The SR-71's slender, streamlined body creates a low-pressure area above the wings and a high-pressure area below them, as it moves forward. This difference in pressure provides the lift, causing the aircraft to move upwards.
To further increase lift, the SR-71 uses supersonic inlets and variable-geometry exhaust nozzles. The supersonic inlets allow air to flow into the engines rapidly, increasing thrust. The variable-geometry exhaust nozzles change the size of their openings, allowing more efficient engine operation at different speeds and altitudes.
In addition to these features, the wings are located relatively far to the rear of the fuselage. This gives them more room to generate lift without being disturbed by the flow of air over the cockpit.
Finally, the SR-71's skin is heated by the friction of air at high speed, which prevents the boundary layer from separating and allows for high amounts of lift.
All these factors combined allow the SR-71 to achieve and sustain flight at speeds of over 3 times the speed of sound.
