Lockheed Martin photo
On April 26, 1971, pilot Lt.Col. Thomas Estes and RSO Lt.Col. Dewain Vick flew #968 15,000 miles in 10 hours 30 minutes non-stop on a gruelling marathon mission to test the endurance of the J58 engines and the blackbird airframe, but mostly to see how many times they could refuel before the liquid nitrogen gave out.
At blackbird speeds and temperatures, oxygen becomes explosive and can spontaneously ignite in the tanks and fuel lines. In order to prevent this, all 6 fuel tanks are purged with pure nitrogen before being filled. The blackbird also carries 260 liters of liquid nitrogen in 3 dewars. This nitrogen expands into its gasous form as it is pumped into the fuel tanks to top them off as fuel is consumed. Without the nitrogen, the empty fuel tanks would cavitate from the increased pressure when returning to lower altitudes to refuel.
Taking off from Beale AFB in California, they flew 2 laps around the continental United States via Missoula, Montana; east to Bismark, ND; southeast to Peoria, IL; east to Columbus, OH; southeast to Cape Hatteras, NC; southwest to Gainsville, FL; south to Tampa, FL;
west to San Antonio, TX; northwest to El Paso, TX; west to El Centro, CA; then back to Beale AFB. Once the second lap was complete, they entered the third lap and turned south at Bismark, for Santa Fe, NM; then west to Las Vegas, NV;
then finally back to Beale (flight plan via Ron Kloetzli).
This 15,000 mile, 10.5 hour flight required five aerial refuellings. After the flight the aircraft was thoroughly examined and found to be none the worse for the experience. The SR-71 remains to this day the only aircraft rated to run in full continuous afterburner. On September 20, 1971, Estes and Vick were awarded the 1972 Harmon International Trophy by President Richard Nixon for their accomplishment. They were also awarded the 1971 Mackay Trophy for the same flight.
L-R Sen. Barry Goldwater (R-Arizona), LtCol. Tom Estes (pilot), President Richard Nixon, and LtCol. Dewain Vick (RSO), at the White House on September 20, 1971 for the presentation of the 1972 Harmon International Trophy. - USAF photo via John Stone|
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