What Could Possibly Go Wrong: Flying Hummers

Last April, Darpa proposed a novel solution to the problem of IED-strewn roads and otherwise impassable landscapes in Afghanistan and elsewhere: fly over them.

The Pentagon agency’s $50-million-plus exploratory program for the Transformer (TX) calls for a “robust ground vehicle” that can quickly transform into a vertical-takeoff-and-landing (VTOL) aircraft with a 1,000-pound payload capacity and a flying range of nearly 300 miles. Darpa has a daunting list of specs for any would-be contractors: It must be able to take on small-arms fire and meet federal standards for safety and crash protection. It’s got to have four-wheel drive and be able to reach an altitude of 10,000 feet. Oh, and should the driver become incapacitated, it has to be able to fly itself.

It’s a lot to ask. The fundamental challenge of making cars fly is combining two distinct sets of optimal design characteristics into one package without sacrificing too much performance on either end. The very phrase “roadable air vehicle” sounds like a sigh of compromise. The military considered developing a hybrid in the 1950s with the ungainly Piasecki PA-59K, or “AirGeep,” but then abandoned it because of cutbacks in military research. Advances in materials science and propulsion technology have lessened the trade-offs, but many challenges remain.

First, weight. NASA engineer Mark Moore says that, as a rule, conventional aircraft grow roughly three pounds heavier for every extra pound of payload they’re supposed to carry, whereas, “VTOL aircraft grow about five to six pounds heavier for every extra pound of weight.” Now picture a VTOL aircraft that happens to be armored and packing four soldiers and their equipment. The required compact, rotorless propulsion system means, Moore says, a “hurricane-speed flow field” of rocks and debris upon takeoff. So much for stealth. And all of this likely would do little to increase security. Transformers may be able to leap over IEDs, but insurgents can simply aim RPGs at the wings, which on one proposed Transformer design are laden with fuel tanks.

Enemy combatants in Iraq have brought down Blackhawk helicopters, which are faster and more maneuverable, with small-arms fire. As for the autopilot function—nearly half of the finalists in Darpa’s 2007 Urban Challenge for autonomous ground vehicles were unable to execute elemental driving tasks. There is little reason to believe that autopiloting an inherently unstable vehicle through a battle space under hostile conditions will work better.

How We Can Do Better

Stay focused on making actual Hummers tougher and more versatile. “We still don’t have a fighting vehicle capable of negotiating rough terrain,” says retired Major General Robert Scales, a military analyst.

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