Operational Sortie

The Accel

The trans-sonic acceleration called for a climb-and-descent maneuver we called the "Dipsey Doodle." The maneuver accelerated the SR-71 to supersonic speeds as rapidly as possible to minimize the time spent between Mach 1.05 an 1.15, an area of excessive drag on the aircraft. The "Dipsey Doodle" started out by lighting both ABs to their minimum setting and climbing at 0.9 Mach.

As you passed through 30,000 feet, the throttles were advanced to max AB, continuing the climb to 33,000 feet and slowly increasing the airspeed to 0.95 Mach. Approaching 33,000 feet, Habus nosed the aircraft over gently an began a descent of 2,500 - 3,000 feet/min. For optimum acceleration, it was important to exceed Mach 1.05 early in the descent and to avoid turning until the climb was established. Going through Mach 1 in the SR-71 behaved no different than any other aircraft. Approaching 420 -430 KEAS (Knot Equivalent Air Speed), the pilot started to bring the nose up slowly, so as to capture and hold 450 KEAS while climbing. Stabilized at 450 KEAS, he engaged the pitch autopilot and the "KEAS HOLD" function. For the remainder of the accel the autopilot held 450 KEAS until the KEAS bleed schedule was reached at Mach 2.6. Pilots watched for the forward bypass doors to begin opening up at around Mach 1.4. During the accel, there was considerable pilot technique and finesse involved in managing the inlets.

What is KEAS?

KEAS stood for Knots Equivalent Air Speed and is calibrated airspeed corrected for compressibility effects of altitude and airspeed. Once the aircraft was supersonic, the only speed (other than Mach) we talked about was KEAS. During the accel, we engaged the KEAS HOLD at 450 KEAS to keep the speed constant until reaching what was called the KEAS bleed schedule. This began at Mach 2.6 and automatically decreased the KEAS 10 knots for each tenth of Mach speed increase. The bleed schedule kept the aircraft from exceeding its maximum KEAS.

Around Mach 2.95, the pilot disengaged the KEAS HOLD function of the autopilot and began to control pitch by rotating the pitch wheel forward to achieve a smooth level off. He slowly lowered the nose of the aircraft until the pitch steering bar on the ADI (Attitude Direction Indicator) barely touched the miniature aircraft while retarding the throttles from full AB to the approximate fuel flow readings for Mach 3 cruise.

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