Excerpts from Popular Science, April 1938, “Can the Zeppelin Come Back?” By Edwin Teale
“Flames streaming upward into the darkening sky above Lakehurst New Jersey nearly a year ago seemed to form a funeral pyre consuming the last hope of the rigid dirigible… Proponents of the big dirigibles were quick to point out that fire, and not structural failure, had produced the disaster. Photographs showed that, in spite of the fire and explosions, the framework of the zeppelin remained intact and settled slowly to the ground. It showed that it could withstand tremendous
strains, far in excess of those they would meet in flight… Months have passed. In the great sheds at Friedrichsaften, on the Swiss — German border, another giant, the LZ-130, is being groomed for its initial tests. A few weeks hence, it’s four 1200 hp diesel engines roar into action and the pointed nose of the great 800 – foot dirigible will turn to the west for the 2 1/2 day transatlantic crossing to Lakehurst. As the new dirigible plows through the sky on a westward trip, it will leave behind 500 workmen busily engaged in the construction of a still larger ship, the biggest Zeppelin on ever built. This monster, the LZ-131, will carry 70 passengers on each North Atlantic run… It is expected to be completed in late 1939. The Germans, with Graf Zeppelin and Hindenburg, retained their faith in the flying cigars. These two skyliners shuttled back and forth to South America and the United States. They piled up hundreds of thousands of miles without a serious accident. The Graf Zeppelin even circled the globe. Completing 10 [should read 18 round] trips across the Atlantic in 1936, the Hindenburg for the first time in history prove that the rigid dirigible to be commercially profitable…
40 years ago, when Count Zeppelin’s first dirigible was under construction in its floating shed on Lake Constance, helium was a rare laboratory gas. It commanded a price of something like $2000 a cubic foot. If that rate today one filling of the LZ -130 would cost more than $14 billion. However, in the intervening years, American scientists have devised methods of washing, cooling, and separation which enable them to extract helium in large quantities from the natural gas of several fields in the Southwest. As a result, the cost has steadily declined until now alien can be obtained for probably a cent a cubic foot. Last year the United States Congress authorized the sale of 17,000,000 ft.³ of helium to Germany for zeppelin use. It will be used for the original inflation of the 16 great cells of the airship, and for replacing helium loss during the transatlantic flights.
Because America has a virtual monopoly on the gas, German scientists have devised a number of ways for conserving their supply. Before the start of a flight, the gas will be warmed to give it its greatest buoyancy. During the trip, moisture coming from the engine exhaust will be carefully collected to balance the loss of weight as the fuel is consumed, and does make it unnecessary to valve off gas to maintain a given altitude. By these steps, the scientists believe they will be able to conserve as much as 95% of the gas which hitherto was lost during a transatlantic voyage. The use of helium conquers the fire hazard. Another problem will take its place. This non-flammable gas is less buoyant than the inexpensive hydrogen. It will reduce the lifting power of the LZ-130 by 17 1/2 tons. Such a loss of payload will cut the profits which can be expected from its operation. Only by raising the rate for passengers and freight, can the income in attained by the Hindenburg be reached by the LZ-130.” (End)
Back in 1921 when the US Navy’s C-7 had been ripped in a routine no-further-damage save, and thereby just happened to be available to do a test flight series using helium, the conversion was simple: cut the altitude, crew and payload in half, inflate, and take off. Of course that test showed it was impractical to operate any C-ship with helium, and also due to the extreme shortage, C-7 was changed back and spent the rest of her days flying under hydrogen. Now the Germans were going to have to learn the same hard lessons as had been learned with LZ-126. Flying to Lakehurst non-stop from southern Germany to borrow ZR-1’s helium, the LZ-126/ZR-3 was never able to return to Europe. Sadly, cutting the fare-paying passenger and freight load in half wasn’t going to be enough for LZ-130. As Bauer and Duggan wrote, “Much of the work already completed would have to be undone and new parts installed. Considerable effort would be needed to covert the passenger accommodation, the lightening of the ship would be expensive, and changes to the electrical control system would engender financial and completion date problems. It was expected that the additional cost would amount to over 1 million RM exclusive of the special development work on the water ballast recovery system and helium gas-heating apparatus. Nevertheless it was hoped the delivery date… would be 15 April 1938… Thus the first flight to the USA was set for the first week in May.”
While the “Popular Science” article and that time and money estimate was somewhat optimistic, nonetheless preparations for helium continued in earnest. As Dörr wrote in 1938, “…by some less visible measures, it was possible to reduce the weight of the hull. This was of importance in respect to the intended use of helium as the lifting agent, because this gas is much heavier than hydrogen, what adds up to a loss of 20 tons considering the size of the ship.” While most everything was re-examined to eliminate all possible excess weight, major changes to the already state-of-the-art completed structure were not practical, so that effort maxed out early on. With only half the passenger load, so too could the crew be trimmed. This allowed the rebuilding of both their quarters to allow greater expansion of the cell in that bay, hoping to push the new pressure height to 600 meters. (Lz-129 easily went twice as high to get over some weather on his last trip.)
When it seemed that at least a majority helium fill was inevitable, the LZ-130, already a wonder of weight efficiency, was extensively reworked, saving 23,582 pounds. This was not even a good start, since the difference between hydrogen and helium first lost 55,125 pounds of lift – and the required water recovery system subtracted an additional 11,466 pounds of payload. They eliminated more than 12 tons of peace-of-mind fuel reserve, dropped 17,640 pounds of operating flexibility of water ballast, and denied a backup of 4,400 pounds of lube oil. Even after all that, ten crew members had to be dropped off, and they still lost the fares of ten passengers!
Given all that, the next most important problem was that of disappearing weight, i.e. fuel tonnage being consumed and the ship’s crippling new inability to valve off lift to compensate. The solution, by Dr. Ludwig Dürr, was as compact as it was elegant: reverse decades of Zeppelin propulsion by engineering completely new “tractor” style power cars.
Superficially the new power cars appeared to be little more than turned around and rounded off versions of the standard Zeppelin models dating to World War One, with the substitution of M-B DB-602s. The literature is not very forthcoming with details, but from the outset, water ballast was going to have to be recovered from the exhaust – from inside the car to reduce the infamous drag dogging the American ships. Dörr wrote, “…these engine cars are much bigger in their dimensions and also their shape is completely different. The reason for this is the installation of a new ballast-water-recovery-system. By this installation, the consumption of lifting gas will be reduced or almost obsolete, while otherwise it is due to the fact that the loss of weight by burning fuel during the flight must be compensated by valving off gas. Now the weight of the used fuel is replaced by the weight of the water gained from the exhaust of the engines by cooling and condensation.
A system to recover water from the exhaust had even even part of HMA No.1, the Mayfly. Stokes wrote, “The system comprised extension of the engine exhaust by 400 ft of thin section pipe along the keel and then forward again to the engine car, in the manner of the keel condenser current in steam launches, terminating in a water separator and storage tank. Trial in the shed gave water recovery of 52% of fuel weight, doubtless enhanced with the speed of flight improving heat transfer. Another trial was carried out in 1917, at Kingsnorth experimental R.N.A.S. station. As related by Wing Commander Cave-Brown-Cave, the contemporary doyen of British aircraft engine development. With a 240 hp engine, probably an “Eagle,” a honeycomb radiator of 25 mm (1″) tubes, 250 mm (10″) long took the exhaust through the tube spaces, with the air from the propeller passing through the tubes themselves. ‘The recovery was very satisfactory with the tubes clean, but decreased seriously after 10 hours running. Internals had stratified with virtually no deposit at the hottest zone, then dry carbon, oily carbon, and where water condensed, slimy oily carbon. A separator box with strands of hairy wool was adopted.’” The Germans had also experimentally tested a setup on the airship “Hansa.”
The optimistic goal for the new LZ-130 water recovery equipment was five tons, which though achieved, of course had to come out of payload as well. The LZ-126, adapted to American helium, had to borrow the exhaust-cooling condenser stacks developed following the ZR-1’s quickly consuming a period’s helium allotment within a few flights. Built in to the ZRS ships, the Akron and Macon were easily distinguished by the condenser stacks extending vertically up their hulls. The new problem with LZ-130: diesel oil does not contain enough hydrogen to produce water in the combustion process. The solution: new engines that would run well on a engineered blend, diesel fuel with added hydrogen. Dörr continued, “For this purpose multistage cooling systems are installed inside the engine cars and the cooling air is pushed into the car by the now forwardly mounted propeller and ejected on its rear end.” Still, there was seriously increased drag in the new setup.
A 1939 technical paper offers some clues to the length and breadth of engineering expertise that went into overcoming the new LZ-130 problems via its advanced power cars. We will never know all the innovations owing to the need for company, let alone state, secrets, but without a doubt the LZ-130’s propulsion system was the most marvelous engineering in the entire ship.
Seen inside is a complex system of multi-stage condensers. Of course there are also radiators to cool the lubricating oil and the engine’s water cooling jacket.
If the completed power cars resembled a modern jet engine nacelle, it was no co-incidence. The clever design hoped to overcome its drag penalty.
A shaft-driven turobfan helped rush that airflow out with such velocity as to produce some forward thrust, said to be enough to overcome the drag penalty. (Some might suggest this was the first hi-bypass turbofan.) The multi-stage cooling of the water-bearing exhaust stream had the extra beneficial effect of quieting the powerplants, and of course goes without being published, greatly reduced the free electrons found the exhaust stream. Sadly, in spite of designed-in screens, it would have eventually been clogged with soot, remembering the ZRS condensers’ rather tedious cleaning process. (Zep mechanic Eugene Bentele told the producer they never did really solve the soot problem.) However temporarily the blend of Ruhrchemie’s synthetic gas oil with 13.5% hydrogen would, if the air temperature and humidity were cooperative, produce 1 kg of water for every kg of fuel consumed. Bauer and Duggan also noted, “However, the problems arising from using the sulfur-laden diesel fuel were already known… such an installation would, after only a short duration of time, cause severe fouling and corrosion of the equipment.” Sadly the water recovered was too laden with SO4 to even use as wash or flushing water.
After return to flight allowed real-world testing, a final refinement of adopting the low-sulfur “Kogasin Diesel,” with the added hydrogen, sweetened the recovered water to the point it did not quickly corrode the condensers, piping and storage tanks. Those first flights were propelled with the same LZ-129 system of bolting two wooden props together. Early on, the forward cars received the new laminate three-blade props without the unique spinners seen in the photo. Proving worthy, the new props were added to the after cars as well, providing improved efficiency.
Since they could no longer start full-cell and just valve gas as it expanded gaining altitude, the plan was to heat up the helium just before take-off. The extra lift was to last just long enough before airstream carried it away. Its loss was replaced with aerodynamic lift, once the ship got moving forward. It was hoped the ship could be rushed out of a warm hangar into colder outside air, and before the superheat difference radiated away, lift off with otherwise impractical loads. It was further speculated that, at the destination, the mission-end light ship could be force-landed in cooler evening times, to have ballast quickly hauled aboard. All that was hardly feasible with helium’s shorter range, since as Bauer and Duggan wrote, “…flights to South America it was assumed that intermediate landings would be necessary, these taking place at Seville and Pernambuco…” One plan subtracting another 800 kg from payload would have used the ship’s electrical system to heat the cells via built in electrical resistance heaters. Another experiment looked to purchase Kärcher heaters and employ them expecting to heat the cells up to 8.5 degrees above ambient.
Lifting gas heating turned out to be unnecessary, since on March 13, 1938, Germany and Austria announced their Anschluss. Hitler marching into his country of birth unopposed was widely seen as the first step toward his planned world conquest. This “invasion” was all the excuse the Roosevelt administration needed to back out of the helium promise. Even a personal visit by Hugo Eckener, with his assurances military applications were impractical, and with reminders the US could cut off the supply at any time, failed to obtain the final signature to get the gas flowing in spite of what the Germans had agreed to pay.
C.E. Rosendahl battled FDR’s Secretary of the Interior in the American press, though Harold Ickes was just doing his President’s bidding when he refused to sign off on keeping the helium promise. In SNAFU, Rosendahl wrote, “In airplanes and tanks, the world might have had abundant reason to suspect or fear Germany’s then growing military strength, but it knew also that Germany possessed no military airships and only two civil lighter-than-air aircraft. Moreover, the helium requested by the Germans for their commercial airships was to be delivered by degrees, not all at one time. We could have known at all times of any attempted accumulation. We could easily have dried up the source or completely controlled the supply as we saw fit. Helium couldn’t be smuggled.” Rosendahl saw the Roosevelt administration’s reneging on the promise as an obvious attempt to stall all airship development. The Dessau would re-load those huge steel bottles and return them to Germany, empty.
Just as the British had a hydrogen-consuming engine to run electrical generators ready for R.101 when she was to return from India, LZ-130 was going to benefit from BMW research into a similar setup. Just as surely as the airship would lose weight while flying even with the water recovery in place, the constant consumption of lift from the electrical generator’s motors would go a long way to keeping the ship in balance. While hydrogen was cheap, obtaining it was dependent on a site having a hydrogen generator. So, not valving lift away made economic sense as well.
Finally, after over a year and an enormous amount of money had expended, the last Zeppelin built would be inflated as originally designed, and return to the skies.
Read on to LZ-130: The Last Zeppelin Missions
Read on to The Rigid’s Final Days and WWII
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