Avionics Multiple Choice Questions on “Strap Down and Gimballed Inertial Navigation Systems”.
1. In which type of inertial navigation system are the gyro and accelerometer rigidly mounted to the body?
a) Gimballed system
b) Fixed system
c) Strapdown system
d) Void system
Answer: c
Clarification: In a strapdown navigator, Gyroscopes and accelerometers are rigidly mounted to a sensor assembly that is usually mounted to the vehicle on a set of strap mounts. The gyroscopes track the rotation of the body and compute the orientation of the body.
2. What the gyro act as in a strapdown system?
a) Angular rate sensors
b) Null sensors
c) Angle indicators
d) Orientation indicators
Answer: a
Clarification: In a strapdown system, the gyros do not act as null sensors as in a gimballed system but act as inertial angular rate sensors. Angle and orientation are computed from the measured angular rates by the algorithms that calculate heading and orientation.
3. Which one of the following is not a purpose of strapdown calculations?
a) Calculate vehicle’s attitude
b) Transform accelerometer measurements into navigational coordinates
c) Perform dead-reckoning computations
d) Provide inputs to air data computer
Answer: d
Clarification: The purpose of strapdown computations are to calculate the vehicle’s attitude relative to the navigational coordinates using the gyro measurements, to transform the accelerometer measurements from vehicle axes into navigational coordinates, and to perform the dead-reckoning computations. Air data computer is independent of inertial navigation system.
4. Which of the following is a four element entity consisting of a scalar and a vector and is used to describe strapdown system rotation?
a) Directional cosines
b) Directional sines
c) Quaternion
d) Triternion
Answer: c
Clarification: Describing rotation motion in the strapdown system employ more than the minimum three parameters. A quaternion is a four element entity ting of a scalar part and a vector part. It defines the instantaneous axis of rotation.
5. What does the quaternion integration algorithm use to control error?
a) Linearization constraint
b) Normalization constraint
c) Differential constraint
d) Integral constraints
Answer: b
Clarification: Quaternion integration algorithms usually make use of the normalization constraint to control error growth in the computations. The sum of the squares of the quaternion elements are subtracted from unity to yield the normalization error.
6. What type of error occurs if the axis of rotation is moving in space?
a) Linearization errors
b) Control error
c) Coning error
d) Differential error
Answer: c
Clarification: Coning refers to a motion in which the axis of rotation is itself moving in space. In this type of motion, the axes of the body trace a cone in space.
7. Pre-processing algorithms are also called as _________
a) Coning algorithm
b) Error control algorithm
c) Differential algorithm
d) Resolution algorithm
Answer: a
Clarification: Pre-processing the gyro data at a higher rate than the quaternion iteration improves the approximation in the vector change in angle in order to follow the actual motion of the rotation axis closely. The pre-processing algorithm is also called as coning algorithms.
8. Why is the gyro and accelerometers shock mounted to the body?
a) Impact protection
b) Reduce drift error
c) Prevent voltage surges
d) Limit vibration errors