VSL SR-71-TB Climb Profiles to Mach 3.0/70,000 ft EXPLAINED!
The SR-71 was a highly powered aircraft. Yet, it accelerated and climbed to the Mach 3.0 cruise altitude (designated Mach 3.2 @ 80,000 ft) using a precise schedule. Reasons behind this were in large: to optimized fuel consumption and to fly within the edges of its flight envelope dynamic boundaries considerations.
Here are some of the unique characteristics of the SR-71 in the light of the above:
Afterburners:
Unlike conventional military jet aircraft, the SR-71 was certified for continuous afterburner (A/B) operation. The throttles had a relatively large range of movement in A/B as the aircraft required various A/B power settings throughout flight (it was a gradual A/B with a large envelope regime).
Typically, at Mach 3.0 cruise, the throttles were set near the minimum A/B position, and the Fuel flow on each engine at Mach 3.0 cruise was around 20,000 pounds per hour.
In general, typical Mach 3 mission was flown as followes:
- Fuel is set to 50% in the VSKYLABS SR-71-TB. In real-world operations fuel load was varied depending on the mission.
- Take off using full A/B.
- Climbing to refueling altitude at Mach 0.9, no afterburner was required when takeoff load was as defined in the VSKYLABS SR-71-TB.
- Refueling session.
- Climbing to 30,000 feet at Mach 0.9 (A/B may be required).
- Acceleration to Mach 1.25 (two main methods):This could be done in level flight, at ~ 30,000 ft.Climbing to 33,000 ft, then performing a pushover to 6000 ft/min, down to 28,000 ft. aiming for hitting 28,000 ft / Mach 1.32.
- Main climb profile: Recommended 450 KEAS climb in full A/B power. (500 KEAS with high payloads).
- Linear decrease in KEAS once hitting Mach 2.6. This is an important phase in which the Mach number keep on climbing, while the KEAS is reduced. In general, it was about 0.1 Mach per 10 KEAS. If performed correctly, you should hit 70,600 ft @ Mach 3.0!
Important:
Refueling to full capacity in the air-refueling phase is a hard-condition for accelerating beyond Mach 2.6. Failing to do so will result with the JP-7 vaporized fuel to to be ignited (!). Filling up the tanks to full capacity allows all pressurized *air* in the tanks to vent out, then, Nitrogen is being used to pressurize the tanks. Nitrogen is an inert gas and the JP-7 would not be ignited.
Here are some more useful references:
