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USS Akron
USS Akron (hull number ZRS-4) was a helium-filled rigid airship of the U.S. Navy, the lead ship of her class, which operated between September 1931 and April 1933. She was the world's first purpose-built flying aircraft carrier, carrying F9C Sparrowhawk fighter planes, which could be launched and recovered while in flight. With an overall length of 785 ft (239 m), Akron and her sister ship the Macon were among the largest flying objects ever built. Although LZ 129 Hindenburg and LZ 130 Graf Zeppelin II were some 18 ft (5.5 m) longer and slightly more voluminous, the two German airships were filled with hydrogen, so the two US Navy craft still hold the world record for the largest helium-filled airships.
Akron was destroyed in a thunderstorm off the coast of New Jersey on the morning of 4 April 1933, killing 73 of the 76 crewmen and passengers. The accident involved the greatest loss of life in any airship crash, and was the deadliest aviation disaster of any kind prior to World War II.
The airship's skeleton was built of the new lightweight alloy duralumin 17-SRT. The frame introduced several novel features compared with traditional Zeppelin designs. Rather than being single-girder diamond trusses with radial wire bracing, the main rings of Akron were self-supporting deep frames: triangular Warren trusses "curled" around to form a ring. Though much heavier than conventional rings, the deep rings promised to be much stronger, a significant attraction to the navy after the in-flight breakup of the earlier conventional airships R38/ZR-2 and ZR-1 Shenandoah. The inherent strength of these frames allowed the chief designer, Karl Arnstein, to dispense with the internal cruciform structure used by Zeppelin to support the fins of their ships. Instead, the fins of Akron were cantilevered:, mounted entirely externally to the main structure. Graf Zeppelin, Graf Zeppelin II, and Hindenburg used a supplementary axial keel along the hull centerline. However, the Akron used three keels, one running along the top of the hull and one each side, 45° up from the lower centerline. Each keel provided a walkway running almost the entire length of the ship. The electric and telephone wiring, control cables, 110 fuel tanks, 44 water ballast bags, eight engine rooms, engines, transmissions, and water-recovery devices were placed along the lower keels. The inert gas helium was used instead of flammable hydrogen, which improved streamlining by allowing the engines to be safely placed inside the hull. A generator room, with two Westinghouse direct-current generators powered by a 30 hp internal combustion engine, was forward of the No. 7 engine room.
The main rings were spaced at 22.5 m (74 ft) and between each pair were three intermediate rings of lighter construction. In keeping with conventional practice, "station numbers" on the airship were measured in meters from zero at the rudder post, positive forward and negative aft. Thus, the tip of the tail was at station −23.75 and the nose mooring spindle was at station 210.75. Each ring frame formed a polygon with 36 corners, and these (and their associated longitudinal girders) were numbered from 1 (at the bottom center) to 18 (at the top center), port and starboard. Thus, a position on the hull could be referred to, for example, as "6 port at station 102.5" (the number-one engine room).
While Germany, France, and Britain used goldbeater's skin to gas-proof their gasbags, Akron used Goodyear Tire and Rubber's rubberized cotton, heavier but much cheaper and more durable. Half the gas cells used an experimental cotton-based fabric impregnated with a gelatin-latex compound. This was more expensive than the rubberized cotton, but lighter than goldbeater's skin. It was so successful that all the gasbags of Macon were made from it. The 12 gas cells were numbered 0 to XI, using Roman numerals and starting from the tail. While the "air" volume of the hull was 7,401,260 cu ft (209,580 m3), the total volume of the gas cells at 100% fill was 6,850,000 cu ft (194,000 m3). At a normal 95% fill with helium of standard purity, the 6,500,000 cu ft (180,000 m3) of gas would yield a gross lift of 403,000 lb (183,000 kg). Given a structure deadweight of 242,356 lb (109,931 kg), this gives a useful lift of 160,644 lb (72,867 kg) available for fuel, lubricants, ballast, crew, supplies, and military load (including the skyhook airplanes)
Eight Maybach VL II 560 hp (420 kW) gasoline engines were mounted inside the hull. Each engine turned a two-bladed, 16 ft 4 in (4.98 m) diameter, fixed pitch, wooden propeller via a driveshaft and bevel gearing, which allowed the propeller to swivel from the vertical plane to the horizontal. With the engines' ability to reverse, this allowed thrust to be applied forward, aft, up, or down. From photographs, the four propellers on each side apparently were contrarotating, so it would appear that the designers were aware that running the propellers in the air disturbed by the one ahead was not ideal. While the external engine pods of other airships allowed the thrust lines to be staggered, placing all four engine rooms on each side of the ship along the lower keel resulted in Akron's propellers all being in line. This proved problematic in service, as it induced considerable vibration, which was especially noticeable in the emergency control position in the lower fin. By 1933, Akron had two of her propellers replaced by more advanced, ground-adjustable, three-bladed, metal propellers. These promised a performance increase and were adopted as standard for Macon.
The outer cover was of cotton cloth, treated with four coats of clear and two coats of aluminum-pigmented cellulose dope. The total area of the skin was 330,000 sq ft (31,000 m2) and it weighed, after doping, 113,000 lb (51,000 kg).
The prominent, dark, vertical bands on the hull were condensers of the system designed to recover water from the engines' exhaust for buoyancy compensation. In-flight fuel consumption continuously reduces an airship's weight and changes in the temperature of the lifting gas can do the same. Normally, expensive helium has to be released to compensate, so any way of avoiding this is desirable. In theory, a water-recovery system such as this can produce a unit by weight of ballast water for every unit of fuel burned, though this is unlikely to be achieved in practice.
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USS Akron AI simulator
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USS Akron
USS Akron (hull number ZRS-4) was a helium-filled rigid airship of the U.S. Navy, the lead ship of her class, which operated between September 1931 and April 1933. She was the world's first purpose-built flying aircraft carrier, carrying F9C Sparrowhawk fighter planes, which could be launched and recovered while in flight. With an overall length of 785 ft (239 m), Akron and her sister ship the Macon were among the largest flying objects ever built. Although LZ 129 Hindenburg and LZ 130 Graf Zeppelin II were some 18 ft (5.5 m) longer and slightly more voluminous, the two German airships were filled with hydrogen, so the two US Navy craft still hold the world record for the largest helium-filled airships.
Akron was destroyed in a thunderstorm off the coast of New Jersey on the morning of 4 April 1933, killing 73 of the 76 crewmen and passengers. The accident involved the greatest loss of life in any airship crash, and was the deadliest aviation disaster of any kind prior to World War II.
The airship's skeleton was built of the new lightweight alloy duralumin 17-SRT. The frame introduced several novel features compared with traditional Zeppelin designs. Rather than being single-girder diamond trusses with radial wire bracing, the main rings of Akron were self-supporting deep frames: triangular Warren trusses "curled" around to form a ring. Though much heavier than conventional rings, the deep rings promised to be much stronger, a significant attraction to the navy after the in-flight breakup of the earlier conventional airships R38/ZR-2 and ZR-1 Shenandoah. The inherent strength of these frames allowed the chief designer, Karl Arnstein, to dispense with the internal cruciform structure used by Zeppelin to support the fins of their ships. Instead, the fins of Akron were cantilevered:, mounted entirely externally to the main structure. Graf Zeppelin, Graf Zeppelin II, and Hindenburg used a supplementary axial keel along the hull centerline. However, the Akron used three keels, one running along the top of the hull and one each side, 45° up from the lower centerline. Each keel provided a walkway running almost the entire length of the ship. The electric and telephone wiring, control cables, 110 fuel tanks, 44 water ballast bags, eight engine rooms, engines, transmissions, and water-recovery devices were placed along the lower keels. The inert gas helium was used instead of flammable hydrogen, which improved streamlining by allowing the engines to be safely placed inside the hull. A generator room, with two Westinghouse direct-current generators powered by a 30 hp internal combustion engine, was forward of the No. 7 engine room.
The main rings were spaced at 22.5 m (74 ft) and between each pair were three intermediate rings of lighter construction. In keeping with conventional practice, "station numbers" on the airship were measured in meters from zero at the rudder post, positive forward and negative aft. Thus, the tip of the tail was at station −23.75 and the nose mooring spindle was at station 210.75. Each ring frame formed a polygon with 36 corners, and these (and their associated longitudinal girders) were numbered from 1 (at the bottom center) to 18 (at the top center), port and starboard. Thus, a position on the hull could be referred to, for example, as "6 port at station 102.5" (the number-one engine room).
While Germany, France, and Britain used goldbeater's skin to gas-proof their gasbags, Akron used Goodyear Tire and Rubber's rubberized cotton, heavier but much cheaper and more durable. Half the gas cells used an experimental cotton-based fabric impregnated with a gelatin-latex compound. This was more expensive than the rubberized cotton, but lighter than goldbeater's skin. It was so successful that all the gasbags of Macon were made from it. The 12 gas cells were numbered 0 to XI, using Roman numerals and starting from the tail. While the "air" volume of the hull was 7,401,260 cu ft (209,580 m3), the total volume of the gas cells at 100% fill was 6,850,000 cu ft (194,000 m3). At a normal 95% fill with helium of standard purity, the 6,500,000 cu ft (180,000 m3) of gas would yield a gross lift of 403,000 lb (183,000 kg). Given a structure deadweight of 242,356 lb (109,931 kg), this gives a useful lift of 160,644 lb (72,867 kg) available for fuel, lubricants, ballast, crew, supplies, and military load (including the skyhook airplanes)
Eight Maybach VL II 560 hp (420 kW) gasoline engines were mounted inside the hull. Each engine turned a two-bladed, 16 ft 4 in (4.98 m) diameter, fixed pitch, wooden propeller via a driveshaft and bevel gearing, which allowed the propeller to swivel from the vertical plane to the horizontal. With the engines' ability to reverse, this allowed thrust to be applied forward, aft, up, or down. From photographs, the four propellers on each side apparently were contrarotating, so it would appear that the designers were aware that running the propellers in the air disturbed by the one ahead was not ideal. While the external engine pods of other airships allowed the thrust lines to be staggered, placing all four engine rooms on each side of the ship along the lower keel resulted in Akron's propellers all being in line. This proved problematic in service, as it induced considerable vibration, which was especially noticeable in the emergency control position in the lower fin. By 1933, Akron had two of her propellers replaced by more advanced, ground-adjustable, three-bladed, metal propellers. These promised a performance increase and were adopted as standard for Macon.
The outer cover was of cotton cloth, treated with four coats of clear and two coats of aluminum-pigmented cellulose dope. The total area of the skin was 330,000 sq ft (31,000 m2) and it weighed, after doping, 113,000 lb (51,000 kg).
The prominent, dark, vertical bands on the hull were condensers of the system designed to recover water from the engines' exhaust for buoyancy compensation. In-flight fuel consumption continuously reduces an airship's weight and changes in the temperature of the lifting gas can do the same. Normally, expensive helium has to be released to compensate, so any way of avoiding this is desirable. In theory, a water-recovery system such as this can produce a unit by weight of ballast water for every unit of fuel burned, though this is unlikely to be achieved in practice.