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Subject: Mach 3. 18 In-Flight Breakup Of An SR-71 Blackbird
Date: Sunday, December 24, 2006 6:50 AM
Mach 3. 18 In-Flight Breakup Of An SR-71 Blackbird
by Bill Weaver, Chief Test Pilot, Lockheed
Among professional aviators, there's a well-worn saying: Flying is
simply hours of boredom punctuated by moments of stark terror. But I
don't recall too many periods of boredom during my 30-year career with
Lockheed, most of which was spent as a test pilot. By far, the most
memorable flight occurred on Jan. 25, 1966.
Jim Zwayer, a Lockheed flight-test specialist, and I were evaluating
systems on an SR-71 Blackbird test from Edwards. We also were
investigating procedures designed to reduce trim drag and improve
high-Mach cruise performance The latter involved flying with the
center-of-gravity (CG) located further aft than normal, reducing the
Blackbird's longitudinal stability.
We took off from Edwards at 11:20 a. m. and completed the mission's first
leg without incident. After refueling from a KC-135 tanker, we turned
eastbound, accelerated to a Mach 3. 2 cruise speed and climbed to 78,000
ft. , our initial cruise-climb altitude.
Several minutes into cruise, the right engine inlet's automatic control
system malfunctioned, requiring a switch to manual control. The SR-71's
inlet configuration was automatically adjusted during supersonic flight
to decelerate airflow in the duct, slowing it to subsonic speed before
reaching the engine's face. This was accomplished by the inlet's
center-body spike translating aft, and by modulating the inlet's forward
bypass doors.
Normally, these actions were scheduled automatically as a function of
Mach number, positioning the normal shock wave (where air flow becomes
subsonic) inside the inlet to ensure optimum engine performance. Without
proper scheduling, disturbances inside the inlet could result in the
shock wave being expelled forward- a phenomenon known as an "inlet unstart. "
That causes an instantaneous loss of engine thrust, explosive banging
noises and violent yawing of the aircraft, like being in a train wreck.
Unstarts were not uncommon at that time in the SR-71's development, but
a properly functioning system would recapture the shock wave and restore
normal operation.
On the planned test profile, we entered a programmed 35-deg. bank turn
to the right. An immediate unstart occurred on the right engine, forcing
the aircraft to roll further right and start to pitch up. I jammed the
control stick as far left and forward as it would go. No response. I
instantly knew we were in for a wild ride. I attempted to tell Jim what
was happening and to stay with the airplane until we reached a lower
speed and altitude. I didn't think the chances of surviving an ejection
at Mach 3. 18 and 78,800 ft. were very good. However, g-forces built up
so rapidly that my words came out garbled and unintelligible, as
confirmed later by the cockpit voice recorder.
The cumulative effects of system malfunctions, reduced longitudinal
stability, increased angle-of-attack in the turn, supersonic speed, high
altitude and other factors imposed forces on the airframe that exceeded
flight control authority and the stability augmentation system's ability
to restore control.
Everything seemed to unfold in slow motion. I learned later the time
from event onset to catastrophic departure from controlled flight was
only 2-3 seconds. Still trying to communicate with Jim, I blacked out,
succumbing to extremely high g-forces.
Then the SR-71 literally disintegrated around us. From that point, I was
just along for the ride. And my next recollection was a hazy thought
that I was having a bad dream. Maybe I'll wake up and get out of this
mess, I mused. Gradually regaining consciousness, I realized this was no
dream; it had really happened. That also was disturbing, because I COULD
NOT HAVE SURVIVED what had just happened.
I must be dead. Since I didn't feel bad- just a detached sense of
euphoria- I decided being dead wasn't so bad after all. As full
awareness took hold, I realized I was not dead. But somehow I had
separated from the airplane.
I had no idea how this could have happened; I hadn't initiated an
ejection. The sound of rushing air and what sounded like straps flapping
in the wind confirmed I was falling, but I couldn't see anything. My
pressure suit's face plate had frozen over and I was staring at a layer
of ice.
The pressure suit was inflated, so I knew an emergency oxygen cylinder
in the seat kit attached to my parachute harness was functioning. It not
only supplied breathing oxygen, but also pressurized the suit,
preventing my blood from boiling at extremely high altitudes. I didn't
appreciate it at the time, but the suit's pressurization had also
provided physical protection from intense buffeting and g-forces. That
inflated suit had become my own escape capsule
My next concern was about stability and tumbling. Air density at hi gh
altitude is insufficient to resist a body's tumbling motions, and
centrifugal forces high enough to cause physical injury could develop
quickly. For that reason, the SR-71's parachute system was designed to
automatically deploy a small-diameter stabilizing chute shortly after
ejection and seat separation. Since I had not intentionally activated
the ejection system--and assuming all automatic functions depended on a
proper ejection sequence--it occurred to me the stabilizing chute may
not have deployed.
However, I quickly determined I was falling vertically and not tumbling.
The little chute must h ave deployed and was doing its job. Next
concern: the main parachute, which was designed to open automatically at
15,000 ft. Again I had no assurance the automatic-opening function would
work.
I couldn't ascertain my altitude because I still couldn't see through
the iced-up faceplate. There was no way to know how long I had been
blacked-out or how far I had fallen. I felt for the manual-activation
D-ring on my chute harness, but with the suit inflated and my hands
numbed by cold, I couldn't locate it. I decided I'd better open the
faceplate, try to estimate my height above the ground, then locate that
"D" ring. Just as I reached for the faceplate, I felt the reassuring
sudden deceleration of main-chute deployment.
I raised the frozen faceplate and discovered its uplatch was broken.
Using one hand to hold that plate up, I saw I was descending through a
clear, winter sky with unlimited visibility. I was greatly relieved to
see Jim's parachute coming down about a quarter of a mile away. I didn't
think either of us could have survived the aircraft's breakup, so seeing
Jim had also escaped lifted my spirits incredibly.
I could also see burning wreckage on the ground a few miles from where
we would land. The terrain didn't look at all inviting--a desolate, high
plateau dotted with patches of snow and no signs of habitation.
I tried to rotate the parachute and look in other directions. But with
one hand devoted to keeping the face plate up and both hands numb from
high-altitude, subfreezing temperatures, I couldn't manipulate the
risers enough to turn. Before the breakup, we'd started a turn in the
New Mexico-Colorado-Oklahoma-Texas border region. The SR-71 had a
turning radius of about 100 miles at that speed and altitude, so I
wasn't even sure what state we were going to land in. But, because it
was about 3:00 p. m. , I was certain we would be spending the night out here.
At about 300 ft. above the ground, I yanked the seat kit's release
handle and made sure it was still tied to me by a long lanyard.
Releasing the heavy kit ensured I wouldn't land with it attached to my
derriere, which could break a leg or cause other injuries. I then tried
to recall what survival items were in that kit, as well as techniques I
had been taught in survival training.
Looking down, I was startled to see a fairly large animal- perhaps an
antelope- directly under me. Evidently, it was just as startled as I was
because it literally took off in a cloud of dust.
(continued)
Subject: Mach 3. 18 In-Flight Breakup Of An SR-71 Blackbird
Date: Sunday, December 24, 2006 6:50 AM
Mach 3. 18 In-Flight Breakup Of An SR-71 Blackbird
by Bill Weaver, Chief Test Pilot, Lockheed
Among professional aviators, there's a well-worn saying: Flying is
simply hours of boredom punctuated by moments of stark terror. But I
don't recall too many periods of boredom during my 30-year career with
Lockheed, most of which was spent as a test pilot. By far, the most
memorable flight occurred on Jan. 25, 1966.
Jim Zwayer, a Lockheed flight-test specialist, and I were evaluating
systems on an SR-71 Blackbird test from Edwards. We also were
investigating procedures designed to reduce trim drag and improve
high-Mach cruise performance The latter involved flying with the
center-of-gravity (CG) located further aft than normal, reducing the
Blackbird's longitudinal stability.
We took off from Edwards at 11:20 a. m. and completed the mission's first
leg without incident. After refueling from a KC-135 tanker, we turned
eastbound, accelerated to a Mach 3. 2 cruise speed and climbed to 78,000
ft. , our initial cruise-climb altitude.
Several minutes into cruise, the right engine inlet's automatic control
system malfunctioned, requiring a switch to manual control. The SR-71's
inlet configuration was automatically adjusted during supersonic flight
to decelerate airflow in the duct, slowing it to subsonic speed before
reaching the engine's face. This was accomplished by the inlet's
center-body spike translating aft, and by modulating the inlet's forward
bypass doors.
Normally, these actions were scheduled automatically as a function of
Mach number, positioning the normal shock wave (where air flow becomes
subsonic) inside the inlet to ensure optimum engine performance. Without
proper scheduling, disturbances inside the inlet could result in the
shock wave being expelled forward- a phenomenon known as an "inlet unstart. "
That causes an instantaneous loss of engine thrust, explosive banging
noises and violent yawing of the aircraft, like being in a train wreck.
Unstarts were not uncommon at that time in the SR-71's development, but
a properly functioning system would recapture the shock wave and restore
normal operation.
On the planned test profile, we entered a programmed 35-deg. bank turn
to the right. An immediate unstart occurred on the right engine, forcing
the aircraft to roll further right and start to pitch up. I jammed the
control stick as far left and forward as it would go. No response. I
instantly knew we were in for a wild ride. I attempted to tell Jim what
was happening and to stay with the airplane until we reached a lower
speed and altitude. I didn't think the chances of surviving an ejection
at Mach 3. 18 and 78,800 ft. were very good. However, g-forces built up
so rapidly that my words came out garbled and unintelligible, as
confirmed later by the cockpit voice recorder.
The cumulative effects of system malfunctions, reduced longitudinal
stability, increased angle-of-attack in the turn, supersonic speed, high
altitude and other factors imposed forces on the airframe that exceeded
flight control authority and the stability augmentation system's ability
to restore control.
Everything seemed to unfold in slow motion. I learned later the time
from event onset to catastrophic departure from controlled flight was
only 2-3 seconds. Still trying to communicate with Jim, I blacked out,
succumbing to extremely high g-forces.
Then the SR-71 literally disintegrated around us. From that point, I was
just along for the ride. And my next recollection was a hazy thought
that I was having a bad dream. Maybe I'll wake up and get out of this
mess, I mused. Gradually regaining consciousness, I realized this was no
dream; it had really happened. That also was disturbing, because I COULD
NOT HAVE SURVIVED what had just happened.
I must be dead. Since I didn't feel bad- just a detached sense of
euphoria- I decided being dead wasn't so bad after all. As full
awareness took hold, I realized I was not dead. But somehow I had
separated from the airplane.
I had no idea how this could have happened; I hadn't initiated an
ejection. The sound of rushing air and what sounded like straps flapping
in the wind confirmed I was falling, but I couldn't see anything. My
pressure suit's face plate had frozen over and I was staring at a layer
of ice.
The pressure suit was inflated, so I knew an emergency oxygen cylinder
in the seat kit attached to my parachute harness was functioning. It not
only supplied breathing oxygen, but also pressurized the suit,
preventing my blood from boiling at extremely high altitudes. I didn't
appreciate it at the time, but the suit's pressurization had also
provided physical protection from intense buffeting and g-forces. That
inflated suit had become my own escape capsule
My next concern was about stability and tumbling. Air density at hi gh
altitude is insufficient to resist a body's tumbling motions, and
centrifugal forces high enough to cause physical injury could develop
quickly. For that reason, the SR-71's parachute system was designed to
automatically deploy a small-diameter stabilizing chute shortly after
ejection and seat separation. Since I had not intentionally activated
the ejection system--and assuming all automatic functions depended on a
proper ejection sequence--it occurred to me the stabilizing chute may
not have deployed.
However, I quickly determined I was falling vertically and not tumbling.
The little chute must h ave deployed and was doing its job. Next
concern: the main parachute, which was designed to open automatically at
15,000 ft. Again I had no assurance the automatic-opening function would
work.
I couldn't ascertain my altitude because I still couldn't see through
the iced-up faceplate. There was no way to know how long I had been
blacked-out or how far I had fallen. I felt for the manual-activation
D-ring on my chute harness, but with the suit inflated and my hands
numbed by cold, I couldn't locate it. I decided I'd better open the
faceplate, try to estimate my height above the ground, then locate that
"D" ring. Just as I reached for the faceplate, I felt the reassuring
sudden deceleration of main-chute deployment.
I raised the frozen faceplate and discovered its uplatch was broken.
Using one hand to hold that plate up, I saw I was descending through a
clear, winter sky with unlimited visibility. I was greatly relieved to
see Jim's parachute coming down about a quarter of a mile away. I didn't
think either of us could have survived the aircraft's breakup, so seeing
Jim had also escaped lifted my spirits incredibly.
I could also see burning wreckage on the ground a few miles from where
we would land. The terrain didn't look at all inviting--a desolate, high
plateau dotted with patches of snow and no signs of habitation.
I tried to rotate the parachute and look in other directions. But with
one hand devoted to keeping the face plate up and both hands numb from
high-altitude, subfreezing temperatures, I couldn't manipulate the
risers enough to turn. Before the breakup, we'd started a turn in the
New Mexico-Colorado-Oklahoma-Texas border region. The SR-71 had a
turning radius of about 100 miles at that speed and altitude, so I
wasn't even sure what state we were going to land in. But, because it
was about 3:00 p. m. , I was certain we would be spending the night out here.
At about 300 ft. above the ground, I yanked the seat kit's release
handle and made sure it was still tied to me by a long lanyard.
Releasing the heavy kit ensured I wouldn't land with it attached to my
derriere, which could break a leg or cause other injuries. I then tried
to recall what survival items were in that kit, as well as techniques I
had been taught in survival training.
Looking down, I was startled to see a fairly large animal- perhaps an
antelope- directly under me. Evidently, it was just as startled as I was
because it literally took off in a cloud of dust.
(continued)
