The dark streaks observed on the wings of the SR-71 aircraft near the engine are caused by jet fuel leaking out of the seams. The SR-71, designed to operate at speeds exceeding Mach 3, utilizes thermal expansion to seal its structure during flight. Notably, the aircraft lacks traditional fuel tanks in those wing sections, storing fuel directly in the bulkhead to minimize weight. The fuel used is JP-7, a thick jet fuel specifically developed for high-speed flight.
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Antiphon said:That's jet fuel leaking out of the seams. The SR-71 was designed to "seal up" at full speed through thermal expansion at Mach 3+. It has no fuel tanks in those sections of the wings. The fuel is stored directly in the bulkhead to save weight.