Approved for Release: 2013/06/25
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Secret NOFORN
Chapter 6
277
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eventually to the fuselage itself, creating what is known as a chine on each side. At first Johnson was concerned that these additions might impair the airworthiness of the plane, but wind tunnel testing determined that the chines actually imparted a useful aerodynamic lift to the vehicle. Because titanium was very brittle and therefore difficult to bend, Johnson achieved the necessary curvature by combining triangular-shaped pieces of titanium called fillets. These fillets were glued to the framework of the chines with a special adhesive, epoxy resin.
On later OXCART models the fillets were made from electrically resistive honeycomb plastic with a glass-fiber surface that would not melt at high speed. When struck by a radar pulse, the composite chines tended to absorb the pulse rather than reflect it. A similar approach was used for the leading edges of the wings. Again electrically resistive honeycomb material was fabricated into triangular shapes, known as wing teeth, and fitted into the titanium wings. Both the metal and composite fillets and teeth were held in place with the newly developed epoxy cements.
The greatest remaining area of concern in the A-12’s radar cross section was the two vertical stabilizers. To reduce radar reflections, Kelly Johnson canted the stabilizers inward 15° and fabricated them out of resin-impregnated nonmetallic materials. Once these changes were completed, the only metal in each vertical stabilizer was a stainless steel pivot. The Air Force, which later ordered several versions of the OXCART aircraft for its own use, never adopted the laminated vertical stabilizers.¹⁸
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THE OXCART CONTRACT
By mid-January 1960, Lockheed had demonstrated that its concept of shape, fuel additive, and nonmetallic parts would reduce the OXCART’s radar cross section substantially. Richard Bissell, however, was very upset to learn that the changes had led to a reduction in the aircraft’s performance, which meant it would not be able to attain the penetration altitude he had promised to President Eisenhower. Kelly Johnson then proposed to reduce the aircraft’s weight by 1,000 pounds and increase the fuel load by 2,000 pounds, making it possible
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¹⁸ Johnson, “Development of Lockheed SR-71,” pp. 6-7; *OSA History*, chap. 20, p. 35 (TS Codeword).
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Secret
Approved for Release: 2013/06/25