Scientist, aviators and military strategists have worked on creating useful jet aircraft since the 1930s, but it was the Cold War that saw the greatest number of jet experiments.
The experiments pushed the envelope of performance and design. Some of the design even tested aesthetic sensibilities of Pentagon officials.
Ranging from flying wings to modest modifications to proven airframes; the x-jets of the Cold War, their engineers and test pilots made huge contributions to military airpower and general aviation.
Concepts made famous by planes like the B-52 Stratofortress, the B-2 Stealth Bomber and even the Concorde were put to the test by these pioneering aircraft. While the the testing of these aircraft cost many lives, the contributions made future flights much safer and proved invaluable to the development of intercontinental bombers. By contributing to the development of strategic airpower, many scholars believe these early explorations in bomber aircraft share credit with the development of intercontinental missiles for America's eventual Cold War victory.
In May 1941, the Army Air Force (AAF) asked Northrop to create a flying wing with range of 8,000 miles, a minimum cruising speed of 250 miles per hour, a service ceiling of 40,000 feet, and a bombload of 10,000 pounds.
On December 17, 1942, the Army Air Force let a contract 13 service test models of the XB-35, designated the YB-35.
The expected cost was $22.7 million. With four rear engines, eight spacious bomb bays capable of carrying 40,000 lbs of bombs.
The initial flight of first XB-35, from Hawthorne to Muros Army Airfield, California, took place at long last on June 25, 1946, and lasted 45 minutes. The initial XB-35 crashed on its 45th flight, killing its Northrop test pilot.
In 1947, Northrop completed two all-jet prototypes. These demonstrated the flight-control capability of an all-jet flying wing and served as the basis for the YB-49 project After several reviews and tests over the next two years, the Air Force cancelled the program in August of 1949 completing the scrapping of the YB-35 prototypes in March 1950.
In Early 1943, the Douglas Airplane Company began studies officially starting the XB-42 project.
The design marked a radical departure from other airplanes while it incorporated features of the World War II proven A-20 and A-26 aircraft. The most remarkable feature of the XB-42 were its two Allison liquid-cooled, reciprocating engines mounted within the fuselage with the two inline propellers protruding from the tail of the plan.
These generated enough power to drive the plane to a top speed of 386 miles per hour.
Designed and constructed in less than a year, the XB-42 first flew on May 6, 1944. Testing continued through August 1948 when Douglas convinced the Air Force that future modification and development of the XB-42 would not be economical.
Essentially a jet version of the XB-42, the XB-43 began development in September 1944.
The Army Air Force wanted the XB-43 to carry an 8,000 pound payload, fly at 420 miles per hour at an altitude of 40,700 feet and have a range1,445 miles.
Two aircraft were developed for testing. The first flew for the first time on May 17, 1946.
The flight lasted just eight minutes. The two aircraft total over 700 hours of flight testing before the last XB-43 left the Air Force inventory in 1953.
Began in 1944, Convair's effort to build a family of jet bombers was accepted in 1944 and eventually delivered test airframes capable of cruising at 381 miles per hour at 40,000 feet while carrying 22,000 pounds of bombs.
The aircraft bears a striking resemblance to the later U-2/TR-1 with its long slender wings and pronounced tail. Results from the tests of this aircraft provide useful data on wing shape and aircraft endurance.
Officially cancelled in August 1947, the Air Force only accepted one XB-46. This aircraft logged 101 flying hours, and the program cost nearly $5 million before its cancellation.
The XB-48 originated from the War Department's demand to create a family of high performance bombers in 1944.
The first prototype was delivered for just $574,826. Ultimately two XB-48s were delivered for testing. The test helped develop features like the tandem bicycle-type landing gear that would later be important to the development of legendary B-52.
Although not officially cancelled, the XB-47 won out over the XB-48 for production and the XB-48 program died in 1949.
The YB-49 evolved from the flying wing work of the XB-35 and would effect the development of bomber and reconnaissance aircraft.
Built as a 1945 modification to the 1942 XB-35 contract, the YB-49 had a short tragic life. The first YB-49 was never accepted by the Air Force and was later destroyed in March 15, 1950.
The second YB-49 crashed less than two weeks after the Air Force accepted it from Northrop in 1948.
The 1950 crash ended further YB-49 development and testing.
Initiated in 1945, the XB-51 was Martin's entry into the Army Air Force's competition to design a light bomber aircraft.
The design promised 505 miles per hour and an 800-mile combat radius for its 6-person crew.
The unique design used three engines. Two attached to the forward part of the fuselage with the third housed beneath the tail.
The Air Force cancelled the program before formally accepting the the two test aircraft.
The single flying XB-51 was totally destroyed in a 1956 crash at Biggs Field, Texas.
The YB-60 was a swept-wing, all-jet version of the B-36.
The YB-60 first flew on Aril 18, 1952. Flight testing eventually ended less than a year later in January 1953 when the Air Force canceled the second phase of the program. The first YB-60 flew a total of 66 hours in 20 flights.
Its sister aircraft was never completed.
The program cost $14,366,022. The two aircraft were scrapped by the end of June 1954.
North American XB-70
Perhaps the most famous and recognized experimental Cold War bomber was North American's Valkyrie.
Designation of the XB-70 came in February 1958 but its roots reach back to Boeing's MX-2145 project which began in 1954.
Funded partially by the budget allotted to the project to create nuclear powered aircraft, the XB-70 was the most expensive of the Cold War experiments eventually costing $1.5 billion.
The first flight of the Valkyrie occurred on Sept. 21, 1964. Before being cancelled, the Valkyrie would demonstrate its capabilities -- flying at Mach 3.1 at altitudes in excess of 77,000 feet for a range of more than 4,200 miles. While never operational, the Valkyrie was the world's first super aircraft.