The next step on the development path from the V 1 M to a heavy,
long-range bomber was a flying model that was the aerodynamic equivalent
of the larger flying wing. Such was the N-9M, a 60-foot scale model about
one-third the size of the projected XB-35 in every comparable dimension,
and designed to provide flight test information from which the
manoeuvrability, controllability, and performance of the XB-35 airplane
could be predicted. Four N-9Ms, the N-9M-1, N-9M-2, N-9MA, and N-9MB, were
Construction and test of the flying mock-up, for
delivery in 360 days, were approved by the Secretary of War on October 3,
1941. The aircraft bore a distinct resemblance to its smaller predecessor,
the N-1M. With two 260-hp Menasco C6S-4 engines buried in the wing, the
7000-pound N-9M was designed for an endurance of 3.2 hours with 100
gallons of fuel, and had a design ceiling of 21,500 feet. Controls
consisted of elevons, rudders, and trim tabs. An hydraulically operated,
retractable tricycle type landing gear was provided, and supplemented by a
fourth retractable wheel extending from the trailing edge just aft of the
canopy to protect the propellers in the event of an extremely tail-low
Cockpit space was at a premium, with various pieces of
test equipment, switches, and gauges using up what little space was
available. Seat and rudder pedals were not adjustable, quite unusual for
an airplane of that size and manoeuvrability. As in the N-1M, the usual
control stick was replaced by a control column and wheel, an awkward and
cumbersome arrangement for the size of the cockpit, but appropriate for
its role as a bomber mock-up.
The first of the four N-9Ms had unusual spilt flap rudders whose hinge
lines were orientated fore and aft. The The aircraft was designed for a
speed of 257 mph at 7000 feet
The first flight of the N-9M-1 was on December 27,
1942, three months later than specified by contract. Over the next five
months there were 45 flights. With a few exceptions, most were terminated
by mechanical failures of one sort or another, with the Menasco engines
the primary source of problems. Consequently, very little data relative to
drag, stability, and control were obtained. After about 22.5 hours of
accumulated flight time, the N-9M crashed approximately 12 miles west of
Muroc Army Air Base on May 19, 1943. The pilot, Max Constant, was killed
as he attempted to recover the aircraft from a right-hand, 60 degree
nose-down spin. Apparently, Constant made every attempt to stop the spin,
since the left hand spin chute had been deployed, and the flaps appeared
to be partially lowered. There was definite indication that the pilot had
attempted to leave the aircraft; the cockpit enclosure had been released,
the propeller brakes had been applied, and Constant had unfastened his
safety belt. Whether he was prevented from bailing out by lack of time or
by some unknown physical circumstance was not determined.
The remains of N-9M-1 after Max Constant's fatal accident on May 19, 1943.
The view is from in front of the aircraft, looking aft. The two propeller
shaft housings are evident, with the cockpit in the middle, canopy
missing, antenna mast at the rear.
It appeared that the N-9M might have dangerous spin
characteristics that could not be controlled by normal use of the control
surfaces; perhaps the spin chutes were inadequate in size or improperly
placed on the airplane for quick recovery. Further investigation in the
NACA spin tunnel was required.
The loss of the first N-9M was followed a month later
by the first flight of N-9M-2 on June 24, 1943. A minor setback was
experienced when the cockpit canopy came off in flight and, despite a
successful landing, slight damage to a landing gear door, radio mast, and
yaw meter resulted. Nonetheless, by mid September 1943, the first reliable
drag data were being obtained on N-9M-2; they indicated the drag of the
XB-35 at cruising speed would be approximately 7 to 12 percent greater
than that estimated from wind tunnel test results.
The N-9M-2 generally exhibited satisfactory
longitudinal and lateral stability and control in high speed and cruising
ranges. Some difficulty in obtaining satisfactory directional control was
experienced. Of more concern, however, was the occurrence of severe
reversal of elevator control forces at high lift coefficients. Due to
premature separation of the airflow over the top surface of the wing as
the stall was approached, flow conditions over the elevons caused them to
trail upward producing a force reversal on the elevator control. This may
have been the reason for the difficulty which led to the crash of the
The third N-9M, designated N-9MA, is shown in final assembly, with the
fourth aircraft, N-9MB, in the background. Arrayed along the trailing
edge, from the wing tip toward the centre line are the pitch trimmer with
the split drag rudder included, the elevon, and landing flap. At the
leading edge is a slot designed to improve flying qualities at high angles
The completed N-9MA awaits flight test. N-9M-1, N-9M-2, and N-9MA all had
semicircular cooling air intakes at the leading edge of the wing. Paint
schemes on the N-9MA and B were distinctive: the "A" was painted blue on
top, yellow on bottom; the "B" was yellow on top, blue on bottom.
By April 1944, the N-9M-2 had completed 33 flights for
a total flying time of 23 hours. Data obtained on the flights were
constructive and contributed to performance predictions for the XB-35,
then in the design phase.
On June 28, 1944, Army pilots flew acceptance flights
on the N-9MA. This model contained practically all of the design features
that were to be used in the XB-35 aircraft. In addition to the split
trailing edge and pitch control flaps that served as devices for
increasing lift and drag, a leading edge slot was installed near the tip
of each wing to lessen stall tendencies at high angles of attack. Flight
characteristics of the N-9MA gave firm indications that the
characteristics of the XB-35 bomber would also be satisfactory. Ground
handling was excellent; the aircraft was very manoeuvrable and responsive
in turns; control was good, although elevator control was quite sensitive.
Flying characteristics in rough air, previously reported as unsatisfactory
for the first two N-9Ms, were satisfactory, due to new rudders and
hydraulically powered elevons.
Wing tip details of the N-9MA above shows an open drag rudder, a split
surface control mounted in another hinged control surface, the pitch
trimmer. Each surface could be operated in conjunction with or
independently of the other. The photograph below shows one of the exit
flaps for engine cooling air and exhaust.
By October 1944, the authorized flight test program for
the N-9MA had been completed. The aircraft had flown about 50 flights, and
stability, control, and flying qualities were judged to be generally
satisfactory. Several inadvertent half-turn spins had been experienced and
recovery had been accomplished without difficulty. Northrop test pilot
Alex Papana, who along with Harry Crosby had experienced some interesting
rides in Northrop's experimental MX-334 glider, had even engaged in some
extra-curricular aerobatics in the N-9MA, in one instance accomplishing
four loops in quick succession.
With the completion of the test program, the N-9MA was
used by the Army to familiarize pilots with the craft. At about the same
time, the fourth and last of the series, the N-9MB, was nearing
completion. It would eventually be used to flight test the latest in
configuration and improved systems that would be incorporated into the
XB-35. As in N-9M-1, space for a passenger was created behind the pilot by
removing a fuel tank.
The N-9MB, with more powerful 300-hp Franklin engines,
provided yeoman service in the flight test program, producing invaluable
data that contributed directly to the engineering of the bomber program.
The production of the B-35 had become bogged down by a shortage of
engineers, design problems, conflicts with other production programs, and
excessive requirements for production engineering. The cumulative effect
was postponement of the first flight date. World War II ended, the program
dragged on, and the N-9Ms continued to do their jobs.
In May 1946, an Army test pilot assigned to Colonel
Albert Boyd's Flight Test Section at Muroc summarized his observations and
impressions of his one-flight evaluation of the N-9MB as follows:
'An hour's flight is hardly a fair basis for drawing
decisive conclusions. However, the airplane flew surprisingly well, was
more stable and handled far better than most would expect. It would take a
few more hours practice to make good takeoffs and get the proper
coordination on turns. But the technique could be mastered without too
much difficulty. It serves its purpose well as a flying model.'
The pilot's name was Captain Glen W. Edwards. Almost
two months later the first XB-35 made its initial flight, beginning a
protracted flight test program during which Edwards would lose his life.