The design and construction of Graf Zeppelin were essentially conservative, based on tried-and-true technology developed over the Zeppelin Company’s decades of experience, and the ship was constructed of triangular Duralumin girders, with frames (or “rings”) spaced 15 meters apart.
The Limited Shape and Size of Graf Zeppelin
The shape and size of Graf Zeppelin was not ideal aerodynamically (in terms of performance), structurally (in terms of strength), or economically (in terms of payload).
The design of the ship was determined — and limited — by the size of the construction shed at Friedrichshafen, which had inner dimensions of 787 feet in length and 115 feet in height.
Since greater size meant greater efficiency in long distance operation, the challenge for Ludwig Dürr and his design team was to create a ship with the largest possible gas capacity that could be built within the confines of the construction shed:
The ship they designed was a long, thin cylinder, 776 feet long and 100 feet in diameter, with a gondola situated far forward, so that it could be slung under the hull where it began to rise toward the bow. The height of the ship from the bottom of the gondola to the top of the hull was 110 feet, just barely clearing the arches of the shed.
LZ-127’s long, slim hull was not the most aerodynamically efficient shape (which was a lesson learned from the efficient teardrop design of Bodensee and Nordstern); it was not the most structurally effective shape (since the thin hull was vulnerable to bending stresses); and it was not the most economically practical design (since its relatively small size limited payload on long flights), but it was the best that could be achieved within the limitations of the hangar at Friedrichshafen.
The Use of Blau Gas
But Graf Zeppelin did incorporate one especially notable innovation, in the use of Blau gas fuel for its five engines. One of the challenges of lighter-than-air powered flight has always been the need to account for the loss of weight as fuel is burned by the ship’s engines. As gasoline or diesel fuel is consumed during flight, the ship becomes lighter, and without a means to compensate for this change, lifting gas must be vented to maintain the ship’s equilibrium. The Zeppelin Company’s innovative solution to this issue with Graf Zeppelin was the use of a gaseous fuel, similar to propane, named Blau gas after its inventor, Dr Hermann Blau. Since Blau gas is similar in weight to air, its consumption during flight did not significantly change the aerostatic balance of the ship, and so it was not necessary to valve lifting gas to compensate for Blau gas burned by the engines.
Blau gas was also more efficient to carry than gasoline, and extended the ship’s range by over 30 hours of flying time; the approximately one million cubic feet of Blau gas carried by Graf Zeppelin could power the ship for over one hundred hours, but if that million cubic feet of Blau gas had been replaced by hydrogen, the additional hydrogen could have lifted only enough gasoline to power the ship for 70 hours or less.
The Blau gas was carried in 12 cells (Kraftgaszelle, or “power gas cells”), in the lower section of 12 of the ship’s 17 gas cell bays, beneath the hydrogen cells (Traggaszelle, or “lift gas cells”). Of Graf Zeppelin’s total gas capacity of 3,707,550 cubic feet, 1,059.300 cubic feet was available for Blau gas. The ship did also carry a supply of gasoline, so that if the ship were heavy, the engines could burn gasoline instead of Blau gas, lightening the ship without the need to drop ballast.
The use of Blau gas was quite hazardous, and many people believe Graf Zeppelin’s Blau gas presented a greater danger to safety than the ship’s hydrogen. The gas cells of that era were not impermeable and always leaked to some extent, and small tears and other minor leaks were also common. Since Blau gas has a similar density to air, escaping Blau gas did not rise like hydrogen but rather settled to the bottom of the hull, including the keel and into the gondola itself, and could even flow out toward the engines. This was an even bigger problem when the ship was on the ground, especially inside an enclosed hangar, since there was no flow of air to carry the gas away.
It should always be remembered that Graf Zeppelin was basically an experimental “proof of concept” design, and that the design of ship was limited by practical considerations such as the size of the construction shed at Friedrichshafen. While a clever response to these limitations in some ways, Blau gas had never before been used in a zeppelin, and it would never be used again.
When it did become necessary to drop ballast to maintain equilibrium, Graf Zeppelin could look to the 17,640 lbs of water it carried as trim ballast, as well as up to 5,280 lbs of water as emergency ballast, and 3,520 lbs of water carried for drinking, cooking, and washing (which was kept on board after use).
Graf Zeppelin was powered by five Maybach VL-2 12-cylinder engines, which could develop 550hp at maximum revolutions, and 450 hp at 1400 RPM in cruise.
Typical Speed and Altitude
The ship typically cruised at 72 MPH, at an altitude of 650 feet above ground level, but it also flew as high as 6,000 feet on occasion (for example, when crossing the Stanovoy mountain range in far eastern Russia during its Round-the-World flight). Graf Zeppelin also cruised well below 650 feet when necessary, as it was German practice to reduce the stress of vertical gusts by flying low to the ground during storms when possible.