Flashcards in Basic Gyro/DG Deck (38):
What are the 2 gyroscope properties, what are they?
1. Rigid in space
How to make a gyro more rigid?
Make it go faster
Make the rotor as big as possible but space is limiting on a A/C
Why does a rotor slow?
Because of fricition
What is wander?
When a rotor slows and the the gyro stops doing what you want it to do i.e stay rigid/erect.
When are the 2 ways a gyro can wander?
Topple in the vertical plane and drift in a horizontal plane
What is precession?
Precession relates to the application of forces. If you apply a force on the frame work of a spinning rotor, then the force (torque) will be applied 90˚ in the direction of the rotor.
How many degrees of freedom does 2 gimbals have?
2˚ of freedom
1 gimbal = 1˚ of freedom
What is a displacement gyro?
A gyro which has 2˚ of freedom and can move freely on all 3 planes.
Which instruments use the displacement gyro?
DI and AI
What is the name of a gyro which has 3˚ of freedom?
These generally aren't used on airliners.
What is apparent wander?
2 types: Earth's rotation and transport wander.
As a gyro stays rigid and fixed to a spot, but the earth spins or the A/C is moving relative to the rigid gyro, it 'appears' as if the gyro is wandering.
What is real wander?
Is the topple and drift of a gyro due to the bearing friction slowing the rotor.
What 2 types of gyros are there and how are they driven?
Pneumatic is driven by air and electric is driven by electrical power
At what RPM do normally pneumatic rotors spin?
At what RPM do AC powered gyroscopes normally rotate?
Due to much higher RPM than pneumatic gyros, electric gyros are far more rigid, but have pitch and roll limits of 85 degrees
What is another name for DG?
Direction indicator (DI)
Directional gyro indicator (DGI)
Why do we use a DG/DI when we have a compass?
Doesn't suffer from the compass errors, deviation and variation.
It does however suffer acceleration and need to reset it to stop it from wandering
So DG is good for short term accuracy.
Compass is good for long term accuracy.
How is a DG tied?
Horizontally tied and mounted vertically.
Which plane does the DG measure to get the angular displacement?
The yawing plane.
The A/C measures the A/C axis (moving) to the gyro axis (fixed) to give the displacement angle.
How is a pneumatic coarse erection maintained?
Air jet method
A jet of air realigns the gyro upright
How is pneumatic fine erection maintained?
Wedge plate method
The separating of exhaust on either side of the wedge plate and uses imbalanced exhaust from either side to push the gyro upright again
How often must a DI be reset?
every 10mins or after a steep turn.
What is gimbal lock?
Gimbal lock occurs whenever the 2 gimbals aren't at right angles to one another
In the building principle of a gyroscope, the best efficiency is obtained through the concentration of the mass:
On the periphery and with a high rotational speed.
Real wander of a gyroscope may be caused by ?
The maximum drift of a gyroscope because of ER is:
What is the main cause of real wander?
Bearing friction, mounting gimbals
or mechanical imperfections
Where is max apparent topple experienced for a vertically aligned gyro?
At the EQ.
Thus min at the poles.
How is apparent topple calculated?
15.04˚/hr x Cos lat
Where is max drift experienced for a horizontally aligned gyro?
At the poles.
Min at the EQ.
How if apparent drift calculated?
15.04˚/hr x sin lat
At which latitude is apparent drift and topple the same?
45˚N at 10.6˚
(15.04˚/hr x cos 45 and 15.04˚/hr x sin 45)
With reference to DGI, when will a gimballing error disappear?
After a turn is completed
Latitude nut is also a type of wander, which type is it?
LN is a type of real wander.
Even though LN is used to compensate for earth's apparent wander, the lat nut is a real device therefore it is also known as real wander.
What is the formula for total drift (TD)?
TD = ER + TR + RD + LN
What is the value of ER in the N. Hemis?
15.04˚/hr x sin lat, and the value is negative.
The value is + in the s. Hemis.
1 bar equals .... PSI
1 bar = 14.5 psi