Gyrodynamics

Question 1

what is a gyroscope?

Answer 1

a rotating wheel or rotor which roatest at high speed.

Question 2

in addition to the plane of rotation, gyroscopes have freedom of movement where?

Answer 2

in one or both of the planes which lie at right angles to the plane of rotation.

Question 3

what are the properties of gyroscopic rigidity?

Answer 3

rotors of the gyro instruments have relatively high mass and are rotated at very high speed.

giving them gyroscopic rigidity through which they tend to maintain their alignment in space

Question 4

what is rigidity dependent on and how is it increased?

Answer 4

dependent on mass, rotational velocity and the distance of mass from the centre of rotation.

greater the mass,` greater the rotational velocity, the greater rigidity and the greater the distance is between the centre of rotation and the mass the greater the rigidity.

Question 5

what are the properties of gyroscopic precession?

Answer 5

if a side force is applied at a point around the rim of a gyro rotor, it’ll tilt the rotor as if the force is applied at 90 degrees further on in the direction of rotation.

Question 6

what do gimbals do?

Answer 6

hold the gyro rotors in place in the instrument case

Question 7

how does a vacuum pump work?

Answer 7

air enters through the inlet and passes through causing the rotor to move clockwise before the air passes out of the outlet.

Question 8

how does a vacuum system work?

Answer 8

when the vacuum pump is operating it causes a suction pulling air into the inlet so that filtered air can then pass through the gyroscopes.

a nozzle releases an air jet that gets caught in the grooves of the spinning disc or mass causing it to rotate.

normally a suction gauge and the cockpit so that the pilot can monitor the suction. relief valve to relieve any excess pressure and sometimes a low vacuum light to warn of low suction.

Question 9

how can you remember which gyro is used for each instrument?

Answer 9

TER
DAT

T - tied gyro = Direction Indicator
E - earth gyro = artificial horizon
R - rate gyro = turn indicator

Question 10

what is the basic principle of a rate gyroscope?

Answer 10

they have the freedom of movement in only one plane other than the plane of rotation.

they utilise movement about in the vertical axis through the aircraft to cause precession in the rotor, which is then used to indicate the rate of turn about that axis.

Question 11

what are the differences between a turn coordinator and a turn indicator?

Answer 11

turn indicators are indicated by deflection the needle whereas turn coordinator is done by tilting of the aircraft symbol.

Question 12

what are the similarities of the two turn indicating instruments?

Answer 12

both deflect towards the direction of turn and have graduation marks and if the needle or the wing of the aircraft is aligned with the first of these marks a standard rate of 1 turn of 3 degrees per second is indicated.

Question 13

can the two turning instruments indicate the angle of bank or attitude in pitch?

Answer 13

no, but the turn coordinator will indicate roll rate.

Question 14

what is the use of the coordination ball?

Answer 14

a device used to indicate the direction of the g forces i.e combined effect of the Earths gravity and any turning force acting on the aircraft.

Question 15

what is the construction of the coordination ball?

Answer 15

a small free to move pendulum bob except that it moves in a curved cylinder filled with damping fluid.

Question 16

in straight flight where should the coordination ball be seen?

Answer 16

the middle where the aircraft is then said to be balanced.

Question 17

what if there is any slip or skid with the coordination ball?

Answer 17

the ball will move to one side in the same way as a pendulum bob would swing. pilot would feel the force pushing him to one side of the cockpit.

Question 18

what if in the vacuum system the suction drops?

Answer 18

a vacuum switch if fitted will operate and illuminate a LOW VACUUM warning light.

the reasoning is that with a low vacuum the flow of air through the instruments and the group speed will be reduced.

as a result, the vacuum-driven instruments could become unreliable and behave erratically, incorrectly or sluggishly.

Question 19

if the vacuum pump fails what occurs?

Answer 19

warning light will illuminate and the suction gauge will read zero.

Question 20

during a coordinate flight the pilot will feel what in regards to the forces?

Answer 20

no sideways forces nor will the ball which would remain centred. any sideways force will be shown on the coordination ball.

Question 21

what are the serviceability checks for the turn coordinator?

Answer 21

• a check of the gyro rotation (whirring sound and no failure flags if electrically drive, correct vacuum if pressure-driven)
• correct indications of both the turn indicator and coordination ball in a turn while taxiing (turning left, skidding right - turning right, skidding left)

Question 22

how does the venturi system work for a gyroscopic instrument?

Answer 22

air enters through the venturi and accelerates through the throat creating a reduction in static pressure and therefore providing suction for the gyro.

Question 23

the artificial horizon utilises what?

Answer 23

the gyroscopic property of rigidity.

Question 24

what is the basic principle of operation of an earth gyro?

Answer 24

the rotor rotates in a plane parallel with the earth’s surface and is free to move in the other two planes.

rotor is controlled in such a way that its axis remains aligned with the centre of the earth. (perpendicular to the surface)

Question 25

the attitude of the aircraft relative to the horizon is symbolised how?

Answer 25

by the position of the fixed small symbolic aircraft in the AI display, in relation to the AH segment which moves behind it.

Question 26

how do the artificial horizon show pitch attitude and bank angle?

Answer 26

pitch attitude is indicated by the position of the centre dot of the miniature aircraft relative to the top of the artificial horizon segment.

bank angle is indicated by the relationship of the wings of the aircraft to the line representing the artificial horizon.

Question 27

what are the serviceability checks of the AH?

Answer 27

• suction gauge should be indicating a minimum of 4.5Hg
• if electrically powered check to see if its receiving power
• the caging device should be used before entering manoeuvers in case of accidental topple

Question 28

what happens if the AH topples?

Answer 28

the horizontal card in the instrument is canted at an angle

Question 29

what are the advantages of a direction indicator over a compass?

Answer 29

• the compass jiggles around making it hard to read in turbulence whereas the DI doesn’t.
• compass is also smaller so the scale can be hard to read, DI is bigger and doesn’t have this problem.

Question 30

DI uses what gyro?

Answer 30

a tied gyro where it has an inner gimble, outer gimble and sits within a case.

as the aircraft changes its heading, the gyro maintains its alignment in space.

Question 31

why must you synchronise the DI with the compass?

Answer 31

as it gradually loses alignment due to the earth’s rotation and friction in the gyro.

Question 32

what is the method of synchronising the HI with the compass? and how often should it be done?

Answer 32

use the knob to align the HI with the compass.

before the flight and about every 10 - 15 minutes during flight.

Question 33

in turbulent conditions how can you synchronise the compass?

Answer 33

hold aircraft on a stay heading wings level using a reference point on the horizon.

Read compass when conditions settle and realign the HI.

Question 34

what are the serviceability checks of the HI?

Answer 34

check the power source of the HI prior to flight. and when taxiing the correct turn indication on the HI. (turning right heading increases, turning left it decreases)

Question 35

what if the gyro has low rotor speed?

Answer 35

if the rotor is at a low speed it’ll have less rigidity allowing it to deviate more readily. it’ll also allow for greater precession.

Question 36

what happens if there’s an indication of a power failure on an electrically driven gyro?

Answer 36

may indicate erratically, respond only slowly to changes in attitude or heading or indicate incorrectly.

Question 37

what happens to the turn indicator if the amount of air passing through the suction pump decreases? like with altitude

Answer 37

cause low suction from the suction pump, not enough air to rotate the gyro, therefore, causing it to under indicate.

Question 38

what causes real drift ( real wander) and what does it do?

Answer 38

caused by friction forces and normal wear and tear within the gyroscope.

cause the direction indicator to slowly indicate the incorrect heading

Question 39

what causes apparent drift ( apparent wander)

Answer 39

rotation of the earth causes the apparent movement meaning over time the DI will no longer be aligned with the magnetic direction.