Muche's Warbirds
Articles, Interviews & Stories
THE N9MB FLYING WING
by
JIM MUCHE
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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