The well-known SR-71 owes its roots to a extra obscure predecessor, the A-12 developed by the well-known Lockheed ‘Skunk Works’ as a successor for the U-2.
When Francis Gary Powers was shot down flying a U-2 over the Soviet Union, it turned obvious the Soviets had lastly discovered a solution to knock the high-flying spy aircraft from the sky eventually. With the Chilly Struggle heating up and with a view to proceed overflights of the Soviet Union and Warsaw Pact territories, a brand new plane was wanted; one with great pace, vary, and altitude capabilities.
Kelly Johnson had already been engaged on simply such a venture at Lockheed within the late Fifties, with the ultimate outcome being an plane with spectacular engineering and capabilities even by as we speak’s commonplace constructed with Sixties expertise.
The Want for Pace
Even earlier than Francis Gary Powers had his U-2 knocked out of the sky on Might 1, 1960, Clarence ‘Kelly’ Johnson of Lockheed’s Superior Growth Tasks, or higher often known as the notorious ‘Skunk Works’, had been engaged on a substitute for the U-2. President Eisenhower had formally and publically ended U-2 overflights of the Soviet Union, however Kelly was decided to create an plane that was leaps and bounds forward of its time and the U-2.
Johnson needed a long-range plane with Mach 3+ cruising pace and that will fly at 90,000 ft, greater than even the U-2. He envisioned an plane that will rule the skies for the following ten years or extra — one the Soviets couldn’t enhance missile techniques in a couple of years and intercept. Johnson needed one thing that had by no means been accomplished earlier than.
A small group of Lockheed’s finest was put to the duty; many had labored on a hydrogen-powered plane design that by no means got here to fruition, however that venture gave them a lot wanted expertise and perspective.
This plane would make the most of typical engines and gasoline however have the flexibility to outrun Soviet missiles. This is able to require new engineering and design in virtually each space. Nearly all the pieces must be constructed from scratch and never robbed from earlier plane techniques.
Working with U-2 project manager Richard Bissell, Johnson promised to deliver such an aircraft to the CIA (Central Intelligence Agency) in a mere 20 months, but it was a more difficult job to sell the idea to President Eisenhower. Eisenhower felt spy satellites offered a safer and less threatening alternative to overflights with aircraft, although the images taken by the U-2 were superior to what satellites could offer at the time, and a spy plane could fly over troubled areas at any given time and loiter if need be, whereas intelligence from satellites was restrained by their orbits.
Going for the Gusto
While Kelly Johnson attempted to sell his aircraft with its altitude and speed advantages, Eisenhower and the CIA became more interested in an aircraft with a low radar cross section (RCS). Eisenhower didn’t want another shoot down, and the best way to prevent that, he rationalized, was if the Soviets never even knew the aircraft was there. This aircraft would not only need speed, altitude, and range, but also stealth characteristics.
A CIA committee led by Polaroid executive Edwin Land was established to help select the replacement for the U-2. Project Gusto was created to explore producing an aircraft with very high speed and altitude characteristics, but built from radar absorbing materials.
At Lockheed a series of design configurations were drawn up for a U-2 replacement aircraft, designated by Lockheed in the beginning as ‘Archangel-1’, ‘Archangel-2’ and so forth, but eventually simply known as A-1 through A-11. Each configuration was further subdivided into variants of the parent design. The A-1 had the look of obvious blazing speed, being a sleek bullet-shaped fuselage with small delta wings mounted two-thirds of the way back on the fuselage. However, it lacked the low RCS desired.
Convair, which was building the B-58 Hustler supersonic bomber, was another major aviation company working on a solution for the CIA. They proposed a piloted ramjet known as the Fish, carried aloft and launched by a Mach 2 B-58B, but the B-58B was still unavailable and it wasn’t proven it could reach Mach 2 with the other aircraft attached. The ramjet technology was somewhat unproven as well.
By May 1959, Skunk Works had successfully dramatically lowered the RCS of design number A-11 by modifying the bullet-shaped fuselage by adding a chine — a lateral downward sloped surface — giving the aircraft the appearance of a hooded cobra. The chines also added lift. The underbelly was now flat and the RCS decreased by 90 percent.
The design now consisted of a large twin-tailed, twin-engine, single-seat aircraft with a long forward fuselage and delta wings. The engines were housed in nacelles set in the extremely thin wings. The vertical stabilizers were canted inward, also reducing the RCS. The 102 ft long new design with a 57 ft wingspan became known as the A-12.
Lockheed’s design was chosen the winner and project Gusto came to an end. The new program to develop the U-2’s successor was named Oxcart, with the aircraft also taking on that name. A full-size mockup of the design was built and placed on a pedestal to have the RCS determined from several angles.
Engineering a Mach 3 Aircraft
Johnson knew his aircraft operating at such high speeds and altitude while maintaining a low RCS would require development or modification of virtually everything needed to make the plane a reality. This included not just the aircraft design, but the engines as well. Special fuels, manufacturing tools, techniques, paints, sealants, plastics, tires, windshields, cables, electronics, and even wiring and wiring connections would all be needed for this unique project.
Material for the structure of the aircraft would have to withstand temperatures of up to 800 degrees F (Fahrenheit) on some areas, which ruled out aluminum. Engine cowlings would reach 1,200 degrees F and the windshield 620 degrees F. Titanium was chosen over stainless steel alloys to save weight. Over 90 percent of the airframe would be constructed of a titanium alloy. However, only one U.S. company milled titanium and in varying degrees of quality, and there were limited reserves.
To alleviate the shortage of quality titanium, the CIA established various shell companies and purchased the base metal from the Soviet Union, the country with the largest known reserves. The very country the aircraft was being built with the intention of spying on, supplied the titanium to help build it. The Soviets were under the impression pizza ovens were being built with the material.
However, titanium would prove challenging to work with. Conventional drill bits broke and cutting tools snapped due to the extreme hardness of the material. New specialized drill bits were obtained from West Germany that could now drill up to 150 holes before needing sharpened, and Lockheed was forced to manufacture their own titanium screws and rivets.
A special press was developed and built to shape the titanium under very high pressures very high temperatures of up to 1500 degrees F. Titanium is too rigid to be forced into place and must be tooled to fit precisely.
Cadmium-plated tools would destroy titanium bolts, the cadmium would flake off and after being exposed to 600 degrees F, the bolt heads fell off. Tool boxes had to be purged and hand tools replaced.
Welds on the wing panels also failed, but mysteriously only if the panels were built in the summer. Winter constructed panels held up fine. It was discovered that the summer water supply in Burbank, California contained chlorine to reduce summer algae growth, but was not used in the winter water supply. The chlorine attacked the welds, and switching to distilled water for washing down the panels after acid treatment solved the issue. In addition, it was discovered certain Pentel pens also contained chlorine and would etch the titanium when used to draw lines on the panels.
Welds were conducted in specially constructed chambers in an inert nitrogen environment to prevent the welds from being brittleness caused by oxidation. A special hydraulic fluid was designed by Pennsylvania State University that included seven ingredients in order to withstand the temperature extremes and still function.
Rubber O-rings or leather seals could not be used at these temperatures, and stainless steel was used to make the hydraulic lines. Elgiloy, the material watch springs are made from, was used to make control cables and plumbing lines were required to be gold-plated. A lubricating oil was formulated to operate from the extreme temperatures of 600 degrees F down to 40 degrees F, containing a diluent in order to remain fluid.
B.F. Goodrich developed a special rubber for the tires containing aluminum particles that provided radiant cooling, giving the tires a silvery appearance. In addition the retracted landing gear rested in the middle between fuel tanks and was cooled by the fuel, keeping the tires insulated against very high temperatures. Also the tires were filled with nitrogen, which is less explosive than air. All of this prevented the plane landing with tires ready to blow out once they touch down.
Shell Oil had created a good fuel for the U-2, so Lockheed turned to Jimmy Doolittle, now a top executive with the company, for a fuel solution for the new Mach 3 aircraft. The fuel would have to remain useful and safe at extreme temps, from minus 90 degrees F at midair refueling to 650 degrees F in supersonic flight. In conjunction with Pratt & Whitney, Ashland, and Monsanto, a new fuel was created, designated LF-2A and known as JP-7 to the military. The fuel had a high-flash point and would not vaporize or explode under tremendous heat and pressure. A lighted match could be tossed into a spill and it would not ignite.
Nitrogen would be pumped into the fuel tanks as an added safety precaution, pressurizing them and preventing vapor ignition. Through heat exchangers and smart valves, the fuel would also act as an internal coolant for critical parts of the aircraft. A cesium additive reduced the radar detectability of the afterburner plume. The aircraft would carry 64,600 lb of fuel in five uninsulated tanks.
New unique plastics would be developed with high heat resistance along with a low RCS and used in the radome, cockpit, and other areas. The inward canted twin tails were constructed of non-metallic substances as well. Plastics made up approximately 20 percent of the aircraft surface. If fuel was spilled on the plastic surfaces and exposed to high temperatures of around 550 degrees F, miniature explosions occurred on the plastic skin. Paint that was fuel proof as well as rain proof would be needed.
Special wiring using Kevlar was created and wrapped with asbestos for heat resistance. Unique plugs were designed so connections could only be assembled one way, after Johnson discovered about 10 percent of his workforce was colorblind, and color coded wiring was sometimes ineffective.
To prevent the wing sections from wrinkling in high temperatures, some skin panels were corrugated and dimpled so, when the titanium heated up, the corrugations deepened preventing wrinkling.
In his book Kelly: More Than My Share of it All, Kelly Johnson states surfaces of the aircraft were also painted a dark blue-black color that was determined after emissivity tests to make the aircraft surface up to 80 degrees F cooler. He goes on to state the paint became bluer as the temperatures increased with speed and altitude. Special paints had to be formulated for the aircraft markings and insignia as well. Red paint would turn brown and white became mottled in the high temperatures.
Anti-radar coatings were created with iron ferrites and asbestos loaded in the mix, and applied to the aircraft, lowering the RCS.
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