Chapter 6 - Ancillary Systems

Functions

Thrust 2 - MK.2 Fuel System

The systems are responsible for making the car start, go and stop and monitoring the manner in which it performs these duties. They put life into the otherwise inert mass of complex machinery and structure. The basic systems are fuel, hydraulic, air and electrics, or combinations of these.

It is essential for safety and reliability that these systems keep functioning under the extreme conditions in which the car is run. These include high temperature, high accelerations, vibration and a maelstrom of fine, highly corrosive desert dust.

Safety and reliability are interlinked. To stop from over 600 mph the car must rely on the chute and brake system functioning. The fuel and hydraulic system must not spill out their flammable life blood and the electrics must not spark off a fire. In the event of a fire the extinguisher system must detect and extinguish it.

Most of the components in the air and fuel systems are standard Lightning parts obtained from obsolete aircraft or the manufacturers. However, their location and the associated pipework is quite different to suit the car layout. Pipework and fittings were stripped from a scrap Lightning and cut up into a mass of convenient bends in order to plumb in the systems. These parts were then rescrambled to suit the car and plasma welded together to form a tailor-made network.

Fuel

In full reheat, the engine burns one gallon a second and as the burn time for a run is approximately 60 seconds, 60 gallons of fuel are consumed. To allow for a reserve the car has a capacity of 124 gallons. This is contained in two saddle tanks of 62 gallons each, located either side of the engine behind the cockpit firewall.

The tanks are located close to the C.G. (centre of gravity) so fuel load does disturb the weight distribution excessively. The tanks consist of rubber bags housed in box-like aluminium containers which transmit all the stresses to the frame. The rubber bags allow distortion or damage without rupture or leakage and are filled with Atomel anti-explosive foam which also holds them in shape. The fillers and vents are protected by flap valves which shut if the car ends up inverted. The tank outlets are closed by 1½ inch diameter shut-off cocks operated by cable from the cockpit.

The original fuel system employed up to 1982 used the two tanks independently. The starboard tank fed the engine via an immersed D.C. tank transfer pump and the port tank gravity fed the reheat turbo pump which is air driven from the engine compressor.

For the 1983 attempt the reheat was 'opened up' to produce more power and to consume more fuel. As the reheat may also have been starved in 1982, it became imperative to have more positive feed to the turbo pump. To achieve this an additional two stage boost pump was fitted. This boost pump consists of twin axial impellers, one drawing from each tank and feeding a common centrifugal stage which in turn pressurises both engine and reheat turbo pump inlets at up to 40 psi. The tanks are linked and balanced through the boost pump.

The two stage boost pump needs considerable power to drive it and this is provided by a fueldraulic system tapping of mechanical power from the engine driven gear train. This gear train drives an hydraulic type pump using engine fuel as its medium, which in turn drives a motor unit integral with the boost pump and exhausts the spent fluid back into the fuel system. The working pressure is about 1600 psi and the motor revolutions up to 5000 rpm.

Engine starter

The Lightning fighters use an I.P.N. (Iso-Propyl-Nitrate) start system on their 302 engines. However, this is a highly volatile and difficult energy source to manage, so it was decided to go for the somewhat tamer air start if possible. An Avon air starter was salvaged from a Sea Vixen, but was a 'mile off fitting the Lightning unit. However, after machining adaptors and a special drive pinion gear and cutting back an engine stay, it was eventually persuaded to fit. Acquiring a couple of Palouste jet engine starter units, batteries, tubes, joints and bellows, and careful plasma welding completed the job. The operational convenience has since justified the work but at the time we did have just a few doubts.

Thrust 2: Monitoring System

Electrics

As the time taken to make a run is only about 90 seconds it was decided to run without the weight and complexity of a charging system. Current is supplied by a 24 volt aircraft battery which is changed for a charged up unit when the voltage drops significantly. Main current drains are the fuel priming pump and the brake system hydraulic pump, both of which are used for short bursts only and not concurrently.

Other electrically run systems are the engine ignition and sequence controls, instruments and monitoring, chute and extinguisher activation. The wiring is to aircraft standards, using fireproof cable and PTFE conduit for safety and reliability.

Monitoring

The driver is too busy during a run to monitor numerous instruments, his concentration being focused on guiding the car.

Speed is displayed on a large 3½ inch diameter 8W mph speedometer set on top of the dashboard. This is visible below the horizon in his peripheral vision and set as far forward as possible to minimise focal change.

Secondary instruments are either observed before rolling or recorded on camera during runs. These include tank levels, engine data (J.P.T. rpm and nozzle position) and battery volts.

Duplicate speedometers and stop-watch are mounted in the port cockpit, observed by a video camera, and from the velocity/time readings true acceleration graphs can be drawn of each run. Maximum/minimum reading accelerometers are also fitted in both horizontal and vertical planes so acceleration, deceleration and 'ride roughness' can be measured.

The vertical 'g' at Black Rock did not exceed ± ½g, less than that recorded when the car was hauled on it's road trailer. The speedometers provide such vital information that they are now triplicated. The original (Revtel) speedometers are driven by rpm sensors in each rear hub which measure wheel revolutions and display this calibrated as mph on two speedometers, one for the driver and one for the port cockpit camera. Earlier reliability problems were cured and the speedometers functioned perfectly in 1983, but just in case, a third speedometer was fitted in the port cockpit. This is an experimental radar (doppler) unit. The antenna is mounted inside the nose intake and scans the ground speed through the grp.

Spare plugs are wired into the cockpits so that if any one speedometer or input fails, one of the alternative units can be connected.

The car has two cockpits to balance the shape on each side. Originally the port cockpit carried passengers but now houses a colour video camera with a driver's eye view encompassing an instrument console and a view of the bonnet, horizon, and mile marker flags as they flash past.

In the driver's cab a small black and white camera is mounted on the hatch cover. When this is closed the camera nestles down into the gap between the headrest and breathing bottle and focuses onto the driver's dash panel, recording speed, engine data and steering wheel. For armchair analysis the recordings can be played back against a timescale or stopped to examine particular events, a facility that proved invaluable in identifying our engine/fuel problem.

The most crucial monitoring of all, related the speed of the car to the aerodynamic lift or downthrust. This information would have given advance warning of any tendency for the car to become airborne and allow the incidence to be set to give the required wheel loading with a good degree of confidence.

Speed and lift were simultaneously 'memorised' and stored in 'black boxes' and printed out on an external recorder plugged in at the end of each run. The print outs were in a graphical form on a time basis so speed, acceleration and lift were immediately visible for any instant of the run.

The speed input was produced by the rear wheel speed sensors and the lift by linear transducers measuring front suspension displacement.

The downthrust becomes critical in the transonic range when shocks off the front wheels dam the underbody airflow. This resulted in a sharp reduction in downthrust. The effect was used to our advantage when the car incidence was increased and the downthrust turned to lift a 600 mph reducing the wheel drag. Without the utmost confidence in our monitoring, we would not have dared to take advantage of this transition.

Extinguishers

Three 12 lb B.C.F. extinguisher bottles were fitted, one in each ancillary bay behind the fuel tanks and one in the front port ancillary bay. The bottles are piped up to 1/2 inch diameter spray tubes which are drilled to spray the rear tank faces, all fuel lines and the engine circumference. The system can be activated manually and automatically. Heat detectors adjacent to high risk areas of engine and reheat illuminate a warning in the centre of the driver's fire button. This button can be operated in one movement at the same time as closing the fuel tank shut-off cocks.

In the event of an accident at speed, the extinguishers are operated by back to back transverse inertia switches set to 4½g. These, in fact, operated successfully in our Greenham Common escapade. The electrical charge for activation is supplied by an independant dry cell power pack.

Brakes

The wheel brake system was developed by Glynne Bowsher of Lucas Girling Limited.

The wheel brakes are identical discs on all four wheels with twin calipers on the fronts and single on the rears. The hydraulic system has been developed in two stages. Up to 1982 the hydraulic pressure was supplied by the standard engine driven aircraft pump. This had various disadvantages. It was vastly over capacity, most of the flow circulating through the by-pass valve. It was located above the fluid reservoir tank and required hand priming and worst of all, only operated when the engine was running. This means that hydraulic pressure had to be stored in the accumulator which allowed a limited number of applications. Before towing, or running, it was necessary to 'dry spin' the engine on the starter to charge the accumulator.

For 1983 a new system was installed. This dispensed with the aircraft pump and a 24 volt electric pump was fitted. This is switched on with the battery master switch, priming a small accumulator. A pressure switch is set to bring in the pump when the system pressure falls to 830 psi and cut it at a maximum of 900 psi so that brakes are always available without running the engine.

This has been a great convenience when manhandling, towing or manoeuvering the car and the intermittent use makes little demand on the battery.

System pressure is visible from outside the car by a pressure gauge, mounted flush in the side panel.

Breathing and communication

Breathing is required for driver comfort and emergency, such as loss of canopy at high speed, fire or fumes, or dust in the cockpit.

Filtered air was selected rather than oxygen, for the following reasons:

short duration required keeps bottle size within practicial limits,
plentiful free supply requiring only a diving compressor to recharge it,
low fire risk,
normal body reaction.

The system is completely contained within the cockpit and consists of bottle, regulator and driver's mask.

The bottle is of 7 litres capacity charged at 2800 psi and gives a duration of 15 to 20 minutes sufficient for three runs. The mask is a standard R.A. F. unit used in conjunction with the R.A.F. helmet.

The driver is in voice contact with the team and emergency services. Transmission is from the standard microphone in the mask and reception through the helmet earphones. A `Push-to-Transmit' button is located on the steering wheel and this transmission over-rides all the other team radios.

Lubrication

As "Thrust 2" is 'jet propelled', it eliminates the need for a power transmission system with its attendant lubrication problems. The engine, turbopump and starter lubrication systems are all built into the components and use OX 38 oil.

At maximum speed the wheels rotate at approaching 8000 rpm making the hubs the most critical lubrication case. Failure of lubricant, and hence bearings, could be catastrophic. British Timken taper roller bearings were selected for the hubs; these are compact and have high load capacity but the high revolutions posed a lubrication problem. Grease would be centrifuged away from the contact faces. Oil would get over this problem, but temperature would rise drastically with the high speed churning. Continuing a theme started for Concorde, Kluber Limited developed a new grease called Isoflex Topas NB52 specifically for the job. The bearings were set to .004 inch end float and a light smear (12 cc) applied to each hub, which was then run-in for 24 hours. Subsequent tests showed that the bearing could be held at 7000 rpm for 15 minutes without exceeding 50°C. This remarkable result has been reflected in service. Inspection revealed that all bearings were in perfect condition after the runs. Servicing was limited to temperature monitoring and occasional inspection. It is hoped that this new lubricant will benefit a much wider need than Record Breakers.