Attitude indicator

SINCE the concept of aviation the pilot has never really been able to tell the attitude of his plane in relation to the ground. He has used his senses, flown by the seat of his pants, developed feel for something that he was never intended to do in the first place. Instruments were developed to help him for level flight that made possible for him to become a better pilot, but still in any kind of maneuver he had to rely on his 'feel' for knowledge of just what position he was in in relation to the ground. Now he has a new instrument that tells him his attitude in relation to the earth's surface even throughout extreme departures from normal level flight.

The new instrument is the Sperry Attitude Gyro Indicator. With this new indicator the man at the controls can now execute all manner of complicated aerobatics with the complete confidence that comes from being able to tell at any second the exact attitude of his plane. Moreover, the picturization of plane movements which this instrument presents, by means of pattern indication, is so simplified that during recently completed tests, pilots were flying perfectly executed loops and slow rolls under the hood with less than an hour's instruction in its use.

As in other gyro flight instruments, a gyroscope is the heart of the new Attitude Gyro Indicator. Electrically propelled around a vertical axis, the 14 ounce gyro employs the familiar gyroscopic properties of rigidity and precession to provide a fixed reference pattern around which the plane may be maneuvered in any direction. This entirely new feature is made possible by a method of suspension which allows universal movement of the instrument case around a spherical gyro rotor housing. The reference pattern is marked on the surface of this stabilized sphere with luminescent paint and is visible to the pilot through a masked opening in the front of the instrument case. The gyro is compensated for turn error and will give better performance in that respect than the Horizon.

The indicating sphere is divided into hemispheres by painting the upper half white luminescent and the lower half black. In order to increase the concept of a spherical surface, as well as to indicate pitch angle, latitude lines in contrasting color, (white on black, black on white) are inscribed at 30 degree intervals, with short 10 degree marks between. A vertical meridian line, also in contrasting color, gives roll angle indication with reference to a fixed index on the mask around the sphere. A lateral lubber line, marked in alternate black and white sections, stretches across the center of the mask opening and provides the basic pitch index for reference to the pattern of the sphere.

No caging mechanism is necessary in this instrument since the gyro has complete freedom around all three axes. The only knob or adjustment available to the pilot is that for the "target," a small circle which adjusts up and down to compensate for change in trim of the airplane for level flight.

The new instrument weighs approximately four and one-quarter pounds.

This article was originally published in the October, 1944, issue of Air Tech magazine, vol 5, no 4, p 48.
Photos credited to Sperry Gyroscope Co.
The PDF of this article includes a small photo of the indicator inset on a duotone image of the inner assembly.