Super-Critical and Critical wing

[adriansecco]

What is the difference between a super-critical wing (as found on a B777) and that of a critical wing (as found on Airbus).

[john_tullamarine]

http://www.aerospaceweb.org/question/airfoils/q0003.shtml

talks about supercritical wings ... not too sure what you mean by "critical wing", though, unless that is some sort of in-house Bus terminology ?

[Old Smokey]

Ummm... All wings are critical, that is, they eventually reach Mcrit. In older design wings, drag rise was pretty fast after Mcrit. The Super Critical wing went one stage further in development in (1) dalaying Mcrit further than before, and/or (2) creating a High Speed drag polar (i.e. Wave Drag) which rose much more slowly beyond Mcrit, giving a much wider speed availabliity above Mcrit with minimal drag rise.

I'm no historian, but I believe that the A300 had the first "Super Critical" wing in commercial production. If you want, you could call the B777 possessive of a Super Super Critical Wing because the technology went one stage further with cambered trailing edges, not apparent on the original 'flat top' super critical wings.

Regards,

Old Smokey

[adriansecco]

Appreciate your answers. I heard the critical wing jargon being directed and assosiated with the Airbus aircraft. In a way it was due to the fact that the B767 / B777 does not have winglets and that most Airbus aircraft do. Thought it had to be because one was called a Super-Critical wing and the other a Critical. There may be incorect use of the wording or jargon due to what I have heard from other people. What makes a Airbus wing then need winglets and a B777 not ?

[Old Smokey]

I cannot comment upon why the aerodynamacists at Boeing chose not to use winglets on the B767/777, but it's important to appreciate that winglets are intended to alleviate Induced drag, i.e. Low Speed Drag, whilst the Super Critical wing is designed to alleviate High Speed Drag, i.e. Wave Drag due to trans-sonic shock wave formation.

One has nothing to do with the other.

Regards,

Old Smokey

[john_tullamarine]

There is also the basic credo that there is no such thing as a free lunch.

Wingtip devices come with structural penalties compared to a basic wing .. either this costs in maintenance or in weight.

The OEM is not going to put on a device just because it can .. rather only if it is necessary to achieve the mission profile for the design.

[adriansecco]

Thanks guys,

Your answers where appreciated

[adriansecco]

Spoke to a friend of mine, he mentioned that the B777 has a more elliptical shape wing compared with the competition. Would this be beneficial for low speed/high speed or both in terms of design? Would this be a reason that B777 wing does not require wing lets in terms of its airflow over the wing. I see Airbus seem to use more of a wing fence design rather than that of a winglet on some aircraft.

[SKIP007]

From my french book "avions et aerodynique"I ve learned that the profile shape of the supercritical wing allowes a higher load factor than the critical wing close to the trailling edge of the wing.

The supercritical wing has a more balanced load factor on a larger surface lof the wing.

The critical wing support his associated load factor on a smaller surface of the wing

Greg :8

[Dave]

Well I did Aerospace Engineering at University and my lecturer said and I quote: "Super Critical means designed by computer"

Always thought that was wrong!! Maybe a Super Critical wing IS designed by computer but it does not MEAN designed by computer!

During my Airbus A320 type rating the instructor said (and I quote again): "I don't know what a Super Critical Wing is, but I know the Airbus had one".

Seems not many people actually know what a Super Critical wing is!

See this: http://en.wikipedia.org/wiki/Supercritical_wing

[Old Smokey]

A good link Dave, I think that their first sentence says it all -

"A supercritical wing is a kind of wing designed to increase aircraft performance within the transonic speed range."

It just so happens that the supercritical wing came along in the computer design era. Being computer designed doesn't make it supercritical! If so, I guess that computer designed fuselages etc. are also supercritical.

Regards,

Old Smokey

[FE Hoppy]

Wasn't the super critical wing designed by a guy called Whitcombe(sp) at NASA/NACA back in the 50's I think the name can be a bit missleading but the principle is that the profile delays the onset of shockwaves therefore giving a higher Mcrit. Same bloke came up with the Area Rule for fuse design.
"Not bad for a yank"

[GearDoor]

Wouldn't the winglets on the airbus be to reduce induced drag at altitude as well? I know induced drag is at a maximum at low speed, but Di increases as air density decreases, ie: at high altitude cruise.

Also, I think they (the winglets) were added on to the A340/330 during flight testing as part of the performance enhancement package when the original engine supplier failed to meet performance targets.

[Conan The Barber]

The engine originally intended for the A340 was never made, thus the CFM-56 was chosen. Since winglets are used on both the A340 and A330 I would suspect that is has more to do with aerodynamics than engine design.

[RMC]

I didnt realise my mother in law had been designed by computer!

[Premium]

Spoke to a friend of mine, he mentioned that the B777 has a more elliptical shape wing compared with the competition. Would this be beneficial for low speed/high speed or both in terms of design?

In theory an elliptical wing balances the upwash along the entire span of the wing. Induced drag directly relates to the amount of upwash created by the wing and upwash in turn is greatly affected by the wing tip vortex. ( Hence you can see why a winglet is beneficial to the reduction of induced drag. )

By balancing the upwash along the wing, the tip produces an equal amount of induced drag as the root....this is the most efficient state for the wing to operate under. A fully elliptical wing is not practicle however as it causes the entire wing to stall at the same time, making the aircraft extremely unstable and difficult to fly near the stall.

Take a look at the factors which effect Di and you will see why a more elliptical wing is beneficial in terms of performance.

[Old Smokey]

Spoke to a friend of mine, he mentioned that the B777 has a more elliptical shape wing compared with the competition.

I've done a few thousand walk-round inspections of the B777, and not an ellipse to be seen. Lots of straight edges abound.

I think that your friend was wrong.

Regards,

Old Smokey

[adriansecco]

Once again, thanking you all for your input and answers!!!!

I know this may sound like it is ground that we may have covered, was at work the other day and noticed that the B777 wing tip had it looked like to possibly be the birth or what we now called a raked wing tip,( it's not that prominant) any idea's and input from the 777 drivers.

Back to super critical and critical wing shape/form again. Heard that the difference between the two is that the one has a greater leading edge radius that the other. one was a improvement on the other. any ideas/answers.