Flight-testing of the vertical-landing version of the F-35 Lightning II is on course for May following Lockheed Martin's public unveiling of the first production-standard F-35B on Tuesday at its plant in Fort Worth, Texas.
Engine ground-testing of the first production F-35B short takeoff/vertical landing (STOVL) Lightning II will begin in March, using an aircraft designated BF-1, said Bill Gostic, vice president of Pratt & Whitney's (P&W's) F135 engine program.
In the interim, two F135 STOVL engines — one at a P&W facility in Florida and the other at the U.S. Air Force's Arnold Engineering Development Center in Tullahoma, Tenn. — will complete 600 to 700 hours of ground-running to complete qualification testing of the F-35B's STOVL propulsion system, Gostic said.
The F135 is the engine that powered the Concept Development Aircraft with which Lockheed Martin won the Pentagon's Joint Strike Fighter competition to design an aircraft that could be developed in three different versions for the U.S. Air Force, the Marine Corps and the Navy.
Developed from the F119 that powers the F-22 Raptor, the F135 also is the engine that has powered the conventional-takeoff-and-landing (CTOL) F-35A since it became the first F-35 variant to fly on Dec. 15, 2006.
40,000 pounds of thrust
Producing 40,000 pounds of thrust with afterburner — officially known as "maximum augmented thrust" — for conventional takeoff and maneuvering, the F135 also can develop 40,000 pounds of thrust without afterburner for STOVL takeoffs and landings. It does so by running hotter under the command of P&W-developed engine control software.
The F135 is the most powerful fighter jet engine in the world, according to P&W.
In April, the first F-35B is due to go to the "hover pit" that Lockheed Martin has built at its Fort Worth plant, said Gostic. A large, concrete-lined hole in the ground covered by a steel grating, the hover pit will allow Lockheed Martin to test the F-35B's STOVL propulsion system at full power while the aircraft is on the ground, safely tied down to the steel grating.
The F-35B is scheduled to make its first flight, a CTOL flight, on May 23, 2008.
"During the summer and into the fall, the flight tests transition from CTOL to semi-STOVL (flights), and ultimately to vertical landings," said Gostic. Later, flight-testing will move from Lockheed Martin's facility, probably to the Navy and Marine Corps test center at Naval Air Station Patuxent River, Md.
While the F-35B is designed to require a short takeoff run when carrying a full load of fuel and munitions, when lightly loaded or empty it will be quite capable of taking off vertically, Gostic confirmed.
The U.S. Marine Corps will fly the F-35B, while the Air Force will operate the F-35A. The U.S. Navy will fly the F-35C, a version with a strengthened landing gear and a tailhook so it can be operated from aircraft carriers.
In addition, the Royal Air Force, the Royal Navy and the Italian Air Force and Italian Navy will operate the STOVL F-35B. The Dutch Air Force also is a prospective customer for the F-35.
Its selection by all three major arms of the U.S. forces is not all that makes the super-high-tech F-35 unique on the military scene: The aircraft has been designed to allow an unprecedented degree of commonality and interchangeability of parts among the three versions.
That includes its propulsion system. Not only will all the F135 engines powering each of the three versions of the F-35 be identical, they also will be completely interchangeable among different forces' aircraft. So the F135 powering a U.S. Air Force F-35A could, say, be interchanged successfully with the F135 powering an Italian Air Force F-35B.
There's more. The Pentagon has required that two engine types, Pratt & Whitney's F135 and the General Electric/Rolls-Royce F136, be developed for the F-35. Uniquely, however, it also has mandated that the two engines have an identical design specification, so that all F135s and F136s will be interchangeable in all F-35s, said Gostic.
"The two engines will also operate with common components," he said.
Pratt & Whitney's F135 has about a five-year development lead over the F136, so it powers the first F-35As, which will be procured by the U.S. Air Force in fiscal year 2009.
It also will power the first F-35Bs for the Marine Corps (for FY2010 procurement) and the first F-35Cs for the U.S. Navy (in procurement/delivery year 4). The UK and the Italian forces are also due to buy their first F-35Bs in year 3 or 4, so their first aircraft will be powered by F135s too.
CTOL F-35A flight-test schedule
Flight-testing of the F135-powered CTOL F-35A will continue while the F-35B's F135 STOVL propulsion system is completing its qualification ground-testing. F-35A flight testing has already confirmed that "the full throttle range, whether dry or augmented with afterburner," is available, said Gostic.
The F-35A flight-test schedule calls for two more flights this year, with near-term testing finding out "how the aircraft handles in formation with a tanker" during aerial refueling, he said.
This is to prepare for ferrying the first production F-35A — which is designated AA-1 — to Edwards Air Force Base, Calif., in the first quarter of 2008. At Edwards AFB, flight-testing will "expand the flight envelope," establishing speed, altitude and systems flight parameters for the F-35A, said Gostic.