1974: On a flight to the Farnborough Air Show outside London, Maj. James Sullivan and Maj. Noel Widdifield fly the Lockheed SR-71 Blackbird from New York to London in 1 hour, 54 minutes, 56.4 seconds. The 1,806-mph flight still holds the transatlantic speed record between the two cities.

Developed during the middle of the cold war, the Lockheed SR-71 was designed as a reconnaissance aircraft that could fly fast enough to avoid being shot down by Russian aircraft or missiles. Initially developed as the A-12 for the CIA, the aircraft evolved and adapted many times in its more than 30 years of flying.

Designed by the legendary Kelly Johnson and his Lockheed Skunk Works team, the SR-71 was designed to fly at more than three times the speed of sound. There were a number of design challenges the Skunk Works team faced as the realities of such high speed flight were realized.

Beyond the obvious sleek aerodynamics needed, one of the biggest challenges was developing an engine that could fly at such speeds. Rocket-powered aircraft such as the North American X-15 had flown faster than the SR-71, but a rocket engine doesn’t need to worry about ingesting air, mixing it with fuel and then igniting the mixture to create thrust.

The challenge of an air-breathing jet engine is the air must be traveling slower than Mach 1 ( the speed of sound), when it enters the engine. Other supersonic jets use relatively simple inlets to the jet engine, to slow down the air so the shock wave created by supersonic flowing air doesn’t get to the engine.

If supersonic air does reach a jet engine, the result is known as an “unstart,” and the engine stalls and needs to be restarted during flight. This could be a problem if you were flying over the Soviet Union trying to stay ahead of fighter jets chasing you.

Because of the speeds flown by the SR-71, a much-more-complex inlet was needed to control the airflow into the massive jet engines over a range of speeds. The spike-shaped cone located at the front of the air inlet could be moved back and forth to control where the supersonic shock wave would enter the engine.

By carefully monitoring the aircraft speed, atmospheric conditions and engine parameters, the pilot could adjust the spike along with a series of doors located along the outer walls of the inlet. By doing this, a shock wave could actually be positioned in such a way that it would act as a speed bump of sorts and slow down the incoming air to Mach 0.6, the ideal speed for air to enter the jet engine.

The result was air would enter the inlet at approximately 2,100 mph, and within 20 feet, it would slow down to a speed of 600 mph. Of course this didn’t always go according to plan, and unstarts still happened in the SR-71. Pilots describe the unpleasant event as a violent jerk to the side of the stalled engine and continued shaking and unwelcome noises until the engine could be restarted.

The result of all of this complex air-inlet management was an engine that could push the SR-71 faster than any other jet aircraft. The official top speed was Mach 3.2, though occasionally pilots inadvertently flew as fast as Mach 3.5. Typical speeds during a mission would be around Mach 3.0.

For the New York–to–London flight, Sullivan flew the SR-71 through an imaginary gate 80,000 feet above New York. Heading east, he flew 3,461.528 miles until passing through another imaginary gate over London. The the trip lasted only 1 hour, 54 minutes, 56.4 seconds.

By comparison the Concorde typically flew from New York to London in around three hours, and a 747 makes the trip in about six hours. Of course the SR-71 did get a bit of a running start, but it also had to slow down over the Atlantic to refuel behind a special Boeing KC-135Q tanker.

After the end of the Farnborough Air Show where the SR-71 was on display outside the United States for the first time, it set another record on the way home. This time the spy plane flew from London to Los Angeles, a distance of 5,446.87 miles in just 3 hours, 47 minutes, 39 seconds. That flight required two refueling slowdowns as well as other speed zones when flying over major U.S. cities.

An SR-71 also set the coast-to-coast record when it flew from Los Angeles to Washington, D.C., in 64 minutes, 20 seconds in 1990.

The last flight of the SR-71 took place Oct. 9, 1999.

Source: Flying the SR-71 Blackbird, by retired Col. Richard H. Graham, U.S. Air Force; others

Photo: Lockheed Martin

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