Buoyancy compensator (aviation)

The static buoyancy of airships is not constant during a run. It is therefore necessary measures are taken in order to control the lift and the flight altitude, the so-called buoyancy compensation.

Responsible for the changes are different effects:

• Change in air temperature (and thus the density of air )
• Changing the carrier gas temperature ( for example, by heating the envelope in the sun )
• Fuel consumption
• Issuance of additional ballast ( for example, rainfall on the cover)
• Discharge of ballast ( for example during a flight maneuver or dumping of loads )

Airships can compensate for this buoyancy changes in different ways.

• Using dynamic on - or -off ( see: Dynamic buoyancy)
• Increase in lift ballast discharge. This usually happens by releasing specially entrained ballast water. With balloons sand is often dropped
• Buoyancy reduction by releasing the lifting gas or recording of additional ballast.
• By changing the density of the carrier gas ( heating = buoyancy increase, cooling = buoyancy reduction )

• 2.2.1 dew and rainwater from the shell
• 2.2.2 Water absorption from the ground
• 2.2.3 silica gel method
• 2.2.4 condensation of exhaust gases

• 2.3.1 Traggasvorwärmung
• 2.3.2 carrying gas cooling

Boost from fuel consumption

Especially in the historic Great airships (especially with the Zeppelins ) the problem of increasing buoyancy has been given some attention by consuming the fuel.

LZ 126 used for example in the transfer from Friedrichshafen to Lakehurst 23,000 kg gasoline and 1300 kg of oil ( average consumption of 290 kg/100 km). During the landing, therefore, had about 24,000 cubic meters of hydrogen to be drained in order to end up with a statically balanced ship can.

On a trip from Frankfurt to Lakehurst with an airship in the size of the Hindenburg tonnes of diesel were consumed about 54. This corresponds to the buoyancy, generate the 48,000 cubic meters of hydrogen. If this value is compared with the total lifting gas volume of nearly 200,000 cubic meters, it is clear that this represents almost one quarter of the total. This amount had to be replaced at the destination airport by new carrier gas.

Buoyancy compensation

Was monitored at Zeppelin two strategies to prevent the discharge of carrier gas:

The Zeppelin NT has no special facilities to balance the buoyancy gain by fuel consumption. It compensates to a by a starting weight that is greater than the buoyancy, so that at the start of and during the flight, a part of the lift is generated by the motors (dynamic buoyancy). Just as he can, if he is lighter than air during flight, landing with the help of the swivel motors and then resume ballast on the ground. The relatively small size and a range of only 900 kilometers (compared to the historical Zeppelins ) allowed the waiver of a ballast recovery plant.

Power gas

As a fuel, with a density similar to or equal to that of air, only a gas in question.

Hydrogen

There were attempts to burn a portion of the carrier gas hydrogen gas in the engines as power, such as LZ 129 However, the attempts were not very successful, and this possibility of buoyancy reduction accounted for the intended use of helium as carrier gas.

Blue gas

As a force gas therefore called blue gas was used. The term blue gas goes back to the Augsburg chemist Hermann Blau, who in 1905 produced the first blue gas in the gas factory in Augsburg Blue Straße. Various sources suggest that this is propane, butane or a mixture, which is usually known in the form of LNG.

However, in the case of Zeppelin a mixture of propylene, methane, ethylene, acetylene ( = ethyne ), butylene, and hydrogen was used.

LZ 127 "Graf Zeppelin" led some rides through with force gas. For twelve fuel gas cells were used which were able to reach a total volume of up to 30,000 cubic meters. This amount was sufficient for 100 hours driving at cruising speed. The fuel tank volume was sufficient for a maximum of 67 hours driving. For long trips, a gasoline and gas power supply for up to 118 hours of driving or 13500 km range was carried. The volume that was occupied by the gas and therefore does not force the carrier gas was hydrogen available, could be used, since no additional buoyancy for the liquid fuel to be consumed must be provided.

Ballast water extraction

In the airship operation, four sources of water were as follows:

• Humidity
• Precipitation on the envelope
• Waters on the ground ( sea, rivers, lakes, ...)
• Water vapor produced by the combustion of the hydrogen contained in the fuel with the oxygen in the air

Dew and rainwater from the shell

In the airships LZ 127 "Graf Zeppelin and LZ 129 " Hindenburg " were tentatively gutters attached to the hull to collect while driving rainwater and so to fill the ballast water tanks. However, this process is strongly affected by weather and therefore can not be reliably applied.

Water absorption from the ground

Water from the bottom can be recorded from the overflown water bodies such as lakes or ocean.

1921 Ballast Creator with the airships LZ 120 "Bodensee" and LZ 121 " North Star " was tested before the airships had to be handed over as reparation on Lake Constance. However, these attempts did not produce satisfactory results.

Silica-gel method

The granular silica gel desiccant (silica gel), dried before use by heating may absorb water from the atmospheric humidity. Through this chemical process, the weight of the airship increases. This procedure was tested at LZ 129 Hindenburg, but discarded again.

Condensation of the exhaust gases

The most promising method for obtaining ballast while driving is the condensation of the exhaust gases from the engines. Fuels consist usually of hydrocarbons. In its combustion occurs mainly water (vapor ) and carbon dioxide. Usually these reaction products of combustion through the exhaust into the environment are given. However, you cool down the exhaust gases, so the water condenses and can be collected. Theoretically, the more mass produced than is lost by the fuel consumption. Main factors influencing the recoverable amount of water, the type of fuel used ( hydrogen content ) and the humidity.

However, complex exhaust gas cooler are required for this procedure. Also, there was in the early years always had problems with corrosion.

Already at DELAG Zeppelin LZ 13 "Hansa" ( 1912-1916 ) which is designed by Wilhelm Maybach on behalf of Graf Zeppelin equipment has been tested. However, the attempts were not satisfactory, so they were abandoned for the time being.

ZR- 1 USS Shenandoah ( 1923-25 ​​), the first helium-filled airship, according to the U.S. Navy was the first airship was recovered in the ballast water from the condensation of exhaust gases. In LZ 126/ZR-3 USS Los Angeles the hydrogen carrier gas was replaced by helium after the arrival of the ship in the U.S.. To the precious helium not to drain unnecessary, a ballast water recovery plant was retrofitted in this context also.

The water should be used on board the airship (for example, LZ 130) as process water. ( Hindenburg, LZ 130, USS Akron, Cargo Lifter CL160, LoftyCruiser )

Temperature change of the carrier gas

Changes in the carrier gas temperature relative to the surrounding air causing a buoyancy gain ( Traggasvorwärmung ) or loss of lift ( lifting gas cooling). The technical implementation requires a lot of energy, as the lifting gas cells against the environment are isolated only by the gas cell wall, an air layer and the airship envelope.

In practice, this method has already been applied for almost all rigid airships, more or less consciously, by used the temperature differences between day and night, surroundings and airship hangar as well as the differences in different layers of the atmosphere.

Traggasvorwärmung

To compensate for the higher wing loading, was experimenting with Zeppelin in any Traggasvorwärmung. So at LZ 127 Graf Zeppelin was warm air to lifting gas cells blown past in order to heat it. The aim of the preheating was to get a boost profit for the launch. During the journey, the carrier gas then allowed to cool again. The lowering of the buoyancy was first balanced by dynamic lift. At the destination airport had then consumed a large part of the fuel and so again achieved a buoyancy gain.

Hot -air airships generate hot air balloons as their total lift by heated air, which also receives the exhaust gas of the heating flame. Do not use special lifting gas.

Carrier gas cooling

There are no technical equipment were used for carrying gas cooling ( buoyancy decrease) in airships. Except for the German LoftyCruiser project no concrete ideas in this direction are known. However, the weather effects were used to obtain the air vessel has a lower temperature than the surrounding air. So airships landed very often in the evening. Often they circled therefore still above the landing site or took " detour " during the approach to their destination.

In the evenings, the air and thus the lifting gas cools. Near the ground, but the air stays warm longer because the soil so that the heat absorbed during the day. Thus it was possible to end up with a reduced buoyancy through a cooler carrier gas warm air layers. If this was not possible, or the lift still higher than the ship's weight, so had to be compensated with dynamic output remaining difference of lift. Further ropes were dropped, with which the ship was pulled to the ground. This was done by holding teams, there were also experiments with motor powered winches ( for example, LZ 130), to reduce manpower requirements. At the bottom of the ship was then moored and immediately filled with ballast. Of course, carrying gas could be vented.

Other forms of propulsion

Another way to avoid the consumption of fuel and the resulting problems, this easy to dispense and use other forms of energy.

• Solar airships store the energy in batteries. Their mass is therefore not changed.
• There were also several concepts which provided for nuclear reactors as a power source. They originate mainly from the 1960er/70er years and did not come on the drawing board out.
• Another possibility is the supply of the airship with energy from the ground, for example by microwaves. Such Airship Model with 17.5 m length and 10 kW beam was developed in Japan by Onda in 1995 and tested in practice ( HALROP ).