LZ 127 Graf Zeppelin (Deutsches Luftschiff Zeppelin 127) was a German passenger-carrying hydrogen-filled rigid airship that flew from 1928 to 1937. It offered the first commercial transatlantic passenger flight service. The ship was named after the German airship pioneer Ferdinand von Zeppelin, a count (Graf) in the German nobility. It was conceived and operated by Hugo Eckener, the chairman of Luftschiffbau Zeppelin.
Graf Zeppelin made 590 flights totalling almost 1.7 million kilometres (over 1 million miles). It was operated by a crew of 36 and could carry 24 passengers. It was the longest and largest airship in the world when it was built. It made the first circumnavigation of the world by airship, and the first nonstop crossing of the Pacific Ocean by air; its range was enhanced by its use of Blau gas as a fuel. It was built using funds raised by public subscription and from the German government, and its operating costs were offset by the sale of special postage stamps to collectors, the support of the newspaper magnate William Randolph Hearst, and cargo and passenger receipts.
After several long flights between 1928 and 1932, including one to the Arctic, Graf Zeppelin provided a commercial passenger and mail service between Germany and Brazil for five years. When the Nazi Party came to power, they used Graf Zeppelin as a propaganda tool. The airship was withdrawn from service after the Hindenburg disaster in 1937 and scrapped for military aircraft production in April 1940.
The first successful flight of a rigid airship, Ferdinand von Zeppelin's LZ1, was in Germany in 1900. Between 1910 and 1914, Deutsche Luftschiffahrts-Aktiengesellschaft (DELAG) transported thousands of passengers by airship. During World War I, Germany used airships to bomb London and other strategic targets. In 1917, the German LZ 104 (L 59) was the first airship to make an intercontinental flight, from Jambol in Bulgaria to Khartoum and back, a nonstop journey of 6,800 kilometres (4,200 mi; 3,700 nmi).
During and just after the war, Britain and the United States built airships, and France and Italy experimented with confiscated German ones. In July 1919 the British R34 flew from East Fortune in Scotland to New York and back. Luftschiffbau Zeppelin delivered LZ 126 to the US Navy as a war reparation in October 1924. The company chairman Hugo Eckener commanded the delivery flight, and the ship was commissioned as USS Los Angeles (ZR-3).
The Treaty of Versailles placed limits on German aviation which the Allies relaxed in 1925. Eckener saw an opportunity to start an intercontinental air passenger service, and began lobbying the government for funds and permission to build a new civil airship. Public subscription raised 2.5 million ℛ︁ℳ︁ (the equivalent of US$600,000 at the time, or $11 million in 2018 dollars), and the government granted over 1 million ℛ︁ℳ︁ ($5 million).
The LZ 127 was designed by Ludwig Dürr as a "stretched" version of the zeppelin LZ 126 rechristened the USS Los Angeles). It was intended from the beginning as a technology demonstrator for the more capable airships that would follow. It was built between 1926 and September 1928 at the Luftschiffbau Zeppelin works in Friedrichshafen, on Lake Constance, Germany, which became its home port for nearly all of its flights. Its duralumin frame was made of eighteen 28-sided structural polygons joined lengthwise with 16 km (10 miles) of girders and braced with steel wire. The outer cover was of thick cotton, painted with aircraft dope containing aluminium to reduce solar heating, then sandpapered smooth. The gas cells were also cotton, lined with goldbeater's skins, and protected from damage by a layer containing 27 km (17 miles) of ramie fibre.
Graf Zeppelin was 236.6 m (776 ft) long and had a total gas volume of 105,000 m3 (3,700,000 cu ft), of which 75,000 m3 (2,600,000 cu ft) was hydrogen carried in 17 lifting gas cells (Traggaszelle), and 30,000 m3 (1,100,000 cu ft) was Blau gas in 12 fuel gas cells (Kraftgaszelle). The Graf Zeppelin was built to be the largest possible airship that could fit into the company's construction hangar, with only 46 cm (18 in) between the top of the finished vessel and the hangar roof. It was the longest and most voluminous airship when built, but it was too slender for optimum aerodynamic efficiency, and there were worries that the shape would compromise its strength.
Graf Zeppelin was powered by five Maybach VL II 12-cylinder 410 kW (550 hp) engines, each of 33.251 L (2,029.1 cu in) capacity, mounted in individual streamlined nacelles arranged so that each was in an undisturbed airflow. The engines were reversible, and were monitored by crew members who accessed them during flight via open ladders. The two-bladed wooden pusher propellers were 3.4 m (11 ft) in diameter, and were later upgraded to four-bladed units. On longer flights, the Graf Zeppelin often flew with one engine shut down to conserve fuel.
Graf Zeppelin was the only rigid airship to burn Blau gas; the engines were started on petrol and could then switch fuel. A liquid-fuelled airship loses weight as it burns fuel, requiring the release of lifting gas, or the capture of water from exhaust gas or rainfall, to avoid the vessel climbing. Blau gas was about the same density as air, so burning it had little effect on buoyancy. On a typical transatlantic journey, the Graf Zeppelin used Blau gas 90% of the time, only burning petrol if the ship was too heavy, and used ten times less hydrogen per day than the smaller zeppelin L 59 did on its Khartoum flight in 1917.
Graf Zeppelin typically carried 3,500 kg (7,700 lb) of ballast water and 650 kg (1,430 lb) of spare parts, including an extra propeller. Calcium chloride was added to the ballast water to prevent freezing. The ship retained grey water from the sinks for use as additional ballast. Both fresh and wastewater could be moved forward and aft to control trim.
The airship usually took off vertically using static lift (buoyancy), then started the engines in the air, adding aerodynamic lift. Normal cruising altitude was 200 m (650 ft); it climbed if necessary to cross high ground or poor weather, and often descended in stormy weather. To measure the wind speed over the sea, and calculate drift, floating pyrotechnic flares were dropped.
When preparing to land, the crew advised the ground either by radio or signal flag. Ground crew lit a smoky fire to help the airshipmen judge wind speed and direction. The airship slowed, then adjusted buoyancy to neutral by valving off hydrogen or dropping ballast. Echo sounding with the report from an 11-mm blank round was used to measure altitude accurately. The ship flew in with its nose trimmed slightly down, made its final approach into the wind descending at 30 m (100 ft) per minute, then used reverse thrust to stop over the landing flag, where it dropped ropes to the ground. Landing in rough weather required a faster approach. Up to 300 people manhandled the airship into a hangar or secured it by the nose to a mooring mast.
Graf Zeppelin's top airspeed was 128 km/h (36 m/s; 80 mph; 69 kn) at 1,980 kW (2,650 hp); it cruised at 117 km/h (33 m/s; 73 mph; 63 kn), at 1,600 kW (2,150 hp). It had a total lift capacity of 87,000 kg (192,000 lb) with a usable payload of 15,000 kg (33,000 lb) on a 10,000 km (6,200 mi; 5,400 nmi) flight. It was slightly unstable in yaw, and to make it easier to fly, had an automatic pilot which stabilised it in that axis. Pitch was controlled manually by an elevatorman who tried to limit the angle to 5° up or down, so as not to upset the bottles of wine which accompanied the elaborate food served on board. Operating the elevators was so demanding and strenuous that an elevatorman's shift was only four hours, reduced to two in rough weather.
The operational spaces, common areas, and passenger cabins were built into a gondola structure in the forward part of the airship's ventral surface, with the flight deck well forward in a "chin" position. The gondola was 30 metres (98 ft) long and 6 metres (20 ft) wide; its streamlined design reflected contemporary aesthetics, minimised overall height, and reduced drag. Behind the flight deck was the map room, with two large hatches to allow the command crew to communicate with the navigators, who could take readings with a sextant through the two large windows. There was also a radio room and a galley with a double electric oven and hot plates.