ON STREAMLINED FORM
ON STREAMLINED FORM
STREAMLINE form has a bigger influence on mankind than is generally realised—we are referring to that streamline form which you contemplate at Brooklands, in the daytime when the motors are going round, of course. Not so very many years ago the general public regarded streamlining as something rather mysterious that you had to do to the back part of a racing-car. Indeed, the racing-car was the only object in the engineering world, if we except the ship, in which the need for streamlining was at all evident. Consequently, the ordinary man and woman in the street found it not too easy to believe that air-pressure could matter so much, nor was every racing-car constructor seriously worried about the matter. Later, motor-cycles built for very high speed record runs were faired-in and in the world of aeronautical eugineering much more thought is now given to the complex problem, or rather problems, of streamlining, than in any other sphere. The ordinary person sees streamlined locomotives, both steam and electric, sees aeroplanes drawing in their undercarriages, perhaps owns a semistreamlined car, and is told quite often in the technical and semi-technical Press that air resistence goes up as the square of the speed. But do not forget that the racing-car started it all. Even early flying machines were not very seriously faired and much of what the pioneers of Aviation knew of streamlining fuselage and undercart in 1909-1910 came from study of racing-car methods. Perhaps to-day the position has reversed. Curious that the very persons who scorned things mechanical should be the slowest to see that the streamlined racing-car was merely in steel and sheet metal what Nature had preached since the beginning of Time. However, we do not intend to labour the psychological aspects of streamlining nor to attempt to show how everyday economics are influenced by man’s growing knowledge of how to combat the slipstream—which reminds one of the aviation’official who, admitting that certain old-type Imperial Airways’ liners had ” built-in headwinds,” observed that they also had ” built7in dividends ” ;
speed, acquired by streamlining, was not the only quality appreciated by the passengers.
But, in view of its extreme importance to vehicle operation in general, it is opportune to trace, very briefly, some of the ways in which streamlining applied to the racing-car, has developed. To-day, good streamlining is absolutely essential to success in record-attacks, in all enginesize categories for sprint runs, and not merely for land-speed record work. In the sphere of road-racing, again, streamline is nowadays of vast importance, albeit factors of control and visibility make its extreme application impossible. For Track work, which really developed streamlining as nothing else has done, few cars are now expressly constructed, but it may be said that those cars built for outer-circuit work are often smallengined or rather dated types, which need all the help possible from good body-form and that their varied chassis styles give scope, as was the case with Brooklarxds’ cars in the past, for great variety and ingenuity to be applied to the mode of attack. Something of the potency of self-created wind pressure was emphasised at Brooklands Track in 1907 when tests were carried out with a 40 h.p. Napier. This racing-car was run at a speed of 79 m.p.h., after which laths were attached and the car timed with varying head resistance erect. It was assumed that engine power dropped proportionately with the
speed. The speed fell from 79 m.p.h. to 60 m.p.h. with an increased drag of 14 square feet and to 50 m.p.h. with a 38 square feet increase, and finally to 48 m.p.h. with 40 square feet of additional drag. [The pressure varies with the square of the speed and the power with the cube.] In 1912 the formula P=0.008 AV’ was used to calculate loss due to drag, P being pressure in lbs., A the frontal area, and V the velocity in m.p.h. It was considered that a typical touring body had alt1 area of about 28 square feet, so that at 80 m.p.h. the loss became P x S over 88,000, P being pressure in lbs. as calculated above, and S speed in feet
per minute, the answer being 4.90 h.p. Thus at 60 m.p.h. 40 h.p. would be absorbed, and at 80 m.p.h. nearly 90 h.p. Which is why your 80 m.p.h. preWar car had a big motor. Here we may digress to observe that before the War Robert W. A. Brewer used a Trotter Accelerometer, made by Everett, Edgecumbe and Co. Ltd. for Track tests—so Tapley and Ferodo performance meters are quite well-established instruments. In modern aeronautical practice windresistance is considered under the headings of frontal resistance, interference drag, parasitic drag and skin-friction. In a racing-car interference drag is at a minimum, because there is not the problem of blending wings, rudder, fin and tail
to the main body. Parasitic drag is confined to axle 3, and wheels, where these are not enclosed, exhaust stubs and windscreen, if we except small catches, straps and studs, etc. In consequence, it seems likely that skin-friction accounts for as much loss as intererence and parasitic drag combined, but, unfortunately, not much is known about it, even in scientific aeronautical circles, although it has definitely been established that drag is set up by the breaking away of the boundary layer, and seemingly at speeds at which ordinary aeroplanes and racing-cars travel. The cure is to polish all exposed surfaces, and Germany has used polished body panels for her recordbreaking cars for some time. Another difficult problem is that of determining the ideal streamline shape. It was originally thought that little could be done beyond fairing-in the nose and making the body as a whole of” airship” formation with a tapering tail, the current theory being that maximum depth, or diameter, should be at a point about I from the nose. However, very little idea exists as to how long the tail should be—witness a photograph used for a front cover of” The Brookland’s Gazette” in 1924, where all lengths of tails are seen at Brooklands. Tommy Hann even claimed that a structural tail could be replaced by an outlet of high-pressure air, and put his theory into practice when he
built his racing Lanchester saloon ” HoiehWayarah-Gointoo.” Now a further problem arises as to whether shape should not vary materially with speed, if maximum efficiency is to be achieved. This may not involve track ears, or cars built to attack a record at a predetermined speed, assuming that wind-tunnel tests indicate when a good form has been achieved. But what of aeroplanes in which cruising and maximum speeds are far apart, or road-racing cars in which acceleration suffers on account of drag from 70 m.p.h. upwards, yet which are required to reach, and hold over double this speed, every lap ? As emphasising the importance of reducing wind drag, remember that on ultra highspeed aircraft the expensive surface-type radiator is used solely to reduce resistance and that on modern record-attacking machines there is hardly sufficient surface, using all the wing and fuselage area, to adequately cool the engine ; and that a quite different class of record-breaking aeroplane, Henshaw’s Mew Gull, found a retractable navigation light worthwhile. Up to 60 or 70 m.p.h. streamlining matters not very much. After that, nearly all your efforts to extract more power from your engine are made to defeat air-drag. It remains to be seen whether cars and aeroplanes will have to give best to air-resistance at speeds around 700 m.p.h., at which pace even light rays crave a better streamline form,
Space is limited in which to enlarge on a very complex subject, and we will content ourselves with a few notes on the development of streamline form in three spheres ; track racing, road-racing and record work.
Although there was at least one airship-nosed racing-car at the opening Brooklands meeting in 1907, Brooklands Track was responsible for a very concentrated application of streamline form. Around 1909-1912 very narrow bodies were the vogue on the then high chassis, silencers, dumb-irons and axles were faired, and disc wheels were popular. The isolated radiator, later introduced on the “Golden Arrow” and “Blue Bird” and then used by the 100 m.p.h. Austin Sevens, Horton’s M.G. and other cars, was used about 1912 by Austin. Very often tails were left open at the end to allow internal air to escape. Percy Lambert’s famous 25 h.p. Talbot had faired dumb-irons front and back and a Sunbeam had the exhaust outlet in the tail centre, presumably to obviate the drag of an outside pipe. Hancock’s famous Vauxhall” KN ” had a narrow off-set body, disc wheels, and. a very tapered radiator cowl. Coatalen’s “12 Hour” 80 h.p. Sunbeam had an absolutely pointed nose and so had the very early Napiers, in which the water-tubes were led along the bonnet sides. After the war, more sober streamlining was used, and at first radiators were usually enclosed by a cowling which merely reduced the opening—the Eldridge
cowl. Later, dumb-iron casings were added, and Parry Thomas introduced a cowling which covered both the cooling element and the forward chassis members, a scheme followed in wide variety ever since, with many individual variations, albeit the simple Eldridge cowl of the early nineteen-twenties still persists in modified forms, notably on the BarnatoHassan, the Pacey-Hassan and Dunham’s Alvis I. The Napier-Railton, BentleyJackson and Dunham’s Alvis II have Thomas-type cowls, and Duller’s Duesenberg, typically American, merely has a curved grille. There was Hann’s remarkable Lanchester aforementioned, an A.C. which had, an undershield so efficient that it could run flat-out over a bit of newspaper without disturbing it, the ” Hour-Record ” Aston-Martin with a razor-blade body designed round Sammy Davis by the De Havilland Aircraft Co. Ltd., with a maximum width of 18, and an Austin Seven with a body the width of the wheels. About 1926 the low-chassis craze started and ” flatiron ” cars like the Eldridge-Special, f.w.d. Alvis, Thomas-Special, G.P. Talbot, Delage, Eyston-M.G., etc., appeared, a low seating position by means of a wide frame and off-set transmission encouraging low, fiat, bodywork. Eventually loss of speed was attributed to the air-friction below the undershield and to-day the tendency is to use a special axle with the prop. shaft running into it at an angle so that a low seating position can be combined with narrower bodywork. Amongst track types to-day streamlining is less of a scientific business and more a matter of adapting the bodywork to the particular chassis available. Apart from Brooklands, in 1926 Panhard built a 1,500 c.c. record-breaker in which the steering column and wheel was replaced by a large ring, to enable the driver to sit really low and within the body. He steered by means of a grip on this ring, which actuated the steering via a rack and pinion. The front brake drums were enclosed in the wheels and the rear
springs within the body. I believe a larger edition was also produced, but one or other crashed with fatal results and the idea was abandoned. True track cars often have rear-brakes only, to reduce drag, amongst other considerations.
In very early times road-racing cars were totally unstreamlined. The idea of fairing-in the chassis, even if it had been thought of, would have seemed incompatible with extensive hole-drilling to reduce weight. However, the ParisMadrid De Dietrich certainly had a truly pointed, bonnet behind its gilledtube radiator, and a tail ending in a knifeedge. It also had proper undershields, but, alas, at weighing-in, both this, and the tail, had to be discarded. The 1904 Wolseley ” Beetles” had very low frames and, pointed bonnets and tails, but no attempt was made to enclose the driver. In road-racing circles streamlining made relatively slow headway, in spite of the lessons of Brooklands, until the 1911 Voiturette races. For the 1911 Coupe des Voiturettes Sunbeam used a decently enclosed driving compartment and a faired tail, Vauxhall used ” V ” radiators and boat-like tails, and Peugeot also decided on a proper tail, albeit his long-stroke engine called for a bonnet too high to blend with the formation of tail employed. Excelsior and Sizaire also faired in their rear ends. In the 1914 G.P. both Peugeot and Fiat ran cars with bodies that were of distinctly good streamline form. Then, in 1919, Ballot had decently streamlined bodywork, with the spare wheel set vertically in the tail, as had the pre-war Peugeot—fancy spare wheels in to-day’s Grand.s Prix ! A most significant development took place in 1921, when the 8-litre Fiats appeared with bodies that had been
wind-tunnel tested on specialised automobile, as opposed to aeronautical, principles. In place of the current round cross-section, the body sides and undershield were nearly flat, and the tails tapered to the by now quite usual knifeedge. This design of two-seater roadracing body remained with us almost as a standard form, until the monoposto era. An exactly opposite idea was tried out by Ballot and Bugatti for 1922, when both used circular section bodies with tapered tails and truncated-cone radiator cowls. For 1923 Bugatti tried another experiment, together with Voisin, although Sunbeam, Fiat, Alfa-Romeo and Rolland-Pilain were content with what we may term the ” Fiat form.” Both these makers used bodies like the wing of an aeroplane, extending out over the wheels. Bugatti reduced his wheelbase and track to 6 ft. x 3 ft. to accommodate this unique two-seater body, and rivals said that if the inmates would duck they would pass them by running up the Bug’s tail and down the curved bonnet. The “Airthie.” Singer saloons, which one still sees about, remind one of these 1928 racing-cars, and we saw a very ugly Wolseley Hornet with a similar body in Esher recently. Voisin only enclosed the rear wheels, put on discs, and had his engine bonnet built out of the curved main bonnet. Very similar bodies were used on large and small Le Mans ChenardWalkers in later years. By 1924 Bugatti had seen the wisdom of Fiat form and has been one of the last to cease using it. In 1927 lower construction was in evidence, but a similar body line persisted. It will be recalled that Delage found difficulty in keeping his drivers coolfooted with his first combination of bodyform and exhaust-system. The EldridgeSpecial took this low build to its logical conclusion by using a semi-circular section, ” half-airship ” sort of body, whereas Parry Thomas, after doing something rather similar on the much higher, track-racing four-cylinder ThomasSpecial, used an extreme fiat-iron form, with fiat bonnet and undershield and vertical sides, for his straight-eight Thomas-Special cars—which, although often regarded as track machines, were actually built for road, and semi-roadcourse races. It seems that bad eddies below the body detracted from the efficiency which these bodies sought to gain by reason of considerably reduced frontal area. As G.P. cars, became larger this difficulty seemed likely to be accentuated, while there was the need. to give the driver a good view and. adequate arm-room, as well as a reasonable seating-position and plenty of elbow room. So the ” Fiat-form ” persisted, an innovation being the monoposto AlfaRomeo of 1938, marking a new era wherein the riding,mechanic no longer had any place in racing, chiefly because of the risk of fatality should he be involved in a crash. Alfa-Romeo used the now famous twin propeller-shaft layout so as to =sit the driver reasonably low down in the car, and ever since great favour has been shown for off-set or at-an-angle transmission with the same object in view, though E.R.A. still used a conventional transmission with the driver perched above It up to the end of last season. As speeds increased, the need for really good streamline became evident in road racing, especially as acceleration is materially reduced by wind resistance at speeds
above 100 m.p.h. Since 1934, when road-racing cars frequently attained a speed of over 140 m.p.h. and had to accelerate up to such a speed, the streamline form of the G.P. car has been up to, or beyond, the general standard of that of track and record-attacking types, with the proviso that enclosure of the wheels and cockpit is not practicable for road contests, although both Mercedes-Benz and Auto-Union have employed wheelenclosure (using new bodies entirely) at Avus, taking special precautions to enable the drivers to inspect the tyres. The modern G.P. body is not built like a glove around the driver, but a low seating position is regarded as essential, to keep head-resistance as low as possible. Axles, etc., are faired over in a manner which obviates interference drag, and reduced air inlets and a small screen alone set up parasitic losses. Good form is as essential to acceleration as to maximum speed— which in any case is greater than that of the track car—as road-racing is played to-day. Weight must be kept to a minimum, but this presents no real difficulty to-day and there is always stressed-skin aircraft technique, whereby the outer covering takes all loadings without recourse to internal bracing, from which to draw.
Record-breaking, particularly at
speeds above 200 m.p.h., demands streamlining of the highest form and we propose to endeavour to find space in which to discuss this aspect of streamline form in the May issue.