Electromagnetic Method for fast erection

Page 102 of 109 13. 4. Directional Gyro

The directional gyro provides a fixed reference against which aircraft’s heading is indicates. The instrument employs a horizontal axis gyroscope and being non-magnetic it us used in conjunction with magnetic compasses. It defines the short-term heading changes during turns, while the magnetic compass provides a reliable long term heading reference as in sustained straight and level flight.

Figure 52.DG

The modern directional gyros are slave to a magnetic sensor, called a flux gate. The flux gate provides a continuously sense to the earth’s magnetic field and servo mechanism constantly correct the heading indicator. These “slaved gyro” will reduce pilot workload by eliminating the need for manual realignment every ten or fifteen minutes.

13. 5. Gyro Wander

Real Wander is actual movement of the spin axis caused by engineering imperfections such as friction and unbalance. Movement about the vertical axis away from its set position is reference to as real drift. Movement about the horizontal axis away from its set position is reference to as real topple.

Apparent wander is the apparent movement of the spin axis away from the local vertical. The cause of this apparent movement is the rotation of the earth combined with gyroscope rigidity. Wander may also occur when a gyroscope is transported from one point on the Earth to another, is called Transport Wander. The apparent rate of displacement is reduced if the distance to the north or south poles is reduced. In fact, when gyro is located at either the north or south pole, the rotation of the earth will cause no apparent wander.

13. 6. Rate Gyro

For the detection of rates of turn, direct use is made of gyroscope precession and in order to do this , the gyro is arranged in the manner shown. Such an arrangement is known as a rate gyroscope.

Page 103 of 109 Figure 53. Rate Gyro

It will be noted that the gyro differs in two respect from those employed in directional gyros and gyro horizon. It has only one gimbal ring and spring connected between the gimbal ring and casing to restrain movement about the longitudinal axis Y-Y1. When the instrument is in its normal operating position, due to the spring restrain the rotor spin axis will always be horizontal and the turn pointer will be at the zero datum mark. With the rotor spinning its rigidity will further ensure that the zero condition is maintained.

A turn to the left causes of force to be applied at the front pivot of the gimbal ring, and this is the same as trying to push the rotor round at the point F on its rim. In the following this through 90 in the direction of rotation, precession will take place at point P, thus causing the gimbal ring and rotor to tilt about longitudinal axis. If the pointer were fixed to the gimbal ring, it would tilt through the same angle and would indicate a turn and also its direction. 13.7. Turn and Bank Indicator

Turn and balance indicator (T/B) and the Turn coordinator (T/C) variant are essentially two aircraft flight instruments in one device. They each act as a rate of turn indicator that displays the rate the aircraft heading is changing and a balance indicator or slip indicator that displays the slip or skid of the turn.

Figure 54. Turn and Bank Indicator

The turn and balance indicator is often referred to under various names interchangeably, such as the turn and slip indicator or the turn and bank indicator.

Simply put, both the turn and balance indicator (T/B) and the turn coordinator (T/C) use a gyro-driven system. The T/B uses a needle and a ball, while the T/C uses a rolling aircraft depiction and a ball. Although the turn and balance indicator is sometimes called the turn and bank indicator, the instrument does not give the aircraft's true bank angle. In fact,

Page 104 of 109 neither the T/B nor the T/C actually give true bank angle information. True bank angle is calculated using the aircraft's speed and rate of turn.

Figure 55. Turn indicator

The turn indicator is a gyroscopic instrument that works on the principle of precession. The gyro is mounted in a gimbal. The gyro's rotational axis is in-line with the lateral (pitch) axis of the aircraft, while the gimbal has limited freedom around the longitudinal (roll) axis of the aircraft.

Balance indicator

Balance information of the aircraft is often obtained by an inclinometer, which is recognized as the "ball in a tube." An inclinometer contains a ball sealed inside a curved glass tube, which also contains a liquid to act as a damping medium. Historically, the balance indicator in early aircraft was merely a pendulum with a dashpot for damping. The ball gives an indication of whether the aircraft is slipping, skidding or in balanced flight. The ball's movement is caused by the force of gravity and the aircraft's precession forces. When the ball is centered in the middle of the tube, the aircraft is said to be in balanced flight. If the ball is on the inside (wing down side) of a turn, the aircraft is slipping. And finally, when the ball is on the outside (wing up side) of the turn, the aircraft is skidding. 13.8. Turn Coordinator Indicator

Figure 56.

The turn coordinator (T/C) is a further development of the turn and balance (T/B) indicator with the major difference being the display and the axis upon which the gimbal is mounted. The display is that of a miniature airplane as seen from behind. This looks similar to that of an attitude indicator. "NO PITCH INFORMATION" is usually written on the instrument to avoid confusion regarding the aircraft's pitch, which can be obtained from the artificial horizon instrument.

In contrast to the T/B, the T/C's gimbal is pitched up 30 degrees from the lateral axis. This causes the instrument to respond to roll as well as yaw. This allows the instrument to

Page 105 of 109 display a balance change more quickly as it will react to the change in roll before the aircraft has even begun to yaw. Although this instrument reacts to changes in the aircraft's roll, it does not display the roll attitude.

The turn coordinator should be used as a performance instrument when the attitude indicator has failed. This is called "partial panel" operations. It can be unnecessarily difficult or even impossible if the pilot does not understand that the instrument is showing roll rates as well as turn rates. The usefulness is also impaired if the internal dashpot is worn out. In the latter case, the instrument is said to be under-damped and in turbulence will indicate large full-scale deflections to the left and right, all of which are actually roll rate responses. In this condition it may not be possible for the pilot to maintain control of the aircraft in partial-panel operations in instrument meteorological conditions. For this and other reasons, many highly experienced pilots prefer the "older" turn and bank indicator design.

Figure 57. 14. MAGNETIC COMPASS

14.1. Earth Magnetic Field

Compasses are used to determine the direction of true North. However, the compass reading must be corrected for two effects. The first is magnetic declination, the angular difference between magnetic North (the local direction of the Earth's magnetic field) and true North. The second is magnetic deviation, the angular difference between magnetic North and the compass needle due to nearby sources of iron.

Page 106 of 109 .

Figure 58. Earth Magnetic Field

The picture above , illustrates the approximate directions of the earth’s field at different places around the earth. It can be visualized as something like that developed by huge cylindrical bar magnet buried in the interior of the earth. The field lines are in a pattern you would expect from iron filings scattered around a cylindrical bar magnet. The direction of the earth’s field at the north and south magnetic poles is vertical. At the magnet equator, it is horizontal and toward the poles.

14.2. Aircraft Compass

Magnetic compass will indicate a direct heading of Aircraft. When aircraft headed to the north, the letter “N” will appear at the lubber lines fixed to the case in the pilot’s view. The compass needle magnet see only the horizontal component of the earth’s field. If the airplane is not wings level, the compass very well be horizontal. This introduces an error called : “ Northerly turning error.

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Page 107 of 109 14.3. Deviation and Compensation

A compass installed in an aircraft is subjected to disturbing influences due to the presence in its vicinity of iron and steel parts as well as electric circuit. It does not, therefore give the same a of bearing as it would if it were removed from all such influences, and were influenced solely by the magnetic field due to the earth

There are some Definition on the Compass system which are :

1 Calibration means the measurement of residual deviation of a compass