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Blog Series: "The SR-71 Blackbird" Part II

DRC21USAF

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blog-0533781001384146617.jpgSo in my last post on the SR-71, I gave a general presentation on the dynamics of the engine, but what about the motherload herself? How could the frame sustain such high speeds? As it turns out, air resistance on the plane caused the exterior to reach very high temperatures, something, that if structured improperly, could mean the plane would burn up before it reached it's max speed.

The plane was made of 85% titanium, and given the expense to build such specialized parts in this metal, Lockheed developed an alloy of titanium which softened at a lower temperature. Another obstacle Lockheed met in development was regarding the structure of the airplane. The planes made were each their own "individual model" so to speak, for the reason that the parts were so individually specific and difficult to make.

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The skin of the wings were corrugated (patterned linearly) instead of smooth, a feature which allowed the skin to expand vertically and horizontally. While one would think smooth skin would be better, perhaps lessening the effect of air resistance, the heat of flight would cause the aircraft's skin to split or curl. The fuselage (core frame) panels were designed to fit loosely while the plane was immobile. In order to align properly, the frame would have to be heated and expanded several inches. At the beginning of each mission, the plane would take a short lap after takeoff to heat the airframe, then refuel before heading off to the destination.

As far as the design of the plane, later designs of the original aircraft included Chines, sharp edges leading aft from either side of the nose along the fuselage. They create additional lift and surprisingly improved the aerodynamic performance of the plane. The angle of incidence for the the delta wings could be reduced for greater stability and less air resistance at higher speeds. This allowed the plane to carry more weight, such as fuel. The only problem was in reaching high angles of attack: the chines created turbulent flow over the wings at high angles of attack, meaning the plane could not stall; what would happen instead is the plane, reaching it's maximum angle of attack, would invert and dive straight towards the ground, a reaction that could not be recovered.

This is all I have on the SR-71, please feel free to comment on either post and ask questions or give some feedback on the information!



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