Carter Aviation is a research company developing an aircraft that can take off as a helicopter and fly as an airplane. The helicopter capability gives it the ability to land without a runway. It is also more tolerant than an airplane to adverse weather.
I spoke to John Coffin, an electrical engineer and angel investor who serves on Carter Avaition’s board, about the recent prototype testing and the how the technology works.
A helicopter’s speed is limited by the fact that the tip of its blades must not exceed the speed of sound. The tip velocity is the sum of its tangential velocity around the rotor center and the helicopter’s velocity. The rotor must maintain a certain speed to provide lift. This limits any helicopter’s speed to around 150 miles per hour. Somewhat higher speeds are theoretically possible, but the asymmetry in drag between blades on the advancing and retreating side becomes a problem. Carter Aviation’s solution is to slow the rotor blade and to begin relying on wings to provide lift in this condition. Depending on design tradeoffs, this could allow speeds above 400 miles per hour with a range of 500 miles. 
Carter Aviation’s technology uses an autogyro to turn the propeller. This eliminates the need for a trail rotor. It reduces cost but removes the ability for the vehicle to hover. It instead takes off and lands at 15 to 30 miles per hour. A larger engine would provide the ability to hover but would eliminate the cost savings.
This video goes over the possibilities and shows some fun and fanciful applications starting about half way through:
Carter Aviation has a working prototype using this technology. They are continuing to work on control systems to increase ease of piloting and safety margin. There are no current regulations regarding safety for an airplane/helicopter hybrid, so aircraft vendors will have to work with regulators to create rules and standards as they commercialize this technology.
Here is some video John and his colleagues recorded of the recent testing in Texas:
This technology could make helicopters as affordable as small single-engine aircraft and make elements of the fanciful depictions in the video come true. I asked John why, if we went from the Wright brothers to the Apollo Program in 60 years, don’t we have more advanced aviation technology today. In other words, “Where’s my jetpack?” Part of it is regulatory issues and bumping up against the laws of physics. Research has gone toward improving efficiency, doubling the efficiency of large commercial jets, which improves cost but not passenger experience. I hope future developments lower cost and make personal aircraft more affordable and accessible.
