The SR-71 Blackbird, introduced in 1966, currently holds the world record as the fastest plane ever designed.  Capable of flying 2,200 mph, the plane was designed with the intention of making it virtually impervious to anti-aircraft weapons.  By flying at an extremely high altitude and a blistering speed, the aircraft was capable of simply outrunning anti-aircraft missiles.  When introduced, no Soviet missile had both the altitude and speed capabilities of catching an SR-71, and consequently no SR-71 has ever been shot down.


The SR-71 Blackbird.

Besides just its ability to reach incredible speeds, the Blackbird is interesting because of the technical innovations developed to hold the aircraft together through Mach-3 flight.  When flying at 2200 mph, the friction from the air is so high that the plane's skin reaches about 1000 degrees F, due simply to the extreme air resistance.  On a normal plane, this would cause the skin on the plane to peel off and would also cause the metal to expand, meaning that the shell of the plane would break apart.

On an SR-71 however, the skin of the plane is corrugated rather than smooth, allowing the metal to expand and cool without altering the shape of the plane.  Further, some parts of the shell are shaped so that they do not seal the plane until the metal expands, meaning that at takeoff some parts of the plane do not seal.  One result of this is that the fuel tanks leak badly before takeoff.

The strange design of the SR-71 means that it can not leave the runway like a commercial airliner, but requires an extremely careful and tenuous process.  For one, JP-7 fuel was used, which doesn't ignite readily, meaning that an extremely flammable chemical called Triethylborane must be injected into the fuel in order to allow it to ignite.  Giant generators had to be used on the ground to allow the engines to start, and pilots had to be fitted with extensive life-support technology to protect them at the high speeds.  Further, the fuel leakage combined with the danger of allowing the aircraft to takeoff with a full tank requires the SR-71 to refuel mid-flight.

An Sr-71 refueling mid-flight.

The mid-flight refueling process is difficult for many reasons, namely the struggle of trying to link two aircraft together while flying at high speeds.  Additionally, the fueling planes have a much slower speed than the SR-71, meaning that during fueling the SR-71 must fly near its slowest allowed speed while the fueling aircraft must fly at its maximum speed.  Imagine trying to fill a Porsche's gas tank while riding a bike at 20 mph, and that's probably a fraction of the difficulty experienced during refueling.  Very few pilots were ever certified to fly the SR-71, and the mid-flight refueling process was responsible for most of the applicants failing.