11.5.2 Instruments- Gyroscopes Flashcards
What indicators use gyros?
Attitude indicator
Vertical Gyros
Directional Gyro
Rate gyro
What does a universally mounted gyro consist of?
Rotor, inner and outer gimbals mounted in a frame
What does gyro stability depend on?
Mass
Rotational speed
Distance between axis and COM
What is the XX axis?
Spinning
What is the YY axis?
Tilting
What is the ZZ axis?
Veering
What dictates the degrees of freedom?
Number of gimbals
What happens if you apply a force to the direction of the gyro axis?
Will cause it to move in that direction, but will not change the direction of the gyro axis.
What is an AI?
Attitude Indicator- position to horizon
What is a VG?
Vertical Gyro- provides indication for Attitude Director Indicator
What is a DG?
Directional Gyro- signal for Horizontal Situation Indicator and RMI
What gyros do modern glass cockpit aircraft use?
Electronic gyros such as laser gyros.
What speed must gyros rotate at to have stability?
22,000 RPM
What three ways can a gyro be classified?
Degrees of freedom
Spin axis orientation
Type
How is the degrees of freedom dictated?
Number of gimbals
When is classification by spin axis orientation used?
If the gyro is mounted with its spin axis either horizontally or vertically.
What is a free (space) gyro?
Has two degrees of freedom in three axis.
What is a tied gyro?
Similar to a free gyro but an external restriction is applied which controls the orientation of the spin axis.
Which indicator uses a tied gyro?
DG
What is an earth gyro?
The spin axis is constrained by the earths gravity, it has two degrees of freedom.
What instrument uses an earth gyro?
Attitude Indicator
What is an earth gyro a sub type of?
Tied Gyro
What is a rate gyro?
One degree of freedom, constrained to measure the rate of rotation in one plane.
What are rate gyros used for?
Turn coordination.
What two properties of a rotor rely on its angular momentum?
Rigidity and Precession
What is a displacement gyro?
Three axis and two degrees of freedom, the rotor orbits the x axis.
What is rigidity?
A gyroscopes ability to maintain its axis while pointing in a fixed direction.
What does rigidity cause?
A gyros axis of rotation to maintain a fixed direction in space if no force is applied.
What three factors effect rigidity?
Mass of rotor
Speed of rotation
Distance at which mass acts from centre.
Why are electrically driven gyros designed to use AC?
To avoid commutators and brush gear that need constant servicing.
The further the mass of the rotor from the axis of spin the ……? rigidity will be for the given speed?
Greater
What does a dished rotor exhibit?
Greater rigidity than a uniform wheel of the same design.
What is precession?
Applying a force that tries to tilt the gyro axis causes the gyro to react by shifting 90 degrees.
When precession is considered, if a aircraft tail is lifted what happens to the nose?
It turns left.
Is precession inversely proportional to the rotor speed?
Yes
What is the rate of precession formula?
Torque divided by inertia x speed
What is gyro wander?
Any deviation from a fixed direction when force is applied to the spin axis.
What two types of wander are there?
Drift and topple
What is gyro drift?
Occurs when the spin axis moves in a horizontal plane.
What is gyro topple?
Occurs when the spin axis moves in a vertical plane.
What is the name for severe and, usually, rapid misalignment when a gimbal limit stop is reached?
Topple
What causes real wander?
Result of any force that causes the gyro to precess.
What is real wander?
Actual movement of the spin axis caused by engineering imperfections, such as friction and unbalance.
Real drift occurs in which axis?
Vertical
Real topple occurs in which axis?
Horizontal
What is the rate of apparent drift at the poles?
15 degrees an hour
What is the formula for apparent drift?
15 degrees x the sine of latitude divided by hour
What is the formula for apparent topple?
15 degrees x cosine of latitude divided by hour
What ensures the rate of apparent drift is accurate?
If the gyro is at a fixed location.
How is the total effect of topple eliminated?
Erection system
How does the erection system work?
Uses the Earth’s gravity as a reference signal; this is detected using a moving mass, e.g., a pendulum, or liquid level switches.
What two categories of gyro wander fall under real wander?
Real drift/topple.
The attitude indicator gyro indicates what around the longitudinal axis?
Degree of bank
The attitude indicator gyro indicates what around the lateral axis?
Pitch
How many degrees of bank is a standard rate turn?
15
What does the caging knob do?
To adjust the wings up or down to align with the horizon bar.
In small aircraft with pneumatic drive gyros what is the suction regulated too, to avoid gyro overspeed?
5 inHg
What does an electrical drive system consist of?
Three phase Squirrel cage induction motor
What is the actual gyro speed of an electrical gyro when taking into account the slip of 6%?
22,500 RPM
In an electric drive gyro where are the torque motors located in relation to another?
90 degrees to each other.
What is a torque motor?
Squirrel cage motor
What two windings does a torque motor rotor have?
Reference winding and control winding.
In electrical gyro’s what erection rate is available when the gyro is switched on after a long power interruption?
20 degrees per minute
When an aircraft is holding why do they take on the racetrack pattern?
To allow the erection system enough time after each turn to correct the topple.
A laser gyro uses what to provide similar function to mechanical gyro’s?
Sagnac Effect beams of light.
What does RLG (Ring laser gyro) installation form part of?
Inertial reference system.
How many RLG’s are there and how are they installed?
3, at right angles to one another
What is meant by coherent when describing a laser?
Wavelengths are in phase in space and time.
Where is the source of a laser?
Cathode
What is one issue with an RGL?
Laser lock
What is laser lock?
When the two beams synchronise and give zero output.
When must a gyro not be moved?
When it is running at medium speed
How does a gyro get gimbal lock?
Removed while running and tilted more than 20 degrees.
What is the main problem with a DG?
No north seeking tendency
What does a vertical card DG, represent?
Dial gauge with a plane on it.
What is nutation?
Wobbling
How is nutation avoided in a DG?
Spin down brake system
How does the spin brake system work?
Holds the gimbal for 30 seconds after shut down.
How often must a directional gyro be set to agree with magnetic compass?
Checked every 15 mins
What is a slaved gyro system?
Takes input from a remotely located compass.
What is a flux valve?
Small segmented rings made of soft iron that readily accept line of magnetic flux.
After departure what three components compromise gyro drift?
Apparent wander
Transport Wander
Real wander
What causes transport wander?
Caused by meridian convergence as you fly east or west.
Where is the horizontal situation indicator?
Normally mounted below the attitude indicator.
What does the horizontal situation indicator combine?
Heading and VOR-ILS
What does VOR-ILS stand for?
Very High Frequency Omnidirectional Range Instrument Landing System
What does the nav warning flag mean?
No reliable signal is being received.
How would you know the compass isn’t functioning properly?
HDG flag
What does a VERT warning flag mean?
Glide slop data is missing
What type of indicator does and turn and slip indicator have?
Needle
On a rate of turn indicator, what does the first mark represent?
180 degrees per minute
On a rate of turn indicator, what does the second mark represent?
360 degrees per minute
On a rate of turn indicator, what does the third mark represent?
540 degrees per minute
On a rate of turn indicator, what does the fourth mark represent?
720 degrees per minute
What type is a turn indicator?
Rate gyro with horizontal axis
Rate gyros have one gimbal which is limited in motion by a spring, how many degrees of freedom does it have?
1.5 degrees
How do you know it the aircraft is slipping or skidding?
Turn coordinator ball is off centre
What are the two typical errors of turn indicators?
Springs adjustment
Rotor Speed
What happens if the turn indicator rotor speed is too high?
The indication is higher than it should be.
