1. Field of the Invention
This invention relates to wind blades and specifically to a device rotating helicopter airfoils or wind blades that will reduce in the wind blade and its related structure. The device as presented, imposes variable moment forces to the blade which are induced by a gyro which has an adjustable precessional rotational rate. The invention is shown applied to helicopter blades.
2. Cross Reference to Related Applications
This invention uses the concept of gyro moment forces to introduce torque forces which are counter to the normal blade forces. An earlier patent, U.S. Pat. No. 4,302,152, describes a constant moment gyro device used on windmills to impose a counter force on an airfoil. The reference Patent does not however provide a means to vary the counter moment force.
3. Discussion of Prior Art
Wind blades are subject to cyclic forces. Cyclic forces produce unwanted blade deflection and vibrations. Vibrations can seriously degrade service life of the equipment by overstressing, fatigue, and wear of components.
In windmills, a cyclic force on the blade is caused by the wind shadow from the supporting structure. This often requires the use of "before the structure" wind blades which increases the orientation problems of the windmill system.
In helicopters, the cyclic forces are the result of:
(a) various lifting forces on the blades since the blade speed differs in respect to still air due to the aircraft's horizontal movement, by PA1 (b) the blade pitch changes imposed for directional control, by PA1 (c) air movements from or to the associated structures, and by PA1 (d) agitating ground resonance.
Cyclic force vibrations are one of the major factors limiting speed of forward flight for helicopters. Secondary vibrations within the body of the aircraft are also a major concern and require absorbing components to limit their influence.
A basic method to reduce the metal stresses in blades is to provide heavier and thicker blades. This approach introduces unwanted weight and air drag to the system. Others have reduced vibrational stresses in rotating members by using "flapping hinges" on the blade/rotor assembly. Other "tuning" or vibrational damping devices have been used on blades and within associated structures. These devices add significantly to the weight and complexity of the aircraft.
Gyros or gyroscopes are weighted spinning bodies. They are well understood and their associated forces can be mathematically determined. Gyros have been used in positional control devices such as pitch control in ships. Precession is the term used for the turning of a gyro's axis. It is the characteristics of a gyro that as the gyro is precessed, it produces a torque at right angles to the precession. The torque from the precession, is proportional to the spinning speed of the gyro and the rotational rate of the precession.