USS Long Island: Theory & Design – Part One

Unlike a different outcome to the Battles of Thermopylae, or Hastings, or Gettysburg, a dreamer dabbling with rigid airship history has a shorter working time period, and limited technological options. Narrowing our focus from the generally possible to the more likely scenario is much more complicated. Some have already speculated what might have happened if Captain Pruss had simply refused the American’s request for a “high” landing: LZ-129 could have made an ordinary on-the-wheel touchdown on May 6, 1937. A world in which Hindenburg’s return with 70 passengers on May 9th in time for King Edward’s coronation, accompanied by the routine launch of Graf Zeppelin on his scheduled May 11th South American run, has long generated speculative debate. Remember that, even after the fire, the Germans had started on LZ-131, whose extra bay would have given that airship a volume about 9 Mft3.

clip_image005

As we have seen on the ZRCV page, logical arguments for much larger airships had been made by men in the know. VADM (then CDR) Rosendahl and even CAPT Buckley (then a young midshipman, later co-author of the 1943 privately published book at left) had flown aboard LZ-129. However these discussions came years after the harsh economic times of 1939. In the real world, where the US Government had been unable to spend itself out of a depressed economy, it was a sure sign of the Administration’s contempt for Goodyear-Zeppelin when the bill HR 3519 of 1939 authorizing construction of a 300-ton Naval Airship never got off Capital Hill for a most certain Presidential veto. (Specifically, ZRCV would have been about 300 tons, vs. LZ-129’s about 242 tons.)

SIZE MATTERS

For the more airship-friendly “ZRS” universe, Burgess’ ZRCV is clearly too small a step. Author Rowan Partridge envisioned Long Island as 12 Mft3 , and we’ll show why we think this about right.

Ismal mast

As we have speculated on the Empire of the Air page, Scott and R.101’s delayed departure would have been pivotal in completion of the “Empire of the Air.” Direct flights to Canada, one-stop trips to India and few-stop trips to Auckland, Sydney or Singapore would in turn have created competition pressure for the German passenger service.

Later, with the German assembly shed extended and their LZ-131 “Super Zeppelin” under construction, 9 Mft3 was the new target. The Americans, at first hobbled by the BofM fraud cutting H2 flight funding, would have continued to believe their own propaganda, and stood behind the eight-ball of helium’s fixed, lesser lift for the dollar. As we see on the ZRS-4 Evolves page, the Americans had been forced to enlarge, to avoid performance embarrassment.  With R.101’s announced capacity of 5 Mft3 the Americans had revised to 6, then 6.5 Mft3, for the Akron/Macon design to keep pace. The Americans would have certainly repeated the airship enlargement process to stay “competitive” in performance.

These figures agree with a British study offering an explanation of their refusing the offer of American helium. P. L. Teed’s paper showed that, to perform like a 9 Mft3 hydrogen rigid, a helium ship would have to be 12 Mft3. Thus we arrive at the first parameter of our hypothetical American rigid airship within the given time/technology limitations – precisely at Rowan Partridge’s envisioned, twelve million cubic feet. That’s a good deal smaller than the Buckley/Barkley vision of 1943, but correctly beefing up the ZRCV reflective of the helium penalty in relation to the LZ-131.

The especially good news is, given the circa 50% increase in payload by conversion back to hydrogen from any design originally enlarged to be competitive with helium, Partridge’s Long Island would be comfortable with full fuel load and aircraft complement even in the vast reaches of the trackless South Pacific that had swallowed so many airplanes (Amelia Earhart being just one) in the past.

In the film production we will stick with Rowan’s overall vision for the basic size and overall design. We will pay special attention to the previous state of the art. We will take direction from those men who flew rigids, and had their own ideas as to the design details of the next generation.

FINENESS COUNTS

The fineness ratio – defined as the relationship of length to diameter – delivered reproducible drag values in rigid airships. Therefore it is possible to predict performance of anything from the football-shaped ZMC-2 (above left) to the torpedo-like stretched L-59 (LZ-104) “Africa ship” (above right). It comes as no surprise that all three of the last rigid airship designs—Akron/Macon, LZ-129/130, and ZRCV—were all within a tenth of a point of each other. We think it logical to split the difference, resulting in Long Island’s fineness ratio: six.

Blessed with the assistance of Mr. Norman Mayer, who had relieved C. P. Burgess at BuAer, the next step was easy. Plugging in the fineness ratio of 6 and the desired volume of 12 Mft3, the formula that Mr. Mayer created (for his AIAA paper and presentation at Bedford, England) yields our airship’s precise dimensions: Length, 944 feet; maximum diameter 160 feet.

From this point forward there are many options, each with their own followers and champions, and no preset formulas to plug in. Dr. Richard K. Smith in his The Airships AKRON and MACON: Flying Aircraft Carriers of the U.S. Navy discussed these options: “The British… in their R100 found their answer… using Barnes Wallis’ novel geodetic structure… and by using deep rings in their R-101. The Germans found their answer by using a supplementary axial keel… the Hindenburg and the Graf Zeppelin II, which ran through their hull’s centerline, of itself a radical departure from the so-called “conventional” Zeppelin… [USN BuAer’s] C.P. Burgess believed that an appreciable increase in performance could be realized through a radical break with the past, by discarding the archaic redundancies of the classic Zeppelin structure for the simplicity of Ralph Upson’s stressed-skin Metalclad design… [thus, with the tri-keel ZRS design of Karl Arnstein] …there were four different answers found to the same problem, and it is doubtful if the alternatives were exhausted.”

In this photo,  Arnstein looks over a special heavy-duty girder section with then-inspector LT “Tex” Settle, right. This larger, heavier type was seen in the hangar bay and other selected ZRS-4 & 5 assemblies.

Indeed, with airplane structures turning to metal, leaving only control surfaces fabric-covered, regardless of girder design, acres of nitrate-doped cloth would still be the weak point. R.101 design engineer V. C. Richmond said “… the fabric work of the rigid airship (i.e. the gas bags and the outer cover) represents the least satisfactory part…” Therefore, the wild card in any construction speculation is the stressed skin or “metalclad” airship which promised lessened manufacturing cost, and flame-safe operation with hydrogen. In the novel, Partridge speculates a balance was struck with the ship’s covering called “metalfoil.” For screenplay purposes, we will speculate the Germans figured out how to add bronze to the covering mix for conductivity, fireproofing and longevity, a few years before they actually did so. Perhaps during the 36-37 overhaul, or even earlier, but once done others had easily followed suit. Therefore, we will be forced to turn our backs on Ralph Upson and what C.P. Burgess called “the ultimate airship” – at least until (perhaps) the sequel.

THINK OUTSIDE THE BOX

Rosendahl wrote, “That German airship men did not like the AKRONMACON design is not exactly a secret, for privately and diplomatically they let us know it. Their main objection centered about our built-up form of main frame, and our use therein of square or ‘box’ girders rather than the previously accepted triangular girder.”

Before R-101 and Akron-Macon, girder design had changed little since before Zeppelin (Schwarz girder, left, 1898). Even pieces of the ZR-1 Shenandoah show a similar basic structural girder design. For the ZRS-4&5, Arnstein’s patented lightening holes were stamped into a sheet whose edges were formed to join with others like it. These were riveted together to form a box beams on bench jigs (photo).

These beams were used extensively in the structure of ZRS-4 & 5, including forming them into the arch-like constructions to create main rings.

By the later 1930s Arnstein had abandoned his complex box girder  in favor of what looks more like “previously accepted triangular girder” in Rosendahl’s Rigid History motion picture clip. The test section found in the Airdock supports this notion. Using ALCOA 24S the new girders could have been spot welded, easing the more complex jig-dependent process of drilling and riveting. Given that our basic building girder will be more “triangular,” without actually being able to employ the simple but strong tubular structures in use today, we can move on to the form used to employ the girders to make a structure.

ONE RING TO RULE THEM ALL

R.101 featured built-up rings whose continuous triangle was more injury-resistant and perhaps less wire-tensioned than earlier methods of building circular flyweight structures.  R.101’s rings (photo) supported the heavy pinpoint loads of diesel fuel tanks. There were no intermediate rings like those in the ZRS-4 & 5. In fact, it has been suggested the R.101 had no actual keel in the “conventional” sense. The R.101’s rings did not enclose the same triangular area as Akron/Macon’s  ladder-equipped main rings, but did allow some access impractical with conventional Zep design.

ZRS-4 & 5 used a similar, but heavier continuous pyramid-like ring design, which in the case of battle damage, was supposed to retain its circular shape. These eliminated the finely tensioned bicycle-like spoke-like wiring used to support the Zeppelin ring shape, let alone the complex and cell-complicating axial cable or corridor. Their interior ladders offered previously unknown access to the ship’s interior and its fittings.

As seen in the assembly films, the more fragile intermediate rings were attached to the mains for hoisting during assembly  in Goodyear-Zeppelin’s Airdock. Carefully spread out for more box beam girders to be added as longerons,  each bay took shape. (The ZRS–4 & -5’s ALCOA 17S structure was said to contain 6.5 million bucked rivets. )

For our USS Long Island, we will retain this built-up main ring  as a compromise between the R.101/ZRS4/5 and the later ZRCV more conventional ring design. We will reduce its height slightly to decrease the overall wasted non-gas space.

With ZRS-4, bay VII had been the first to be completed,  and was the first to be tested by installation of a gas cell and inflated with helium. In both ZRS ships, bulkhead wiring prevented a full cell from surging into an adjacent deflated-cell bay. These were fastened to the main rings with “resiliency devices” (marked with an “R” in the photo) which worked somewhat like automobile shock absorbers, and managed the tension of surging cells. The combination was designed to prevent adjacent cells from squeezing into nearby bays whose cells were deflated.  Various photos show cells purposely overpressurized to test the construction and design, thus resembling a sort of quilted blanket.

Our typical Long Island bay will be generally similar, likely with one smaller intermediate ring spacing owing to our larger number of bays and cells. There will be retaining bulkhead wiring to prevent surging.

It should be noted that, once designed and built, only to find performance expectations not met in the real world, it’s rather difficult to change airship capacity by enlarging the diameter. Therefore it was not uncommon to cut a rigid in two, so an extra cell could be inserted for more lift. (C P Hall has pointed out R-101’s extension spoiled her perfect aerodynamic symmetry and that structural section did not fare as well in her final impact. Yet, our movie will  have yet another bay added to our “R.101D”.)


So far, then, we have resolved to use ZRCV-like channel girder material in the construction of ZRS-4 &-5 like “main rings.” This offers compromises the designers of 1937-1938 would have considered the best choices, for crew access, least wasted non-gas enclosed area and damage resistance. For the movie, our USS Long Island set can use less complex tubular material to simulate spot-welded girder sections. A set including some lower-third main ring sections above will have to be built to support hangar bay and habitable sections where actors will perform their scenes. Intermediate rings would not normally be seen, obscured by fabric walls or simulated gas cells, which will easily be incorporated into the set.

Now we need only decide how all the rings will be joined together to form the framework, which will be addressed in the next post.

Read on to Long Island Part Two

Back to Home Page