### This Claim Won't Fly

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.

## 1 Comment so far

1. Uncle Al on June 17th, 2013

Fuel ethanol returns 0.9 joule net for every joule input overall. How is that not wildly successful?

A hermetically isolated hard vacuum envelope contains two closely spaced but not touching, in-register and parallel, electrically conductive plates having micro-spiked inner surfaces. They are connected with a wire, perhaps containing a dissipative load (small motor). One plate has a large vacuum work function material inner surface (e.g., osmium at 5.93 eV). The other plate has a small vacuum work function material inner surface (e.g., n-doped diamond “carbon nitride” at 0.1 eV). Above 0 kelvin, spontaneous cold cathode emission runs the closed isolated system. The plates never come into thermal equilibrium when electrically shorted. The motor runs forever. (No Shottky barrier – heavy doping, ohmic contact for the diamond.)

http://www.mazepath.com/uncleal/htoo.htm
The future – from a pop bottle.