GPC - Glider Pilot Certificate Aircraft Systems and Instruments Questions and Answers — Questions and Answers
Question 1: A glider's pitot-static system provides data for which combination of instruments?
- Airspeed indicator, compass, and variometer
- Altimeter, attitude indicator, and airspeed indicator
- Airspeed indicator, altimeter, and vertical speed indicator (variometer) (Correct answer)
- Vertical speed indicator, yaw string, and altimeter
Correct answer: Airspeed indicator, altimeter, and vertical speed indicator (variometer)
The pitot-static system measures and compares ram air pressure (from the pitot tube) and static pressure (from the static port). This information is used by the airspeed indicator, the altimeter (which uses only static pressure), and the vertical speed indicator or variometer (which measures the rate of change of static pressure).
Question 2: During a pre-flight inspection, you notice the yaw string is frayed and partially detached. What is the primary consequence of flying with a malfunctioning yaw string?
- Inaccurate airspeed readings during turns.
- Difficulty in maintaining coordinated flight. (Correct answer)
- Incorrect altitude indications in windy conditions.
- The variometer will show a constant climb.
Correct answer: Difficulty in maintaining coordinated flight.
The yaw string is a simple and crucial instrument that indicates whether the glider is in coordinated flight. It shows the direction of the relative wind. A malfunctioning yaw string makes it difficult for the pilot to sense and correct for adverse yaw, leading to inefficient and uncoordinated turns.
Question 3: What is the primary function of a total energy compensated variometer?
- To indicate the rate of climb or descent due only to the movement of the surrounding air mass. (Correct answer)
- To show the glider's vertical speed relative to the ground.
- To measure the potential energy of the glider based on its altitude.
- To provide an audible warning of excessive airspeed.
Correct answer: To indicate the rate of climb or descent due only to the movement of the surrounding air mass.
A total energy (TE) compensated variometer filters out changes in vertical speed caused by the pilot's control inputs (i.e., converting kinetic energy to potential energy, or 'stick thermals'). It aims to only show the vertical movement of the air the glider is flying through, which is crucial for locating and utilizing thermals for soaring.
Question 4: A pilot in a glider without flaps or a retractable undercarriage needs to significantly increase the rate of descent without a corresponding increase in airspeed. Which control system should be used?
- Rudder
- Ailerons
- Elevator
- Spoilers/Air Brakes (Correct answer)
Correct answer: Spoilers/Air Brakes
Spoilers, also known as air brakes, are deployed from the wings to disrupt airflow, which simultaneously decreases lift and increases drag. This allows the pilot to increase the glider's descent angle for landing or to escape strong lift without building up excessive airspeed.
Question 5: While performing a coordinated right turn in a glider, how are the primary flight controls manipulated?
- Stick moves right, left rudder pedal is pressed.
- Stick moves left, right rudder pedal is pressed.
- Stick moves right, right rudder pedal is pressed. (Correct answer)
- Stick moves back, right rudder pedal is pressed.
Correct answer: Stick moves right, right rudder pedal is pressed.
To initiate a coordinated right turn, the pilot moves the control stick to the right to actuate the ailerons, causing the glider to roll. Simultaneously, the pilot applies right rudder pressure to counteract adverse yaw and keep the nose of the glider aligned with the flight path. Elevator back pressure is then typically required to maintain altitude in the turn.
Question 6: If the static port on a glider becomes blocked during flight, how will the altimeter and airspeed indicator be affected?
- The altimeter will be unaffected, but the airspeed indicator will read zero.
- The altimeter will freeze at the altitude where the blockage occurred, and the airspeed indicator will be inaccurate. (Correct answer)
- Both instruments will read zero.
- The altimeter will indicate a continuous climb, and the airspeed indicator will read higher than actual.
Correct answer: The altimeter will freeze at the altitude where the blockage occurred, and the airspeed indicator will be inaccurate.
If the static port becomes blocked, the altimeter will no longer sense changes in ambient air pressure and will remain fixed at the altitude of the blockage. The airspeed indicator will also be affected; it will read lower than the actual airspeed as the glider descends and higher than the actual airspeed as it climbs from the altitude where the blockage occurred, because the trapped static pressure is no longer correct for the current altitude.
