Automobile Traditions Challenged by First Streamlined Stock Cars (Feb, 1934)
Automobile Traditions Challenged by First Streamlined Stock Cars
Startling Changes in Body Design Are Expected to Boost Road Speed and Cut the Cost of Operation
by Robert E. Martin
AS THIS issue of Popular Science Monthly is published, in automobile shows and dealers’ showrooms all over the country are being exhibited the world’s first scientificially streamlined stock cars. Introduced by leading American manufacturers, they mark a new stride toward a goal to which automotive engineers have been working for years—the development of a car in which fuel economy, riding comfort, and speed are brought about by reducing to a minimum the losing battle with air resistance that has been waged by every automobile that ever was placed on the roads.
There have been streamlined cars before—experimental cars. Designers and drivers of racing cars and the freak vehicles built for a single try at a world’s record also have utilized streamlining principles in body construction. Speedway daredevils, for example, for years have been tying and tapeing streamlined wooden forms to the rear of their axles to cut down wind resistance a trifle. Aviation and automobile engineers, research men in aerodynamic laboratories, and designers of railway rolling stock long ago worked out the “teardrop” form that means minimum air resistance in a moving vehicle. But an attempt to use fully the known principles of streamlining in a stock passenger automobile never had been made until it was decided that this year the motoring public was ready to accept what hitherto had been called “the car of the future.”
Standard cars in the past have had flattened mudguards, rounded projecting corners, reshaped radiators and slanted windshields, as a gesture toward streamlining. But solving the real problems of streamlining meant entirely redesigning the body to secure a new shape around which the air currents would flow smoothly, meeting at the back without any swirls or disturbances. The task was further complicated by the car’s wheels, axles, door handles and other features, each presenting its own streamlining difficulties. Obviously, then, the problem confronting the automotive engineers who designed the new machines, of which the public is, at this moment getting its first view, was highly involved and could not be solved in a moment.
Late in the summer of 1927, the engineers tackling this job, decided to start from scratch and learn for themselves all they could about air pressure and a moving body. To do this they enlisted the aid of Orville Wright who helped them build an inexpensive wind tunnel such as he and his brother, Wilbur, had used when they invented the airplane. The tunnel was set up in a locked room in Dayton, O., a secret laboratory hardly more than twenty feet square.
Here the workers carved small wooden blocks into every imaginable shape. They mounted them on ball bearing rollers and placed them on metal tracks in the blast of the wind tunnel. A cord ran from each block over a pulley to a weight resting on a simple post-office type scales placed on the floor. As the air resistance drove the block back, the cord lifted more and more of the weight from the scales. Thus the experimenters could easily determine the resistance of any given block in ounces simply by subtracting the reading when the cord was pulling from the reading when it was relaxed and not under strain.
Immediately, surprising discoveries began to pop up. So far as efficiency in the matter of wind resistance is concerned, the engineers found, all the cars in the world are running backward! If they were turned end for end on their chassis, with the blunt rear facing forward and the narrow hood behind, the air would offer far less resistance to their passage. Not long ago, Harry Hartz, the noted racing driver, amazed New Yorkers by driving down Broadway in a sedan whose body was reversed on its chassis.
In many of the tests, the same blocks were altered slightly and the differences in resistance noted. They showed me blocks in which notches were cut, bulges added, tops altered, sides changed. And each variation left its record on the data sheets of the investigators.
Then streamers of silk were added to the tunnel equipment. As long as the air flowed smoothly, they stretched out straight as pencils. But when they struck disturbed currents, they vibrated violently, permitting the engineers to study the exact location and extent of the various swirls. Smoke streamers gave additional information about what happened to the currents and finally, the air was made to write its own record through an arrangement of metal plates and lampblack.
In explaining the process, they showed me block models which were bisected fore and aft vertically and had the two halves clamped together with an upright metal plate between them. This plate was heavily coated with a mixture of lampblack and linseed oil. At the end of the test, the wind had carved its record on the plate. Where its velocity was greatest, the metal was bare, all the coating having been carried away. A careful comparison of the amount of lampblack remaining on different parts of the plate gave a complete picture of how the currents had acted in passing over the block. Scores of these wind-written records were assembled. They gave invaluable insight into the problems of rear-end eddies and front-end disturbances. Thus they slowly worked out the designs now on the market and at the same time learned some curious things about the cars and air pressure.
For instance, when Sir Malcolm Campbell streaked across the wet sand at Daytona Beach, Fla., last February, his Blue Bird was traveling 272 miles an hour. The spectators saw the moisture sucked up from the sand twenty feet ahead of the flying car. The nose of the Blue Bird was driving a cone of air before it as it bored its way through the atmosphere.
While a twenty-eight-inch cube of air weighs only a pound, as compared to 100 pounds for a similar cube of water and 784 pounds for one of steel, its resistance climbs rapidly with speed. At Campbell’s pace, the air (Continued on page 97) pressure was in the neighborhood of 5,000 percent greater than it was at forty miles an hour. Each additional mile of speed above forty is twice as hard to get as the preceding one because wind pressure increases with the square of the speed.
IN AN ordinary machine, making seventy miles an hour, eighty-five percent of the engine’s power is required just to force the body through the air; only fifteen percent is needed to overcome rolling resistance, friction, and load. The average modern driver, hitting fifty miles an hour on the open highway, burns up seventy percent of his gasoline just to get through the air!
A perfectly streamlined car, according to Prof. Alexander Klemin, of the Guggenheim School of Aeronautics, in New York City, would cut fuel bills thirty percent at thirty miles an hour and would clip them in half at a sixty-mile pace. Such machines would consume less gasoline when traveling fifty miles an hour than a present-day car uses at thirty-five. Fifty miles on a gallon of gas is entirely possible with proper streamlining, tests conducted at the University of Michigan by Prof. W. E. Lay have indicated.
It is interesting to note that the finest streamlined sedan of 1933, according to Prof. Klemin, is actually only nine percent better in point of reducing wind resistance than a sedan of 1922. At sixty miles an hour, present-day automobiles produce virtually fifty percent as much resistance as they would if they pushed before them flat plates equal to their head-on area.
During the last decade, manufacturers have increased speeds by piling on horsepower. How vital streamlining is to higher speeds, with no increase in power, is illustrated by the records of the Schneider Cup Race. The winner of this aviation classic in 1915 traveled sixty miles an hour. In 1931, the winner touched 340 miles an hour. Had there been no advance in streamlining during the intervening years, aeronautical authorities calculate, the engine required to drive the first machine at the speed of the second would have had to have 29,200 horsepower. As a matter of fact, the 1931 seaplane carried an engine of 2,300 horsepower, approximately one-thirteenth the former figure. Streamlining and aerodynamic advance accounted for the difference.
AT LOW speeds, under forty miles an hour, wind resistance is not so important. But the average highway speed, with improved roads and better cars, is now placed at fifty miles an hour. By 1940, it is expected to be sixty-four miles an hour.
Consequently, in research laboratories, on proving’ grounds, in university workrooms, scientists, motor-car makers, and body builders have been busy grappling with the problems of streamlining. In their studies they have used curious instruments and special apparatus. They have driven at high speeds strange cars studded with pitot tubes which recorded air pressures at different points on the body. They added lines of brilliant dye to streams of water passing over wooden models to learn the points of most disturbance. They have placed full-sized machines on “rolling carpets” which showed the horsepower required to carry the cars over the ground when the wind pressure was nil.
In fact, many laboratories worked out special equipment of their own. At the University of Michigan, for example, “floating-envelope” trucks, machines with special bodies balanced so they moved on the chassis when wind resistance forced them back, recorded head-on pressures under road conditions.
Supplementing this research work have been numerous experimental cars embodying ultra-streamlining. In England, the curious steel beetle built by Sir Dennis Burney scooted along the roads at surprising speeds. In America, the Dymaxion of W. Starling Burgess, the Dream Car, exhibited at a recent Detroit show, and the Arrow Plane of Lyman Voelpel, have all pointed the way to the future.
Because automobiles run close to the ground instead of flying through the air, compromises and modifications of the ideal teardrop streamline shape are necessary. No one knows exactly how the ultimate streamlined car will look.
THAT it may carry fins at the rear like an airplane, is indicated by tests completed, not long ago, by the U. S. Bureau of Standards, in Washington, D. C. Fully streamlined cars, their wind tunnel experiments revealed, have a tendency to turn under certain wind conditions. Thus side winds might produce forces causing the car to skid. Vertical fins, such as are used on ultra-speed machines, may solve the difficulty.
Another problem, however, awaits the designers of streamlined cars. The curve of the auto’s top, acting in the manner of the upper surface of an airplane’s wing, may provide sufficient lift to interfere with the traction of the wheels. Sir Dennis Burney’s English machine, for example, developed an estimated lift of 300 pounds when its speed reached a hundred miles an hour.
Outweighing these problems, are the obvious benefits of streamline constructor The wider front will enable three people to sit comfortably in the forward seat. The curving body, replacing the straight lines of present cars, cuts out blind spots and increases visibility as much as twenty-five percent. In the Dream Car of the Detroit show, a periscope above the driver’s seat afforded practically 100 percent visibility to the rear.
Closely connected with the streamlining experiments, have been recent investigations into the riding quality of motor cars. Using original apparatus—three directional accelerometers, steadiness meters, and vibrating platforms and seats—workers at Purdue University, Ind., under the direction of Professors H. M. Jacklin and G. J. Liddell, have analyzed riding comfort and the effects of vehicle vibration upon human beings.
A RECENT announcement of great importance in connection with increased riding comfort is the introduction on several makes of cars of independently mounted front wheels. In the cars of one manufacturer, by eliminating the front axle and attaching each front wheel directly to the chassis by means of its own spring, the wheels are permitted to rise and fall independently of each other and thus absorb road shock without transmitting it to other parts of the frame. The opinion expressed in automobile circles is that this and other improvements in the American cars of 1934 give them speed and riding comfort never before known.
To sum up. Since less power will be required to overcome air resistance in streamlined machines, there will be more power available at any speed for acceleration and hill climbing. Since the body curves farther out to the sides, it will be roomier and the windows will provide better vision. And, since smaller engines will be sufficient to reach speeds that require large-horsepower motors today, gasoline consumption will be greatly curtailed and economy of operation increased.
These are the goals toward which the wind-fighting automotive engineers are working in creating their new designs.