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DGCA Technical General · 52 questions

Gyroscope: DGCA Technical General Questions and Answers

52 practice questions on Gyroscope with answers and explanations, plus the key concepts and formulas, from the TrueHeading question bank.

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About this topic

Use this page to revise Gyroscope for the DGCA Technical General paper. Below are the key ideas first, then 12 practice questions with answers and explanations, picked from the 52 questions in the TrueHeading bank for this topic.

In short: Rigidity: the spin axis stays fixed in space. Precession: a force applied to the rim acts 90° on in the direction of spin.

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Key concepts: Gyroscope

4 ideas to know cold.

Two properties of a gyro?

Rigidity: the spin axis stays fixed in space. Precession: a force applied to the rim acts 90° on in the direction of spin.

  • Rigidity increases with mass, speed and radius
  • Rate gyros use precession; attitude and heading gyros use rigidity
spinapplied force Fprecessionrigid in space · precesses 90° on in the direction of spin

Drift and wander of a gyro?

Earth rate gives an apparent drift; moving over the Earth adds transport wander.

Earth-rate drift=15∘/h×sin⁡ϕ\text{Earth-rate drift}=15^\circ/\text{h}\times\sin\phi
Transport wander≈VEWtan⁡ϕ60 ∘/h\text{Transport wander}\approx\frac{V_{EW}\tan\phi}{60}\ ^\circ/\text{h}
  • Zero earth-rate drift at the equator; 15°/h at the poles
  • Real drift comes from friction and imperfections

Types of gyro?

Mechanical gyros, and ring-laser or fibre-optic gyros with no moving parts.

  • Ring laser gyro uses the Sagnac effect
  • Directional gyro needs resetting to the compass about every 10–15 minutes

What are gyroscopic rigidity and precession?

Rigidity: the axis tends to stay fixed in space. Precession: an applied force produces a movement 90° later in the direction of rotation.

Drift=15sin⁡ϕ (∘/h)\text{Drift}=15\sin\phi\ (^\circ/\text{h})
  • Rigidity increases with mass, radius and rpm
  • Apparent drift = 15 sin(lat) °/h
  • Transport wander = (E-W GS/60) tan(lat)

Practice questions: Gyroscope

Tap “Show answer” after you have tried each one.

Q1The apparent drift rate of a free horizontal-axis gyro (earth rate) at latitude 10° N is approximately:

  1. 1.3°/h
  2. 14.8°/h
  3. 2.6°/h
  4. 15.0°/h
Show answer

Answer: C. 2.6°/h

Apparent drift = 15° × sin(latitude) per hour (15 sin φ). It is zero at the equator and 15°/h at the poles.

Q2The apparent drift rate of a free horizontal-axis gyro (earth rate) at latitude 25° N is approximately:

  1. 15.0°/h
  2. 6.3°/h
  3. 13.6°/h
  4. 3.2°/h
Show answer

Answer: B. 6.3°/h

Apparent drift = 15° × sin(latitude) per hour (15 sin φ). It is zero at the equator and 15°/h at the poles.

Q3The apparent drift rate of a free horizontal-axis gyro (earth rate) at latitude 40° N is approximately:

  1. 11.5°/h
  2. 9.6°/h
  3. 4.8°/h
  4. 15.0°/h
Show answer

Answer: B. 9.6°/h

Apparent drift = 15° × sin(latitude) per hour (15 sin φ). It is zero at the equator and 15°/h at the poles.

Q4The apparent drift rate of a free horizontal-axis gyro (earth rate) at latitude 60° N is approximately:

  1. 13.0°/h
  2. 7.5°/h
  3. 15.0°/h
  4. 6.5°/h
Show answer

Answer: A. 13.0°/h

Apparent drift = 15° × sin(latitude) per hour (15 sin φ). It is zero at the equator and 15°/h at the poles.

Q5Transport wander rate = (east-west ground speed / 60) × tan latitude. For 300 kt due east at 30° N the value is approximately:

  1. 8.7°/h
  2. 2.5°/h
  3. 4.3°/h
  4. 2.9°/h
Show answer

Answer: D. 2.9°/h

Transport wander (°/h) = (E-W groundspeed/60) × tan φ. Flying east or west changes the longitude, and a gyro fixed in space appears to wander.

Q6Transport wander rate = (east-west ground speed / 60) × tan latitude. For 480 kt due east at 30° N the value is approximately:

  1. 4.6°/h
  2. 4.0°/h
  3. 6.9°/h
  4. 13.9°/h
Show answer

Answer: A. 4.6°/h

Transport wander (°/h) = (E-W groundspeed/60) × tan φ. Flying east or west changes the longitude, and a gyro fixed in space appears to wander.

Q7Transport wander rate = (east-west ground speed / 60) × tan latitude. For 180 kt due east at 60° N the value is approximately:

  1. 1.5°/h
  2. 5.2°/h
  3. 2.6°/h
  4. 1.7°/h
Show answer

Answer: B. 5.2°/h

Transport wander (°/h) = (E-W groundspeed/60) × tan φ. Flying east or west changes the longitude, and a gyro fixed in space appears to wander.

Q8A heading indicator without latitude nut compensation is aligned on the ground at 50° N. After 3 h its apparent error from earth rate alone is about:

  1. 34°
  2. 69°
  3. 29°
  4. 45°
Show answer

Answer: A. 34°

Error = 15 sin φ × time. The latitude nut or erection torquer is set to counteract this.

Q9The two basic properties of a gyroscope are:

  1. torque and drift
  2. rigidity in space and precession
  3. tilt and wander
  4. inertia and gravity
Show answer

Answer: B. rigidity in space and precession

Rigidity: tendency to keep the axis fixed. Precession: reaction 90° to the applied force.

Q10Real drift of a gyro is caused by:

  1. the aircraft motion over the earth
  2. magnetic variation
  3. the rotation of the earth
  4. bearing friction and imperfections in balance
Show answer

Answer: D. bearing friction and imperfections in balance

Apparent drift comes from earth rotation and transport wander.

Q11A rate-integrating gyroscope output is proportional to:

  1. the rate of turn
  2. the angle turned
  3. the acceleration
  4. the speed
Show answer

Answer: B. the angle turned

It integrates the rate over time.

Q12The heading indicator (DGI) is aligned with the magnetic compass:

  1. never
  2. automatically
  3. only on the ground at start-up
  4. periodically, as it has no north-seeking property
Show answer

Answer: D. periodically, as it has no north-seeking property

It must be reset every 10–15 minutes.

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