# Avionics Questions and Answers – Gyroscopes – 1

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This set of Avionics Multiple Choice Questions & Answers (MCQs) focuses on “Gyroscopes – 1”.

1. What is the purpose of a gyro in an inertial navigation system?
a) Space-stabilize the accelerometer
b) Angle of rotation
c) Measure rotation rate
d) Calculate velocity

Explanation: The purpose of gyroscope or gyro in an inertial navigation system is to space stabilize the accelerometers. In gimballed platforms, the gyros measure the rotation of the platform, which is angularly isolated from the vehicle’s motion.

2. What is the range of an order of angular rate magnitude that gyros used in military planes need?
a) 8
b) 8.5
c) 7.1
d) 3

Explanation: A gyroscope on a military aircraft must sense angular rates as low as 0.005 deg/hr and as high as 400deg/sec, a range of 8.5 orders of magnitude. Strapdown gyros in civil aircraft need only sense an 8 order of magnitude range of angular rates.

3. Why are unfloated instruments with ball bearings not suitable for air navigation?
a) Weight restrictions
b) High drift rate
c) Low drift rate
d) Power restrictions

Explanation: Gyroscopes are used as heading references. The spinning wheel, large angle, unfloated instruments with ball bearings that have drift rates on the order of 50deg/hr . and hence are useless for navigation.

4. Which of the following is false with respect to SDF floated gyros?
a) Wheel is floated at neutral buoyancy
b) Used in launch vehicles
c) Three gimbals are used
d) Magnetic pickoff used to sense rotation

Explanation: In SDF floated gyros or single degree of freedom floated gyros, a spinning wheels were mounted inside a single gimbal that was floated at neutral buoyancy. A magnetic pickoff was used to sense rotation and they were primarily used in space launch vehicles.

5. Which of the following spinning wheel gyro has an accuracy of 0.001 deg/hr?
a) Floated TDF gyro
b) Electrostatically suspended TDF gyro
c) Floated SDF gyro
d) Unfloated ball bearing gyro

Explanation: In electrostatically suspended TDF gyro, the spinning wheel is suspended electrostatically hence reducing friction and achieving 0.001 deg/hr accuracy but at costs orders of magnitude higher than the floated TDF gyros.

6. The input, output and spin axes of a gyro are always perpendicular to each other.
a) True
b) False

Explanation: The input, output and spin axes of a gyro are always perpendicular to each other regardless of the motion of the gyro or the platform in which it is fixed. If a gyro is used for heading reference, then the gyro’s spin axes are mounted perpendicular horizontally to the platform.

7. Which of the following is false with respect to spinning rotor gyros?
a) Mechanically complex
b) High probability of failure
c) Low run up time
d) High power consumption

Explanation: The major disadvantage of spinning wheel or spinning rotor gyros is that they are mechanically complex and have a high probability of failure due to the moving components. They also require high powers and have high run up time. Run up time is the time taken for the gyro to start spinning at the required RPM after engine start.

8. What is the basic principle under which MEMS gyro work?
a) Sagnag effect
b) Coriolis effect
c) Angular momentum conservation
d) Mass conservation

Explanation: MEMS Micro Electro Mechanical System gyro exploit the effects of Coriolis force. Coriolis force is experienced when a vibrating mass is subjected to a rate of rotation about an axis in the plane of vibration.

9. Which part of the insects acts as gyros?
a) Wings
b) Halteres
c) Thorax
d) Legs

Explanation: Every flying object needs to maintain its orientation and insects that fly use halteres. Halteres work in the same principle as MEMS gyro, the vibrate and use Coriolis force to know their orientation.

10. Which of the following is false with respect to MEMS gyro?
a) Low failure rate
b) Low cost
c) High maintenance
d) Less power consumption

Explanation: Micro machined vibrating mass rate gyros exploit semiconductor manufacturing technology for mass production. They are extremely reliable and rugged devices with low power consumption and offer the major advantage of relatively low cost. They also do not require the very high maintenance that spinning rotor gyros require.

11. Gyros are used as feedback sensors in FBW.
a) True
b) False