rated 2 1/2-minute OEI (one engine inoperative) power. 14 CFR Part 1: “With respect to rotorcraft turbine engines, means the approved brake horsepower developed under static conditions at specified altitudes and temperatures within the operating limitations established for the engine under Part 33 of this chapter, and limited in use to a period of not more than 2 1/2 minutes after the failure of one engine of a multiengine rotorcraft.”
rate gyro. An instrument which measures the rate of rotation of an object about an axis. A spinning gyroscope precesses, or tilts, when it is rotated in a plane at right angles to its own spin axis. The amount the gyroscope tilts is proportional to the rate at which it is rotated about an axis at right angles to both its spin axis and the axis of its precession (the axis about which it tilts). Rate gyros are used in turn and slip indicators and turn coordinators.
rate-of-climb indicator (aircraft instrument). An instrument used to show the pilot the rate at which the aircraft is climbing or descending. A rate-of climb indicator is a pressure instrument that compares the pressures inside and outside a metal capsule inside the instrument case. Static pressure is directed into the instrument case and also into the capsule, but to get into the capsule, the air must flow through a calibrated orifice (a tiny hole of a specific size).
When the aircraft is not changing altitude, the pressure inside the capsule is the same as that inside the instrument case. But when the aircraft is climbing or descending, the orifice causes the pressure inside the capsule to change more slowly than the pressure inside the case. This lag in the pressure change causes the capsule to expand or collapse until the pressure equalizes. The amount of expansion or collapse is measured, and it indicates on the instrument dial as the number of feet-per-minute climb or descent. Rate-of-climb indicators are also called vertical-speed indicators.
rate-of-temperature-rise fire detector. A type of fire detection system that uses a series of thermocouples to detect a fire condition by the rate at which the temperature being monitored rises.
A series of thermocouples is placed in the area being protected, and a reference thermocouple in the area is insulated so its temperature always changes slowly. When the overall temperature rise is slow enough that the insulated thermocouple remains at the same temperature as the measuring thermocouples, no signal is sent to the fire warning system. But if a fire occurs and the measuring thermocouple gets hot before the insulated reference thermocouple, a voltage is produced that causes a current to flow and actuate the fire warning system.
rate of yaw. The rate, usually expressed in degrees per second, at which an aircraft rotates about its vertical axis.
rating. 14 CFR Part 1: “A statement that, as a part of a certificate, sets forth special conditions, privileges, or limitations.”
ratio. A relationship between two quantities. A ratio of two to one (2:1) is a relationship in which the first quantity is two times as large as the second.
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