Built for Speed - The SR-71 Blackbird

Notes from the Mini Museum: SR-71 Blackbird Specimen

"Nothing had prepared me to fly that fast... My God, even now, I get goose bumps remembering."

Air Force Colonel Jim Wadkins

Posted September 18th, 2017

The SR-71 was built for speed and stealth. Setting records as the world's fastest manned aircraft, the SR-71 easily cruised at more than three times the speed of sound. The spy plane was also the highest-flying manned aircraft, soaring to over 85K feet (26K meters). Development of this incredible aircraft required rethinking every aspect of aeronautical design. In fact, an entire industry grew up around the program as nearly every component was custom made, from the titanium alloy skin to the fuel the huge engines consumed.

The Blackbird program got off the ground in 1957 when the US Central Intelligence Agency commissioned the development of an undetectable aircraft capable of high altitude, high speed reconnaissance. The agency turned to Lockheed's "Skunk Works" operation and aeronautical engineering legend Clarence Leonard "Kelly" Johnson.

Clarence Leonard 'Kelly' Johnson (1910-1990) - A lifetime of service and innovation. Pictured: the Model 10 Electra, with Amelia Earhart, in the cockpit of the P-38 Lightning, and later in life with the SR-71 Blackbird.

For decades, Johnson helped develop some of the most important aircraft in US Air Force history, including such diverse craft as the P-38 Lightning and the U-2 Spy Plane. The Blackbird would be Johnson's penultimate aircraft, surpassing all previous engineering efforts and establishing a technology platform that still holds every record it set, even more than 50 years after its maiden flight.

The video below is a tribute piece to Kelly Johnson by Cameraman Devin Hawker and produced by Lockheed Motion Media, a division of Lockheed-Martin. The short piece was distributed with Lockheed's 1987 film about the SR-71 called Blackbird.

The first official Blackbird test flight occurred on April 30th, 1962. This model, the A-12, was a smaller, single seat version of what would become the SR-71. The test took place at the secretive Groom Lake, Nevada Air Force base also known as Area-51. The first SR-71 flight took place less than two years later on December 22, 1964.

Though many mission records about the Blackbird have been declassified, the full extent of the Blackbird's operations is unknown. What is known is that in 35 years not a single SR-71 was lost to hostile actions. For enemy fighters, the aircraft was simply too fast and flew too high. For surface to air missiles, the radar signature of the SR-71 was too small to be detected until it was too late to react.

For those lucky few who were able to fly the SR-71, the experience turned out to be something also quasi-religious. That sense of reverence also extended to those who faced the SR-71 as an enemy aircraft. Viktor Belenko, the soviet MiG pilot who defected to Japan in 1976 wrote, "They taunted and toyed with the MiG-25s sent up to intercept them, scooting up to altitudes we could not reach, and circling leisurely above them or dashing off at speeds we could not match."

When you see a picture like the one above of Major Brian Shul, you get a sense of just how different the SR-71 was from other aircraft. Major Shul is the author of Sled Driver:Flying the World's Fastest Jet, a book which is sadly out of print. However, you can hear Major Shul talk about the fascinating experience of flying in this aircraft in this talk he gave at Lawrence Livermore National Laboratory in November of 2016. The talk is just over an hour long and filled with incredible images and stories:

In 1989, despite the continued superiority of the platform, the SR-71 program was slated for retirement. It's generally believed that politics were at the root of the retirement since the SR-71 remained the fastest plane in the sky by a wide margin and its reconnaissance capabilities were still needed. For nearly a decade, opponents and proponents of the SR-71 wrestled with the issue, reactivating the program in the mid-90s and then permanently retiring the craft in 1998. The final SR-71 mission occurred on October 9th, 1999. During the delivery flight from Los Angeles, the aircraft flew coast to coast in just 67 minutes.

Officially, there is no known replacement for the SR-71, though most capabilities have been replaced by satellites and unmanned aerial vehicles (UAV).

Creating the Specimen

The specimen in the Mini Museum is a fragment of a "turkey feather" from SR-71 61-7972. It was purchased from Daniel Freeman, Supervisor and Chief of Metals Technology for the 9th Reconnaissance Wing I. During his time with the USAF, Daniel worked on an amazing range of aircraft including the SR-71, U2, A-10, and B-52G just to name a few. His dedication to sharing this mission-flown material is very inspiring and his guidance was invaluable. SR-71 61-7972 was retired in 1990 and is currently on display in the Smithsonian's Air & Space collection at the Udvar-Hazy Center just outside Washington, D.C.

The turkey feathers are overlapping flaps which surrounded the exhaust of the SR-71. Opening and closing according to the pressure output of the afterburner, they are considered one of the hardest working parts of the aircraft.

SR-71 Turkey Feather

Cutting the titanium alloy was one of the biggest challenges with this specimen. R.R. Boyer's study "The use of β titanium alloys in the aerospace industry" mentions that the alloy B120VCA, which is used in 93% of the SR-71, can be difficult to work with. Daniel Freeman, who supplied the SR-71 material, explained that there were at least three (3) different types of titanium alloy used on the SR-71's:

The type used on the wing skins is the B120 but the type used on the turkey feathers is "A110AT Titanium". It is also called "Grade 6 Titanium". The specific alloy content is: 5% aluminum and 2.5% tin. It is also known as Ti-5Al-2.5Sn. This alloy is used in airframes and jet engines due to its good weldability, stability and strength at elevated temperatures.

SR-71 Technical Repair Manual. (source: Daniel Freeman, Supervisor and Chief of Metals Technology for the 9th Reconnaissance Wing I)

Daniel also provided the reference page from the technical data manual above. We added a dark red highlight to show the portion of the turkey feather used in the Mini Museum along side and included an image of the actual part itself.

Large Shear and Special Jig

To make our first cuts we used our largest bench shear to make even strips. We built a special jig with clamps to hold the turkey feather in place while cutting.

Completed SR-71 Strips

Given the limited amount of material, it was important to maintain a consistency in the width of each strip. Even a millimeter off can cause a problem over many thousands of cuts.

Smaller Shear with Guide

With strips in hand, we used our smaller shear to carefully cut isometric triangles. The guide shown above is used to make sure we are cutting at a precise angle. The blade of the shear is only 4 inches long (100mm), so it seems quite large in comparison with the titanium strip. It's very close work. Care and patience are required with each cut.

Mini Museum Helper Jamie replacing and adjusting the blade

It should also come as no surprise that we ended up going through several blades during this process.

Completed SR-71 Specimens

Again, as with every specimen in the Mini Museum, we repeat processes thousands and thousands of times. Small errors can sometimes be difficult to detect but they add up over time. So even with the guide, it is important to have another set of eyes inspect the final specimens.

As you might expect, it's really difficult to wrap up this specimen. There are just so many stories about the aircraft, the program, and the people involved in the creation and operation of this one-of-a-kind aircraft. So here at the end of this post, I'd like to recommend you continue the journey with The Complete Book of the SR-71 Blackbird by Colonel Richard H. Graham. We have quite a few books in the Mini Museum library, but I have to say that this is one of the finest in the collection. Not only has Colonel Graham shared the technical details of this magnificent aircraft but he's managed to fold in the behind-the-scenes history of one of the most complex and tense periods of modern history.

Now, it’s back to work!

Hans Fex, Creator and Chief Curator for the Mini Museum

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