North American XB-70A Valkyrie on the taxiway with a cherry picker. Photo taken Sept. 21, 1964, the day of the first flight. Note: the left main landing gear brakes locked during the landing causing two tires to blow. (U.S. Air Force photo)
North American XB-70A Valkyrie in flight landing configuration, with Convair B-58A flying chase. Note the blotched appearance is due to the white paint being flaked and burned off during the high speed flight portion of the test. (U.S. Air Force photo)
The XB-70, one of the world's most exotic airplanes, was conceived for the Strategic Air Command in the 1950s as a high-altitude bomber that could fly three times the speed of sound (Mach 3). Because of fund limitations, only two were built, not as bombers, but as research aircraft for the advanced study of aerodynamics, propulsion, and other subjects related to large supersonic aircraft. The Valkyrie was built largely of stainless-steel honeycomb sandwich panels and titanium. It was designed to make use of a phenomenon called "compression lift," achieved when the shock wave generated by the airplane flying at supersonic speeds supports part of the airplane's weight. For improved stability at supersonic speeds, the Valkyrie could droop its wingtips as much as 65 degrees.
The initial XB-70A (S/N 62-1) was rolled out on May 11, 1964 and made its first flight on Sept. 21, 1964. It flew a total of 83 times when, on Feb. 4, 1969, it made its final flight to Wright-Patterson Air Force Base, Ohio, for delivery to the National Museum of the United States Air Force where it remains on public display in the Research & Development/Flight Test Gallery.
The aircraft flew supersonic (Mach 1.1) for the first time on its third flight, Oct. 12, 1964. On March 24, 1965, the aircraft surpassed Mach 2 for the first time during its 15th flight. Mach 3 was achieved for the first time on Oct. 14, 1965, during the 17th test flight.
On April 25, 1967, XB-70A-1 made its initial flight as a NASA test aircraft. Of the 83 flights of this aircraft, the USAF flew the first 60 and NASA conducted the last 23.
The No. 2 airplane (S/N 62-207) first flew on July 17, 1965, but on June 8, 1966, it crashed following a mid-air collision.
The delta wing of the XB-70 has a span of 52 feet 6 inches and is swept back 65.5 degrees. The outboard sections of the wings (20 feet) were capable of being drooped (lowered) in flight to increase high speed flight performance. The maximum drooped position was 65 degrees down angle and was used during supersonic flight. A transitional position of 25 degrees down angle was used as the XB-70 accelerated into supersonic flight. The variable geometry wingtips acted as vertical stabilizers when in one of the two drooped positions; however, their primary function was in the compression lift system. The lower fuselage was designed in a "Vee," or wedge shape, specifically to slow the airflow around the lower fuselage by creating an air dam. At speeds around 2,000 mph (Mach 3), this "air dam" slowed the air stream to about 1,600 mph, creating the compression lift -- the aircraft essentially rode on top of the compressed air dam thus creating the lift. At 2,000 mph, with the wingtips drooped to the full down position, compression lift carried approximately 35 of the aircraft's weight. The drooped wingtips acted to confine the airflow and increased to efficiency of the compression lift phenomenon. With the wingtips in the full up position (0-degree droop) compression lift was lessened by about 10 percent.
The XB-70 was equipped with two fully moveable vertical stabilizers, 12 elevons -- six on each wing trailing edge (an elevon is a combination elevator and aileron for pitch and roll control) -- and a canard surface mounted just behind the cockpit on the forward fuselage. The reason for having 12 small elevons rather than just two was to allow for greater control of the aircraft over the entire flight speed range. At landing speeds of less than 200 mph all twelve elevons were needed. At 2,000 mph with the wingtips drooped, the three outboard elevons on each wing were locked to prevent over stressing the airframe if sudden violent control inputs were required. The canard surface was all flying but also had trailing edge flaps. The canard's primary purpose was to balance pitch forces (up and down movements) normally controlled by the horizontal stabilizer and elevator on a conventional airplane.
The two XB-70As completed were never intended to be anything other than very high speed test aircraft. Because of advances in enemy air defenses during the late 1950s and early 1960s in both interceptor and surface-to-air missile design, the high-speed, high-altitude penetration bomber mission was seen as too risky and left the aircraft and crew very vulnerable to attack. Bombers capable of low level penetration or standoff weapons delivery were judged more practical. The growing value of the Intercontinental Ballistic Missile for strategic deterrence also had a negative effect on the XB-70 and similar programs (e.g. XF-108).
Mach 3 bomber
TECHNICAL NOTES: Armament: None (designed for up to 50,000 lbs. of nuclear or conventional bombs carried internally) Engines: Six General Electric YJ93-GE-3 turbojets of 31,000 lbs. static sea level thrust each with afterburner Maximum speed: 2,056 mph (Mach 3.1) at 73,000 ft. Cruising speed: 2,000 mph (Mach 3.0) at 72,000 ft. Range: 4,288 miles Service ceiling: 77,350 ft. Span: 105 ft. Length: 185 ft. 10 in. without boom; 192 ft. 2 in. with boom Height: 30 ft. 9 in. Tread (distance between main landing gear): 23 ft. 2 in. (strut to strut centerline) Wheel base: 46 ft. 2 in. (strut to strut centerline) Weight: 534,700 lbs. loaded Crew: Two (pilot and copilot) Serial numbers: 62-1 and 62-207
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