USS Akron (ZRS-4)

USS ''Akron'' (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. It was the world's first purpose-built flying aircraft carrier, carrying F9C Sparrowhawk fighter planes, which could be launched and recovered while it was in flight. With an overall length of , ''Akron'' and her sister ship were among the largest flying objects ever built. Although LZ 129 ''Hindenburg'' and LZ 130 '' Graf Zeppelin II'' were some longer and slightly more voluminous, the two German airships were filled with hydrogen, and 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.

Technical 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. ''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 degrees up from the lower centreline. 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, 8 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 2 Westinghouse d.c. generators powered by a 30-h.p. internal combustion engine, was forward of the No. 7 engine room.

The main rings were spaced at 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 , the total volume of the gas cells at 100 percent fill was . At a normal 95 percent fill with helium of standard purity, the of gas would yield a gross lift of . Given a structure deadweight of , this gives a useful lift of available for fuel, lubricants, ballast, crew, supplies and military load (including the skyhook airplanes)

Eight Maybach VL II gasoline engines were mounted inside the hull. Each engine turned a two-bladed, 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.Smith (1965). p. 193 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 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 and it weighed, after doping, .Smith (1965). p. 182

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 and any way of avoiding this is desirable. In theory, a water recovery system such as this can produce 1 lb of ballast water for every lb of fuel burned, though this is unlikely to be achieved in practice.

''Akron'' could carry up to of gasoline () in 110 separate tanks which were distributed along the lower keels to preserve the ship's trim, giving her a normal range of at cruising speed. Theoretical maximum ballast water capacity was in 44 bags, again distributed along her length, though normal ballast load at unmasting was . Maximum ballast was never an option, because a full fuel and ballast load would have left only lifting capacity for aircraft, crew, and supplies, and each fully loaded F9C fighter alone weighed .

The heart of the ship, and her sole reason for existing, was the airplane hangar and trapeze system. Aft of the control car, in bay VII, between frames 125 and 141.25, was a compartment large enough to accommodate up to five F9C Sparrowhawk airplanes. However, two structural girders partially obstructed ''Akron''s aftmost hangar bays, limiting its capacity to three airplanes (one in each forward corner of the hangar and one on the trapeze). A modification to remove this design flaw was pending at the time of the ship's loss.Smith (1965). p. 67

The F9C was not the ideal choice, being designed as a 'conventional' carrier-borne fighter. It was heavily built to withstand carrier landings, downward visibility was not very good and it initially lacked an effective radio. But the primary role of ''Akron''s airplanes was long-range naval scouting. What was actually needed was a stable, fast, lightweight scouting airplane with a long range, but none existed capable of fitting between the structural members and into the airship's hangar, as the F9C could.

The trapeze was lowered through the T-shaped door in the bottom of the ship and into the slipstream, with an airplane attached to the crossbar by the 'skyhook' above its top wing, its pilot on board and its engine running. The pilot tripped the hook and the airplane fell away from the ship. On his return, he positioned himself beneath the trapeze and climbed up until he could fly his skyhook onto the crossbar, at which point it automatically latched shut. Now, with the engine idling, the trapeze and airplane were raised into the hangar, the pilot cutting his engine as he passed through the door. Once inside, the airplane was transferred from the trapeze to a trolley, running on an overhead 'monorail' system by which it could be shunted into one of the four corners of the hangar to be refueled and re-armed. Having a single trapeze raised two problems: it limited the rate at which airplanes could be launched and recovered and any fault in the trapeze would leave any airborne scouts with nowhere to land. The solution was a second, fixed trapeze permanently rigged further aft along the bottom of the ship at station 102.5 and known as the 'perch'. By 1933 a perch was fitted and in use. Three more perches were planned (at stations 57.5, 80 and 147.5) but these were never fitted.

''Akron'' revived an idea used, and eventually rejected, by the German Navy zeppelins during World War I: the '' spähkorb'' or 'spy basket'.Smith (1965). p. 55 The "angel basket" or "sub-cloud observation car", allowed the airship to remain hidden in a cloud layer, while still observing the enemy below. The small car, rather like an airplane fuselage without wings, could be lowered on a 1000 foot long cable. The observer on board communicated with the ship by telephone. In practice, the device was unstable, almost looping over the airship during its only test flight.

During the design stage, in 1929, the navy requested an alteration to the fins. It was considered desirable for the bottom of the lower fin to be visible from the control car. Charles E. Rosendahl had witnessed, from the control room, '' Graf Zeppelin'' almost snagging her fin on high-tension power lines during her heavy take off into an unsuspected but very marked temperature inversion from Mines Field, Los Angeles at the start of the last leg of her round-the-world flight earlier that year. The design change would also allow direct vision between the main control car and the emergency control position in the lower fin. The control car was moved aft and all the fins were shortened and deepened. The leading edge root of the fins no longer coincided with a main (deep) ring and instead the foremost attachment was now to an intermediate ring at frame 28.75. This achieved the required visibility, improved low-speed controllability, due to the increased span of the control surfaces, and simplified stress calculations, by reducing the number of fin attachment points. The designers and the navy's inspectors, led by the very experienced Charles P Burgess, were entirely satisfied with the revised stress calculations. However, this alteration has been the subject of much criticism as an "inherent defect" in the design and is often alleged to have been a major factor in the loss of ''Akron''s sister ship ''Macon''. Construction for both ships amounted to $8,800,000 (in 1931 dollars) with the ''Akron'' accounting $5,538,400 of the total.

Construction and commissioning

Construction of ''ZRS-4'' was begun on 31 October 1929 at the Goodyear Airdock in Akron, Ohio by the Goodyear-Zeppelin Corporation. Because it was larger than any airship previously built in the US, a special hangar was constructed. Chief Designer Karl Arnstein and a team of experienced German airship engineers instructed and supported design and construction of both U.S. Navy airships USS ''Akron'' and USS ''Macon''.

On 7 November 1929, Rear Admiral William A. Moffett, the Chief of the U.S. Navy's Bureau of Aeronautics, drove the "golden rivet" into the main ring of "ZRS4". Erection of the hull sections began in March 1930. Secretary of the Navy Charles Francis Adams chose the name ''Akron'' (for the city near where it was being built), and Assistant Secretary of the Navy Ernest Lee Jahncke announced it in May 1930.

On 8 August 1931, ''Akron'' was launched (floated free of the hangar floor) and christened by First Lady Lou Henry Hoover, the wife of the President of the United States, Herbert Clark Hoover. The maiden flight of ''Akron'' took place around Cleveland on the afternoon of 23 September with Secretary of the Navy Adams and Rear Admiral Moffett on board. The airship made ten trial flights, including a 2000-mile journey, over 48 hours, to St. Louis, Chicago, and Milwaukee. On 21 October ''Akron'' left the Goodyear Zeppelin Air Dock for the Naval Air Station (NAS), with Lieutenant Commander Charles E. Rosendahl in command, arriving the next day. On Navy Day, 27 October 1931, the ''Akron'' was commissioned as a Navy vessel.

History of service

Maiden voyage

On 2 November 1931, ''Akron'' departed on her first cruise down the eastern seaboard to Washington, D.C. On 3 November the ''Akron'' took to the air with 207 persons on board. This demonstration was to prove that in an emergency airships could provide limited but high speed airlift of troops to outlying possessions. Over the weeks that followed, some 300 hours aloft were logged in a series of flights, including a 46-hour endurance flight to Mobile, Alabama, and back. The return leg of the trip was made via the valleys of the Mississippi River and the Ohio River.

Participation in a search exercise (January 1932)

On the morning of 9 January 1932, ''Akron'' departed from Lakehurst to work with the Scouting Fleet on a search exercise. Proceeding to the coast of North Carolina, ''Akron'' headed out over the Atlantic where it was assigned to find a group of destroyers bound for Guantánamo Bay, Cuba. Once these were located, the airship was to shadow them and report their movements. Leaving the coast of North Carolina at about 7:21 on the morning of 10 January, the airship proceeded south, but bad weather prevented sighting the destroyers (contact with them was missed at 12:40 EST, although their crews had sighted ''Akron'') and eventually shaped a course toward the Bahamas by late afternoon. Heading northwesterly into the night, ''Akron'' then changed course shortly before midnight and proceeded to the southeast. Ultimately, at 9:08 am on 11 January, the airship succeeded in spotting the light cruiser and 12 destroyers, positively identifying them on the eastern horizon two minutes later. Sighting a second group of destroyers shortly thereafter, ''Akron'' was released from the evaluation about 10:00 a.m., having achieved a "qualified success" in the initial test with the Scouting Fleet, but the performance could have been better with radio detection finding equipment, and scout planes.

As the historian Richard K Smith wrote in his definitive study, The Airships ''Akron'' and ''Macon'', "...consideration given to the weather, duration of flight, a track of more than flown, her material deficiencies, and the rudimentary character of aerial navigation at that date, the ''Akron'' performance was remarkable. There was not a military airplane in the world in 1932 which could have given the same performance, operating from the same base."

First accident (February 1932)

''Akron'' was to have taken part in Fleet Problem XIII, but an accident at Lakehurst on 22 February 1932 prevented her participation. While the airship was being taken from her hangar, the tail came loose from her moorings, was caught by the wind, and struck the ground. The heaviest damage was confined to the lower fin area, which required repair. Also, ground handling fittings had been torn from the main frame, necessitating further repairs. ''Akron'' was not certified as airworthy again until later in the spring. Her next operation took place on 28 April, when it made a nine-hour flight with Rear Admiral Moffett and Secretary of the Navy Adams aboard.

As a result of this accident, a turntable with a walking beam on tracks powered by electric mine locomotives was developed to secure the tail and turn the ship even in high winds so that it could be pulled into the massive hangar at Lakehurst.

Testing of the "spy basket"

Soon after returning to Lakehurst to disembark her distinguished passengers, ''Akron'' took off again to conduct a test of the " spy basket"—something like a small airplane fuselage suspended beneath the airship that would enable an observer to serve as the ship's "eyes" below the clouds while the ship herself remained out of sight above them. The first time the basket was tried (with sandbags aboard instead of a man), it oscillated so violently that it put the whole ship in danger. The basket proved "frighteningly unstable", swooping from one side of the airship to the other before the startled gaze of ''Akron''s officers and men and reaching as high as the ship's equator. Though it was later improved by adding a ventral stabilizing fin, the spybasket was never used again.

Experimental use as a "flying aircraft carrier"

''Akron'' and ''Macon'' (which was still under construction) were regarded as potential "flying aircraft carriers", carrying parasite fighters for reconnaissance. On 3 May 1932, ''Akron'' cruised over the coast of New Jersey with Rear Admiral George C. Day, and the Board of Inspection and Survey, on board, and for the first time tested the "trapeze" installation for in-flight handling of aircraft. The aviators who carried out those historic "landings"—first with a Consolidated N2Y trainer and then with the prototype Curtiss XF9C-1 Sparrowhawk—were Lieutenant D. Ward Harrigan and Lieutenant Howard L. Young. The following day, ''Akron'' carried out another demonstration flight, this time with members of the House Committee on Naval Affairs on board; this time, Lieutenants Harrigan and Young gave the lawmakers a demonstration of ''Akron''s aircraft hook-on ability.

"Coast-to-coast" flight and second accident (May 1932)

Following the conclusion of those trial flights, ''Akron'' departed from Lakehurst, New Jersey on 8 May 1932, for the American west coast. The airship proceeded down the eastern seaboard to Georgia and then across the southern gulf states, continuing over Texas and Arizona. En route to Sunnyvale, California, ''Akron'' reached Camp Kearny in San Diego on the morning of 11 May and attempted to moor. Since neither trained ground handlers nor specialized mooring equipment were present, the landing at Camp Kearny was fraught with danger. By the time the crew started the evaluation, the helium gas had been warmed by sunlight, increasing lift. Lightened by , the amount of fuel spent during the transcontinental trip, ''Akron'' was now uncontrollably light.

The mooring cable was cut to avert a catastrophic nose-stand by the errant airship which floated upwards. Most of the mooring crew—predominantly "boot" seamen from the Naval Training Station San Diego—released their lines although four did not. One let go at about and suffered a broken arm while the three others were carried further aloft. Of these, Aviation Carpenter's Mate 3rd Class Robert H. Edsall and Apprentice Seaman Nigel M. Henton soon plunged to their deaths while Apprentice Seaman C. M. "Bud" Cowart held on to his line and then secured himself to it before being hoisted on board the airship an hour later. ''Akron'' moored at Camp Kearny later that day before proceeding to Sunnyvale, California. Footage from the accident appears in the film ''Encounters with Disaster'', released in 1979 and produced by Sun Classic Pictures.

West Coast flights

Over the weeks that followed, ''Akron'' "showed the flag" on the West Coast of the United States, ranging as far north as the Canada–US border before returning south in time to exercise once more with the Scouting Fleet. Serving as part of the "Green Force", the ''Akron'' attempted to locate the "White Force". Although opposed by Vought O2U Corsair floatplanes from "enemy" warships, the airship located the opposing forces in just 22 hours, a fact not lost upon some of the participants in the exercise in subsequent critiques.

In need of repairs, ''Akron'' departed from Sunnyvale on 11 June 1932 bound for Lakehurst, New Jersey

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