Y

Source edition 1965. Please read the Introduction to find out about this dictionary and our plans for it. Caution, many entries have not been updated since the 1965 edition.
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yagi antenna

A type of directional antenna used on some types of radar and radio equipment consisting of an array of elemental, single-wire dipole antennas and reflectors.

yard (International)

Exactly 0.9144 meter.

The U.S. yard before 1 July 1959 was 0.91440183 meter.

yaw

1. The rotational or oscillatory movement of an aircraft, rocket, or the like about a vertical axis.

2. The amount of this movement, i.e., the angle of yaw.

3. To cause to rotate about a vertical axis.

4. To rotate or oscillate about a vertical axis.

yaw angle = angle of yaw.

yaw axis

A vertical axis through an aircraft, rocket, or similar body, about which the body yaws. It may be a body, wind, or stability axis. Also called a yawing axis.

yawing axis = yaw axis.

yawing moment

A moment that tends to rotate an aircraft, an airfoil, a rocket, etc., about a vertical axis.

The moment is considered positive when it rotates clockwise.

year

A period of one revolution of the earth around the sun.

The period of one revolution with respect to the vernal equinox, averaging 365 days 5 hours 48 minutes 45.68 seconds in 1955, is called a tropical, astronomical, equinoctial, natural, or solar year. The period with respect to the stars, averaging 365 days 6 hours 9 minutes 9.55 seconds in 1955, is called a sidereal year. The period of revolution from perihelion to perihelion, averaging 365 days 6 hours 13 minutes 53.16 seconds in 1955, is an anomalistic year. The period between successive returns of the sun to a sidereal hour angle of 80 degrees is called a fictitious or Besselian year. A civil year is the calendar year of 365 days in common years, or 366 days in leap years. A light year is a unit of length equal to the distance light travels in one year, 9.460 X 10E12 kilometers. The term year is occasionally applied to other intervals such as an eclipse year, the interval between two successive conjunctions of the sun with the same node of the moon's orbit, a period averaging 346 days 14 hours 52 minutes 52.23 seconds in 1955, or a great or Platonic year, the period of one complete cycle of the equinoxes around the ecliptic, about 25,800 years.

Young modulus (symbol E )

The ratio of normal stress within the proportional limit to the corresponding normal strain.