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I just came across this article on LinkedIn, and I have a few questions about it.

Some of the claims are things such as:

Aircraft set to become more human as engineers develop smart skins which can detect injury

The revolutionary ‘smart skin’ concept will enable aircraft to continually monitor their health, reporting back on potential problems before they become significant. This would reduce the need for regular check-ups on the ground and parts could be replaced in a timely manner, increasing the efficiency of aircraft maintenance, the availability of the plane and improving safety.

In the past I have seen some claims of a similar nature (such as skin that adapts its shape to be more aerodynamic based on phase of flight). What I am wondering is: - Is this really technically feasible? - Can such a skin really do what BAE claims? - Will this have any adverse effects on the aviation industry? (Usually people are so enamored with new technology and the good it can do, I am more curious if anyone has thought of the downside.)

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broad claims over vague specs is standard for a PR department to get funding for their newest toys –  ratchet freak Aug 21 at 12:20

3 Answers 3

up vote 11 down vote accepted

Smart skins are at least 20 years old and, like fusion energy, just around the corner since then. The usual concept is to embed optical fibers in the structure and shine laser pulses through them. If the fiber is damaged, it will transmit less light, and by measuring the return time of a very short laser pulse, even the location of the damage can be detected. This concept requires fibers with the same break elongation as the load-carrying material, so they break just when a crack in the structure starts. To detect even small cracks, a lot of fibers must be evenly placed, which is only possible with fiber reinforced plastics. The effort to place a light source and a detector at each end of every fiber has so far prevented a practical application, at least to my knowledge.

Other techniques send clearly defined "pings" through the material and detect the propagation of the sound wave with a number of microphones. By comparing the measured signal with a reference signal, damage can be detected in metal structures as well. This technique needs some processing power, but is easily within the scope of modern microcontrollers. However, outside noise will interfere with the measurement, so it needs well defined conditions to be effective.

The downside would be more mass, investment and operator training. Generally, more advanced techniques for structural health checks have been steadily introduced in the last 80 years. Given the high cost of maintenance today, I expect that deployed damage detection technology will continue to advance, with a healthy time gap to what is possible in the laboratory. So there is some truth to those BAe claims, but I would hardly call it revolutionary.

Even more advanced are concepts of self-healing structures which contain capsules of a two-component resin. When the structure breaks, the capsules break as well and the freed resin helps to mend the crack.

If you ask me, the mass of those microcapsules would be better invested if it carries load right from the start, so the structure will tolerate higher loads and more load cycles. But I guess those research grants need to be spent somehow, and marketing departments need to write about revolutionary discoveries on a regular basis.

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"like fusion energy, just around the corner since then" - LOVE that observation! –  user19555 Aug 21 at 14:01
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rather than sound, a standing EM field could also be used, changes in the field caused by breaks in the skin triggering sensors. –  jwenting Aug 21 at 14:03
    
@jwenting: Good point, changes in conductivity and local capacitance give hints to damage, but sensors need to be fairly close to pick up the change. With acoustic excitation the sensors can be fewer and farther away. –  Peter Kämpf Aug 21 at 19:11
    
@PeterKämpf possibly, though you want them in a reasonably dense grid to get an accurate location of the breach anyway, and acoustic sensors tend to be larger and more fragile than most. –  jwenting Aug 22 at 6:28

If they ever get it to work on a production scale (and that's a big if) and economical to implement, it could mean aircraft detecting hairline fractures caused by metal fatigue themselves, rather than relying on regular X-ray scans of their structural components.

But that's for the future. For now the main application is the generation of funding for more research, which is the main application of most all research done in the last 20 years or more. Hence the mandatory phrase "more research is needed" at the end of every report coming out of every research department.
I once committed the mortal sin of not including that in a report, in fact I made it quite clear in my report that no further research into the topic was needed because the whole concept was bonkers and not economically viable (I was slightly more political in my wording but not all that much). It wasn't received kindly by the people who'd ordered the research, nor by its funders. It did get quite a few chuckles from my then colleagues outside of the specific department, there being little love lost between them and the team lead of the project I had been working on for the last 6 months as an intern.

So yes, it can in theory have very interesting implications for aircraft maintenance procedures, in practice though I seriously doubt we'll see any of it in more than a proof of concept form for a very long time.

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I believe there is a prototype panel already in existence so the answer is yes it is possible...it's just a case of improving upon it and getting it onto a real plane Also, you wouldnt want to use ant form of wiring (including optic cables) as that it big costs, and also would compromise the structure, and what happens if you break one of the bits?

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