The axis taken parallel to the length of the wings, and through the center of gravity. This is sometimes called the "Y" axis.
An axis passing fore and aft parallel to the center line of the propeller. This axis is sometimes called the "X" axis.
A vertical axis, passing through the center of gravity, around which the machine swings when being steered in a horizontal direction under the action of the rudder. This is the "Z" axis.
B
BALSA WOOD.
A very light wood obtained from South America. It is lighter than cork.
A form of aircraft of the lighter than air type comprising a gas bag and car. It is not provided with a power plant, and depends upon the buoyancy of the gas for its sustentation. A balloon restrained from free flight by means of a cable is known as a "Captive balloon." A kite balloon is an elongated form of captive balloon, fitted with a tail to keep it headed into the wind, and is inclined at an angle so that the wind aids in increasing the lift of the gas.
A small air balloon within the main gas bag of a balloon or dirigible used for controlling the ascent or descent, and for keeping the fabric of the outer envelope taut when the pressure of the gas is reduced. The ballonet is kept inflated with air at the required pressure, the air being controlled by a valve or by regulating the speed of the blower.
To incline the wings laterally when making a turn so that a portion of the lift force will be opposed to the centrifugal force.
An instrument used for recording pressure variations in the atmosphere. The paper charts on which the records are made are used for determining the altitude of aircraft.