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Aircraft build up a static charge during flight which is currently discharged through static dischargers:

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I recently read the abstract and summary of this paper:https://www.sciencedirect.com/science/article/abs/pii/S1359836820334235

Which explores using certain types of polymers with conductive cores (graphene) for aircraft bodywork and wings to utilize the static charge build up over the aircraft surface to act as a large capacitor. For example, this would be achieved by creating a potential difference across the wings.

What magnitude of energy could be created and what systems could this run - if any? Would this be relevant for commercial airliners, electric aircraft, civilian aircraft or even superlight solar powered aircraft, such as the Solar Impulse which flew round the world.

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I understand there would be a weight increase with additional equipment but I am wondering about the feasibility and whether it would even power a clock on the dashboard.

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Here's a very back of the envelope calculation for precipitation static:

  • The wetted area of a 787 is around $1800~\rm m^2$
  • The most triboelectric materials are around $.2~\rm nC/g$
  • The density of water in a cloud is at most a few $\rm g/m^3$
  • The cruise speed is on the order of $300~\rm m/s$

Putting this all together gives a few hundred microamps of current at maximum. Even if you develop a few thousand volts of potential difference across the plane, this amounts to around a watt. Enough to power a clock maybe but certainly not enough to power an instrument panel. By comparison, a ram air turbine produces thousands or tens of thousands of watts.

This estimate is likely much too high- the density of clouds decreases with altitude, and 787s do not spend much time at cruise speed at low altitude.

One watt is certainly not anywhere near enough to accept any weight penalty to the airplane.

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  • $\begingroup$ One watt, that you only get sometimes... definitely not worth adding weight to an airframe that's optimized to be as light as possible! $\endgroup$
    – Ralph J
    May 4, 2023 at 21:57
  • $\begingroup$ Just for the record, a wristwatch uses vastly less than 1 Watt of power. How much power does a wrist watch use to function? estimates 12 microwatts for a wind-up mechanical watch; quora.com/… estimates 0.7 microwatts for a battery-powered watch with an LCD screen. (0.006 Watt-hours per year estimated from battery capacity). A clock with an LED display or a backlit LCD might use a few milliwatts: emitting light costs vastly more than keeping time but still not much. $\endgroup$ May 4, 2023 at 23:44
  • $\begingroup$ @PeterCordes From a cursory check, many instrument clocks use several watts. Presumably there is no strong impetus to optimize the power draw since it is negligible compared to everything else. $\endgroup$
    – Chris
    May 5, 2023 at 0:13
  • $\begingroup$ @Chris: That makes sense; I'd guess a typical plug-in clock-radio might use a whole watt (even with the radio part off). I only noticed after commenting that the question specifically asked about a clock on an the dashboard. If you had to power a clock from triboelectricity, just as an exercise in silliness, you could, though. $\endgroup$ May 5, 2023 at 0:33
  • $\begingroup$ probably, but it wouldn't even be worth the weight of the wiring to carry the energy to the clock $\endgroup$
    – user253751
    May 5, 2023 at 2:22

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