Why do Airbus aircraft typically have less wing flex than Boeing aircraft?

Question

I was watching this video on YouTube about Boeing vs Airbus aircraft, and at around the 5:09 mark the female pilot stated that Airbus wings are much "stiffer" and "less aerodynamic" compared to Boeing's' more "aerodynamic" wings.

I looked at a few videos and it does appear that Airbus aircraft have some wingflex but not to the same extent as Boeing aircraft.

Taken from: this video

I gather that wing flex is mostly beneficial for aerodynamics so why then, do Airbus aircraft typically have less wing flex than Boeing aircraft?

Answer 1

It's not a super scientific statement. There may be some half-truths referring to half-truths inferring that some design is better, just for show business sake.

"The Boeing wing is way more aerodynamic than the Airbus wing" is not something that has any value at all. All wings are by definition aerodynamic, there is no sliding scale. All wings are the result of a design process, balancing many input parameters. If an aircraft manufacturer cannot get the aerodynamics of a wing right, they have no place in the aerospace industry. Both Airbus and Boeing make very fuel efficient and safe aircraft that compete head to head in the market place.

Wing flex is one of these things that the structural engineers must cater for, after the aerodynamicists have had their go at the external shape: the planform, aerofoils etc. It can be considered a secondary design parameter that:

• provides dihedral in flight, for stability when banking;
• acts as a spring against turbulence;
• can cause grief with flutter;
• may provide difficulty for the ailerons to operate.

For a given wing shape, wing flex is the result of the ratio of strength and elasticity of the wing material. Composites are the latest in aircraft material, being lighter and stronger than aluminium. It is five times stronger than aluminium, and flexes about half when under load. But because it is stronger a lot less material can be used to make the wing lighter - even though a certain amount of carbon fibre flexes less than the same amount of aluminium, there is simply less of it. The ratio of strength over flex of carbon fibre is much higher than that of aluminium.

All aircraft with wings made of carbon fibre flex a lot more than aircraft with wings made out of aluminium. Both the A320 and the B737 have aluminium wings. For a given material and wing area, wing flex is a function of

• Aspect ratio: a long, slender wing flexes more than a short, stubby wing. Or the long aluminium wing of a large airliner flexes more than the shorter wing with the same aspect ratio of a smaller airliner.
• Wing thickness. The thicker the wing profile, the less sweep angle needs to be used to delay drag divergence. This is actually a sign of an aerodynamically more advanced wing, and the thicker profile makes the wing bend less

Those sort of comparisons make much more sense than "the wing of a Boeing is much more aerodynamic than that of an Airbus". That's only showbiz.

Answer 2

I get what you are referring to. I have carefully observed it myself.

Airbus A320 is a popular aircraft, when the flaps are fully extended, the wing and flap together has a sharp angle.

On the other hand when a Boeing 737 has its flaps fully extended, the wing overall has a very smooth curved shape.

To a layman, the Boeing wing definitely seems more aerodynamic. But that's only what we infer from the shape. I have friends who work for both Boeing and Airbus. All of them talk about how they spend a LOT of time optimizing and re-optimizing their designs. Unfortunately they design the cabin not the wings.

I'm pretty sure in the wind tunnel, both wing designs offer similar lift and drag. Hence their lack of interest in fixing something that works well. Airbus is famous for retaining things that work. The infamous barking noise of the hydraulic pumps is well known. It has worked for so long that it's "side effects" can be ignored. Here the "side effect" is the wing looking sharp, weird and stiff. As long as the drag and lift values are fine the business does not justify the cost of modification.

Another important factor as stated above, is the structural stability. The wing must undergo least vibration, less stress and strain for it to last long. The shape and structure of an Airbus wing may require it to be shaped such that stress is minimum. Or maybe the Boeing wing was designed like that. We can't know since both manufacturers are not that open to sharing such details to the public.

The stiffer looking Airbus wing requires less moving parts and may offer better structural integrity. That too cannot be stated as a fact by me.

Answer 3

Wing shape ie planform, stiffness, thickness, chord length etc are driven by the design parameters that the designers are tasked with. The wingtip shape and the subtle changes in each of those parameters along the chord and span are dictated by the need to extract maximum energy from the air flow so as to minimise drag and maximise the lift. This is where science and a degree of art creeps in to maximise the yield. These parameters are to be true for the entire range of speed and mach number including low speed etc.

The Boeing 737 series has a more conventional high speed wing whilst the A320 has a supercritical wing with their respective benefits. Flexing of wings are an aero-servo-elastic phenomenon that can be tailored in composite wings and to a lesser extent in conventional material wings. It's a finely orchestrated task between the aerodynamics, structural, stability & control, materials and weight management engineers to optimise all of the above.

Needless to mention the increments in performance are limited to single digits only and so is the differential between Boeing737 and A320 wing performance.