Fly-by-Wire ( FBW) Technology

One of the first lessons that student pilots are taught in their training is the relationship between the pitch attitude and power settings required to control the aircraft. Once you get more comfortable and experienced as a pilot, you start your instrument flying journey where you notice how important those initial lessons were on pitch and power as the margin of error is limited and your workload is at it’s peak.

Hence it could be so much easier if there was a system which could control the path of the airplane without the pilot constantly trying to adjust the controls and just obtain the desired pitch attitude and leave the yoke/side-stick without trimming or adjusting the power setting (with the help of the auto thrust – more on this later) . The fly by wire system makes flying much more easier by being that system. It not only controls the path of the aircraft but provides a flight protection envelope as well.

Conventional Flight Control Mechanism

Picture Credits: Slideshare

• The Wright Brothers used combinations of their body movements to deflect the portions of their FLYER, causing it to move in the desired directions.
• In a conventional light weight trainer type aircraft , cables are connected to the controls in the cockpit through a bell crank and the other side of the bell crank is connected to the control surface.Movement of the cockpit controls transfers force through the cable to the bell crank, which moves the control surface.
• However in a high performance aircraft, the control surfaces have great pressure exerted on them and hence it is physically impossible for the pilot to manually move the controls. Hence, hydraulic actuators (cylinders) are placed in the link to assist the pilot in moving the control surface.

Fly-by-Wire System

• As discussed above, flight controls could be handled mechanically or hydro-mechanically.However, a fly wire system is an electrical way of controlling the flight controls in an aircraft.
• The fly by wire system adds in an electronic interface to control the aircraft . The pilots command are converted into electronic signals that are interpreted by the flight control computers.The computers interpret the pilot input and determine how to move the actuators connected to the flight control surfaces,as necessary, to follow their orders.
• The actuators are still hydraulically operated that are similar to the hydro-mechanical system.The computer monitors the aircraft’s response to the flight control movement and modifies its output accordingly to the actuators.

Airbus 320 Fly-by-Wire System

• In the Airbus 320, there are 7 flight control computers and 3 hydraulic systems to take care of the primary flight controls (elevator, aileron, rudder) .
• Each primary control has 2 hydraulic actuators, each fed from one of the three independent hydraulic systems.
• The 7 flight control computers are :
  • There are 2 Elevator and Aileron Computer (ELAC) to control the elevators, ailerons and stabliser.
  • There are 3 Spoiler Elevator Computer (SEC) to control the spoilers ( more on the functioning of spoilers in a separate post) and elevators.In the event of the ELAC failing , the SEC will control the elevators and stabiliser.
  • The rudder is controlled through hydro-mechanical pedals by the pilot, however there are 2 Flight Augmentation Computers (FAC) that operate the rudder to keep the aircraft balanced in a roll.
  • The stabiliser trim can be mechanically controlled by the pilots trim control wheel.
• To summarise, the elevators and ailerons have access to 5 computers in total and only one is needed for operation.There are 3 hydraulic systems out of which only 1 or 2 are needed for operation, it shows that the system has electrical and hydraulic redundancy built into it .
• In the event of a total electrical failure, the pilot can control the aircraft manually using the trim wheel for lateral control and rudder pedals for longitudinal control.

Advantages of the Fly-by-Wire System

• Reduced Weight :Mechanical and hydro-mechanical flight control systems are relatively heavy and require careful routing of flight control cables through the aircraft by systems of pulleys, cranks, tension cables and hydraulic pipes.Hence replacing these with actuators , sensors directly reduces the weight of the aircraft .
• Flight Envelope Protection: The protection prevents the aircraft from performing manoeuvres outside the flight envelope. For example , stalling or over speeding.
• Improved Flight Controls: With the help of the fly by wire system, the pilot need not provide excessive control inputs as the computer determines how to move the actuators connected to the flight control surface.
• Increased Commonality: After the rise of the Airbus 320 family, In terms of Airbus aircraft’s, no matter how one aircraft varies in size or weight from another, fly-by-wire commonality allows the pilot to fly them in the same way because the computer “drives” the aircraft’s flight controls. This leads to considerable reductions in the time and costs involved in training pilots and crew to operate them.

Advantages of the Fly-by-Wire System

Disadvantages of the Fly-by-Wire System

• Redundancy: The failure of an electrical system could lead to a complete shutdown where as the traditional mechanical flight control system fails gradually and makes the pilot more aware of the failure. The loss of the aircraft flight control computer could immediately make the aircraft uncontrollable.However, in commercial airplanes, this problem is solved by using redundant computers and providing mechanical backup in case of total electrical failure.As seen above, in the working of the Fly-by-Wire system of the Airbus 320.
• Lack of visual feedback: As the control is not physically connected to the control surface, feedback is lost. The side sticks in the aircraft are not connected to each other that, this means that, the input provided on one side stick cannot be felt on the other and hence visual feedback from the stick is lost.
• Over dependence on FBW: Murphy’s law states that : “Anything that can go wrong will go wrong ”. Pilots are sometimes guilty on relying heavily on automation. There is no doubt that computers aid pilots in making flying easy but Murphy’s law holds true and there is always a chance for them to fail.

History of the Fly-by -Wire System

• AVRO CANADA CF-105 ARROW: The Avro Canada CF-105 Arrow (the Arrow) was a supersonic interceptor jet aircraft designed and built in the 1950s by A.V. Roe Canada (Avro). It was fitted with innovative technologies, including a fly-by-wire control system and a computerized control system that allowed the pilot to operate the aircraft electronically. It was canceled on the February 20, 1959 (known as “Black Friday”), a decision that remains controversial today.It was the first non experimental aircraft with fly-by-wire controls.
• LUNAR LANDING RESEARCH VEHICLE (LLRV) : On May 25, 1961, President John F. Kennedy committed the United States to landing a man on the Moon and returning him safely to the Earth before the end of the decade.In December 1961, NASA Headquarters in Washington, D.C., received an unsolicited proposal from Bell Aerosystems in Buffalo, New York, for a design of a flying simulator to train astronauts on just that challenge.Bell Aerosystems delivered the LLRV-1 on April 8, 1964, where it made history as the first pure fly-by-wire aircraft to fly in Earth’s atmosphere. Its design relied exclusively on an interface with three analog computers to convert the pilot’s movements to signals transmitted by wire and to execute his commands.
• F-8C CRUSADER: In 1972, NASA gave the world the next big thing in flight controls when the agency’s Dryden Flight Research Center showed how to use the digital fly-by-wire (DFBW) system, the computerized system is used today on everything from jet airliners to cutting-edge fighters and stealth bombers. Dryden’s DFBW aircraft — an F-8C Crusader given to NASA by the U.S. Navy — flew for the first time on May 25, 1972.The program’s chief research pilot, Gary Krier said “Everyone on the program knew that what we were doing was going to be a major breakthrough in flight control”.
• AIRBUS Fly-by-Wire SYSTEM :One of the A300-600 and A310’s notable innovations had been the introduction of electrical signalling on secondary flight controls, replacing the web of cables and pulleys tradionally used. Airbus wanted to take this evolution further with the next Airbus aircraft – to computer-driven digital “fly-by-wire”, in which the deflections of the flying control surfaces on the wing and tail are no longer driven directly by the pilots’ controls, but by a computer which calculates exactly which control surface deflections are needed to make the aircraft respond as the pilot wishes.
• DASSAULT FALCON 7X: From its inception, the Falcon 7X was destined to be a revolutionary aircraft, introducing business aviation to the industry’s first Digital Flight Control System.Not only does the 7X handle like a fighter jet, it’s controlled like one. In the cockpit, the pilot’s hand falls naturally on a side-stick controller. Pilots love the 7X intuitive responsiveness and precision. Passengers appreciate its silk-smooth ride and the contribution such an advanced technology makes to aircraft safety.

FACT OF THE WEEK:

It was on February 10, 1929 that India got its first licensed pilot in Jehangir R.D. Tata, who qualified with number 1 on his flying license, giving birth to Indian aviation.J.R.D’s license, then called an ‘aviators certificate’, was issued by The Aero Club of India and Burma, an associate of the Royal Aero Club of Great Britain, which was authorised to issue licences by the British Empire’s Federation Aeronautique Internationale. The Aero Club of India and Burma was recognised by Federation Aeronautique Internationale as a sporting authority.

J.R.D. launched India’s first airmail service in 1932, when he flew into Mumbai in a De Havilland Puss Moth from Karachi’s Drigh Road Aerodrome to the Juhu Airstrip via Ahmedabad on the basis of this flying license.This later became the country’s national carrier, Air India.Click the link to know more about iconic figure in aviation history : https://www.tata.com/newsroom/wings-for-a-nation

This is it for this weeks post. I hope you gained some knowledge and if you did, please share it with your fellow aviators . Please feel free to reach out to me via Email, Instagram or Twitter, you’re feedback is always valued. Thank you for you’re support . Until next week , stay and stay healthy.

YOUR COPILOT

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