The McDonnell Douglas KC-10A Extender is an advanced aerial tanker and cargo aircraft designed to provide increased global mobility for U.S. armed forces. Although the KC-l0's primary mission is aerial refueling, it can combine the tasks of a tanker and transport aircraft by refueling fighters and simultaneously carrying the fighter support personnel and equipment on overseas deployments.
Based on the McDonnell Douglas DC-10 Series 30CF Convertible Freighter, the KC-10A Extender emerged victorious in a contest with Boeing's Model 747 aerial tanker variant to satisfy the U.S. Air Force's Advanced Tanker Cargo Aircraft requirement. In December 1977, it was selected by the USAF based on integrated assessment of capability, price, life-cycle costs and technical features of the DC-10.
The KC-10's maiden flight took place on 12 July 1980. The first aerial refueling occurred during testing on 30 October 1980, with the receiver aircraft a C-5 Galaxy. The first KC-10 was delivered to the USAF on 17 March 1981. The 60th and last was formally handed over on 29 November 1988.
In the mid-1990s, the major USAF reorganization that witnessed the elimination of the Strategic Air Command (SAC) resulted in the KC-10 Extender fleet being reassigned among units of the Air Mobility Command (AMC) and Air Combat Command (ACC), before all being controlled by AMC. All KC-10's, apart from a single aircraft that was destroyed in a fire on the ground in September 1987, are still in service.
The KC-10 is powered by three General Electric CF6-50C2 high bypass-ratio turbofan engines, each generating 52,500 pounds of thrust. Versions of the CF6 engine family are installed on most of the DC-10s in commercial airline service and have compiled an impressive reliability record. One of the engines is mounted at the base of the tail above the aft fuselage, and the other two are installed on pylons beneath the wings, one on each side of the fuselage.
Although the KC-10 retains 88 percent of systems commonality with the DC-10-30, it has additional systems and equipment necessary for its Air Force mission. Additions include military avionics, director lights for receiver aircraft, an aerial refueling boom, an aerial refueling hose and drogue system, a 3-seat aerial refueling operator station (ARO) and an aerial refueling receptacle. Several aircraft in the KC-10 fleet have been modified with wing-mounted pods to further enhance aerial refueling capabilities. The hose and drogue WARP (Wing Air Refueling Pod) modification allows for the aerial refueling of two aircraft simultaneously. This is extremely helpful when refueling naval fighter groups - a fighter group can be refueled two at a time, reducing the waiting period of the other aircraft and allowing each aircraft to "save" fuel.
In addition to the DC-10's standard wing and auxiliary tanks, the KC-10 has a bladder-type supplementary fuel tankage system which includes seven unpressurized integral-body fuel cells, four aft of the wing and three forward, all located in under-deck vented cavities. A crashworthy design makes use of keel beams and strategically placed energy absorption material to protect the tanks. Under-fuselage panels permit direct access to each cell for installation, removal, and system, maintenance and structural inspection. Combined, the tanks carry more than 356,000 pounds (160,200kg) of fuel - almost twice as much as the KC-135 Stratotanker.
During boom refueling operations, fuel is transferred to the receiver aircraft at a maximum rate of 1,100 gallons (4,180 liters) per minute; the hose and drogue refueling maximum rate is 470 gallons (1,786 liters) per minute. The KC-10 can be air-refueled by a KC-135 or another KC-10 to increase its delivery range.
The aerial refueling operator's station in the KC-10, located aft of the rearward lower fuselage fuel tanks, features improvements in comfort, viewing capability, and environment. Instead of assuming the prone position required by the KC-135, the refueling operator sits in an aft-facing crew seat. Station equipment includes handy refueling controls, a wide viewing window facing aft and additional periscope-type viewing arrangements for traffic management. Accessible from the upper deck, the ARO station is pressurized and has independent thermal control, a quiet environment and an arrangement suited for both training and operational missions. While refueling requires only one operator, two additional seats are provided to accommodate an instructor and an observer.
For cargo-handling, the KC-10 is equipped with a large, upward-hinging cargo door, located on the left side of the forward fuselage, which provides the capability to transport a significant portion of the tactical support equipment of fighter squadrons. The cargo loading system, adapted in part from the commercial DC-10 freighter, has been enhanced with the addition of powered rollers, powered winch provisions for assistance in fore and aft movement of cargo, and an extended ball mat area to permit loading of larger items. The cargo compartment can accommodate loads ranging from 27 pallets to a mix of 17 pallets and 75 passengers. In an all-cargo configuration, the KC-10 accommodates 25 standard 88 x 108-inch 463L cargo pallets in the cabin with aisles down both sides, or 27 pallets with a single aisle.
Other modifications to the aircraft include elimination of most upper deck windows and lower deck cargo doors, and provisions for additional crew. Several configurations exist for personnel and crew accommodations. One arrangement is for a crew of five, plus six seats for additional crew and four bunks. The same area also has space for the installation of 14 more seats for support personnel. In another arrangement, the bunks can be shifted rearward, making room for 55 more support personnel, along with the necessary utility, lavatory and stowage modules, raising the capacity to a total of 80 crew and support personnel. Although all eight of the DC-10 upper deck passenger doors are installed as standard, three are deactivated. Normal entry and exit are through the two forward passenger doors on each side, and the aft right-hand door is available as a ground emergency exit for people in the aerial refueling operator's station.
During Operations Desert Shield and Desert Storm (1990-91), the KC-10 fleet provided inflight refueling to aircraft from all branches of the U.S. armed forces as well as those of coalition forces. This allowed for continued air operations without costly and time-consuming ground refueling. Aerial refueling was key to the rapid airlift of materiel and forces. In addition to refueling airlift aircraft, the KC-10, along with the smaller KC-135, moved thousands of tons of cargo and thousands of troops in support of the massive Persian Gulf build-up. The KC-10 and the KC-135 conducted about 51,700 separate aerial refueling operations and delivered over 125 million gallons (475 million liters) of fuel without missing a single scheduled rendezvous.
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