Replacements sought for Boeing's reliable, versatile C-17s.

The prospect that the Air Force might not order additional C-17 cargo jets due to federal budget pressures raises a big question: If not the C-17 then what?

While the current fleet of 145 cargo jets is expected to remain in service for at least two more decades (with 35 additional planes already on order), it could take more than a decade to design, build and deliver any replacement.

That means it's not too early to starting exploring what a next-generation cargo transport would look like.

"All three prime contractors have ideas for airplanes that could carry a C-17 payload," said Tom Bennett, senior analyst of future concepts for the Air Force's Air Mobility Command.

"It's not faerie dust or anything. We're talking about jet-powered, fixed-wing aircraft. We think they could be ready to test in five or six years."

Any replacement would have a lot to live up to. First delivered in 1993, Boeing Co.'s C-17 is a reliable and versatile plane that has been used heavily in airlifting everything from aid supplies to war machines.

With its 171,000-pound payload, it can carry an Abrams tank, two helicopters, Humvees and trucks, or heavy artillery. It flies at a cruising speed of 520 miles per hour and has an unlimited range because of its ability to be refueled in the air. It also has the ability to take off and land on dirt fields, roads or runways as short as 3,000 feet.

But in looking to help pay for the war in Iraq, the Pentagon wants to make $15 billion in cuts and many previously sacrosanct programs are in the mix. Other programs up for review include the Joint Strike Fighter, the Pentagon's next generation, all-purpose fighter.

Though it's still early in the process, all three major defense contractors--Los Angeles-based Northrop Grumman Corp., Lockheed Martin Corp. and Boeing--are working on a replacement plane.

All the plans at this point are mostly on the drawing board, and it's unclear whether any of the concepts would even be affordable. "We're just now getting the artwork on these," said John Pike, a defense analyst who runs the non-profit think tank GlobalSecurity.org in Alexandria, Va.

Good plane

Boeing, in a joint contract with the National Aeronautics and Space Administration, is developing something called the Blended Wing Body plane.

In its current conceptualization, the plane would have three jet engines with a flying wing design similar to the B-2 Stealth Bomber, instead of the conventional tube-and-wings layout. The thick wings, which would span 280 feet (85 feet wider than a Boeing 747), would be divided into 10 cargo bays running front to back.

The space age craft is attractive because the aerodynamics of the flying wing gives it 56 percent more lift than conventional planes and speeds of up to 560 mph. The use of composite materials would enable it to carry its 231,000-pound payload 7,000 miles non-stop using 20 percent less fuel.

Because the entire body of the plane is a wing, it would handle more like a jet fighter than a cargo plane. That would require major engineering advances, according to GlobalSecurity.org., a defense policy think tank based in Alexandria, Va.

There are no estimates on the cost of developing the plane, but NASA is currently test-flying scale sized models. There is also the possibility of a commercial version that would carry 450 passengers.

Meanwhile, Lockkheed is developing a "Global Range Aircraft" concept with a radical wing layout that would provide extra lift. The craft would have a "box" wing that harkens back to the early days of flight.

Extra large rear wings, mounted high above the tail, sweep forward and are connected by vertical segments to the front wings, which are mounted under the fuselage, according to the Air Force and Global Security.

The plane would make extensive use of interchangeable components, so that a single plane could function as a cargo hauler or be reconfigured as an aerial refueler. Unlike the C-17, however, it could not use short, unpaved runways. Rather, it would have similar performance characteristics of the Air Force's 700 smaller C-141 transport and KC-135 tanker planes. Lockheed hardly has more than sketches and has no cost or schedule estimates.

Information about Northrop's plans was not available.

Of course, there's the option of not replacing the C-17s. The transformation of the military to a lighter, faster force interconnected by cutting-edge communications technology could actually save the program.

The Pentagon's Mobility Requirements Study, being conducted as part of the Defense Department's top-to-bottom needs assessment, is due out in a few months. The study is examining the military's new airlift requirements.

The transformed military could use a combination of big, long-distance aircraft to move gear into a region, and smaller cargo aircraft to move inside a region. The C-17 is the only plane that can serve both of those roles, and currently none of the military cargo plane concepts exactly replicates those abilities.

"It's in a class by itself," said Richard Aboulafia, senior aerospace analyst at the Teal Group Corp. in Fairfax, Va.