Styling himself as "Captain" Slate for the media (what he was captain of, other than the dirigible, I can't find any record of), the inventor made his fortune by developing a commercially viable method of producing frozen carbon dioxide, and his company came up with the name that we all know it by, "Dry Ice". He then turned around and essentially lost that fortune on Slate Aircraft Corp and his dirigible project, in which he combined a host of technologically radical "better ways" together in one doomed effort. Slate received four patents for various aspects of the airship's concepts.
leased land at the southeastern corner of Glendale Airport (it wasn't yet known as the Grand Central Air Terminal), dug a big trench and started to build the airframe in 1925. Twice, Santa Ana winds destroyed the partially built frame-work. He then built a large hangar (our first image, above) to better protect the project.
In an era when non-flamable helium supplies were tightly controlled and flammable hydrogen was readily available, Slate supposed that he could make the dirigible "fireproof" - keep in mind, this was 6 1/2 years before the Hindenberg disaster - by constructing the shell, or "envelope" from duralumin (the contemporary trade name for the age-hardened copper-aluminum alloy most commonly used in early airship and aircraft construction). The metal was formed into long strips that were interlinked and then riveted together to produce a gas-tight structure, one of the features he patented. To save weight, Slate designed the envelope to be a monocoque structure, with no underlying framework to carry the loads.
|An early advertisement for Slate's dirigible. If you were |
a snazzily-dressed high society type, would you be willing
to get into this elevator?
Another of Slate's patented "innovations" was a passenger elevator system. With it, Slate claimed that the Glendale would not have to land to off-load and take on passengers. Slate envisioned a network of hotels and "stations" across the country where his transcontinental airships would make passenger stops, the first of which was built on the roof of the Glendale Hotel.
To get the passengers up and down, an "anchor", which doubled as a reserve fuel tank, would be lowered from the car on a cable. At the same time, the ship could be refueled while floating high overhead. Once the anchor and cable were secure on the roof of the station, a small, one-person "elevator" would then descend, attached to the anchor cable so that it wouldn't be blown in the wind. Slate's advertisements showed only a single elevator, while the actual patent featured a more complex dual elevator system, with both running up and down independently.
|The original caption is missing from the Archive's copy of this press photo,|
which is date stamped Jan 10, 1929.
published an article on the Glendale in February 1929. As such testing continued through the year, the final touches were put on the ship. One of the design elements that changed were the tail control surfaces, which were enlarged, but clearly still not large enough.
Finally, on December 19, 1929, the Glendale was pulled from the hangar for final checks, and on the 20th, a crowd of several thousand gathered to watch the pride of the city take flight for the first time. It was a rather warm first day of winter in Southern California, and the sun on the aluminum shell quickly began to heat the hydrogen, which naturally expanded. Slate had expected this, and designed pressure relief valves, but on this day, they stuck. As the giant airship finally began to rise, the pressure inside exceeded the structural strength of the envelope, and rivets began to pop, sounding to some like gunfire; the crowds scattered. As the hydrogen escaped, the Glendale ingloriously settled back to the ground. One aspect of Slate's goals was achieved, however: despite the rupture, the craft did not catch fire.
article in the July 4, 1930 edition of the Berkeley Gazette (buried on page eleven, and full of other errors, so I don't consider it terribly reliable) indicates that some rebuilding was attempted and that a subsequent test flight was to be tried. However, there are no records that this actually came to fruition.
|A comparison of the tail surfaces from January 1929 (left) to December 1929.|
In an ironic twist, ten months after the failure of the Glendale to achieve her maiden flight, one of Slate's engineers, A. H. Watkins (who filed Slate's UK patents) was serving as a crew member on the British airship R101 when it crashed and burned; Watkins was one of 48 killed and his body was never identified.
But if the Glendale hadn't come apart at the seams, would it have actually worked? For the rest of this article, we'll dive a little deeper into the technical and engineering aspects of Slates designs, as described in the actual patents (so if you're not an engineer, you just might find the rest a bit boring...you've been warned!).
Slate said the blower would take "a great volume of air in at its forward open end and discharge it in a solid radial sheet at the periphery of the fan...so that the rear surface of the of the current of air...comes in contact with the surface of the nose of the ship. The fan is open at both ends, and a suction from the rear end of the fan pulls the radial flow of air tightly against the surface...at the point of contact and thus seals the passage, the current of air following the contour of the ship."
Slate went on to describe his aerodynamic propulsion concept by stating, "The tendency of a great volume of air discharged from the fan at high speed is to cause a less than atmospheric pressure between the surface of the ship and the air flow, causing the ship to move toward the radial air stream at a speed goverened by the velocity given to the radial air stream by the fan." Low pressure in front, normal pressure in back, the ship should move forward, as Slate saw it.
To aid in this effect, Slate believed his idea would reduce the ship's form drag, which he described as the "vacuum" behind the craft. He said that "The great volume of air thrown around the nose of the ship and past its largest diameter at high speed, then loses its velocity and begins to replace immediately behind the ship the space occupied by that portion of the ship, thus allowing the ship to travel on without producing a partial vacuum behind the ship. This result relieves the power plant of the burden of pulling a volume of air behind the ship for replacement."
|Close-up view of the impeller as it was seen in January, 1929.|
Slate believed that the "solid radial sheet of air" would bend back along the surface of the envelope, and besides the direct result of producing propulsion, would also have some additional benefits. The first of these was that the airflow would eliminate the problem of parasite drag (the drag imposed on an object as it encounters and pushes out of the way the static air ahead of it). "The remaining volume of air in front of the ship that does not flow through the fan will be entrained into the stream of air flowing from the fan at high velocity and will follow the contour of the ship without building up pressure on the nose of the ship, and will pass the volume of air for the ship's displacement past its largest diameter at high speed. Consequently, pressure on the ship's hull is relieved."
He was obsessed with the ship's stability in "cross currents". "Complete replacement [ie, complete elimination of the turbulence created by form drag] of the air following the passage of the ship tends to hold the rear end of the ship steady and will not allow it to swing around from one side to the other of the area displaced by the ship. If a ship is forced through the air by the ordinary means and has to draw its displacement from the surrounding atmosphere it will bring it from the course of least resistance and if the atmosphere is at all disturbed by wind or storm conditions this course of least resistance is liable to be from any direction, causing cross currents over the rear of the ship where the rudders are located."
Granted, in the era when Slate was working, the sciences of aerodynamics and fluid dynamics were still very immature, so it's not surprising that concepts which seem obvious to engineers today were relatively unknown then. Slate had shown his knowlegebility over the years for engineering refridgeration concepts (besides the commercial dry ice manufacturing process, Slate held numerous patents for refridgeration-related inventions), and while these deal in manipulating fluid pressures, he certainly does not seem to have had any formal training or professional experience in aerodynamics.
Thus, it seems that Slate made some fundamental mistakes in his understanding of airflow, thinking that the blower would produce a "solid sheet" of air that would produce the pressure drops and the cushioning effects that he imagined. With the impeller completely unducted, all that would be produced in front of it would have been turbulent, circular airflow as the output swirled around and compensated for any low pressure that might be present from air being pulled into the fan. In addition, Slate never seemed to account for the turbulent interaction between his supposed sheet of air and the ambient air, an interaction that would all but eliminate any flow all the way to the widest part of the hull, much less all the way to the tail. Finally, while the concept of laminar flow hadn't been enumerated in Slate's time, the hull of the ship, with protruding-head rivets, would not have been conducive to the laminar flow needed to produce the kind of pressure differences that Slate imagined.
In a way, then, the structural failure due to the faulty valves was a really a blessing in disguise, as it saved Slate from the embarrassment of the ship making lots of noise but going nowhere, and publicly finding out that the propulsion concept was a complete dud.