Three airplanes-a sailplane, a piston powered sailplane, and a twin turboprop-have been instrumented to measure electric fields inside electrified clouds and the net electric charge on the airplanes. In unelectrified clouds the powered airplanes become negatively charged during collisions with liquid cloud water droplets whereas the sailplane does not. In thunderstorm clouds, several airplane charging mechanisms are found to operate. These involve collisions with liquid water droplets of the cloud and the shedding of polarization charge in the presence of strong electric fields. For these charging processes, the sign of the acquired charge depends on the sign of the component of the atmospheric electric field along the direction of flight. When the amounts of charge on the powered airplanes are small, the engine exhaust acts to discharge the airplane, while for larger charges, corona emission becomes the predominant mechanism of discharge. ¿ American Geophysical Union 1990