Articles, Interviews & Stories
THE N9MB FLYING WING
PHOTOGRAPHS BY LANI MUCHE
(These photos may be seen in a larger size at Muche's Warbirds: N9MB)
Fifty-five years after it last military flight the Northrup N9MB Flying Wing can once again be seen in the skies over Southern California. The aircraft, which is the sole survivor of the original XB-35/YB-49 long-range bomber program, was restored by an all-volunteer group at The Air Museum Planes of Fame in Chino, CA in a project that took over 13 years to complete. Each of the four N9M Flying Wings were developmental aircraft and differed in several ways. In addition, numerous changes were made directly to the aircraft during testing so that little in the way of formal documentation on design and construction exists. Because of this, restoration volunteers had to, literally reverse engineer the entire project. Don Lykins, Chairman of the Board for the Museum and one of the current N9MB pilots, summed up the enormity of the task when he stated: "The men and women who worked on this project deserve enormous credit. This was the most complicated aircraft restoration project ever undertaken by a museum volunteer crew."
The N9MB, and all of the Northrop flying wing designs, came about because Jack Northrop became convinced as early as 1923 that the limit had been reached in conventional airplane design development. He felt that the next logical step was an all-wing aircraft which would do away with the drag-producing fuselage and tail. The entire airframe would create lift and significantly increase overall performance. By 1929 he had produced the X-216H which, while it still employed a small twin-boom tail, refined the concept of the wing and led to the first successful all-wing design, the N1M "Flying Jeep". First flown in 1940, the N1M made over 200 flights before being retired in 1941.
In November 1941 Northrop was awarded a contract for the development and construction of the XB-35 long-range bomber. This aircraft, a true flying wing design, was to have a wingspan of 172 ft and be capable of carrying a bomb-load of over 52,000 lbs with a range of 7500 miles. In conjunction with this program, a contract was also awarded for the construction of four operational design models. These 1/3 scale models, designated N9M, were to act as flying test beds and also serve to familiarize Air Force pilots with all-wing operations.
Constructed primarily of wood around a metal tube center section, these 60 ft wingspan aircraft flew hundreds of hours at Muroc Dry Lake Bed (now Edwards AFB, CA) over a 3-year period. Once design testing was completed, they were turned over to the Air Force as trainers and were flown until the late 1940s. Among those who flew the aircraft were Chuck Yeager and Bob Hoover.
The first three aircraft, the N9M-1 (which was lost in a flight test accident), -2 and -A were all powered by two 260 hp Menasco C6S-4 engines which were considered underpowered. The Museum aircraft, the N9MB, is powered by two 300 hp 8 cylinder Franklin 0-540-7 engines which drive extension shafts to the 2-bladed Hamilton Standard pusher propellers via a fluid drive coupler. The coupler helps to reduce engine/propeller vibration problems and also allows the disengagement of the propellers from the engines to stop rotation in the event of an emergency.
The flight control system consists of a conventional control wheel connected to elevons and rudder pedals operating split trailing-edge rudders independently. Elevon surfaces (combined elevators and ailerons) are deflected together for pitch control and differentially in opposite directions for roll control.
The N9MB was also further modified by the removal of the 50 gal fuel tank located behind the pilot, which allowed the installation of an observer's seat. This seat was occasionally occupied by Jack Northrop, himself, to observe first-hand the program's progress.
Restoration of the Wing , which had last flown in May 1945, was a long and painstaking process. Acquired by the Museum in 1950, nothing was done with the aircraft until 1982. The original wood, which had decayed over the years, was used as patterns for the fabrication of new parts. Pragwood, a special laminate available only in Germany, was imported for the load-bearing sections and laboriously hand shaped and fitted. All other components were inspected and refurbished or replicated as the need arose. Lack of documentation complicated the project (Northrop had been approached early on but had declined to assist because of the liability involved in a flying restoration) and each part or section had to be disassembled, identified as to construction, material and function, and then either refurbished or remanufactured.
The Franklin engines presented their own unique problems. Only 13 of these powerplants had been built and today only three are known to exist. Those three were leaking oil from the cylinder heads. An engine overhauler who had worked on Franklins for years was able to determine that the crush gaskets between the steel cylinders and the aluminum heads had for some reason been omitted on these engines, thus causing the problem.
This was only one of the thousands of details that had to be worked out by the restoration crew. They have literally rewritten the book on the N9MB which made its first official flight on November 11, 1994. Following that flight a genuine flight test program was undertaken and completed. The tests, which returned the aircraft to full operational status, were meant to revalidate Jack Northrop's original concept. The Museum, which has dedicated the plane to the memory of Northrop, feels that this test program was a truer evaluation of the Flying Wing concept than is the B-2 Stealth Bomber currently in service. The aircraft is now a much sought after air show attraction and often shares the sky with the B-2 as a featured attraction. "The N9MB is not a product of the computer age but sprang directly from Northrop's mind. It flies because of the soundness of that design and the craftsmanship of the people who built it by hand." Project leader and primary N9MB pilot Ron Hackworth expressed the feeling of all those who worked on the project: "This is our gift to the Museum and aviation history." A history made much richer by the genius of Jack Northrop and the efforts of Planes of Fame.
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