Going Forward

Here’s what happens in flight when a pilot wants to control the forward track of his helicopter, for example.

To move forward, the pilot would move the cyclic pitch control stick forward, causing the front pencil to drop down and the rear pencil to lift up. That would tip the hockey pucks, or in the real helicopter, the swash plates, forward. The upper swash plate, rotating on its bed of ball bearings, would also tilt forward, pushing its rear pencil up and pulling its front pencil down. In the example of forward flight, the left and right pencils would neither rise nor fall. They would only come into play if the pilot were moving the cyclic pitch control stick left or right.

To say it another way, when one of the rotor blades began to swing toward the rear of the helicopter, its “pitch link” that we’ve been representing with rotating pencils resting on the top puck would be pushed upward. That would cause the angle of the blade to increase, give the blade more lift, and cause it to rise. At the same time, the pitch link on the blade that was swinging toward the front would respond to the downward tilt in the swash plate, flattening the pitch of the blade. The blade would lose lift as a result and drop downward slightly.

Put it all together, and you have a rotor disc that tilts forward and a lift vector pointing in the same direction. The result is a helicopter moving forward.

Going Forward

On Course

In some models of helicopters, including some used by military pilots, only one bolt attaches the rotor blade assembly to the top of the main rotor shaft You can just imagine the dire conse­quences if that bolt fails, as it has on a few occasions. For that rea­son, pilots call it the “Jesus bolt" naming it after the next person you’re likely to see if it breaks.

Going Forward

On Course

Some helicopter designs combat torque by combining two main rotors spinning in opposite direc­tions. When the rotors spin in different directions, the torque created by one cancels the torque of the other. Because і there is no antitorque rotor, the foot pedals act as cyclic pitch controls. The addition of a sec­ond main rotor also boosts the amount of weight the helicopter can lift making the two-rotor design the perfect one for cargo helicopters.

The same principles apply to other directions as well. The helicopter’s ability to move backward or to slide sideways is one of its key attractions, and it is made possible by the cyclic pitch control.

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