Jurbocars
If problems of noise and low fuel mileage ran be solved, the turbine-d riven car will yet make its appearance on American highways.DBNNIS MAY,well-known authority on British automobile design, gives an up-to-date report on overseas developments with this type of power plant.
by DENNIS MAY
NEWS and nonsense were made in about equal proportions when on March 9, 1950, the world’s press bore down on Silverstoue Airfield, Northamptonshire, England, to witness the first overt demons! rat ion of a turbinedriven automobile. Despite the constructors’ supplications, the completely misleading term “jet motor” was used to describe the new Rover’s power unit in the public prints of a score of countries, not excluding the United Kingdom. This Silverstoue debut, the illiterati could infer, marked —or anyway, immediately foreshadowed — Autopia’s dawn.
The following month, three further events brought the turbocar fresh though milder limelight broadsides. One was the lirst public exhibition of the Rover, in New York’s Grand Central Palace, as part of a successful show of British cars in general. (Here, apparently undecided on how elean a breast it would be fitting to make at ibis stage, the Rover people compromised with transparent purdah, roofing the turbine compartment with Plexiglas.)
The second was the disclosure that the Boeing Airplane Company of Seattle had experimentally installed a gas turbine, roughly comparable in power with the Rover’s, in a 10-ton trailer-tractor, and tested it on the highway.
Third, a Los Angeles enterprise by the name of AiResearch was reported to have rigged the smallest known gas turbine, developing a mere 60 horsepower and originally designed to drive electric generators for the U.S. Navy, into the chassis of a small M.G. sports car.
Since that time, the British automotive press has carried no reports of new American turbocar projects, which does not mean that new developments are not afoot. Meanwhile, fanfares of secrecy accompany talk of gas turbine cars under development in at least five English plants, and the British Automobile Racing Club, a body with a distinguished and nationwide membership, has earmarked a £1000 purse as first prize for a turbocar race which it intends to promote as soon as a worth-while line-up is assured. This sum clearly bears no relation to the huge cost of designing and building a turbocar and mothering it through to raceable form.
The gas turbine differs fundamentally from the piston motor in having a purely rotary motion and thus banishing that bane of the engineer, inertia loading; and also in the continuity of its combustion process — like a blowtorch’s — in contrast to the piston movement’s timed and interrupted combustion. As for the manner of its going, the turbine is primarily distinguished by its ability to generate full torque from a standstill, thus making any form of gearbox or torque-converter superfluous.
When we go from general to particular the choice of example isn’t ours to make, Rover being the only turbocar of which details are known at this writing. The Rover motor is of the straight-through type with two combustion chambers, and is equally happy on a gasoline, kerosene, or fuel oil diet. For convenience — considering the vehicle purely as a perambulating laboratory—the power plant is housed in rear of the driving compartment of a three-seat roadster body. Each flank of the body has three grilled-over embrasures through which air is gulped into the initial compressor, whence it passes to the combustion chambers, the compressor turbine, and a power turbine. Efflux from the two turbines escapes at the moderate speed of about 100 miles an hour via four vertical stacks in the lid of what corresponds to a rumble seat. There are two quite independent shafts, the first connecting the compressor to its turbine, the second forming the axis of the power turbine and carrying the drive to the transmission line through step-down gearing with a ratio of around twentyfive to one.
From its exterior appearance, squarish and much freer from excrescence than a piston engine, it would be impossible to judge that this motor in effect comprises four subunits, as described above. Very high rates of turnover are of course inherently characteristic of the gas turbine, and this one idles at 7000 revolutions per minute — faster than many piston engines can be made to operate on zero load and full throttle. Turnover at maximum highway speed is 40,000 r.p.m. Designed for an output of 200 horsepower, Hover’s turbine had been deliberately “hopped down” at the time of its Silverstone demonstration, leaving the car with a top gait of something over 90 miles an hour and take-off from zero to a mile a minute in just over 14 seconds.
Power for power, the typical gas turbine is both smaller and lighter than a reciprocating movement, but the example in question has a substantially higher output than the piston engine it replaces in its stock chassis: in this instance, therefore, the turbine is rather bulkier than the regular unit.
Turbocar driving drill could hardly be simpler. Assume the vehicle to be stationary and its prime mover dead. Manipulation of a normal ignition switch (a) cuts in a starter motor, which in turn motivates the interim messed compressor and compressor turbine, and (b) energizes an ordinary spark plug in each combustion chamber. Kerosene fuel, fed into the combustion chambers by atomizers, mixes with the air introduced by the compressor and, almost instantly, continuous self-ignition takes over from the now redundant spark plugs; at this stage the current to the plugs is automatically cut off.
So long as the driver keeps his foot off the accelerator — which, with the brake pedal, comprises the sole furnishings of the toeboard — the turbine runs at its preset idling speed. Then, as he depresses the accelerator, having first released the holder brake, the independent power turbine goes into action and the vehicle takes off, picking up gently or with fierce gusto, according to the rate of pedal depression. Thereafter, aside from the tachometer’s evidence of astronomical revolutions per minute, and the matching crescendo of the efflux, the sensation and the manipulation method are hardly distinguishable from those typical of American ears with torque-converter transmission: to go faster or gobble gradients, step on it with the right foot; to slow, lift the right foot and cram down the left.
How long will it he before the turbocar can hope to compete commercially with its piston-engine rival? Among knowledgeable technicians in Britain, estimates range from two years to a decade. Others, visualizing giant-stride developments in the reciprocating motor field, say it never will.
What, at the current stage of turboear advancement, is the weightiest problem confronting the producers of the Hover and their British and American antagonists in this shadow race? High fuel consumption, undoubtedly. “ The fuel used is inherently cheaper than gasoline, “ as the technical editor of the London Motor wrote last year in a review of the subject, “but since the final cost of fuel to the motorist in most countries is largely determined by tax, even halving the basic price will have little effect on the sum required at the pump.”
In its demonstrated form, at medium to fast road speeds, the Rover was covering about 5 miles per U.S. gallon of kerosene. True, this experimental car did not at that time incorporate a heat exchanger, by means of which economies of probably 20 per cent should be attainable. But the fact remains that the day is still far off when the turbocar, despite its undiscerning palate for fuel, can be operated as cheaply as a normal vehicle of comparable performance.
Noise and lack of power braking, in that order, rank as the second and third hardest nuts to crack, although in the reports of the Boeing project mentioned earlier it was claimed that a system of power braking had been evolved which actually surpassed the retarding effect of engine compression in a normal unit.
Noise, however, presents a dour conundrum, because the turbine’s total throughput of air — which serves as coolant as well as combustion promoter— is about ten times greater than a piston engine’s. The Rover, which had no form of muffling device on either intake or exhaust sides when paraded for the press, appeared to inhale at least as audibly as it exhaled. By sports car standards it certainly was not unduly boisterous, but Rolls-Royce and Cadillac sibila nee will be the only acceptable criterion when the production stage arrives, and that kind of bated euphony can be achieved only by the use of elephantine silencers. The savants who scheme passenger and baggage space for us just don’t have room for silencers on that scale.
Posers like this take time, and patience, and cunning, and that propensity which frustrated researchmen and technicians have for tangent ing off at the lake’s brink instead of just throwing themselves in. They cracked just as tough ones when they subdued the clatter in the mechanically monstrous poppet valve, devised transmissions that think for themselves, made tires that didn’t skid and practically wouldn’t puncture. No doubt they will do it. again.
