◆ 7、 Air Craft Controlling Devices

All airplanes have hydraulic systems to control rudders, flaps and all other attitude controlling devices.  The larger the airplane, the more it relies on hydraulic systems because of the requirement for high thrust and durability of components.

But hydraulic system must have piping network on a airplane, and on top it for safety purpose the system has to have at least three back-ups working in parallel with the main network.　Even though this very conservative, nerve-racking safety measure is strictly maintained, in the past many disastrous accidents occurred due to the failure of all of four hydraulic pipe lines.
These accidents are one of reasons which triggered the development of the hybrid actuator “HySerpack”.  The thought was simple. “If the pipes are the source of the troubles, then the best measure to get rid of troubles is to eliminate the pipes themselves.”

Now Boeing B777’s have replaced all conventional hydraulic systems with hybrid actuators. But the hybrid actuators on B777 are still using servo-valves while HySerpack is a perfect DDVC (Direct Drive Volume Control) unit which regulates the rod movements only by the volume and the direction of fluid flow without using any valves to control the flow. HySerpack for the use of attitude control of air planes are patented in USA, UK and Japan.

The system employed for B777 is called “Fly-by-Wire” by technical terminology because electric cables are used to transmit signals to each hybrid actuator from the central control unit.  Recently optical fibers are started being used for signal transmission.  This system is now called as “Fly-by-Light.”