At the close of the 1920s, the world’s aircraft manufacturers — there were a lot of them then — were all pursuing the same goal: building a faster airplane. With passengers clamoring for quicker flights, every manufacturer knew that a breakthrough in speed would spur big orders from airlines and other buyers, bringing them immediate riches. They also knew that most of the technological innovations required to construct faster aircraft had already been accomplished. Engines were powerful enough, fuselages were light enough, and steering and navigation systems were precise enough. The holy grail of faster flight was almost in hand.
But not quite. Progress was being held up by one of the oldest and most mundane of all the technologies used in aircraft: the wheel. A plane’s landing gear had always hung in a fixed position beneath the fuselage or the wings. Because of its simplicity and accessibility, the rigid external gear was easy to maintain, and it was generally reliable and safe. But the bulky apparatus had a drawback: it created a lot of wind resistance. That had never been a problem when planes flew at relatively slow speeds, but as manufacturers tried to achieve higher velocity, the drag created by the wheels became a very big problem. The next leap in air speed would be possible only with a much more streamlined landing mechanism.
It was obvious to everyone that there were two possible solutions to the problem: Either improve the aerodynamics of the traditional fixed gear or figure out a way to retract the gear into the body of the plane between takeoff and landing. In theory, retractable gear was the superior approach because it would eliminate the drag altogether. In practice, however, it didn’t work very well. For one thing, it was hard to find space within planes to fit the wheels. For another, the gearing and motors required to retract the wheels were heavy and clumsy. Hydraulic systems would have been an attractive alternative, but at the time they were prone to failure. Because the cylinders could not be sealed tightly, hydraulic fluid tended to leak out, which not only increased maintenance costs but made landings riskier. Engineers could not be sure the wheels would actually descend when they were supposed to.
Despite the flaws in retractable gear, many manufacturers continued to tinker with the concept, hoping they could work out the bugs. But John Northrop, whose eponymous company was a leader in aircraft design, took the alternative route. Believing that the best solution was simply to streamline the existing gear, he invented a particularly elegant metal sheath that could be wrapped around a plane’s wheels. It didn’t eliminate wind resistance, but it reduced it enough to boost flight speeds another notch. And it gave planes a sleek, stylish look that appealed to pilots and passengers. By the mid-1930s, it appeared that Mr. Northrop had made the smart choice. His popular sheathing system seemed likely to win out over retractable gear.
Then, in 1937, a 72-year-old inventor named Niels Christensen invented the O-ring, and that changed everything. A thin, circular piece of rubber that fit into a groove on a metal fitting, the O-ring provided a leakproof but flexible seal for hydraulic systems. The tiny gasket proved to be a revolutionary innovation, making it possible to design a simple, reliable, and lightweight mechanism for retracting landing gear, and it opened the way to much faster flights. By the end of the decade, retractable gear was routinely being installed on planes. Far from being the victor in the technological contest, Mr. Northrop’s sheathing had become obsolete.