F-35 Lightning II News

F-35B exceeds STOVL thrust requirement

April 24, 2009 (by Eric L. Palmer) - The F-35B Lightning II short takeoff/vertical landing (STOVL) variant has demonstrated during testing that it produces excess vertical thrust – more than required to carry out its missions.

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F-35B from last years tests.

The tests, conducted on a specially instrumented “hover pit,” also validated the performance of aircraft software, controls, thermal management, STOVL-system hardware and other systems.

“The performance level measured was absolutely exceptional,” said J.D. McFarlan, Lockheed Martin F-35 Air Vehicle lead. “We demonstrated 41,100 pounds of vertical thrust against our requirement of 40,550 pounds.This means we will deliver excellent margin for the vertical landing and short takeoff performance we’ve committed to our STOVL customers,” he said. Those customers include the U.S. Marine Corps, the United Kingdom’s Royal Navy and Royal Air Force, and the Italian Navy and Air Force.

The F-35B is powered by a single Pratt & Whitney F135 engine driving a Rolls-Royce lift fan. The F135 is the most powerful engine ever flown in a jet fighter.

During hover-pit testing, the aircraft is anchored to a metal grate 14 feet above a sloped concrete floor, separating the jet from ground effect and enabling it to simulate free-air flight. Sensors measure thrust and the aircraft’s response to pilot inputs. The testing also demonstrates control of the doors associated with the STOVL propulsion system: engine auxiliary inlet, fan inlet, fan exit, roll posts, and doors that open to enable the Rolls-Royce three-bearing swivel duct to articulate and vector engine thrust.

The testing demonstrates functional operation of all systems required for vertical flight, and measures the installed forces and moments on the aircraft during STOVL operations.The hover-pit tests are the final series of ground tests before airborne STOVL testing begins.

“We've demonstrated critical performance such as inlet pressure recovery, pitching moment, rolling and yawing moment, effective vector angles of the exhaust, and control-input response time,” said Doug Pearson, vice president of the F-35 Integrated Test Force. “Each of these measurements correlates extremely well with our computer models. The outstanding STOVL performance gives us plenty of confidence to begin in-flight transitions to STOVL-mode flight and ultimately our first vertical landing at the Naval Air Station Patuxent River, Md., this summer.”

There are still some concerns for the U.S. Navy on how amphibious vessels will handle the new aircraft. According to quotes in a recent Inside the Navy story, “At the end of the hover pit cycle, we’re going to plate over a portion of it to start getting some of the downwash data on the hover pit. We’ll also collect thermal data at the same time to see if there should be any concern relative to what temperature environment I might induce on the decks, on ships, on asphalt, et cetera, to see if there’s a thermal issue relative to steel plate heating on the amphibs.”

"Navy officials have expressed concern that the powerful, high-temperature downwash caused by the STOVL’s lift fan could damage ships’ antennas and radars stationed in the rear, as the aircraft is more powerful than legacy AV-8B Harriers."

The U.S. Marine Corps is scheduled for initial operating capability (IOC) with the F-35B in 2012. Currently there is only two percent of the F-35 flight testing that is complete. The service intends to re-capitalize their whole fighter force with F-35B's.