Final answer:
In-flight, emergency AC power can be provided by RAM air turbines, battery systems, and APUs, with military aircraft often using 400-Hz AC power. Systems like Thermawing and Thermacool utilize DC power and high-output alternators for deicing and air conditioning in general aviation.
Step-by-step explanation:
In flight, emergency AC power can be provided through several means, including ram air turbines (RATs), battery backup systems, and Auxiliary Power Units (APUs). Aircraft like military planes use 400-Hz AC power, which allows the design of lighter-weight equipment due to the higher frequency. In terms of complete cycles, a 400 Hz frequency means that one cycle takes 1/400 of a second, which is 0.0025 seconds. For general aviation aircraft, innovations like Thermawing and Thermacool systems serve the purpose of deicing/anti-icing and air conditioning, respectively, and are powered by high-output alternators or DC power sources.
For example, the Thermawing is an anti-icing and deicing system that enables pilots of single-engine aircraft to fly through ice encounters safely. It utilizes heated wing technology akin to that used in larger, jet-powered aircraft. The Thermacool system is an electric air conditioning system featuring a highly efficient, brushless DC motor, which even allows the air conditioner to be used before the aircraft's engines start. In the extreme case of total power loss in flight, pilots need to rely on emergency power generation such as the RATs, or on gliding and navigation skills to land at a suitable nearby airport or airstrip, as was famously done during the Gimli Glider incident.