Acceleration and flight

How acceleration made the SR-71 the greatest spy plane ever

By Smithsonian's National Air and Space Museum

SR-71 Blackbird SR-71 TakeoffSmithsonian's National Air and Space Museum

Acceleration is understood to be any change in an object’s velocity and was first defined by Issac Newton in his Second Law of Motion. It’s something we intuitively understand as we move every day, but it becomes crucial when attempting to design the fastest jet-propelled airplane ever.

Lockheed SR-71 Blackbird Landing at Dulles (1964)Smithsonian's National Air and Space Museum

The U.S. Air Force SR-71 or “Blackbird”, designed in 1964, still holds the record as the fastest ever piloted jet aircraft. It could cruise at over three times the speed of sound, the equivalent of 2,100 mph (3,380 km/h). 

Lockheed SR-71 BlackbirdSmithsonian's National Air and Space Museum

The Blackbird had two specially designed Pratt and Whitney J-58 turbojet engines that were capable of creating enough thrust to accelerate the plane to its cruise speed of Mach 3.2. To reach these record speeds, designers found an innovation that has never been replicated.

SR-71 Blackbird SR-71 BlackbirdSmithsonian's National Air and Space Museum

The key to the Blackbird’s record speeds were its cone-shaped turbojet engine air inlets. These adjustable cones optimized the flow of air into the engines allowing it to create 32,500 pounds of thrust. 

SR-71 Blackbird SR-71 BlackbirdSmithsonian's National Air and Space Museum

The Blackbirds fast speeds and high-altitude ability, along with its low radar shape made it the perfect spy plane. The U.S. Air Force’s fleet of SR-71 flew hundreds of missions over 20 years during the Cold War, making a vital contribution to US foreign policy.

Kelly Johnson with BlackbirdOriginal Source: National Air and Space Museum Archives, Smithsonian Institution

It was the Blackbird’s extraordinary acceleration that made it such an effective spy plane. If a missile was launched at it, the pilot simply accelerated and flew faster than the anti-aircraft missile. During its active life, no SR-71 was ever shot down.

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