Tutorial Questions Flashcards
State the two basic characteristics of a free gyroscope
1) Rigidity in space. Gyroscope wants to maintain angular momentum
2) Procession. The resulting angular velocity acquired by the spin axis when a torque is applied to the gyroscope in a plane perpendicular to the plane of the rotor.
Explain the following terms
Free gyro
Gimbal lock
Caging
Nutation
1) A Free gyro consists of a relatively heavy motor mounted in such a way that it has two or more degrees of freedom.
2) Gimbal lock is when the spyness of a 2° of freedom gyroscope is possessed to align with the outer gimbal axis. The results is uncontrolled talk resulting in violent processional movements.
3) Caging is when a gyro motor is protected from processional forces at low speeds.
4) Nutation is when a sharp blow is applied to a gyro causing oscillation of the spin axis
In which direction does a gyro precess if a force is applied to it and why?
Processional movement takes place in a plane 90° ahead of the applied force in the direction of the wheel rotation. This is due to the resultant momentum of the force as applied to the wheel and the angular momentum of the wheel.
What factors is processional rate dependent upon?
1) Direction of wheel rotation. Effects direction of processional turn/tilt
2) Magnitude and direction of force applied. More force gives a higher rate of procession
3) Angular momentum (Rotor speed). Larger angular momentum reduces rate of procession
Processional rate=Applied torque/angular momentum
Define the meaning of degrees of freedom of a gyro
Number of axis the the gimbals of the gyro can rotate in
State in general terms what effects the following have on a free gyroscope and how we compensate for them.
1) earth rotation
2) vehicle velocity in both north-south and east-west directions.
1) Horizontal earth rate (HER). Maximum at the equator and zero at the poles. Only exists when spin axis is not aligned with a meridian. Causes axis of rotation to TILT up or down
HER is accounted for by applying precessional control to the spin axis to cause a TURN to North.
Vertical earth rate (VER) Maximum at poles and zero at equator. Causes TURN of the spin axis. Compensated by applying precessional control to spin axis to cause a TiILT.
2) N-S wander will act to TILT the gyro
E-W wander will act to TURN the gyro
Assuming the gyro is aligned with a meridian and the E-W travel is not along the equator
Describe the effect of a loss of vertical earth rate compensation with the gyrocompass operating in the southern hemisphere
In the southern hemisphere VER would cause the gyro to drift east to west
What is meant by real wander? give four possible causes
Real wonder of a gyroscope is the actual movement of the spin axis caused by engineering imperfections or external torque.
Bearing friction
Mass imbalance of wheel
Rotor speed variations
Power supply variations
Explain the basic construction and operation of a rate gyro and state the relationship between input and output functions.
A rate gyro consists of a wheel running at high speed on low noise ball bearings, usualy driven by an electric motor.
The rate gyro gives an output angle proportional to the input rate.
Describe how the restraint of a rate integrating gyro differs. State to the relationship between input and output functions
In a RATE gyro the damping restraint is kept as small as practicable. In a RATE INTEGRATING gyro the spring restraint is as small as possible.
A rate integrating gyro gives output angle proportional to the input angle.
Explain the requirement for a stable platform in an initial navigation system, mentioning accelerometer corrections. What other type of initial navigation system could be employed and how does this correct for accelerometer tilt?
An inertial/stable platform uses gyroscopes and gimbals to maintain the attitude of accelerometers no matter how the vehicle moves. This will provide a frame of reference for the direction of acceleration measured by the accelerometers. This allows for the correct adjustments to be made for gravity, centripetal force, the coriolis effect and the convergence effect.
A strap down system can also be used where accelerometers and gyros in the X,Y and Z directions are all rigidly mounted to the vehicle body. The gimbals in the stable platform are replaced with a computer and simulated electronically.
Explain the principle of operation of a basic pendulous accelerometer.
Consists of a single degree of freedom pendulum in a closed loop. Acceleration = Torque/Pendulosity
P=mass*distance to centre of hinge
