bitterlyclingin
Silver Member
- Aug 4, 2011
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[The company I worked for 1962 -1966 in their R&D section specialized in manufacturing fuel pumps and fuel controls for helicopters and jet engines. The major departmental effort until the fuel pump for this aircraft landed in our laps was to find some means of countering the accelerated wear and premature failure the pumps and controls were experiencing due to fuel contamination acquired during transport and storage in Vietnam, including, but not limited to a trial of tungsten carbide pumping gears instead of the usual hardened steel.
The pump for this aircraft was a monstrous beast occupying roughly three times the volume of the normal jet engine fuel pump, and where the normal pump was housed inside aluminum castings, this one was three stainless steel castings large, sealed by means of soft metal seals crushed between the casting sections rather than the usual rubber o-rings. The qualification run took place over the Christmas / New Years holiday period to satisfy the engine makers requirement that the pump be able to run continuously for 14 days non stop without failure or having to be shut down for any reason while being alternately and continuously cycled between extreme high temperature and extreme low temperature running environments. Due to the constant non stop cycling between high and low temperatures the connections on the fuel lines gradually loosened so the test shed was filled with floor to ceiling flame for a majority of the qualification run. One of the members of the group noted, off hand, that after doing some rough calculations, it looked like the pump could theoretically shoot a stream of fuel one mile straight up into the air.]
"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."
SR-71 In-Flight Breakup
The pump for this aircraft was a monstrous beast occupying roughly three times the volume of the normal jet engine fuel pump, and where the normal pump was housed inside aluminum castings, this one was three stainless steel castings large, sealed by means of soft metal seals crushed between the casting sections rather than the usual rubber o-rings. The qualification run took place over the Christmas / New Years holiday period to satisfy the engine makers requirement that the pump be able to run continuously for 14 days non stop without failure or having to be shut down for any reason while being alternately and continuously cycled between extreme high temperature and extreme low temperature running environments. Due to the constant non stop cycling between high and low temperatures the connections on the fuel lines gradually loosened so the test shed was filled with floor to ceiling flame for a majority of the qualification run. One of the members of the group noted, off hand, that after doing some rough calculations, it looked like the pump could theoretically shoot a stream of fuel one mile straight up into the air.]
"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."
SR-71 In-Flight Breakup
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