The SR-71 Blackbird remains to this day the only aircraft rated to run in full continuous afterburner.
Engineered to maintain speeds of Mach 3 at altitudes exceeding 80,000 feet, the Pratt & Whitney J58 turbojet engine was responsible for powering the entire Blackbird family: the Lockheed A-12, YF-12, and SR-71. A remarkable achievement in engineering, the J58 featured a single-shaft rotor configuration paired with an innovative compressor bleed bypass, allowing it to operate at extraordinarily high speeds. What set this engine apart was the six bypass tubes that channeled airflow from the compressor stage straight into the afterburner. This allowed the Blackbird to operate at a much higher fuel efficiency than other afterburning jet engines when in full afterburner (AB).
The daughter of Col. Richard (Butch) Sheffield, who served as a Reconnaissance Systems Officer for the SR-71, shares this on her Facebook page, Habubrats:
‘On Apr. 26, 1971, pilot Lt. Col. Thomas Estes and RSO Lt. Col. Dewain Vick (he and his family were one of my neighbors at Beale AFB) flew SR-71 #968 15,000 miles in 10 hours 30 minutes non-stop on a grueling 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 [for this flight, the SR-71 only had 2 – 106-liter liquid nitrogen dewars. The 3rd 50-liter dewar was added in the mid-1980s]. This nitrogen expands into its gaseous form as it is pumped into the fuel tanks to top them off as the 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 refuelings. 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.’
Sheffield Miller recalls how another SR-71 Blackbird pilot reacted after a long flight: ‘I interviewed Colonel Shelton about his 13-hour flight during the Yom Kippur War. And he said that after a long flight like this, his adrenaline was hyped up so high that he was unable to sleep even though he was exhausted.
‘To help with his adrenaline being on overdrive, he would go for a long walk to settle down.’
Sheffield Miller concludes,
‘On Sep. 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.’
*Crew Chief Floyd Jones explains, ‘The SR-71 does have three LN2 Dewars, two in the nose wheel and the third in the left chine just outboard of K bay. The LN2 goes from the Dewars to coils (heat exchange) in tanks 1 and 3, which turns the Liquid into gases of nitrogen. The wing tanks are the ones that have the worst leaks. The reason is that during the in-flight refueling, tanks 3 & 6 are empty. During the refueling, the excess Hot tanks and the very Cold Fuel cause the Tank Sealant to fracture (crack), causing leaks.’
Source www.Habu.org
Photo by Lockheed Martin via www.Habu.org and U.S. Air Force
