Gyroscope principles
Navigation · Chapter 25 · DGCA CPL and ATPL
What a gyroscope is, why its axis holds still (rigidity), why a push acts 90° on (precession), how gyros wander, and the kinds of gyro.
Remember
- Rigidity ∝ mass, radius, rpm. Precession: 90° on in the spin direction; rate halves if rpm doubles.
- Degrees of freedom = gimbals. 1: rate gyro; 2: displacement gyro (DGI, horizon).
- Drift: horizontal; topple: vertical. Real: friction/imbalance; apparent: earth rate, transport.
- Earth rate 15 × sin(lat) °/h: north −, south +; 0 at the equator, 15 at a pole.
- Space (nothing), tied (outside force), earth (gravity), rate (spring).
What is a gyroscope made of?
Rotor and gimbals
- A heavy spinning wheel • A gyroscope is a heavy wheel, the rotor, spinning very fast: 4 000 to 55 000 rpm. • A spinning wheel hates being tilted. That is all there is to it.
- One ring • Put the wheel in a ring on pivots, a gimbal. • Now its axis can tip one more way.
- Two rings, and a frame • A second ring gives a second freedom. • The outer frame is the aircraft. It can move about, and the rotor need not follow.
Why does a spinning gyro keep pointing the same way?
Rigidity
- The aircraft moves, the gyro does not • Watch the frame swing about. The rings give way. • The rotor keeps pointing the same way. The red dot on the wall never moves. • This is rigidity, and every gyro instrument rests on it.
- What makes it stiffer • More mass. • Mass further out at the rim. • More rpm.
Push a spinning gyro at the top: where does it move?
Precession
This lesson is part of the Navigation plan. See plans
The words for a gyro going wrong
Drift and topple, real and apparent
This lesson is part of the Navigation plan. See plans
The Earth turns under the gyro: how fast does it seem to wander?
Earth rate
This lesson is part of the Navigation plan. See plans
Solve it: earth rate at any latitude
Solve it: earth rate
This lesson is part of the Navigation plan. See plans
Space, tied, earth, rate: which is which?
Kinds of gyro, drive and caging
This lesson is part of the Navigation plan. See plans
Test yourself on chapter 25
Test yourself
This lesson is part of the Navigation plan. See plans