The concept of the flying wing bomber had been on the minds of aeronautical engineers for quite some time before the forms of World War 2 (1939-1945) had made their presence known. The most famous of these wartime models became the German Horten Ho 229 (detailed elsewhere on this site) which utilized an early form of stealth and was jet-powered to boot. However only three of the type were completed after a first flight on March 1st, 1944. The remains of the project fell to the to the Americans in the immediate post-war period and ended its days in museum storage.
Jack Northrop, founder of Northrop, had been playing with the concept of flying wings during the 1930s and 1940s and eventually produced the N-1M and N-9M designs while the proposed XP-79 fell to naught. All of this work paved the way for something grander still to come - the XB-35/YB-35 flying wing strategic bomber.
The flying wing offered several key qualities that conventionally-arranged aircraft did not - more internal space meant more volume for fuel, increasing operational ranges, and there would be more storage room for internally-held ordnance. Lacking vertical tail fins, there was also less drag encountered and the wide-area wings aided in natural lifting tendencies which reduced fuel consumption. The major problem facing engineers was in the inherent instability of flying wings due to the technology made available at the time.
During the war years, the United States Army Air Corps (USAAC) sought to develop a long-range strategic bombing platform that could range from Allied-controlled bases outside of Europe and Britain in the event that the British Isles would someday fall to a German invasion - leaving few viable airbases for the Allies to continue warfare against the Nazi regime. Authorities sought an aircraft with a minimum range out to 10,000 miles hauling a war load of 10,000 pounds and reaching speeds of 450 miles per operating at altitudes up to 45,000 feet. The formal request originated in April of 1941.
The primary players involved became Boeing, Consolidated and Northrop (the request was eventually fulfilled by the Convair B-36 "Peacemaker" in the post-World War 2 years). Northrop pursued the requirement along the lines of its flying wing approached and developed the aforementioned N-9M as a starting point - this vehicle mimicking the form and function of what was to become a dimensionally larger future bomber. A development contract was signed in November of 1941 (the USAAC now having become the United States Army Air Forces = USAAF). The agreement covered one flyable aircraft with an option for a second and direct work on the XB-35 began in the early part of 1942 with the intent to have the completed form made available for testing before the end of 1943.
Engineers returned with a futuristic-looking design: an all-wing configuration was used which lacked vertical tail fins so rudder control was handled by a double split-flap arrangement found along the wing trailing edges. The crew cabin was set forward, at the apex of the arrowhead-like design, and the wing mainplanes were swept back for aerodynamic efficiency. A retractable undercarriage was fitted that sported a tricycle arrangement. As a flying wing, the fuselage and body were blended as one seamless structure - further eliminating drag.
The original design approach incorporated full creature comforts like sleeping bunks for long sorties and a pressurized cabin for high-altitude work. As many as six internal bomb bays would be used to house conventional drop ordnance and a tail" stinger" with remote-controlled machine guns would protect the vulnerable "six" of the large aircraft. As many as six machine-gun- or cannon-armed turrets would be installed about the aircraft to provide greater, flexible defense against intercepting enemy fighters. Four engines (2 x Pratt & Whitney R-4360-17 and 2 x R-4360-21 radial engines of 3,000 horsepower each) were to power the airframe and drive contra-rotating propellers in a "pusher" configuration, the engines installed on the dorsal side to either side of fuselage centerline, peering out over the wing trailing edges.
The USAAF ordered thirteen pre-production vehicles under the YB-35 designation on September 30th, 1943.
First flight of the XB-35 was on June 25th, 1946 but by this time World War 2 had ended with the fall of Germany in May of 1945 and the collapse of the Japanese Empire that August. Nevertheless, the Northrop product survived the large post-war drawdown of military projects and continued its development phase. During early testing, engines (provided by the USAAF directly) and propellers gave issues and the problem evolved into a sticking point between the USAAF, Northrop, engine-maker Pratt & Whitney and propeller-maker Hamilton Standard - all sides blamed the other.
Delays in the program meant that the first YB-35 did not achieve a first-flight until May 15th, 1948 and only one YB-35 ever made it airborne. Despite its performance when compared to contemporaries, interest in the flying wing bomber waned and this example was left alone until scrapped in July of 1949, ultimately joined by an incomplete YB-35 airframe in August of that year. The remaining airframes were finished to varying degrees, differing mainly by engine fits. The two XB-35 prototypes were, themselves, scrapped in August of 1949.
XB-35s served as prototypes while YB-35 were developmental craft. This left production-quality airframes to utilize the designation of "B-35" and the USAAF envisioned a fleet of 200 such aircraft but the line was never made ready in time to participate in the war. The Glenn L. Martin Company was set to assist Northrop in wartime production but this agreement proved a moot point in the XB-35's history - the B-35 would not have been made wholly ready before 1947.
With the end of the war, the USAAF inevitably began turning its interest to jet-powered types and called on Northrop to build two YB-35 aircraft into YB-49 bombers outfitted with 8 x Allison J35 turbojet engines. The move reduced operational ranges by as much as 50% but increased performance - particularly maximum speed which was raised to 520 miles per hour and operating altitudes which reached 40,000 feet. Three YB-35 aircraft were converted to the YB-49 standard, the second model crashing and killing its crew on June 5th, 1948.
YRB-49A, built from an existing YB-35, was outfitted with only six turbojets and proposed as a long-range reconnaissance platform. The USAF ordered thirty of the type and a single prototype managed a total of thirteen flights before the USAF reversed its commitment to the aircraft. The sole example was scrapped in December of 1953. Another YB-35 was used in constructing the EB-35B meant to evaluate the new in-house T37 "Turbodyne" turboprop engine driving contra-rotating propellers. This example was not furthered.
The end of the war, industry and governmental politics as well as technical challenges all contributed to the demise of the B-35 - delaying the entry of a frontline flying wing bomber for decades. Jack Northrop's dream of the flying wing bomber finally materialized through the B-2 "Spirit" introduced in 1997. Northrop was able to view the in-development creation prior to his death in 1981 - technology had finally made the flying wing concept a viable military platform and the B-2 series has gone on to find its own level of success in the conflicts of the late 1990s and the decades following.
Official performance numbers revealed for the YB-35, with its 8 x radial engine array, included a maximum speed of 393 miles per hour, a range out to 8,150 miles and a service ceiling up to 39,700 feet. Proposed armament was 20 x 0.50 caliber (12.7mm) Browning M3 heavy machine guns and an internal bomb load of 51,070 was expected. Its total crew complement numbered nine made up of two pilots, a bombardier, a navigator, flight engineer, radioman and three dedicated gunners.
The XB-35/YB-35 program was officially cancelled in 1949.