I ENGINEERING ANDI SCIENCE JUNE/ 1954 PUBLISHED AT THE CALIFORNIA INSTITUTE OF TECHNOLOGY Only STEEL can do so many jobs so well Famous Finger of Metal and stone pointing 1472 feet into the skv is The Empire State Buildi~g in New York City. This mightiest of bujldings makes liberal use of Stainless Steel for both decorative and utiEtarian purposes: in ver tical strips beside the win dows, in bands around the tower, in the two entrance corridors. "Maintenance?" said the assistant operating manager when asked about the exterior Stainless Steel. "What maintenance? We haven't touched the stain less steel since it was in stalled. And the condition of the steel is as good as ever." Dragon's Teeth Sprouting? No, these are steel bearing piles in Not a bad record after more the foundation of a dam spillway. When the dam is finished, than 20 years. you'll never know the steel piles are there. 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EC54-S 2 ENGINEERING AND SCIENCE ENGINEERING AND SCIENCE I I IN THIS ISSUE JUNE,1954 VOLUME XVII NUMBER 8 PUBLISHED AT THE CALIFORNIA INSTITUTE OF TECHNOLOGY CONTENTS Hypersonic Research at Caltech 5 Studies of how air flows around a body at speeds "faster than supersonic" keep research ahead of the ever-growing needs for knowledge imposed by the high-speed flight of the future. On the cover this month, and on by James M. Kendall pages 11-13, you'll find pictures of Caltech's 60th commencement and on page 14 is the text of Dr. 1. 1. Rabi's George R. MacMinn 10 fine commencement address. A camera portrait This issue is not entirely given over to commencement activities, though. On page 5 there's an account of the Commencement 1954 11 hypersonic research now in progress at the Institute, written by James M. Kendal!, graduate assistant in aero Man's Right to Knowledge and the Free Use Thereof 14 nautics - and the first entry in the Only by the fusion of science and humanities E&S Science Writing Contest (which can we reach the wisdom appropriate to you can read more about on page 31). our day and generation. George R. MacMinn, Professor of The 1954 commencement address .English, retires this year after 36 years of service. Y ou'l! find an im by I. I. Rabi pressive portrait of him on page 10. Unwilling to let it go at that, we've added the characteristic portrait below, The Month at Caltech 23 just to remind all the students who've knocked at his door during the past 36 years of the expression that invariably Alumni News 24 greeted them after they got inside. Personals 28 S T A F F Publisher ....... _. ............................................ _Richard C. Armstrong '28 Staff Photographers._ .. __ ._ ................................. _Byron Johnson, J r. '56 Tom Bergeman '56 Editor and Business Manag~r .. -.-... -.. -... -.. -.... -.-Edward Hutchings, Jr. Editorial ConsultanL_ ...... Professor of English George R. MacMinn Published monthly, October through June, at the Californa Institute of Tech nology, 1201 East California St., Pasadena 4, Calif., for the undergraduates, graduate students and alumni of the Institute. Annual subscription $3.50, PICTURE CREDITS single copies 50 cents. Entered as second class matter at the Post Office at Cover W. W. Girdner Pasadena, California, on September 6, 1939, under the act of March 3, 1879. All Publisher's Rights Reserved. Reproduction of material contained herein p. 5 Hank Hoag forbidden without written authorization. ManUSCrIpts and all other editorial pps. 6·7 James M. Kendall correspondence should be addressed to: The Editor, Engineering and Science, pps. 10·14 W. W. Girdner California Institute of Technology. JUNE, 1954 Printed in Pasadena PP~6 3 teeth for a 1000 h. p. hite ... Undoubtedly you will recognize more fully - gain recognition and this application of a familiar tech advancement. nique for studying stresses. In this Many of our engineers who had case, it was used to develop gears important roles in developing the that are less than 5 inches in most powerful jet engine known to diameter yet easily transmit over be in production - rated in the 1000 horsepower. 10,000-pound thrust class - are still in their twenties. Inherently, the design and de velopment of aircraft engines offers To those young graduates who unusual opportunities for applying can see the career possibilities in basic engineering principles the rapidly evolving field of air learned in school. In few other craft propulsion, we can offer a places can a technical graduate real opportunity for growth and utilize his education and abilities professional development. PRATT & WHITNEY AIRCRAFT Division of United Aircraft Corporation East Hartford 8, Connecticut 4 ENGINEERING AND SCIENCE Volume XVII ENGINEERING AND SCIENCE June, 1954 The principal part of a hypersonic tunnel is the set of contoured blocks of steel which comprise the nozzle. HYPERSONIC RESEARCH AT CALlECH PIONEERING WORK in one of the newest phases of aerodynamics is being carried forward at Caltech's Guggenheim Aeronautical Laboratory (GALCIT) by a Studies of how air flows around a body research group under the direction of Dr. Henry T. at speeds "fa,ster than supersonic" keep Nagamatsu. The group is investigating, both experiment research ahead of the ever-growing ally and theoretically, how air flows around a body in needs for knowledge imposed by the the hypersonic speed regime. Literally, this means high-speed flight of the future. "faster than supersonic," and is arbitrarily taken 'to be Mach 5 and higher. The group is currently operating two hypersonic wind tunnels, one of which has recently achieved flow at Mach 11, or 11 times the speed of by JAMES M. KENDALL sound. Graduate Assistant in Aeronautics The reason for the extensive research program is the rapidly growing need for fundamental knowledge about hypersonic flow to be 'used in the design of high-speed JUNE, 1954 5 the surface are heated by friction as the air flows over the surface, even though air is only slightly viscous. It so happens that these two processes produce nearly UNDISTURBED fTURWBAUKLEE NT identical final temperatures, but the rate of heat trans FREE STREAM fer is in general widely different at different parts of the surface. The final temperature depends mostly on the Mach number of the flow. By way of illustration, two missiles sustaining flight at Mach 5 and 10 respectively, on a day when the air Shock wave pattern and growth of boundary layer on a temperature is 70°F, are heated to 2650° F and body in hypersonic flow. The drag results from the 1O,600°F. Because steel melts at about 2600°F, it is pressures and from the boundary layers. quite evident that high-speed missiles can withstand flights of only short duration so that 'time does not per mit heating to the equilibrium temperature. Flight time decreases, however, as speed goes up, and a missile vehicles. The United States now has some 18 types of traveling vertically upward from sea level at Mach 5 guided missiles, many of which are capable of very high would remain in the earth's atmosphere less than 10 Mach numbers. As early as the spring of 1949, a two seconds. stage rocket consisting of a V-2 and a Bumper WAC attained a Mach number of about 7.5 during tests at Pressure distribution White Sands. As newer missiles are designed, aerody namic data at ever higher Mach numbers are needed. A second unfortunate effect is that the pressure distri For example, a long· range ballistic rocket of 4000 miles bution about a body in high·speed flight is highly un range would require a speed corresponding to Mach 13 symmetrical fore' and aft, so that a large drag results. at the end of burning, and a rocket designed to escape High pressures occur on the nose of the body as it pushes from the earth would require about Mach 35 at the end aside the air in much the same fashion as a nail pene of burning. But the hypersonic program at Caltech is trates wood, while parts of the surface behind the definitely not concerned with the design of missiles or thickest section of the body experience virtual vacuum, space stations. The models tested are not futuristic because it is difficult for the air to accelerate sidewards shapes; they are simple cones, spheres and wedges, be· fast enough to follow the surface contour. cause the information obtained from these is more basic. The power used to drive the body forward against th!l Hypersonic flow differs from low-speed flow in sev· drag force due to the pressure is converted to heat by eral ways, many of which can only be regarded as the dissipative action of the shock waves produced-as disadvantageous to high.speed flight. One of these is shown in the diagram at the top of this page. extreme aerodynamic heating. Transfer of heat to a body The shock waves are the interface of the lower pres surface is brought about on the region near the forward sures of the undisturbed free stream and the high pres· parts' of the surface by rapid compression of the air sures produced 'by the motion. These waves extend with as the body pierces the atmosphere. The after parts of decreasing strength to great distances from the body, Leg 1 of the hypersonic wind tunnel. The worker here is checking a flat plate model before installing it in the tunnel for an experi· ment. 6 ENGINEERING AND SCIENCE and their action is to deflect the air outward as the body MODEL contour passes by. It is of importance that the higher the Mach number, the closer the shock waves lie to the surface, and correspondingly the stronger they become. h TEST_J These changes produce subtle effects which are peculiar SECTION! to hypersonic speeds. For hypersonic studies, as with most other phases of AIR AIR HEATER COOLER aerodynamics, the basic instrument of experimental re search is the wind tunnel. In 1885, Horatio Phillips used the first aerodynamic tunnel for experiments, and since that time tunnels have become ever more extensively used. The justification for wind-tunnel testing is usually 16 COMPRESSORS 1000 HORSEPOWER a matter of economy in the form of reduction of design costs. At the present time, the development of a new Components of a hypersonic wind tunnel system. The aircraft requires a vast amount of research, the cost of wind tunnel, in which scale models are tested, offers a which may well run into millions of dollars and take means of reducing time and costs in the development of many months. The wind tunnel, wherein scale models a new aircraft. are tested, offers a means of reducing time and costs, and offers to hypersonic research, in particular, certain ease of gathering data. ample, is a function of Mach number and Reynolds Similarity parameters number, and if these two are adjusted to be the same The comparison between data obtained in a tunnel in the tunnel a's in tl;te desired free-stream conditions, and that needed for full-scale application is made on then the value of coefficient of drag measured is the the basis of so-called similarity parameters. These are correct one. It is on the basis of this similarity that one dimensionless numbers which depend on various im is able to use wind-tunnel measurements to predict full portant physical quantities, such as the density, viscosity, scale performance. and speed of the air. The two most important of these The experimental facilities of the CaItech hypersonic parameters are the Mach number and the Reynolds group center around two tunnels referred to as Legs 1 number. The Mach number is the ratio of the air speed and 2, both with 5-by-5-inch test sections. The principal to the speed of sound. The Reynolds number depends on part of a hypersonic tunnel is the set of contoured blocks the viscosity, density, and speed of the air, and on the of steel which comprise the nozzle. High pressure air length of the body. This number, in a sense, provides a enters the nozzle at a low Mach number, and when it certain measure of all processes which depend on viscous gets to the narrowest part, which is known as the throat, effects, such as heat transfer rate and surface or skin it has attained Mach 1. friction. When air moves at supersonic speeds the familiar This notion of similarity parameters is expressed principle of "the larger the area, the slower the flow by saying that the coefficient of drag of a body, for ex- speed" is reversed. Thus the air is accelerated by a dif- Leg 2 of the hypersonic n:ind tunnel. The sidewalls of the tunnel have been removed to show the 5-by-5- inch test section. JUNE, 1954 7 ference in pressure until it reaches a final high Mach As previously mentioned, the Mach number produced number and a low pressure at the widest part of the by a hypersonic tunnel depends only on the area ratio nozzle, the test section. of throat to test section, and not on the pressure avail As the air expands in going from the high to the able. However, to keep the test section pressure at a low pressure, the temperature drops very sharply; for realistic value in comparison with conditions a missile example, by a factor of 6 for Mach 5 and by a factor might meet, the supply air pressure is elevated. The of 21 for Mach 10. Also, the speed of sound, which supply pressure of both Legs 1 and 2 may be raised to depends on temperature, goes down correspondingly, 1000 pounds per square inch. In spite of this compres so that high Mach numbers may be produced with some· sion, the pressure falls to a hundredth of atmospheric what lower air speeds than might seem necessary at first pressure or less at the test section. thought. The actual air speed in Leg 2 operating at Observation of the flow over the model being tested, Mach 11 is about 3,000 miles per hour. and the shock-wave configuration, is made possible by the use of a Schlieren apparatus. The Schlieren employs Heat and high Mach numbers a beam of parallel rays of light from a mercury vapor arc which is passed through the test section of the tun To prevent its temperature from dropping below the nel, illuminating the model. The variations of air density liquefaction point, the air must first be heated. It is this in the regions of the model and of the shock waves re heating that places the limitation on producing higher fract the light, thus causing an increase or decrease of Mach numbers in wind tunnels. A steam heat exchanger illumination in the image formed on the ground glass raises the temperature of the air supply of Leg 1 to or photographic plate used for observation. 300 ° F, and 300 kilowatt electrical heater raises the tem· perature of the Leg 2 air supply to 1100°F, so that the Operating schedules temperature at the test section of either tunnel is not lower than -385°F, which is approximately the tem· Tunnel running time, is scheduled, whenever possible, perature of liquefaction. After the air passes the test so that while one tunnel is running, the other is being section, a series of shock waves slows the air to low instrumented and prepared to run. In this way, maxi speeds, and simultaneously the temperature returns to mum usage of the compressor plant is obtained. Prepa that to which it was initially heated. The air must then ration takes somewhat longer in Leg 2 than in Leg 1, be cooled by a water h~at-absorber before it can be because the higher operating temperatures pose addition returned to the compressors. al problems. For example, the plastic medical tubing When either tunnel is run without heating the supply used for connecting pressure probes in Leg 1 must be re air, the air becomes so cold that it condenses into tiny placed by stainless steel hypodermic needle tubing in droplets of liquid air, which look like fog if illuminated Leg 2. All joints made with this stainless steel tubing by an intense beam of light passed into the tunnel must be silver-soldered, because ordinary solder would through a window. No satisfactory comparison between melt. data of condensed air flows and single-phase air flows There are two principal aspects of hypersonic flow has been obtained; most experiments, therefore, require that one may wish to study: the pressure distribution the use of tbe air heaters. about a body, with its corresponding shock-wave con figuration; and the viscous effects, which are known as boundary layer phenomena. However, the pressure dis Flow conditions tribution is already well understood as a result of the The contours of the nozzle blocks are of an exact more classical compressible-flow theory. In fact, the shape which depends on the desired Mach number. The shock-wave equations were deduced as early as 1870. specific shape produces uniform flow conditions across Consequently, most hypersonic research is currently di the height of the tunnel at the test sections for only the rected toward an understanding of boundary layer one Mach number the nozzle was designed for. However, phenomena, which are of very great interest. because the Mach number produced by a nozzle depends only on the height ratio of the throat and the test sec Boundary layer tion, one may vary the Mach number by changing the throat height. The flow conditions across the test section The boundary layer is a layer of air that clings to height will still remain acceptably uniform for a fairly a surface because of the viscosity of the air. It is respon wide range of Mach numbers. The throat height for Leg sible for both the viscous drag and the aerodynamic 1, which normally operates at Mach 5.8, is .080 inches; heating and may take two forms: laminar or turbulent. for Leg 2, operating at Mach 8, it is .020 inches. Be In the laminar form the air within it flows smoothly over cause the nozzle throat is so narrow for hypersonic flow, the surface, and the speed varies in an orderly fashion the rate of flow of air through it is correspondingly low, between the surface and the outer edge of the boundary and consequently the power required to drive the com layer. On models in the tunnel, the laminar boundary pressors is not excessive. The 16 compressors, compris layers get as thick as an eighth of an inch. In the tur ing 7 stages of compression, are driven by electric bulent form the flow in the boundary layer is highly motors of about 1000 horsepower total. irregular. It is not difficult to imagine that this chaotic 8 ENGINEERING AND SCIENCE