Every time some startup shows off renderings of a radical new airplane, aviation experts offer some variation of "If it looks right, it flies right." It's a polite way of saying that anything that looks underpowered or short of lift-generating aerodynamics probably is.
With that in mind, you can see why eyebrows arched when Lilium Aviation started talking about a battery-powered, fan-propelled vertical takeoff and landing commuter aircraft that looks like a football glued to a harmonica.
The "Lilium Jet," which is not, in fact, a jet, inspires a few thoughts, including: That thing looks seriously front-heavy. Can those narrow wings generate the lift needed to carry two adults 300 miles at an average speed of 180 mph? If the max takeoff weight is just 1,322 pounds, how much battery could possibly be in there?
It’s hard to see this idea getting off the ground by 2018 like Lilium says. Electric cars with thousand-pound batteries max out at 300 miles between charges---and don't have to overcome gravity. The ultralight Airbus E-Fan may be the most advanced electric aircraft yet, but it can barely muster an hour aloft at 99 mph and it doesn't take off and land vertically.
The Lilium team, which declined to comment or provide detailed specs, includes aerodynamicists and structural engineers from the Technical University of Munich and has European Space Agency support. Lilium promises "the most advanced personal aircraft the world has ever seen," one that doesn't rely on airport infrastructure, according to Gizmag, or require a commercial license. The aircraft appears advanced and it's definitely eye-catching, but it's not terribly practical.
Based on the renderings, the "jet" will fly, but not far, says Charles Eastlake, an aerodynamicist at Embry-Riddle Aeronautical University. Concepts like this often soar on hopes and dreams before slamming into hard realities, he says.
Eastlake knows what he's talking about---he has a long history with electric and vertical-lift aircraft, including the Navy’s experimental XFV-12 fighter in the 1970s. “In general, the public has a hopelessly optimistic view about how straightforward and wonderful electric vehicles are,” he says---a view that often doesn't consider the challenges of safety, weight, and cost.
Huge investments can overcome development costs and address many of those challenges, but could put the price of the final product beyond reach of prospective customers. And safety is manageable, despite the complications of vertical takeoff and horizontal flight. "High-tech active flight control systems can manage that now," he says.
Lilium says the plane will use automatic flight controls for stabilization during takeoffs and landing. Rows of ducted fans along the trailing edge of each wing will handle propulsion. More fans will extend from the nose to keep the front end up, then retract once they're no longer needed. The fuselage is designed to work as a lifting body, so the wings aren't doing all the work. "It’s uncommon, but technically possible," Eastlake says.
The big problem is power, he says. Lilium promises 435 horsepower from the ducted fans. That's plenty to achieve flight, but "a hell of a lot of power to draw out of batteries," Eastlake says. “I have grave doubts that you can do that within the weight limit.” Even if it's possible, the demands of vertical takeoffs and landings likely won't leave much juice for going anywhere. "You’re not going to be able to get around the weight demands of a battery for a long time, nor the cost of that battery,” Eastlake says.
Sorry, folks, but your wait for a practical private electric plane isn't over quite yet.
