Bell's Trisonic X-2

Flight Journal, Aug 2000 by Miller, Jay

A lean, mean, flying machine

For many years, a mysterious, obelisk-like object sat on my desk. Triangular in cross-section and about 12 inches high, the part represented the state of the art in aerospace engineering during the early 1950s. Only the most knowledgeable could identify the aircraft it came from, and even fewer knew anything about the aircraft itself. blade of K-monel alloy and covered with blistered white paint, the part was in fact a section that had been laboriously hand-sawn out of the leading edge of the world's first Mach 3 aircraft-the Bell Aircraft Corp. X-2, serial no. 46-674.

Highly temperamental, the X-2 new faster and higher thao anything of its day. Born during late 1944, its sweptwing configuration represented Bell's hope for a follow-up to the then unproven, bullet-shaped X-1. Known at Bell as "Design 371)," it was proposed to the Air Force as an X-1 successor with nearly twice its performance.

During the mid-1940s, little was known about the attributes and pitfalls of sweptwing aerodynamics. Predictably, the Air Force initially rejected Bell's proposal, and that forced the company to move on to a second-generation X-1 family (X-1A, X-1B and X-1D) that used the same straight wing as was used on the first generation. During October 1945, however, George Ray, Bell's preliminary design department head, formally initiated work on a totally new X-1 successor with a wing that had a 40-degree leading-edge sweep.

On December 14, 1945, the Air Force and Bell, with the National Advisory Committee for Aeronautics (NACA) in attendance, signed a contract calling for the development, construction and initial flight-testing of two XS-2 sweptwing research aircraft (the "S" for "supersonic" had been dropped from its designation by 1947)-Air Force serial numbers 46-674 and 46-675.

The X-2 was conceived and built to explore flight at speeds and altitudes far beyond anything achievable with the first generation-and, in fact, second-generation-X-1s. At the time, the swept wing was an unknown quantity. Later, reference data based on the ingenious research of the U.S.'s Robert Jones and the seminal studies of Germany's Adolph Busemann provided Bell and the Air Force with a convincing argument that a swept wing could significantly enhance the performance of a third-generation high-speed research aircraft.

"Project MX-743," as the X-2 was officially called at Wright Field, formally got under way at Bell's Wheatfield, New York, plant on September 11, 1945. Stanley Smith (who was soon appointed chief project engineer) called together Bell engineers Jack Strickler, Paul Emmons, Jack Woolams, Harold Hawkins, Charles Fay and Robert Stanley to initiate discussions that would soon lead to the production of the fastest, piloted, sweptwing aircraft ever built. In Stanley's office, he and his team agreed to submit a preliminary design proposal to Wright Field no later than October 1 that year.

Some five years later, on November 11, 1950, the second X-2 airframe, 46-675 (the first completed), minus its rocket engine, was rolled out through the Wheatfield plant's doors and prepared for extensive static ground tests. This took no less than eight months, inadvertently allowing time for the completion of modifications to the EB-SOA (SIN 46011) carrier aircraft-also at Bell.

During July 1951, mated to the EB-50A mother ship, the X-2 took to the air over Wheatfield on the first of several trial hops. These were completed during early 1952 and followed by a crosscountry delivery flight to Edwards AFB, California, on April 22. After ground checks had been completed, there were two more captive flights to verify compatibility. Finally, on June 27, with Bell test pilot Jean "Skip" Ziegler at the controls, 46-675 was launched on its first glide flight. Although Ziegler assessed the X-2's general control and handling characteristics as "adequate," its landing qualities were somewhat less than ideal. On touchdown, the nose gear collapsed and caused enough damage to warrant a two-month delay for repairs.

On October 10, again with Ziegler at the controls, a second glide flight was completed; this time, the landing went without incident, but as time would tell, this was purely serendipitous.

Two days after Ziegler's second glide flight, Air Force test pilot Capt. Frank Everest took over the X-2's controls. His first flight was successful, though there was considerable concern over the right balancing skid's failure to extend just prior to landing. (The main gear-skid area had been increased by 300 percent, and two small balancing skids had been installed at mid wingspan in an attempt to cure the landing-instability problem.) The touchdown jarred the stuck skid into the down-and-locked position, and the rest of the rollout went without incident.

Six days later, the X-2 and the EB-50A were mated and flown back to New York so that the first flightworthy engine could be installed. They hoped to start powered flight trials very soon; unfortunately, during the Curtiss-Wright XLR2S two-chamber rocket engine's development, significant problems had surfaced, partly because the engine was unquestionably the most advanced man-rated rocket-propulsion system in the world. The XLR25 was throttleable, it used circulation-type (regenerative) liquid cooling for each of its two thrust chambers, and it had a complex turbo-pump system that was the lightest and most powerful of its kind.