Variable Wing-Loading

KJ_Lesnick

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I know you can vary a wing's loading, or more accurately it's L/D ratio via the use of variable geometry wings (which I'm not fond of) or through the use of leading and trailing edge devices.

Is it possible, though, to tailor a plane's aero-elastic properties so that at high airspeed when G-levels go up, the wing responds by twisting down in disproportionately greater amounts such so that overall lift levels drop (while maintaining a reasonable L/D ratio) relatively? The idea would be to allow a wing with a pretty light wing-loading to at higher speeds reduce it's overall lift (and thus the drag that goes with it) so it could sustain reasonable G-levels?

I do remember hearing that most wings respond to loading by twisting leading-edge down (forward swept wings are exceptions and I've been told require a very sturdy structure to resist this tendency) so I'm wondering if a trick like this could work?


KJ Lesnick
 
Is it possible to achieve this result just without memory alloy? Just cleverly tailored aeroelastic qualities?

KJ Lesnick
 
KJ,

I was thinking about that too last night. Perhaps a mission-adaptive wing (MAW) or sometihng similar could be what you need? IIRC NASA tested the basic concept on an F-111 years ago. Here's something a little more current for you:

http://www.sbirsttrmall.com/Library/Documents/FlexSys-AF98-180%20Innovation%20Story.pdf

Maybe that's what you're looking for. Or perhaps a variation on the idea maybe.

Moonbat
 
You're not understanding me... The idea isn't to increase lift -- You can just use leading and trailing edge devices for that (Like the F-16).

The idea is to *decrease* lift during high-g maneuvers at high airspeeds -- wings with light-loading tend to bleed off too much airspeed at high-speed during high-G maneuvers. The idea is to kind of cause the wing to twist down (I've been told wings twist down in respnse to loading naturally), but in a disproportionate manner in response to g-loads at higher-airspeeds to reduce lift, (and with it, drag) so the lightly loaded wing can continue to sustain high G's even at speeds beyond where a typically lightly-loaded wing would bleed too much speed off...

See what I mean?


Kendra Lesnick
 
What you're talking about, controlling the bending and twisting of the wing under loading is called aero-elasticity and it's what made the X-29 possible.

As for variable wing loading, all powered aircraft have it; it's called fuel burn. ;)
 
Aeroelastic tailoring has been a part of every high-performance aircraft design since HiMAT and X-29. HiMAT used the directional properties of carbomfibre laminates to make the wing twist leading-edge down at higher angles of attack, decreasing drag and delaying stall. X-29 used the same technique to prevent the leading-edge-up structural diverge inherent in a forward-swept wing. No aircraft since appears to have used aeroelastic tailoring to such extremes, but it is now part of the designer's toolbox.

In a conventional metal structure the torsional axis around which the wingbox twists under load cannot be changed, but by controlling the mix of laminate directions used in the layup of a carbonfibre wingbox, the twist axis can be different to the geometric axis.
 
I had completely forgotten about the HiMAT. I thought that was the coolest airplane when I was in Junior High School. I've seen the threads here on it's various iterations but had forgotten it's excellent work in the area of aero-elasticity. Although, when I was in college, I attended a speech given by some of the researchers from that program and it was quite an interesting talk.
 
The Himat derived "Rockwell wing" was offered to Sweden for the JAS-39. It only offered improvements in the transonic regime and added about 20% to the cost, so it was not used.
 
CammNut

Aeroelastic tailoring has been a part of every high-performance aircraft design since HiMAT and X-29. HiMAT used the directional properties of carbomfibre laminates to make the wing twist leading-edge down at higher angles of attack, decreasing drag and delaying stall.

Were there any aircraft before HiMAT that had aeroelastic tailoring (you said it's been a part of every major high performance aircraft design since HiMAT, however the wording does not clearly say that the HIMAT was the first; just all planes after it featured aeroelastic tailoring, though you did state that the X-29 and HiMAT used aeroelastic tailoring to an unusual degree) ?

In a conventional metal structure the torsional axis around which the wingbox twists under load cannot be changed, but by controlling the mix of laminate directions used in the layup of a carbonfibre wingbox, the twist axis can be different to the geometric axis.

I'm suprized it couldn't be done without a composite structure. I figured if the wing-box was set up right it would twist more and more during increased loads even with metal. I guess I'm wrong...


Kendra Lesnick
 
Aero-elastic tailoring requires a material where you can choose the direction of strength/stiffness in your material. Metal tends to be homogenous and have the same properties in all directions, though I suppose you could perhaps uses techniques like directional solidification and single crystal used for turbine blades to give some directionality?. Really however aero-elastic tailoring requires use of composites in structural areas, something that didn't really happen before the 1980s.
 
Overscan,

Aero-elastic tailoring requires a material where you can choose the direction of strength/stiffness in your material.

Even if it worked both ways? (i.e. The wing twists leading edge down disproportionately in response to high positive-G's at higher airspeeds, and twists leading edge up disproportionately in response to high negative G's at high airspeeds)


KJ Lesnick
 

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