page_title: USS Akron
section_title: Technical description
hierarchical_section_title: USS Akron / Technical description
caption_attribution_description: USS Akron (ZRS-4) under construction in the Goodyear-Zeppelin Corporation "air dock" hangar at Akron, Ohio (USA), 5 November 1930. this point, the airship's framework had been completed far enough to hold seven bags of lifting helium.
context_page_description: USS Akron was a helium-filled rigid airship of the U.S. Navy, 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 she was in flight. With an overall length of 785 ft, Akron and her sister ship Macon were among the largest flying objects ever built. Although LZ 129 Hindenburg and LZ 130 Graf Zeppelin II were some 18 ft longer and slightly more voluminous, the two German airships were filled with hydrogen and so the US Navy craft still holds the world record for 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.
context_section_description: 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' round 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 break up 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. Zeppelin and other rigid designs used a single keel at the lowest point of the hull circumference but Arnstein gave Akron three keels, one running along the top of the hull and one each side, 45 degrees up from the lower centreline. Each keel provided a walkway running almost the entire length of the ship. The strength of the main rings, the lower keels, and the fact that helium, instead of flammable hydrogen, was to be used, also allowed the designer to mount the engines inside the hull, improving streamlining.
  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 centre) to 18 (at the top centre) port and starboard. Thus a position on the hull could be referred to, for example, as "6 port at station 102.5" (the number 1 engine room).
  While Germany, France and Britain used goldbeater's skin to gas-proof their gasbags, Akron used Goodyear Tire and Rubber's rubberised 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 rubberised cotton but lighter than goldbeater's skin. It was so successful that all the gasbags of Macon were made from it. There were 12 gas cells, 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 percent fill was 6,850,000 cu ft (194,000 m³). At a normal 95 percent 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. It appears from photographs that the four propellers on each side were contra-rotating, each one turning the opposite way to the one ahead of it. Thus 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 was to prove problematical in service, inducing considerable vibratio
caption: Akron under construction in the Goodyear Airdock at Akron, Ohio in November 1930. Note the three-dimensional, deep rings.
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