TAPE 1, SIDE 1
MR. COLLINS: I think, sir, just to set the framework for the discussion, we wanted to follow up from last time on some of your aviation work at Langley and perhaps a little later at Wallops, and to start this off we're going to let Howard (Wolko) introduce some of the questions.
MR. WOLKO: The period that I'm really interested in is when you started at Langley in 1937, with the Flight Test Group, under Tommy, Floyd Thompson.
DR. GILRUTH: Yes it was under Floyd Thompson.
WOLKO: Right, and of course I didn't know Floyd back in those days. I did a little bit later on. Who were the other people who were in that group, when you first joined it?
GILRUTH: All right. There were two sections. They called them sections then. One was Flight Research Maneuvers, and Tommy Thompson was head of that group, and that's the one I was assigned to. In the same building there was one called Flight Research Loads, and Dick Rhode was head of that group. They were concerned with the loads that airplanes experienced, and they tried to do research on how to predict them better. They were located upstairs, we were in the downstairs. Both the upstairs and downstairs were adjacent to a hangar where the airplanes we used for our research were housed, worked on and instrumented. Over the two sections was a man named John W. Crowley, who later became a deputy administrator in Washington, about the time that Sputnik happened.
COLLINS: A deputy administrator with NASA?
GILRUTH: Well, it was NACA in those days. He never made the transition to NASA.
Okay, now -- that's the setting, and we did the same kinds of things all the other people did there at Langley. That is, we did research in our field, and most of the branches and sections had to do with wind tunnels. There was one with a towing basin under Star Trusket, and there was an engine lab under Carlton Kemper where research was done on aircraft engines, which later went to Cleveland and became a laboratory all to itself forengine research.
WOLKO: Which side of Langley, there's Langley East and Langley West?
GILRUTH: Well, at this time, when I first came there, it was all in the East area, and it wasn't until the rapid expansion occurred, during wartime, that it spread out to the west area as well as the east area. Located at the east area was a Flight Research hangar, the Atmospheric Wind Tunnel, the Variable Density Wind Tunnel and the Full Scale Wind Tunnel, and there was also a vertical tunnel that was used for airplane spinning research, called the Spin Tunnel. About the time I came there, they invented a new tunnel called the Free Flight Tunnel, in which they could vary the axis of the tunnel so that the gravity gradient would propel a freely flying model, so you could fly little models in there using clever little devices to move the controls and see how the models would fly and how well they could be controlled. So that, together with flight research maneuvers and flight research loads, made the research facilities of the NACA.
WOLKO: The instrumentation for flight tests was this part of the flight test groups or was this a separate section?
GILRUTH: This was a part of the Instrument Research Group. They were their own boss but they worked for wind tunnels and for the flight research people.
WOLKO: And you people worked in a cooperative effort, like putting something on that would measure stick loads?
GILRUTH: That's right, if we had to have something to measure stick forces, they built it. We told them how we thought it should be done, and then they built it the way they wanted to, and it had better work!
WOLKO: I can remember talking with Dick Rhode on this. Dick used to occupy the office just down the hallway from me. I remember talking with Dick on this loads work that he had done there -- very, very interesting.
GILRUTH: Yes. He was there when I came, as was Floyd Thompson, and I knew them both very well. Fine men.
WOLKO: Was Donlan there? Donlan wasn't with the Flight Research, was he? Charlie Donlan?
GILRUTH: No, he was never with the Flight Research. He was with the wind tunnel group.
WOLKO: Well, when you first went with Langley, it was thepre-war years. We were starting the buildup toward the military aircraft. Did you notice a significant amount of difference between the way testing was carried on in '37 as opposed to the way it was conducted after the war started? Was there a change in the emphasis of the testing? In '37 you were still basically doing research. From 1940 on, it was mostly to put fixes on the aircraft, is the way I've always understood it.
GILRUTH: Well, that's true in some of the wind tunnels. The Full Scale Tunnel spent a good deal of its time doing drag cleanup work. That is, they'd take an actual fighter off of the production line, and mount it in the tunnel and try all the various things they knew of to try, fairings and so on, to see if that would improve the drag characteristics of the airplane. That was very popular with the defense services because it made the airplanes go faster. It was popular with everyone because it was an effective way to improve performance.
So every new airplane, not every one of a kind but every new type would go through the Full Scale Tunnel drag cleanup, and that was a good sized part of their work for a while.
WOLKO: After they went through the drag cleanup test in the tunnel, were these aircraft then turned over to people in the Flight Test Group?
GILRUTH: No, that wasn't necessary.
WOLKO: They didn't actually get to fly those airplanes.
GILRUTH: Well, we'd get them for other reasons, but not in connection with the drag cleanup. If there wasn't something else that needed work, we would not get it.
WOLKO: There were problems with many of those military aircraft.
GILRUTH: Well, we had many military airplanes that we worked on. Mostly it was control problems. Stability and control. The P-47 was one of them we worked on.
WOLKO: The P-38 had problems. The stick freezing problem.
GILRUTH: Yes, it did. We had all those airplanes for various reasons and put dive recovery flaps on them and fixed the ailerons and put spring tabs on them if they wouldn't roll at high speeds, and so on and so forth.
WOLKO: Were any foreign aircraft, such as British aircraft, available to you?
GILRUTH: Yes, we had a Hurricane and a Spitfire, and a Jap Zero, but didn't have any German airplanes. I don't know why but we didn't. We never could get our hands on a German airplane for some reason.
WOLKO: The Japanese aircraft, I wouldn't be a bit surprised if that's the one we have in our collection, because it was an aircraft that was captured and flown by our pilots enough to become familiar with the handling and characteristics of the Zero.
GILRUTH: Right.
LINDA EZELL: Could you go into more detail about the kinds of things that were done with these aircraft?
WOLKO: This is what I'd like to find out, is specifically what the test procedures were, not the drag clean up so much, but the flight test procedures.
GILRUTH: Right. Yes. Flight tests.
WOLKO: You people would instrument these machines?
GILRUTH: Yes.
WOLKO: You had test pilots assigned to your group.
GILRUTH: Right.
WOLKO: Or did you people actually do your own flying?
GILRUTH: Well, no, we had a test pilot group. The procedure was, I, as a member of Flight Research Maneuvers, being a project engineer, would write a flight request, which would say what instruments I wanted, where the center of gravity should be, what the gross weight should be. Then in a general way what maneuvers, what did I want the pilots to do -- go up and make 6 G, 8 G pullouts -- would be what you might say, if you really wanted to see if there was anything wrong with the way it responded. You might want to start with 2 G and 4 G, before you went to 6 G. I certainly would. So you'd make a flight request, you'd post it up there, and the chief test pilot would decide who would do it. Then the people would put the right instruments in. The project engineer would make sure that everything was the way it ought to be, and the test pilot knew why you wanted it and how he was supposed to do it. It was up to you to make it come out right. The mechanics would see that the airplane was serviceable and so on. We had scales and all the things we needed to determine center of gravities and gross weights and so on, and if there was a problem with the structure, why, we had a certain limited amount of ability to repair the airplanes.
So that was the procedure. We had some very good test pilots. One of them that I worked with the most was named Mel Gough. He particularly didn't like to make flight tests for people who, he felt, just really didn't understand what they were doing. Especially to go and make -- some people would say, "Make 9 G pullouts right off the bat." He didn't like that, because he felt that you should explore the airplane first. I learned a lot from Mel Gough. I flew a lot with him in airplanes that you could get two people in. So I learned a lot of the test pilot lingo, and I learned quite a lot about flying from him. I wrote a lot of reports with him, and so, I felt I was very lucky to have him as a person to teach me, and he learned a lot from me because I could tell him why some of these things were happening.
COLLINS: When a plane came to you, did you have a standard procedure that you put every plane through, or did the plane come to you and there would be certain characteristics about the stability and control that you knew you had to deal with beforehand? How did that work?
GILRUTH: We would get the airplane. We would request from the Air Force or Army Air Corps, depending on the time in history, or from the Navy or from some company perhaps that had built an airplane, we would request the airplane for certain kinds of things, certain kinds of tests. And when we got it, why, we would load it properly and put the instruments in and make those tests. If it was a Navy airplane, unless they had requested something be done, we would of course give them a report of what we did and what we learned -- as a matter of courtesy -- but that was it. They would just loan us the airplane to do what we wanted to do with it, if they were able to spare it.
WOLKO: And when you finished testing the airplane it was returned to service?
GILRUTH: It was returned to service, that's correct. And we had all kinds of airplanes. We tested almost all the mainstay airplanes during the war.
WOLKO: Those were punishing years that you people put in down there during the war.
GILRUTH: We tested a lot of those airplanes, and it's quite interesting, because it's only those airplanes that anybody really knows anything about, how they flew. But we do know how they flew. We don't know how a lot of others flew.
WOLKO: These were recorded in the wartime reports.
GILRUTH: That's right. That's right.
WOLKO: Did telemetry play a major part in your testing in the early days?
GILRUTH: No, it didn't.
WOLKO: It certainly did after you got to Wallops. Somewhere along the line this whole field of telemetry opened up and started to change the complexion of flight testing.
GILRUTH: Well, it never affected the flight testing of manned airplanes during my stay there. I know later on, you could put a zillion different instruments in.
WOLKO: Now they do it with real time monitoring on the ground.
GILRUTH: Sure.
WOLKO: That was not available then.
GILRUTH: No.
WOLKO: Because computers just weren't available.
GILRUTH: No, and neither was telemetry. The first telemetry I ever saw was in these streamlined bodies that we dropped from high altitudes to see what happened going through the speed of sound.
WOLKO: Speaking of speed of sound, when you started to run these tests, dropping these special shapes, you dropped them from high altitudes and they would exceed the speed of sound on the way down. Was that at the specific request of industry or was that just a research project? We knew we were coming up on the speed of sound as the next step in aircraft development, but it's always been my impression that industry was particularly sold on building a supersonic aircraft until midway through the war. Is that a correct assumption?
GILRUTH: Well, they didn't know how. The first streamlined body through the speed of sound was dreamed up during a meeting of the Aerodynamics Committee, one of the standard NACA committees of which I was a member. We had the director of Farnborough from England as a guest at this time, and we were all talking about how we really ought to find out what the heck happened, because von Karman would tell you what happened above and we all knew what it was below the speed of sound, but nobody had an idea what happened going through it. If it weren't for the fact that bullets went right through all the time, we'd probably say it was impossible. So we said, why don't we do something about it? Why don't we take something up, put a telemeter in it with an accelerometer and see what happens to the drag?
Bill Farren, the director of the Royal aircraft establishment, was going to do it in England, too. They were going to make an experiment like that. But they never did. I think they tried but it never materialized while it was still a pertinent thing. We started then and in a few years we had all kinds of data through the speed of sound, and we weren't looking for anything that the British might have come up with. The British did something like I was doing at Wallops Island. They went for the rockets rather than dropping things. In any case, that's how this thing got started, on the Aerodynamics Committee, and we got it done in a hurry. In a few months we had borrowed a B-29 and crew from the Air Force and had dropped our first test model through the speed of sound. This was still during the war. It was probably '43, '44.
WOLKO: The drop testing with the models at Wallops, did that precede your work that you did with the P-51?
GILRUTH: You're not talking about the wingflow?
WOLKO: I'm talking about the little vertical sting that went up over the top of the wing.
GILRUTH: That was almost concurrent. I was getting data from my wingflow, on the P-51, about the time we were getting the data from the falling bodies.
WOLKO: That little vertical sting is in our collection.
GILRUTH: Oh, is that right.
WOLKO: I wanted to bring it in and put it on display downstairs in our flight testing area.
GILRUTH: Well, there was a lot of that kind of work done in both this country and England.
WOLKO: How well received was that work? You used very small models.
GILRUTH: That's right.
WOLKO: That caused people to criticize.
GILRUTH: Well, of course, you know, the wind tunnels were aghast. They were smarting, very much, because here was somebody with ten cents worth of instruments (not really--but it was really small compared with the millions of dollars that those wind tunnels cost). And everything that you could find that you could compare was not in conflict with the data that I got. The wing-flow tests showed conclusively that a thick wing like you had on the P-47 lost its lift curve slope when you got above a Mach number of about .7 or .8, which caused it to have this so-called stick freezing characteristic. The stick didn't actually freeze; you could still move it the usual amount, but when the wing lost its lift curve slope, it wouldn't do anything for the airplane. It kept going straight down, till it got to the lower altitudes where the drag was great enough to slow it down to a Mach number where the lift effectiveness was restored. Then you could pull it out -- if you could wait that long. It was tough on the pilots the first time it came. They didn't know it was going to stop. To this day I still meet people who flew the P-47 who say, "My God, I never knew why that was."
WOLKO: I remember Doug Michele talking about flying the 38 and being unable to pull it out.
GILRUTH: That's right, it had a similar kind of wing.
WOLKO: And he dropped a rocket say from something like 30,000 feet down to 5000 feet, before he was able to get out of it. They made some modifications to the 38, they put that little dive --
GILRUTH: --they put that little dive recovery flap on it. It also worked on the P-47. It was about the time the war was over, and with that airplane, and the jets were coming in, so the P-47 had a rather short life.
EZELL: As a result of the NACA tests, were dive recovery flaps recommended?
GILRUTH: Right, that was a fix so that you could pull it out of a dive.
WOLKO: But that was done in the Flight Test Group, not the Wind Tunnel Groups, is that right?
GILRUTH: Well, they didn't have a wind tunnel that would go that fast. In those days. See, they were out of business. You can imagine how they felt, sitting there with these big wind tunnels, and some kid puts a little model on top of a wing of an airplane and starts turning out data. Of course, the Reynolds number was very low. But I'm telling you, the power of the Mach number was much more powerful than the power of Reynolds, and the results were very true to full scale. Of course, you didn't know that unless you had some full scale to go with it. But anyway, that's a whole story in itself, and it didn't last very long. It didn't last very long because we found from falling bodies and from wing flow, and then we got better wind tunnels in a few years.
WOLKO: That was not until John Stack and Ray Wright came up with the slotted throat tunnels, but that was after the Bell X-1 actually flew.
GILRUTH: That's right. At Wallops Island we flew a whole model of the X-1, flew it right through the speed of sound.
WOLKO: You flew it through the speed of sound?
GILRUTH: Right, with the pulse control, so we could see what it did.
WOLKO: This was a drop test of it?
GILRUTH: No, it had a rocket in it. It was much easier to do it with rockets, once we got the techniques developed.
EZELL: How big a model?
GILRUTH: Oh, about four or five feet long, like a wind tunnel model, only it had to be designed and built to fly over the speed range you were testing. The center of gravity had to be in the correct place and you would control the elevators to go up and down the proper amount to produce the left responses of the flight range. You would boost the model up to a Mach number of maybe 2, and then it would gradually slow down, and as it slowed down the elevators would move up and down to make pull ups and push downs and you'd record the response as it went back through the speed range.
WOLKO: All of those recordings had to be telemetry.
GILRUTH: Oh, of course. Without the rocket and without the telemetry you couldn't do this. But it all grew out of starting with simple models and finally we'd get to these pulse models. We did this with the X-1, the X-2 and with many of the new fighter designs of the Air Force and Navy.
COLLINS: How were these results fed back into supersonic flight research?
GILRUTH: They were all fed back with reports that went to the industry.
WOLKO: Were you in on any of the discussions with Ezra Cotcher when he was down there?
GILRUTH: Yes, the original ones, yes, I was still in flight research, and Cotcher came in, and he said I can get, I forget how many million dollars, and "I want to build something that goes past the speed of sound even if it's 1.001."
WOLKO: A .9999 airplane?
GILRUTH: Cotcher said "It's got to be over the speed of sound." I'll tell you, we perked up our ears, because he could get the money, and we could design the airplane to be built. Then we got into all kinds of fights with the wind tunnel people, because they wanted to put a thick wing on it because then you'd get lots of transonic flow. This was about the time that I was getting my wingflow data which showed that a thick wing would not permit flight through the speed of sound! I showed my boss, Tommy Thompson. It was awkward because Dr. Lewis, who was the head man in Washington, had made the wing flow data top secret. Anyway, I had showed Tommy my data and I had convinced him that we should not put that thick wing on because you'd never do what Ezra Cotcher wanted to do, you'd never get supersonic. And he went for a 7 percent wing. We really wanted a 5 percent wing, that was the neatest wing, but 7 percent wasn't all that bad. It didn't lose its life, it just had a certain amount of buffeting and so on but it still would respond. It still generated lift if you would increase the angle of attack, so that was the compromise, I think it was around a 7 percent wing, and so that was the reason, really, we were able to go above the speed of sound. If we had put the wing that the boys, Russ Robinson and Harvey Allen and those people wanted to put on, we would have waited a while before we got the first airplane to go supersonic. That was really a good effort, that research effort.
WOLKO: There's always been a bit of controversy about the rocket engine that Cotcher kept proposing and it's my understanding that somewhere along the line Langley opposed it?
GILRUTH: Not to my knowledge.
COLLINS: What time period are we talking about?
GILRUTH: Well, we didn't go supersonic in a flight until after the war was over.
WOLKO: It was '47 when we went supersonic.
GILRUTH: '47, but this was back around '45.
MRS. GILRUTH: May of '45.
GILRUTH: Okay.
EZELL: Ezra Cotcher was what?
GILRUTH: He was a major.
WOLKO: He was a major at Wright Field
GILRUTH: Yes.
WOLKO: He was then with, was it AFIT? The Air Force Technology Institute or something of that type? He worked closely with von Karman, and somewhere around 1945 Cotcher wrote a report for Hap Arnold in which he proposed the so-called Mach .999 airplane, which was a tongue in cheek way of saying supersonic, and HapArnold became interested in it.
GILRUTH: Yes.
WOLKO: And because of that I guess it was always planned that the Air Force would be the one to come up with the primary amounts of money for funding.
GILRUTH: Yes, and they would furnish the pilot.
WOLKO: They would furnish the pilot.
GILRUTH: We had a pilot who would just have given anything to fly it, Herbie Hoover.
WOLKO: He eventually did.
GILRUTH: He flew the second flight, yes. But he wasn't allowed to fly the first one, of course, because the Air Force said it's got to be an Air Force man.
WOLKO: Getting into what leads to the X-1, about that same time frame, they also started the Douglas D-558.
GILRUTH: That was a Navy one.
WOLKO: That was a Navy version.
GILRUTH: They wanted to get in on it and that was just a jet. It did not have a rocket.
WOLKO: That was the D-558-1.
GILRUTH: Yes.
WOLKO: It did a great deal of work that was subsonic but it never did go supersonic.
GILRUTH: That's right. It couldn't.
WOLKO: The D-558-2 did go supersonic.
GILRUTH: Did it?
WOLKO: Yes, as a matter of fact it hit Mach 2.
GILRUTH: Oh!
WOLKO: I don't know what kind of a rocket it had. It was flown by Scott Crossfield. It had a wing sweep, and it was the first one that I know of that wasn't an X series but it was the first of those high speed rocket aircraft that had a swept wing.
GILRUTH: I think that was quite a bit later, and it lost its actuality, really. Any airplane that went that fast was interesting, but it was really very late in the business to my recollection.
WOLKO: So the primary interest at Langley was in the X-1.
GILRUTH: Oh yes. Then there was this airplane that went very fast, and it was flying about the time we were flying the first spacecraft. What was that? It was made of inconel.
WOLKO: Oh yes, it was the X-15.
GILRUTH: X-15, that's right, and that one, you'd go as high as you could and then dive it, with a rocket, too. That's the one that Scott Crossfield flew a lot.
WOLKO: Crossfield was assigned down to the Test Group, wasn't he?
GILRUTH: Yes, he was assigned. When I first met him, a government pilot, and then he went with North American and flew a lot of things from that position. I forget how all the times and so on and so forth, but he was both, initially he was a government --
WOLKO: Initially he'd been a NACA pilot.
GILRUTH: Yes, that's right.
WOLKO: He was a Navy pilot during the war.
GILRUTH: That's right..
WOLKO: It was shortly after the war, I guess, that he joined the NACA.
GILRUTH: That's right, and he was a heck of a smart, nice guy. Then, as he got older and more wary, he was a little harder to deal with.
WOLKO: Now he's virtually impossible.
COLLINS: Just to back up a minute, what was your contribution and Langley's contribution to aeronautical design, to begin to build craft to go into the supersonic region?
GILRUTH: My contribution?
COLLINS: And Langley's. Was there another research center that was working on the same sorts of problems?
GILRUTH: Well, let's see, we didn't have an Ames Laboratory then--did we?
WOLKO: Ames gets started during the war.
GILRUTH: During the war, but it really --
WOLKO: Ames starts during the war. Lewis starts during the war.
GILRUTH: Yes. Ames built a lot of great big wind tunnels. It built a huge full scale wind tunnel, and there were some other wind tunnels, and one or two hypersonic wind tunnels. Al Eggers' was a hypersonic type. But there was very little transonic stuff at Ames, and of course, Lewis didn't have any.
WOLKO: Lewis was the engine --
GILRUTH: That's right. They still had wind tunnels. Abe Silverstein had to have wind tunnels, you know.
WOLKO: -- Well, the people that started those, Lewis and Ames -- came from Langley.
GILRUTH: They sure did. But actually Langley did most of the transonic work, and most of it came out of flight research for a while, until the slotted tunnel came along. Then we, the flight people sort of quit, because if you had wind tunnels, a wind tunnel that would work, that was the way to go. It still took a very small model to go through Mach 1 in a wind tunnel because of the interference problems. But in any case, it was a very, very interesting period of a few years when you either did it in flight in some way, or you didn't do it.
WOLKO: One question I've wondered about, this little sting that went over the wing of the 51. Did you ever measure the Mach numbers that you actually reached with that?
GILRUTH: Oh sure.
WOLKO: You were able to measure those.
GILRUTH: Sure.
WOLKO: What range, about 1.1 or 1.2?
GILRUTH: It would go absolutely smoothly from 9/10 to about 1.2 and the curve was perfectly continuous. There were no jumps or anything like that. And coming back down it was the same.
WOLKO: The same way, so you could measure both on the way up and also --
GILRUTH: --yes, and I would oscillate the wing. I had a mechanism in there that would move the wing from one side to the other, and you recorded with recording instruments so that you'd get a complete lift curve out of every oscillation of the wing. And so for every Mach number you'd have that whole thing. One good flight would give you the whole story on that. It would do swept back wings. I tested Bob Jones's swept back wing, and showed it was very, very good. I don't know any case where it was very badly wrong.
Surprisingly, I got up one time in a conference and said, "Well, I think maybe, it works even at low Reynolds numbers because the transonic effects are so strong that they impose themselves over everything else," which I think is true. And von Karman, that really upset him. I forget what his objection to it was, but he wasn't helping anybody, you know, he hadn't come up with any answers, all he was trying to do was pull the rug out from under me. And of course, with his background, people would say, "Well, you know, if von Karman doesn't think it will work, it probably is--" But the people who were designing airplanes --
EZELL: Can you remember what the conference was, where you stood up and said this?
GILRUTH: Yes. It was in England. And that's the only time I ever gave a paper on wing flow, and Dr. Lewis had told me I was working too hard and "Why don't you take a little time off? All you have to do is give a paper." On the other hand I'd never been to Europe at that stage and I thought it would be great fun to go, so I said, "I've never done anything with this wing flow, so why don't I just give a paper on that?"
So it was at this session over there, in one of those great halls that they have their conferences in, and von Karman was there along with a lot of other people. The English were very, very interested in this thing, and they did try it, but it was very late in the business to be trying it.
COLLINS: This was just postwar?
GILRUTH: This was a couple of years after the war; it was really the only way that you could get data. This was after the war, '47 I think is when that conference was.
COLLINS: Did you have contacts with von Karman previously to that, carry on correspondence with him or just generally have a forum to discuss --?
GILRUTH: I used to talk with him. He used to come down to Langley and -- but, I was not a theoretical aerodynamicist, and he was way, way over my head in the things he knew in mathematics and so on. He was really something else.
WOLKO: I remember that, too. I remember he was a man who could speak many languages but with a very bad accent.
GILRUTH: He could speak many languages. I think he was a very brilliant man. I don't think he could design an airplane.
WOLKO: I don't think he could either. He tried once when he was at Achen. I looked at the result he turned out and I agree with you, he couldn't design an airplane.
GILRUTH: He was a brilliant man, though.
WOLKO: He knew mathematical physics.
GILRUTH: Oh, you bet.
EZELL: That conference was in September, '47.
GILRUTH: Good for you.
WOLKO: Now we can take up the various drop tests that you ran. You used to drop shapes.
GILRUTH: Yes.
WOLKO: These were like specially shaped bombs?
GILRUTH: Well, they were bodies of revolution, as a fuselage, only they didn't simulate a cockpit. It was just a pure body of revolution, high fuselage ratio, and it was stabilized by a sting with a couple of vanes, and we also measured the drag of the vanes. They were airfoil sections, so that we got a zero-lift drag of the airfoils as well as the zero-lift drag of the fuselage shape, and the speed range was about from 0.9 to 1.2. There was quite a variation in Reynolds number, although much less than you would have with a full sized airplane.
WOLKO: But again your transonic effects are going to dominate.
GILRUTH: Right, they dominated.
TAPE 1, SIDE 2
GILRUTH: We didn't do many of those streamlined dropped bodies, I think three or four was the limit. By the time we'd done those, we thought we knew in general what happened to drag of bodies and wings. We didn't know what happened at lift conditions and it fell on the Wallops Island guys really. We were anxious to find out how wings, control surfaces, and airplane configurations behaved in free flight as a measure of how well wind tunnels were working out as a research and development tool.
We developed all kinds of such techniques. For example, we investigated aileron effectiveness with a very simple technique at Wallops Island. We would take a streamlined body containing a solid rocket to propel it, and we'd put a wing on this streamlined body with deflected ailerons set, at say, 5 degrees. A spin-sonde in the nose of the body would send out a polarized signal to the ground where we would have a receiver record that polarized signal, so that you could measure the rate of roll produced at the various Mach numbers traversed. You would fire this rocket nearly vertically into the sky, and the rocket would take it to a Mach number 2, and then the rocket would burn out. The test model would coast nearly vertically into the sky as the rate of roll was continuously recorded. Knowing the air speed and the rate of roll, you had a measure of the effectiveness of the ailerons from Mach number of say 2 down to 9/10 or 8/10 of the speed of sound.
We had a number of techniques in flight that filled the gap in control, stability and drag, during the few years that wind tunnels were not able to cover the transonic and supersonic speed ranges.
WOLKO: You couldn't get the transonic tunnel?
GILRUTH: We couldn't. No one knew how to do it. I remember, this was a very popular thing with the industry, because at one of our NACA meetings, Gene Root, who was a first class aerodynamicist and the chief engineer of Douglas at that time, led a group that said, "We want to triple the output of the Wallops Island group." So the people in Congress said, "If you want to triple it, how much money does that mean?" and the NACA figured out what it was and the Congress appropriated that money. So we had a lot of backing in those days.
EZELL: Did the size of your team then grow?
GILRUTH: A little bit. But mostly the money went into more models, equipment.
EZELL: You said last time that even though this was Wallops work, you were spending a lot of your time at Langley doing --
GILRUTH: -- oh yes, I was mostly at Langley. The shops were at Langley. The models were built there. The data were reduced there. The reports were written there. Wallops Island was the remote area with the necessary equipment for launching and recording the data, and sufficient equipment to set things up and get everything right. It was also a place to sleep and a place to eat and so on. But we found it not very adaptable to having a highly technical group of people live there. They wouldn't want to live there.
WOLKO: They wouldn't want to live there, not with what I remember of Wallops!
GILRUTH: No. Deathly, those mosquitoes!
COLLINS: What year was it, when industry lobbied for you to get an increased budget?
GILRUTH: That would be in the early forties, I don't know, it might be, I think it was '43, something like that.
EZELL: In the forties, I thought we had worked our way up to the late forties.
GILRUTH: This was fairly early in the business.
COLLINS: Clearly industry was finding your performance data very valuable.
GILRUTH: Yes.
COLLINS: And they acquired it through the published reports, for the most part?
GILRUTH: Yes, and they'd come down and talk with us. That was a very good way to do it because that way you could find out things that probably never did get published. There were always a lot of people down at Langley to talk with you about your problems and what did you think and so on and so forth, and you'd try to help them as best you could and show them any data you had, whether it had been published or not.
EZELL: That give and take was encouraged by the administrators at NACA.
GILRUTH: Yes, it was. You bet.
EZELL: And with military also?
GILRUTH: Oh, of course. We'd knock ourselves out for the military, yes. Ezra Cotcher, we were sure glad to see him come along with 30 million dollars to build the X-1 airplane.
WOLKO: Ezra Kotcher's a strange guy.
GILRUTH: I haven't seen him for many, many years.
WOLKO: He's blind now. He stopped in at the museum I think it was last year or the year before last. He's living in California, but he no longer can see at all. I had a chance to spend a couple of days with him when he was here, talking about the development of the X-1. I wasn't in on the X-1. I got to Bell Aircraft in time to work on the X-2, which was the ill-fated one, but I even missed the alphabet series, the whole X-1A, B - all of those.
GILRUTH: What was the name of the fellow that got killed in the X-2?
WOLKO: Captain Apt, Melvin Apt.
GILRUTH: Melvin Apt, yes, went too fast for that fin.
WOLKO: It had been predicted on the BAPA - which was Bell's analogue performance analyzer - it had been predicted that if he tried to go into his turn, a high speed turn at too high a speed, the aircraft would become unstable.
EZELL: You used a word I didn't catch - BAPA.
WOLKO: BAPA - Bell Aircraft Performance Analyzer. We called it BAPA.
COLLINS: Did you work closely then with Bell engineers as the X-1 was being developed? Did they come to you for advice on wing design and that sort of thing?
GILRUTH: Yes, we worked with Bob Stanley who was their chief test pilot.
WOLKO: Paul Emmons probably was in on that.
GILRUTH: Paul Emmons was the chief engineer, and Bob Woods, I think, had abdicated Bell at that time, I'm not sure -
WOLKO: I think he was still with Bell when they built the X-1. He was gone I guess when they built the X-2.
GILRUTH: Ok, somewhere in there he left, yes. But we did work very closely with the Bell people and Bob Stanley, I remember. He was a fearless pilot, absolutely fearless, and he also got killed.
COLLINS: I'm trying to get the picture here. Between industry, the military and Langley, there was a very close personal kind of interaction.
GILRUTH: Yes.
COLLINS: You were accumulating performance data and you were trying to design aircraft that would be able to -
GILRUTH: - yes, it was, and it wasn't just with Bell. It was with North American, and mostly, though, it was not the same with every company, but Bell was one that was very progressive in building far out airplanes. North American was not quite so wild, but they really were advanced in their way of thinking and what they wanted to do with airplanes, and I think that Douglas and Grumman were much more conservative.
COLLINS: Was this partly a reflection of how they saw the potential market for these types of aircraft?
GILRUTH: I don't think so. I think it was the kind of people who were at the head of the engineering departments, had a lot to do with it, in the course of - Grumman built awfully good airplanes and they built what the Navy wanted, which was important for a good relationship, and Bell got into these advanced airplanes. They didn't do as well with their regular fighters and so on as some of the other companies did, like Bell, this one with the -
WOLKO: - the Barracuda, the pusher?
GILRUTH: The Baracuda was one and then the other one, the Aracobra. And then the P-63. I worked hard with them on all those airplanes trying to make them serviceable airplanes, and of course, the Aracobra was bad because you couldn't bail out without going through the propeller disk.
WOLKO: They had explosive charges on that, didn't they, to blow the propellers?
GILRUTH: They may have later on, but I had a good friend who went through the propeller and was very badly hurt, although he lived.
COLLINS: So this would be an example of where industry would bring a plane to you and say, "We're having problems with certain performance characteristics. Take it through the test procedures and give us an indication of how to improve it." Is that a summary? How would that work?
GILRUTH: It didn't ever work that way with Bell, because they'd gotten too far away, they were in too much trouble for us to take it and try to do anything with it. Enough was known of what was wrong with it without us flying it. We tended to get the kind of jobs where they weren't sure there was anything wrong with it, but "...it has a bad reputation; can you find out what...?" Like, we got a Lockheed airplane, not a bad airplane, but there were some serious questions and the Air Safety Board asked us to take this airplane, fly it, and see if we thought there were any real bad things in it.
WOLKO: It was the Electra.
GILRUTH: The Electra, yes. We did that, and made a special effort, and we couldn't find anything that we thought was dangerous. There were some extreme things you could do, and could do with almost any kind of airplane to get it in trouble. It had these great big Fowler flaps. If you stalled that airplane at full throttle and with the Fowler flaps fully extended, you'd be down to about 40 miles an hour or so - and when it did stall, it was really hard to recover. But that was the only thing we could find, and that was something that was unreasonable to do with an airplane.
WOLKO: When we first came in with the swept wings, I've always understood that there was a bit of a cross-flow that you got on the swept wing that caused some of the early swept wing aircraft to encounter some difficulties with stalling from the tips, from the wing tips inward rather than from the fuselage outward. Was this really a severe problem that you people had to wring out for industry, or was industry able to handle it?
GILRUTH: It was always a problem to make the airplane stall in a reasonable way, and sweepback certainly aggravated the stall, because the boundary layer would get much thicker at the tips than at the root.
WOLKO: So you'd lose aileron -
GILRUTH: You would tend to lose aileron control and when it finally broke it was apt to be more unstable. You had to have sweep if you were going to meet your high speed performance, so it was a matter of trying to use either the right kind of vortex generators, or fences on the swept wing to make it have a satisfactory stall. It was a matter of cut and try. You always take a risk with a new airplane, and stalling characteristics were difficult to predict. They often had to be worked on with a new airplane in flight tests. There's no guaranteeing it ahead of time.
WOLKO: This is again getting back now to Bell Aircraft, on the P-39, did you ever get the P-39 down at Langley to test it?
GILRUTH: Yes.
WOLKO: Was there a tumble problem with that aircraft?
GILRUTH: People thought it did.
WOLKO: That was one of the rumors that went around with the P-39.
GILRUTH: Yes, people tended to think it did. I don't think we were ever that adventurous with it. But it would dig in, and the force per G was pretty nominal until you got to high Gs and then the force per G went to about zero, and it would pull itself in. I know that. I remember that. And that was bad.
WOLKO: Was that because of the engine in the rear?
GILRUTH: I have no idea why. I don't think so. I think it had something to do with the fabric on the elevators. There are all kinds of possibilities. For so many years we just took ailerons and other control surfaces and put canvas over them and dope and when you got to high speed, you had no idea what the shape of that aileron was. It depended so much on the internal pressure, the tension on the fabric and the dynamic pressure.
WOLKO: It could balloon out on you.
GILRUTH: It could balloon out or it could suck in, depending on how it was vented. And similarly with the elevators. So in those days, you could get all kinds of things that you wouldn't understand. It was the British that finally said, "Isn't it time we quit fooling around with the fabric on something as sensitive as that?" My goodness, sure.
WOLKO: So the British were first to put metal skin on their -?
GILRUTH: Well, at least they were the first ones that started talking about it. We didn't start talking about it. All of a sudden we said, "Gee, they're right, it probably doesn't look like that at all."
COLLINS: What time period is this?
GILRUTH: This is during the war. The latter part of the war.
COLLINS: In this conversation, time-wise, we've sort of gone back and forth. One thing I remember from our last interview, you outlined as one of the central questions of your work was, how do you design a plane with good stability and flying qualities? Over this time period, say from the late thirties up into the fifties, had it become a certain sense in your mind of what you knew the proper characteristics for stability and good flying qualities were? Had this become reasonably understood over this course of time?
GILRUTH: I think it had. I think it had become reasonably understood. As you got things like sweep back, though there were new problems that were not understood right at first. But the requirements for good flying qualities remained the same.
WOLKO: Well, your TR 755 solved a lot of them. That's a good report.
COLLINS: What report are you referring to?
WOLKO: Gilruth's report, "Technical Report 755."1 It was on the handling qualities.
GILRUTH: Well, I think if you could make it do all those things, it would be a good airplane.
WOLKO: Just to specify what was required, what was good and what was bad.
GILRUTH: That's right, that's important.
WOLKO: That was the important part of that paper.
GILRUTH: That's important, yes.
WOLKO: And I think really, up until that paper came out, people were talking around the problem, but nobody had really gotten down to saying, this is what it should be, as opposed to, this is what we can get. At least it gave people a target as to what to shoot for.
EZELL: TR 755 was Requirements for Satisfactory Flying Qualities, 1943.
GILRUTH: Yes, was it published in '43?
EZELL: '43 is what I've written down.
GILRUTH: It came out as an advanced confidential report for the...
WOLKO: Annual report?
GILRUTH: Oh, the annual report, it wasn't published on a TR?
WOLKO: Oh, yes it was.
GILRUTH: It was finally but many years later.
WOLKO: Many years later. It was published as a TR in '43. I have a copy of the Technical Report. I do not have the Technical Note version of it.
GILRUTH: All right. I think that was the first version of it. I never re-wrote it or anything, but it was first a confidential report and it was many years later before it was published as a regular NACA publication.
EZELL: So it was '43 that the original or the date of the...?
GILRUTH: I think '43 had to be the original.
WOLKO: Probably '37 because '43 -
GILRUTH: '37, I just came to work there, so it had to be something like '43. I don't know. I'd have to look at some of these old reports. I don't have any of them with me. But it's not important. It was some time in coming, though, I tell you, to put all those things together. I finally wrote the report and it turned out to be very short, very simple.
WOLKO: That was due to those editing committees they used to have.
GILRUTH: That's right.
EZELL: Did you find as you took on more managerial work that you did less actual report writing? It seems to me that I found fewer reports with your name on it after you started assuming more of the -
GILRUTH: - yes, I didn't write many reports after that, and such things I did write were given at special meetings and things like that, so I think everybody went through that situation. Yes, I quit writing reports after a while, and gave papers.
EZELL: And left report writing to others.
WOLKO: Well, you were at Langley at a time when they started up their Structures Group down there?
GILRUTH: No, they already had that.
WOLKO: They already had a Structures Group?
GILRUTH: You're probably right. Gene Lundquist became head of the Structures Group, and he originally worked under Rhode in Flight Research Loads. I know that he and Rhode didn't get along very well together, and Lundquist split off from Rhode and started with his testing machines. They did a lot of good work, for Structures Design people, and Rhode would work on what were the criteria for what the loads would be. So, that was something that I didn't do - I was an old stress analyst myself back in my earlier years. but I didn't do much of that at Langley.
WOLKO: You didn't get into that at all?
GILRUTH: I did initially, when I first came there, they found out I could design things to be air-worthy, so if they wanted a new set of ailerons or something, they'd say, "Gilruth, how about doing that?" And I could do that. But I didn't do much of that. A little bit at the beginning. It was always fun, though. I always liked to design something and see it built.
WOLKO: That's an engineer talking right there, without design, you haven't got one.
EZELL: Earlier you used the phrase "the folks at the wind tunnels looked over and saw the kid with the nickel instrument producing data" when they weren't--did you actually make your instrument? You drew up the specs and people produced the instrument?
GILRUTH: You see, the P-51, which was the airplane that I used for tests of model wings of different sections, had an ammunition bay right in the wing below the test region above the wing surface. It was fairly deep and very accessible, and it was an ideal place to put the equipment that I needed to measure the lift, drag and moment of these little models. There was also a device that would cause the model to vary its angle of attack with time, so that while the pilot was diving the airplane, this little model would go from negative to positive angles of attack in a controlled way. During all this, the forces on the model and the angles of attack would be recorded against time, so that when you got your flight data, you could then determine by working it up (with all the conversions and so on) the variation of lift, drag and moment with angle of attack, at all the different Mach numbers that the pilot covered. Actually, the pilot only covered a Mach number up to about 0.80, but the flow over the model would go from say 0.7 to about 1.25.
WOLKO: How was the data recorded? Was this done on a strip recorder?
GILRUTH: No, it was done on a tape. Some of them were photographic film. A light would shine and it would leave a trace on the film. It was nothing unusual, just regular recording tape.
WOLKO: And you fitted all this into what? You pulled the guns out of a P-51? Took advantage of the ammunition bay?
GILRUTH: Yes, the ammunition bay, and the ammunition door was what you mounted, right above the ammunition door was where the test model was mounted. We had beefed up the door because the pressure loads of the air would cause it to vary its shape a little bit. At those Mach numbers, that would make a big difference in the way the Mach number progressed with time, so we put a new door on there. It was aluminum alloy about half an inch thick, and that didn't vary.
WOLKO: Didn't budge.
GILRUTH: That's right. Well, let's see, that was about as far as my encounter with the transonic went. Of course, I was very concerned with the full scale handling qualities, as affected by Mach numbers. It was fun to be able to get some of the data, and it was kind of fun to be able to go on Wallops Island and do it with a complete airplane model. So I got to see all different sides of this problem. Then, all of a sudden, we really felt that we knew quite a lot about the transonic, and went ahead and tried to get bigger and better engines. Of course, the atom bomb came along there and everything else seemed to be sort of insignificant for a while. I think that with the transonic, today everybody knows that you've got to use thin wings, and use all moving controls for the elevators, and ordinary ailerons work all right for the wings if you have a good power system to move them.
COLLINS: Your mention of the atom bomb, is there some sense in which the character or medium of your research or perception of your research changed after that?
GILRUTH: Sure.
COLLINS: In what way?
GILRUTH: Well, war wasn't that much fun any more. It was awesome. And still is.
COLLINS: The feeling filtered down to the test pilot and flight research level, is that fair to say?
GILRUTH: Well, I don't now. It certainly did to me. I felt that things had really gotten out of hand. I felt that we had to rely on a lot of restraint on the part of people. We were no longer able to guarantee the safety of people in the country any more just by very superior types of aircraft. I still think this is true because they can get terribly hurt even if you have probably a better Air Force than the other fellow. He can still get through to where he can cause all kinds of problems. And I think everybody really feels that, and some people probably haven't really said, "Oh, yes, I feel this way about it." but we all feel it, I'm sure. Everyone feels it.
COLLINS: Well, certainly in the present time there's still a tremendous push to improve aircraft quality.
GILRUTH: Oh, sure, of course.
COLLINS: Simply because the issue of the bomb sort of overrides and seems such an impossible step to take, that at the lower level you still need to develop a capable military.
GILRUTH: Of course you do. But it's not like it used to be. It's changed.
COLLINS: That's a very interesting perception.
GILRUTH: What's next, chief?
WOLKO: I've just about exhausted the questions that I have.
EZELL: I'd rather not launch into what David and I want to go into next, which is the late years leading up to Mercury, now. I'd like to make a clean break and start with that next time. Are there issues that you would like to pursue more with Howard being here, from the last interview, anything that has to deal with the engineering profession, those years when you were in school learning to be an engineer, that David and Martin and I couldn't get at last time?
In reading this transcript, it's probably going to seem terribly disjointed and not as satisfying as the other two, because we didn't take a chronological approach, but we've answered a lot of questions that we had.
GILRUTH: Well, I think that I might just go back over a little bit of that. I graduated as an aeronautical engineer, and before I graduated I worked for one of the professors who was an airplane designer, and I had a chance to help design an airplane that Roscoe Turner was going to fly in the National Air Races. In the course of this work, I started out doing stress analysis, which a lot of other boys did too, but I ended up doing a lot of the aerodynamic design, like I designed the wing and the empenage - of course, under the scrutiny of the professor. I'll tell you, stability and control was not a well understood thing back in the middle thirties, and this was around 1936. I had the problem of making sure that the horizontal tail was big enough, and in doing this I would go to the library and look up all of the fighting and racing airplanes that I could find data on. I'd take the ratio of the tail area times the tail length to the wing areas. The same thing for the vertical surfaces. Other criteria on the size of the ailerons. I knew that the ailerons had to overcome the torque of the engine, and this was a great big engine that Roscoe Turner was going to have, so I made the ailerons a little bigger than they would have been normally. I was trying to keep out of trouble, keep my boss out of trouble, by making sure that the airplane had a tail that was just about as big in proportion to the wing as other airplanes had that were racers, and so and so forth.
I also made wind tunnel tests that were very primitive because we just had a 4 x 4 foot wind tunnel at the university, but I was interested to see whether or not the airplane would be stable at the center of gravity that we were going to fly at. This was about all I could do; I didn't know that much about it, but I think most of the designers really did just what I was doing. They tried to make it about the same proportion that others were. The airplane apparently was all right, because it never did crash and Roscoe won the Thompson Trophy twice with it!
Stability and control was never a course that was taught at the University of Minnesota when I was there. But as a model airplane builder, I knew that it was important, that they had to have good stability. I was always interested to know what others would think of this kind of a procedure, without ever really finding out.
WOLKO: It's a perfectly good empirical procedure. The same thing was done when people used to keep track of aircraft weights. They would look at past experience and base their judgments on past experience. If this airplane worked all right, if this other one was the same proportions, it should work all right, you bootstrap your way up. That's the game.
GILRUTH: Yes, right. I think we've covered the aviation side of this.
EZELL: We'll be ready to launch into the years leading up to Mercury, then next time?
GILRUTH: Right.
EZELL: That's what we're especially looking forward to, although I recognize that this was a very important thing as well. Are you ready to complete this session?
COLLINS: Yes, I don't have any further questions.
1 Gilruth, Report 755.
Rev. 09/06/96