Manufacturers have concluded that aerobatics or the g-loads associated with them won’t materially damage or shorten the life of running gyros as long as they are free or uncaged during these movements. Locking the gyros restaurant in a caged position during these motions may injure the spin bearings and/or gimbal bearings because of the massive angular momentum of the spinning mass and the resulting quadrature forces. The best course of action is to fly straight and level while doing aerobatic manoeuvres and using caging to reset the gyro as needed.
Aerobatic Manoeuvres’ Effects on Gyros
A directional gyro’s cage feature makes it simple to raise the rotor into a horizontal plane and align it with the magnetic compass. While performing aerobatic manoeuvres, the heading card may start to spin; in this case, the pilot should pull the caging knob to stop the spinning. Once he is back in level, straight flight, he should pull the caging knob and align the heading card with his magnetic compass.
Standard Horizontal Gyros without a Caging Feature: These gyros feature +/- 85 degrees of pitch mobility and 360 degrees of roll freedom. Erection and the necessary pitch and roll information are kept during full loops by carefully managed precession. For the majority of aerobatic manoeuvres, the Horizon Gyro will maintain its erection (spin axis aligned to the dynamic vertical) and provide precise pitch and roll references. However, the Horizon Gyro might be vulnerable to certain manoeuvres that could cause it to lose its vertical reference and even “spin out.” The biggest disadvantage of this scenario is that it can require 10 to 20 minutes of level flight for the Horizon Gyro to fully develop and start providing precise pitch and roll data.
If the Horizon Gyro tumbles during an acrobatic performance, the pilot can pull the caging knob to rapidly align the gyro rotor with a vertical reference and return to level flight (*using the earth’s horizon as a reference). The gyro indication may be a few degrees off, depending on how well the pilot aligns his aircraft with level flight during the caging procedure, but the pilot will still have useful pitch and roll information, and a slight inaccuracy will be corrected by the internal erecting system in 2 or 3 minutes.
Conclusion
My name is Jerry Bishop, and I’ve owned and restored a variety of vintage aircraft. I have 45 years of experience designing gyros, vacuum pumps and engine instruments for aircraft.
