With a cruising speed of Mach 3.2 and an estimated top speed of Mach 3.5, the SR-71 Blackbird holds
seven aircraft records, including the fastest air-
breathing manned aircraft, officially measured at 2,193.2 miles
per hour; though its top speed is still classified.
In a climb the aircraft has been known to reach an altitude of 95,000', twice as high as the highest altitude
permitted for a commercial passenger jet. The Mikoyen Gurevich MiG 25 is the second
fastest, jet-powered manned aircraft in the world It's made to go Mach 2.8, but that uses so
much fuel they it can only go that fast for a few minutes In extreme circumstances the plane has
been pushed to Mach 3.2, but at a cost of major damage to the plane's engines. On the other hand, at Mach 3.2, the
SR-71 Blackbird, is just getting warmed up. So how did Lockheed Skunk Works
get a plane that weighs up to 78 tons to fly around the world, nonstop, at three times the speed of sound, 16
miles up? Considering it was designed in 1962 in a time before computer aided design,
The answer is: Very carefully. The Blackbird program, originally called OXCART, pioneered
many of the technologies found only in the most advanced
military aircraft today, including in all titanium airframe,
a mostly titanium skin, the use of lightweight composite
materials for the rest to the skin, and some key components. chines that run down the length
of the aircraft, to reduce drag and increase lift. a stealthy design that minimizes
its radar cross-section, and, in a time before GPS, the ability
to circumnavigate the globe with pinpoint accuracy. But the real key to the Blackbird's
success came down to two things: An extremely aerodynamic design,
and a very unique engine. When you look at the Blackbird you can see the sleekness in
its aerodynamic design. Looking at its vertical cross-section,
you can see how balanced it is above and below a central horizontal plane. Its delta wing is relatively thin,
minimizing its disturbance through the air. When you look at it from above, you can see how it whole body
fits within a single elongated triangle, running from the
front Pitot tube to the wing tips. This makes sure that the front shock wave,
created by the nose at supersonic speeds, doesn't intersect with the rest the
aircraft, reducing overall drag. Its main body straight and long, like an arrow, with a small amount of
taper as it reaches the back, to gracefully shed the air flowing
above and below the aircraft. But all the aerodynamics in the world
won't push a plane up to Mach 3. For that you need the Blackbird's
very unique engine: The Pratt & Whitney J58 turboramjet. At slow speeds, the J58 works just like
other jet engines with an afterburner: air flows into the front of the engine
through bladed compressor fan, which squishes the air and pushes
it into tubes called burners. Here fuel is added and burnt. The hot exhaust flows out of the
burners through the rear turbine, making its spin, which turns the
compressor to keep the cycle going. The force of the exhaust leaving the
engine pushes the airplane forward. But jet engines are limited in the
amount of force they can generate through exhaust alone. The fuel supply has to be limited in
the burner to reduce the heat of the exhaust so that the turbine doesn't melt! this means that the exhaust still
contains a lot of oxygen. So, in order not to waste it, additional fuel is added into the stream of exhaust and
burnt after it passes the turbine, but before it exits the aircraft
for additional thrust. This is what we call: the afterburner. Up until Mach 2.2, this is the same cycle
that the Blackbird uses for thrust. However, above Mach 2.2, the
J58 pulls out a big trick. Six large tubes open, that direct
20% percent of the dense air from the compressor around the
burner and turbine, moving it directly into the afterburner. This helps get around the biggest
problem with all afterburners: they are incredibly inefficient! They can provide a lot of force,
but at a huge fuel cost! on the other hand, the cool, dense, slow-
moving air coming directly from the compressor extracts more power out of
the fuel added afterburner. When these bypass tubes open, the
standard turbojet is converted into what's called a turboramjet. A ramjet uses the forward motion
of the aircraft to compress the air before combustion, and fuel is burnt directly before
exiting the engine, kinda like a rocket. But ramjets can't be started on the ground:
the plane has to be moving before the ramjet can start working. so, for takeoff and landing, the turbojet
part of the J58 does all of the work, while at the cruising speed of Mach 3.2,
it only provides about 20 percent of the plane's forward thrust, with the ramjet afterburner providing the rest. Ahh, Synergy! The interesting thing is that above Mach 2, ramjets are more fuel-efficient than turbojets, which means that the Blackbird gets better gas mileage at Mach 3.2, than it does traveling at slower speeds! Whaaa? These unique design elements are what
allowed the plane to cruise higher and faster than any other manned aircraft its convertible engines give it
the best of both worlds: A turbojet to take off, land, refuel,
and bring it up to speed, and a ramjet to give it the power
to fly 3200 nautical miles, at three times the speed of sound,
on one tank of gas. And considering that all that was
designed with just a pencil, paper and a slide rule, it makes the Blackbird
even that much more of a technological achievement. Unfortunately the Blackbird will never fly again. Although it out ran everyone of the 4,000
missiles fired at it during its missions, the cost to fly and maintain the
aircraft was so great that in 1990, with the increased
availability of surveillance and strike drones, the US Congress
ordered the birds retirement. Three planes were reactivated in 1993 due to increased tensions in
North Korea and the Middle East, but these planes were again retired in 1998. NASA continued to operate two
SR-71s as scientific test platforms, until they too retired the plane in 1999. You may have heard at the end of 2013,
Lockheed Martin proposed a successor to the SR-71, called the SR-72 Even if it is ever produced, it will still
never break the SR-71's records. Though it's designed to fly at
speeds from 0 to Mach 6, like many other recent advances in
aviation, the SR-72 is a drone. It's turbojet engine for takeoff and landing is housed separately than it's supersonic
scramjet, leaving the J58 in the Blackbird family to be forever
unique, a fantastic and surreall memory in the history of aviation. "The plane that dreams are made of." For Tech Laboratories, I'm Tech Adams, saying Keep Thinking, and thanks for
watching.
