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Concorde Mechanical control channel

Concorde has been fitted with a mechanical control linkage between the flight compartment and the PFCU’s, this is a stand-by system and therefore only used in the event of any failure in the electrical channel (Fly-by-wire)

The mechanical control channel is made up of the following items:

  • Hand wheels

  • Chains

  • Torque tubes

  • Control rods

  • Artificial feel and integral trim assembly

  • Synchro packs

  • Autopilot force limiter

  • Relay jack

  • Load limiting mechanism

  • Jam detection strut

  • Cable tension regulator

  • Control cables

  • Mixing unit

  • Spring rod for outer and middle elevens, rigid rods for inner elevons

  • Bulkhead pressure seals

  • Control rods and bellcranks in the wings

  • Power flight control units (PFCUS)

  • Elevons 1, 2, 3, 4, 5 and 6 for each wing

The load limiting mechanism

The load limiting mechanism is composed of two parts pivoting about a common axis and installed on the relay jack support chassis. It comprises of a spring pot directly controlled by the relay jack and an output lever to the control linkage downstream.


The spring pot consists of two chambers each equipped with two concentric springs fitted around and loading a spring retainer. The spring retainers each receive a piston operated by a spigot hinged on the roller carrying arm. The roller carrying arm pivots on the spring pot housing.


The output lever is equipped with a cam which engages the roller on the roller carrying arm. Under the action of the relay jack, the spring pot drives the output lever via the roller maintained in the cam notch by the loading of the springs. If the load exerted on the lever exceeds the opposing load of the springs, the roller carrying arm compresses the springs via the pistons and the spring retainers.


The roller leaves its notch and rolls on the cam profile.


As the load exerted on the lever decreases, the cam profile and the action of the springs tend to return the roller to its neutral position in the cam notch.


The cable tension regulator

The tension regulator, which is fitted aft of the relay jack chassis beneath the passenger compartment floor, comprises of a compensating mechanism, two cable quadrants and two slack absorber jacks. The compensating system forms an assembly pivoting between two support plates which are attached to the structure. The hub, the main part of the system, comprises of two machined flanges perpendicular to the pivoting axis. Between these two flanges are attached two split cylinders guiding two springs, and a balance arm sliding on a locking shaft.


The cable quadrants pivot independently about the compensating system on bearings.


The slack absorber jacks connect each quadrant to one end of the compensating system balance arm. Because of different coefficients of expansion of materials


(structure/cables), temperature variations cause a change in cable tensions. The object of the regulator is to compensate for these differences in tension.


When cable tension increases, the quadrants pivot, pulling on the balance arm via the slack absorber jacks. Under the effect of the balanced load applied, the balance arm slides a long the locking shaft compressing the compensating springs. A new balanced position of the system is obtained; corresponding to that of an adjusted cable tension.


When cable tension decreases, the compensating springs push back the balance arm a long the locking shaft. The slack absorber jacks then transmit the movement and pivot the quadrants. Correct cable tension is maintained.


When a control load is applied, the control lever operates the compensating mechanism assembly.


The quadrant which actuates he cables must overcome the inertia and friction of the control linkage.


The balance arm held by the slack absorber jack of the quadrant loaded pivots and wedges against the locking shaft, neutralizing the compensating system. The regulator assembly then acts s a single pulley. The balance arm, via the second slack absorber jack, maintains load opposite to the movement of the assembly on the second quadrant and consequently, a tension on the cable.


The mixing unit

There is a  mixing unit which  is installed between frames 69 and 70 beneath the passenger compartment floor, and this consists of two independent stages.


The upper stage controls the inner elevons and the lower stage the middle and outer elevons.


The mixing unit comprises:


An assembly of four quadrants and crank levers joined and pivoted via support beams anchored on the structure.


A crank lever assembly pivoted on a beam and used to mix the pitch and the roll commands.


To the left of the assembly, there are two cable quadrants (Rl & R2) of opposite and combined displacement, these form the roll mixing input system.


The forward quadrant (Rl) is fitted with two crank levers pivoted on the same pin. The lower crank lever which is longer than the upper crank lever controls the middle and the outer elevon linkage, whereas the upper crank lever controls the inner elevons.


These crank levers determine the variations of displacement in roll between the inner elevons, and the middle and the outer elevons to minimize yaw moment.


To the right of the assembly, there are two cable quadrants (P1& P2) of opposite and combined displacement, these form the pitch mixing input system


The forward quadrant (P1) is fitted with two crank levers pivoting on the same pin. The lower crank lever which is shorter than the upper crank lever controls the middle and the outer elevons.


These crank levers determine the variations of displacement between the middle and outer elevens.


The crank lever comprises of two superimposed bellcranks (PB) controlled by the pitch cable quadrants and two superimposed crank levers (RL) controlled by the roll quadrants. At the rear two other superimposed bellcranks (CB) distribute the movements to each wing; they serve communally both pitch and roll. The two independent stages of the mixing unit operate on the same principle. Only the displacement values are different. Therefore only one stage is described.



Roll Control

The quadrants RI and R2 are operated by the roll control cables. Quadrants PI and P2 are immobile in the absence of pitch commands. Therefore bellcrank PB is immobile. In its movement, quadrant RI via rod 1 drives the crank lever RL pivoted at O.

The crank lever RL via rod 2 drives the bellcrank CB which pivots about point OP (fixed in absence of pitch commands).

The bellcrank CB drives the linkage in each wing.


Maximum control handwheel displacement 45° from one side of neutral to the other. Elevens displacement, outer and middle 20°, inner t 14°.

Pitch Control

The quadrants PI and P2.are operated by the pitch cables.


Quadrants RI and R2 are immobile in the absence of roll commands. Crank lever RL is immobile.


In its movement, the quadrant PI via rod 3 drives the bellcrank PB which pivots about the fixed point O.


The bellcrank PB drives the bellcrank CB which, connected to the fixed crank lever RL displaces in parallel, operating the control Linkage in each wing.


Maximum control column displacement:

  • Nose down 9° 16’


Nose up, spring pot assembly compressed 10° 44


Maximum eleven deflections:

  • With spring pot assembly compressed: 17° nose down and nose up.

  • Spring pot assembly not compressed: 17° nose down and 15° nose up.


In mixing, only the pivot points of the quadrants and the point O remain fixed. According to the flight configuration, the commands add or subtract for each wing. The elevons of the same position therefore have different deflection.


For a maximum nose down or nose up position of the control column, with spring pot assembly compressed; a roll deflection of 2° 52’ can be obtained.


For a maximum nose up position of the control column with spring pot assembly not compressed, a roll deflection of 4° can be obtained.


The elevons are connected in pairs by means of a shackle. Each eleven is operated by the two rods of a PFCU.


Each elevon is hinged on the wing structure and connected to a PFCU control rod.

Operation of each control section

Forward Fuselage Section



The roll control handwheels, installed on the Captain’s and First Officer’s control columns drive a chain, the ends of which are extended by two cables which run inside the control column down to two guide pulleys fitted below the floor.


These pulleys lead the cables forward where they are anchored to two quadrants integral with the corresponding roll torque tube.


In addition to the cable quadrants, the Captain’s torque tube comprises:


Two end of travel stops

A crank Lever which controls the artificial feel input lever via a rod

A crank lever which controls the flight data recorder potentiometers.

In addition to the cable quadrants, the First Officer’s torque tube comprises:

A control lever which actuates the artificial feel input lever via a rod

A cam, on which runs a roller integral with the First Officer’s pitch torque tube.

This system ensures a direct limitation of the travel of the linkages in pitch-roll- mixing. Twin rods, in parallel, link the artificial feel input lever to the resolver control lever for the electrical control channel.


The input lever to the synchro packs drives an autopilot force limiter spring rod with its upper crank. The spring rod directly actuates the spool-valves of a relay jack used to compensate the inertia due to the length of the linkage, and as an interconnection of the autopilot with the flight controls. The relay jack drives the mechanical linkage via a load limiting mechanism which protects the downstream linkage.


The Centre Fuselage Section


At the load limiting mechanism output, a jam detection strut equipped with a micro-switch drives the cable tension regulator which maintains the cables at the correct tension despite length variations caused by thermal expansions.

In the event of the mechanical controls jamming compression of the jam detection strut acting on the micro-switch causes the MECH JAM warning light on the overhead panel to illuminate. The cables anchored to the tension regulators run under the cabin floor, guided by pulleys, and are then attached to two cable quadrants forming the input to a double mixing unit.


The latter comprises of two stages of superimposed bellcranks, the upper stage set controlling the inner elevens, and the lower stage controlling the middle and outer elevons. This arrangement serves to modify the control ratio between the elevens. These bellcranks are also operated by the pitch control. In this manner they ensure the mixing of the mechanical pitch/roll commands.


Wing Section


 At the mixing unit output, there are four rods, (two rigid rods for inner elevon control, and two spring rods for middle and outer elevon control.) these drive two double rod and bellcrank assemblies which are mounted in pressure seals, one for each wing. The control linkages, which consist of two rods per wing, run the length of the web behind the wing spar box in an unpressurized zone. These rods, connected to a bellcrank at rib 26, transmit their respective travel to a bellcrank at rib 24. This bellcrank transmits movement to control the outer and middle elevons and, via a spring rod, the spool-valve of the PFCU operating the inner elevon.


The control of the outer and middle elevens consists of a single linkage from rib 24 onwards and is comprised of nine rods and seven bellcranks located respectively at ribs 22, 19, 15, 12, 9, 6 and 3.


The servo controls are located at ribs 9 and 3. They operate the elevons via fixed rods anchored to the body of the servo control and to the control surface. The PFCU spool-valves are controlled by rigid rods for the outer elevens and spring rods for middle elevons.



When the Captain’s and First Officer’s control handwheels are operated, their rotational movement, transmitted through the columns, becomes a linear movement from the torque tubes onward.

This linear movement via a rod actuates the relay jack input crank lever.

The displacement of this crank lever opens the relay jack spool-valves, hydraulic pressure is admitted, the body of the relay jack displaces and causes the rotation of the cable tension regulators. The cables actuate the mixing unit which drives a system of rods and cranks, and the input levers of the six PFCU’S. The displacement of these levers controls the spool-valves of each of the PFCU’S, hydraulic pressure is admitted to the pistons; the PFCU bodies displace and cause the elevens to deflect.



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