Avionics Multiple Choice Questions on “Vertical & Heading References”.
1. How to determine the true vertical reference?
a) Differentiating
b) Time average of apparent vertical
c) Integration
d) Sum of all the apparent vertical
Answer: b
Clarification: The simplest approach to the determination of the true vertical is to time-average the direction of the apparent vertical(vector sum of gravity and vehicle acceleration).
2. When is the gyro interrupted in erection cutoff method?
a) Deviation is large
b) Deviation is low
c) Never interrupted
d) Always interrupted
Answer: a
Clarification: The error caused in the vertical referencing can be rectified by introducing nonlinearities. One such method is the erection cutoff where the precession of the gyroscope is interrupted when a large deflection is sensed.
3. Which one of the following is the basic vertical reference in all forms of heading and attitude devices?
a) Line perpendicular to artificial horizon
b) Earth’s gravitational field
c) Line perpendicular to actual horizon
d) Earth’s magnetic field
Answer: b
Clarification: The basic vertical reference in all forms of heading and attitude reference devices is the Earth’s gravitational field. The direction of Earth’s gravitational field can be sensed with great accuracy in stationary systems. However, when the platform moves, all the instruments indicate the vector sum vehicle acceleration and local gravity.
4. The error that occurs due to the rotation of Earth as well as the aircraft’s own motion is called as ______
a) Asymmetrical error
b) Precession rate error
c) Rate compensation error
d) Standoff constant error
Answer: d
Clarification: A stand off constant error exists since the direction of the local vertical changes as a result of both the rotation of the Earth and the aircraft’s own motion around the Earth.
5. A special mode for initial leveling is needed when using erection cutoff mode.
a) True
b) False
Answer: a
Clarification: When erection cutoff is used, there is a need for a special mode of operation that provides initial leveling, because no precession rate would exist in the presence of large initial tilt.
6. What can be done to reduce to avoid poor acceleration error averaging?
a) Use higher order leveling loop
b) Use lowest order leveling loop
c) Use switch gravity sensors
d) Use differential leveling loop
Answer: a
Clarification: The stand off error depends upon the gravity sensors switch’s dead and gives poor acceleration errors. Significant improvement can be obtained in the averaging vertical reference by using a high order leveling loop.
7. The relative acceleration of a vehicle moving with respect to a rotating Earth can be divided into three parts.
a) True
b) False
Answer: a
Clarification: When a vehicle moves at a velocity relative to the rotating Earth, the inertial acceleration can be divided into three parts: Acceleration relative to the surface of Earth, Coriolis acceleration caused by rotation of Earth, and a correction that depends on the coordinate frame in which the gyro is constrained.
8. Inertial heading references are better than a magnetic compass.
a) True
b) False
Answer: a
Clarification: The best airborne heading references are the inertial navigators. Less expensive, smaller and less accurate references are those that depend on the Earth’s magnetic field, those that depend on the use of gyroscopes to retain a preset azimuth, and those that use subinertial gyros to maintain a three axis reference.
9. Which of the following is not a unit of the magnetic field?
a) Gamma
b) Gauss
c) Tesla
d) Maxwell
Answer: d
Clarification: The magnetic fields B are measured in Gauss and Tesla(104 Gauss). In geomagnetism, Units of “Gamma”(10-5 )are used.
10. What is the orientation of the Earth’s magnetic axis with respect to its spin axis?
a) 2°
b) 0°
c) 11°
d) 24°
Answer: c
Clarification: The Earth’s magnetic field is produced by a bar magnet oriented 11°away from the spin axis and passing within a hundred kilometers of its center.
11. Which of the following is not the angle between the horizontal component of B and true north?
a) Magnetic declination
b) Magnetic variation
c) Dip angle
d) Magvar
Answer: c
Clarification: The magnetic declination, also called the magnetic variation or magvar, is the angle between the horizontal component of B and true north. Navigators use ‘magvar’ in order not to confuse astronomical declination with magnetic declination.
12. Why does magvar have diurnal change?
a) Magnetic pole migration
b) Static buildup error
c) Sensitivity of the instruments
d) Variation in aircraft magnetic effects
Answer: a
Clarification: Magvar has a diurnal change, a long term change due to the migration of magnetic poles, and random changes because of magnetic storms. The magnitude of the magnetic field changes about 0.5% per year.
13. Which of the following is used to sense aircraft magnetic fields?
a) Magnetic compass
b) Airborne magnetometer
c) Accelerometer
d) Gyroscope
Answer: b
Clarification: Aircraft have magnetic fields that add to the Earth’s field and are sensed by the airborne magnetometers. The induced error, called deviation, can be 10° or more.
14. Magnetic compass is also called as whiskey compass.
a) True
b) False
Answer: a
Clarification: The simplest compasses measure the orientation of the nearly free permanent magnet attached to a buoyant body floating in a liquid. Since the liquid is usually alcohol, it is also called as whisky compass.