This article first appeared in the July-August 1972 Flight Test News.

St. Louis
An F-4 Phantom, modified by MOC under an Air Force program, made its first flight on April 29 with a Survivable Flight Control System including fly-by-wire flight control. This is the first flight of fly-by-wire on a high performance fighter aircraft.

Pilot of the test aircraft on the flight from McDonnell Douglas facilities at Lambert-St. Louis International Airport was Charles P. Garrison, McDonnell Douglas experimental test pilot. Garrison said that no problems were encountered and that control of the aircraft was noticeably improved.

Electrical sensors
In the fly-by-wire system, electrical sensors measure both pilot commands, in the form of stick and pedal movements, and the aircraft’s flight path responses in pitch, roll and yaw. Computers process the sum of the sensors’ inputs and act to provide electrical signals which move the primary control surfaces, such as ailerons, to produce the desired aircraft motion. The electrical signals are carried to the controls over four redundant channels.

The aircraft used in the test flight was equipped with mechanical controls as a backup and they were used during take-off and landing and some parts of the flight. The mechanical controls will be removed later in the program, which is directed by the Air Force Flight Dynamics Laboratory, Wright-Patterson Air Force Base, Ohio.

In present central systems, a failure at any one point in the mechanical control system could result in loss of control and subsequent loss of the aircraft. In fact, combat experience has shown that minor damage of small arms fire can result in destruction of aircraft due to loss of pilot control. This is caused either by weapon hits in the hydraulic power distribution system or by damage which cuts single-thread mechanical flight control linkages.

With the fly-by-wire approach, suitable identical channels of electrical signals or paths of information can be provided to minimize the effects of failures within the system.

Other benefits
The fly-by-wire configuration has other benefits: superior aiming, tracking and weapon delivery; reduced pilot “Power-by-wire” workload; flight control design and installation savings; decreased cost; and more airframe design freedom.

Incorporation of motion sensors and analog computers gives the pilot a simple means of commanding’ the aircraft flight path with significantly reduced physical effort. Thus the pilot can fly smoothly and precisely with less effort devoted to flying the aircraft, enabling him to concentrate more on other important tasks.

A second significant element of the Survivable Flight Control System is “power-by-wire” which incorporates an integrated actuator package. Since the integrated actuator package generates its own hydraulic power in proximity to where it is used, the vulnerable hydraulic lines interlaced throughout the aircraft disappear.

The program is being conducted by McD.onnell Douglas under a $16 million contract.

This article first appeared in the July-August 1972 Flight Test News.

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