Fishman, a retired jeweler from New Jersey, has been flying planes and gliders for 30 years. In the mid-1990s, he put together a motorized glider kit, but it was noisy and undependable. It sat in storage until two years ago, when he replaced its gas engine with an 18-horsepower electric motor he and a colleague designed to minimize noise and vibration. He then raised the plane body eight inches off the ground to accommodate a 45-inch propeller, increasing the prop's thrust by more than half. He also designed battery packs to hold two 75-volt lithium-ion-polymer batteries, which can juice up in midair and propel the plane at 70 miles an hour for 90 minutes on a single charge.