ROVER-BRM Le Mans Car
THIS IS A road test of a unique car built for a particular purpose to suit a specific driver -the Rover-BRM turbine driven at Le Mans last June by Graham Hill and Jackie Stewart. During the race a foreign object found its way into the intake and resulted in damaged compressor blades, which forced a reduction in speed. The car nevertheless completed the 24 hours at an average of 98.8 mph and finished 10th overall, second in the 2-liter prototype class.
The first two things everybody wants to know about a turbine car are whether it uses a lot of fuel and whether there's a big acceleration lag. The car we tested had the latest Owens Corning rotating ceramic heat exchangers, which had made an enormous.
difference in thermal efficiency. If you drove it fast the consumption (of kerosene) was not excessive relative to the performance. When idling, or at lower speeds, fuel consumption was poor, but of course this car wasn't designed for that kind of use.
We found that the acceleration lag was very pronounced. It is essential to anticipate by at least two seconds the need for full power; this leads directly to the one great, modification necessary in driving techniques-the left foot must be used for braking, the right for acceleration and the two must be played against each other simultaneously.
The acceleration figures show that, for a road car, some ratio changing transmission would be desirable for low speed acceleration. Output torque from the turbine reaches a maximum at rest but the ratio of this value to top speed torque is about 2.2:I. A conventional gearbox usually provides a reduction ratio of about 3-to-1 in bottom gear so the single-speed turbine is at a disadvantage-a disadvantage accentuated in this case by the high final drive gearing appropriate to the Le Mans 24-hr race on a very fast circuit.
The chassis, typical of modern racing practice, is based on the Formula I BRM of the 2.5- liter era. The springing is relatively soft and the ride is comfortable; admittedly the tires feel almost as hard as iron bands and the steering is so positive that it transmits every tremor, but comparing the result with the soft and spongy feel of modern road cars one wonders whether insulation has gone too far.
For some reason we expected a complicated starting routine in fact, it is simpler than a conventional car; you switch on the ignition and push a spring-loaded starter button-no need to hold it down because it has an automatically engaged circuit to keep the electric motor engaged. By 20,000 rpm the engine is just about, self-sustaining; the starter cuts out at 30,000 (a green warning light goes out) and the engine accelerates to the impressive idling speed of 35,000 rpm. All this takes rather a long time of course-some 12-15 sec - but on the other hand you can then drive it flat out because there is no such thing as warming-up.
At its minimum running speed the engine develops a small amount of power (about 9 bhp) so it tends to creep away from rest. Given time it will reach a speed in the region of 35-40 mph and we timed a lap of our banked circuit at 37.5 mph without touching the accelerator at all.
When you bang your foot down on the accelerator the tachometer of the compressor turbine accelerates at an increasingly rapid rate until it reaches its governed maximum of 65,000
rpm. As it approaches this speed the acceleration becomes impressive-until it does so it tends to be leisurely, so the performance available depends strongly on successful anticipation.
Starting from rest you simply hold full throttle until the compressor turbine revs reach 65,000 and then release the brakes. Under these conditions the engine develops its maximum torque but with a Le Mans final drive ratio and no lower gears, there is no question of wheelspin; it will, in fact, re-start slowly on a l-in-4 gradient but not on a l-in-3. So from a standstill to 50 mph takes 9 sec, about the same as an MGB or a Porsche SC.
But at this stage it is just reaching the conditions for which it was designed and the next 50 mph up to 100 mph comes up in only 16.4 seconds.
On a banked circuit we timed a speed of 127 mph and this represented a very unfavorable condition since the car had to be held hard down on the banking. From our experience with other 'cars we estimate that this corresponds to a maximum speed in the region of 140 mph. During our short possession it was not possible to check this, but at Le Mans the car was officially timed at 141-142 mph on the Mulsanne straight. Since that time it has acquired a slightly more efficient heat exchanger which has reduced its output by a few bhp.
The engine is always perfectly smooth although far from quiet. The whole feel and sound of the unit and the way its revs rise to a constant value during hard acceleration is exactly like that of a jet aircraft taxiing on the ground.
There is no clutch and the gearbox offers only a choice of forward or reverse gears. Reverse, which is necessary to comply with FIA and legal requirements, has never been used and we were advised to use it only in emergency. Sliding toothed gears are employed. If you tried to change from one gear to the other with the engine running and got stuck in neutral, the power turbine, which is normally positively geared to the back wheels, would be completely free and would overspeed and probably seize its bearings. On a production car, some sort of epicyclic gear would almost certainly be used for reverse.
The Rover turbine prefers kerosene although it will consume other fuels from gasoline to diesel oil in an emergency. We found no difficulty in this because many large. modern garages in England now have kerosene pumps;. it would, of course, be illegal to use untaxed fuel in Britain except in a special test car.
With the latest rotating ceramic heat exchangers, which are fitted to this engine, we found that fuel consumption at high speeds is very moderate; for example, it does 17.5 mpg at 100 mph and there are very few sports cars indeed which will equal this figure. In the region of 40-50 mph it returns figures about 25 mpg and by far the best results are obtained by dropping below this speed as little as possible.
Over nearly 700 miles running we averaged about I 1.8 mpg. The worst average was 9.9 mpg on the performance testing day when there was much standing around, and the best figure of 14.1 mpg resulted from a fast 120 mile run on quiet minor roads.
It is interesting to compare these figures with the over-all consumption of 11.2 mpg at Le Mans this year when averaging 98.8 mph for 24 hours. It is also worth noting that no lubricating oil was consumed in the course of our test.
The steering is very high geared, only 1.7 turns lock-to-Iock, and every slight movement is translated immediately into a directional change. As far as you can detect there is no roll on corners, no tire squeal, no recognizable understeer or oversteer with such a direct connection to the front wheels, the driver knows exactly what is happening at the road surface and he only has to decide what line he wants to take on a corner and the car seems to follow it.
You don't get all these advantages for nothing-the disadvantages appear on rough road surfaces where the steering feels very harsh; the wheel shakes in the 70-80 mph region and it kicks back quite strongly. Contrary to the usual pattern, the steering is light at low speeds and for maneuvering (the front tires only support 670 Ib) but it gets much heavier when you drive it fast round corners because the tires themselves develop very high self-centering forces. On bumpy roads with sudden changes of camber the steering wheel must be held forcibly to keep the car on line-on smooth roads it is entirely stable and, as far as we could judge, the stability is good in cross winds, in spite of the 40/60 weight distribution.
We could describe the brakes by saying that they are the most powerful that, we remember and also among the heaviest in operation-simply because Graham Hill prefers them like this. At 160 Ib. pedal force, the decelerometer recorded 32 ft /sec/sec deceleration; at 180 lb, which was all we could extract from our left foot, it had gone off the scale but there was still no sign of wheel locking. The hand brake held on a l-in-3 gradient.
In talking about the suspension it is necessary to distinguish very carefully between its response to low and high frequency road disturbances. There is no rubber insulation and racing tires are notoriously harsh, so that every ridge, pothole and sharp-edged ripple comes through strongly. But ordinary major road bumps and undulations are ironed out extremely well by soft springs and heavy damping. In other words, there is little bounce, jolt, sway or float to make the occupants uncomfortable, but there is a fair amount of vibration.
If the car were quieter, a lot of road noise might be audible. As it is, every other noise is drowned by the high-pitched scream of the engine, which makes conversation difficult even at idling speed. Since the car is not unduly noisy from outside and since most piston-engined racing coupes are just as noisy inside, this could presumably be reduced to a normal level by the usual soundproofing techniques. Insulation is also needed to keep the inside cool; the seat gets uncomfortably hot while the feet get cold.
It has, of course, hard, almost unpadded, seats which lock you in place. The two seats are very close together, there is very little foot width for two people because of enormous wheel arches, nothing is adjustable and the wheel is relatively close to the driver's seat-again to suit Graham Hill's preferences. Visibility is superb in the forward direction, adequate to the rear but non-existent to the rear quarters, where the air intakes create a large blind spot. There are four headlights, the upper ones pivoting out of the upper surface of the nose, and all of them have quartz-iodine bulbs which create a tremendous blaze of light on main beam.
We have mentioned before that left-foot braking came naturally. There is no doubt that this was because the left heel was imprisoned by a sunken pan in the floor which automatically poised the toe over, but just clear of, the pedal. This, we thought, was vitally important-had the foot been allowed to wander away to some other position, it might well have reverted to habits conditioned by other cars.
Many of the instruments and switches on the instrument panel are familiar; some of the others like the thermocouple selector (for jet pipe temperature) and the fuel pump switch are there for special experimental or racing reasons. There are two tachometers, one for the compressor turbine and one for the output turbine; the latter, being geared to the rear wheels, is also calibrated in mph on an inner scale.
The least familiar instrument is the jet pipe thermometer which should never exceed 7500 C and which always stayed well below this figure in our test. Turbine inlet temperature is really the critical safety parameter, but this is too high to measure with a reliable dashboard instrument.
If a turbine car were put on the market, chassis maintenance would be entirely conventional. The interesting point, of course, is engine maintenance and whether ordinary garages, would be "converted" to do the necessary work. Here one must distinguish between the basic parts (i.e. the compressor/turbine assembly) and the accessories.
The former, which is fundamentally simple and reliable, would have to be returned to the manufacturer for attention just as an automatic transmission has to be. The rest is well within the scope of trained mechanics who would, of course, be guided by workshop manuals. There is, for example, nothing very unusual about the electrical gear and general plumbing. Fuel pump checking would demand special equipment, as is the case with fuel injection systems on piston engines.
The various gear and auxiliary drives follow conventional engineering practice and the combustion chamber, which might occasionally have to be dismantled for decarbonization, presents no special difficulties in reassembly.
As we said earlier, this was a test of a unique car built for a particular purpose to suit a particular driver. It doesn't in any way represent the sort of car that either of its parent companies would offer for sale, but it still has tremendous significance. The fact that we were able to take it away for a week without supervision and use it for ordinary driving reflects the progress that has been made in simplifying controls. . . and demonstrates the confidence the companies have in the reliability of this unusual machine.
More Le Mans Cars from the 60ies onwards
ACCELERATION Time to speed, sec
0-30 mph .5.0
0-40 mph... .. ... . .. .. . .. . .. .7.0
0-50 mph... . . . . . . . . . . . . . . . . .9.0
.0-60 mph.. .. . . . . . . . . . . . . . . .11.3
0-70 mph. . . . . . . . . . . . . . . . . . .14.4
0-80 mph ..17.4
0-100 mph... .. .. .. .. .. . .. .. 25.4
50-70 mph.. . . . . . . . . . . . . . . . . .5.4
SPEEDS IN GEARS
BRAKES Panic stop from 80 mph :
Deceleration rate, ftjsecjsec. .32+
Parking: hold 30% grade ..yes
Overall brake rating. . . . . excellent
30 mph indicated . . . actual 30
40 mph. . . . . . . . . . . . . . . . . . . . .40
60 mph . . . . . . . . . . . . . . . . . . . . .60
80 mph. .81
100 mph. . . . . . . . . . . . . . . . . . . .102
Odometer correction. . . . . . . . . . n.a.
Normal driving, mpg .11.8
Top speed (40,500 rpm). .mph 142
Cruising range, mi .340
not for sale
Type: Rover gas turbine model 25/ 150/R with Owens Corning ceramic heat exchanger.
Displacement: equivalent to 1600cc pe"r FI A regulations.
Compression ratio. . . . . . . . . . . .4:1
Bhp @rpm: 126@63,500(gasgen
erator), 39,000 (power turbine).
Torque, Ib-ft: 267 @ zero rpm at
Max. torque ratio. . . . . . . . . . .2.2:1
Clutch. . . . . . . . . . . . . . . . . . . . . none
Final drive ratio. . . .23.09:1
Differential type. . . . . . . . . . . helical
Frame type: tubular space type
Brake type Dunlop disc
dia, front/rear .11.0/10.0
Tire size, front. . . . . . . . . . .550-15
rear .. .6.50-15
Make ... Dunlop Yellow Spot
Steering type. . . . . . . rack & pinion
Tu rns, lock-to-Iock . . . . . .1.7
Turning circle, ft. . . " .. .. .38.8
Front suspension: independent by unequal-length A-arms, coil springs, tube shocks, anti-roll bar.
Rear suspension: independent by upper control arms, lower Aarms, trailing arms, coil springs, tube shocks, anti-roll bar.
Normal capacity, persons. . . . . . . .2
Seat width, in .2xI6.5
Head room, front/rear. .. .. ... n.a. Seat back adjustment, deg. . . . . .0 Entrance height, in. . . . . . . . . . . n.a. Step-over height. . . . . . . . . . . . .16.0 Door width. . . . . . . . . . . . . . . . . .33.5 Driver comfort rating:
Driver 69 in. tall. . . . . . . . . . . n.a. Driver 72 in. tall. . . . . . . .'. . . n.a. Driver 75 in. tall. . . . . . . . . . . n.a. (85-100, good; 70-85, fair; under
Curb weight, lb. . ... .. .. .. ..1670
Test weight .2100
Weight distribution (with driver),
front/rear % .41/59
Wheelbase, in.. . . . .. . .. . . .. .93.5
Track, front/rear 52.5/51.5
Overall length, in .166.8
width. . . . . . . . . . . . . . . .64.0
height. . . . . . . . . . . . . . .42.5
Frontal area, sq ft. . . . .15.5
Ground clearance, in. .4.8
Overhang, front/rear. . . .37.5/35.0 Departure angle, deg. . . . . . . . .27
Usable trunk space, cu ft. .1.9
Fuel tank capacity, gaL .29
Instruments: power turbine tachometer & speedometer, jet pipe temperature, compressor tachometer, fuel pressure, oil pressure & temperature, ammeter, oil level.
Warning lights: starter.