Gyroscopic Principles - اسأل الطيار ask pilot


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الأربعاء، 14 أكتوبر 2020

Gyroscopic Principles


In aircraft instruments, gyros are used in attitude, compass and turn coordinators. These instruments contain a wheel or rotor rotating at a high RPM which gives it two important properties: rigidity and precession. The rotor or gyro can be electrically or vacuum / pressure driven by a special pump on the engine. Construction wise the gyro is fixed in the instrument by rings or gimbals and these give the gyro certain motions of freedom. It is these motions or movement in each planes which allow for certain characteristics used in these instruments. Pilots flying under VMC will normally only rely on these instrument when getting out of IMC situations. Keep in mind that to be proficient in flying on instruments you will need regular training with a safety pilot, aka flying under the hood. Without being current on instruments, most if not all VFR pilots, will probably crash when attempting to fly in IMC conditions due to the lack of experience and training. Gyros offer two properties that aircraft exploit: Rigidity in space (a gyro will resist any attempt to displace it along the axis that it spins), and precession (a force applied to a gyro perpendicular to the axis of rotation will manifest itself 90° further along the axis of rotation). Any IFR-capable aircraft has three gyroscopic instruments -- a vacuum gyro, powered by an engine-driven vacuum pump, and two electric gyros. The vacuum gyro functions whenever the engine is running and generating sufficient power as to create enough suction to spin the gyro. It powers what is considered the most critical gyro instrument, the #ALTITUDE INDICATOR:The attitude indicator substitutes for the pilot's view of the horizon during poor visibility, and is the primary instrument the pilot references during instrument flight. For that reason, the attitude indicator must be able to continue to function even during an electrical failure.(#REFERFIGURE1AND2) The attitude indicator works by exploiting rigidity in space. The gyro in the attitude indicator remains level with the horizon even as the airplane banks and pitches around it, and is attached to two gimbals that control the height and bank of the index. #The most critical electric-powered gyro instrument is the TURN COORDINATOR , which gives the pilot rate of turn information.(#REFERFIGURE3AND4) The icon of the airplane provides bank and rate of turn information. At the onset of the turn, the airplane icon directly indicates bank. Once the turn is established, it indicates rate of turn. There are hatch marks at level and 2-minute turn (3°/second), a so-called "standard rate turn." All turns in instrument flying must be standard rate. As you can see, the words "D.C. ELEC." on the turn coordinator are a reminder that this is an electrically-powered gyro instrument. This is the second most critical gyro instrument, because in the event of a vacuum pump failure (and thus attitude indicator failure), this instrument can be used in conjunction with the altitude indicator to maintain straight and level flight. The enclosed ball beneath the airplane icon is the slip indicator. It functions exactly like a leveler, and indicates any side-loading during the turn. The pilot strives to keep the ball centered at all times. The turn coordinator works by exploiting precession. As the aircraft turns, a force is applied to the gyro, which via precession translates to a perpendicular force applied on the gimbal, causing the airplane icon to bank. If the gyro were flush with the longitudinal axis of the airplane, it would purely indicate rate of turn. By canting the gyro slightly, you allow it to provide bank information at the start of the turn, because now banking the aircraft no longer purely rotates the gyro perpendicular to its axis of rotation. #The final electrical gyro instrument is the HEADING INDICATOR, which displays the aircraft's heading.( Refer figure 5 and 6) This instrument displays the current magnetic heading in degrees. However, because a gyro only offers rigidity, and not any sort of sensitivity to magnetic fields, the heading indicator must be calibrated against the magnetic compass; otherwise it will simply display an arbitrary heading. The directional gyro exploits the principle of rigidity in space. As the aircraft rotates around the gyro, the gimbal drives a gearing system that turns the compass card. Precession will cause the instrument to become steadily more inaccurate, so pilots must remember to re-calibrate the heading indicator against the magnetic compass every 15 minutes or so. (Some advanced heading indicators can be automatically slaved to the magnetic compass.) Despite these downsides, heading indicators are still considered the primary source of heading information (rather than the magnetic compass), due to the fact that they remain accurate in banks, during acceleration, and rough maneuvering — all of which cause a magnetic compass to be inaccurate.

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