| High
Mach Cruise |
| Above
60,000 feet, the airspace was all ours! Since there was no other
aircraft to concern ourselves with above 60,000 feet, we flew
the SR-71 in what was called a cruise/climb maneuver for maximum
efficiency. Because of the tremendous rate of fuel consumption
in afterburner cruise (around 44,000 lbs./hour), we flew continuously
at the optimum cruise altitude for the aircraft as our gross
weight decreased. That worked out to about 100-150 feet/minute
rate of climb for the aircraft. |
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With
a full load of fuel, Habus typically started off a mission with
an initial level-off altitude of around 71,000 feet. By the time
they were ready to descend, they were cruising up around 78,000
feet. We generally flew the Mach programmed on the flight plan as
long as "temp devs" were not a factor. Often, because
of warmer temperatures, we flew slightly faster to keep the forward
bypass doors running tighter. The SR-71's cruise performance was
not like other jet aircraft. In other jets, if you wanted to fly
considerably faster, it cost you more fuel. The Blackbird was just
the opposite; the faster you flew, the more fuel you saved.
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What
was it like to fly so high?
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Above
80,000 feet the horizon-to-horizon view of the ground beneath
was tremendous, providing a pronounced view of the curvature
of the earth. Colors in the sky were deeper and more vivid,
and the sun was so brilliant that it washed out cockpit instrumentation
as it moved across the panel in turns. During the day the horizon
was a deep blue color, slowly changing to the black of night
as you looked higher and higher above the horizon. Peering upward
into the dark sky, you could see the stars in the daytime. |
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| The
design Mach of the SR-71 was Mach 3.2. However, when authorized by
the Commander, speeds up to Mach 3.3 could be flown. The maximum altitude
was 85,000 feet unless specifically authorized higher. After the SR-71
cruised for about 15-20 minutes, the entire aircraft had heated up
to cruise temperatures. This ranged from around 500-699 degrees F
on all leading edges to 1,100 degrees F at the exhaust nozzle area.
At our cruising altitudes, there is very little sensation of traveling
at 2,200 mph. I always had a greater sensation of speed over the ground
flying a T-38 on one of our low level navigation routes at 415 mph
at 1,000 feet. The only sense of speed at high altitude was watching
the DME (Distance Measuring Equipment) click off at 33 miles per minute.
More than a speed sensation, Habus gained a greater appreciation of
time and distance relationships. To be able to fly from California
to England in only four hours, or Japan in five hours, was a remarkable
feat for any aircraft. |
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Return to Sortie
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| ©
Copyright
Richard Graham |
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