Winner Take All

All the nail biting, second guessing, and sheer engineering brilliance in the battle to build the better Joint Strike Fighter.

Air & Space Magazine | Subscribe

(Continued from page 3)

By now brimming with confidence in the demonstrator’s handling qualities, O’Donoghue brought the X-32B gently down over the hover pit, a cavity in the runway designed to keep the exhaust from blowing back into the engine and minimize ground effect. The airplane coasted down to 40 feet, then O’Donoghue abruptly felt the bottom drop out underneath him. He jammed the throttle full forward and a red engine light flicked on, the automated voice he had hoped never to hear barking: “Warning, Warning, Engine, Engine.” Red lights were flashing in the control room too, and flight controller Howard Gofus tensely ordered O’Donoghue to abort the landing. But O’Donoghue was already at full power, and there was nothing more he could do. Bracing himself for a crash, he radioed, “I’m coming down!”

Then, with only seconds to spare, he got a reprieve. With around 20 feet to go, the engine recovered and the cockpit warnings ceased. The X-32B slowed its descent until it made a gentle touchdown at almost precisely its targeted landing speed. For the onlookers who rushed forward to congratulate O’Donoghue, it appeared to be a normal landing. Only Gofus and his team in the tower knew about the close shave, and they quickly figured out what the problem was. The wind that normally helped clear exhaust from the hover pit had momentarily died, and as the X-32B came down, its own exhaust gases had risen up from the walls of the pit and been sucked into the engine.

Confident in the diagnosis, Gofus went ahead with a second landing over a normal runway surface. O’Donoghue touched down without incident.

One week later, pilot Paul Stone of Britain’s Royal Navy took O’Donoghue’s place for another test: the X-32B’s first vertical takeoff. The flight plan called for a vertical landing followed immediately by a vertical takeoff. As Stone brought the airplane down gently, with the tires almost touching the runway, it wobbled momentarily, then a bright flash and a loud pop went off underneath the fuselage. Once again, hot exhaust had been sucked into the engine, and this time had caused a split-second engine “pop stall.”

The media were quick to seize on the episode, but O’Donoghue was unruffled. “All of us who worked with Harriers knew what that pop stall was and it was no big deal,” he says. “In fact, our simulations had predicted exactly what happened: If the plane tilted more than four degrees near the ground, the jet screen would no longer protect the engine and a stall would likely follow. We had already fixed the problem in our final design proposal with a bigger jet screen.”

As far as the Boeing team was concerned, the pop stall had been a nonevent, but the members knew it hadn’t looked good. Perception is everything, and the episode was a reminder of other inherent drawbacks that direct lift had and Lockheed’s fan didn’t. As with the Harrier, the 1,350-degree heat of the Boeing airplane’s exhaust gases would pose a threat to the surface of carrier decks, if not to the life and limb of Navy crews (the downdraft from Lockheed’s lift fan was some 1,000 degrees cooler). Since Lockheed’s fan boosted engine thrust, its powerplant could run at lower temperature and with less strain, and these differences would translate into longer life. Most significant, assuming its reliability could be ensured, the lift fan would offer an extra margin of power and safety in a hover. In the end, that ensured Lockheed’s victory.

The record of the flight tests offers an important clue to why Lockheed won. At the program’s conclusion, the X-35B had performed 38 STOVL flights, most at Edwards Air Force Base at an altitude of 2,500 feet. In contrast, Boeing’s X-32B had flown 57 STOVL flights, but these were all at the sea-level Patuxent River Naval Air Station. Despite the altitude advantage, the Boeing airplane flew with its inlet cowl and undercarriage doors removed to increase the thrust-to-weight margin. (“I would have left my underwear home that day,” says O’Donoghue.)

“In my mind, it was physics versus technology,” says Lockheed test pilot Paul Smith. “In the area of STOVL performance, Boeing just didn’t have the physics behind them—they didn’t have the thrust of the engine up and the weight of the airplane down, while we had a technology that made efficient use of engine power, but it was so technologically advanced that it was touch-and-go whether it would work. A month before we were supposed to demonstrate STOVL, we were still having problems with the lift fan that we thought we might not be able to fix. Boeing had done so many cool things, and were ahead of us on schedule so much. It was like the tortoise and the hare.”

On October 26, 2001, several hundred members of the Lockheed Martin team gathered in the X-35 hangar at Palmdale. On a big-screen TV, the Pentagon announced the company’s victory, causing the team to erupt in deafening cheers. “We did as much as we needed to win this thing,” an ecstatic Rezabeck told NOVA. “We were very comfortably—anxiously and nervously—confident!” In a contest in which both sides had displayed astonishing inventiveness, Lockheed had taken the bigger risk. And if the reliability of Bevilaqua’s lift fan has yet to be proven, it seemed reliable enough to win Lockheed the biggest military contract of the new century.

Comment on this Story

comments powered by Disqus