John K. "Jack" Northrop designed the N-1M (N for Northrop, 1 for 1st model, M for mockup). It was a company-funded project that became the first entirely all-wing aircraft designed, built, and flown in the USA. Northrop planned to use the aircraft for experimental flying to determine how best to stabilize and control an all-wing aircraft. An all-wing aircraft is aerodynamically clean with no protruding engine nacelles and no fuselage, tail, or other type of external surface that contributes to stability or control but produces no lift. General of the U. S. Army Air Corps (renamed U. S. Army Air Forces after June 1941) Henry H. Arnold was interested in the potential of all-wing aircraft, and Northrop planned to use the information derived from flying the N-1M to eventually build an all-wing heavy bomber. He followed the N-1M with a of larger flying mockup called the N-9M. Four N-9Ms were built and flight tested.
Going back to 1927 when he designed the Lockheed Vega, Northrop had worked to improve the structural and aerodynamic efficiency of aircraft. After working as chief engineer at the Lockheed Aircraft Company from 1927-29, he designed the Avion in 1930. Northrop made the Avion’s wing large enough inside to completely enclose the cockpit, engine, fuel tank, and other components, thus loading the aircraft across the span of the wing, rather than the length of the fuselage. He mounted a conventional tail with twin rudders and an elevator to enable the pilot to control the Avion about the yaw and pitch axis.
After forming his own aircraft company, Northrop Aircraft, Inc., in 1939, Northrop could finance research and development of the N-1M. For design assistance, Northrop enlisted the noted aerodynamicist Dr. Theodore von Karman, Director of the Guggenheim Aeronautical Laboratory at the California Institute Technology, and von Karman’s assistant, Dr. William R. Sears. Northrop assigned Walter J. Cerny, Northrop’s assistant design chief, to supervise the project. Engineers conducted extensive wind tunnel tests using models to determine the flight characteristics. The design of the N-1M utilized new low-drag NACA airfoils for increased stability.
The N-1M, nicknamed the "Jeep," emerged a year later in July 1940. Workers built the wing using a wood and tubular steel airframe covered with thin plywood. An elevon is a control surface that combines the actions of an elevator and ailerons. Northrop attached elevons to the wing trailing edge to give the pilot control of the wing in the pitch and roll axes. Yaw control is the most difficult to establish in all-wing aircraft, but Northrop managed to implement adequate control using split flaps mounted near the wing tips.
The test pilot controlled the split flaps by pushing foot pedals one at a time to yaw the wing left or right. Pushing the pedals together simultaneously made the split flaps work like air brakes to slow the wing. Technicians on the ground could adjust the wing’s center of gravity, dihedral, wing sweep, arrangement of control surfaces, and they could adjust the wing tips up or down to determine the configuration that provided the best stability and control.
The fuselage completely enclosed the two 65-hp air-cooled Lycoming O-145 four-cylinder engines that powered the wing. Test flying showed that the engines lacked sufficient power and they were replaced with two 117-hp air-cooled Franklin 6AC-264F2 six-cylinder engines. Engine cooling issues plagued the program from start to finish.
Test pilot Vance Breese took the N-1M on its first test flight at Baker Dry Lake, California on July 3, 1940. The “flight” was very short and premature. During a high-speed taxi run, the aircraft hit a rough spot, bounced into the air, and remained airborne for a few hundred yards. Breese reported after further tests that the aircraft could climb no higher than 5 feet off the ground, and he had to maintain a precise angle of attack to hold that altitude. Von Karman was summoned and he solved the problem by adjusting the elevons.
When Vance Breese left the N-1M program to join the team developing the North American B-25 twin-engine bomber, Moye Stephens took over testing the aircraft. With Richard Halliburton, Stephens had flown a Stearman C-3B around the world in 1931 and he had helped Northrop found his company in 1939. After making nearly 30 flights by November 1941, Stephens reported that the N-1M tended to oscillate about the roll axis. Stephens feared the oscillations could become uncontrollable, but technicians made adjustments that resolved the problem. Test pilot John Meyers replaced Stephens in May 1942. Test pilots completed more than 200 flights in the N-1M.
Even with the more powerful Franklin engines, the N-1M remained underpowered. Notwithstanding this design weakness, Northrop convinced General Arnold that the N-1M was successful enough to continue developing the all-wing concept into a heavy bomber. Northrop built and tested four larger mockups called the N-9M and followed up this work with a series of prototype all-wing heavy bombers. The XB-35 powered by 4 Pratt & Whitney R-4360 reciprocating engines first flew in June 1946. A version called the YB-49 powered by jet engines first flew in October 1947. Neither aircraft satisfied the needs for a production heavy bomber and the U. S. Air Force ended the all-wing program in May 1950.
On November 8, 1943, Northrop officially transferred the N-1M to the Army Air Forces as a “museum piece” for the Army Air Forces Museum. The wing was moved to Freeman Field, Indiana, then to Park Ridge, Illinois. After the Korean War started in 1950, the U. S. Air Force shipped the aircraft to the Smithsonian. At the Paul Garber Facility, restoration began in May 1979 and Museum staff completed the work in March 1983.
