Concorde nose & visor hydraulic system description & operation

Concorde’s hydraulic system provides the power for raising or lowering the visor and droop nose. The movement is obtained by a system of selector valves, jacks and locks using the green hydraulic system for normal operations and the yellow system for standby operations. In the event of both normal and standby systems failing, the nose up-locks can be manualy released to allow the nose to free fall to the 5 deg. position, then which automatically releases the visor up-lock. This allows the visor aided by a spring assister mechanism, to free fall. During the free fall the hydraulic fluid is vented to return via orifices which control the rate of lowering, control of the normal system is from the co-pilot’s dash panel.

Two interconnected groups of components are arranged to provide the normal and standby sequenced operation of the visor and droop nose. The visor “group consists of a shut-off valve, normal and standby selector valves, an up-lock and the visor actuating jack. The up-lock and jack are mounted in the droop nose and the selector and shut-off valves in the forward equipment compartment.The nose group consists of an actuator made up of two side by side mounted jacks, twin up-lock units and lock selector valves. The actuator is secured to the fuselage front pressure bulkhead and to the droop nose structure in gimbals. The up-locks are mounted on the forward fuselage and the lock selector valves in the forward under-floor equipment compartment.Hydraulic supplies to the visor jack and the droop nose actuator are finally directed through flexible hoses to allow for visor and nose movement, all other pipes are rigid.Two swivel units secured to the lower part of the fuselage front bulkhead connect the hydraulic pipes in the fixed fuselage to the pipes and components in the droop nose fairing.There are six panels which allow engineers to access the hydraulic components and pipe lines during maintenance work. Four of these are situated in the under-surface of the nose structure which provides access to the components situated in the nose. The other two permit access to components and pipelines in the forward equipment compartment.Normal raising and lowering of the visor is affected by the green hydraulic system circuit after the appropriate solenoid of the visor selector valve is energized. Hydraulic supply to the droop nose actuator is taken from the visor down line. When visor down is selected, the selector valve directs pressure to the visor up-lock jack and visor jack (which unlocks and lowers the visor), also to the nose actuator and to the nose lock selector valve ready for a subsequent droop nose down selection. On selection of visor up, pressure is applied to the visor jack to raise the visor.The standby system for lowering the visor and nose is through a visor standby selector valve. Yellow hydraulic system pressure can be selected to lower the visor and release the nose up-locks and actuator collet locks for free fall to intermediate and fully down positions.

Droop Nose Actuator

The droop nose actuator comprises of two jacks, each having two cylinders, one at each end of a piston rod. The jacks are mounted in parallel with their upper cylinders individually gimbals mounted to support members on the fuselage front pressure bulkhead. The lower cylinders are similarly secured to the droop nose.

Stroke equivalents to droop nose angle are 5 deg. for the lower cylinders and 7 1/2 deg. for the upper cylinders to give a total 12 1/2 deg. when both cylinders are fully extended.Solenoid operated selector valves mounted on the jacks control each cylinder.

 

These solenoids are energized to contract the jacks and determine the droop nose position as follows:-

0 deg. – All solenoids energized

5 deg. – Both 5 deg. selector solenoids de-energized both12 1/2 deg. – Selector solenoids energized

12 1/2 deg. – All solenoids de-energized

 

In addition, each 12 1/2 deg. cylinder incorporates a collet lock which engages automatically when the cylinder is retracted. The collet locks prevent the nose lowering below 5 deg. and are hydraulically released when the 12 1/2 deg. solenoids are de energized to select 12 1/2 deg. droop. Alternatively, each Lock may be released by applying pressure to a standby release jack mounted on top of the 12 1/2 deg. cylinder.

 

The inlet port on each 5 and 12 1/2 deg. jack is connected via a non-return valve to the annular piston chamber allowing it to become pressurized whenever pressure is applied to the jack. The two-position selector valve is supplied from the chamber. It is spring and pressure loaded into down selection, and in this position connects the piston chambers to provide pressure to both sides of the piston. The piston rod is extended by pressure which is effective on the rod area.

 

Energizing the selector solenoid operates the pilot valve to allow pressure to be applied to the selector valve, moving it into the up position. In this position the full jack chamber connects to return and the piston rod is retracted by pressure on the annular piston area. A small bleed hole drilled through the valve ensures that fluid can escape from the jack in the event of the selector valve sticking in the up position.

 

Pressure relief valves fitted to each cylinder prevent over pressurization of the cylinders occurring in the event of a malfunction. They allow fluid in the full jack chamber to escape to return if the pressure exceeds the supply pressure by a pre-determined amount.

 

The rate of operation of the nose actuator is governed by fixed chokes which control the flow in and out of each jack chamber. In addition, the nose is decelerated during lowering as it approaches the intermediate and fully down position by spring-loaded snubbers in each cylinder. These reduce pressure in the full jack chamber by closing the supply to the selector valve just before the jack piston reaches full travel.

Nose Up-Lock Units

 

Small hydraulic jacks are incorporated in the droop nose up-lock units to provide normal release of the up-locks. The jacks are single acting, the piston being returned by the combination of an internal spring and return tine pressure. This arrangement ensures that return line transient pressures cannot release the lock. A shuttle valve incorporated in each jack allows for operation of the yellow standby system.

Visor Jack

 

The visor jack is mounted in the droop nose fairing and extends to raise the visor by means of a swinging A-frame as shown in. In the visor down position the jack bottoms against an internal stop and normally remains pressurized down. In the up position it automatically stall’s without bottoming to load the visor into an up-lock which off-loads the system by a micro-switch operation of the visor selector valve.

 

A transfer valve, a restrictor valve and a shuttle valve are mounted on the jack body to direct normal and standby pressure, as appropriate, to the piston. To extend the jack, pressure from port A is directed by the transfer valve to both sides of the piston; it is then effective on the larger area only. For retraction the valve directs pressure from port B to the annular piston area only and port A becomes the return line. In both the retraction and the extension movements the restrictor valve provides a 4 – 8 second operating time.

 

Standby jack retraction is achieved by the shuttle valve directing yellow system pressure from port C to the annular chamber. Fluid from the full jack chamber returns via port A.

Visor Up-lock Jack

 

The visor up-lock jack is bolted between the side plates of a twin hook up-lock, mounted on the front face of the nose fairing mid bulkhead. The jack plunger is retained in the retracted position by the combined action of an internal spring and return line pressure. In the extended position the plunger releases the up-lock.

Visor Selector Valve

 

The normal selector valve for visor and droop nose operation is a three position electrically operated valve mounted in the equipment bay (in the area known as zone 121) beneath the flight compartment pressure floor. It is operated to direct green system fluid to one of two services (raise visor and Lower visor) and simultaneously to open the return line from the other service.

 

The main flow of hydraulic fluid is controlled by a slide valve positioned by fluid pressure from two solenoid operated pilot valves.

 

In the normal de-energized position, pressurized fluid supplied to port A flows to the slide valve and to each of the slide valve centralizing pistons. Equal pressure on each piston centralizes the slide valve and allows return fluid from the service ports C and D to flow past the valve to the return port B.When one of the solenoids is ‘energized, the relevant pilot valve cuts off the pressure supply to its associated pistons and simultaneously provides pressure relief through return port B.

 

Fluid pressure on the opposing actuating piston moves the slide valve to align the supply port A and the selected service port C. At the same time the slide valve allows return fluid from service port D to pass through port B to return.

 

When the solenoid is again de-energized, equal supply pressure is applied to both pairs of pistons, and the differential loading between the actuating and centralizing piston areas moves the pistons and slide valve back to the central position.

Visor Standby Selector Valve

 

The visor standby selector valve is a solenoid operated two position valve mounted in the equipment bay (In the area known as zone 121) beneath the flight compartment pressure floor. It has seven ports, and it functions by yellow system pressure via a pilot valve to control the standby lowering of the visor and droop nose, normally the solenoid is de-energized with the pilot valve directing pressure from port E to the rear of the piston and relieving pressure from the piston head through port C. In this position the spool ducts allow full flow between ports A to B and ports F to H, and restricted flow between ports D and F with all other ports closed.

 

When the visor standby switch is operated, the solenoid is energized to position the pi lot valve so that both sides of the piston become pressurized from port E. The differential loading moves the piston and spool to line up ducts for full flow between ports B, C and H, and ports D and E.

 

When the system controls are returned to normal the pi lot valve returns to the de-energized position. In both normal and standby positions the valve returns any leakage, which may occur past the visor jack and visor up-lock jack shuttle valves, to the appropriate reservoir.

Lock Selector Valves

 

Three identical solenoid operated two-position selector valves direct green hydraulic pressure to provide normal release of the droop nose up-locks and yellow pressure to provide standby release of the nose up Locks and 5 deg. collet locks. All three valves are situated in the equipment bay (zone 121) beneath the flight compartment pressure floor.

 

The normal up-lock selector valve is supplied by the green system from the visor down line, which is pressurized when the visor is selected down and depressurized when the visor is selected up. The two standby lock selector valves are both supplied by the yellow system from the visor standby selector valve. The return ports of all three valves are piped to the common return port of the visor standby selector valve.

 

The main flow from the lock selector valves is by a slide valve actuated by fluid pressure via a solenoid operated pilot valve, and two opposing pistons of different diameters. In the normal position the solenoid is de-energized and fluid from supply port A is applied to both pistons. Area differential between the two pistons results in the larger piston being retained at the limit of its stroke. In this condition the slide valve cuts off the flow from port A to service port C and allows any return fluid entering the valve to pass to return port B.

 

When the solenoid is energized the pilot valve operates to release the large cylinder pressure via return port B and directs supply pressure solely to the small opposing piston. In this condition the pressure acting on the smaller piston moves the slide valve to connect supply A to serve C and close off return B.

Non-return Valves

 

Four spring-loaded non-return valves are incorporated in the return tines of the hydraulic system. One valve is situated beneath the forward vestibule floor, (Zone 123), and the other three are beneath the flight compartment floor (Zone-121). Three of the valves ensure minimum fluid loss in the event of system failure, one being fitted to the standby selector valve green return connection, and one in each of the green and the yellow return linesA fourth valve is fitted in the return pipe line from the standby collet locks and standby nose up-lock selector manifold to prevent pressure pulses displacing the shuttle of the nose up-lock jacks.

Visor Supply Shut-off Valve

 

A solenoid operated two-position selector valve is fitted in the green hydraulic system supply line, and is controlled by the visor and droop nose normal selector switch to shut-off the hydraulic supply to the visor and droop nose system when the visor and nose are up.The valve (identification No.5116) is mounted on a manifold in the forward equipment bay beneath the fight compartment floor and is similar to the lock selector valves.Three hydraulic pipes connected to the manifold are for green system supply to the valve (port A), the delivery from the valve to the visor and droop nose system (port C) and the system return (port B).When the valve solenoid is de-energized the pilot valve is open, fluid then enters port A and passes to both ends of the piston. The pressure differential on the larger end of the piston overcoming the pressure on the small end moves the piston to close delivery port C, but fluid from port C may return via port B.When the valve solenoid is energized the pilot valve is closed, fluid entering port A is directed to the small end of the piston which moves to permit the supply entering port A to pass out of port C. Fluid displaced by the large piston returns via the pilot valve to port B.

                                    Hydraulic Swivel Units

 

The hydraulic supplies to the visor and droop nose system are carried from the fixed fuselage pipelines to the droop nose fairing pipes and components through two manifold mounted swivel units. These are mounted on the lower part of the fuselage front bulkhead, one on the left and one on the right-hand side just forward of the nose fairing hinge.The manifolds are attached to the aft face and the swivel units to the forward face of the bulkhead. Hydraulic sealing between the manifolds and the swivels is effected by the use of sliding bobbins fitted with seals.Each unit consists of two pivoting arms having three fluid ducts. One of these ducts in the right-hand unit is not used and is blanked off.

Operation

 

The visor and droop nose hydraulic system circuits are interconnected and sequenced to provide four possible selections:-

Visor up, nose up

Visor down, nose up

Visor down, nose intermediate (5 deg. down)

Visor down, nose down (12 1/2 deg.)

 

With the visor and droop nose locked up, all solenoids are de-energized, the visor shut-off valve has closed the green pressure supply line, and the entire circuit is connected to green return through the visor normal, and standby selector valves. When the visor is selected down, solenoids are energized, the shut-off valve opens and the green system pressure is applied to the nose lock selector valve and to all four cylinders of the droop nose actuator. This causes the actuator jacks to retract pulling the nose into the up Locks. The visor up-lock is released and the visor lowers.

 

Selection of 5 deg. nose down causes the nose lock selector valve to be energized and green system pressure to operate the up-lock jacks. The 5 deg. selector solenoids remain energized until both up-locks have released and are then de-energized to lower the nose. Selection of nose fully down causes the 12 1/2 deg. selector solenoids to be de-energized, the actuator collet locks to be released and the nose to be lowered to 12 1/2 deg. Raising the nose is achieved by energizing the 12 1/2 deg. selector solenoids for the 5 deg. position and the 5 deg. solenoids for the O deg. position.

 

Both collet locks and up-locks engage automatically. Selection of visor up de-energizes the 5 deg. selector solenoids and the down solenoid and energizes the visor up solenoid in the selector valve to apply pressure to the visor jack. Pressure is applied to both areas of the jack by means of a transfer valve and the jack extends to raise the visor. Operation of an up-lock micro-switch de-energizes solenoids to off-load the nose 12 1/2 deg. jacks and the visor selector valve and to close the visor supply shut-off valve.

 

The yellow hydraulic system provides power for lowering the visor and droop nose in the event of normal, system malfunction. Selection of the system isolates the normal selector valve and directs pressure through the visor standby selector valve to the visor up-lock, visor jack, nose standby up-lock selector and the standby collet lock selector. The applied pressure releases and lowers the visor and un-locks the nose for free-fall lowering to a selected 5 deg. or 12 1/2 deg. position. During standby lowering of the visor a volume of fluid corresponding to the visor jack rod volume is transferred from the green to the yellow system. The fluid Levels of the hydraulic reservoirs must therefore be checked after each standby lowering and corrected if necessary.