The US Navy's trade studies on whether its Boeing F/A-18 Hornet replacement, the F/A-XX, should be piloted have concluded that unmanned air vehicles could operate for 20 times longer than manned systems in some circumstances.

The studies' details were revealed at the Association for Unmanned Vehicle Systems International North America 2008 symposium in San Diego, California, and follow January's publication of the USN's Naval Aviation Vision document, which said: "With an [initial operating capability] of 2025, [the navy-unmanned combat air system] is envisioned to be the strike fighter recapitalisation platform [F/A-XX]".

Studying operational capabilities, the USN examined an aircraft carrier group operating at an air tanker "safety line" of 925km (500nm) from the shore.

Calculating how long manned and unmanned systems could loiter at 925km from the fleet, 1,380km and 1,850km, a tailed manned aircraft could only last for 30min at the middle distance, while a tail-less UAV could stay for 20.5h. At 1,850km manned vehicles had zero loiter time.

Speaking at the AUVSI event, US Naval Air Systems Command programme executive officer Gary Kessler said: "Manned endurance estimates [are] conservatively high, while [the] unmanned endurance estimate is conservatively low."

The USN trades examined two broad manned and unmanned configurations: one with a new fuselage, wing and tail and a tail-less Northrop Grumman X-47B unmanned combat air system demonstrator-like vehicle.

Assuming both had the same 460kt (850km/h) cruise speed and unrefuelled ranges of 3,330km for a vehicle with a tail and 5,550km for the tail-less version, pilot performance was the manned system's limitation, giving a maximum mission endurance of 10h, while the UAV, with refuelling, could achieve 50h.


Source: Flight International