SR71 Blackbird was the gate through of modern aviation. A plane that not just broke any aviation record but, simply shattered them. The fastest and highest flying plane which holds it’s record still now even 60years after. An engineering marvel that shows how much humans are capable of when they got pushed to their limits. These planes did remain in service for nearly 30years, and in between these years approximately 4000missiles were fired at them but, non succeed to bring one down. Because the plane was just simply too fast. After the operational flight in 1968 Lockheed ordered too destroy all of the tools used in making the SR71 Blackbird.
It is definitely an serious aircraft to know about the development and history.
1. SR71 Blackbird History :
During the heights of cold war, both the Soviets and US were on an arms race. US countered that keeping eye on the enemy’s activity is very advantageous in combat or to attack. Spy satellites were still in research stage. So, US flew several reconnaissance mission flights over the Soviet ordered by President Harry S. Truman in 1950s. Lockheed Skunk works division’s U2 spy plane (Dragon Lady) was designed specifically for reconnaissance missions and took first mission flight on 1956. The plane could fly at altitude of 65000-70000 feet, pretty impressive for a plane to fly and take detailed pictures. But, soon it showed several malfunction and crash incidents. Putting the pilot’s life, top secret military hardware and valuable information at risk of loosing.
Tension raised at the top in 1960, when an U2 was shot down and crashed over Soviet territory. Pilot Francis Gary Powers caught with the secret spy plane and detailed pictures he took. President Dwight D. Eisenhower ordered CIA to contact Lockheed and develop a new spy plane, project named Archangel. The conditions were, it need to fly at altitudes over 70000 feet, super fast and invisible to enemy radar. Again, Mr. Kelly Johnson and his Skunk works team went to the drawing board and needed to reinvent everything from scratch. After several challenges ultimately a new state of the art spy plane came out from the manufacturing, named A12 (A for Archangel). Which was later known as RS71 (Reconnaissance, Strategic) but, misspelled as SR71 (Strategic Reconnaissance) by president Johnson and got the name afterwards.
SR71 was capable of flying at altitudes over 70000 feet having sustain speed of more than a rifle bullet (3times the speed of sound).
2. The body :
In 11 months of drawing and designing, several designs came up. Skunk works team was divided into 3 teams to work on different aspects like high speed flight, stealth and engine. But, none of them were able to put all of the parameters into one design. Eventually a young designer managed to develop a prototype design by slight modifications in the existing designs. He took the front and tail section front individual drawings and made the lower body flattened.
The final design named A12 got finalized. The plane was sleek which pierce through air, has leading extensions at front to create more air pressure under the nose, the delta wings ensured good stability, On paper it was promising enough but, complications raise as work started. The speed demanded was 3times the speed of sound (Mach 3), at which speed aerodynamic friction plays vital role. The surface of the aircraft would become so hot, almost 313 degrees at the nose and over 500 degrees at the engine rear parts even the cockpit would heat up near 400 degrees. Typically air-crafts are made of Aluminum, which is lightweight and strong. But, not suitable in these temperatures. Kelly’s team need think of different material. The solution was Titanium. It is light strong and highly heat sustainable metal.
The problem was the ore Rutile to process Titanium was not available in quantity as much required to produce these planes. The biggest supplier of Rutile was Soviet. CIA used their relation with allied countries and create fake dummy organizations or firms to procure Titanium. Now, they have the metal but normal machines and welding process corrodes the metal and disrupts in precision processes. So, special tools were brought and specialized welding techniques had been mastered.
Also Read: The Evolution and History of Submarine.
93% of the aircraft’s body was made of Titanium, the cockpit glass was made by special epoxy resin and welded with the body applying supersonic waves. Pilots reported that the canopy Glass were untouchable due to immense heat at flight. The total plane was not fully welded as metal expands in heat, the pieces were left unwelded at places. For this reason Blackbirds often found loosen sheets, lost rivets or bolts after every flight. The inboard air needs to cool also.
Hence, the team felt the need of an air cooling system to cool down the cockpit. Special heat ex-changers were designed which used to transfer the heat from the cockpit to the fuel providing additional efficiency of the engines. The pilots were given special pressurized suits to maintain body pressure at 80000 feet or above and special helmets attached with straws to drink and have food in flight. The plane was painted by special radio absorbing black coating which gave its unique black appearance hence, the name also “Blackbird“.
The flattened lower section and the paint gave the aircraft 90% reduction in radar cross section and better heat transfer also.
3. Engine :
The Blackbird need to cruise supersonic, and need to achieve Mach 3 or above, additionally could able to take off or land at low speeds. No existing engine can provide all of these. Skunk works needed a hybrid of turbojet and ramjet engine. Basically, The SR71 used Pratt and Whitney j58 turbojet engines. But housed inside a specially designed chamber which made it a ramjet engine. The engine tip was able to move inwards and outwards by 41mm to create ram air before entering the turbojet engine. With the engine tip nose and cleverly positioned valves Lockheed successfully developed a ramjet engine without having such of a kind.
Although, even with this clever engineering the efficiency was not so great as it was very thirsty, giving the plane an average flight of 90 hours or 5400kms which was one way trip to the target, whether the targeted site was Russia, Vietnam or North Korea. So, these planes were capable mid-air refueling which extended their range.
4. Fuel and fuel tanks :
SR71 was a military plane but, the purpose was reconnaissance mission. So, they don’t carry missiles or bombs. The entire fuselage was the fuel tank. The plane don’t have any separate metal fuel tanks as it creates more weight or plastic fuel tanks which couldn’t withstand the temperature. But, as Titanium will expand by the heat, the body was not welded to make a liquid proof tank but, designed to leak fuel. Hence, it was a common site to see the Blackbird leaking its fuel on the runway. Although the dripping was calculated and considered not effective to loose much fuel.
Also Read: 50 Things You Need To Know About WWI.
The empty SR71 bird was 32 tons when fuel tanks were empty and 60 tonnes with full tanks. Making 59% of it’s body weight of fuel. The fuel injecting mechanism to the engines were also highly engineered. As the front of the wings get hot so do the fuel stored in there. These hot fuel were pumped to the engines for better efficiency.
This fuel was not just any aviation fuel. Lockheed asked Shell to make such fuel with low volatility, and high flash point. The fuel known as JP7 (Jet Propellant 7) was used for these blackbirds. It has been tested that when a blackbird is leaking fuel on the runway cigarettes were thrown on them but, the fuel didn’t ignite, but extinguished the cigarettes. Which helped the crew to avoid unexpected fuel ignition in the fuel tank when speeding the aircraft in such speed. But, having high flash point means the fuel need to be heated before injecting into the engines.
So, at take off the Pratt and Whitney j58 engines were fed with Tri Ethyle Borane or TEB, which has low flash point. This fuel gave the Blackbird it’s unique green flame at time of take off. These planes need to carry TEB in the fuel tanks and refueled by JP7 after take off. There is a myth that SR71s need to refuel just after taking off, the reason was not those thirsty engines but, the fuel.
Also Read : 30 Amazing Unknown Facts About Space.
5. Weapon :
Being a reconnaissance spy plane the SR71’s weapons were camera and radar. The SR-71 originally included optical/infrared imagery systems, side-looking airborne radar (SLAR), electronic intelligence (ELINT) gathering systems, systems for countering missile and airborne fighters, and recorders for SLAR, ELINT. The SR-71 carried a Fair-child tracking camera and an infrared camera, both of which ran during the entire mission. These were investigated post flight. The HYCON Technical Objective Camera could be directed at 45degrees from center line.
Advance Synthetic Aperture radars were placed at the nose. ELINT gathering systems, or the Electro-Magnetic Reconnaissance System, built by AIL could be carried to analyze electronic signal fields being passed through, and were programmed to identify items of interest. The Blackbird used ASTRO-Inertial Navigation system. These systems were highly accurate in tracking stars which contained data and list of stars for celestial navigation. First, the list was of 56 stars later expanded to 61 stars. These ANS track stars continuously day and night by the blue light source through a circular quartz canopy behind the Reconnaissance System Officer. This system could supply altitude and position to flight controls and other systems, including the mission data recorder, automatic navigation to preset destination points, automatic pointing and control of cameras and sensors, and optical or SLR sighting of fixed points loaded into the ANS before takeoff.
6. Records :
On 28 July 1976, SR71 Sl no- 61-7962, pilot Robert Helt, broke the world record. An “absolute altitude record” of 85,069 feet (25,929 m).
That same day SR-71 Sl no- 61-7958 set an absolute speed record of (2193.2 mph, 3529.6 km/h), approximately Mach 3.3.
On 1st September 1974, record of flying from New York to London having distance of 3,461.53miles or 5,570.79kms in 1 hour 54 minutes and 56 seconds. To compare, covering the same distance a commercial Concorde took 2hours and 52 minutes as best timing, and a Boeing 747 averages 6 hours 15 minutes.
On retirement day also the Blackbird made 4 speed records which were accepted by National Aeronautic Association (NAA), USA.
SR71 is not just another engineering height but an ingenious development and a legend. From 1964, first flight to 1999, last flight and retirement, the Blackbird flew with pride. After 60 years it is still the most futuristic looking and fastest plane ever flew, and records are still unbroken. The remaining Blackbirds are in display in aviation museums. They may not fly once more but, they definitely left the mark of ultimate birds of the skies.