The Cuban Missile Crisis once again demonstrated the U-2’s vulnerability to SA-2 attack in spectacular fashion when Air Force Maj Rudy Anderson was shot down and tragically killed during a reconnaissance mission over the Caribbean island on October 27, 1962. But still there was no sign of Oxcart entering service.
On January 15, 1963, the first flight of an A-12 powered by two J58s finally occurred and by the end of the month ten engines were available and the test program began to gain momentum. The biggest hurdle facing both test pilots and engineers was perfecting the air induction system, designed to vastly augment engine thrust. To achieve Johnson’s design goal of sustained Mach 3.2 flight, the air inlet spike’s aft-movement, together with the precise position of various bypass doors, had to initially be manually programed extremely accurately by the test team to ensure that the terminal shock wave was positioned in exactly the correct position in order to stabilize airflow in the inlet duct for future flights. When these parameters were finally achieved, the A-12’s thirst for fuel — particularly during the transonic phase of acceleration — was notably reduced. In all, it took 66 flights to extend Oxcart’s speed envelope out from Mach 2.0 to Mach 3.2.
But success came at a price. On May 24, 1963, Ken Collins was forced to eject from Article 123 during a subsonic engine test sortie, following an aircraft pitch-up and subsequent loss of control. The cause was found to be ice encrustation in the pitot static system, leading to the display of erroneous flight data. Article 133 (60-6939) was lost on July 9, 1964, just as Lockheed Test Pilot Bill Park was turning onto final approach into Area 51 having just completed a tri-sonic test flight. The aircraft experienced a complete flight control lock-up and Park was forced to eject at about 200kts as the aircraft continued to increase bank-angle at just 200ft above the desert floor. The cause was loss of hydraulic fluid to the flight control system.
On December 28, 1964, Agency pilot Mele Vojvodich taxied out in Article 126 (60-6929) for a Functional Check Flight (FCF), after the aircraft had undergone deep maintenance. With both burners lit and immediately upon rotating the aircraft, it yawed viciously to one side; corrective rudder application caused 126 to pitch-up. It became apparent that all pilot control inputs were having a reverse effect to those intended — in the midst of these uncontrollable divergent effects, Vojvodich was forced to eject from the aircraft not even 100ft above the ground. With just one swing on the open parachute, Vojvodich narrowly missed the flaming pyre of 126, which signified the end of yet another aircraft. The sortie had lasted just six seconds — the shortest of any “Blackbird” flight. A subsequent inquiry established that the SAS had been wired back into the aircraft incorrectly.
On November 20, 1965, the final stage of the validation process was completed when a maximum-endurance flight of six hours and 20 minutes was achieved, during which time an Oxcart demonstrated sustained speeds above Mach 3.2 at altitudes approaching 90,000ft. But the question remained — where to deploy the bird?
TECHNICAL SPECIFICATIONS
A thermal thicket
The innovative use of shape and materials to produce as stealthy a vehicle as possible was equaled by the necessary use of exotic materials and manufacturing techniques. The best frontline fighter aircraft of the day were the early Century-series jets, like the North American F-100 Super Sabre and McDonnell F-101 Voodoo. In a single bound, the A-12 would operate at sustained speeds and altitudes treble and double respectively those of such contemporary fighters. The technical challenge facing the Skunk Works team was vast and the contracted timescale in which to solve them was incredibly tight. Johnson would later remark that virtually everything on the aircraft had to be invented from scratch.
Operating above 80,000ft, the ambient air temperature was often below -60 degrees C and the atmospheric air pressure just 0.4 pounds per square inch; but cruising in afterburner at a speed of a mile every two seconds, airframe temperatures soared from between 245 and 565 degrees C. However, during the subsonic air refueling phase of a mission, the airframe would be subjected to steady-state temperatures of -65 degrees C. Thermodynamic considerations therefore were fundamental.
Sustained operation in such an extreme temperature environment meant lavish use of advanced titanium alloys, which accounted for 85 percent of the aircraft’s structural weight; the remaining 15 percent was comprised of composite materials. The decision to use such materials was based upon titanium’s ability to withstand high operating temperatures; it also weighs half as much as stainless steel but has the same tensile strength — high-strength composites were not available in the early 1960s. The particular titanium used was Beta-120/Ti-13V-11Cr-3A1, which can be hardened to strengths of up to 200 Ksi. But using this advanced material wasn’t without problems — titanium is not compatible with chlorine, fluorine or cadmium. For example, a line drawn on sheet titanium with a Pentel pen will eat a hole through it in about 12 hours — so all Pentel pens were recalled from the shop floor. Early spot-welded panels produced during the summer had a habit of failing, while those built in the winter lasted indefinitely. Diligent detective work discovered that to prevent the formation of algae in the summer, the Burbank water supply was heavily chlorinated. Subsequently, the Skunk Works washed all titanium parts in distilled water. As thermodynamic tests got underway, bolt heads began dropping from installations; this, it was discovered, was caused by tiny cadmium deposits, left after cadmium-plated spanners had been used to apply torque. As the bolts were heated to temperatures in excess of 320 degrees C, their heads simply dropped off. The remedy: all cadmium-plated tools were removed from toolboxes.