ZMC-2

The ZMC-2 was built in Grosse Ile, Michigan by the Aircraft Development Corporation, a division of Detroit Aircraft Corporation, on a site shared with, and later acquired by Naval Air Station Grosse Ile.[1] The ZMC-2 was the brainchild of Ralph Hazlett Upson, a balloonist and engineer who had previously won the Gordon Bennett Cup for balloon racing in Europe, bringing the cup to the United States for the first time.[4] Upson teamed up with Carl B. Fritsche of Detroit and together they formed the Detroit Aircraft Corporation, with backing from Henry Ford and Edsel Ford, as well as Charles Kettering of General Motors, Alex Dow, president of Detroit Edison, and William B. Stout, a local industrialist.[1] Chief of hull design was the young Czech-American designer Vladimir Pavlecka.[5]

The airship was constructed in a special hangar built in 1925 for the construction of the ZMC-2, and expandable for the construction of much larger metal-clad airships the company envisioned would be produced later.[1] The hangar measured 120' high, 120' wide and 180' long,[3] and remained the largest structure on the Naval Air Station property until 1960, when it was dismantled and the roof reused in the construction of a bowling alley in nearby Trenton, Michigan.[6]

The ZMC-2 was nicknamed the "Tin Bubble" and was also sometimes called a "tinship". The skin was not tin but Alclad. The airship was roughly teardrop shaped and had eight small stabilizer fins, four of which had rudders. It was held together with over 3.5 million rivets,[7] which were applied by an innovative sewing machine-like device which produced airtight seams.[1]

Ralph Hazlett Upson holding a model of ZMC-2

The ZMC-2 was 52 feet in diameter and 150 feet long.[1] The control car was 24 feet long by 6 feet wide.[1] It contained three fuel tanks to give a maximum cruising range of about 600 miles.[8] The ZMC-2 was powered by two Wright Whirlwind J5 engines of 200 hp each, carried on outriggers and mounted in a tractor arrangement, rather than the pusher position usually employed on blimps.[1] At first the landing gear was an unusual hollow steel ball about the size and shape of an American football, mounted on a tripod attached to the car.[1] This was done to create a shape with less drag in order to guarantee the Navy's requirement of a 62 mph top speed. Later, after the ZMC-2 had attained this speed with ease, the ball was replaced with a conventional swivelling soft tire.[1]

The crew consisted of a pilot, copilot and flight engineer-navigator, with space for one or two additional passengers.

The ZMC-2 was constructed out of Alclad, corrosion resistant aluminium sheet formed from high-purity aluminium surface layers metallurgically bonded to high strength aluminium alloy core material.[1] The result was about as strong as carbon or mild steel.[1] The downside was that Alclad was thicker than sheet aluminum, making the ship several hundred pounds heavier than originally envisioned.[1] The aircraft was already under construction, and over 20 feet of the nose completed using duraluminum when the decision was made to switch to Alclad.[1] The reason for the switch was that duraluminum is highly susceptible to corrosion, particularly in a salt water environment, the exact sort of environment a Navy blimp operates in.[1] The ZMC-2 was the first aircraft constructed from Alclad in the US, and no previous experience could be drawn upon for its handling.[1]

To assemble the ZMC-2 a skin-riveting machine was developed by the Aviation Tool Co., a division of the Detroit Aircraft Corporation.[1] The device was invented by Edward J. Hill, who had come to work on the ZMC-2 after leaving the Naval Aircraft Factory in Philadelphia, Pennsylvania.[1] The machine consisted of an aluminum casting, weighing about 100 pounds, and was supported on springs from a framework that ran on concentric circular rails set into the floor of the hangar. There were two sets of circular rails, one at each end of the building. Three riveting machines were made, one for each set of tracks, and one for reserve when repairs might be needed. The reason for two sets of tracks was that the hull was built in two sections, front and rear. Each end started from a circular plate suspended from the hangar roof by a cable and free to rotate as each 18 inch wide strip Alclad was added. In this manner, each end of the ship slowly grew as succeeding rows were added, looking like a bulls eye at first and later like a huge inverted teacup.[1] Both sections were under construction continuously 24 hours a day, seven days a week, once the hull was started. The riveting machine fed three small aluminum wires from large spools to make a seam about a quarter inch wide composed of three rivets, one above the other in a staggered pattern.[1] In theory the machine could sew about 50 feet of seam in an hour, but in practice about 10 or more feet was the average.[1] The sheets of Alclad used were eight to nine thousandths of an inch thick.[1] As the each section of the hull grew internal annular rings were added at appropriate distances to give stiffness and reinforcement to the hull skin.[1] In addition, lightweight longitudinal channels were added between the circular rings, giving the internal structure the appearance of a huge bird cage.[1] The helium gas was contained by the hull only, no fabric was used to contain the helium.[1] Inside the hull were two large airbag cells, called ballonets, made of rubberized fabric and containing air.[1] These cells could be expanded or contracted to control pressure as the helium expanded or contracted with the heating or cooling of the atmosphere or to adapt to changes of atmospheric pressure with altitude, and to control fore and aft trim.[1] In operation the ZMC-2 was susceptible to heating and cooling effects of the sun causing it to pop and buckle in the evenings if pressure from blowers was not applied.[9] During its service life the ZMC-2 was found to have a gas diffusion rate much lower than that of fabric-hulled blimps, meaning that a much longer time would pass before additional helium needed to be added.[1]

As the airship neared completion a decision had to be made on how best to fill it with helium. Once the two halves were completed they were suspended horizontally from cables attached to the hangar ceiling, and the two halves were joined with a final array of rivets.[10] Since helium mixes freely with air and is hard to separate from it, it was impractical to pump helium directly into the airship until the air was removed. It was decided that the airship would first be filled with carbon dioxide (CO₂), a heavy gas that mixes less freely with helium and which is easier to separate from helium. Once filled with CO₂ the helium could be pumped in under pressure from valves at the top of the chamber, forcing the CO₂ out through valves located on the bottom, and then recovering any helium that did mix with it.[10] Only a few weeks before this procedure was to begin a bright young engineer noted that once filled with CO₂ the ZMC-2 would be many thousands of pounds heavier than when filled with air. The rest of the airship's assembly had to be postponed for several weeks while additional reinforcing panels and stronger connectors were attached in order to support the increased weight of the CO₂ filled airship.[10]

The airship was first flown on August 19, 1929, and transferred to Lakehurst, New Jersey in October 1929.[11] The airship was nicknamed "the Tin Blimp". Its first Navy skipper was Red Dugan, who expressed reluctance at operating the airship, believing it unsafe.[12] Dugan's concerns would be proven wrong, though he would later lose his life in the crash of another airship, Akron.[12]

As a sub-scale test vehicle, it was considered to be very successful, but the company that built it did not weather the Great Depression well, and by the time a successor might have been built, there was little interest in pursuing it. In the year before the Depression, the U.S. Army was seeking funding for an airship based on the ZMC-2, that would have been larger than the German Graf Zeppelin, and powered by eight engines of 600–800 hp (450–600 kW; 610–810 PS)}. The U.S. Army planned to use it as a tender for air-launched aircraft, similar to plans the U.S. Navy had for future dirigibles. The $4.5 million need for construction was never approved by Congress.[13]

The ZMC-2 was operated with a zero internal pressure at speeds up to 20 mph, sufficient for it to be considered a 'rigid' airship.[14] With its low fineness ratio of 2.83, the ZMC-2 was difficult to fly.[15] By 1936, the airship had traveled over 80,000 miles with little sign of corrosion. In its lifetime the ZMC-2 logged 752 flights and 2265 hours of flight time.[16] In its final years its use had dropped significantly. Between December 1938 and April 1941 it only logged five hours flight time.

Considered by the Navy as too small for anti-submarine patrols, the aging ZMC-2 was decommissioned and scrapped in 1941 after nearly 12 years of service.

USA

• United States Navy

General characteristics

• Crew: 2
• Capacity: 750 lb (340 kg) payload
• Length: 148 ft 11 in (45.4 m)
• Diameter: 53 ft 2 in (16.2 m)
• Height: 64 ft 6 in (19.66 m)
• Volume: 200,100 cu ft (5,667 m³)
• Useful lift: 12,868 lb (5,837 kg)
• Powerplant: 2 × Wright J-5 Whirlwind 9-cyl. air-cooled radial piston engines, 220 hp (160 kW) each

Performance

• Maximum speed: 70 mph (112 km/h, 60 kn)
• Range: 675 mi (1,087 km, 587 nmi)

The ZMC-2 plays a key role in the Clive Cussler novel Cyclops (1986) in which it is fictionally saved from scrapping and renamed Prosperteer.

Wikimedia Commons has media related to ZMC-2.

• List of airships of the United States Navy
• David Schwarz

• Althoff, William F. (2003). USS Los Angeles: The Navy's Venerable Airship and Aviation Technology. Dulles, Virginia: Potomac Books.
• "Metal Covered Airship To Carry Twenty Tons". Popular Mechanics. 55 (4): 552. April 1931. Retrieved May 4, 2011.
• Melton USNR, Lt. Comdr. Dick. (1970). The Forty Year Hitch. Wyandotte, Michigan: Publishers Consulting Services.
• Morrow, Walker C.; Carl B. Fritsche (1967). The Metalclad Airship ZMC-2. Grosse Ile: W.C. Morrow.
• Outlaw, Stanley; Hal Neubauer; Marcia Neubauer; Dwanda Outlawand (2004). A Pictorial History of Naval Air Station Grosse Ile, Michigan 1927 to 1969 Second edition. Charleston: University of South Carolina Press.
• Pace, Kevin; Ronald Montgomery; Rick Zitarosa (2003). Naval Air Station, Lakehurst. Charleston: Arcadia.
• Sullivan, George (1988). Famous Blimps and Airships. New York: Dodd, Mead & Co.
• Vaeth, Joseph Gordon (2005). They Sailed the Skies: U.S. Navy Balloons And the Airship Program. Annapolis: Naval Institute Press.
• Van Treuren, Richard G. (Spring 2007). "Making it Happen: Captain C.V.S. Knox and Aeronautical Evolution". Foundation. 28 (1): 89–98.

• Lakehurst: International Airport (a picture of the ZMC-2 is near the bottom of the page)
• ZMC-2 in hangar, under the nose of the Hindenburg
• This has a short history of the ZMC-2 along with pictures of construction and flights of the ZMC-2