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NASA HEADQUARTERS NACA ORAL HISTORY PROJECT ORAL HISTORY TRANSCRIPT
STEFAN A. CAVALLO INTERVIEWED BY SANDRA JOHNSON JOSE, CALIFORNIA ­ 30 SEPTEMBER 2005

SAN

The questions in this transcript were asked during an oral history session with Stefan A. Cavallo. Mr. Cavallo has amended the answers for clarification purposes. As a result, this transcript does not exactly match the audio recording. J
OHNSON

: Today is September 30th, 2005. This oral history session is being conducted with

Steve Cavallo from New York, New York, formerly working with the Langley Research Center [Hampton, Virginia], as part of the NACA [National Advisory Committee for Aeronautics] Oral History Project sponsored by the NASA [National Aeronautics and Space Administration] Headquarters History Office. The interview is being held in San Jose, California, during the NACA Reunion XI. The interviewer is Sandra Johnson. I want to thank you again for taking your time to meet with us today. I'd like to begin today by asking you how you began working with the NACA, the National Advisory Committee for Aeronautics.

CAVALLO: Sometime just before December 7th, 1942, about October or November of 1942, the NACA solicited the senior class of Engineers of NYU [New York University, New York], that they were accepting interviews for the job of Aeronautical Engineer at their Langley [Aeronautical] Laboratory at Hampton, Virginia, so I applied for the job. It was fortuitous timing, for I had applied for the job before the start of the war, which made me eligible for consideration. At that time, I was at the New York University Guggenheim School of

Engineering and I was majoring in aeronautical engineering. At the same time I was also taking

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a Civilian Pilot Training Program [CPTP]. The CPTP was made available to all the students, but especially to aeronautical engineers. I was also an officer, a cadet officer, in the ROTC [Reserve Officers Training Corps]. When the war started, I was in a class that was scheduled to graduate in June 1942 but was accelerated to April 1942. At the time of my graduation, I presumed I would be

indoctrinated in to the Air Force because I was graduating into a war as an Officer in the cadet corps and due to be sworn in as a Second Lieutenant in the Army Air Corps, as it was called in those days. However, I got a notice from NACA at Langley that if I wanted to, I could report for duty with the lab. The notice came on a Wednesday and stated that I was to report on the following Monday. Being that the call was unexpected and the time allowed so short, I thought it was unusual, I called Langley for verification and said, "Can I do this?" They said, "Yes, sure." I said, "But I'm supposed to be an officer in the Army Air Corps." They said, "We have priority." When I told that to the ROTC Colonel, he said, "If you report to Langley Field, I'll have you arrested." He further said, "You belong to the Air Corps. You spent four years in ROTC. We are swearing you in Saturday." So I called Langley to reconfirm their offer. I said, "Can you put it in writing? Colonel said he is going to arrest me if I report to Langley Field." They said, "Well, we have priority. But it is your choice." And they sent me a telegram saying to report to Langley the following Monday. With great trepidation, I got into my model A Ford and drove for two days to get to Langley Field, Virginia.
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I reported to an administrative officer by the name of Elton Miller.
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After a cursory interview, he assigned me to the full scale tunnel. I said to him, "But, I have a pilot's license and I am interested in the flight aspects of engineering." So he changed the assignment and said, "Okay, I'll put you I the Flight Section," as it was called in those days. And so, I was assigned to the Flight Section as an engineer--not as a pilot. The rating was as a P-1 Aeronautical Engineer paying $2000 a year, with an automatic $18.75 deduction every other paycheck for a $25 war bond and fifty cents for income tax. I kept these bonds for their full life of paying interest and the amount I received was very significant. For six months I worked reading manometer film. The data that the pilots had collected on their test flight runs would be registered on film in a manometer. The engineers and the "computers" would read the deflections caused by sensors through a microscope. The computers were ladies who had a college degree in math and assisted the engineer in charge of the project in reading and working up the data. When I'd been doing that for about six months, I heard that a couple of the pilots had left for one reason or another. In those days all the pilots at Langley were civilians. However, some of them had been in the military or had military training before coming to Langley as pilots. Herbert H. Hoover had flown bombers in the Army Air Corps in the 1930s and Melvin N. Gough, who was the chief test pilot at that time, had gotten his training in the Naval Reserve. I approached Mel Gough and asked him, "Is there a possibility that I could fly with the Flight Section?" as it was called. I told him of my credentials, and much to my delight and amazement, he accepted me as a pilot, and I was assigned to the Pilots Office. It was as simple as that in those days. Today you would have to have a doctorate in physics and be an Air Force

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Academy graduate. But the war was on, they needed pilots, and I was available with an aeronautical engineering degree and couple of hundred hours of flying time.

J

OHNSON

: Where had you learned to fly?

CAVALLO:

The Civilian Pilot Training Program, which I mentioned before, was held at

Teterboro Airfield in New Jersey in 1940 and 1941. After school and on Saturdays or Sundays and whenever I could, I would get into my Model A Ford and commute to New Jersey. The George Washington Bridge was fifty cents each way and the ferry was a quarter. The flight program was divided into two parts, called the Primary and Secondary Course. In the Primary Course instructions were given in a sixty-five horsepower two-seat Aeronca Champ. All the flight training and tests leading up to a final check-out and a private pilot's license were given. Generally that would take about six months, after which one was eligible for and could take the Secondary Course. The Secondary Course consisted mainly of acrobatics and was flown using Waco UPF-7 airplanes. They were open cockpit, fabric covered biplanes, with a 450 horsepower engine. They were very similar in appearance and performance to a World War I fighter. The instructor sat in the front and the student in the seat behind him and all signals were given by hand. The methods seem crude by today's standards but it was all hands-on flying with an extensive program of aerobatics. We did maneuvers that they don't teach, and can't do in today's, aircraft. There was no avionics and no electronics in this airplane. It was all basic flying and but we all learned to fly pretty well. By the time I graduated from NYU, I had the credentials of a pilot's license. Not that I knew what to do with it at that time, but fortunately it fit into the NACA requirements for an

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engineering test pilot. So that's how I got into flying at Langley. Today it seems almost that it was magical. It was wonderful! It was probably the best years of my life, certainly in terms of technical achievement and in satisfaction in what I was doing. However, when I reported for duty in the pilot's office, Herb Hoover had become the chief pilot and had taken over the training of engineers to be pilots. This concept had been created by Mel and turned over to Herb when Mel became Division Chief. Herb was an

excellent pilot, dedicated and courageous. He was patient and very fair with me. But, this was a program that he had inherited. I remember his admonishment to me on the first day that, "I'm not running a flying school." Mel Gough had trained two other engineers and supervised their transition into test pilots. Mel was the designer and prime mover of the program which was based on the premise that it is easier to make a test pilot out of an engineer than it is to make an engineer out of a test pilot. Jack Reeder and Bill Gray, the previous two "converts," and all of us had civilian pilot training, but we had not served in the military and did not have any military flight training. So, with a background of having worked as an engineer in the Flight Section, as well as being shown "tricks of the trade" by Mel and Herb, I was eased into test flying. It went very well and it came very easy. I was able to contribute and make what I felt was significant progress to the point where I was doing the work that was required. The programs at Langely, in those days, were much diversified. We had everything to test, from very simple airplanes such as the XR2K-1 which was a high wing monoplane, to large amphibians such as the PBY-5A as well as the P-80 jet powered fighter. The monoplane allowed us to attach various shaped wing forms and ran through a series of stability and control tests. This airplane could not go over 130 miles an hour which would simulate large scale tunnel

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results but under actual flight conditions. Stick forces at various roll rates were measured by using a unique device. It was a hand-held instrument that fit between the pilots hand and the stick. It had a small dial with numbers indicating the pressure being applied. These

measurements were read by the pilot and copied by hand onto his knee pad. In those days NACA was very busy with designing wing shapes of different cord lengths and a variety of upper surface camber. These flights required the simplest type of flying. However, I can remember flying in the open cockpit of the XR2K-1 in the winter time. I would put on all the winter flying clothes I could, including a face mask. However, I could not keep flying for more than twenty to thirty minutes on those cold winter days. Our biggest range of types of airplanes was in the fighters. For test purpose, the Air Corps sent us the Brewster XSBA Buffalo, Curtiss P-36, the Bell P-39, Curtiss P-40, Curtiss P42 (P-40 with a radial engine), Republic P-47D and N models, North American P-51A, B, D, and H, Bell P-59 (swept wings), Bell P-63, and the P-80. The Air Corps also sent us the Boeing B17, Consolidated B-24, Douglas C-47, Boeing B-29, Douglas R4D, and the YR4B Sikorsky helicopter. The Navy sent us, and we tested, the North American SNJ, Consolidated PBY Amphibian, Grumman F6F, Curtiss SB2C, the Grumman JRF Amphibian, Curtis SC-1, and Douglas SBD. There was also a large selection of civilian aircraft, which we flew, including airplanes from Lockheed, Fairchild, Piper, Beech and Culver. These are not all the planes that came through our flight section while I was at Langley but they are the ones that I got from referring to my log book. Most of our work on these planes was in determining and then improving the stability and control of the handling qualities of these planes. We had a brilliant engineer in Robert R. Gilruth and we had a marvelous engineering test pilot in Melvin N. Gough. Together they

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created the bible of stability and control. The handling qualities of all future airplanes would be based on the parameters they outlined. Up to that time a pilot would fly an airplane, and the attitude was, "Well, if you go back and fly it the second time, it must be a good airplane." Or the pilot would be asked, "What is it that you like about the plane?" And those early-time pioneer pilots would try to describe what it was they liked about the airplane. Whether the stick forces seemed too heavy or if the plane didn't roll fast enough, etc. It was all kind of subjective stuff based on pilots' opinions. Then Mel and Bob decided, "Let's quantify this. Let's put some numbers to these opinions." What is it that a pilot likes in a fighter as well as in all other categories of planes? What does the pilot want to feel? What response is he looking for? How much G [gravitational] force does he want to pull? How much can he handle in a roll? When does he get uncomfortable or reach his limit of physical response. Is any of this different in a fighter or a bomber? Does he expect the same stick forces and rudder forces in a fighter as he does in a bomber? So all of that became a matter of negotiation, and between the two of them, the pilot and the engineer, they quantified the parameters. They wrote what I call a bible of stability and control and described what ideal handling qualities are in any type of aircraft. It was no longer up to the designer and manufacturer to produce and present a product that was satisfactory to their designers and test pilots. It was a mandate to meet the requirements outlined by NACA. In those cases where the plane did not meet the parameters outlined, the Lab would take on the problem and correct it. For example, we increased the roll rate of the P-51 by installing cusped ailerons. As time went on, very exotic testing and measuring equipment began to be developed. From a crude handheld pressure-measuring device, to where all the instrumentation was installed in the wings

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or fuselage. These were activated by the pilot at the start of each test run. The basic recording device was a manometer which put trails and blips of light onto a wide film. These light deflections were activated by sensors installed anywhere on the plane where measurements were required. Some could measure deflection, some could measure force, and others could measure angles. The film was developed and the deflections were read through a microscope by the engineers and computers. A lot of flight test work was required and accomplished at Langley in the war years. The airplanes varied from Cubs to B-29s and included helicopters and multiengine amphibians. All of these planes came to us with a flight problem that needed fixing. We also had the responsibility of transporting people who needed to go to our office in Washington D.C., which was located at DuPont Circle in those days. We also had a rocket testing facility at Wallops Island, Virginia that required transportation service. To get to

Wallops, we needed to fly a Grumman Goose Amphibian into a creek. The creek was a body of water about 50 meters wide and 2500 meters long which ran parallel to the ocean and was about 150 meters from it. The sand strip between was where the testing facility was located. I was checked out to fly into the creek and it became pretty much my specialty. I got very proficient at landing and taking off into that small area, in all kinds of wind and current conditions. At first we would "make buoy." This involved taxiing up to and hooking on to a buoy anchored in the creek. Someone from the land base crew would come out in a boat to meet us. The plane could carry the two-man crew, eight people and a considerable amount of baggage. The seaman would then "scull" a flat-bottom, rectangular boat from shore. The boat had a cut-out in the center backboard into which an oar was place and "fanned" back and forth, like a fishtail. The boatman would stand up and face forward while everyone else sat down. It

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was easier for these men to scull than it was to row and I've seen them do it in all kinds of wind, wave and current conditions. Later on, a metal ramp was installed on the shore and I was able to put the gear down and taxi up onto shore to discharge personnel and equipment. Most of the people and equipment were concerned with rocket research. But the rocket launching that I viewed was for the most part very disappointing. The rockets would go up these long seaward pointing ramps and often end up in the ocean. I saw some that never got out of view. And this was the time the Germans had their V-1s and V-2s hitting London. It was a sad commentary on our viability in rocketry. America was fortunate to be out of range of enemy weapons. There was a big Quonset hut on the island where everyone would have lunch. It had big sign over the front door with the name "Club 75." The cook had learned his trade in the army and the main course was always roast beef with potatoes and vegetables. The cook fascinated me as he could make the best gravy for the roast beef out of vanilla extract, mustard, ketchup, onions, flour and other condiments. It had the color and taste of the real thing. There might have been other things on the menu but I don't recall what they were. It cost 75 cents to have lunch and hence the Club 75 on the sign over the entrance. To me, 75 cents was a lot of money for lunch, so I generally brown-bagged my lunch, as many others did. We got a check twice a month and they would take out a mandatory $18.75 for a war bond and 50 cents for income tax. I had a wife and child by 1944, so of course we operated on a limited diet and a budget. There was enough for civilians to eat of course, but the selection in the food store was limited, especially with meat. As I said, we operated a large variety of military aircraft. The largest was the B-29, which I flew as a co-pilot with Bill Gray at Pilot-in-Command. We flew long missions,

generally over Wallops Island where would drop various bomb-shaped vehicles to test their drag

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and velocity. We often brought the B-29 back with one engine feathered as the Curtiss Wright #3350s had a reputation for overheating and failing. However, we were lightly loaded and close to home. I used to wonder what the air force did in the Pacific on those long over water flights with a full load of fuel and bombs. Most of my flight test work was in fighters and addressing whatever problems that they were having. However, in one area, I flew the P-51 when it was being used as a test bed for scale model testing of current and future airplane designs. In this program we had modified a P-51 by adding a "cuff" around the main wing. This was actually an airfoil overlay which had been carefully polished and buffed to almost mirror smoothness. Under this part of the wing and in the gun camera compartment, a miniature wind tunnel balancing device was installed with a measuring rod sticking up and protruding through the cuff. On this rod was attached a very accurately made one-half shape of a plane under study. The X-1 and many futuristic planes were tested that way. The rod would rotate the model through various angles of attack and readings would be taken on the lift, drag, angle of attack and pitching moments and transmitted, through the rod, to the mechanism in the wing. This data was collected by the manometers in the wing and traced by light deflections on the film. The technique involved was to take the P-5l to about 32,000 feet, level off to get stabilized and turn on the instruments. This would start the model on the wing, turning through various angles of attack. The P-51 would be pushed over into a dive of about 45 degrees which would continue to accelerate to Mach No. 0.73. At about 10,000 feet, a recovery or pull-out was started. This generally would produce anywhere from 2 ­ 4 Gs. The idea was to dive through as smooth air as possible. Flying through rough or gusty air would superimpose extraneous forces and conditions upon the flight data being collected. This would make the work-up and analyzing

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of the data very difficult. The engineers and the computers were pretty skilled and no matter what you gave them, they could correct for any "pollution" and sort it out. However as the expression goes, "garbage in is garbage out." And I had been on their side of the program when I was the one reading the data, so I was very sensitive to the problem of the film readers. On the climb up to altitude, I would look for areas of clear air. And in the dive, if I encountered rough air, I would go back and repeat the dive, as long as I had film left. This conscientiousness was one of the results of a pre-flight training period in the engineering office. I would start my pull-out at about 10,000 feet. The idea was to be out of the dive by 5000 feet. In the course of pulling out from the dive, a G force of between three to four Gs was experienced. If the dive continued past 10,000 or a patch of rough air was encountered in the pullout, the G forces could go as high as 4 to 6 Gs. At this point the pilot would black-out for a period of time as the plane came around to level flight. We did not have G suits in those days for these flights. There was one case where one of our other pilots did run into a condition which required a 6 G pull out. He blacked out and came to climbing back through 10,000 feet. In a pullout, the pilot was in an area of significant risk in these dives. We were always dealing with the negative effects that compressibility could cause. This was the tendency of the plane, once in a dive, to increase its dive angle and speed. If the speed built up was allowed to continue it could lead to destruction. Fortunately the only casualty I suffered from these pull-outs was from hemorrhoids. At the thickest part of the wing, where the model was mounted, the highest velocity of air flow occurred. If the airplane in the dive was at Mach .73, the airflow over the wing where the model was located was at Mach 1.2. In essence this provided data through the speed of sound at

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a time when the high speed tunnels could not provide it. The models of all of the oncoming fighters and the X-1 were tested that way. When the airflow over the wing exceeds the speed of sound, a shock wave occurs. At the same time a shock wave occurs on the wing, where the velocity of the air exceeded Mach 1 or the speed of sound, a shock wave also occurs on the horizontal tail at the hinge line between the stabilizer and elevator. This shock wave weakens the effectiveness of the elevator, which is operating behind the shock wave and is blanketed by it. The wing has a natural pitching moment, or tendency to dive, with an increase in speed. This would require additional upelevator or an increasing pull force to trim for a steady dive. Eventually the pilot would reach a physical limit to his ability to hold this pull force. Either a pullout had to be started before this point or the plane would continue into a catastrophic dive. Many P-47 and P-38 pilots in combat would get into a diving condition and reach their physical limit to recover. These two airplanes were noted for this catastrophic tendency. Because we were doing these dives on a daily basis, we were aware of this problem, called the "compressibility effect." Use of the trim tab to reduce the pull force as the speed increased would have to be done judiciously. The pilot would be pulling increasing forces as the speed of the dive increased. The elevator was losing its

effectiveness. The pilot would try to compensate by pulling to get more up-elevator. He'd crank in trim tab to help him with the pull force. At some point he would decide he had reached the limit of his ability to handle the pull forces and would start his recovery. The airplane would

slow down and start to recover. As the air over the tail surface went subsonic and the shock wave disappeared on the hinge line, the elevator suddenly became effective again. The elevator forces, helped by the up-trim tab, suddenly became light. The pilot who had been pulling to his

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limit now finds himself with the stick "in-his-lap." G forces on the wings.

This condition will provide excessive

A memorable P-51 flight occurred when we did studies on the effect of gust loads at high Mach numbers. As least that was the understanding I had as the bases for the study. I had also heard that there was an interest in this project because we were losing P-51s who were escorting the B-17s on their way back from Germany. The pilots and planes were lost over enemy territory and consequently there was no empirical data on the cause of these losses. Typically, these losses were occurring when the group would be flying through cumulonimbus clouds, in the evening, when the clouds couldn't be seen or avoided. The B-17s would transit these summer storm clouds and experience high buffeting, often accompanied by a significant change in altitude. The P-51s seemed to fare less favorable. Often one would be seen spinning out the bottom of the clouds with no attempt of recovery. It was assumed that the wings were failing. So we started a study on the effect of high gust loads on the P-51. I did a series of tests on one of the P-51s. By using very abrupt pull-ups at the normal cruise speed, I was able to get a reading of plus 12 and minus 4 Gs. These loads certainly exceeded the design parameters of the wings but these were loads achieved in rough air and were very short duration. These were called "gust loads." However, in one of the tests I tried to pull out abruptly while I was flying in rough air and I wrinkled the wings on one plane, but the wings did not fail. Hence, these tests did not produce a definitive answer as to why we were losing the P-51s in rough air. In an accelerated or sudden pull-up in the P-51, the pilot would find it difficult to reach a G force sufficient to lose the wings. In a sudden pull-up, at any speed, the wing pitches up and the Gs build to a limiting condition. As the angle of attack and the G forces build up in this pilot induced pull-up, the wings would stall and the G force would be relieved. At least that was what

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was thought. When I was assigned to do tests on accelerated stalls, I was told that in any pilotinduced sudden pull-up, the plane could not reach a condition where the Gs were excessive. Another pilot had preceded me and had recorded this effect. He did what he considered "abrupt" pull-ups and the wing had stalled at all dive speeds before destructive G forces were encountered. I was given the task of continuing and completing these preliminary tests. On the first flight I pushed out into a fairly high speed dive and after starting the instruments, pulled the stick back as hard and fast as I could. I had been assured that this was okay. The wing was supposed to stall and buffet, but not fail. Apparently, I had pulled the stick back very much faster than the previous pilot and the wing rotated rapidly through the angle and region where it was supposed to stall. It pitched to a high angle of attack, at high speed, and accompanied by heavy buffeting, significantly exceeded its design limits. However, because the loads were of short duration, the skin on the wings became wrinkled, but the wings did not fail. My enthusiastic performance did not find favor in the office. But it did indicate what might happen in combat with a pilot under stress. The Air Corps assigned us two high-time P-5ls, which had been used in a pilot training school. The fuselages had about 3000 hours of flight time on them. Probably the engines had less flight time. However, these planes were accepted for this test because we were going to fly them into high gust-load conditions and the planes would get beaten up more than they had been. Their high time made them unacceptable for combat. It was unusual for Mel and Herbie to accept such high time planes for test work as they had always insisted on first class equipment and maintenance. This was in keeping with the pilots and the mechanics that were all very dedicated and well-trained. We had an enviable safety record. In the five and one-half years I

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was at Langley there were only two bail-outs. Bob Baker left a P-47 and I had to bail out of one of the P-51s. These P-51B model that we got for this summer storm testing were unique. They had the "Messerschmitt" canopy. This canopy is flat on the top and follows the line of the upper fuselage. It had a very streamlined appearance. All subsequent P-5ls had a bubble canopy. The visibility was better, but the trade off was that it lost some of its top speed, and it was harder to bail out of because you were seated lower in it. So, on one hot July day when there were plenty of billowing summer clouds around, Bob Baker and I went out in these two fighters. The concept of the test was to have one plane fly through the storm cloud at 18,000 feet and 185 mph. A second plane would stay outside of the test area and conditions and fly at the same altitude and airspeed. Both pilots would take records simultaneously. This would produce ambient air and actual rough air records to compare. This flight would simulate the conditions that the B-17 and P-5l group encountered on their return from Germany. Because I was in the lead, I found a suitable cloud and flew into it. I

experienced instant and considerable roughness. The accelerometer on the instrument panel hit the limits of