SR-71 In-Flight Breakup

[Darrell]

Wow.

Subject: Test Pilot Bill Weaver tells about a Mach 3.18 in-flight breakup of an SR-71 Blackbird

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.

You can read the rest here:

http://www.barthworks.com/aviation/sr71breakup.htm

Found via Insty. Not sure the War Room is really the right place; mods, feel free to move if you think appropriate.

[Aesop]

I'm disappointed.

No mention whatsoever about how long it took afterwards for the flight surgeons to remove the seat cushion from being clenched all up his ass.

After that little incident, I'd suspect it may still be up there 40+ years later

[JustinR]

Wow. That is an amazing story.

[Netpackrat]

Holy shit.

[Greg]

Holy shit.

The ejection seat had never left the airplane.

[JustinR]

It was probably something along the lines of "tell the Congressman something to calm him down so he doesn't do or say something stupid."

[Jericho941]

Finally, my CDCs were actually good for something.

[308Mike]

I'd read of them losing a couple of birds due to "unstarts" when transiting certain speed zones and basically going from jet-engine powered flight to almost RAMJET (or whatever they called it at the time) flight, which is why they needed to continuously monitor the intake valve inlets and the front nacelles to monitor the supersonic shock-wave heading into the engines (which were fitted with bypass air chambers to facilitate the management of the incoming supersonic shock-wave), and on occasion they had one engine go through what they called an UNSTART (from Wikipedia):

In the early years of operation, the analog computers would not always keep up with rapidly changing flight environmental inputs. If internal pressures became too great and the spike was incorrectly positioned, the shock wave would suddenly blow out the front of the inlet, called an "Inlet Unstart." During an unstart, air flow through the engine compressor immediately stopped, thrust dropped, and exhaust gas temperatures rose. The remaining engine's asymmetrical thrust would cause the aircraft to yaw violently to one side. SAS, autopilot, and manual control inputs would fight the yawing, but often the extreme off-angle would reduce airflow in the opposite engine and stimulate "sympathetic stalls". This generated a rapid counter-yawing, often coupled with loud "banging" noises, and a rough ride during which crews' helmets would sometimes strike their cockpit canopies.[39] One response to a single unstart was unstarting both inlets to prevent yawing, then restarting them both.[40] Lockheed later installed an electronic control to detect unstart conditions and perform this reset action without pilot intervention.[41] Beginning in 1980, the analog inlet control system was replaced by a digital system, which reduced unstart instances.[42]

From what I recall/understand, we lost at least TWO (2) of our birds to violent UNSTARTS, which at the speed they were going and the EXTREME stresses involved in those instances were not recoverable and ultimately resulted in the destruction of those aircraft and the loss of the pilots (but I'm not sure if ALL those pilots died in the process, but I have a feeling MOST of them did - and that is quite sad, since those pilots were heroes pushing the envelope of speed and reconnaissance). We lost FOUR (4) crew members due to this EXTREMELY violent action, but after computers were introduced to monitor and manage the spikes and the potential for UNSTARTs, we didn't have any more losses of aircraft or crew members due to these UNSTART events).