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AIRCRAFT INSTRUMENTS

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PITOT STATIC SYSTEM

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• Difference between the dynamic and static pressures is used to determine the indicated airspeed (IAS) that is displayed to the pilot on the airspeed indicator in the cockpit

• calibrated airspeed: Corrected for Instruments position error

• Equivalent airspeed : corrected for compressibilty

• True Air speed : corrected for air density

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• GROUNDSPED: defined as the speed at which an object travels relative to a fixed point on the Earth's surface

• airspeed

• Mach number, however, is measured with respect to the velocity of the object through the air, or its airspeed

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Airspeed Indicator

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• The white range is the normal range of operating speeds for the aircraft with the flaps down

• The green range is the normal range of operating speeds for the aircraft with the flaps up

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• It receives pressure from Pitot tube

• Instruments case is sealed and connected to static port

• As the pitot pressure increases, or the static pressure decreases, the diaphragm expands, and this dimensional change is measured by a rocking shaft and a set of gears that drives a pointer across the instrument dial.

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ALTIMETER

• To measure the altitude

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• Mechanical errors

• Inherent errors

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• It consist of an aneroid barometer

• This aneroid capsule(cell) is made from an alloy of beryllium and copper.

• The box is tightly sealed after some of the air is removed, so that small changes in external air pressure cause the cell to expand or contract

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Mach meter

• Ratio of the true air speed and speed of sound

• True air speed: with density correction

• As an aircraft in transonic flight approaches the speed of sound, it first reaches its critical mach number

• shock waves formed

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• The indicated airspeed at which these conditions occur changes with temperature

• Therefore airspeed, in this case, is not entirely adequate to warn the pilot of the impending problems

• Mach number is more useful

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Mach meter

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Variometer or vertical speed indicator

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• It is a both rate and trend instruments

• instantaneous rate of descent or climb

• In powered flight the pilot makes frequent use of the VSI to ascertain that level flight is being maintained

• As a trend instrument, it shows immediately the initial vertical movement of the airplane, which, disregarding turbulence, can be considered a reflection of pitch change

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• Variometers measure the rate of change of altitude by detecting the change in air pressure (static pressure) as altitude changes

• The instrument consists of an air bottle connected to the external atmosphere through a sensitive air flow meter

• As the aircraft changes altitude, the atmospheric pressure outside the aircraft changes

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• Air flows into or out of the air bottle to equalise the pressure inside the bottle and outside the aircraft

• The rate and direction of flowing air is measured and displayed to the pilot

• Air flowing out of the bottle indicates that the altitude of the aircraft is increasing

• Air flowing into the bottle indicates that the aircraft is descending

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• Lag: The delay that occurs before an instrument needle attains a stable indication

• Lag is directly proportional to the speed and magnitude of a pitch change

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• Pitot-static instrument used • rate of climb or the rate of descent • The vertical airspeed is measured through a

mechanical linkage to a diaphragm located within the instrument

• The area surrounding the diaphragm is vented to the static port through a calibrated leak

• when an aircraft begins to increase altitude, the diaphragm will begin to contract at a rate faster than that of the calibrated leak

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• the needle to show a positive vertical speed

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TURN AND SLIP INDICATOR

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• shows the rate and direction of a turn • It tells the pilot if he is performing a

coordinated turn using all his controls most efficiently.

• If the indicator at the top turns towards 'L' to the left marker, then the pilot is making  a standard rate coordinated turn to the left.

• If the indicator arm turns towards 'R' to the right marker, then the pilot is making a standard rate coordinated turn to the right.

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• Near the center of the indicator is a bubble and 2 white lines

• When the bubble is outside the lines and to the right, the plane is slipping to the right.

• Co-ordinated turn:

• To correct adverse yaw (yaw in opposite to the roll direction), rudder is deflected

• 1 international knot = 1 nautical mile per hour = 1.852 kilometre per hour exactly.

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