_Engulfed in Disappointment_
“Three minutes to drop,” Charlie Bock intoned on the radio circuit.
We were turning over Rosamond Dry Lake at 38,000 feet for a final run
to the launch point, within sight of the Edwards base and Rogers Dry
Lake, where if all went well we would launch and I would dead-stick
the X-15. It was June 8, eighteen days since our last successful
captive flight. We had been airborne thirty-five minutes.
I reached up and set the sweep second-hand on the X-15 dashboard
clock. Then I checked all the gauges. With one exception they
couldn’t have looked better. The APUs, which had been running eight
minutes, were holding. APU bearing temperatures were a mere 116
degrees, well within safe limits. The nitrogen gas coolant supply
was ample for both APUs, defogging, suit ventilation, and cockpit
pressure. I rechecked the altimeter setting and listened when Edwards
tower called the winds on the lake bed: 10 to 12 knots from 240
degrees.
A yellow light near my knee beaconed the single malfunction in
the X-15’s machinery. It was an indicator on the X-15 Stability
Augmentation System (SAS), the automatic control damping device,
which in flight would sense an impending violent maneuver and take
action to forestall it. Most of the new supersonic fighters we
had tested at Edwards, such as the F-100, were equipped with SAS
to minimize the possibility of unwanted yaw, pitch, or coupling
divergence. The X-15 was the first experimental airplane to have such
a system, and, like most of the gear, it was more sophisticated than
ordinary versions.
The “pitch mode” of the SAS, which would sense an abrupt rising or
falling of the nose and automatically move the controls to correct
for it, was out of commission. On the climb to launch altitude, I had
quietly reported this fact to Q. C. Harvey. He in turn had consulted
with the SAS expert, Blake Staub. We tried a dozen different tricks,
switching electrical circuits, to correct it. But the yellow
malfunction light remained on steadily.
The decision to “go” or “no go” was entirely up to me. I had elected
to “go.” For our first low-speed glide test the pitch damper was not
vital. I had had much experience in dead-sticking airplanes without
the help of such a device. We simply could not cancel another flight.
More than a thousand eyes on the Edwards base were trained skyward
for this milestone in aviation history. There were one hundred
reporters, photographers, and TV cameramen camped along the edge of
the lake bed. If we failed again, the press would not be so patient
and generous this time. In brief, we were on the spot. But this was
just another time when the skill and training of a test pilot could
overcome the deficiency of a piece of machinery.
I was busy turning switches. I shut off the B-52 power source. The
X-15 was now operating on its own power generated by the APUs. I
shifted the oxygen supply to my helmet from B-52 to X-15. I armed the
ballistic charge in the lower ventral fin, which I would jettison
close to the ground just before touchdown. I started the data
instrumentation and cameras, which would operate throughout the glide
to earth. Finally I flashed a green light in Charlie Bock’s cockpit,
indicating I was ready to launch. I confirmed this fact orally:
“Ready when you are, buddy.”
“One minute to launch,” Bock replied calmly.
My right hand moved to the sidearm control handle, which I had
elected to use on this flight in place of the center stick, to show
there was no question in my mind that it was an improvement. I
cranked in one degree of nose-up-trim to make certain that when Bock
cut me loose, the X-15 would not dive too steeply. If I launched at
higher trim, it was possible the X-15 might hang momentarily beneath
the wing, bumping against the mating pylon or the B-52 engine pods.
Chase pilot Bob White, flying just off my wingtip, confirmed the trim
change by radio.
I waited, my eyes alternating between the gauges and the handle of
the clock. In the last few seconds, I prayed. My extremely sensitive
tape recorder picked up the movement of my vocal chords, but not the
words. I said: “God. Please help me make this a good one. Please
don’t let me let these people down.”
Bock called a brief countdown, unkeying his mike between each number
in case I wanted to break in and say “no drop.”
“Three” ... “Two” ... “One” ...
“DROP.”
Inside the streamlined pylon, a hydraulic ram disengaged the three
heavy shackles from the upper fuselage of the X-15. They were so
arranged that all released simultaneously, and if one failed they all
failed. The impact of the release was clearly audible in the X-15
cockpit. I heard a loud “kerchunk.”
The X-15 hung in its familiar place beneath the pylon for a split
second. Then the nose dipped sharply down and to the right more
rapidly than I anticipated. The B-52, so long my constant companion,
was gone. The X-15 and I were alone in the air and flying at 500
miles an hour. In less than five minutes I would be on the ground.
My flight plan called for me to make a huge “S” turn in the sky,
spiraling down toward Rogers Dry Lake. It was designed to provide me
with a wide margin for error. Should the glide calculations be wrong,
I could vary the S turn to correct the error and land where I wanted
to on the lake. The glide-path was laid out over an uninhabited area,
so the airplane was no hazard to the lives of people on the ground.
There was much to do in the first hundred seconds of flight. First
I had to get the “feel” of the airplane, to make certain it was
trimmed out for the landing just as any pilot trims an airplane after
take-off or in flight as passengers move about or when dwindling
fuel shifts the center of gravity. Then I had to pull the nose up,
with and without flaps, to feel out the stall characteristics, so
that I would know how she might behave at touchdown speeds. Her
characteristics had been calculated on machines, and of course I
had “flown” the simulator a thousand times or more, both at North
American and in the Navy’s Johnsville centrifuge. I had also made
many low L over D landings in the F-100 and F-104, with engine
idling, wheels down, and dive brakes extended. But these amounted,
all in all, only to an approximation of the real thing.
The real thing, as it developed immediately, wasn’t such a challenge.
Our engineering was sound. The X-15 is not the easiest airplane in
the world to fly, but she responded as we expected. Sensitive in
roll because of her shape, sensitive in pitch because of the damper
failure, but even as a heavy glider spirited to the touch of control,
responsive, and high-strung. Not designed to mush around at low
speeds, she still handled like a champion.
Falling down and to the right, I moved the sidearm control gently
to bring the X-15 to level flight. The response was remarkable. The
plane porpoised through a huge oscillation, hanging on its side. I
again moved the control arm gently. At 36,000 feet, after a drop of
1,400 feet, the tiger leveled out and the nose held steady.
I put the plane in a shallow dive. Having lost the momentum of the
launch, it slowed from 500 to 400 to 300 miles an hour. When I
pulled the nose up, the speed dropped even lower. I performed these
maneuvers with extreme care, tentatively, so as not to offend her
lest she bite back as so many others have and become unmanageable.
The three chase planes were having no difficulty in keeping up at
my ever-decreasing speed and altitude, and they hung in close. The
radio circuit was dead silent. Except for the roar of the ventilation
blowers, there was a tomb-like silence in the cockpit.
Now at about 30,000 feet and three minutes from touchdown, I
simulated a landing. I pushed the nose down sharply until my speed
had picked up to 300 miles an hour. I lowered the flaps. The nose
rose slightly, but the ship did not buffet as it did when we lowered
the flaps while mated to the B-52. Satisfied, I raised the flaps and
put the ship into a steep descending turn, aiming for the broad lake
bed. My altimeter unwound dizzily: from 24,000 to 13,000 feet in less
than forty seconds.
I knew that the men on the ground--Stormy, Feltz, Q.C., Sam, and the
others--were holding their breath, waiting in nearly indescribable
anguish for some word. My mind was too busy trying to learn about
this ship, planning for the touchdown, now less than a hundred
seconds away, to think of some way to put them at ease, tell them we
had a winner, and still not stick my now proud and cocky neck out.
What came out was this: “I’d like to try a roll,” the words Yeager
had uttered on his first X-1 flight.
Passing over the Edwards skeet range at about 6,000 feet, I touched
off the ballistic charge which blew off the ventral fin. It fell away
as predicted, and a small parachute deployed, lowering it gently to
the ground. Chase pilot White reported: “Ventral away.” The desert
was coming up fast. At 600 feet altitude I flared out.
I lined up for my approach, sighting along the three black strips
painted on the desert dry lake. Then, for the first time, I noticed
a peculiar distortion caused by the fact that I was looking through
three panes of glass: the helmet visor and the double-layer X-15
windshield. I knew the black lines on the lake bed were parallel.
From my position in the cockpit they now seemed to spread out in a
large V. It was not a serious matter, but one I had to adjust to
quickly. The distortion might affect my depth perception and cause a
rough touchdown.
In the next second without warning the nose of the X-15 pitched
up sharply. It was a maneuver that had not been predicted by the
computers, an uncharted area which the X-15 was designed to explore.
I was frankly caught off guard. Quickly I applied corrective elevator
control.
The nose came down sharply. But instead of leveling out, it tucked
down. I applied reverse control. The nose came up but much too far.
Now the nose was rising and falling like the bow of a skiff in a
heavy sea. Although I was putting in maximum control I could not
subdue the motions. The X-15 was porpoising wildly, sinking toward
the desert at 200 miles an hour. I would have to land at the bottom
of an oscillation, timed perfectly; otherwise, I knew, I would break
the bird. I lowered the flaps and gear.
My mind was almost completely absorbed in the tremendous task of
saving the X-15, of getting it on the ground in one piece. But I
could not push back a terrible thought that was forming. _Something
was dreadfully wrong. We had pulled a tremendous goof. The X-15 in
spite of all our sweat and study, our attempt at perfection, had
become completely unstable._ Somewhere along the line we or one of
our machines had made an unbelievable miscalculation. Four years of
work, ten million engineering man-hours, 120 million dollars, and our
machine from a stability standpoint was less satisfactory than the
man-killing X-2.
My speed dropped below 200 miles an hour. In the middle of a wild
oscillation I tried to grind the two rear skids into the lake bed.
But apparently the windshield confused me. I missed the ground by a
good four feet, pumping in more control as the nose started to rise
again. For minimum strain on the tail skids and nose wheel we had
calculated ideal X-15 landing speed to be 210 miles an hour. I was
already down to 170 miles an hour. The X-15 would soon not fly at all
and would fall toward the ground like a brick. In my mind’s eye I
could see the final picture: a big ball of Inconel X.
Now I was half a mile beyond my intended touchdown point and drifting
off to the right toward a rough spot on the lake. Instinctively I
pumped in a little left rudder control to get back on the marked
landing strip. With the next dip I had one last chance and flared
again to ease the descent. At that moment the rear skids caught on
the desert floor and the nose slammed over, cushioned by the nose
wheel. The X-15 skidded 5,000 feet across the lake, throwing up an
enormous rooster-tail of dust. The emergency helicopter swooshed down
and landed alongside the ship. A long caravan of emergency trucks
roared out from the sidelines. I sat in the cockpit, canopy still
closed, engulfed in disappointment.
* * * * *
“Stormy,” I said, “something is radically wrong.” Stormy had driven
out to the airplane and snatched me away before the press arrived. We
were tearing across the lake at seventy miles an hour in a company
car headed for Captain Richardson’s van. I had given Stormy a quick
run-down on the landing.
“That airplane _can’t_ be unstable,” Stormy said.
He was right, of course. I had jumped to the wrong conclusion. Others
did too, blaming the instability on the sidearm control. But these
critics were wrong. In the days following we carefully analyzed the
recorded data and found out what really happened.
The control system in the X-15 is quite similar to the power steering
in a car. The pilot makes a control motion, but hydraulic pressure
supplies the “muscle,” does the work, and moves the control surface,
just as the power boost in the car turns the wheels. This hydraulic
pressure operates the flight controls and the flaps.
Given limitless space and weight, it is no problem to design a
hydraulic system which can perform almost any job on the airplane,
and if necessary, all jobs simultaneously. However, the hydraulic
pump in the X-15, like all the other equipment, was a carefully
calculated compromise from the weight standpoint. It was not
limitless in power. It could not do everything at once; nor did it do
one assigned task fast enough.
One result was that when the pilot pumped in a motion on the stick,
the control surfaces were slow in responding. Years earlier I had
run up a warning flag in this area; in fact, I had _demanded_ a
faster control response. However, since it is pretty hard before
flight test for a pilot to support his opinions against simulators
and calculations, and because my demands meant more weight, we had
settled on low-control response, thinking we could live with it. This
had almost done us in.
When the X-15 nose pitched on landing, I had instantly applied
corrective control. The hydraulic “muscle,” then also working to
lower the flaps, fell behind and then overshot trying to catch up.
As a result, the controls were doing one thing and I another. In
an effort to regain control of the porpoising airplane, I pumped in
full up-and-down control, in effect chasing back and forth from one
extreme to the other, and by great luck or possibly intuition, struck
some kind of crude balance, bringing the ship safely to earth. Had
our bird been an unmanned missile, I’m certain it would have been
destroyed. But for future operations we knew the pilot couldn’t live
with that slow control response: the X-15 landing was difficult
enough. The pilot _had_ to have absolute and positive control of the
airplane.
By the simple expedient of adjusting a valve, to borrow power, in
effect, from other places in the ship, we increased the control rate
upward to more like my original request. Thereafter, we never again
experienced the porpoising motion, either in the air or at touchdown,
with center and sidearm control.
X-15 number one, which had been used on these five pioneering
flights, was pulled out of action so that the engineers could make
many minor fixes that were long overdue. We then turned to X-15
number two, the airplane designated for the first rocket-powered
flights.