Gyroscopes Flashcards
Describe a typical aircraft vacuum (suction system)
Air is sucked from within the gyroscopic instruments using a suction pump.
The other that is sucked is replaced with a air filter where air enters and then goes through the grooves of the gyro rotor which cause them to move and make the instruments work
Distinguish between venturi, and positive pressure systems.
Venturi system - A Venturi is on the side of the aircraft. Engine slipstream can affect it and it has increased drag and is prone to icing. Suction also reduces with altitude
Positive pressure gyro system - Instead of turning the gyroscope rotors by using suction (a vacuum), air can be blown over the rotor by an air pump. At high altitudes, pressure driven gyroscopes are more efficient, and they have a pressure regulator, rather than a suction relief valve.
Describe the inherent properties of a spinning gyroscope rotor and what they’re dependent on. Rigidity and precession
Rigidity - the property of a rotating rotor that tend to maintain their alignment in space.
Dependent on:
- mass off the rotor, rpm of the rotor and the distance of the mass from the axis of rotation, the greater the better for all of them
Precession - if a side force is applied at some point around the rim of a spinning gyro rotor, it’ll till the rotor as if the force was applied 90 degrees further on in the direction of rotation.
Dependent on:
- strength and direction of the force, greater the force and closer it is to a right angle to the plane of rotation the greater the precession.
- moment of inertia of the rotor, the greater this moment the less the rate of precession
- rpm, the higher, the less the rate of precession.
Explain what is meant by the term gimbal.
Cages which hold gyro rotors.
List the types of gyroscope.
Tied - freedom in all three planes but kept in one plane
Earth - freedom in all three planes but is kept in one plane by the force of gravity.
Rate - freedom in one plane other than plane of rotation
Space - free in all planes
Explain the principle of operation of a turn indicator.
Uses a rate gyro, freedom in one plane other than rotation.
Utilises movement about the normal axis causing precession in the rotor which is used to indicate the rate of turn about that axis and is balanced against a restraining spring.
Damping unit used to correct for some turbulence.
Distinguish between a turn indicator (TI) and a turn co-ordinator (TC).
turn indicators are indicated by deflection the needle whereas turn coordinator is done by tilting of the aircraft symbol.
Describe the errors which a turn indicator is subject to.
Incorrect rotor speed - TI require constant rotor speed at rated rpm, if too fast excessive rate of turn will be indicated.
Yaw with pitch - aircraft subjected to yaw whilst positive g forces are applied, indicator will overread.
Suction - if less the minimum TI will become sluggish and underread. 2.5Hg minimum
Explain the principle of operation of the balance ball.
Device that indicates the direction of g forces.
Simply a ball, free to move like a pendulum bob except that its in a curved cylinder filled with a damping fluid.
Explain the serviceability checks for the TI/TC. (6)
- Whirring sounds and no flags visible
•Correct indications while taxiing
•Turn to the left, TI/TC indicates left turn, Ball indicates a skid to the right
•Turn to the right, TI/TC indicates right turn, Ball indicates a skid to the left
•Check balance ball central when on level ground
•Timing of a balanced rate 1 turn
Explain the principle of operation of a direction indicator/heading indicator (DI/HI).
Uses a tied gyro which spins in the vertical plane ( rotor lies horizontally)
Rotor is placed inside two gimbal rings and the rotors rigidity is utilised to provide a steady reference for the aircrafts direction.
Outer gimbal lies vertically and is free to rotate 360 degrees on aircrafts normal axis, has the index card to indicate direction. Inner gimbal is used to keep it in place while moving around.
Explain the following errors which the DI/HI is subject to; (a) gimbal error; (B) real drift (real wander) (C) apparent drift (apparent wander) (D) low rotor speed.
(A) results from changing relationships between the gimbals and unwanted precession when the orientation between the rotor axis and the aircrafts longitudinal axis. (During pitch and roll of aircraft)
(B) caused by friction forces and wear in the gyroscope, maximum allowable is 4 degrees per 15 minutes.
(C) caused by the earths rotation. As earth rotates so does the instrument and the gyro has no way of compensation except that theres no error at the equator and largest at the poles and varies from 0º at the equator and 15º at the poles.
(D) low suction leads to increased rate of precession and reduced rotor rigidity leading to higher deviation from the compass heading. 3.5 - 4.5Hg
Describe the characteristics of a toppled directional gyro (DI/HI).
Index card rotates rapidly one way around the dial.
Explain the DI typical:
(A) operating limitations
(B) serviceability checks
Limit - 55 degrees in pitch and roll are common limiits
Serviceability - requires 3-4 minutes to spool up to operational rotor rpm after engine start.
Taxiing, readings must increase during right hand taxi turns and decrease during left-hand.
In flight, DI must not precess more then 4 degrees per 16 minutes. Check and resynchronise.
Explain the advantages of an electrically-driven DI/HI versus an air-driven instrument. (4)
Higher RPM so greater rigidity
•More freedom in pitch and roll before toppling (may have no limits)
•Less wear and tear as instrument case can be sealed (doesn’t rely on air)
•Better and faster erection system
