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The ground handling of airships is complicated as a result of the fragility of the airship structure, its continual variation in buoyancy (internal temperature lags behind ambient), and the large surface it presents to the wind (Camplin 167ff).
All airship operations are affected by the wind, and the effect is far greater than on aircraft, because airships are so much larger. The force exerted by the wind on an airship is proportional to the projected area perpendicular to the wind, and to the square of the wind speed.
Similar forces of course are exerted on the sails of a sailing ship. At sea, if winds get too strong, sailing ships reduce sail. In extreme conditions, they may sail “bare-poled.” Even then, the force of the wind on the exposed portions of the hull can be considerable. But airships can’t “reduce sail,” they must remain fully inflated to be buoyant.
Takeoff, landing, and ground handling are dangerous because a sudden loss of buoyancy can drive the airship into the ground and damage it, and a sudden wind gust can carry the airship into a ground hazard, or aloft and off into the sunset.
According to Camplin (166), of the rigid airships lost 1900-1940 other than from enemy attack, 25% were lost during landing and 10% during ground handling. And looking at US Navy blimp accidents 1946-61, 49% involved takeoff or landing, and another 33% were on the ground.
Unmoored Takeoff and Landing
Early airships generally took off and landed from open areas, and were walked to and from hangars. Dick provides a good description of the procedures followed by the Graf Zeppelin, a large rigid airship.
For takeoff, the airship faced upwind, held down by the ground crew. Facing upwind minimizes the effect of the wind on the airship. (If you imagine an airship as a cylinder, the area presented to the wind is π*r2 for a headwind (or tailwind) and 2*r*L for a crosswind, so the area is reduced by the factor (2/π)*(L/r). And streamlining reduces the wind force further.)
The airship dropped ballast to make itself lighter by 900-1200 pounds (the Graf Zeppelin had a useful lift of 60,000 and gross lift of 210,000 pounds) and on the command “Let go” (American crews said “Up Ship!”), the ground crew released it (on smaller airships, they actually threw the airship up). It started up engine #1 at 150 feet and all engines would be idling by the time it reached 300 feet. It typically cruised at 575-820 feet (Dick 48, 67).
If circumstances dictated that it take off facing downwind, it would let the engines idle, and make lift aft so the tail ascended first. This caused the ship to be lifted dynamically (109).
For landing, it would contact the ground to determine the landing conditions. It then faced upwind, idled the engines, and “weighed off.” If conditions were calm, it would adjust buoyancy to neutral. If the air was bumpy, it would make itself statically light but hold the nose down to generate negative dynamic lift. It would increase speed and make a long approach with the nose down. The rate of fall was perhaps 100 feet per minute. Once it was over the field, it reversed the engines to bring it to a stop and dropped lines for the ground crew (70). Note that while the approach was a downward glide, it still hovered over the landing site and then was pulled down.
The AS105, one of the world’s few hot air airships, requires a launch or landing site of 80 meters square, and a ground crew of three to four. The maximum wind speed is not supposed to exceed 8-12 knots (depending on pilot experience). With the envelope alongside and attached to the gondola, the envelope is about three-quarters inflated with cold air, and then hot inflation is started, mostly with the rear burner so the nose stays down. The crew on the nose lines keep the envelope level as it inflates and moves up over the gondola. With the envelope buoyant, they bring it precisely into the wind. When the envelope reaches takeoff temperature, the pilot commands them to release the nose lines and the AS105 climbs vertically (GEFA-FLUG).
Landing is also made into the wind, with the engine turned off just before touchdown, and the ground crew catches the nose lines to bring the airship to a complete stop. The burners are cooled, the rip panel in the envelope is opened, and the envelope is disconnected from the gondola. The residual air is pressed out and the envelope packed up.
Prior to WWII, Goodyear developed a rolling method of takeoff and landing, used by small helium-filled blimps. They took off statically heavy, taxiing down a runway and lifting their nose to generate enough dynamic lift to become airborne, like airplanes (Khoury 281)
As the blimp decelerated for landing (whether by brakes on the wheel, reversing its engines, or ground crew pulling on nose lines), the nose dropped because of the high center of gravity of the airship (Camplin 43).
These procedures require that the blimp have an undercarriage similar to that of an aircraft, i.e., with wheels (or skids) and shock absorbers.
A rolling takeoff is probably not feasible for a large airship, which would need a much longer runway to build up the speed to give it sufficient aerodynamic lift, and which can’t count on having such a runway pointing upwind (Camplin 41).
Airship Hangars in Canon
In Spain, an airship hangar houses the semirigid Richard Peeke in May 1635. The hangar ”looked to be about two hundred feet long, with a central span that looked nearly as wide as it was high” (“nearly eighty feet”) (“Modern Medicine,” Offord, Grantville Gazette 36). There is also a larger hangar under construction, intended to protect a transatlantic airship, the São Martinho. The latter is based on the SL20, and it appears likely that the new hangar has a 30 by 30 meter front and is more than 170 meters long (the airship length), (“A Trans-Atlantic Airship, Hurrah,” Offord, Grantville Gazette 36).
In Copenhagen, in October, 1635, the Danes began clearing the foundation for their first airship hangar, and gathering construction materials for the airship (and probably also the hangar) (“No Ship for Tranquebar,” Evans & Evans, Grantville Gazette 27). In late December, 1635, after consultation with Marlon Pridmore, the Danes decided to build a hangar about 700 feet long and 90 feet high; this was to house an airship about 650 feet long and 70 feet in diameter. This was about two-thirds the size of the Graf Zeppelin, the airship the Danes had previously been using as a reference (“No Ship for Tranquebar, Part Two,” Evans and Evans, Grantville Gazette 28).
The construction was faster than it might have been because the Danes had already prepared frames for the construction and dug post holes, before they settled on the dimensions of the airship (and thus the hangar). It appears that the day after Pridmore tells them the necessary dimensions, the framework is “lifted into the sky.” It is unclear how soon the hangar is completed, but the implication is very soon after that, and the hangar is in use for airship frame construction at least by April, 1636.
As to the structural design of the hangar, we are told, it’s “not unlike an oversized version of the cattle barns you find all over the country.” There are big tied arches that presumably bridge the width of the hangar, and there are small arches that form the dormers (and an unspecified number of these small arches establish the length of the hangar). There are windows in the dormers, and the hangar has a brush pile and thatch roof. To keep the structure from blowing away, it is tied by cables to ground anchors.
There is also an airship hangar in Russia, to house the Czarina Evdokia (Flint, Huff, Goodlett, 1636: The Kremlin Games, Chapter 82). The airship was the same shape as the Graf Zeppelin, if a bit smaller (Chapter 83).
The specifics of the Swordfish-class airship bases constructed by Estuban Miro in the USE are not yet revealed by canon. However, the time aloft for a hot air airship is more limited than for one using hydrogen lift because it must burn fuel to generate buoyancy. So that implies that “hot air” airship bases shouldn’t be far apart. We do know that Miro contemplated the use of the airships to “transport high-value items a hundred miles in three hours” (Flint and Gannon, 1636: Papal Stakes, Chap. 4), consistent with the 35-mph top speed stated in “Upward Mobility”, and that a journey from Grantville to Brescia, Italy is carried out in four legs, with a flight every two or three days (“Upward Mobility,” Gannon, Ring of Fire III). Whether those bases are true hangars or just mooring masts remains to be seen.
By July, 1636, a Dutch consortium has a wooden hangar in Hoorn. Rita Stearns and Bonnie Weaver estimate its interior dimensions as being, as a bare minimum, “five hundred feet long, sixty feet wide and sixty feet high.” Moreover, it rested on “what amounted to big barges” floating just offshore, anchored most of the time and freed to rotate with the wind when an airship was taking off or landing (Flint, 1636: Ottoman Onslaught, Chapter 30). The advantages and disadvantages of floating hangars are discussed below.
If the purpose of the hangar is to provide a safe place in which to assemble or make major repairs to a rigid airship, the most important considerations are 1) easy access to the necessary materials (e.g., by a harbor or on a navigable river or rail line so the materials can be brought in or by a forest if wooden construction is intended), 2) availability of the required labor force, and 3) security from enemy attack.
If, instead, it is to be an operational base, then other considerations come to the fore: 1) the intended destinations are in range of the airships to be operated from this hangar, 2) it enjoys favorable weather conditions (relative freedom from fog, storms, and high winds) and 3) it is at a low elevation (altitude reduces lift). Moreover, if intended for military operations (scouting or bombing), it may have to be closer to the enemy than would otherwise be desirable.
It was of course very frustrating when a military airship couldn’t embark on a mission because the wind kept it from leaving its hangar. At airship bases with several hangars, each might be deliberately given a different orientation to improve the odds that one airship would be able to fly out.
Stationary Hangars (Sheds)
These are essential for the assembly, maintenance, and storage of rigid airships, and have also been used for nonrigid airships when inflation would be inconvenient (for example, the envelope is filled with precious helium, or the airship must be ready to fly on a moment’s notice) but the craft must be protected from the weather.
The first purpose-built airship hangar was Hangar Y in Paris, built in 1876 at Chalais-Meudon and used by the pioneering airship La France in 1884. It had a peaked roof, giving it a pentagonal cross-section. It had a length of 70, width of 24, and height of 20 meters. Near the top of the walls was a row of windows that provided natural lighting.
Ideally, the hangar is oriented “so the cross wind component will be a minimum under conditions when it is likely that the airship will be docked or undocked” (Fulton 55). If a hangar in the new universe is to be sited in a settled area, the inhabitants will have some idea as to the direction and strength of the prevailing winds at different times of year. If you are very lucky, there is some local scholar who has kept a weather diary. Of course, prior to the Ring of Fire, there was no apparatus routinely used to measure wind speed or even an objective scale for wind speed. See "Fair of Foul: Part 2, Observing Pressure and Wind," Cooper, Grantville Gazette 73.
For authors who want to know the prevailing winds of any locale (whether their characters know them or not), I recommend looking at meteoblue. It uses a climate model to calculate a “wind rose;” here is an example for Hoorn:
You can specify latitude and longitude for any location and get a wind rose.
If the hangar is located in an area where winds come often from any of several directions, or shift suddenly, a rotating hangar may be desirable. But first we analyze the problems common to all hangars.
The fundamental design problem is that airships must be large in order to have a useful lift. That means that the length, height, and width of the hangar must be large enough to accommodate the airship and the assembly or maintenance crew and equipment. Moreover, the support for the roof ultimately comes from the ends and sides, as the interior space cannot be obstructed with columns, and at least one end is compromised by needing an opening large enough for the airship to enter. (And if there is an opening at only one end, then the airship must either leave or enter tail-first.)
In designing a hangar, bear in mind the following. First, even though the balloon (hull, envelope) usually has a circular cross-section, the fully rigged airship will have a height greater than its width, because the gondolas (cars) are suspended below it (unless built into the ends of the streamlined hull of a rigid airship). For example, on the Italian semirigid Roma, the beam was 25 meters but the height 27.5 meters (Aerial Age 11:478). USS Shenandoah was 79 feet wide and 93 feet high (Wikipedia). USS Akron was 132.9 feet wide and 146.5 Feet high (Allen 76).