on the World Today
RESTING on the floor of a hangar at Princeton’s Forrestal Laboratory, the Air Scooter looks like a bicycle growing out of a giant white mushroom cap. Mounting the dome, you climb gingerly into the saddle and grip the handle bars. The tiny engine roars like the power mower next door as it spins a miniature propeller. Suddenly you feel a lift, and you are drifting across the room as light as thistledown, a few inches off the floor.
This brand-new kind of vehicle neither rolls on the earth nor flies through the heavens. It operates on a device so new that there is still no agreement on what to call it — “ground effect system,” “free air suspension system,” “air-cushioned car,” “peripheral jet vehicle.”
These floating discs are of burning interest to aviation engineers — not that most of them can offer anything spectacular in practical transportation right now. As the Air Scooter’s designer, Tom Sweeney, and his chief, Professor Courtland Perkins, hasten to tell you, you are not likely to do much scooting on their machine. Built of airplane fabric stretched over an eight-foot metal frame, the vehicle is steered by the seat of the pants and moves at a scant 10 mph. But it can do one thing remarkably well: weighing only 130 pounds and powered by a 5-horsepower chain-saw engine, the Air Scooter can lift three grown men (700 pounds), fifteen times the load lifted by a helicopter of the same power.
Both the eight-foot scooter and a larger, twentyfoot model are designed primarily for study of the phenomenon that makes this lift possible — ground effect. Long known to aeronautical engineers but little studied until two years ago, ground effect is today being investigated not only by Princeton but by every big aircraft manufacturer in the United States, as well as at least one major auto company, the U.S. Army and Navy, the National Aeronautics and Space Administration, and a variety of researchers in Europe.
Helicopters, flying jeeps, and vertical take-off aircraft all can move straight up, but only by brute power of propeller or jet. Ground-effect vehicles take advantage of the earth’s surface to multiply their lift.
The principle is simple. If a cushion of air can be trapped between the bottom of a vehicle and the ground, the air’s natural resistance to compression will keep the vehicle floating in space with a relatively small output of energy. It will not rise very far, for the higher it goes, the easier it is for the air cushion to escape. The maximum altitude is figured theoretically at one to oneand-a-half times the diameter of the vehicle. In practice, the limit is considerably lower because the power demand rises rapidly with rise in altitude. Current experimental vehicles rise only a few inches.
All ground-effect vehicles create the cushion by sucking in air through the top with a fan or propeller and blowing it out the bottom. Experts differ on the best way to do this. In one method, a large column of air is continually blown out through the open bottom of the vehicle, which maintains a cushion by pushing the air in as fast as it leaks out around the edges (usually curtained to reduce such loss). Altitude is increased by increasing the flow of air.
The other basic approach, taken at Princeton, uses the annular, or peripheral, jet. In this case, the bottom of the vehicle is closed but ringed by vents that send jets of air slanting down, in, and under. These jets form a pressure curtain that traps an inert cushion of air under the vehicle. The annular jet can lift a heavier load per horsepower than the open-bottom type.
Principal example of the open-bottom type is Curtiss-Wright’s 300-horsepower Air-Car, the only ground-effect vehicle actually scheduled for commercial production. Curtiss-Wright has demonstrated a twenty-oneby eight-foot prototype, weighing 2800 pounds with four passengers.
Fans on top suck in air to provide approximately a one-tenth-pound pressure per square inch under the vehicle. The Air-Car is designed to travel over unobstructed terrain six to twelve inches off the ground. Release of low-pressure, low-velocity air through louvers in the shell can either propel the car in any direction or brake it. CurtissWright says it can climb a 6 per cent grade and reach a speed of 60 mph.
The rival peripheral-jet system is used in what is probably the most spectacular of the groundeffect vehicles, the British Hovercraft. Designed for overwater travel by inventor Christopher Cockrell, an experimental Hovercraft carried a three-man crew across the English Channel last summer in a cloud of spray. The craft, built by Saunders Roe, is a thirtyby twenty-foot oval with a broad, squat intake funnel in the center and a two-seat cabin on the forward end.
A 435-horsepower engine provides air for both the lifting jets and the propulsion jets, ducted to the stern. The inventor is working to increase its 25-knot speed fivefold and boost the lift from twelve to eighteen inches. Some observers question how the Hovercraft would behave in really rough water, but its inventor confidently predicts that it would ride triumphantly above the wave crests.
Another variation of ground effect is used in the only vehicle developed — or, at least, announced — by an auto company, Ford’s Levacar. On the underside of this 450-pound, five-foot vehicle are three “levapads” — seven-inch discs that eject air downward at pressure of fifty pounds per square inch. The car rides a quarter of an inch off the ground and therefore can make its 15-mph run only on a smooth test track. Ford engineers believe the Levacar’s future is in track or monorail systems, where the air bearing would eliminate friction, permitting speeds of several hundred miles an hour.
Recently Ford has been testing a model of a low-wing plane, designed by Vertol Aircraft, in which a portion of the air stream from the propeller is ducted to peripheral jets set around the wing edges. The ground-effect lift produced beneath the wings would enable the plane to rise a few feet from the ground before starting its regular take-off. On landing, the device would permit the pilot to hover before touching down.
Certainly there is an imposing list of sticky problems to be mastered before ground-effect vehicles can become important in the transportation field. Better horizontal propulsion systems are needed. Will low-pressure air jets counteract a strong cross wind? Steering is difficult. Stability is an untried factor: How will an air-cushioned vehicle behave aerodynamically at 100 miles an hour? What about dust or spray kicked up by the downward blast of air?
Undeterred by such difficulties, ground-effect enthusiasts envisage a tremendous future for their dream boats. Ferry service is an obvious application. The Navy would like to use ground-effect craft for sub hunters and amphibious assault boats. The army sees in aerial suspension a possibility of finding vehicles that could carry ground troops over the roughest countryside at highway speeds.
Curtiss-Wright visualizes its Air-Car’s operating as a bus or truck over unpaved roads made by simply running a scraper across the countryside. Carl Weiland, the Swiss inventor, talks of 350,000ton vehicles crossing the ocean eight feet above the waves.
A new automatic machine is designed to bring the advantages of automation to short-run operations. Called the Transfe Robot, it performs the simple repetitive motions normally done in manufacture or assembly by an unskilled worker. Relatively low-cost, it can be used for a wide variety of production jobs and can be quickly and easily reset for a new routine.
According to its manufacturer, Robodyne Division of U.S. Industries, the TransfeRobot can pick up, put down, hold, and transfer parts and subassemblies, it can hold and operate a variety of tools, and it can operate other machines, such as presses or riveters.
TransfeRobot does all this with an arm which electric servos move up and down, in and out, and around in a four-foot circle. Tipped by a hand with eight fingers - four pairs of tonglike grippers on the underside of a rotating disk — the arm is mounted on a box containing the electronic controls. Once the sequence and duration of arm movements have been established, they are recorded on a template that serves as a memory to control the switches in the required order automatically. The machine can be programed and tooled without special training in about thirty minutes by the same foreman who would instruct an unskilled worker.
The TransfeRobot can be used not only for actual production but for such jobs as assembling, inspection, and packaging. Robodyne expects to find its principal market in plants with short to medium production runs, of from 5000 to 50,000 units. The machine will sell for less than $10,000.
Most of the space in a carload of pipe is taken up by the holes. To save this waste space, a new kind of pipe can be squeezed flat and shipped as a long roll of metal ribbon and inflated at the site. Called Strubing by its developer, Wolverine Tube, the strip tubing can be made of a number of metals. It can be as small as a pencil lead or big enough to walk through, with walls as thin as household foil or as thick as conventional pipes.
Hydraulic pressure — for some sizes even tap water has push enough — air pressure, or mechanical methods can be used to restore the pipe to shape. Besides a wide range of conventional uses, Wolverine suggests that the strip tube might be inserted into a leaky pipe and then inflated, thus forming an inner tube. Wolverine makes the tubing by first producing conventional piping and then cold-rolling it flat, which lengthens the tube but leaves the inside diameter the same. Strubing is expected to be in production by the first of the year.
A somewhat similar tubing produced in Russia is not cold-rolled but made from hollow cast ingots, which are heated and flattened between rollers. The Russians have made flat tubing in both steel and aluminum — the latter more costly than steel but lighter and cheaper to ship and more corrosion resistant. The Russians have already laid six experimental aluminum-ribbon pipelines to carry gas and oil.
Diesel engines have been used in ships for fifty years. Until recently their great weight and high cost have limited them to large vessels. Now, however, a diesel has been designed for the smallest powercraft afloat, the outboard.
The American Marc 10 will make its debut in a 7.5-horsepower model that is said to be able to carry without loss of speed three times the load of a gasoline engine of similar capacity. A one-cylinder, two-piston opposed engine, the Marc 10 has the traditionally simple design of all diesels - no magneto, spark plugs, carburetor, valves, rocker arms, cam shafts, or push rods. Because it burns only diesel oil, fire hazard is reduced, and the fuel costs only about two fifths as much per gallon as gasoline. Fuel consumption is said to be one half that of a comparable gasoline engine. The compression ratio is twenty to one.
The weight problem that has hampered the development of small diesels in the past - they must be strong enough to stand very high compression ratios — is apparently solved in the Marc 10 by a combination of good design and extensive use of aluminum. The Marc 10 weighs 90 pounds, considerably more than the 67 pounds of a typical 10-horsepower gasoline outboard but still light enough to be handled. At the same time, it is said to be so rugged that it will outlast a gasoline engine six to one. Starting — another difficult problem, resulting from high compression — is made easy with an electric starter. The Marc 10 will cost between $350 and $450 and is scheduled by the manufacturer, American Marc Inc., to go into production in January.