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Blog post: swansont: This Claim Won't Fly

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One of things I like to do, as you know, is to run an order-of-magnitude calculation when I see a claim that seems off, to see if it's plausible.

 

The future of flight: Shape-shifting engines and body heat power

 

This claim caught my eye

 

Tan Kai Jun, the team leader, envisions cabin seats upholstered with a thermoelectric fabric that can convert a person's energy into 100 nanowatts of voltage. Alas, that amounts to about one-millionth of what your iPhone needs to stay on standby. Still, Jun maintains that it does ultimately add up.

"It's a small amount, but imagine this collected from 550 seats throughout 10 hours of flight. A plane has a lifespan of a few hundred flights -- over time that's a big reduction," he says.

 

This one's pretty easy. Ignoring that nanoWatts is a power, not a voltage, let's assume a 10 hour flight. That gets you a total of 1 microWatt-hour per passenger. Let's be generous and assume 1000 flights, which gets you to a milliWatt hour. Another further generous assumption of 1000 passengers gets you to a Watt hour. I think you can see where this is going. US grid electricity costs around ten cents per kiloWatt-hour. Even if we assume that the cost of electricity on a plane is ~100x more than commercial US electricity, because of the inefficiency, this system will save, at most, a penny over the lifetime of the plane. If the components and installation are free, that is, and the weight of the system costs no additional fuel.

 

So, not a big reduction.

 

 


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