| Onboard Electrical System (II) |
 Pablo Edronkin
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Onboard electrical systems are battery-fed; usually, 12V or 24V batteries are used that are quite similar to those designed for land vehicles, only that they are made of better quality materials and seldom carry liquid or fluid electrolytes in order to avoid leakages. You can, of course, improvise if the situation merits that and place a car battery, but be very careful! First of all, remember that only authorised and qualified technicians should make repairs on an aircraft so if you are not one of them leave this for very, very difficult situations. Only if your survival is at stake you should attempt to toy with the electrical system without being a specialist.  The magnetos that actuate the sparkplugs in the engine are independent from the main electrical system. The consequences of tampering with the electrical system are usually very expensive: Frying a whole set of instruments, producing fires due to short-circuits, letting corrosive substances leak into the fuselage structure… So, be extremely careful if it comes to cannibalisation or improvisation in this regard. Aeronautical batteries are constantly being recharged as the aircraft is in use; generally a generator, alternator, APU (auxiliary power unit) or EPU (external power unit) are used, depending on the design and weight of the vehicle in question. Generators and alternators are widely used among GA (general aviation) aircraft, EPUs can be used with many different sort of airplanes, helicopters, etc. and they are commonly seen in hangars and military installations because they can be used to feed any aircraft without actually having to turn any sort of internal power unit on (you wouldn't start the turbines on an F-15 just to turn on the cockpit lights, would you?); APUs are carried generally by relatively large aircraft and are, in essence, electrical generators moved by a small engine, which in turn, is generally a small turbine.  The small button-like forms that appear at the bottom are the fuses fur each electrical subsystem. You will also see, particularly in vintage airplanes, external alternators that transform wind (aeolic) into electricity; these look like small electric engines with a small windmill-like propeller placed underneath the wings of an airplane. |
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