The U.S. Navy is finally accepting proposals for stealthy unmanned combat aerial system (UCAS) vehicles that can demonstrate a capability to operate from carriers.

The technology, if eventually embraced and purchased, could alter how carrier aviation is employed by extending the reach of U.S. surveillance and enabling strikes on remote locations without relying on nearby land bases.

Boeing and Northrop Grumman have been dusting off their earlier X-45 and X-47 designs for the Navy's recent request for proposals (RFP) on the UCAS-D (demonstrator) program. The RFP involves a specific set of requirements for carrier operations, including catapult launch, arrested landing and deck handling. Both manufacturers prepared more advanced vehicles for earlier demonstration projects, and both are expected to submit proposals that exceed the Navy's immediate needs with UCAS-D, according to a Pentagon official.

Northrop Grumman will offer two UCAS-D aircraft, the first slated for an initial flight in November 2008 and the second following about a year later. Northrop Grumman is teamed with its Joint Strike Fighter partner, Lockheed Martin, which is designing the leading edges of the aircraft, control surfaces, engine inlet and is providing the systems integration, says Scott Winship, Northrop Grumman's UCAS-D program manager.

Lockheed Martin officials say they have conducted significant secret work on unmanned aerial vehicle technology, despite a scarcity of public information on those projects or a public showing of demonstration flights. Its Polecat UAV demonstrator, which was unveiled at last year's Farnborough air show, crashed in December after only three flights (AW&ST; Mar. 19, p. 44). But company officials say they did manage to validate some flight-control and handling work with Polecat. Winship says work on UCAS-D with Lockheed Martin could feed into Northrop Grumman's proposal for the Air Force's upcoming bomber competition.

However, Lockheed Martin is said by an industry official to be considering a partnership with Boeing on the Air Force long-range bomber project.

Northrop Grumman's first stealthy UCAS-D demonstrator--a flying-wing design--will use a single Pratt & Whitney F100-PW-220U engine with stealthy inlets and a standard, straight exhaust handling system. The engine inlets are "deep inside" the aircraft, Winship says, adding that they are similar to the Polecat's inlets. However, the FJ44-3E Williams International engines on the Polecat were smaller, as were the inlets.

The alternative exhaust system for the second demonstrator, built by Pratt & Whitney, will be a stealthy S-shaped design incorporating new materials. The shape eliminates radar returns from the engine and cools the air before it exits the aircraft.

"For the demonstrator, we have the capability of putting in either an S-duct, which is a serpentine exhaust system, or a lighter-weight, lower-cost one that is [straight and] simply metal," Winship says. The Pratt & Whitney design is an improvement on technologies developed by Northrop Grumman and General Electric on the B-2 stealth bomber (AW&ST; Apr. 4, 2005, p. 26).

The extended deck aft of the internal exhaust system incorporates a new composite coating specifically designed to help further reduce the heat signature of the aircraft in flight, Winship adds. He would not provide details on the composition of the coatings.