The Mysteries of the B2
August 20, 2002
Page 1
The problem of long-range bombing
Once the United States acquired the atomic bomb, the problem arose of developing intercontinental delivery vehicles capable of striking deep into the territory of its potential enemy: the USSR. In 1945, the Americans had at their disposal the B-29 Stratofortresses, which were used to bomb Hiroshima and Nagasaki. These planes formed the 509th Bombardment Group, based in Roswell. However, these aircraft lacked sufficient range to reach Soviet territory. Northrop then developed flying wing aircraft, which were supposed to have a very long range and be highly stealthy—that is, barely detectable by radar at the time. Jack Northrop initiated this project even before World War II. The first prototype with counter-rotating propellers, the XB-35A, made its maiden flight at Edwards Air Force Base on June 26, 1946.
Later, these aircraft were equipped with eight turbojet engines and became known as the YB-49.
They were assembled in Hawthorne, California, in 1947. Both aircraft had identical wingspans: 52 meters. A pre-production batch of about a dozen aircraft was built. But flight tests proved disastrous. At the time, little was known about the aerodynamics of swept-back wings. It wasn’t understood that at high angles of attack, airflow separation tended to occur at the wingtips, leading to sudden nose-down movements. This happened several times during tests, resulting in the loss of both aircraft and pilots. It was impossible to put such aircraft into service when they couldn’t fly under normal conditions. Additionally, competition between Northrop and Boeing led to Boeing gaining the upper hand. All YB-49s were destroyed. Interestingly, this problem didn’t seem to occur with the XB-35A, though no one really knew why. This problem affected all swept-back wing aircraft; the solution was to add “fences” along the wings. Here’s how it worked (similarly applied to the wings of the Caravelle):
Later swept-back wing aircraft, including delta-winged ones, used two other solutions. One involved creating a notch at the leading edge of the wing; this created a vortex that acted as a barrier preventing airflow separation from spreading forward.
The standard modern solution (used in the Mirage III) involves creating a notch at the leading edge; this also serves as a barrier against airflow separation. Note that the zigzag shape of the trailing edge serves two purposes: it reduces radar reflectivity, and at high angles of attack, it creates vortices that prevent airflow separation from spreading forward.
If this solution had been known in 1947, Jack Northrop’s aircraft might have been saved. The U.S. would have had a highly stealthy aircraft right from the start. But it seems that this problem wasn’t the only issue encountered during testing; there were also problems related to engine overheating.
It’s worth noting that the Germans seem to have been the first to understand the importance of stealthiness (they suffered heavy losses due to early detection of their aircraft by British radar systems). In the final years of the war, they developed an aircraft designed by the Horten brothers.
This aircraft had no vertical stabilizers and was constructed using materials that reflected radar waves poorly. This principle was later applied to the famous British fighter-bomber, the Mosquito, which was made of wood. Readers may wonder how such aircraft can be controlled. The answer is simple: it’s done by opening two flaps at the ends of the wings, thereby increasing drag locally.
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