“_She Blew Sky High_”
X-15 number two, identical in appearance with X-15 number one, was
anchored to the concrete ramp in the engine-test area. Her fuel
tanks were brimming. In the big forward tank there were four tons of
liquid oxygen, so cold that a thick coating of ice had formed on the
outside fuselage and all the machinery in the vicinity of the tank
had chilled. In the after tank there were five tons of a mixture
of water and alcohol or, as we called it, “Walc,” a very volatile
liquid. Altogether, then, nine tons of liquid energy, the fantastic
stuff that would propel the X-15 through the air faster than man had
ever flown.
Wearing street clothes, I climbed into the cockpit to begin the
practice engine test, a simulated launch and engine run just as it
would take place in the air. The men who had fueled the X-15 moved
back their big tank trucks. The specialists on the propulsion system
grouped at a distance and talked to me by radio from Sam’s van. Q. C.
Harvey manned his post in the North American tower two miles away.
I quickly ran through the familiar pre-launch routine: APU start,
shift to X-15 power, and so on. Now for the first time I added to
this routine the involved rocket-engine start procedure.
First I turned a switch which touched off a flow of nitrogen gas
through all the fuel lines. This was a safety measure to purge fuel
which might ignite prematurely in the lines and cause an explosion.
Next I pressurized the big Lox and Walc tanks with helium gas to
force the fuel through the lines aft to the rocket-engine pumps.
The helium is stored in a cylindrical tank surrounded by the Lox
tank. We purposely put it there to keep it as cold as possible. By
cooling the helium we can store almost three times as much in the
same size cylinder, or cut down on the size of the cylinder and save
weight. The regulator valve which adjusts the gas flow from helium
tank to the fuel and Lox tanks is a fantastically sensitive device
which operates at a temperature of minus 300 degrees Fahrenheit. The
pressure inside the helium tank is 3,600 pounds per square inch; the
regulator reduces this to a mere fifty pounds per square inch, which
is all we need to get the fuel moving aft. The regulator had already
caused a lot of trouble. It would cause much more in the future.
The X-15 is designed to land empty of fuel. If something goes
wrong--if the engine should fail to start--it is absolutely necessary
to get rid of the nine tons of fuel weight. Like other rocket
airplanes, the X-15 is equipped with a fuel jettison system. This
is carefully arranged so that both tanks exhaust fuel at about the
same rate. If one tank emptied too far ahead of the other, it would
throw the X-15 out of balance and possibly into a flight attitude
from which the pilot could not recover. There is a control mounted
in the cockpit to adjust the flow-rate for each tank. Before the
launch, before lighting off the engine, we always check the jettison
system to make sure it is not clogged or frozen shut. (Every time
I jettisoned the Walc, I could not help feeling a twinge. I was
throwing away 6,000 fifths of pure vodka that some unimaginative
temperate had contaminated to prevent useful consumption other than
in rocket engines.)
At launch altitude of 38,000 feet, where the air temperature is
about minus 60 degrees Fahrenheit, the rocket engine and pumps are
very cold just prior to launch. If we ignite the engine cold there
is danger of erratic and rough starts or malfunction. Thus just
prior to launch, the pilot must turn a switch which allows a trickle
of hydrogen peroxide to flow through the engine pump gas generator,
warming it up or, as we say, “pre-heating.” Thirty seconds or so
before launch the pilot “primes” the engine with a burst of Lox and
fuel. The prime is dumped overboard so it can be checked visually by
the chase pilots. The purpose of the prime is to make certain the
fuel and Lox lines are full--right up to the rocket-engine fuel pump
which sucks the fuel from the tanks and forces it into the burning
chamber at a tremendous rate.
Now on the ground as I went through these procedures, the outside
observers reported: “Prime looks good.”
Simulating a drop from the mother plane, I then ran my hand across
eight toggle switches on the left side of the X-15 cockpit, igniting
each of the eight barrels of the rocket engine. They roared to life
with a noise that could be heard for twenty miles across the desert.
A long blast of rocket exhaust--flame, fire, and smoke--spewed from
the rear of the X-15. The little ship strained against its ground
moorings. One barrel of the engine ignited improperly and, as
designed, automatically shut down. The other seven blazed on, gulping
the fuel at the rate of two and a half tons a minute. Then after 250
seconds, fuel exhausted, the seven barrels “blew out” or stopped,
making a “pop-pop-pop-pop-pop” sound. The ground crew moved in to
check the results.
* * * * *
The ground tests on the X-15 rocket engines, supposedly reliable X-1
types with a great backlog of experience, revealed many surprising
weaknesses and faults. It might have been a case of familiarity
breeding contempt. Or perhaps the experts who had originally designed
and wrung out these engines had moved on to other fields, leaving
behind personnel lacking their genius. There were many difficulties
too in the X-15’s infinitely complicated tankage and fuel plumbing
system.
The regulator valve on the Lox tank is one good example. That
extremely sensitive piece of equipment was tested in the laboratory
at least ten thousand times. Yet when we put it in the airplane, it
failed again and again. Each time it failed, the ground crews had to
tear into the airplane to get inside and replace it.
The tale of woe with this single valve would make a book in itself.
Charlie Feltz, Bud Benner, and John Gibb, his assistant, stayed up
around the clock many nights, almost hand-building and testing new
regulators. Then, like some priceless set of jewels, these were
carried to Edwards by hand and installed in the airplane--only to
fail again at the crucial moment. Before long, Stormy entered the
picture. He and the engineers redesigned the valve a dozen times. I
don’t think any valve in the history of the world received so much
high-level probing, so much laboratory testing, so much money and
engineering man-hours. This single item had to be perfect. A failure
could cause a catastrophe in the air and wash out the whole X-15
program.
Slowly--all too slowly for my money--our complex bird was gaining
in reliability, inching ahead toward the pay-off point. Her story
was accumulating in tens of thousands of pieces of paper--reports,
work change-orders, engineering analyses, written by hundreds of
people. Our ground crews, feeling their way with this strange tiger
and her dangerous fluids, grew in maturity and experience. Where
once they resembled a platoon of raw recruits, they now worked with
carrier-deck efficiency and enthusiasm.
But men are fallible. They can’t think of everything. Somewhere an
obscure mistake was made, and the consequences were nearly disastrous.
After a ground engine run one day, I hurried to my Bonanza and flew
back to the plant in Los Angeles. When I landed, one of the company
guards came up to me and said:
“Is it a total loss?”
“Is what a total loss?” I asked.
“The X-15. Didn’t you hear? She blew sky high.”
I raced for a telephone and put through a call to Q. C. Harvey, my
mind spinning with anxiety and apprehension. Q.C. got on the phone
and rattled off the awful story.
After I had left, the ground crew began grooming the X-15 for
her next test. Part of this routine called for purging the
hydrogen-peroxide lines of all residual liquid. This was usually
accomplished by connecting a nitrogen gas hose to a fitting on the
outside of the X-15 and blowing gas through the plumbing. Despite
careful procedures and great caution the hose used for this had
a residue of oil, doubtless left there a long time back when it
was tested in some remote factory. When the mechanic applied gas
pressure to the hose, the film of oil was forced into the X-15
hydrogen-peroxide lines. When these two hostile chemicals met, a
violent explosion was set off. Fire raced through the engine bay of
the airplane.
The firemen at Edwards rushed to the X-15. By then the ship was
an inferno of flame and white smoke, reminiscent of the Queenie
explosion. They put out the fire, but not before it inflicted severe
damage in the engine bay. The fire gutted the rear end of the
airplane. When the peroxide blew, one of the X-15 crewmen was badly
burned. If he had been standing two feet closer, he would probably
have been killed.
It took weeks to repair the airplane.
* * * * *
24 July, 1959. Forty-six days since my first glide flight in the
X-15. The fire damage in X-15 number two had been repaired. The
rocket engine had been tested on the ground several more times. The
Lox tank helium regulator had been redesigned and replaced almost
daily. Now we were nearing the second big milestone: a powered flight.
But before this could take place there were many more pieces to fit
into our technological puzzle. X-15 number two had not yet been
aloft. No X-15 had yet been aloft with fuel on board.
Uppermost on the list of items to check was the B-52 Lox top-off
system. As previously related, unstable Lox “boils” away at a fast
rate at high altitude. As much as 600 pounds an hour of the X-15’s
four tons of Lox evaporates through the tank vents. This loss could
throw the ship seriously out of balance at launch time. A Lox loss
also reduces the rocket-engine running time.
The B-52 Lox top-off system is a highly sophisticated piece of
machinery, far advanced over anything installed previously in
mother planes at Edwards. A complicated pressure system moves the
Lox from two huge storage tanks in the B-52 belly, through pipes in
the B-52 wing, down into the X-15 mating pylon, and then into the
X-15 Lox tank itself. A probe in the X-15 Lox tank “senses” when the
Lox supply drops and automatically relays this “word” to the B-52
storage tank pumping system. Then the B-52 Lox valves go into action,
refilling the X-15 Lox tank. In theory, this system is supposed to
keep the X-15 brimming with Lox all during the climb and the flight
to launch point. The system had been checked on the ground and in
flight many times, although never with an X-15 mounted on the B-52
pylon in flight.
I boarded the X-15 at 0830. The ship with its load of Lox was
like some massive deep-freeze. I noticed, for example, that the
temperature of the hydraulic oil in the control system was minus
80 degrees Fahrenheit. We had anticipated that. We would have to
watch this carefully. If it completely froze in flight, it would be
impossible to operate the X-15 control system. I droned off the gauge
readings into my tape recorder. Then I received news from the ground
crew that there would be a two-hour “hold” in take-off. Some seal,
sensitive to the intense cold, had failed at the last minute.
The take-off delay seemed interminable. When at last the ground crews
finished repairing the faulty piece of X-15 equipment, a baffling
new problem arose. In the repair process the mechanics had removed
an access door on the ship, a piece of the fuselage skin. The X-15,
influenced by its freezing load of Lox, had shrunk considerably in
size. The access door, lying in the hot desert sun, had expanded to
its normal size. Now it wouldn’t fit back in its original place. We
couldn’t go up without it. What to do? Five hundred people wondered.
It was one of the X-15 crewmen, Joe Jingle, who provided an ingenious
solution. He hurriedly soaked the access door in a bucket of liquid
nitrogen until it shrank enough to fit back in place. As I watched
this operation from the cockpit--Joe’s gloves were too thin for
the intense cold and I knew he was suffering--I was filled with
admiration. Our team was becoming truly professional.
Charlie Bock poised the B-52 and its precious load at the end of the
runway. We were now much heavier. The Lox in the B-52 storage tanks
and the fuel and Lox in the X-15 had upped the B-52 gross take-off
weight by almost twenty tons, including the extra B-52 jet fuel
required to operate the heavier airplane. The X-15 alone weighed
32,215 pounds, or about the same as a heavily loaded DC-3. Bock
cobbed the engines. It was a long run. We broke ground at 11,500 feet.
The X-15 and its jewel-like machinery underwent an amazing
kaleidoscope of temperature ranges. On the ground the little ship was
intensely cold. Now as we flew through the hot desert air, it began
to warm up. The hydraulic temperature zoomed from minus 80 degrees
to plus two degrees Fahrenheit. Then as we climbed in the thinner,
colder air, the temperatures fell again to well below zero. I kept an
almost continuous log of these temperatures. It was important to know
just how the X-15 responded. If we overlooked the possibility of a
frozen valve, it could result in serious trouble and more delay.
Bill Berkowitz in the B-52 reported by radio: “The Lox top-off system
is erratic.” Bill was watching a panel of gauges and lights in the
B-52 which continuously kept tab on the stream of Lox flowing from
the B-52 to the X-15 tank. The lights had signaled a malfunction.
Bill shifted from one B-52 Lox storage tank to the other. But it was
no use.
“I have no indications here of a top-off,” I reported.
Something had gone haywire in that sophisticated, vital piece of
machinery. I would have to stay on guard. The X-15 Lox was boiling
away rapidly, imbalancing the airplane. If we had an emergency
launch--always a possibility--I would have my hands full. The system
was intensely cold, it was mechanical, it was electrical, it was new,
Murphy’s Law prevailed: “If it can fail, it will.” (Murphy’s Law, the
enigma of designers, is in engineering lore akin to the natural laws
referred to by Robert Louis Stevenson when he speaks of a piece of
dropped toast which always falls buttered side down, and of assuring
sunshine by wearing a raincoat.) We never really got used to this
tarnish on our most hopeful engineering.
There followed a half hour of diligent test and search for the
trouble. The top-off system was clearly on the blink. Berkowitz tried
to prove top-off by looking through the closed-circuit television set
beamed on the X-15. But we were not in a TV studio. The expensive set
was not discriminating enough to tell him what was happening at the
overboard spill on top of the X-15 fuselage. We later got around the
inadequacy of the TV circuit by installing a hemispherical window in
the side of the B-52 so Bill could look with his own eyes.
Following this, we turned to other drills in the sky. As usual,
we proceeded to a launch rehearsal, this time including the
rocket-engine pre-start routine. I pressurized the X-15 fuel and Lox
tanks and for once--or so it seemed--the helium regulator performed
as designed, or as redesigned. At one minute before “Launch” I shut
down the propulsion system. Then to see how long it would take to
get rid of the X-15 propellants at altitude, I jettisoned the six
hundred pounds of hydrogen peroxide, four tons of Lox, and five tons
of Walc. The peroxide streamed away in 140 seconds. The Lox and Walc
tanks, jettisoned simultaneously, ran dry in 110 seconds, leaving a
long white contrail across the deep blue sky. The jettison times were
exactly right. If the X-15 pilot encountered trouble after launch he
would be mighty busy, but we knew he could dispose of nine tons of
fuel before the ship touched down dead-stick on the lake.
With the exception of the B-52 Lox top-off failure, we considered the
flight a whopping success. The X-15 had weathered its temperature
extremes without difficulty. The pressure suit, the APUs, operated
for the first time in _this_ airplane at altitude, the engine-start
rehearsal and other checks were entirely satisfactory. The fact that
the helium tank regulator worked was a reward for Gibb’s sleepless
nights. In short, once the Lox top-off system had been debugged, the
bird was ready for powered flight.
In spite of these setbacks, inevitable in a craft so advanced as
the X-15, we were on schedule. Four years before this--in the early
fall of 1955--North American promised delivery of a debugged X-15
airplane to NASA by August of 1959. Even including a thousand or more
changes from the original concept, including a major shift of mother
ship, and a switch to the interim engine, we believed then that we
would meet this schedule. We would get off one powered flight to make
some of our demonstrations and then turn an X-15 over to NASA. The
agency was eager, although it seemed to me that the line of volunteer
X-15 pilots was beginning to thin out considerably. Bob White and
Joe Walker and their “back-ups” were still in there pitching, flying
chase on most of our flights. However, we noted there was no great
rush of new applicants.
* * * * *
We failed to meet our four-year-old X-15 schedule. August, 1959, came
and went without a successful powered-flight demonstration and we
were not able to deliver an airplane to NASA. It took much time to
repair the balky B-52 Lox top-off system and to install an emergency
by-pass in case it failed again. The little ship itself suddenly
developed a hundred minor leaks and pains, each requiring thousands
of agonizing man-hours to rectify. The weeks ticked by at an alarming
rate. Finally on September 4 the X-15 was mated, fueled, and ready.
If all went well on the flight I would drop and fire off the rocket
engine.
Because our tight schedule had “slipped” by a week, we prepared
for this climactic flight with a growing sense of urgency. All
hands worked and talked as though they were Marines on the verge of
invading a beach-head. On the night before the flight I stayed up
late in the BOQ memorizing the flight plan. We wanted to collect data
readings at about forty different combinations of speed, altitude,
and angle of attack during the flight. After I fell away from the
B-52, there wouldn’t be time to consult the flight plan.
I arrived at Captain Richardson’s van at 0540, put on the pressure
suit, and checked its systems. By 0625 I was strapped in the X-15
cockpit. At 0717 the B-52 took off, climbing slowly to launch
altitude. I kept a sharp eye on the gauges, although I was blinded
somewhat by the early morning sun, and droned the numbers into
my portable tape recorder. The B-52 Lox top-off system performed
adequately. As we approached this dramatic moment in X-15 history, we
joshed on the radio.
“Say,” Charlie Bock called out, “looks like they have a heavy
overcast down in Los Angeles. Scotty, you want to make an instrument
approach in the bird into Los Angeles International Airport?”
“I don’t have a glide-path indicator in here,” I said.
“You might create something of a new noise problem with that engine.
Everybody would move away from the airport,” Bock said.
We climbed to launch point.
“Seven minutes to drop,” Charlie Bock said. We had reached 38,000
feet, heading southwest, to make a final turn over Randsburg. Then
we would aim for Mojave, swing over Lancaster, and if all went well
launch over Rosamond Dry Lake. I was busy flicking switches in the
X-15 cockpit. I made a note on the tape recorder: “The black gloves
may look fine with the silver suit, but they have to go. They soak up
the bright high-altitude sunlight and they’re uncomfortably warm.”
Q. C. Harvey wanted to make certain the Lox top-off was complete. He
broke in from the ground: “Hold at seven minutes.”
We waited, boring holes in the sky, while Bill Berkowitz checked to
see if the top-off was successful. When he reported it was, Q.C.
“released” us and we proceeded toward the final countdown.
“Five minutes,” Bock announced.
“I’m going to pressurize the Walc and Lox tanks NOW,” I said. I
emphasized “now” so that we could get the precise time of the
operation. When I spoke the word I moved the lever that set in motion
the worrisome Lox tank regulator. Helium gas rushed into the large
X-15 tanks. I watched the gauges as they swept from zero to 50 pounds
per square inch in ten seconds. The Lox tank pressure continued up.
Then I heard a strange, loud clank in the rear of the X-15.
“Oops,” I said on the radio. “What was that?”
The clank came from a safety relief valve on the Lox tank. Too much
helium gas had rushed into the tank, the pressure was too high, and
it tripped. The helium regulator had failed again. I swept my eyes
back to the gauges. The Lox tank read 65 pounds per square inch.
I double-checked with the chase pilots: “Is the Lox venting
overboard?” There was clearly no possibility of a powered flight
that day, but I wanted to make certain the safety vent was operating
properly. If not, the mounting helium pressure could cause the thin
X-15 tanks to burst. At 38,000 feet, that could be a real mess.
“Affirmative,” chase reported. “Safety vent operating.”
By then I was sure it was operating properly. The vent, in fact, was
flapping rhythmically, in time with the gauges, which fluctuated as
the gas pressure built up in the tanks to limits, tripped the safety
vent, and then fell off again.
“I’m dead,” I reported on the radio. “Regulator is running away.
Relief vent cycling. Letting out the over-pressure.”
“Abort,” Q.C. responded. I could imagine his disappointment. I know
because I felt it too. We would have to try again.
We jettisoned the unused fuel--its cost, about $1,000, was a mere
drop in the bucket--and returned to base. That night, as I recall it,
we spent several very uncomfortable hours in Stormy’s office. For the
next three nights Charlie Feltz, Bud Benner, and John Gibb slept not
at all. They spread their time between the Manufacturing Division and
the Testing Laboratory, hand-carrying the handbuilt helium regulators.
* * * * *
There was a new and urgent reason for reaching X-15 flight perfection
at the earliest possible date. Almost casually the U. S. had drifted
to a major turning point in its history of aviation and national
defense. Guided missiles were pushing the manned combat aircraft to
the side. The missile zealots in their eagerness to obtain funds had
convinced the powers that be in Washington that the manned aircraft
was an obsolete concept. Anti-aircraft missiles, such as the Nike
and Bomarc, could do the job of the manned fighter in defending the
nation against air attack, they claimed. Surface-to-surface ballistic
missiles, such as Atlas, Titan, and Polaris, could replace the manned
combat aircraft for the retaliatory mission.
All of us, of course, believed in missiles. Few could deny that they
would ultimately become a dominant weapon in the deterrent force.
But we believed this day was still a long way off and, moreover,
that there would always be a place for the manned combat aircraft.
Manned airplanes are flexible. They can be moved about or dispersed
quite simply, or shifted in flight from one target to the next,
or assigned to several targets. If there is an alert, they can be
launched and, more important, recalled, if it should all turn out
to be a mistake. Airplanes can approach the enemy’s borders from a
wide range of points on the compass at a variety of altitudes, vastly
confusing the enemy radar warning and interception system. The simple
fact of having manned combat airplanes in our inventory forces the
enemy to take tremendously expensive countermeasures to prepare a
defense against them. Manned aircraft are fundamentally more reliable
mechanically than missiles, and they can be repaired without total
loss if something goes wrong. (This we had demonstrated again and
again in the X-15.) By building military airplanes we keep the art
of aviation alive in this country and enable the nation to compete
and prepare for the fantastic future already being revealed on the
technical horizon.
In the industry we had noticed the drift a long time ago. I first
picked it up in 1954 during the meeting of the old NACA Aerodynamics
Subcommittee when the X-15 was under discussion. Since then, the
number of Air Force planes on order and types under development
shrank rapidly. As I have related, by the time we began the X-15
flight-test program there were only _two_ advanced combat Air Force
airplanes on the drawing boards: the F-108 fighter and the B-70
bomber, both North American designs. In the summer of 1959 as we
approached the climax of the X-15 flight program, we received the
stunning news that one of these planes, the F-108, had been canceled
outright. In the field of Air Force manned combat airplanes for the
future this left only the B-70, and from what we could ascertain it
too was in jeopardy.
These fateful decisions were made--over the protests of the Air
Force and NASA--by men temporarily on loan to the government from
fields other than aviation. The decisions were made in comfortable
Washington offices far removed from the reality of Cape Canaveral and
Edwards and failing helium-regulator valves. That fall we hoped that
a successful flight of the X-15 might dramatize the validity of the
manned-aircraft concept and bring about a reconsideration of these
decisions. All my life I had staked my all to foster and further the
concept of manned airplanes. Now, with the X-15, we had our last
chance to make intelligence prevail and I intended to help, even if
it killed me.