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Rare aircraft, extraordinary people
and remarkable stories

Bell's Trisonic X-2
A lean, mean, flying machine
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by Jay Miller
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x2_1.jpg High over Edwards AFB, the Bell X-2 begins its descent to landing. A wing-mounted camera documents the subsonic flow of wing tufting for later review (USAF via Jay Miller collection).
x2_cap or 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. Made 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 flew faster and higher than 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 37D," 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.

x2_2.jpg An early model is subjected to wind-tunnel landing-configuration tests at the NACA's Langley, Virginia, facility (NASA via Jay Miller collection).

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-50A (S/N 46-011) 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 cross-country 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.

x2_3.jpg Left: at Edwards AFB, hydraulic lifts were installed in the concrete ramp specifically to raise the Boeing EB-50D carrier aircraft. The lifts provided the necessary clearance for the X-2's tail during the bomb-bay mounting procedure (USAF via Jay Miller collection).

Right: the Boeing EB-50D and the Bell X-2. The pilot boarded the X-2 via a cockpit platform in the bomb bay (USAF via Jay Miller collection).

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 XLR25 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.

Not surprisingly, the XLR25 engine's numerous technological advances did not come without penalty; in fact, the problems were so complex and, at times, so exasperating that serious thought was given to program cancellation. Delays in Curtiss-Wright's ability to deliver a flightworthy engine led eventually to the X-2's falling no less than three years behind schedule. The demise of the engine would almost certainly have led to the termination of the entire project, and in light of the emergent X-15, many in the Air Force and the NACA considered this prospect untenable.

x2_4.jpg Above: The two X-2s' initial glide trials were done without an engine. They had a serious landing-instability problem that took several years to solve (Bell via Jay Miller collection).

In early 1953, one flightworthy engine at last reached Bell. Following its installation in 46-675, it was statically ground tested with generally favorable results. With the engine in place, mated flights over Lake Ontario (just a few minutes by air from Wheatfield) were conducted in March 1953.

On May 12, during a routine propellant-system emergency-dump test while attached to the mother ship, 46-675 exploded and fell, in pieces, into Lake Ontario, taking company test pilot Jean Ziegler and EB-50A observer Frank Wolko with it. The EB-50A was damaged on its underside and flap areas, and after the aircraft landed, a closer inspection revealed a crack in the main spar. Several years passed before the cause of the tragic explosion was determined: the culprit was the infamous Ulmer leather gasket of the type used extensively in the X-2's powerplant compartment to accommodate sealing requirements for propellant plumbing joints. Ulmer leather, when saturated with liquid oxygen, was found to be highly unstable; a shock of virtually any significant magnitude would cause the gaskets to explode. Eventually, this was concluded to have been the cause of 46-675's demise.

Coupled with the aforementioned engine and landing-gear problems, the loss of 46-675 brought the X-2 program to its knees. Wright Field informed Bell that contractor flight trials would have to be completed as quickly as possible, as it would soon be too late for the X-2 to make any meaningful contribution to high-speed, high-altitude flight research. The X-15 would be arriving in 1958 and would quickly take over in the flight arena that the X-2 was attempting to explore. Addi-tionally, the Air Force had agreed to turn the X-2 over to the NACA at some point, and that deadline was beginning to encroach on Air Force flight-test scheduling as well.

On July 15, 1954, the surviving X-2—46-674—with its still untested XLR25 engine, was mated to a new EB-50D carrier aircraft and flown to Edwards AFB. On August 15, following a month of static testing, Capt. Frank Everest flew 46-674, unpowered, for the first time.

Everest's flight was successful until touchdown. Almost at the instant the nosewheel contacted the lakebed, the aircraft yawed left and instantaneously rolled in the opposite direction. Just as quickly, the instability corrected itself, only to begin again in reverse. During each rapid cycle, the wingtips slammed the ground, scraping paint and bending metal. As speed decayed, the rolling oscillations slowly decreased in frequency until the aircraft came to a dusty stop.

That the X-2 was inherently unstable during landing rollout could no longer be denied. It was also apparent that a complete solution would not be possible until a more thorough investigation had been undertaken. In the interim, the aircraft was loaded aboard the EB-50D and transported back to Bell for repairs. It was not returned to Edwards until late February 1955.

On March 8, 46-674's second glide flight was undertaken. Unfortunately, the landing—like Everest's first—became another wild ride, and the aircraft was seriously damaged. On April 6, like its predecessors, the third glide flight ended with damage that required that 46-674 be sent back to Bell.

x2_5.jpg Above: Flying the X-2, Frank "Pete" Everest became "the fastest man alive." Today, he is the only surviving member of the four who flew the world's first Mach 3 aircraft (USAF via Jay Miller collection).





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