Turn indicator
Encyclopedia
A turn indicator is an aircraft
flight instrument
that shows the rate of turn. It is used by the pilot to maintain control when flying under Instrument flight rules
.
The first gyroscopic aircraft instrument was the turn and bank indicator
(also known as turn indicator in the needle and ball, or more recently turn and slip indicator).
The major limitation of this instrument is that it senses rotation only about the vertical axis of the aircraft. It tells nothing of the rotation around the longitudinal axis, which in normal flight occurs before the aircraft begins
to turn.
The turn coordinator
was created to overcome this problem by having its gimbal frame angled upward about 30° from the longitudinal axis of the aircraft. This allows it to sense both roll and yaw.
The dial of these instruments is usually marked "2 min. turn", although some turn-and-slip indicators used in faster aircraft like the Concorde
are marked "4 min. turn". In gliders
, the calibration spring is usually set for a one-minute standard rate turn. A standard-rate turn is being made whenever the needle aligns with a turn marking ("doghouse").
Both instruments incorporate an inclinometer
-like indicator, which is either a pendulum
or a black glass ball sealed inside a curved glass tube that is partially filled with a liquid similar to the fluid
used in a compass
. This ball measures the relative strength of the force of gravity and the force of inertia caused by a turn. When the aircraft is flying straight-and-level, there is no inertia
acting on the ball, and it remains in the center of the tube between two wires. In a turn made with a bank angle that is too steep, the force of gravity is greater than the inertia and the ball rolls down to the inside of the turn. If the turn is made with too shallow a bank angle, the inertia is greater than gravity and the ball rolls upward to the outside of the turn. The ball does not indicate the amount of bank, neither is it limited to an indication of slip
; it only indicates the relationship between the angle of bank and the rate of yaw.
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
flight instrument
Flight instruments
Flight instruments are the instruments in the cockpit of an aircraft that provide the pilot with information about the flight situation of that aircraft, such as height, speed and altitude...
that shows the rate of turn. It is used by the pilot to maintain control when flying under Instrument flight rules
Instrument flight rules
Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....
.
Types
Turn and bank indicator
In aviation, the turn and bank indicator shows the rate of turn and the coordination of the turn. The rate of turn is indicated from a rate gyroscopically and the coordination of the turn is shown by either a pendulum or a heavy ball mounted in a curved sealed glass tube. No pitch information is...
(also known as turn indicator in the needle and ball, or more recently turn and slip indicator).
The major limitation of this instrument is that it senses rotation only about the vertical axis of the aircraft. It tells nothing of the rotation around the longitudinal axis, which in normal flight occurs before the aircraft begins
to turn.
The turn coordinator
Turn coordinator
The turn coordinator is a flight instrument which displays to a pilot information about the rate of yaw , roll, and the coordination of the turn...
was created to overcome this problem by having its gimbal frame angled upward about 30° from the longitudinal axis of the aircraft. This allows it to sense both roll and yaw.
Use and operation
Concorde
Aérospatiale-BAC Concorde was a turbojet-powered supersonic passenger airliner, a supersonic transport . It was a product of an Anglo-French government treaty, combining the manufacturing efforts of Aérospatiale and the British Aircraft Corporation...
are marked "4 min. turn". In gliders
Glider (sailplane)
A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...
, the calibration spring is usually set for a one-minute standard rate turn. A standard-rate turn is being made whenever the needle aligns with a turn marking ("doghouse").
Both instruments incorporate an inclinometer
Inclinometer
An inclinometer or clinometer is an instrument for measuring angles of slope , elevation or depression of an object with respect to gravity...
-like indicator, which is either a pendulum
Pendulum
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...
or a black glass ball sealed inside a curved glass tube that is partially filled with a liquid similar to the fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
used in a compass
Compass
A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...
. This ball measures the relative strength of the force of gravity and the force of inertia caused by a turn. When the aircraft is flying straight-and-level, there is no inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
acting on the ball, and it remains in the center of the tube between two wires. In a turn made with a bank angle that is too steep, the force of gravity is greater than the inertia and the ball rolls down to the inside of the turn. If the turn is made with too shallow a bank angle, the inertia is greater than gravity and the ball rolls upward to the outside of the turn. The ball does not indicate the amount of bank, neither is it limited to an indication of slip
Slip (aerodynamic)
A slip is an aerodynamic state where an aircraft is moving somewhat sideways as well as forward relative to the oncoming airflow. In other words, for a conventional aircraft, the nose will not be pointing directly into the relative wind .A slip is also a piloting maneuver where the pilot...
; it only indicates the relationship between the angle of bank and the rate of yaw.
Sources
- Advisory Circular AC 61-23C, Pilot's Handbook of Aeronautical Knowledge, U.S. Federal Aviation AdministrationFederal Aviation AdministrationThe Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
, Revised 1997. - FAA-H-8083-15 Instrument Flying Handbook, U.S. Federal Aviation AdministrationFederal Aviation AdministrationThe Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
(IFH), (Update 25 Nov 05)