Report of Airship “Hindenburg” Accident Investigation
Taken from the Air Commerce Bulletin of August 15, 1937 (vol. 9, no. 2) published by the United States Department of Commerce.
In an order, dated May 7, 1937, made by the Secretary of Commerce pursuant to the Air Commerce Act of 1926, as amended, relating to the investigation of accidents in civil air navigation in the United States, South Trimble, Jr., Solicitor, Major R. W. Schroeder, Assistant Director of the Bureau of Air Commerce, and Denis Mulligan, Chief, Regulation and Enforcement Division of the Bureau of Air Commerce, all of the Department of Commerce, were designated to investigate the facts, conditions and circumstances of the accident involving the airship Hindenburg, which occurred on May 6, 1937, at the Naval Air Station, Lakehurst, New Jersey, and to make a report thereon.
Commander C. S. Rosendahl, United States Navy, Col. C. de F. Chandler, United States Army, Col. Rush B. Lincoln, U. S. Army, Col. Harold E. Hartney, Technical Adviser to the United States Senate Committee on Commerce, Hon. Gill Robb Wilson, Director of Aeronautics for the State of New Jersey, and Hon. Grover Loening, Aeronautical Adviser to the United States Maritime Commission, were designated as technical advisers. Gen-lt Friedrich von Boetticher, German Military Attache, was selected by the German Ambassador at the invitation of the Secretary of Commerce, as an observer at the investigation.
On the fourth day of the hearings, the members of the German Commission appointed to investigate the accident, including Dr. Hugo Eckener, Lieutenant Colonel Joachim Breithaupt, Professor Guenther Bock, Professor Dr. Mav Dieckmann, Director Dr. Ludwig Duerr, and Staff Engineer Brieirich Hoffman, appeared and thereafter acted as observers and testified as witnesses. The U. S. Navy Board of Inquiry was represented throughout the hearing by an observer.
When the accident occurred, an aeronautical inspector of the Department of Commerce was present. Before midnight of the same day, other representatives of the Department reached the scene of the accident. After a preliminary inspection had been made, public hearings were held, from May 10th to May 28th, in the main hangar at the Naval Air Station, Lakehurst, New Jersey, in Asbury Park, N. J. and in New York City.
In addition to that provided by the Departments representatives, assistance was received from the U. S. Navy Department, Bureau of Investigation, Department of Justice, Weather Bureau, Department of Agriculture, Bureau of Standards, Department of Commerce, New York: City Police Department, and the Bureau of Explosives. Aviation companies, newspapermen, newsreel representatives, and photographers, many of whom were eye witnesses to the event, and others, furnished valuable information.
Part 1. – Introduction[Note: All times reported herein, unless otherwise indicated, are Eastern Standard Time (E.S.T.).]
The airship Hindenburg was destroyed by fire at 6:25 P.M., E.S.T., May 6, l937, at the Naval Air Station, Lakehurst, New Jersey.
The airship was completing its first scheduled demonstration flight for the 1937 season, between Frankfurt, Germany, and Lakehurst. It had departed from Frankfurt about 8:15 P.M., G.M.T., Monday, May 3, and was due at Lakehurst on the morning of Thursday, May 6. It was due out of Lakehurst at 10:00 P.M. E.S.T., that night. Because of unfavorable winds encountered en route, its arrival at Lakehurst was deferred until 6:00 P.M., Thursday evening, and departure was to be postponed until midnight or later in order to reservice and prepare for the return voyage.
Ownership and Operation
The ship was owned and operated by the Deutsche Zeppelin Reederei, G.m.b.H., of Berlin, W. 8, unter den Linden, Germany. The flight, which was to have been one of a series to be range into United States territory during 1937, was authorized by a provisional air navigation permit from the Secretary of Commerce, and a revocable permit issued by the Secretary of the Navy to the American Zeppelin Transport, Inc., of 354 Fourth Avenue, New York City, as general United States agent of the Deutsche Zeppelin Reederei, G.m.b.H., for the use of the landing field and facilities at the Naval Air Station at Lakehurst.
Certificate of Airworthiness
In March, 1937, the German Government renewed the airworthiness certification of the aircraft, reporting that all of its safety devices had been inspected and found satisfactory.
According to the crew list (See Appendix I) furnished by the American Zeppelin Transport, Inc., the personnel on board, including officers, numbered 61, of whom 22 died as a result of the accident.
The passenger list (See Appendix II), likewise furnished shows that 36 persons besides the Crew were on board. Of these, 13 died as a result of the accident. Other passengers and members of the crew sustained serious injuries.
Total weight of the freight carried was 325 pounds and was stowed in the main freight compartment at Frame 125; 2 dogs were kenneled at Frame 92, and 3 packages were stowed in the control car. Mail was carried in a compartment on top of the control car. Of the freight and mail only a few pieces of mail were recovered.
Ground Crew and Facilities
The ground personnel consisted of 92 naval personnel and 139 civilians. Practically all of the ground crew had previous experience in landing airships. One member of the ground crew died as a result of burns received during the accident.
Flight Across the Atlantic
Across the Atlantic from Germany to the United States, the flight had been uneventful, save for retarding winds which were not unusually turbulent. The route traversed by the ship on this side of the ocean was from Nova Scotia, via Boston, Providence, Long Island Sound, New forks and thence to Lakehurst. After passing over Lakehurst the first time, it proceeded to cruise along the coast for a few hours before retracing its course from Tuckerton, N.J., to the Naval Air Station.
Part II. – The Airship
Design and Construction
The airship was placed in service early in 1936. It bore builder’s number LZ 129 and had been constructed by the Luft Schiffbau Zeppelin of Friedrichshafen, Germany, an organization which had previously built 118 Zeppelin type airships. Briefly described, this type of design provides for a frame work of duralumin metal girders with tension wires. There is division by fringe wirings of the body into different compartments, into which the gas bags are placed to receive the lifting gas; a keel walkway to take certain loads; a framework with an outer cover of fabric to give form, and engine cars suspended from the frame outside the ship. The Hindenburg was a Zeppelin type airship, having an axial corridor constructed longitudinally through the center of the hull.
During its 9 months of operation in 1936, this airship had made more than 55 flights; flown 2,764 hours, cruised l9l,583 miles, crossed the ocean 34 times, carried 2,798 passengers and more then 377,000 pounds of mall and freight, all without mishap.
Dimension Capacities, Other Characteristics
Its length was about 803.8 feet; height, 147 feet; maximum diameter, 135 feet; fineness ratio (length over diameter), about 6; total gas volume, 7,063,000 cubic feet; normal volume, 6,710,000 cubic feet. Weight of ship with necessary equipment and fuel was 430,950 pounds; maximum fuel capacity, 143,650 pounds; total payload 41,990 pounds, and total lift (under standard conditions) was 472,940 pounds. Its rated cruising speed was about 75 statute m.p,h.; its maximum speed was slightly over 84 m.p.h. Passenger space was entirely within the hull.
The control system was the conventional Zeppelin type control, with two rudders acting as a Unit for horizontal control, and two elevators acting likewise for vertical control. Emergency elevator and rudder control wheels were installed in the stern of the ship. An electrical gyroscopic device attached to the forward rudder wheel provided automatic steering.
The outer cover consisted of cotton fabric on certain parts of the frame; on others, linen, depending upon stresses to which it was exposed. All exterior surface of such fabric was treated with several coats of cellon and a mixture containing aluminum powder. As protection against ultra violet rays, the inner surface of the fabric on the upper part of the ship was coated with red paint.
In each of the sixteen compartments of the ship was a gas cell containing the lifting gas, hydrogen. The middle cells were seperate, whereas the two bow and the two stern cells were inter-communicating. The gas cell material consisted of a film placed between two layers of fabric. Nettings were provided to prevent all sharp edges from damaging the gas cells. It was stated that the amount of gas leakage through this fabric approximated a maximum diffusion rate of about 1 liter per square meter per 24 hours.
Fourteen automatic and an equal number of manually operated or maneuvering valves were affixed to the cells. A single maneuvering valve was affixed to cells numbered 1 and 2 and cells 15 and 16, Gas could be released from the cells by manual operation of the valve controls located in the control car, and hooked up with the valves by a series of wires and pulleys. This was done under the supervision of the captain or the watch officer in charge. The automatic or emergency valves were provided to reduce the pressure of the gas in the cells under certain circumstances. The cells were numbered from stern to bow, from 1 to 16. The maneuvering valves of cells No. 3, 4, 5, 6, 7, 8, 9, 10, 11, 13 and 14 were connected to a master wheel in the control car which operated all of them as a unit, and there also were independent control for the separate maneuvering valves so that the gas in them could be released as desired.
Cell Fullness or Pressure Indicator
Electrically actuated gas fullness or pressure units were connected to the gas cells to indicate visually by sensitive meters in the control car the pressure and hence the relative fullness of the gas in the cells. These units were located in the ships axial corridor, or walkway. The accuracy or sensitivity of this system was not definitely established. An appreciable amount of gas might have been able to escape before such escape would show on the visual indicator unless that indicator was kept under close observation. According to Witness Eckener, a cell could lose at least 200 to 300 cubic meters of gas before the indicator would show such a loss. Such an amount is only a very small proportion of a cell’s content.
Between every two cells a gas shaft was provided into which gas could be valved directly from the cells. The shafts extended vertically from the lower walkway through the axial walkway to the top of the ship for ventilation purposes. On the top they came in contact with the outside air under the protection of specially designed gas hoods or ventilators.
Four Daimler Benz diesel engines, type LOF-6, each having a maximum rating of 1,100 horsepower were used to propel the air ship. They were contained in four outside engine cars, or gondolas, and were suspended laterally on the ship’s hull by struts, Engine-room telegraphs provided communication between the control room end the individual engine cars. The fuel used by the engines was a Diesel oil.
The four-bladed propellers attached to each engine were of wood and 19 feet 9 inches in diameter. The blades were armored with brass sheathing about 1-1/2 inches in width, on the leading edge, from about the 43-inch radius to the tip of the blade. The sheathing was bonded to the ship’s structure through the engine. Tests were made with the prototype of the propellers used on the ship. They were tested to loads 50% in excess of the thrust to which the propellers would be subjected at take-off, which was three times greater than the thrust which would be imposed at cruising speed. They also successfully withstood the block tests. They were limited to 1,400 revolutions per minute in forward rotation and 1,120 revolutions per minute in reverse rotation. These revolutions were below the fluttering speeds of the blades.
Electrical Power Plant and Installations
The electrical power plant of the ship consisted of two 50 horsepower Diesel-driven generators with switchboards and distribution system. These generators were independent of the outside propelling engines. The electric generators and principal members of the system were located amidships on the port side of the keel. Current was generated for purposes of lighting, cooking, radio and steering. There were two circuits one of 220 volts, the other of 24 volts. The ship’s electric wiring was of copper and was installed in accordance with the rigid regulations governing the German Lining Societies. The lead to the stern light, which was on a 220-volt circuit, using a very heavy cable protected by a special fuse, extended from the electrical power plant along the lower walkway and thence to the light. No electric wiring extended above the equator except in the extreme nose of the ship.
Ropes and Cables
The main mooring steel cable was fixed to the tip or nose end of the ship. The port and starboard bow trail ropes were attached to the ship at frame 244.5. These trail ropes were about 413 feet in length. It is understood that in landing the ship, it was the practice to approach the ground mast from leeward and drop the wire cable and the two trail ropes. The main cable was then coupled to a mooring mast cable leading through the top of the mast. By moans of a winch, the cable was then reeled in, pulling the mooring cone on the ships nose into the corresponding cup on top of the mast. The trail ropes were coupled to ground ropes and led out to the sides to keep the ship headed into the wind and towards the mast and to prevent it from over-riding the mast structure, In the stern, at ring 47, an after mooring cable was in practice let through a metal fair lead. At ring 62 a port and starboard spider was let out at landing. Besides those enumerated, the ship was provided with other mooring or landing tackle, for such use as circumstances warranted.
Water was generally used for ballast. The emergency ballast was contained in fabric containers, four of which, of 500 kilograms of water, Were suspended in the bow and an equal number in the stern. To the right and left of the lower walkway were suspended a number of other ballast tanks, some of 2500 liters each and others of 2000 liters each. The ballast tanks could be emptied partially or totally by the elevator men by means of control wires connected the ballast stand in the control room. Several of the fuel tanks could also be used for ballast purposes.
The radio-room was located above the after end of the control car. Its equipment provided for two-way radio telephone and telegraph communications. It included a short wave and a long wave transmitter, each with 200-watt antenna capacity; two all-wave receivers and two direction finders. The frequency of the short wave transmitter was 4160 to 17,500 kcs. The frequency of the long wave transmitter was 120 to 500 kcs. The frequency range of the receivers was 12 to 20,000 kcs. Power for the transmitters was obtained from a 220-volt direct current supply generated by the ship’s electric power plant. The receivers obtained their high voltage from batteries, and power for their filaments was obtained through a series resistor from the 24-volt ships generator. For the short wave transmitter, there was a trailing antenna of 26 meters length. For the long wave transmitter, a trailing antenna of about 90 meters length was used. These trailing antennas were located directly below the transmitters and ran through an aperture in the keel of the ship. There was a fixed antenna extending from the control car about 15 meters toward the stern. The fixed antenna was used only for receiving purposes. In addition to this equipment, there was located in the bow an emergency transmitter and receiver, current for which was obtained from a generator driven by pedal power. This emergency set employed a trailing antenna about 20 meters in length.
The ship was inflated with hydrogen. According to the evidence adduced, this gas has the following characteristics: It is colorless, odorless and tends to diffuse in all directions. The only way that hydrogen could be detected by smell would be due to the presence of impurities as a result of the process by which it was produced, or contamination from some source such as rubberized fabric. Hydrogen, for lifting purposes, has a density of approximately 5 pounds per 1000 cubic feet, depending on the temperature and pressure. Its lifting power is the difference between the density of air and its own density. The density of air is about 75 pounds per 1000 cubic feet. Assuming pure hydrogen, its lifting power would therefore be about 70 pounds per 1000 cubic feet. An opinion was advanced that the general order of pressure of the gas within the cells of the ship was somewhere between half an inch and one inch of water pressure. It was stated that the density of hydrogen corresponds to air at a temperature of 5000° F. and that the chimney effect of its escape through the gas shafts of the ship was so very great that there was no possibility of its moving down the shafts into the lower parts of the ship.
The flammable limits of a mixture of hydrogen and air are probably between 4.5% and 62% of hydrogen. Other experiments have shown variances from 8 – 9.8% to 66%. The temperature at which chemical activity between hydrogen and oxygen takes places is between 507° to 557° Centrigrade. This temperature range is dependent upon the amount of hydrogen present. The range of activity of combustion will be from the lower limit of 4.5%, at which there will probably be an invisible union without evidence of flame. A combustible mixture would be more hazardous in an atmospheric condition of 98% relative humidity, and temperature 60° Fahrenheit, than in dry air with relatively low humidity, since dry hydro-oxygen is more difficult to ignite and its ignition temperature is higher. In an explosion the flame propagates in all directions in the combustible range between 15 to 45% of hydrogen. These figures were arrived at experimentally with glass or metallic apparatus which did not have effect upon the combustion temperatures. Catalytic metals having adsorption properties would be likely to affect the combustion at lower temperatures. Finished duralumin would not be expected to have material catalytic effect upon hydrogen.