The attitude gyro

FOR many years a glance at the instrument panel told the pilot how fast he was flying, how high, and in what direction. When weather conditions obscured the horizon he flew by the seat of his pants or remained grounded. But flying by "feel" has proved highly fallible. Experience gathered over a number of years from the accidents and deaths of courageous men shows conclusively that level flight cannot be maintained for any sustained period without visual reference to the ground. Equilibrium and the kinetic sense are inadequate substitutes for sight; gravity, centrifugal force, and longitudinal acceleration cannot be distinguished by senses which normally indicate only the pull of gravity. Consequently, unless man can use his eyes for orientation, he loses his sense of balance. The possible and even probable result is a stall on one wing and, subsequently, a spin.

Although the artificial horizon, a gyro instrument, eliminated much of this danger, the last vestige of guesswork was taken out of combat and aerobatic flight when the Sperry Attitude Gyro joined the other instruments on the panel. Combining the salient features of the artificial horizon with a number of additional services, the Attitude Gyro is the only instrument which represents the plane's attitude through all possible aircraft maneuvers. It becomes effective the instant the ignition switch is turned on, never requires caging, and has no angular limitations. Through 360° of roll and pitch around the axes of the plane, full freedom as well as continuous indication is allowed. So simple is the pattern on the face of the Gyro that a pilot can interpret his reading quickly and accurately — with practice, almost subconsciously.

The face pattern consists of a polar axis which points constantly to the center of the earth. The lower half of the sphere is luminous-painted white, while the upper half is black. A fixed lubber line, marked off in alternating light and dark dashes, divides the halves horizontally, and in level flight coincides with the equator line on the sphere. A bull's eye, used as a pitch index in steep turns, is set at the center of the lubber line. Every 30° above and below the equator, latitude lines are marked off in contrasting colors and, between the latitude lines, short dashes indicate spacings of 10°. At 90° the lines appear as solid circles at each end of the polar axis. The sphere is bisected vertically by a meridian line which passes through both polar positions.

Representing a vast improvement over reading systems which depend on the relation of one line to another, the Gyro delivers increased efficiency in normal instrument and night flying. But a far more valuable contribution to aviation development is the Gyro's utility as a primary combat flying instrument. Whereas certain night maneuvers were once impossible in clouds, or under the blind flying hood, any conceivable maneuver or combination of maneuvers may now be executed with complete knowledge of the plane's attitude at all times. This literally opens broad horizons to the combat pilot whose situation must determine his procedure. He may now feel free to use his plane to the utmost of its inherent capabilities without considering extraneous problems heretofore presented by inadequacy of equipment. Furthermore, since caging is foreign to the new Attitude Gyro, the pilot may go on instruments immediately after maneuvers without the concern of first leveling off and then adjusting the gyro.

A primary concept in the use of the instrument is always to visualize the polar axis as vertical to the earth's surface and the sphere as a stable object. The resultant impression is that of a stationary sphere about which the plane and instrument panel rotate to give the pilot an exact picture of the plane's movements in relation to the earth.

In level flight, the sphere's equator is perfectly aligned with the lubber line. Deviations from straight and level may be determined quickly from the position of the equator line and, more explicitly, from a reading of the degree of deviation from the lubber line. If, for example, a large portion of the white is hidden and the vertical index on the case rotates counterclockwise with respect to the pattern, the pilot knows instantly that the plane is diving to the left. Noting the circle and degree readings, he finds that the dive is at 30° and the turn is 30°. Conversely when a major portion of the black is obscured, immediate indication of a climb is made. As the climb increases to the perpendicular mark, the black disappears completely; and at 90° the white background, with concentric black circles and a black bull's eye, is in the center of the case.

Aside from the safety factor which is brought about by facilitated maneuvering and recovery from hazardous or abnormal Right attitudes, the introduction of the Attitude Gyro to modern flying affords fuller realization of the potentialities of the modern plane. Engineering achievements in operational design have been matched by the triumph of the Sperry Attitude Gyro over another natural obstacle in man's flight for the skies.

This article was originally published in the February, 1945, issue of Air News magazine, vol 8, no 2, pp 35-36.
The PDF of this article includes a photo of the display and diagrams showing the display in various attitudes of the aircraft.
The original was printed on 9½ by 12¾ paper. The images in the PDF have been reduced to print on letter-size paper.
Photos and diagrams credited to Sperry.