The KC-135 Stratotanker's primary mission is to refuel long-range bombers. It also provides aerial refueling support to Air Force, Navy, Marine Corps and allied aircraft.Four turbojets, mounted under wings swept 35 degrees, power the KC-135. Nearly all internal fuel can be pumped through the tanker's flying boom, the KC-135's primary fuel transfer method. A special shuttlecock-shaped drogue, attached to and trailed behind the flying boom, is used to refuel aircraft fitted with probes. An operator stationed in the rear of the plane controls the boom. A cargo deck above the refueling system holds passengers or cargo. Depending on fuel storage configuration, the KC-135 can carry up to 83,000 pounds (37,350 kilograms) of cargo.
The KC-135 tanker fleet made an invaluable contribution to the success of Operation Desert Storm in the Persian Gulf, flying around-the-clock missions to maintain operability of allied warplanes. The KC-135s form the backbone of the Air Force tanker fleet, meeting the aerial refueling requirements of bomber, fighter, cargo and reconnaissance forces, as well as the needs of the Navy, Marines and allied nations.
Because the KC-135A's original engines are of 1950s technology, they don't meet modern standards of increased fuel efficiency, reduced pollution and reduced noise levels. By installing new, CFM56 engines, performance is enhanced and fuel off-load capability is dramatically improved. In fact, the modification is so successful that two-re-engined KC-135Rs can do the work of three KC-135As. This improvement is a result of the KC-135R's lower fuel consumption and increased performance which allow the tanker to take off with more fuel and carry it farther. Since the airplane can carry more fuel and burn less of it during a mission, it's possible to transfer a much greater amount to receiver aircraft.
The quieter, more fuel-efficient CFM56 engines are manufactured by CFM International, a company jointly owned by SNECMA of France, and General Electric of the U.S. The engine is an advanced-technology, high-bypass turbofan; the military designation is F108-CF-100. Related system improvements are incorporated to improve the modified airplane's ability to carry out its mission, while decreasing overall maintenance and operation costs. The modified airplane is designated a KC-135R.
Because the KC-135R uses as much as 27 percent less fuel than the KC-135A, the USAF can expect huge fuel savings by re-engining its fleet of KC-135s - about $1.7 billion over 15 years of operation. That's enough to fill the gas tanks of some 7.7 million American cars each year for a decade and a half. Annual savings are estimated to be about 2.3 to 3.2 million barrels of fuel, about three to four percent of the USAF's annual fuel use. This equals the fuel needed to provide electrical power for 145 days to a city of 350,000 to 400,000.
Re-engining with the CFM56 engines also results in significant noise reductions. Area surrounding airports exposed to decibel noise levels is reduced from over 240 square miles to about three square miles. This results in a reduction in the noise impacted area of more than 98 percent. Maximum take-off decibel levels drop from 126 to 99 decibels. This meets the tough U.S. Federal Air Regulation standards -- a goal for commercial aircraft operated within the U.S. In addition, smoke and other emission pollutants are reduced dramatically.
Boeing has delivered approximately 400 re-engined KC-135Rs and is under contract for about 432 re-engine kits. Each kit includes struts, nacelles, 12.2 miles of wiring, and other system modification components. Engines are purchased directly by the Air Force from CFM International.
Boeing has completed work on a program to re-engine all KC-135As in the Air Force Reserve and Air National Guard fleet -- a total of 161 airplanes. In that modification program, which began in 1981, KC-135As were modified with refurbished JT3D engines taken from used, commercial 707 airliners. After modification, the airplanes are designated KC-135Es. This upgrade, like the KC-135R program, boosts performance while decreasing noise and smoke pollution levels. The modified KC-135E provides 30 percent more powerful engines with a noise reduction of 85 percent.
The program included acquisition of used 707s, procurement of purchased parts and equipment, basic engineering, some parts manufacturing, and refurbishment and installation of the engines, struts and cowling. Kits also included improved brakes, cockpit controls and instruments.
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