The SR 71:Heatshock Stealth Armour

 The SR 71:Engine flame and turbulence as it attains Mach velocity

 A Front view of the SR 71 showing Chines and Vert.Stabilizers

     THE AIRFRAME of the SR-71 is very unique. To withstand the friction-generated heat at Mach 3+, over 90 percent of the airframe is made of titanium composite. Also to withstand heat, the main gear tires have been impregnated with aluminum and are filled with nitrogen.The airframe was made of titanium obtained from the USSR during the height of the Cold War. Lockheed used all possible guises to prevent the Soviet government from knowing what the titanium was to be used for. In order to keep the costs under control, they used a more easily worked alloy of titanium which softened at a lower temperature. Finished aircraft were painted a dark blue (almost black) to increase the emission of internal heat (since fuel was used as a heat sink for avionics cooling) and to act as camouflage against the sky.Before the Blackbird, titanium could only be found in aircraft in high-temperature exhaust fairings and other small parts directly related to supporting, cooling, or shaping high-temperature areas. The decision to build the Blackbird's structure using 85% titanium and 15% composite materials was a first in the airplane industry. The advances made by Lockheed in learning to deal with this material have been used in subsequent high-speed aircraft such as most modern fighters.
Studies of the aircraft's titanium skin revealed the metal was actually growing stronger over time due to the intense heating caused by aerodynamic friction, a process similar to annealing.Major portions of the upper and lower inboard wing skin of the SR-71 were actually corrugated, not smooth. The thermal expansion stresses of a smooth skin would have resulted in the aircraft skin splitting or curling. By making the surface corrugated, the skin was allowed to expand vertically as well as horizontally without overstressing, which also increased longitudinal strength.
Due to the great temperature changes in flight, the fuselage panels did not fit perfectly on the ground and were essentially loose. Proper alignment was only achieved when the airframe warmed up due to the air resistance at high speeds, causing the airframe to expand several inches. Because of this, and the lack of a fuel sealing system that could handle the extreme temperatures, the aircraft would leak its JP-7 jet fuel onto the runway before it took off. The aircraft would quickly make a short sprint, meant to warm up the airframe, and was then air-to-air refueled before departing on its mission. Cooling was carried out by cycling fuel behind the titanium surfaces at the front of the wings (chines). Nonetheless, once the plane landed no one could approach it for some time as its canopy was still hotter than 300 °C. Non-fibrous asbestos was also used, as in non-ceramic automotive brakes, due to its high heat tolerance

The Stealth Element
     The aircraft was designed to minimize the radar cross-section and as such, the SR-71 was an early attempt at stealth design.There were a number of features in the SR-71 that were designed to reduce its radar signature.Lockheed hoped to achieve this by carefully shaping the airframe to reflect as little transmitted radar energy (radio waves) as possible, and by application of special paint designed to absorb, rather than reflect, those waves. This treatment became one of the first applications of stealth technology, but it never completely met the design goals. The first studies in radar stealth seemed to indicate that a shape with flattened, tapering sides would reflect most radar away from the place where the radar beams originated. To this end the radar engineers suggested adding chines* to the design and canting the vertical control surfaces inward. The plane also used special radar-absorbing materials which were incorporated into sawtooth shaped sections of the skin of the aircraft, as well as cesium-based fuel additives to reduce the exhaust plumes' visibility on radar. However, the radar signature aspects of the SR-71 design did not take into account the extremely hot engine exhaust and the particles in the hot exhaust reflect radar extremely well. Ironically, the SR-71 was one of the largest targets on the FAA (Federal Aviation Administration) long range radars, which were able to track the plane at several hundred miles.Despite Lockheed's best efforts, it was still easy to track by radar (and had a huge infrared signature when cruising at Mach 3+). It was visible on air traffic control radar for hundreds of miles, even when not using its transponder**.This fact is further corroborated by the fact that missiles were fired at them quite often after they were detected on radar.The SR-71 was the first operational aircraft designed around a stealthy shape and materials. The most visible marks of its low radar cross section (RCS) are its inwardly-canted vertical stabilizers and the fuselage chines. Comparably, a plane of the SR-71's size should generate a radar image the size of a flying barn, but its actual return is more like that of a single door. Though with a much smaller RCS than expected for a plane of its size, it was still easily detected, because the exhaust stream would return its own radar signature (even though the special cesium compound was added to the fuel to reduce this signature). Furthermore, this is no comparison to the later F-117, whose RCS is on the order of a small ball bearing
[*Chine is an aerodynamic term referring to the intersection of the upper and lower fuselage surfaces of the SR-71 Blackbird which form a 'lip' around the forward fuselage of the aircraft. These chines generate lift-bearing vortices at high angles of attack and reduce the aircraft's lateral radar signature]
[**The type of transponder occurs in friend or foe identification systems in military aviation and in air traffic control secondary surveillance radar (beacon radar) systems for general aviation]
     The red stripes found on some SR-71s are there to prevent maintenance workers from damaging the skin of the aircraft. The curved skin near the center of the fuselage is thin and delicate. There is no support underneath with exception of the structural ribs, which are spaced several feet apart.