Hydrogen Future?

Phantom Eye at Edwards AFB image for public release. Edwards AFB image #ED11-0159-07 Photographer Tony Landis 5/26/11 Tony Landis

We've heard a lot lately about biofuel breakthroughs, batteries and solar power as potential replacements for avgas at some point in the not-so-distant future, but what about liquid hydrogen?

The maiden flight of Boeing's Phantom Eye UAV last week proved that hydrogen could indeed serve as a replacement for traditional fuels in piston-powered airplanes. Phantom Eye uses a pair of modified 2.3-liter Ford engines, similar to those the carmaker eventually wants to bring to the open road. If hydrogen one day becomes a viable fuel source for cars, there's no question it can make the transition to general aviation airplanes as well.

Oh, but what a giant if that is.

The Phantom Eye UAV flew for less than half an hour during its debut autonomous flight, but that was just a brief test in preparation for flights that could last as long as four days and at altitudes as high as 65,000 feet. Best of all, the only byproduct of the hydrogen combustion process is water.

Phantom Eye is a demonstrator that is designed to pave the way for larger high-altitude spyplanes. It is powered by liquid hydrogen that is burned inside a pair of 150-horsepower Ford engines connected through a reduction gearbox to two four-blade propellers.

Because liquid hydrogen weighs about a third of kerosene-based jet fuel for the same amount of energy, it’s an excellent fuel source. Unfortunately, it also has about four times the volume of jet fuel and so, unlike most GA airplanes, which use the wings for storing fuel, hydrogen aircraft are usually designed with their liquid hydrogen fuel carried inside the fuselage, taking up precious space normally reserved for people and bags. The Phantom Eye UAV is a pudgy, bulbous thing because its liquid hydrogn fuel tanks must fit inside.

Liquid hydrogen production is also expensive, as is the engine conversion process. Ford has conceded that hydrogen-powered cars would cost about $400,000 to build apiece. That’s a big part of the reason carmakers have put the brakes on liquid hydrogen and hydrogen fuel cell research in favor of electric vehicles.

But that doesn’t mean hydrogen-powered cars, and by extension GA airplanes, will never come to pass. Obviously it will be some time before Cessna or Cirrus offers a four-seater that runs on hydrogen. But who knows, maybe one day the economics will catch up with the technology and enable mass production of both liquid hydrogen fuel and the engines to burn it.

Wouldn't that be something?

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