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Hi guys,

Can anyone explain wing flex (I think I understand why it happens...)

And, more importantly, how to replicate it in model form.

Giles

the "why" is simple. they wing has to lift itself before it lifts the fuselage..so it flexes up. if it was rigid it would snap as soon as it hit turbulence.

as to the "how". I have no idea...sorry

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Hi giles,

I will suggest you a method I used to correct a too low dihedral on RoG's 737-800 kit wing: use a strip of metal thin enough to be glued in the wing inner surface (either upper or lower part) while retaining the shape you bend it, it will act as a spare. In my case, I used a steel flat profile of 5 x 2 x 12 or 15mm long, bent to the right shape and epoxied to the inner surface of the upper wing part, worked wonderfully.

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Hi Giles,

Yes, a nice warm massage does wonders for flexing, or just straightening the wing.

Begin near the root, thumbs on the upper surface and fingers on the bottom, then work your way out a little at a time. (don't bend it hard, just a little as you go, and repeat the process until it's in shape)

flexingwing.jpg

Reduce bending pressure as you get near the wingtip, constantly checking for the desired shape.

flexingwing3.jpg

flexingwing2.jpg

bCO7381.jpg

Take care,

Frank

Edited by oldHooker
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While it can be argued on the minutiae, basic aerodynamics holds that straight wings do not flex (they would break), but swept wings do (otherwise *they* would break). There are exceptions both ways, but in general in aerodynamics and aeronautical engineering, that's the way it is.

If you ride in a straight winged airplane such as a Cessna or a Piper, the wing does not flex. The entire airplane rides the wing. On a swept wing design such as almost any airliner these days (with swept wings), the wing flexes depending on the amount of lift it's generating, turbulence, etc. One side effect of that is a smoother ride in rough air in a swept wing airplane than an equivalent sized straight winged airplane. Anybody who's ever flown in a C-130 in turbulence can attest to that!

J

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While it can be argued on the minutiae, basic aerodynamics holds that straight wings do not flex (they would break), but swept wings do (otherwise *they* would break). There are exceptions both ways, but in general in aerodynamics and aeronautical engineering, that's the way it is.

If you ride in a straight winged airplane such as a Cessna or a Piper, the wing does not flex. The entire airplane rides the wing. On a swept wing design such as almost any airliner these days (with swept wings), the wing flexes depending on the amount of lift it's generating, turbulence, etc. One side effect of that is a smoother ride in rough air in a swept wing airplane than an equivalent sized straight winged airplane. Anybody who's ever flown in a C-130 in turbulence can attest to that!

J

Jennings,

Thank you for that explanation. i had no idea that only swept wing aicraft's wings flexed..but looking back at all the aircraft I have seen...it holds true. more uselss knowledge for me to remember.

Sean

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While it can be argued on the minutiae, basic aerodynamics holds that straight wings do not flex (they would break), but swept wings do (otherwise *they* would break). There are exceptions both ways, but in general in aerodynamics and aeronautical engineering, that's the way it is.

If you ride in a straight winged airplane such as a Cessna or a Piper, the wing does not flex. The entire airplane rides the wing. On a swept wing design such as almost any airliner these days (with swept wings), the wing flexes depending on the amount of lift it's generating, turbulence, etc. One side effect of that is a smoother ride in rough air in a swept wing airplane than an equivalent sized straight winged airplane. Anybody who's ever flown in a C-130 in turbulence can attest to that!

J

Jennings, thanks for explaining it so well. And, I always thought it was because I had to pay for my own Airbus/Boeing rides now while the C-130 rides in the past were paid for by someone else :cheers:.

Frank, thanks for your tutorial. Cool pictures :salute:. And, Tony P, thanks for making it sound so simple!

Sean, your A340 in the GB is inspiring. I only hope my first airliner would turn up half as good.

Giles

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While it can be argued on the minutiae, basic aerodynamics holds that straight wings do not flex (they would break), but swept wings do (otherwise *they* would break). There are exceptions both ways, but in general in aerodynamics and aeronautical engineering, that's the way it is
.

All wings will bend, depending on their rigidity. On a lightplane like a C172, it is fairly easy to engineer a wing which will not bend obviously under normal loads, simply because the bending moments and loads are less. For an example of straight wings bending, watch a sailplane going up on a winch or doing aerobatics.

On a smaller wing with less loading, it is easier to build a more rigid wing within decent weight limits. Practicality dictates that whilst it would be technically possible to build an airliner wing which doesn't bend, it would be too heavy, plus, too much rigidity would transmit turbulence more significantly to passengers.

The reason airliner wings seem to bend more than other aircraft wings is partly because they usually employ a higher AR. That narrow chord means a thinner wing (for the same wing section) and thus, less space to build in a rigid spar structure. If you think of some aircraft with high AR straight wings, a lot of the exhibit some degree of wing flex, but most are not working at such high reynolds numbers.

Think of it this way - Cessna 172 - Span 11m, AUW 1100kg = 100kg/m, 737-700 - Span 36m, AUW approx 72,000kg = 2000kg/m

So, it is easier to engineer a wing to resist bending which is loaded at 100kg per metre of span.

In comparison, if the C172 were loaded to the same level, it would have an AUW of 22,000kg.

The same applies to any aircraft, in the RC sailplanes I make, it would be possible to design wings which don't bend, and some competition models do so, but in general, there is little performance gain in actually stopping bending. As long as the structure is strong enough to withstand the bending moment, its easier, cheaper and more comfortable to allow the bend.

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  • 2 weeks later...

:), As one who has spent many hours riding in the back of C-130s and watched many thousands of C-130 take offs and landings I can assure you the wings do indeed flex a fair bit. If you watch a Herc taking off for a long flight with full tanks they start the take off roll with anhedral on the wings and finally become airborne with quite a dihedral angle. As well as this the wings do flex along their length in turbulance (not a great deal, but still visible from inside the aircraft).

:thumbsup:,

Ross.

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Also some similar aircraft have different amounts of flexing. 737NGs for example seem to flex (based on my observations!) more than A320s, although it is more noticeable with the winglets.

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Or the old B-47, which had wings that go up and down in level and smooth flight! They used to oscillate, according to a book I read ('WideBody, the story of the 747' I think)

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