For many decades of aviation history, pilots controlled aircraft physically, through direct mechanical movements. When a pilot moved the control “stick”, rods, cables and hydraulic systems all moved in unison to affect the control surfaces on wings and the tail. However, today, most modern aircraft no longer operate this way. Most aircraft, especially modern commercial airliners, use a new system called Fly-By-Wire, where the pilot and the aircraft almost have a “mediator”, a series of clever computers.
So what is Fly-By-Wire?
Fly-By-Wire (FBW) is a system where inputs from pilots are transmitted electronically, rather than mechanically.
Each input from the pilot is converted to electronic signals, which are sent to multiple onboard computers, that are known are Flight Control Computers (FCC), which calculate how the aircraft should respond.
These important flight computers then command actuators to move different control surfaces based on the decided final inputs. One important thing to note about FBW is that the computers don’t “blind-obey” the pilots. Rather, they apply complex aeronautical and control laws that take into account multiple variables such as speed, altitude, angle of attack and most importantly, structural limits.
The pilot, essentially, isn’t in complete direct control of the aircraft anymore with FBW. As said online, with FBW, “The pilot requests a manoeuvre, and the computer decides the safest and most efficient way to achieve it.”
Check out this 1:400 scale Boeing 747 with a glass stand!
What Was The Traditional Flight Control Method?
Prior to FBW, aircraft used mechanical and hydromechanical control systems. These were systems in which cables and pulleys etc. ran directly to the cockpit, and from the cockpit to the control surfaces. As aircraft became larger, pure mechanical systems that only relied on cables and pulleys had to switch to the hydromechanical control systems, which used pressurised fluid to amplify pilot input.
Advantages and disadvantages of Mechanical Flight Controls
| Advantages of Mechanical Flight Controls | Disadvantages of Mechanical Flight Controls |
| Pilots receive direct physical feedback through control forces as they would be able to feel some of the force exerted on the control surfaces, allowing the pilots to directly feel “what” the plane is doing, with many pilots stating that they felt that the plane was “talking” to them. | Mechanical Flight Controls do have serious limitations, however. As an aircraft becomes larger in size, the forces required to move the control surfaces become larger, so more complex and heavy hydraulic systems are required to move control surfaces which also increase maintenance. |
| Simplicity. The aircraft simple obeys the command of the pilot, without questioning a decision, which can be very useful in unusual/emergency situations. | These controls offer no protection against pilot error. A pilot could accidentally enter the aircraft into a stall, and the aircraft would comply. |
| Gives the pilots the peace of mind, and a re-assurance that, “there is nothing between me and the plane, it does as I want it to, and it can’t go rogue.” | MFC rely on pilot skills, which degrade over time, therefor increasing risk of emergencies over the course of a pilots carreer. |
Advantages and disadvantages of Fly-By-Wire
| Advantages of FBW | Disadvantages of FBW |
| Computers can prevent aircraft from: – Stalling – Overspeeding – Excessive bank angles – Excessive pitch attitudes – Structural overload This makes modern aircraft more resilient from minor and extreme errors. | Pilots no longer feel direct feedback from the aircraft. Essentially, the pilot can no longer “talk” to the aircraft and feel how the plane is acting. This can reduce awareness of the pilot if designed poorly. |
| “Allows for aerodynamically unstable aircraft to exist. Many modern military jets and some commercial aircraft designs rely on inherent instability for efficiency or maneuverability. Such aircraft would be impossible to fly without constant computer correction.” | Pilots can become too accustomed to flying with assisted controls, reducing their manual flying skills over time. |
| Reduces the weight of an aircraft as there is no longer a need for complex pully/hydraulic systems. | FBW relies on lots of computers, sensors, redundancy and software, and failures can happen, even though there are multiple backups, pilots may lose their trust in some electrical systems of an aircraft. |
To Conclude
Modern aircraft don’t fly the way people think as now, aircraft have traded direct physical control for safety, efficiency and reliability.
Rather than weakening the pilots control, FBW re-shapes it. The pilot still directly command the aircraft, but now, there is almost a second “authorisation” needed when the pilot makes an input. This information is key to understanding how modern aircraft work.
Also, see my post on Benefits of Fuel Efficiency in Aircraft
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