The SR-72 will travel at six times the speed of sound as well as the fastest military jet ever made and fly as high as 80,000 feet. Born within the spy-vs.-spy cauldron of this Cold War, the iconic SR-71 “Blackbird” remains the fastest air-breathing military aircraft the planet has known. It flew so high and so fast that enemy defenses had been powerless to intercept it. Eventually, satellite technology and advanced level radar eroded its advantage. In 1998, the U.S. Air Force retired it. Now, with regional threats growing and portable surface-to-air missiles evolving, designers have once again set out to build the fastest military jet on the planet. This time, it may need the form of a 4,000-mile-per hour reconnaissance drone with attack capability.
Referred to as SR-72, the aircraft will evade assault, take spy photos, and assault targets at speeds of as much as Mach 6. That is doubly fast as its predecessor.
Aeronautical engineers at Lockheed Martin and Aerojet Rocketdyne have been creating the SR-72 at their Skunk Works black site in California for the past years. It will require a hybrid propulsion system: a conventional, off-the-shelf turbo jet that may take the plane from runway to Mach 3, and a hypersonic ramjet/scramjet that will push it the remainder of the way.
Its body may have to withstand the extreme heat of hypersonic trip, whenever air friction alone could melt metal. Its bombs will need to strike goals from perhaps 80,000 feet. Lockheed says the craft could be deployed by 2030. When it is, the plane’s ability to cover one mile per second means it could reach any location on any continent in an hour not you will see it coming.
Lockheed describes the SR-72 as an intelligence, surveillance, reconnaissance, and attack platform, but its precise payload is secret. Most likely, it hasn’t yet come to exist. Using spy photos or dropping bombs at Mach 6 will require extraordinary engineering. It will need a huge selection of miles to make a turn. It will need effective guidance computers to line up targets, 80,000 feet below. Additionally, you can’t just start a bomb bay at 4,000 miles per hour. The SR-72 will need new sensors and weapons to operate at such high speeds. Concepts & Prototypes + JUNE 2015
Turbojet engines can take an airplane from runway launch to about Mach 3; speeds faster than that need an air-breathing ramjet, which compresses high-speed air for combustion, but which typically begins running at about Mach 4. To bridge the space, engineers are developing a hybrid engine that may run in three modes. The aircraft will accelerate to about Mach 3 under turbojet energy, change to ramjet power to take it to about Mach 5, and then switch again to scramjet mode, which uses supersonic air for combustion.
The stresses on a plane shift because it travels through subsonic, supersonic, and hypersonic speeds. For example, whenever a jet is accelerating through subsonic journey, the center of lift moves toward the rear of the aircraft. But once the craft hits hypersonic speeds, drag on the plane’s leading edges result in the center of lift to go forward again. If the ceter of lift gets too close towards the center of gravity it can cause dangerous uncertainty. The plane’s shape must tolerate these changes, and more, to keep the craft from tearing apart.
HOW RAMJETS WORK
Ramjets forgo the big rotary compressors needed on turbojets and instead rely on their own forward motion to compress air. First, air is scooped into an inlet and compressed as it funnels into a diffuser. The diffuser also slows the air to subsonic speeds for easier combustion. From here, atmosphere and fuel are fed into a combustion chamber and ignited. Finally, an exhaust nozzle accelerates the resulting burst of hot, expanding atmosphere, producing massive thrust.
Aerodynamic friction at speeds exceeding Mach 5 will heat an aircraft’s exterior to 2,000 levels. At the period, mainstream steel airframes will melt. So engineers are looking at composites similar types of high- performance carbon, ceramic, and metal mixes used for the noses of intercontinental ballistic missiles and space shuttles. Every joint and seam must be sealed: Any air leak at hypersonic speed, and the in-rushing temperature would cause the aircraft to collapse. (That’s just what doomed the space shuttle Columbia).