Saturday, December 13, 2014

Iconic Planes: SR-71 Blackbird

This post will cover the Boeing Sr-71 Blackbird, the fastest non-rocket-powered manned aircraft in the world and the highest flying in the world. This plane was so fast that it could actually outrace surface-to-air missiles. It is one of the few planes in the world which can go to Mach 3.

The Sr-71 was designed by Boeing as a reconnaissance aircraft which could quickly get in and out of enemy territory and could fly high enough to avoid conventional SAMs. The Blackbird grew out of the U-2, the first attempt by Boeing to create an aircraft that satisfied the above requirements. However, the U-2 was much slower and, even though it could fly at altitudes above 70000 feet, one was shot down in Soviet Russia, which lead to the infamous 1960s U-2 incident. That, however, is another story.

Dryden's SR-71B Blackbird, NASA 831, slices across the snow-covered southern Sierra Nevada Mountains of California after being refueled by an Air Force tanker during a 1994 flight. SR-71B was the trainer version of the SR-71. The dual cockpit to allow the instructor to fly. Note the streaks of fuel from refueling spillage.The SR-71 was constructed out of radar absorbent materials to reduce its radar cross section, but after a while, renowned aerospace engineer Clarence "Kelly" Johnson said that radar technology was advancing faster than stealth technology. However, the almost-flat structure was retained. The picture on the right shows a trainer aircraft flying over the Sierra Nevada Mountains.

The engines of the Blackbird were quite revolutionary. The Sr-71 employed two Pratt and Whitney J58 turbojet engines which were most efficient at speeds in excess of Mach 3. The whole engine compressed air a lot and in the end, injected fuel to give a huge amount of thrust. At Mach 3, the engines handed over thrust responsibility to the afterburner, which gave an extra push. The spike in the front slows the air down to subsonic speeds relative to the engine. The impressive thing was that the faster the engines went, the less fuel they used, which meant that pilots who flew faster to avoid interception consumed less fuel. The engines needed a smaller engine known as a "start cart" to get them running before take off. The start cart rotated the engine to 3200 rpm, after which the engine started running on its own. This process was repeated on the other engine. Later on, a quieter system was developed to jump-start the engines. (Left): A diagram showing the working of the engines.

The Blackbird had a very strong air-conditioning system because flying at speeds of Mach 3.2 heated the skin to 500 degrees Celsius. The system took heat from the cabin and injected it into the engines to provide extra energy.

A total of 32 aircraft were made, and they flew for quite a bit of time until the American Congress retired them saying that they were costing to much to maintain. Each aircraft cost 400 million dollars to maintain per year, and old planes had to be scavenged for parts as manufacturing had stopped. The Blackbird was finally retired in 1989. However, within four years, the USAF looked at the SR-71s again, debating whether or not to reactivate them due to their unmatched aerial reconnaissance. This met resistance though, by the Congress and new developers alike. By then, new unmanned aircraft were being developed which could take over the job of the SR-71 and in 1998, it was permanently retired. Old Blackbirds are now on display. (Below): A SR-71 on display at the Steven F. Udvar-Hazy Museum.

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