A flight control system consists of the flight control surfaces, the respective cockpit controls, connecting linkage, and necessary operating mechanisms to control aircraft in flight

The fundamentals of aircraft controls has been explained in aeronautics. Discussion here centers on the underlying mechanisms of the flight controls. Generally the cockpit controls are arranged like this: Aeronautics is the science and practice of aerial locomotion, i. ...

• control yoke for roll which moves the ailerons
• control column for pitch which moves the elevators
• rudder pedals for yaw which moves the rudder

Some light aircraft use a control stick for both roll and pitch; the rudder pedals for yaw.

Classification

Flight control systems (FCS) are classified as follows:

• mechanical FCS
• hydromechanical FCS (powered flight control units(PFCU))
• fly-by-wire FCS

Mechanical FCS

The mechanical FCS are the most basic design used. They were used in early aircraft designs and currently in small aeroplanes where the aerodynamic forces are not excessive. The FCS uses a collection of mechanical parts such as rods, cables, pulleys and sometimes chains to transmit the forces of the cockpit controls to the control surfaces. The Cessna Skyhawk is a typical example. 1971 Cessna 172 The Cessna 172 Skyhawk is a four-seat, single-engine, high-wing airplane that is probably the most popular flight training aircraft in the world. ...

Since an increase in control surface area in bigger airplane leads to an exponential increase in forces needed to move them, complicated mechanical arrangements are used to extract maximum mechanical advantage in order to make the forces required bearable to the pilots. This arrangement is found on bigger or higher performance propeller aircraft such as the Fokker 50. In physics and engineering, mechanical advantage (MA) is the factor by which a machine multiplies the force put into it. ... A propeller can be seen as a rotating fin in water or a wing in air. ... Fokker F50 VLM Airlines Fokker F50 The Fokker F50 was a small turboprop-powered airliner designed as a refinement of and successor to the highly successful Fokker Friendship. ...

Some mechanical FCS use servo tabs that provide aerodynamic assistance to reduce complexity. Servo tabs are small surfaces hinged to the control surfaces. The mechanisms move these tabs, aerodynamic forces in turn move the control surfaces reducing the amount of mechanical forces needed. This arrangement was used in early piston-engined transport aircraft and can even be found in early jet transports such as the all mechanical Boeing 707. Pan Am 707 The Boeing 707 is a four engined commercial passenger jet aircraft developed by Boeing in the early 1950s. ...

Hydromechanical FCS (powered flight control units(PFCU))

Among the drawbacks of a purely mechanical FCS is that complexity and weight of the FCS increases considerably with size and performance of the airplane. The use of hydraulic power overcomes this limitations and consequently aircraft size and performance are only limited by economics rather than technology. Hydraulics is a branch of science and engineering concerned with the use of liquids to perform mechanical tasks. ...

The FCS is made of 2 parts

• the mechnical circuit
• the hydraulic circuit

The mechnical circuit provides the link between the cockpit controls and the hydraulic circuits. Just like the mechanical FCS, it is made of rods, cables, pulleys, and sometimes chains.

The hydraulic circuit is made of hydraulic pumps, its assorted parts and the actuators. The actuators are powered by the hydraulic pressure generated by the hydraulic circuit and they convert hydraulic pressure into control surface movements. The servo valves control the movement of the actuators.

The pilot commands will cause the mechanical circuit to signal the servo valves in the hydraulic circuit to power the appropriate actuators which will then move the appropriate control surfaces.

This arrangement is found in virtually all big jet transports and high performance aircraft such as Antonov An-225, the Lockheed SR-71 and anything in-between. An-225 carrying a Buran shuttle The Antonov An-225 Mriya (Антонов Ан-225 Мрия, NATO reporting name: Cossack) is a strategic airlift transport airplane that was built by Antonov (ASTC). ... The Lockheed SR-71, unofficially known as the Blackbird, is a long-range, advanced, strategic reconnaissance aircraft developed from the Lockheed A-12 and YF-12A aircraft by Lockheeds Skunk works, which was also responsible for the U-2 and many other advanced aircraft. ...

Artificial feel devices

In the mechanical FCS, the aerodynamic forces on the control surfaces are transmitted through the mechanisms and can be felt by the pilot. This gives a tactile feedback of airspeed and is vital for flight safety.

The hydromechanical FCS does not have this "feel". The aerodynamic forces are only felt by the actuators. Artificial feel devices are fitted to the mechnical circuit of the hydromechanical FCS to simulate this "feel", giving for example, increase in resistance with increase in airspeed and vice-versa. The pilots will then feel as if they are flying an aircraft with mechanical FCS.

Fly-by-wire FCS

With the invention of autopilot, it is possible to electrically control an aircraft. The pilot utilize various switches on the autopilot for control. Later version autopilots can accept steering commands directly from cockpit controls which are fitted with transducers. The autopilot is still an addon equipment. As its reliability improves, the next stage of FCS evolution is to totally remove the mechanical circuit creating the fly-by-wire FCS. Autopilots mechanically guide a vehicle without assistance from a human being. ...

Analog fly-by-wire FCS

The fly-by-wire FCS dispenses all the complexity of the mechanical circuit of the hydromechanical FCS and replaces it with an electrical circuit. The cockpit controls now operate signal transducers which generate the appropriate commands. The commands are processed by an electronic controller. The autopilot is now part of the electronic controller.

The hydraulic circuits are similar except that mechanical servo valves are replaced with electrically controlled servo valves which are operated by the electronic controller. This is the most elementary and the earliest configuration, the simple analog fly-by-wire FCS, first fitted to Avro Vulcan in the 1940's. The Avro Vulcan was a British built jet engined, delta_winged subsonic bomber, once part of the RAFs V bomber force. ...

In this configuration, it is necessary to simulate "feel". The electronic controller provides feel signals to electrical feel devices that provide the appropriate "feel" forces on the controls. Presently this is used in EMBRAER 170, EMBRAER 190 and was used in the Concorde, the first fly-by-wire airliner. The EMBRAER 190 initial flight The EMBRAER E-Jets are a series of twin-engine jet airliners, produced in Brazil. ... The EMBRAER 190 initial flight The EMBRAER E-Jets are a series of twin-engine jet airliners, produced in Brazil. ... The Aérospatiale-BAC Concorde supersonic transport (SST) was one of only two models of supersonic passenger airliners to have seen commercial service. ...

On more sophisticated versions, analog computers are used in place of the electronic controller. The cancelled supersonic Canadian fighter, the Avro CF-105 Arrow, was built this way in the 1950's. Analog computers also allowed certain amount of customization of flight control chracteristics, inluding relaxed stability. This is exploited by the early versions of F-16, giving it impressive maneuverability. The Avro CF-105 Arrow was a delta-wing interceptor aircraft, designed and built in Ontario, Canada by Avro Canada during a short period of time in the 1950s. ... In aeronautical engineering, relaxed stability refers to airplanes with no inherent natural stability, at least at low speeds. ... The F-16 Fighting Falcon is a modern multi-role jet fighter aircraft built in the United States and used by dozens of countries all over the world. ...

F-8C Crusader digital fly-by-wire testbed

Text and image from nasa. ... Text and image from nasa. ... F-8C digital fly-by-wire testbed (NASA) Two F-8 Crusaders Prepare to Launch from the USS Midway (CV-41). ...

Digital fly-by-wire FCS

It is similar to its analogue conterpart, the main difference being that the signal processing is done by digital computers. The pilot literally can "fly-through-computer". This increases flexibility as the digital computers can receive input from any aircraft sensor.

The computers compare all data received from the pilot's control stick, airspeed indicator, altimeter, angle of attack, and other aircraft sensors. They configure all flight controls for best flight characteristics and performance of the aircraft.

The internal program running the digital computers is called "Flight Control Laws". The Flight Control Laws allow designers to tailor aircraft handling characteristics precisely—for example, preventing the aircraft from being handled dangerously by preventing pilots from exceeding preset limits (the aircraft's envelope).

Sidesticks and conventional control yokes are used to fly the aircraft, it's often argued that the lack of visual feedback from the side stick is a problem, which is why Boeing went with a conventional yoke assembly with the 777 and the upcoming 787.

As the computers continuously fly the aircraft, pilot workload is reduced. It is now possible to fly aircraft with relaxed stability. The primary benefit for military aircraft is better and more responsive flight performance. It enabled inherently unstable aircraft such as Lockheed Martin F-117 Nighthawk to fly. A modified NASA F-8C Crusader was the first digital fly-by-wire aircraft, in 1972. In aeronautical engineering, relaxed stability refers to airplanes with no inherent natural stability, at least at low speeds. ... The United States Air Forces F-117A Nighthawk is the worlds first operational aircraft designed to exploit low-observable stealth technology. ... This article needs cleanup. ... F-8C digital fly-by-wire testbed (NASA) Two F-8 Crusaders Prepare to Launch from the USS Midway (CV-41). ... 1972 was a leap year that started on a Saturday. ...

For airliners, it reduces weight, both by eliminating bulky mechanical items as well as smaller flight control surfaces, thereby lowering their operating costs. The pattern started by Airbus A320 has been continued with the Airbus family and every new Boeing design since the Boeing 777. Boeing and Airbus however differ in their FBW philosophies in that in Airbus aircraft, the computer always retains ultimate control and will not permit the pilot to fly outwith the airplane's normal flight envelope under any conditions, while a Boeing 777 pilot can override the system allowing the plane to be flown outside this envelope in emergency situations. The Airbus A320 is a short to medium range commercial passenger aircraft manufactured by Airbus. ... The Boeing 777 is a family of long range widebody twin engine airliners built by Boeing Commercial Airplanes. ...

Aircraft-engine integration

The advent of FADEC-controlled engines, opens up the possiblity of fully integrated operation of both the FCS and the engines. On modern military aircraft in particular, other systems such as autostabilisation, navigation, radar and weapons system are all integrated with the FCS. FADEC is the acronym for Full Authority Digital Engine Control. ...

In addition, it allows maximum care-free performance to be extracted from the aircraft without fear of engine or airplane damage. Movable exhaust ducts jointly controlled by the FCS and FADEC delivers maximum agility through thrust vectoring. Thrust vectoring is the ability of an aircraft to direct the thrust from its main engine(s) in a direction other than parallel to the aircrafts length. ...

In the civil field, the integration increases flight safety. The Airbus A320 and its fly-by-wire bretheren are protected from low-speed stall. In such conditions, the FCS will command the engines to increase thrust without pilot intervention. The Airbus A320 is a short to medium range commercial passenger aircraft manufactured by Airbus. ...

Power-by-wire FCS

Having eliminated the mechanical circuits in fly-by-wire FCS, the next step is to eliminate the bulky and heavy hydraulic circuits.The hydraulic circuit is replaced by an electrical power circuit. The power circuits power electrical actuators which are controlled by the digital flight control computers. All benefits of the digital fly-by-wire are retained.

The biggest benefits are huge weight savings and tighter integration between the aircraft FCS and its avionics systems. The absence of hydraulics greatly reduces maintenance costs. This system is used in the Lockheed Martin F-35. The F-35 Joint Strike Fighter The F-35 Joint Strike Fighter (JSF) is a fighter plane currently in early development by Lockheed Martin (with partners Northrop Grumman and BAE SYSTEMS.) The primary customers are the United States armed forces and the United Kingdom (RN and RAF), but the Netherlands...

Intelligent FCS

A newer flight control system, called Intelligent Flight Control System (IFCS), is an extension of modern digital fly-by-wire FCS. The aim of IFCS is to intelligently compensate for aircraft damage and failure during mid-flight, such as automatically using engine thrust and other avionics to compensate for severe failures such as loss of hydraulics, loss of rudder, loss of ailerons, loss of an engine, etc. Several demonstrations were made on a flight simulator where a Cessna-trained small-aircraft pilot successfully landed a heavily-damaged full-size jet operated by IFCS, without prior experience with large-body jet aircraft. This development is being spearheaded by NASA Dryden Flight Research Center[1] (http://www.dfrc.nasa.gov/Newsroom/FactSheets/FS-076-DFRC.html). It is reported that IFCS is mostly a software upgrade to an existing fully computerized digital fly-by-wire FCS. A flight control system consists of the flight control surfaces, the respective cockpit controls, connecting linkage, and necessary operating mechanisms to control aircraft in flight The basic fundamentals of aircraft controls has been explained in aeronautics. ...

Fly-by-optics FCS

Fly-by-optics is sometimes used instead of fly-by-wire because of higher data transfer potential and avoidance of interference from electromagnetic radiation.