Soft-Kite Aeroelasticity Solution

As aeronautical engineering scaled up and high speed became a goal, aeroelastic limits became a core design problem. Rigid wing aircraft literally shake themselves apart when they fly too fast.

Soft kite wings are different. A larger slower wing of equivalent power is less aeroelastically excited. Bridling further constrains the wings from developing normal-mode oscillations. Wing softness itself damps aeroelastic modes.

For all these reasons, soft kites are the COTS TRL9 solution to AWE’s aeroelasticity problem, a limit formally posed in papers like this example from TUDelft-

https://www.researchgate.net/publication/326954168_Aeroelastic_Analysis_of_a_Large_Airborne_Wind_Turbine

I studied Aeroelasticity under Prof. Ronald Stearman, a pioneer in the field, held in great regard by Dave Lang and other experts. Its nice to be able to see how the soft kite does not follow the rules of rigid-wing design.

This paper is about rigid wings, as precised in the abstract: “The device considered in this study consists of a tethered rigid wing with onboard-mounted wind turbines designed for wind energy harvesting in crosswind flight operation”.

So can you quote the extract(s) supporting your statement ("…soft kites are the COTS TRL9 solution to AWE’s aeroelasticity limit problem…")?

Pierre,

No wing is truly “rigid”. That’s why aeroelasticity is what it is. The reference clearly sets out the aeroelasticity problem for a sparred kite wing.

It may be this topic is the first time that the aeroelasticity of soft kites is identified as more benign than an equivalent “rigid” wing of the sort considered in the paper.

Power kites really are COTS TRL9 tech. Because they are resilient instead of brittle, they recover from upsets that destroy brittle wings. They do not fail aeroelastically, by breaking spars.

Dave,

Apparently you cannot. So your statement I put again is not supported by the publication you quoted:

The paper does not confirm what you wrote.

Pierre,

Can’t you tell that soft kites DO NOT break up due to the brittle aeroelasticity described in the paper? And now WIndy Skies’ profoundly ignorant Moderation has hidden this topic because you seem unable to understand the soft-kite’s inherent resilience to aeroelastic effects.

Ok, now the topic is unhidden again. When will mis-moderation by Windy Skies end? Don’t the wrongly moderated parties deserve to know who is trampling on their contributions?

The topic about heat-resistant kites and their conceptual origin and possible applications is still hidden, for no good reason. This has to stop.

I changed the syntax of the introductory statement to make clear that the reference only validates aeroelastic brittle failure as a known limit on rigid wing structure. It does not claim that soft kites are a solution to that problem. That claim originates here, on the self-evident fact that soft kites are inherently resilient, not brittle.

Another approach to seeing that soft kites are not as vulnerable to brittle failure by aeroelastic effects is the engineering toughness of structure. A soft kite can be shaken by aeroelastic motions or hit with a hammer, and does not fail under conditions that a rigid wing fails. Structural fabric is inherently tough, by being both strong and ductile.

The TUDelft paper is only to confirm that the rigid turbine blades simulated do have a serious problem with aeroelastic brittle failure compared to strong ductile blades.

Part of the picture is that more-rigid higher-mass wings have more internal inertial forces to risk structural failure. Aerobatic loops with a massive wing in a gravity field further concentrate internal forces that cause brittle failure. Soft power kites are tough enough to crash and a pop right back up. Flown as a quiver, they never come close to aeroelastic failure. As noted in the air-as-structure topic, a soft kite’s structural air is not brittle while rigid wing structure is.

A final remarkable aeroelastic advantage of a ram-air soft kite is progressive stiffness with velocity. At velocity limit, a string breaks or fabric tears, and the wing self kills, then repairs easily in the field. A hot rigid wing can essentially explode into countless tiny pieces when high excess energy in the airframe is released catastrophically at the velocity limit (aeroelastic divergence).

No TUDelft paper I can cite addresses these facts properly, nor is that gap a cause for censorship. Open-AWE techne is for kite-pros to verify by long experience and study, regardless of whether their art is in academic papers to cite. Kitegods give superior correct life-lessons about kites. Those who only depend on academic references are mistaken.

More interesting to me would be an exploration of quantitative research into flutter in (tensioned) fabrics. What exact computed characteristics would a fabric wing need to have to be able to fly close to the speed of sound and not be ripped apart for example.

One reason fabric kites are less efficient than rigid wings is flutter after all, so if you want to explore the use of efficient fabric kites, understanding the effects of flutter on fabric kites is important.

I have a feeling the references from the linked paper might be a good starting point to learn more.

However the linked paper is about rigid wings. The Aerodynamic characterization of a soft kite by in situ flow measurement paper about soft wings would be more suitable.

After that @kitefreak could try to compare aeroelasticity of soft and rigid wings.

I had already looked again at that paper, Pierre.

You will not find the insight that soft kites are comparatively superior in resistance to aeroelastic destruction, by being inherently less brittle.

This topic is where such insight is presented.