Under a clear blue sky, a new kind of electric aircraft flew from Kennedy International Airport into the heart of Manhattan this April. The trip took around 10 minutes, a fraction of the hour or more it could take in a car. The flight offered a glimpse at how the aircraft, which is made by Joby Aviation and combines features of a helicopter and an airplane, and others like it could someday operate in cities. It was made possible by a federal program that is trying to hasten the arrival of what