Elon Musk has repeatedly stated that he has plans for a supersonic, VTOL (vertical take off and landing) electric plane. He mentioned it in a cameo in Ironman 2. So here is what is known about the airplane.
Electric plane engines will fly more efficiently at high altitudes because the atmosphere is thinner and there is less wind resistance. Jet engines don’t fly more efficiently at higher altitudes because they require air intake to combust the fuel. The aperture of the engine is fixed and it is designed to get the right amount of air through at sea level and it’s highest cruising altitude. It also becomes less efficient because of super sonic combustion. You have to slow down the air to combust it. In 2001, Helios, an electric plane made by NASA, set an altitude record of 96,863 feet.
Elon states that you could fly transcontinental range (LA to New York). It would require batteries with 400 Watt Hours per kilogram, and 70–80% of the craft would be battery cells.
It will not look like other planes
Elon has stated the aircraft will not have tails, rudder, or elevators. “You don’t need the rear control services if you gimbal the motor” That means no wings on the back of the plane. To gimbal the motor and the electric fan means to tilt it in order to navigate. Rockets gimbal the motor to control their trajectory (illustrated in the picture). It may likely to look more like a rocket than a plane.
Elon states the planes can be designed to have no sonic boom and no more noise than a conventional aircraft. The VTOL will also reduce the need for long runways at airports.
Currently Tesla batteries are about 250 Watt-Hour per kilogram. Battery energy to weight ratio typically improves at 5–8% per year . At this rate 400 Wh/kg will be achieved in about 5 to 10 years.
Elon says he has no plans to pursue this because he has too much on his plate. However, this is an important step in the move to a sustainable energy future. It would make sense for Space X to build something like this since it is similar to the design of the reusable rockets. Obviously Tesla could supply the batteries.