Moments in History

Big Bad Blackbirds

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The alternate title for this post should probably be Bill Weaver: The Biggest Badass You Might Not Know. What most of you likely do know is that the SR-71 was a) awesome, and b) developed after/with the single-seat A-12. Mr. Weaver’s tale harkens back to the early days of testing and wringing out the kinks of the SR-71. I don’t want to retell the entire tale, just wet your whistle and send you over to read for yourself, but let me assure you, the whole story is definitely worth reading!

The flight in question, which Weaver calls his “most memorable”, occurred on Jan. 25, 1966, and along with him was Jim Zwayer, who was a Lockheed flight test reconnaissance and navigation systems specialist. Those recon and nav systems were one test focus, and the other bits of beta testing were “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, which reduced the Blackbird’s longitudinal stability.” Reducing stability usually doesn’t sound like a good idea, but it can offer performance enhancements in certain flight regimes, much like having a racecar drive “loose” can make a car a faster on a given track.

After in-flight refuelling for the second leg of their flight, and accelerating to Mach 3.18, they initiated a 35 degree banked right turn. It was at this point they experienced a benign sounding “inlet unstart”. That unstart was actually a bit of a big deal. In Weaver’s words, “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 air flow 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.”

What if the aircraft was in a relatively hard right turn and the right engine unstart did not clear? Here is your teaser: “AS FULL AWARENESS took hold, I realized I was not dead, but had somehow separated from the airplane.” Got you curious to read the rest? Hit the jump and follow the link, plus bonus SR-71 links!!

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Read the full story here, with its somewhat understated title: Bill Weaver Mach 3+ Blackbird Breakup.

Plus, because I know many of you have a mildly inappropriate love for the Blackbird, here are some of the copious quality posts previously done here on AT:

Can’t See It, Can’t Catch It: The CIA’s OXCART Dart.

Making OXCART.

Project TAGBOARD.

SR-71 Cockpit Checkout.

Flame Shockwaves.

And, because you all no doubt not only enjoy the Blackbird, but also want to accomplish nothing this week, here are some rabbit hole links to peruse:

Lockheed’s Creating the Blackbird, where I found this 1st flight video:

Swag made from engine parts, with historical video. The lead and engine spike diagram images are both from this site, mach3ti.

A former maintainer’s fan site.

Roadrunners Internationale.

And the Roadrunners News Blog, not updated that recently it doesn’t appear, but where I found this story.

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