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The excerpt represents the core issue or deciding factor on which you must meditate, and is drawn from Aeroplanes and Dirigibles of War by Frederick A. Talbot: reversed while the engine is running. When one motor only is
being used, the pitch is lowered until the propellers revolve at
the speed which they would attain if both engines were in
operation. This adjustment of the propeller pitch to the most
economical engine revolutions is a distinctive characteristic,
and contributes to the efficiency and reliability of the Parseval
dirigible to a very pronounced degree.
Steering in the vertical plane is also carried out upon
distinctive lines. There are no planes for vertical steering,
but movement is accomplished by tilting the craft and thus
driving the gas from one end of the balloon to the other. This
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