EVEN DOZEN OR SWEET SIXTEEN?
Though seemingly outwardly similar, LZ-129/130 and ZRCV had more bays & gas cells than the slightly smaller ZRS-4 and –5. In any rigid, a smaller number of larger cells offered greater lift, via less structure and cell weights. A larger number of smaller cells made for a stronger if possibly heavier structure, and greater survivability in case of battle damage or stuck-valve type cell casualty.
We will opt for a larger number of cells with the knowledge the 1937 designers could thereby make much stronger cell bays via tighter intermediate frame spacing. Therefore Long Island will return to 16 cells in an equal number of bays, numbered from aft to forward.
SPINELESS OR BONE-IN
Some sort of backbone has been featured in a good many airships which, from the turn of the century, have sought to smear the pinpoint loads like petroleum fuel tanks, aviators and engines across the feeble gas bag(s). A notable exception was R.101 herself, which had no keel at all in the conventional sense. (Refer to the previous post, some fuel tanks located in the rings themselves.)
Photo: R.36’s keel demos its hospitality to weight-extremes of gasoline cans and ballast bags alike. A ZR-1 crewman would have felt somewhat at home in this similar arrangement.
ZR-3’s heavy centerline keel (photo) helped carry an airplane trapeze later in her life. The next Zep, LZ-127, did not have so many heavy gasoline tanks testing his keel strength. The “weightless” gaseous fuel was carried in fabric cells below the hydrogen cells. The heavy gasoline carried aboard was used as trim.
LZ-129’s giant diesel tanks (photo) hung from his heavy keel. This strong keel bent, but did not break, during his fatal fall.
The Arnstein Goodyear-Zeppelin design won the US Navy approval in part because of its three-keel design. The triangle of reinforcement they offered eventually lead to the incorporation of not just fuel, oil and ballast loads on the two lower keels, but the airship’s propulsion plants as well, while offering crew access to a large cross-section of the interior.
While the ZRS 4/5 upper keel carried no concentrated loads, its walkway provided access to the airship’s topside, the logical mounting of gas valves used for maneuvering and to prevent overpressure during extremely rapid altitude changes. Thus Akron and Macon had direct valve access without any complex tower or center walkway arrangement. The two forwardmost valves were athwartships, off the centerline keel, but were still reachable via their main ring (photo).
This useful upper keel appears to have been retained on ZRCV.
The centerline walkway created by the LZ-129’s spoke-like rings’ construction (photo) permitted access to gas vent towers, but not all valves could be easily reached by the crew.
On the first return trip from Brazil, a valve stuck open and vented tens of thousands of cubic feet of hydrogen. The riggers could only watch as the cell went limp right up to the level of the stuck valve. Mixed in outside air, it dissolved, disbursed and, when it found enough oxygen in the static-rich atmosphere at that altitude, doubtless burned with great ferocity. No one noticed, since the heat generated was headed upwards, and most of the energy would have been absorbed in the air’s water vapor.
Selection of a keel design is also dependent on how much non-gas space is expected to be habitable within the hull. In this faint original print, the Akron / Macon Bay VII airplane truss appears to be quite intrusive.
How much room can be efficiently chiseled out of the gas cell space? The passenger sections of the R.100 and R.101 (below) were arguably not quite as gas-capacity-efficient as the LZ-129 and –130.
With the ZR mission emphasis switching from scout to attack, it becomes obvious an airplane with the wing area capable of supporting two-man, three-gun crew and a 1,000 lb. bomb simply would not be practical to stow inside an airship. At the same time, the only practical way of also carrying small fighter planes would be to stow them inside. A compromise between multi-story luxury compartments and more functional keels would have been reached.
Therefore, we settle on one 4-truss centerline keel, and one “conventional” V-shaped upper keel for our USS Long Island design. Our wide, quad-reinforced lower keels will carry the heavy and dynamic loads of fuel tanks, ballast bags, and transitory airplanes. The upper keel will allow access to gas valves, as well as topside navigation & defensive stations.
Rosendahl continued, “…German airship men did not like the AKRON-MACON design … they did not like the idea of the considerable unsupported length of upper fin forward of its attachment at Frame 17-1/2, a frame they considered weak anyhow.” Author Thom Hook followed Rosendahl’s unpublished lead in suggesting Akron was lost for the same reason—tail structural failure and resulting gas cell loss—as Macon.
In disagreement, Jeffery Cook’s intense study of airship empennage set the LTA world abuzz, writing:
“It has been a widely held belief that Goodyear-Zeppelin’s failure to include one or more cruciforms to support the fins was a fundamental flaw in the ZRS-4/5 design… The Germans had used cruciforms in all of their ships since 1915, without any fin failures, and they (along with many other LTA experts and enthusiasts over the subsequent half century) believed that the American ships’ deep frames were not strong enough to take the place of the cruciforms. The Zeppelin Company also pointed to the fact that Goodyear had assumed the same loads for all three upper fins. In their years of operating experience, the Zeppelin Company had learned that the upper fin of an airship should be designed for higher loads than the other fins… The fact that no such allowance had been made in the ZRS-4/5 fins, and the Macon girder failures in April 1934, led the Germans to feel that the American ships’ fins and aft hull structure were under-designed for the loads imposed on them… Both of these arguments are unsupportable… Arnstein was intimately familiar with German practice, for he had helped to establish that practice; had he felt it necessary to use cruciforms or increase the strength of the upper fin, he would have done so at the outset.”
Meanwhile, belief that stability could be enhanced by increasing the fin area from the German originals was not followed with R.101 (photo). Critics charge R.101’s fins and control surfaces were undersized, but at least structural strength seemed adequate.
Arnstein’s winning proposal for BuAer Design #60 (photo) featured large fins which, in deepening for Design Change #2, lost their root main-ring support.
LZ-127 (Roy Gibbens photo) shows the most successful fin design, if by 1935 disfigured with the symbol of the national socialist party paying the operating bills.
As Jeff Cook’s study revealed, Akron/Macon’s production tails were designed with incorrect pressure distribution data which directly caused the horizontal fin failure in flight over Texas and the Macon’s loss from upper fin failure. C.P. Burgess’ 1938 ZRCV design showed both this real world education, and studies completed after Akron’s loss. Our movie effort is also blessed to have Jeff Cook on the design team.
Jeffrey Cook’s USS Long Island fin structure concept (above) reflects studies that designers would have possessed even if Macon had not been lost in 1935. Unlike the ZRS-4 & -5 fins that were basically enlargements of the LZ-126 fins, this design has its structure in the right place to handle flight loads. Of course, like the rest of the structure, it would also benefit from the stronger 24S aluminum and improved spot-welded construction techniques.
Back up at the bow end, the LI structure design would have no need to deviate from the accepted practice of supporting the three-winch mooring system and internationally-accepted “plumb bob” sized to fit all the world’s mooring cups. The diagram shows this design in relation to one of the standard “Empire of the Air” mooring towers.
Of course a regular bow boarding door connecting to the keel walkway is a must—perhaps not as finely finished out as the R-100 seen here (photo).
Likewise, a forward lookout platform would be fitted above the winch room, though on our warship it would be equally useful for shooting at attacking enemy planes via a machine gun mount, as it would the stars with a sextant (as on R-100 in the photo).
Now we have the hull structure design. We follow the recommendations of the Macon “post-mortem report” …
and here she is: Length, 944 feet; maximum diameter 160 feet. 16 bays housing 16 gas cells totaling 12 Mft3. Our USS Long Island could have been constructed in the Goodyear-Zeppelin airdock, even if the major assemblies had to be built by the Naval Aircraft Factory and trucked over to Akron, ZR-1 style. While it would not fit in the Lakehurst hangar owing to length, the rarely used roadside doors could have been removed and the hangar extended.
Admittedly it would not have fit in Scott Field or Sunnyvale Hangar #1 owing to height, so, as the novel suggests, a second hangar would have to have been built at Sunnyvale, perhaps in the current footprint of the WWII era timber hangars 2 & 3.
Command bridge, crew facilities, airplane handling and other parts of the design will be laid out in follow-on posts.