Chapter 32: ►

_Time for Extraordinary Action_

By January of 1958 the X-15 team had moved into high gear. North American’s F-100 contract was running out. The production space was absorbed by the jigs and dies for our three “space craft.” We had subcontracted about two hundred items on the airplane to vendors, but most of the ship was manufactured right on the premises.

By then all the engineering drawings--some six thousand altogether, and one of them fifty feet long--had been released. The never-ending battle to get the most from a part for the least weight was reaching a climax. Charlie Feltz had detailed every man on our team to keep track of the weight, to make certain the total did not climb above our final estimate of 31,000 pounds. Since there were more than 10,000 parts on the X-15 weighing a pound or more, our weight-watchers were firm and exacting.

Everything about the fabrication of the X-15 was new and challenging and therefore, from a technological standpoint, exciting. Every day at his command post on the second floor of the engineering building, Charlie Feltz faced a hundred new problems, each one of them a minor crisis. As I look back on those long days and nights, I wonder how he kept his sanity. We hear much about pressure on Madison Avenue and in the city rooms of newspapers at press time, but no one can persuade me that it is any greater than that we experienced on the X-15 project. Night after night I returned to my home late--punchy, almost shell-shocked. Month by month I watched Feltz aging, long before his time. But no matter how intense the work, or how baffling and seemingly insoluble the crisis, he seldom lost his country-boy composure. I believe this fact, more than any other, held the team together amicably under the great strain and enabled us to achieve our goal.

Most of the technical details of the fabrication of the X-15 are, sad to say, too involved to relate here. Thus I fear this marvelous technological story will never be told in full. But there is one understandable detail which I would like to describe. This is our pioneering metallurgy with the skin of the X-15, Inconel X. In the sense that it was new and untried, it was fairly typical of most of the fabulous shopwork on the X-15.

Inconel X, as I have said, is a tough nickel alloy, capable of withstanding high temperatures without losing its structural integrity. When we launched the X-15 project, Inconel X had been proven in a laboratory. But no one had ever built a machine of it. There were no handbooks to tell us how to work it. For example, only a few people in the nation had ever tried to weld Inconel X. The skin of the X-15 had to be welded because traditional rivets were not strong and resilient enough to stand the temperature beating without leaking. Besides, we figured we could save a thousand pounds of weight by eliminating rivets.

Consider half of the X-15 wing as typical of the metallurgy problem we licked. From fuselage to wingtip, the wing is only six feet long. At its peak cross-section the wing is only eight inches thick. There are seventeen spars in the wing. At the root near the fuselage joint the spar caps are 3/16 of an inch thick. At the tip they are a mere 30/1000 thick.

When the X-15 re-entered the heavy atmosphere of the earth, we had calculated, the leading edges would be subjected to 1200 degrees Fahrenheit. They would glow red from the heat. A few inches aft on the wing, however, the temperature would be much lower. Where the temperature is higher, the metal must be thicker and heavier to carry the load. But at the same time it is foolish to waste weight by overloading at points where the temperature is low. Thus we viewed the wing skin in hundreds of sections, each capable of withstanding a certain maximum temperature, plus a safety margin, and each of different thickness to save weight and still carry its share of load.

Inconel X came to us from the manufacturer, International Nickel, in sheets 36 inches wide and 140 inches long, rolled and milled to normal aircraft specifications. We figured that if the total skin of the X-15 were as much as 1/1000 of an inch too thick, it would cost us a critical 100 pounds in weight. Thus when we received the sheets, we re-milled them in grinders down to incredibly low tolerances. Since each different piece of the wing skin varied in design thickness from the others, each had to be ground separately to those tolerances. (The same was true of the fuselage and tail-skin.) It was like making a Stradivarius, if not even more delicate.

Once these pieces were completed and the spars set in massive jigs, the technicians then set about welding the many parts into one solid piece. Ordinary welding is difficult enough: extreme care must be taken to see that no “bubbles” form to weaken the joints. Welding Inconel X almost drove our men to distraction. They worked like artists, experimenting with new strokes and mixtures until they were able to produce a true masterpiece of craftsmanship. Each of the thousands of joints was X-rayed to make certain no bubbles had formed.

The pieces, after welding, were heat-treated like fine steel knife-blades. Let me explain that further. When you weld two pieces of metal together, each is subject to varying temperatures from the welding torch. As the torch moves along, the new area heats up while the one just passed cools. Thus there are stresses and strains in the molecular structure of the metal undetectable to the naked eye. By placing the entire structure in an oven after welding and raising the temperature to 1900 degrees we were able to cool it uniformly, ironing out the strains. After this stress-relieving process each piece remained in the oven for twenty-four hours at high temperature to heat-treat or “age” the metal. Then the joint and the parent metal were stronger than originally. After a fine polishing, the hundreds of welds were impossible to locate with the human eye. The wing looked like one solid piece of smooth metal.

Our metallurgists didn’t learn this new craft overnight; it took years. They started out experimentally by building three mock fuselages of the X-15 to serve as ground-test beds for the rocket engines. One of these was installed at Edwards, the other two at the RMI engine factory in New Jersey. This experience brought our welders to the artist level, but when it came to building the three airplanes, Feltz was even more demanding. In fact, as I recall, about seven different wing-skins were built for the first airplane before he gave his approval. In the end, I think, the experience and knowledge we gained on this new frontier alone were worth the entire cost of the X-15 program. It was one big reason we believed our case for the advanced X-15 was sound. All future space projects will benefit directly or indirectly from our work with Inconel X.

* * * * *

The RMI XLR-99 rocket engine was steadily falling behind schedule. This fact was no secret. It was well known in the Air Force, NASA, and throughout the entire aircraft industry. There were many technical locusts plaguing the RMI engineers. One of the biggest was the fact that during tests, while burning the X-15’s exotic fuel mixture of Lox and ammonia, the rocket-engine chamber had a habit of exploding. By February, 1958, the XLR-99 engine was exactly one year behind schedule and considerably heavier than originally planned.

I believe that under ordinary circumstances our customer would simply have ordered us to wait for, or “sweat out” the engine. But the X-15 was not being put together under ordinary circumstances. She loomed on the horizon as a national symbol of our ability, or lack of it, to make good in space. Because of this and other factors, insofar as the engine was concerned, it was time for extraordinary action. But complex rocket engines don’t grow on trees. What to do?

Charlie Feltz called for help. Stormy, who was then also busy laying out plans for the Air Force F-108 fighter and the B-70 bomber among other things, took over the X-15 engine crisis at full throttle, bringing his authority to bear. He got on the telephone to North American’s Rocketdyne Division. Could they run some Lox-ammonia tests on a Redstone chamber and see what happened? Rocketdyne converted a Redstone chamber and successfully conducted the tests. (Rocketdyne engineers even made the Redstone chamber throttleable.) We were impressed, because these tests were run off in a matter of weeks without interfering with Rocketdyne’s major ballistic-missile projects, and at no cost to the government.

After the tests Stormy again asked the Air Force to allow us to equip the X-15 with a working engine. Again the proposal was turned down, for most of the aforementioned reasons. But the Rocketdyne demonstrations had a dramatic impact at RMI. RMI engineers, beaten at their own complex game by the great depth of North American engineering talent, turned to the XLR-99 engine with new and vigorous enthusiasm. But we knew that no matter how hard they worked they couldn’t make up much of the lost time. What was the answer?

We debated that question during countless meetings with Stormy and Charlie Feltz in the following weeks. Then one day our “dreamer,” Bob Carmen, spoke up.

“I’ve been doing a little figuring here. Suppose that instead of waiting for the XLR-99 engine we substitute, pending its arrival, two X-1-type engines. They could be built in a few months, at most.”

I flew out of my chair.

“Boy,” I said, “if you really want to kill off a project, this is one way to do it. Start yielding. Start making inferior substitutions. Make the airplane more complex. Sure. That’s what happened to the X-3, the X-1-A series and the X-2. If we allow that to happen to the X-15, we’re going to wind up with nothing again.”

“Now, hold on a minute, Scotty,” Feltz said. “We’re really up a tree here. We can’t use a Rocketdyne engine. We have to wait for the XLR-99. Maybe Carmen has got a point here. Pending the arrival of the big engine, we could be checking out the other systems in the airplane.”

“Damn it, Charlie,” I snapped. “I think we’d be making a big mistake.”

“Let’s take a look at the performance we might get out of the two X-1 engines,” Feltz said, obviously warming to the idea.

“Can we use the same fuel-tank system?” an engineer asked.

“Yes,” Carmen said. “Nothing about the fuel tanks would have to be changed. You just change the engine, substituting the eight small chambers for the one large one. I think we could fix it so that when it arrives the big engine could be installed with hardly any delay.”

“What’s the fuel for the X-1 engine?”

“Lox and alcohol. We just put the alcohol in the ammonia tanks. No sweat.”

“There’s another advantage, too,” someone else put in. “Those engines have a lot of time on them. They ought to be reliable. The X-1 engines are not throttleable. But each engine has four barrels. That’s a total of eight barrels, all of which can be lighted off separately. Thus you can attain just about any speed range you want within the limits of the airplane. I mean, it would be almost the same as being throttleable.”

“I figure the extreme performance with these two engines at about Mach 3.5 and 150,000 feet,” one engineer said. Each X-1 engine would have a thrust of about 8,000 pounds or a total in both chambers of about 16,000 pounds--compared to 57,000 pounds for the XLR-99. The two X-1 engines together weighed more than the single XLR-99 engine.

“Mach 3.5 and 150,000 feet,” Feltz repeated. “That would give us enough performance to make a good many demonstrations on the airplane. In fact, we could make all the structural demonstrations, as well as re-entry, ballistic controls, Lox top-off, and so forth. Let’s see what the customer says.”

The substitution of the two smaller X-1-type engines was the obvious solution to our dilemma. Actually, the customers had already considered exactly the same idea. They approved it at once, and Edwards got busy building up a dozen “proven” X-1 engines from old parts. We planned to put two each in the first two X-15s, holding the third X-15 in the factory for the first XLR-99 engine and other improvements which flight test would generate. The remaining X-1 engines would be used for ground tests in the X-15 engine test beds at Edwards and RMI.

A few nights after this decision was firmed up, Stormy, Feltz, and I met after work in Charlie’s office at the North American plant. I was still grumbling about “interim measures.” I let off steam.

“As far as I’m concerned, we’ve botched the whole deal,” I growled. “You watch. We’re never going to get that big engine. The X-15 is going to die on the vine. I’ve seen it happen before.”

“You’re wrong there, Scotty,” Feltz said. “We’ll get the big engine sometime. Meanwhile, we’ll get a lot of Mach 3 data which will really help the F-108 and the B-70. We’ll prove out the X-15 systems and by the time the big engine comes the ship itself will be as reliable as an F-100.”

We debated this point for a long while. Stormy was also in favor of substituting the smaller engines. “I want to get this thing in the air as fast as possible,” he said. “I think that as soon as we start flying the X-15 and prove our systems and landing and the rest, Washington will be impressed and may look with more favor on an advanced X-15 or the X-15B.”

That remark was typical of Stormy. He was always looking far down the pike. He had cornered the Air Force combat aircraft market with the F-108 and the B-70, but he was stung when we lost out on the X-15B. He had not given up--and never would.

“Frankly, Scotty,” Charlie Feltz broke in, “this engine thing may be a blessing in disguise. I’ll tell you honestly that all along I’ve been a little concerned about busting into space all at once with a brand-new airplane and a brand-new, untried engine. They did it with the X-1, it’s true, and it was a real good show. But this is a new dimension we’re getting into. They were just trying to crack Mach 1. We’re trying to crack space, with a new pressure suit, re-entry, new metal, landing--everything at once. I’ve got a real good buddy who’s going to be flying that airplane for the first time, and I’d just as soon have him around for a while.”

Put that way, on a personal basis, there was nothing I could say in reply. From that point on, I resigned myself to the engine substitution, even though, in a sense, it marred my dream to help build and then fly the perfect airplane. In fact, after some weeks, I came to believe that even from a pilot’s point of view the engine substitution was wise. We could learn to crawl before we entered the Olympic hundred-yard dash. I was confident that in time and with God’s help we would eventually succeed with the big engine. There was too much at stake to allow it to fall by the wayside.