hyper engines. A series of experimental high-performance aircraft engines built with U.S. Army and Navy financing in the early 1930s. The goal of these engines, which had been unattainable up to that time, was to develop one horsepower for each cubic inch of piston displacement.
hypersonic flight. Flight at air speeds greater than five times the local speed of sound, more than Mach
5.0.
hyperventilation. A breathing problem caused by too little carbon dioxide in the lungs. Hyperventilation causes a person to breathe too rapidly, and this results in dizziness and may even lead to unconsciousness.
hypotenuse (mathematics). The side of a right triangle opposite the right angle.

hypoxia. A physiological condition in which a person is deprived of the needed oxygen. The effects of hypoxia normally disappear as soon as the person is able to breathe air that contains sufficient oxygen.
hysteresis. A condition in which a physical action lags behind its cause. A spring is often slow to return to its original length when the load is removed. This slow return is caused by friction within the material of which the spring is made. This internal friction causes hysteresis.
hysteresis error (instrument indication error). An instrument error that causes a difference in the readings of an instrument when the indicated values are increasing, compared with the readings at the same point when the values are decreasing. Hysteresis error is caused by internal friction in the instrument mechanism.
hysteresis loop (magnetic materials). A curve showing the way flux density in a magnetic material varies with the magnetizing force applied to it. The shape of a hysteresis loop gives an indication of the magnetic characteristics of the material.