Soon7x7 From United States of America, joined May 2006, 2527 posts, RR: 16 Reply 3, posted (2 years 5 months 1 week 16 hours ago) and read 10672 times:
Is the entire wing re designed on this NG version?
UAL747 From , joined Dec 1969, posts, RR: Reply 6, posted (2 years 5 months 1 week 14 hours ago) and read 10629 times:
Yes, it has drooped ailerons, or flaperons.
This wing is super critical whereas the others were not. Don't ask me to define it, because I don't really know what it means other than the underside is scooped out near the rear? I'd love a definition of super-critical.
Vikkyvik From United States of America, joined Jul 2003, 6516 posts, RR: 29 Reply 8, posted (2 years 5 months 1 week 12 hours ago) and read 10540 times:
Quoting UAL747 (Reply 6): This wing is super critical whereas the others were not. Don't ask me to define it, because I don't really know what it means other than the underside is scooped out near the rear? I'd love a definition of super-critical.
While I don't know the technical reason they're called super-critical, what it basically does is push the shockwave farther back on the wing. At that point, you get a weaker shock, and reduced drag.
The spirit of Massachusetts is the spirit of America!
Tdscanuck From Canada, joined Jan 2006, 11033 posts, RR: 72 Reply 9, posted (2 years 5 months 1 week 10 hours ago) and read 10481 times:
Quoting UAL747 (Reply 6): This wing is super critical whereas the others were not. Don't ask me to define it, because I don't really know what it means other than the underside is scooped out near the rear?
The scoop at the back is called a reflexed trailing edge...it's not essential to a supercritical airfoil, but most of them have it to improve the pressure recovery at the back and make the moment curve a little nicer.
Quoting UAL747 (Reply 6): I'd love a definition of super-critical.
It's like a Supreme Court justice once said "I know it when I see it." A hard technical definition is quite difficult, but anybody with solid aerodynamics knowledge can recognize a super-critical airfoil when they see one. The giveaway is usually a fairly flat upper surface and an evenly thick middle. Put another way, a supercritical airfoil usually looks like a thick plate with a leading and trailing edge stuck on. A conventional airfoil usually doesn't have a near-constant thickness section in the middle.
Quoting Vikkyvik (Reply 8): While I don't know the technical reason they're called super-critical, what it basically does is push the shockwave farther back on the wing. At that point, you get a weaker shock, and reduced drag.
Critical Mach number (Mcr) is the Mach number when some portion of the airflow somewhere on the airfoil first hits Mach 1. In conventional airfoils, this usually happens right around the thickest part, is a relatively strong shock, and causes a fairly abrupt drag rise if you go much beyond Mcr. As a result, conventional airfoils rarely operate very far above Mcr.
A supercritical airfoil is designed to have more gradual velocity gradients over the top surface (they spread out the low pressure area) so that the supersonic point is farther back and the shock is weaker. This lets them get farther past Mcr before the drag gets too unpleasant, so they can perform better above their critical Mach number...they work OK when super-critical.
Vikkyvik From United States of America, joined Jul 2003, 6516 posts, RR: 29 Reply 10, posted (2 years 5 months 1 week 10 hours ago) and read 10477 times:
Quoting Tdscanuck (Reply 9): Critical Mach number (Mcr) is the Mach number when some portion of the airflow somewhere on the airfoil first hits Mach 1. In conventional airfoils, this usually happens right around the thickest part, is a relatively strong shock, and causes a fairly abrupt drag rise if you go much beyond Mcr. As a result, conventional airfoils rarely operate very far above Mcr.
A supercritical airfoil is designed to have more gradual velocity gradients over the top surface (they spread out the low pressure area) so that the supersonic point is farther back and the shock is weaker. This lets them get farther past Mcr before the drag gets too unpleasant, so they can perform better above their critical Mach number...they work OK when super-critical.
Wow, I can't believe that never crossed my mind as the meaning of "supercritical"!
Thanks Tom.
The spirit of Massachusetts is the spirit of America!
Would you know what is the main component of drag experienced by airfoils operating near their critical Mach numbers? Is it the shock wave itself or the shock induced separation?
Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair.
Prebennorholm From Denmark, joined Mar 2000, 5810 posts, RR: 56 Reply 12, posted (2 years 5 months 6 days 18 hours ago) and read 10206 times:
Quoting UAL747 (Reply 6): This wing is super critical whereas the others were not. Don't ask me to define it, because I don't really know what it means other than the underside is scooped out near the rear? I'd love a definition of super-critical.
Supercritical wings are the industry standard on airliners and have been so for quite a few decades. I am pretty sure that the 744 was the very last airliner to be produced with non-supercritical wings.
"Supercritical" was a buzzword in the 70'es, but since it became the industry standard in the 80'es, it mostly went out of use.
It is much like my grandfather's Ford model T which he in the mid 20'es had modified with automatic windscreen wipers. In this case "automatic" means that the wipers were driven by an electric motor, and not by a handle.
Always keep your number of landings equal to your number of take-offs, Preben Norholm
Tdscanuck From Canada, joined Jan 2006, 11033 posts, RR: 72 Reply 13, posted (2 years 5 months 6 days 15 hours ago) and read 10115 times:
Quoting JetMech (Reply 11): Would you know what is the main component of drag experienced by airfoils operating near their critical Mach numbers? Is it the shock wave itself or the shock induced separation?
I suspect it's the shock wave itself, but that's just a gut feeling...I'd be curious to see some wind tunnel data or Schlieren photos of a wing right at Mcr.
Faro From Egypt, joined Aug 2007, 1327 posts, RR: 0 Reply 14, posted (2 years 5 months 6 days 7 hours ago) and read 9965 times:
Are the flap track fairings unchanged? The ones on the 744 are big, hefty contraptions, maybe Boeing took the opportunity to streamline them a bit with the 748?
Maybe it' just a question of detail that a closer-up image might clarify, but I have the impression that those fairings on the 748 are in fact the same as the 744's...
FWI747 From France, joined Jul 2007, 70 posts, RR: 0 Reply 18, posted (2 years 5 months 5 days 22 hours ago) and read 9714 times:
I think the most inboard flap fairing has its max thickness a little more fore on the -8 than on the 744... and it seems to me that the outboard ones are a little thinner toward the end but, I agree one need sharp eyes
DocLightning From United States of America, joined Nov 2005, 14050 posts, RR: 55 Reply 19, posted (2 years 5 months 5 days 21 hours ago) and read 9652 times:
Quoting Tdscanuck (Reply 4):
New loft, new control surfaces, mostly the same structure.
New airfoil, new bending moment, new materials... a very different wing from the original. AFAIK, the 744 wing, was essentially identical to the 741 wing except for the winglet/extension and an improved wing root fairing.
Quoting Faro (Reply 17):
Maybe it' just a question of detail that a closer-up image might clarify, but I have the impression that those fairings on the 748 are in fact the same as the 744's...
The fairings are not just covers for the flap apparatus. They also serve as anti-shock bodies. They soften the sudden decrease in aircraft cross-section at the trailing edge of the wing. The nacelles, mounted way out in front of the wings, also serve the same role ahead of the wing.
Dynamicsguy From Australia, joined Jul 2008, 678 posts, RR: 4 Reply 20, posted (2 years 5 months 5 days 7 hours ago) and read 9466 times:
Quoting DocLightning (Reply 19): New airfoil, new bending moment, new materials... a very different wing from the original.
Still mostly the same structure though - same architecture, regauged for the changes in loads. The loft changes the shape a little, but it's still the same layout. Are the materials different for the structure?
I'd say it means that Boeing adjusted the shape of the airfoil sections used in the wing. This could be done by adjusting the camber line and / or thickness distribution as well as other parameters.
Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair.
The loft is the shape of the wing. The term is a throwback to aviation's naval roots:
"Lofting is a time honored tradition amongst boat builders. It refers to the tradition of building full scale templates for the boat's hull in the loft of a boat building building(?), then dropping lines down through the loft to the building area that periodically delineate the curve." http://www.recumbents.com/wisil/Plans/lofting.htm
Quoting Jetmech (Reply 22): I'd say it means that Boeing adjusted the shape of the airfoil sections used in the wing.
Changing airfoils is definitely relofting, but it could also include changes to the twist, sweep, di/anhedral.
Starlionblue From Greenland, joined Feb 2004, 15102 posts, RR: 69 Reply 24, posted (2 years 5 months 3 days 22 hours ago) and read 9135 times:
Ok so if there is relofting does that mean there is a new wing? I mean when does a redesign of an existing wing become an "all new" wing?
Tact Is For People Who Aren't Witty Enough To Be Sarcastic
25 Soon7x7: The 747 has proved the success of the flexible variable leading edge flap...why other models and or manufacturers not utilizing this concept?
26 Dw747400: As I understand it, the primary structure of the wing (spars, ribs, etc) is pretty much the same as on prior versions of the 747, with two obvious ex
27 DocLightning: I've always wondered this myself. The 747 was the only model with this curious design. I never understood why. I would imagine that during extension/
28 Tdscanuck: In my book, yes, since the biggest design factor in the wing is the aerodynamics. I don't think there's any clear-cut definition, but Dw747400's soun
29 Starlionblue: As I recall, the reason for the design was that the 747 leading edge was quite thin in order to achieve the speeds required by Pan Am. But I could be
30 Western727: This is also how I understand it; the "thinness" of the 741/4's wing leading edge meant that installing slats (and the associated hardware) was not p
31 Starlionblue: The legendary Juan Trippe, then CEO of Pan Am, was one of the strongest forces behind the 747. With a handshake between him and Bill Allen at Boeing,
32 DocLightning: I read that the plane was originally designed to cruise above above M 0.9, but it was found to be uneconomical. Still, the shape of the nose is desig
33 747classic: The improved wing root fairing as seen on all 747-400's is a product improvement developed to decrease the fuel consumption with approx. 0.5%. It's a
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