a reply to: paradoxious
The performance characteristics of the Blackbirds have all been fully declassified.
Mach 3.32 was the design cruise speed, but maximum allowable Mach number was dependent on outside air temperature and its effect on compressor inlet
temperature (CIT). The pilot was authorized to accelerate to Mach 3.3 as long as CIT remained at or below 427 degrees Centigrade. Speeds exceeding
Mach 3.3 were occasionally recorded, but generally the pilot tried to avoid this area of the performance envelope because it placed excessive thermal
stress on the airframe.
Some maximum speed milestones:
YF-12A, 1 May 1965, Mach 3.14 (2,070 mph)
A-12, 8 May 1965, Mach 3.29 (2,171 mph)
SR-71A, 28 July 1976, Mach 3.32 (2,193 mph)
The Blackbirds were designed to cruise at 85,000 feet with a useful fuel load and reconnaissance package. Because the A-12 was 20,000 pounds lighter
than the SR-71, it had an altitude capability about 3,000 feet higher than that attained by the SR-71 at any given point in a flight profile for
missions of the same range.
Some maximum altitude milestones:
YF-12A, 1 May 1965, 80,257 feet
SR-71A, 1968, 89,650 feet
A-12, 14 August 1965, 90,000 feet
In 1975, Lockheed studied the possibility of expanding the flight envelope of the SR-71 with some modifications. The results of several studies
concluded the maximum speed limit could be extended to Mach 3.5 for short periods of time. The only structural limit to speeds above Mach 3.5 was a
KEAS (knots equivalent airspeed) limit of 420, set by inlet duct pressures and temperatures that exceeded acceptable values. Limited inlet
capture-area and excessive engine CIT also limited operation at higher Mach numbers, even with proposed modifications.
Similar studies addressed the possibility of achieving flights well above 85,000 feet. results indicated the SR-71 could briefly reach an altitude of
about 95,000 feet in a zoom-climb profile. The proposed mission could have been accomplished with an airplane having a gross-weight of 85,000 pounds.
According to the flight profile, the pilot would accelerate from Mach 3.2 to 3.5 at an altitude of 80,000 feet, then zoom to 95,000 feet as speed
decreased to normal cruise mach numbers. The airplane would subsequently settle back down to an altitude of about 84,000 feet. Sustained flight above
85,000 feet was limited by wing surface-area and engine thrust capabilities.
Stories about the Blackbirds leaking fuel while on the ground are true. Maintenance crews had to place numerous pans and buckets underneath the
airplane while it was parked in the hangar. It was kind of a nightmare for Air Force firefighters who were accustomed to seeing any fuel leak as a
serious fire hazard, but the flash point of JP-7 was extremely high. You could drop a lit match in a puddle of JP-7 and the flame would be
extinguished. I once tested this with a small sample I collected from a drip pan beneath the SR-71B. Igniting JP-7 required a shot of tri-ethyl borane
(TEB) -- you can see the effect in archival photos and videos as a green flash in the afterburner at engine start. I once got to see this phenomenon
close up in real life (from a distance of less than 20 feet).