The Ultimate Fighter?
With the F-35, Lockheed Martin takes a turn trying to make one combat plane that can do everything.
- By Richard Whittle
- Air & Space magazine, February 2012
Andy Wolfe/Lockheed Martin
(Page 2 of 5)
In the early 1990s, though, after years of careful study, Pentagon leaders decided to try a joint program once more, but with a twist. The result, after a competition that lasted seven years and left Lockheed the only U.S. defense contractor still making fighters, is essentially fraternal triplets—three aircraft that look much the same and have enough common or similar parts and equipment to be built on the same production line and share the designation “F-35,” yet differ enough to suit the varying needs of the Air Force, Navy, Marines, and allies.
Creating the ultimate multi-mission aircraft is not the only audacious goal of the F-35 program. Lockheed Martin and engine designer Pratt & Whitney are also introducing a propulsion system that gives the B model the ability to take off within far less than the 800-foot length of an amphibious assault ship’s flight deck and hover above it before landing vertically—the feature the Marine Corps most wants. Dozens of schemes to make aircraft capable of short takeoff and vertical landing have been tried and failed; they populate a colorful STOVL diagram, “The Wheel of Misfortune” (vstol.org/wheel.htm). The Harrier, for instance, uses four thrust- vectoring nozzles to aim its jet engine’s exhaust down for vertical flight. The F-35B relies on a new and ingenious mechanism called a lift fan, patented by Lockheed engineer Paul Belivaqua, that offers major advantages.
Contained in an oil-drum-like cavity about 53 inches in diameter and located behind the cockpit, the lift fan consists of two counter-rotating blades connected to a right-angle gearbox and a clutch, which connects through a driveshaft to the F-35’s 40,000-pound-thrust Pratt & Whitney F135 engine. When the pilot, flying at less than 130 mph, pushes a button labeled HOOK/STOVL—the same button drops the F-35C’s tailhook or the F-35A’s emergency landing hook—the airplane transforms itself. (Watch it on YouTube: As it prepares to lift off or land, the F-35B looks like the 1980s transformer toys that shifted their parts to change identities.) Doors in the fuselage above and below the lift fan open simultaneously. The engine’s nozzle swivels to direct its exhaust down. The clutch engages the driveshaft, which spins the fan’s blades. Now the F-35B can hover or land on two columns of air, one hot, one cold (by thermodynamic standards), and each moving fast enough to provide about 18,000 pounds of lift. Two far smaller streams of exhaust funnel down ducts to a small nozzle under each wing called a roll post, providing roughly 2,000 more pounds of lift apiece plus side-to-side balance and control. Unlike the Harrier, whose pilot has to manipulate the aircraft’s stick, throttle, and controls to swivel the nozzles by hand, the F-35B has flight control computers to do all the work of balancing the airplane atop its thrust.
Part of the lift fan’s genius is that it allowed designers to put the F-35’s engine at its rear, the best placement in a non-STOVL aircraft as well, says Paul Park, who left Lockheed last year after three decades but previously led the team of engineers who determined the outer shape, internal arrangement, and other major aspects of the F-35. Having two equally powerful columns of vertical thrust is yet another big advantage in a STOVL plane, Park adds, for in designing such an aircraft, “the number-one challenge is not just the lift, it’s getting the vertical lift balanced around the weight.” That’s why the Harrier’s engine is in the center of the fuselage, he says. The cool air coming from the F-35B’s lift fan also “shields people around the airplane from the hot exhaust in the back,” Park says, and helps prevent the engine from ingesting its hot exhaust, which could cause it to stall.
The F-35B has a smaller wing because weight is an overriding issue for STOVL aircraft, which during landing have to produce at least a pound of thrust for each pound they weigh. The B variant could not afford the extra pounds of a wing-fold mechanism; consequently, its wingspan could be no greater than 35 feet, the maximum width that an amphibious assault ship elevator can accommodate.
Like its predecessors on the Wheel of Misfortune, the F-35 STOVL variant has not been an easy airplane to design. It has been responsible for much of the program’s well-publicized delays, and in January 2011 caused then-defense secretary Robert Gates to put the F-35B on “probation”—an unofficial but damning description—after design problems were found in a bulkhead within its wing and in the propulsion system. By late 2011, after Gates had left office, Lockheed had solved the problems, and last month Secretary Leon Panetta decreed an end to the F-35B’s probationary status. But redemption had come last October, during the variant’s first sea trials, when test pilots performed 72 vertical landings on the USS Wasp amphibious assault ship and took off again from a 400-foot length of the ship’s deck. Among other things, those tests showed that crews could work around the F-35B despite the heat of its aft exhaust. Nor did the exhaust damage the flight deck, as critics had predicted, in part because after landing, the airplane’s engine automatically goes to idle and the nozzle swivels back up.
Given such progress, the Marine Corps commandant, General James Amos, said he was sure his service’s long-awaited STOVL fighter was over its problems. So important to the Marine Corps is the F-35B that Amos had promised the House Armed Services Committee last March that he would be “personally involved with the program and closely supervising it.”
The Marines badly want the F-35B “because of the way we fight,” says John R. “Jack” Dailey, who retired in 1992 as a four-star general after serving as assistant commandant of the Marine Corps. Trained and equipped to invade hostile shores and travel light and fast on land, “the Marine Corps depends on [strike fighters] as our heavy artillery,” explains Dailey, a former fighter pilot who since 2000 has been director of the National Air and Space Museum. The corps wants strike fighters it can base not only on the amphibious assault ships that carry Marines around the globe, but also at austere sites close to the fighting, ideally making it possible to get ground troops close air support within 30 minutes of a call for help. That’s why the Marines bought the Harrier, stuck with it despite a horrific crash rate early in its history, then passed up the chance to buy far more capable conventional fighters in the 1990s while awaiting the F-35B. Dailey is so eager to see the corps get it he bought a vanity license plate that reads “F35STV,” the closest he could come in the space allowed to “F-35 STOVL.”