Coronet_Arch
Well-Known Member
How were the engines started on the SR-71 spy plane? Was it an electric starter like a car?
Starting the Pratt & Whitney J58 engines for the SR-71 Blackbird was a lot of fun, especially in the early days. It was a bit more complex than an electric starter on car, but not too far off. Some of the early starting fluid was over the top, but that is another story. The J58 engines each weighed about 6,000 pounds, had a 9-stage axial flow compressor, and a lot of secret stuff that enabled the SR-71 to fly at Mach 3.3.
An engineer figured they would need about 3500 RPM and at least 800 pounds of torque to start the engine. One of the fabricators grinned and said, “my Buick Wildcat has at least half of what you need. I bet if we put two engines together, we can start those engines easily.”
Buick Wildcat Nailhead Engine
The engineer said, “Make it so.” Two Buick 401 V8 engines arrived in crates. A welder and a few fabricators with a vision went to work. The AG-330 “Start Cart” was produced.
One AG-330 could be used for each SR-71 engine. If those engines were brought to life at the same time, it was almost indescribable. Early on, there were no mufflers on the Buick engines. As the RPM increased, a long stream of flames burst forth from the start cart. It sounded like a drag strip with those four Buick V8s stretching their muscles. As the Blackbird came to life, the ground shook with anticipation of the launch.
Years later, the big-block Chevy 454 became available and replaced the aging Buick Nailhead engines. The Chevy 454s were a lot of fun, especially with headers. As technology advanced, the college boys came up with a quieter, pneumatic starting system. Although the new system worked great, it wasn’t nearly as fun as those V8 engines.
BUICK ENGINES AND THE STARTUP PROCESS:
The two Buick engines were mounted tandem side by side with automatic transmissions. They were paired together with a steel woven drive belt to drive a vertical shaft that was inserted into the starter mechanism on the bottom of the SR-71's engine to spin it to 3200 RPM.
The pilot said to the Crew Chief via intercom "Engage Buicks.” The Buick operator activated the "Jet Start" and began to move the Buick throttle downward engaging the transmissions. One lever ran both engines. The "Transmissions Shifted" indicator illuminated green, and the Buicks started to torque the J58. The Buick operator had to be careful not to apply too much initial torque to the J58 as it spooled up. Too much torque would cause the probe to drop out. The probe was needed to prevent damaging the gearbox.
If the probe fell out, the Crew Chief would tell the pilot “Cut off throttle” which would delay the starting process. There was also a danger when the Buick disengaged while the J58 engine was unable to sustain itself during the start. There was a high risk of overheating. The probe was not able to be re-inserted to a spinning engine, but it was imperative to quickly re-insert it and blow out any fire. In short, too little torque during the Buick start process caused overheating and too much torque damaged the gearbox. It had to be just right.
The pilot would watch his gauges to determine minimum oil pressure, fuel pressure, and rising RPM. The pilot would then set the jet throttle to idle. At this point, 30cc of TEB was injected into the burner cans. A green flame was emitted, the J58 lit, and then accelerated and started to run on its own. As it accelerated, it unloaded the Buicks. At 3200 RPM, the pilot said, "Buicks out" and the Crew Chief signaled "Cut." The Buick operator hit "Cart Shutdown" and the probe dropped free as the cart throttle automatically returned to idle.
On a few occasions, if the J58 began to spool up before the Buicks were disengaged, the J58 would easily spin the Buicks beyond their redline resulting in at least one connecting rod ejecting through the Buick block causing a lot of oil on the airstrip.
Starting the Pratt & Whitney J58 engines for the SR-71 Blackbird was a lot of fun, especially in the early days. It was a bit more complex than an electric starter on car, but not too far off. Some of the early starting fluid was over the top, but that is another story. The J58 engines each weighed about 6,000 pounds, had a 9-stage axial flow compressor, and a lot of secret stuff that enabled the SR-71 to fly at Mach 3.3.
An engineer figured they would need about 3500 RPM and at least 800 pounds of torque to start the engine. One of the fabricators grinned and said, “my Buick Wildcat has at least half of what you need. I bet if we put two engines together, we can start those engines easily.”
Buick Wildcat Nailhead Engine
The engineer said, “Make it so.” Two Buick 401 V8 engines arrived in crates. A welder and a few fabricators with a vision went to work. The AG-330 “Start Cart” was produced.
One AG-330 could be used for each SR-71 engine. If those engines were brought to life at the same time, it was almost indescribable. Early on, there were no mufflers on the Buick engines. As the RPM increased, a long stream of flames burst forth from the start cart. It sounded like a drag strip with those four Buick V8s stretching their muscles. As the Blackbird came to life, the ground shook with anticipation of the launch.
Years later, the big-block Chevy 454 became available and replaced the aging Buick Nailhead engines. The Chevy 454s were a lot of fun, especially with headers. As technology advanced, the college boys came up with a quieter, pneumatic starting system. Although the new system worked great, it wasn’t nearly as fun as those V8 engines.
BUICK ENGINES AND THE STARTUP PROCESS:
The two Buick engines were mounted tandem side by side with automatic transmissions. They were paired together with a steel woven drive belt to drive a vertical shaft that was inserted into the starter mechanism on the bottom of the SR-71's engine to spin it to 3200 RPM.
The pilot said to the Crew Chief via intercom "Engage Buicks.” The Buick operator activated the "Jet Start" and began to move the Buick throttle downward engaging the transmissions. One lever ran both engines. The "Transmissions Shifted" indicator illuminated green, and the Buicks started to torque the J58. The Buick operator had to be careful not to apply too much initial torque to the J58 as it spooled up. Too much torque would cause the probe to drop out. The probe was needed to prevent damaging the gearbox.
If the probe fell out, the Crew Chief would tell the pilot “Cut off throttle” which would delay the starting process. There was also a danger when the Buick disengaged while the J58 engine was unable to sustain itself during the start. There was a high risk of overheating. The probe was not able to be re-inserted to a spinning engine, but it was imperative to quickly re-insert it and blow out any fire. In short, too little torque during the Buick start process caused overheating and too much torque damaged the gearbox. It had to be just right.
The pilot would watch his gauges to determine minimum oil pressure, fuel pressure, and rising RPM. The pilot would then set the jet throttle to idle. At this point, 30cc of TEB was injected into the burner cans. A green flame was emitted, the J58 lit, and then accelerated and started to run on its own. As it accelerated, it unloaded the Buicks. At 3200 RPM, the pilot said, "Buicks out" and the Crew Chief signaled "Cut." The Buick operator hit "Cart Shutdown" and the probe dropped free as the cart throttle automatically returned to idle.
On a few occasions, if the J58 began to spool up before the Buicks were disengaged, the J58 would easily spin the Buicks beyond their redline resulting in at least one connecting rod ejecting through the Buick block causing a lot of oil on the airstrip.
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