow over the fuselage; when it did stall engine surges became prevalent. Not good characteristics for a training jet.
They cured this by adding two winglets to each intake. One caused flow separation that would generate pre-stall buffet (thus giving warning of an impending stall), the latter smoothed the flow through the intakes meaning that an engine surge was less likely.
When the JP5A came out (sans tip tanks) the spin was found to be highly oscillatory (again not good for a jet where students were regularly practicing spinning), so a strake was added either side of the nose to cure this effect.
On the Hawk we would teach MLTs (Medium Level Turns), that is to say, maximum performance turns - the basis of Air Combat Manoeuvres and the 'bread and butter' of any fighter pilot (whether he/she went on to be a Mud Mover or a Steeley Eyed Air Defender).
A Max Perf. Turn will occur at the point where you have Max. Lift on the wing vs Max. G applied to the airframe. Obviously this will translate as a Speed vs a Height.
At low altitude you will hit the limiting G of the airframe before you hit Max Lift, and at height vice versa.
So there is an ideal height/speed where a max turn will occur.
Now, teaching this in one respect is easy - pull till you hit the G limit at the right speed (ok it's a bit more complicated), but how do you know you have max lift on the wing?
Well, this occurs just around the pre-stall buffet, so what you do is pull to the light buffet then allow the a/c to climb or descend AT the light buffet (whilst still pulling) until you have the max G applied.
In order to do this, the student NEEDS to be able to feel the light buffet. Unfortunately the early Hawks didn't show any light buffet, or rather the transition from light buffet - heavy buffet - stall was so fast and easy to miss. Thus some of the vortex generators on the Hawk wing are there to magnify the pre-stall buffet by causing flow seperation at high alpha which then impinges upon the tailplane and 'tells' the pilot that he/she is at Max Alpha.
Ginetta G15 Girl said:
In order to do this, the student NEEDS to be able to feel the light buffet. Unfortunately the early Hawks didn't show any light buffet, or rather the transition from light buffet - heavy buffet - stall was so fast and easy to miss. Thus some of the vortex generators on the Hawk wing are there to magnify the pre-stall buffet by causing flow seperation at high alpha which then impinges upon the tailplane and 'tells' the pilot that he/she is at Max Alpha.
The buffet is your friend, no doubt about it - but how does that translate to operational types? - did the Phantom / Shaguar / Tornado / Harrier actually have a tactile buffet you could rely on, or was it a case of reverting back to juggling the indications from the the AoA indicator, the G-meter, what was hanging off the airframe, and the stick position to feel if you were setting yourself up for the mother of all flicks?eharding said:
The buffet is your friend, no doubt about it - but how does that translate to operational types? - did the Phantom / Shaguar / Tornado / Harrier actually have a tactile buffet you could rely on, or was it a case of reverting back to juggling the indications from the the AoA indicator, the G-meter, what was hanging off the airframe, and the stick position to feel if you were setting yourself up for the mother of all flicks?
As we've discussed before, Operational FJ tend to have the unfortunate habit of Gyroscopic forces overcoming Aerodynamic forces when Critical Alpha is reached, especially with centre-line stores.So 'pulling to the buffet' isn't really an option.
One sets AoA for the particular stores fit/fuel state.
Edited by Ginetta G15 Girl on Wednesday 9th November 13:20
Winglets are fitted to far more aircraft than just the 737NGs
Press here for a good article
It explains why and also shows the different types of winglets commonly seen today.
Press here for a good article
It explains why and also shows the different types of winglets commonly seen today.
Ginetta G15 Girl said:
In order to do this, the student NEEDS to be able to feel the light buffet. Unfortunately the early Hawks didn't show any light buffet, or rather the transition from light buffet - heavy buffet - stall was so fast and easy to miss. Thus some of the vortex generators on the Hawk wing are there to magnify the pre-stall buffet by causing flow seperation at high alpha which then impinges upon the tailplane and 'tells' the pilot that he/she is at Max Alpha.
Interestingly (to me anyway!) one of the few modifications that the Red Arrows Team make to their Hawk aircraft is the addition of a small, aluminium 'wedge' on the leading edge of the wing. It's designed to produce a far more tactile (and obvious) buffet through the controls, enabling pilots to 'pull to the buffet' with great accuracy and consistency 
Gassing Station | Boats, Planes & Trains | Top of Page | What's New | My Stuff