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"On This Day" In Engineering History

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November 9, 1956 – Crash of the Martin XP6M-1 SeaMaster

Posted November 09, 2007 12:01 AM by Steve Melito

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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#1

Re: November 9, 1956 – Crash of the Martin XP6M-1 SeaMaster

11/10/2007 10:16 AM

!! WARNING !!

My Anti virus software warns that the first (top) URL you gave has dangerous software on it that tries to load its self onto anyone's PC who logs onto that page......!!

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#3
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Re: November 9, 1956 – Crash of the Martin XP6M-1 SeaMaster

11/12/2007 8:34 AM

Thanks, Andy. I've broken the link and added a warning in the original article.

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Re: November 9, 1956 – Crash of the Martin XP6M-1 SeaMaster

11/12/2007 9:03 AM

No problem Sir....!

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#2

Re: November 9, 1956 – Crash of the Martin XP6M-1 SeaMaster

11/11/2007 9:26 AM

Isn't the Seamaster a Canadian fire-extinguisher-tank used in forest management there?

Maybe I just got it mixed up with something else

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#7
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Re: November 9, 1956 – Crash of the Martin XP6M-1 SeaMaster

03/09/2008 11:54 AM
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#5

Re: November 9, 1956 – Crash of the Martin XP6M-1 SeaMaster

11/16/2007 10:26 AM
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#6
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Re: November 9, 1956 – Crash of the Martin XP6M-1 SeaMaster

11/16/2007 10:57 AM

Magnificent pictures! Thanks for sharing.

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