In 1918, long before George Jetson commuted to Spacely Space Sprockets, the U.S. Patent Office issued Felix Longobardi the first patent for a vehicle capable of both driving on roads and flying through the air. But given all the impractical prototypes built since Longobardi's original whimsy, history suggests that any vehicle design combining these two modes of transport will be a commercial failure: aero-auto hybrids always seem to result in a compromise that serves both functions poorly.
Now a group of MIT alums believe that they are on their way toward overcoming this problem. Founded in 2006 and called Terrafugia, their startup, based in Woburn, MA, recently produced the first automated folding wing for a light sport aircraft. (A light sport aircraft is a type of airplane deemed by the Federal Aviation Administration to be easier to fly and hence more accessible than regular private planes.) The wing, however, is just the first step toward an aero-auto hybrid that the company plans to call the Transition.
This summer, the group demonstrated its folding wing at the annual AirVenture aviation festival in Oshkosh, WI. With more than 650,000 attendees, the festival is the most important event in experimental-aircraft aviation.
"Going into this, we knew our two biggest design challenges to make it practical would be the wings and the power train," says Anna Mracek Dietrich, an engineer at Terrafugia and the company's chief operating officer. "By validating the durability of the wing's construction and engineering, we've checked one major design challenge off of the list, and now our focus is on the second."
Previous prototypes of road-drivable aircraft have featured manually folding or detachable wings. But to allow for a seamless and quick transformation from plane to car and back, the Terrafugia team has devised a system that allows the pilot to enfold or extend the wings by pushing a button in the cockpit. Dietrich says that at Oshkosh, the researchers opened and closed the wings more than 500 times--the equivalent of three to five years of typical use--and that they're more than pleased with the wings' durability.
The wing features off-the-shelf electric actuators, but Dietrich says that the team had to design from scratch the mechanical linkages between the actuators and the rest of the craft. The group also uses dual electromagnetic locks to hold the wings tightly to the fuselage when they're enfolded.
"We're building the rest of the first vehicle now," Dietrich says. "Our schedule calls for us to start flight testing by the end of 2008, and so far we're on track for that."
The technical challenge now before the team is to build a power train that uses one engine both in the air and on the ground and is capable of running on a tank of super unleaded gasoline--the kind that can be bought at any gas station. To make the transition between engine uses smooth, the team is devising a mechanism to transfer power from the propeller to the wheels and back as needed. The difficulty here, Dietrich says, is that the system has to be as simple, reliable, and lightweight as possible. (For the team, the weight of the vehicle is a constant concern, not only because the vehicle has to be relatively light in order to fly, but also because FAA regulations require it to be less than 1,320 pounds.)