On this day in engineering history, a Martin XP6M-1 SeaMaster
crashed into Delaware Bay because of a problem
with its hydraulic control actuators. Built by the Glenn L. Martin Aircraft Co.
of Baltimore, Maryland,
the "Mighty Martin SeaMaster" was the U.S. Navy's first all-jet seaplane and
one of the world's first all-jet flying boats. The crash of November 9, 1956
was the second such disaster for Martin's SeaMaster, a revolutionary
aircraft that the Navy planned to use for mine laying, photo-reconnaissance,
and long-range bombing operations.
In April of 1951, the U.S. Navy requested proposals for a high-speed
seaplane that could carry 30,000 pounds of payload to a target over 1,500 miles
away. At the time, the Navy lacked a strike force of super-carriers that would
enable it to attack America's Cold War rivals - and "compete" with the U.S. Air Force and its long-range bombers. After
reviewing plans from six aircraft companies, the Navy approved Martin's "Model
275" and awarded a contract to the Baltimore-based company. The Martin design
team was led by George Trimble, an aeronautical engineer; and included J.D.
Pierson, a specialist in hydrodynamics; and J.L. Decker, an expert in
aerodynamics.
Using Martin's P5M Marlin flying boat as a starting point,
the designers developed a new hull with a length-to-beam ratio of 15:1. The
power plant was supposed to use Curtis-Wright turbo-ramjets, but persistent
engine problems caused the design team to instead use four Allison J71-A-4
turbojets, each with 13,000 lbf of afterburning thrust. The SeaMaster's engines
were mounted in pairs in nacelles above the wings, which were swept back 40
degrees. The ends of the wings served as floats and were fitted with gears that
helped dock the aircraft. Capable of speeds of 600-mph, the SeaMaster featured a T-tail, which was designed to keep tailplane surfaces out of the
airflow behind the wing.
With the exception of a design-flaw that caused the J71's afterburners
to scorch the aircraft's fuselage, the SeaMaster's testing program began uneventfully. Then, on December 7, 1955, the first XP6M-1 prototype crashed
into Chesapeake Bay. Because the secret aircraft
lacked onboard flight-data recorders, however, the Navy's accident-investigation
team struggled to pinpoint the cause. Nearly a year later, the Navy prepared to
test a second SeaMaster prototype with flight data recorders, test
instrumentation, and ejection seats.
On November, 1956, Navy flier Bob Tuner lost pitch control
of his SeaMaster while recovering from a shallow dive at high-speed. The violent
outside loop caused the airframe to break apart, but the crew ejected to safety.
Later, a Navy crash-investigation team used information from the flight data
recorders to determine that the SeaMaster's tail T-tail configuration had been
overpowered by dynamic forces at high speed, due to a mathematical error in
calculating loads for the hydraulic control actuators.
Resources:
http://www.globalsecurity.org/military/systems/aircraft/ p6m.htm*
http://www.combatreform2.com/p6mseamaster.htm
http://www.anigrand.com/AA2061_XP6M-1.htm
http://aeroweb.brooklyn.cuny.edu/specs/martin/xp6m-1.htm
http://en.wikipedia.org/wiki/T-tail
*Please see the comment below before choosing this link.
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