VC10 Engine Installation

Each pair of nacelles is suspended from a torque box made up of curved front and rear beams (or spars), ribs and top/bottom skin with stringers. Fuselage cross beams are extended by the front and rear nacelle beams which are bolted to them.

A complete box structure is made by skinning the upper and lower surfaces of the beams.

Nacelles are formed by inner and outer sidewalls and a centre rib. Forward extensions of ribs 1 and 3, and the outer side wall carry the double intake fairings for two engines, whilst rearward extensions carry a fireproof bulkhead. Between the engine intakes is a single intake for the cabin compressor. The strut, which is streamline in cross section, is built around a centre structure that is a continuation of the nacelle torque box.

Access to the top of an engine is provided by hinged doors (hinge pip pins allow complete removal), removable stressed panels, and holes and small accesses. Access to the bottom of an engine is provided by two doors at the bottom of each nacelle that hinge away from rib 3 and expose the engine from the nacelle intake to the fireproof bulkhead. Each has three hinges, one being adjustable for door rigging. Behind the fireproof bulkhead a removable double fairing, which covers the jet pipe and thrust reverser, is attached to mounting rings on each engine and jet pipe.

The front and rear beams of the torque box each carry fittings for attachment of the engine support links. Engines are attached by tapered sleeves and bolts. A drag fitting on the front beam of the torque box accommodates the engine thrust pillar. The engine attachment fittings on the front and rear torque box beams also have provision for fitting a hoist for use when changing engines, thrust reversers, and jet pipes.

The CSD serves to drive the generators at a constant speed of 6,000 rpm in spite of varying engine speeds and also to synchronize them so that their outputs are in phase. The CSD is driven by gearing from the HP compressor via a disconnect unit and a universal joint. It is mounted under the LP compressor casing on the left side of the engine; the generator is bolted to its front face.

Drive is transmitted through a hydraulic pump and a hydraulic motor, each of the "wobble-plate" type. The "input" from the engine drives the pump, and the "output" to the generator is from the motor. A servo-piston can vary the delivery of the pump by altering the angle of the wobble plate; this in turn varies the rpm of the motor relative to the rpm of the pump. If the pump wobble plate angle is increased, the delivery of the pump is increased and output rpm will increase relative to input rpm, and vice versa.

A centrifugal governor called the speed governor controls the position of the servo piston and therefore the output rpm. It works in the same way as a "constant speed unit" used with oil-operated propellers. It is driven from the "output" side e.g. If output rpm are below 6,000:

Fly weights move IN.
Piston valve moves towards the driving end.
Oil is directed to the servo piston to increase wobble plate angle.
Hydraulic pump increases delivery.
Hydraulic motor increases rpm up to 6,000.
Governor fly weights return to the neutral position and conditions stabilize.

If output rpm are above 6,000, the opposite will take place and rpm will return to 6,000.

Generators operating in parallel have a natural tendency to remain in phase. However, if the load on individual generators varies, they will move out of phase. Magnetic Trim is fitted to keep the generators in phase and therefore their loads equal. The Magnetic Trim is an electro-magnet which can be made to attract or repel the fly-weights in the speed governor, which are themselves permanent magnets. It can therefore bias the setting of the governor and cause the output rpm to change. If the generator does move out of phase, a signal is sent to the magnetic trim to slightly speed up or slow down the generator and bring it back into synchronization.

A limit governor operates in conditions of underspeed or overspeed. It is somewhat similar to the basic governor and is also "output" driven. It has four functions:

Before Engine Starting — Its oil valve is bottomed, the servo-piston is opened to drain, the pump wobble plate is at "minimum stroke" and output rpm are selected to minimum. Also the pressure switch is released so that the generator circuit breaker cannot be made.
During Engine Starting (Underspeed) — Pressure builds up in the CSD output, rpm begin to increase and the limit governor ports oil to the shuttle valve to put the servo-piston under the control of the speed governor. As output rpm are less than 6,000, the speed governor will increase the angle of the pump wobble plate and increase output rpm The pressure switch is still released and the generator circuit breaker is still out during the underspeed condition.
At 6,000 Output rpm — The pressure switch is made and the generator circuit breaker can be made.
Overspeed — If output rpm reach 7,200, the oil valve in the limit governor moves to an overspeed position that ports oil as in (1) above so that the output rpm are reduced and the circuit breaker trips. At the same time, oil pressure is directed underneath the valve to hold it in the overspeed position and look the generator out. The only way to release this pressure and so regain the generator is to shut down the engine.

Oil for the operation of the CSD and its lubrication is supplied from a tank on the port side of the engine. The CSD has two pressure or "charge" pumps and one scavenge pump. The circulation is completed back to the tank via an oil cooler employing "ram air" as the cooling medium and a thermostatic by-pass valve. A bank of "jet-pumps" in the outlet from the cooler provides ground cooling. The oil system is self contained, and though using oil of the same type as the engine, has no connection with it. A pressure filter and a sight gauge are accessible through an access panel in the lower front cowling. The oil tank and the CSD are both pressurized with P.2. air tapped from the engine, to prevent aeration.

A Disconnect Unit allows the CSD to be disconnected from the engine in case of malfunction. The disconnect unit is bolted to the engine and contains dogs that drive the CSD A disconnect switch on the engineer's electrical panel operates a solenoid in the disconnect unit which withdraws a pin and allows a large spring to disengage the dogs. The CSD can only be re-connected on the ground, requiring a manual operation at the disconnect unit itself.

Indications:

Low Pressure Warning — When CSD oil pressure is less than 220 psi a red Low Pressure Warning Light on the engineer's electrical panel illuminates, and the master Warning Lights on the Pilot’s panel flashes.
Temperature Rise Indicator — Located on the engineer’s panel, it indicates the rise in temperature from the inlet to the outlet of the CSD It is a measure of the work being done by the CSD It has a green (safe) range and a yellow (danger) range for different electrical loads.

A thrust reverser mounted on the rear of the outboard engines provides a means of reducing aircraft forward speed by reversing the direction of the exhaust gas flow and therefore engine thrust.

The reverser consists of two doors or eyelids, hinged about the horizontal axis, which in the normal or "forward thrust" position form part of the jet pipe inner casing and for "reverse" pivot rearwards to blank off the exit nozzle and uncover outlet ports at the top and the bottom of the unit. Cascade vanes in the top outlet deflect the gases forward at 45° while in the bottom outlet the outer vanes deflect the gases forwards at 30° and outwards at 35°, and the inner vanes deflect the gases backwards at 15° and inwards at 20°. This arrangement prevents ingestion of hot gas or debris into the engine intakes.

Control is by individual "reverse levers" mounted on the outboard throttle levers, which utilize the throttle control run to the Fuel Control Units, and thence by Bowden flex cable to control valves on the thrust reversers. Lever movement is instinctive (rearward for reverse and further rearward to increase reverse thrust) and is interconnected with that of the throttle lever such that:

Reverse may only be selected if throttle is at Idle.
Throttle levers cannot be advanced beyond Idle until reverse has been cancelled.

A cam and roller assembly on the thrust reverser provides for the following safety features:

Power in reverse cannot be selected until the reverser doors have completed their travel.
If a thrust reverser should inadvertently move into reverse, the throttle lever will be returned to Idle, and power correspondingly reduced. If during landing a thrust reverser should fail into "forward thrust", the reverse lever will be returned to "Forward Idle" and power correspondingly reduced.
When reverse is selected on the reverse lever, the control valve on the thrust reverser is moved. It directs P.3 air firstly to a lock plunger to break a lock and then to four double rams to move the reverser doors. When reverse is cancelled, the doors are returned and the lock re-engaged.

Individual amber warning lights mounted on the pilots centre instrument panel and repeated on the engineer's engine panel are illuminated whenever the reverser lock is broken.

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