North American XB-70 Valkyrie

North American XB-70 Valkyrie

Design
The Valkyrie was designed to be a high-altitude Mach 3 bomber with six engines. Harrison Storms shaped the aircraft with a canard surface and a delta wing, which was built largely of stainless steel, sandwiched honeycomb panels, and titanium. The XB-70 was designed to use supersonic technologies developed for the Mach 3 Navaho, as well as a modified form of the SM-64 Navaho's inertial guidance system.

The XB-70 used compression lift, which arose from a shock wave generated by the sharp leading edge of the central engine intake splitter plate below the wing. At Mach 3 cruising speed, the shock wave attached along the wing leading edge, preventing the high pressure behind the shock front from leaking up over the wing. The compression lift provided five percent of the total lift.

The wing included inboard camber to more effectively use the higher pressure field behind the strong shock wave. Unique among aircraft of its size, the outer portions of the wings were hinged, and could be pivoted downward by up to 65 degrees, acting almost as a type of variable-geometry wingtip device. This increased the aircraft's directional stability at supersonic speeds, shifted the center of lift to a more favorable position at high speeds, and strengthened the compression lift effect.

With the wingtips drooped downwards, the compression lift shock wave would be further trapped under the wings.

Like a number of other delta-wing aircraft designed to cruise at very high speeds, the Valkyrie included a droop-nose that allowed the pilots to view the ground during the nose-high takeoff and landing.

The Concorde or Tupolev Tu-144 both used a design where the entire nose section was angled downward, including outer window panels, exposing interior windows that were more vertically angled. In the B-70 design, only the upper section of the nose moved down into a fixed lower section, and the outer window panels moved with it to become more vertical, at 24 degrees slope. With the nose raised into its high-speed position, the outer windows were almost horizontal. A system that blew 600 F air from the engines was used for both defogging and rain removal.

The lower forward section included a radar bay, and production machines were to be equipped with a refueling receptacle on the upper surface of the nose.

The XB-70 was equipped with six General Electric YJ93-GE-3 turbojet engines, designed to use JP-6 jet fuel. The engine was stated to be in the "30,000-pound class", but actually produced 28,000 lbf (120 kN) with afterburner and 19,900 lbf (89 kN) without afterburner.

The Valkyrie used fuel for cooling; it was pumped through heat exchangers before reaching the engines.

To reduce the likelihood of autoignition, nitrogen was injected into the JP-6 during refueling, and the "fuel pressurization and inerting system" vaporized a 700 pounds (320 kg) supply of liquid nitrogen to fill the fuel tank vent space and maintain tank pressure.