KC-135R Stratotanker

The Boeing KC-135 Stratotanker is a United States aerial refueling tanker aircraft. It has been in service with the United States Air Force since 1957.

All KC-135s were originally equipped with Pratt & Whitney J-57-P-59W turbojet engines which produced 10,000 lbf of thrust dry, and approximately 13,000 lbf of thrust wet. Wet thrust was achieved through the use of water injection on takeoff. 670 gallons of water were injected into the engines over the course of two and a half minutes. This water allowed a second set of fuel injectors to activate without melting the turbine buckets. The water turned to steam, was ejected out the rear of the engine, and increased thrust. The water and the extra fuel increased the mass through the engine, increasing thrust. The engine ran a little hotter, increasing thrust as well as engine noise. The A-model on takeoff was a loud jet. In the 1980s the first modification program re-engined 157 Air Force Reserve (AFRES) and Air National Guard (ANG) tankers with the Pratt & Whitney TF-33-PW-102 engines from 707 airliners retired in the late 1970s and early 1980s. The re-engined tanker, designated the KC-135E, (now retired) was 14% more fuel efficient than the KC-135A and could offload 20% more fuel on long duration flights. (The difference is that the A-model weighed only 104,000 lb empty, while the E-model weighed 115,000 lb empty. But the maximum takeoff weight was not increased for the E-model. Therefore, the A-model could takeoff with 200,000 lb of fuel, while the E-model could only takeoff with 190,000 lb of fuel.) Only the KC-135E aircraft were equipped with thrust-reversers for takeoff aborts and shorter landing roll-outs.

The second modification program re-engined 500 with new CFM International CFM56 (F-108 for the military designation) engines produced by General Electric and Snecma. The re-engined tanker, designated either the KC-135R or KC-135T, can offload up to 50% more fuel (on a long duration sortie), is 25% more fuel efficient, costs 25% less to operate and is 96% quieter than the KC-135A.

The KC-135R's operational range is 60% greater than the KC-135E for comparable fuel offloads, providing a wider range of basing options.