Cockpit of a typical Trainer: Blanik L-23
Each of our aircraft are slightly different. Aircraft instrumentation can change over time. Always review and familiarize yourself with your specific aircraft’s instrumentation before flying.
The altimeter measures the height of the glider above sea level. The glider port is 300 feet above sea level so the altimeter should indicate 300 feet if it is set correctly and the glider is on the ground.
PRINCIPLE OF OPERATION
The pressure altimeter is simply an aneroid barometer that measures the pressure of the atmosphere at the level where the altimeter is located, and presents an altitude indication in feet. The altimeter uses static pressure as its source of operation. Air is denser at the surface of the Earth than aloft, therefore as altitude increases, atmospheric pressure decreases. This difference in pressure at various levels causes the altimeter to indicate changes in altitude.
The magnetic compass, which is the only direction-seeking instrument in the glider, is simple in construction. It contains two steel magnetized needles fastened to a float around which a compass card is mounted. The needles are parallel, with their north-seeking ends pointed in the same direction. The compass card has letters for cardinal headings, and each 30° interval is represented by a number, the last zero of which is omitted. For example, 30° would appear as a 3 and 300° would appear as 30. Between these numbers, the card is graduated for each 5°.
The airspeed indicator displays the speed of the glider through the air in knots. 100 knots equals 115 miles per hour. During flight training, you will typically experience airspeeds in flight between 35 and 90 knots although the glider is capable of going faster.
The airspeed indicator is the only instrument that depends on both pitot pressure and static pressure. When pitot pressure and static pressure are the same, zero airspeed is indicated. As pitot pressure becomes progressively greater than static pressure, indicated airspeed increases. The airspeed indicator contains a small diaphragm that drives the needle on the face of the instrument.
The variometer(aka vario) indicates the rate of climb and descent of the glider in units called knots. One knot is equal to approximately 100 feet per minute.
The variometer operates on the same principle as the altimeter, however, it indicates rate of climb or descent instead of vertical distance. The variometer depends upon the pressure lapse rate in the atmosphere to derive information about rate of climb or rate of descent. The variometer pictured to the left is a mechanical vario. Electrically powered varios serve the same purpose but often include an audio output to that correlates to the strength of the lift that they are experiencing at the moment. The audio output is a beeping noise that varies in pitch and rate of beeping. High pitch and fast beeping correlates to strong lift(rate of ascent). These sounds allow the glider pilots to maintain a good visual scan outside of the cockpit for other nearby aircraft instead of looking at the instrument itself.
When you move the control stick left or right to bank, you are moving the glider around the longitudinal axis – roll. This axis would appear if a line were drawn through the center of the fuselage from nose to tail. When you pull the stick back or push it forward, raising or lowering the nose, you are controlling the pitch of the glider or its movement around the lateral axis. The lateral axis could be seen if a line were drawn from one side of the fuselage to the other through the center of gravity. When you move the rudder left or right, you cause the glider to yaw the nose to the left or right. Yaw is movement that takes place around the vertical axis, which can be represented by an imaginary straight line drawn vertically through the center of gravity.
The glider pilot pulls on the tow rope release handle when she is ready to end the tow.
The trim handle can be positioned to relieve control stick pressure for easier pitch control(nose up and down).
The wheel brake handle actuates the wheel brake on the main wheel of the glider during the landing roll after touchdown.
The microphone is used for speaking on the radio. Most gliders have radios that allow them to communicate with other aircraft and people on the ground.
The yaw string is a short piece of yarn taped to the canopy(clear, plexiglass “windshield”).
- Primary flight reference instrument in gliders
- Valued for its high sensitivity
- Does not require the pilot to look down at the instrument panel
- Even the most sophisticated modern racing sailplanes are fitted with yaw strings
- Referenced constantly throughout the flight
If the yaw string is off center, the glider is flying sideways through the air. This creates undesirable drag when the airflow pushes against the side of the fuselage and at an angle across the wing instead of straight across as it should. The result: an unnecessary loss of performance. It is important to keep the yaw string straight by using the controls properly.
The yaw string dates from the earliest days of aviation, and actually was the first flight instrument. The Wright Brothers used a yaw string on their 1902 glider tied on their front mounted elevator. Wilbur Wright is credited with its invention.