Landing gear is not a simple structure. It is part of the design philosophy of any aircraft, and its design requirements are influenced by a number of factors. On a supersonic aircraft, the conditions are harsher and call for a well-thought design engineering with great precision and accuracy.
General Design:
The landing gear system of the SR-71 consisted of a two-wheeled nose gear and two main gears, each with four wheels. The main gear was located very aft beneath fuselage and was of the trailing-link type.
The gear structure was extremely lightweight, machined from high-strength steel. The nose gear featured a single oleo-pneumatic shock strut, while the main gear had two shock struts. The nose gear was steerable, and the gear was retractable into the fuselage.
The landing gear of the SR-71 Blackbird was designed to withstand the tremendous heat generated by the aircraft's engines. It was also designed to allow the aircraft to land at speeds of up to 200 mph.
The SR-71 Blackbird's landing gear was a complex system that required a great deal of engineering and expertise to design and build. It was a testament to the skill of the engineers who worked on the SR-71 program that the landing gear was so successful.
Operating The Gear
The landing gear is retracted by hydraulic power, acting on a mechanism with a single cylinder and a large worm-gear-type actuator. The mechanism also locks the gear in both the up and down positions using cam-lock arrangements. The gear extension and retraction is controlled by the pilot with a switch on the left side of the cockpit.
An emergency free-fall system can also be used to extend the gear in the event of lost hydraulic pressure.
Each of the 6 wheels carries a load at touch down of some 100,000 pounds. That means an average tire foot print of about 1/10 of a square inch!
SR-71 Heat Considerations
The primary design constraint for the SR-71 landing gear was heat. Landing gear design of the SR-71 was particularly difficult due to the airframe reaching temperatures between 510 and 650 °F (265 and 343 °C) during flight, making it impossible for typical hydraulic lines and tires.
The gear doors were closed by electrical actuators after takeoff and remained closed during the aircraft's high-speed cruise (Mach 3+) to reduce drag. They only opened again when airspeed dropped to between Mach 2 and Mach 2.5.
As a result, many unique design features had to be incorporated to allow safe landing and to handle the extremely high temperatures the aircraft encountered during its missions.
Thermal Insulation
The landing gear was also equipped with a special heat-resistant coating to protect it from the heat of the engines. This coating was made of a ceramic material that was able to withstand temperatures of up to 2,500 degrees Fahrenheit.
Heat Management System For Tires
The tires of the SR-71 were made of a special rubber compound that was able to withstand the heat of the engines. They were also inflated with nitrogen gas instead of air, which is less likely to catch fire.
In addition to the heat-resistant coating and special tires, the landing gear was also equipped with a water spray system. This system was used to spray water on the landing gear during takeoff and landing to help keep it cool.
The landing gear of the SR-71 Blackbird was a complex system that required a great deal of engineering and expertise to design and build. It was a testament to the skill of the engineers who worked on the SR-71 program that the landing gear was so successful.
