giles Posted March 29, 2009 Share Posted March 29, 2009 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 Quote Link to post Share on other sites
martin_sam_2000 Posted March 29, 2009 Share Posted March 29, 2009 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 Quote Link to post Share on other sites
GearDownPlease Posted March 29, 2009 Share Posted March 29, 2009 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. Quote Link to post Share on other sites
Tony P Posted March 29, 2009 Share Posted March 29, 2009 Hot water and skill. Quote Link to post Share on other sites
oldHooker Posted March 29, 2009 Share Posted March 29, 2009 (edited) 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) Reduce bending pressure as you get near the wingtip, constantly checking for the desired shape. Take care, Frank Edited March 29, 2009 by oldHooker Quote Link to post Share on other sites
Jennings Posted March 29, 2009 Share Posted March 29, 2009 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 Quote Link to post Share on other sites
martin_sam_2000 Posted March 30, 2009 Share Posted March 30, 2009 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 Quote Link to post Share on other sites
giles Posted March 30, 2009 Author Share Posted March 30, 2009 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 . Frank, thanks for your tutorial. Cool pictures . 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 Quote Link to post Share on other sites
Grey Ghost 531 Posted March 30, 2009 Share Posted March 30, 2009 Hmmmm, I'd be willing to bet the lack of flex in a Cessna compared to the flex of an airliner is more of a factor of a 2000 pound aircraft vs a 900,000 pound aircraft. I bet a C-130s wings flex more than an F-86s. Quote Link to post Share on other sites
MattC Posted March 30, 2009 Share Posted March 30, 2009 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. Quote Link to post Share on other sites
ross blackford Posted April 10, 2009 Share Posted April 10, 2009 :), 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). , Ross. Quote Link to post Share on other sites
vc-10 Posted April 11, 2009 Share Posted April 11, 2009 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. Quote Link to post Share on other sites
tigermeet Posted April 12, 2009 Share Posted April 12, 2009 If you want to see scary wing flex-try a B-52 Quote Link to post Share on other sites
vc-10 Posted April 12, 2009 Share Posted April 12, 2009 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) Quote Link to post Share on other sites
GCA333 Posted April 12, 2009 Share Posted April 12, 2009 The Handley Page Victor's wings would bounce massively during turbulence. They were like giant shock absorbers, as one report put it. The wings had to be checked often for cracks due to the flex. Quote Link to post Share on other sites
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