Winner Take All
All the nail biting, second guessing, and sheer engineering brilliance in the battle to build the better Joint Strike Fighter.
- By Evan Hadingham
- Air & Space magazine, January 2003
Heather Greasley/Lockheed Martin
(Page 2 of 5)
But other drawbacks of the Harrier approach were not so easy to overcome. The total reliance on the engine for lift in takeoff and landing meant that weight was always a crucial factor. “Boeing was the first to get the cost message,” says Flight International reporter Graham Warwick, “and the simplicity of direct lift gave them a great rationale. But like the Harrier, their plane’s STOVL performance always depended on the engine. They were always asking for more thrust from the engine than Lockheed, and always fighting weight from day one. Though every aircraft test program fights weight, for Boeing it became their most critical factor.”
Lockheed’s solution to STOVL was the lift fan, a groundbreaking design that brought with it different kinds of headaches. The concept dates to 1987, when officials from the U.S. government’s Defense Advanced Research Projects Agency asked Skunk Works engineer Paul Bevilaqua to come up with a way to improve the Harrier’s performance. In his subsequent patent, Bevilaqua sketched out his idea: installing a pair of horizontal, counter-rotating fans that would provide a pillar of air for the airplane to hover and land on, in addition to the vectored thrust from the engine. But what would drive this extra source of lift? Bevilaqua had a “Eureka!” moment when he figured out an efficient way to extract additional power from the engine. This power was transferred to the lift fan by a drive shaft that projected from the front of the engine. The drive shaft had to make a 90-degree turn to the horizontal fan via a clutch and gearbox similar, in principle, to those of an automobile.
Bevilaqua’s back-of-the-envelope calculations suggested that the drive shaft could supply a phenomenal 28,000 horsepower, enough to make the lift fan support nearly half the hovering weight of the airplane. “Several of my colleagues sat up and said ‘Holy smoke!’ ” chief engineer Rick Rezabeck recalls, “ ‘You’re going to have 28,000 shaft horsepower running through the middle of a fighter jet.’ That’s about half the level that the Navy puts through the shaft of a destroyer. So the whole question was: Would it hold itself together and could we make it mechanically and structurally sound enough so it was reliable and added up to a viable jet fighter?”
“We’re dead in the water!” For nearly a year, Boeing engineer George Bible had been experimenting with a novel composite material for the delta wing of the JSF, a project that grew out of a series of Boeing decisions to make sturdy and cost-efficient components for its new fighter.
The concept was a winner: Build the wing as a rugged, one-piece metal structure, sandwiched by two layers of composite—an upper skin and a lower skin. To make the skins more durable, Boeing would embed carbon fibers in an advanced thermoplastic resin. But no one had tried to build a wing skin 30 feet across from a single piece of thermoplastic. Now, as Bible stared at his ultrasound monitor, it was clear that the skin was riddled with bubbles.
The experiment had begun encouragingly enough. Bible’s team had spent weeks laying down sheets of carbon fiber into resin until the wing skin was 90 sheets deep but still less than an inch thick. It was then cured in a massive oven-like autoclave under high pressure, which forced the fibers to blend with the resin. Emerging from the oven, the quality of the first upper skin seemed to bode well for Boeing’s gamble. But the lower skin had a more complex shape, and patches of the material ended up sticking to the mold. One of the advantages of working with thermoplastic is that it can be “re-cooked” if defects show up in the manufacturing. Bible’s team added more release agent—similar to cooking spray—to the mold and tried again. This time the skin didn’t stick but the pressure hoses leaked, and out came the bubble-ridden mess that had distressed Bible.
Bible launched a desperate effort to make the advanced resin pay off: If he cooked the wing yet again, perhaps the bubbles would disappear. For 30 hours the team members held their breath. Gingerly, they peeled away the orange pressure bags—and Bible’s face fell. Patches were still sticking to the mold, and there were wrinkles where the resin had been compressed unevenly. Now Bible felt as if the weight of the whole JSF program was on his back. “If we don’t have a wing skin, we don’t have an airplane,” he said. “We don’t make first flight—it’s pretty much ‘game over.’ ”
As the wing-skin crew struggled, Boeing’s main design team wrestled with its own crisis. The Navy had come back with new demands for performance and weapons-carrying capability. Flight simulators revealed that, with the extra weight on its delta wing, Boeing’s airplane could no longer meet the Navy’s demands. For months, the engineers worked on various fixes. Some sparked protracted debate, notably a design for a novel tail configuration advanced by a former McDonnell Douglas engineer, Ralph Pelikan. A normal four-post fighter tail layout features a twin pair of tail surfaces. The Pelikan tail would replace this conventional layout with a striking two-post layout in which just two angled tail surfaces controlled both pitch and yaw.