In The Works: Cessna 850 Citation Columbus
Cessna is adopting “hybrid” fly-by-wire technology to actuate the flight controls on the Citation Columbus, formerly known as the Large Cabin Concept jet. This is Cessna’s first use of fly-by-wire flight controls in a Citation design, and the system combines electronic and mechanical control of flight control actuators.
The Columbus’ ailerons, elevators and rudder are moved with hydraulic actuators, which are controlled via both the fly-by-wire system and mechanical control cables. The ailerons and elevators are each split into two control surfaces, with the hydraulic actuators on the inboard sections of each flight control hooked to the fly-by-wire system and the outboard sections’ actuators hooked to cables attached to the pilots’ yokes.
The rudder consists of two hydraulic-actuator-powered control surfaces, and the fly-by-wire system is used to make the two surfaces provide rudder trim and yaw damper functions. Rolf Anderson, a supervisor on the Columbus control system, said that the hybrid system combines the safety and backup benefits of mechanical controls and the tailored performance available with fly-by-wire. Either system can be used to fly the airplane.
“Together they deliver reliable, superior performance,” he said. And unlike a full-up fly-by-wire system, the Cessna design does not require three redundant hydraulic systems–the Columbus has two–nor does it need extra backup power systems or autopilot servos, saving a lot of weight.
Cessna engineers have been working on the fly-by-wire control system for many years, Anderson said, and have applied for a patent on the hybrid architecture.
While Cessna engineers laid out the architecture of the fly-by-wire control system, supplier Parker Aerospace will design and manufacture the primary and secondary flight controls. Cessna said that the fly-by-wire system will provide “improved pilot handling and ride quality” as well as safety benefits such as “improved envelope warning and protection functions and control redundancy.”
The fly-by-wire system will also save weight by eliminating control cables or pushrods and by incorporating autoflight and flight augmentation functions, according to Cessna. The Columbus will be equipped with a standard yoke, not a sidestick.