The emergence of corrosion as a major factor in the continued service life of the KC-135 forces AMC to place emphasis on the development of corrosion treatment and prevention technologies. Until the effects of corrosion can be determined, an accurate economic service life will not be known. AMC’s goal is to accurately define the KC-135’s economic service life with the effect of corrosion by FY00. The possibility exists that studies will show an economic service life beyond that of other air mobility aircraft, but a tentative replacement is scheduled for FY13 pending analysis results.The KC-135 and KC-10 will continue to meet AMC's air refueling requirements and bolster the air mobility system into the next century. Although cargo transportation is not their primary mission, both aircraft are playing an increasing role in cargo operations. Tankers are flying more worldwide, low-volume channel and scheduled cargo missions allowing strategic airlifters to be dedicated to the tasks only they can accomplish. A cargo floor roller system eases the burden of hand loading the aircraft and reduces the time spent accomplishing airlift requirements during unit movements. Procurement of the Tunner (60K) loader will greatly enhance the en route supportability and cargo loading for the KC-10. In an effort to improve the capabilities of AMC's tanker fleet and to provide support to carrier based aircraft, wing mounted drogue refueling pods were installed on 20 KC-10s and will be installed on 33 KC-135s to provide an extra margin of safety for receivers necessary for over water operations.
|Part No.||Model||Fuel Flow (GPM)||Aircraft Application|
|149R1001||FR300 B, D, E, F||150-330||KC-130, HC-130|
|149R1051||FR300 C||150-330||KC-130, HC-130|
|Part No.||Mounting||Fuel Flow (GPM)||Major Dia. (Inches)||Aircraft Application|
|34-000-48317||Wing||400||34.0||B-707 T/T, KC-135, KC-10|
|Part No.||Mounting||Capacity (US gal.)||Fuel Flow (GPM)||Major Dia. (Inches)||Aircraft Application|
|31-300-48053||Fuselage Centerline||300||200||31.0||A-4, A-6, A-7|
|31-301-48310||Fuselage Centerline and wing||301||220||31.0||A-4, A-6, A-7, S3A,F-18|
Although these dare-devil feats were labeled barnstorming gimmicks, military aviators were the ones who recognized the value of air refueling. The basic complaint of aviators during World War I was that they could not stay aloft for more than 20-40 minutes before they had to return to base for refueling. Army Air Service Lieutenant John Richter sought help from Major Hap Arnold, then commander of Rockwell Field in San Diego to test the idea of using the force of gravity. They tested this refueling idea with success. In 1923, he and Lieutenant Lowell Smith flew their DH-4B aircraft aloft for more than 37 hours. They contacted each other fifteen times to receive oil, supplies and 75 gallons of gasoline by means of a fuel hose.
This exchange was followed by others, including a few that ended in tragedy. But, it was a Fokker C-2 trimotor monoplane called the Question Mark and two Douglas C-1 biplanes which demonstrated the value of mid-air refueling. The Question Mark was fitted with additional tanks to receive fuel; the biplanes, dubbed RP #1 and RP #2, were configured with two 150 gallon fuel tanks and a 50 foot hose with a lead weight attached to the end. The hose would be lowered through a trap door in the bottom of the C-1's fuselage. Despite numerous problems, which in themselves are a great story, the refueling was a great success. The Question Mark was kept aloft for more than six days during which time it had received 40 tons of material, including 5,660 gallons of gasoline, 245 gallons of oil, meals, water, batteries and other supplies.
Even with this success, refueling progress was limited. When the US was drawn into World War II, to reach their German targets bombers had to be based in England and the Mediterranean area. With no refueling capability, fighter escorts with limited range had to return to base for refueling. The Luftwaffe waited until the escorts headed for home and then attacked the bombers. On the Pacific front, inadequacies of long-range bombing also became clear. A proposed attack on Tokyo from Hawaii was scrubbed because of lack of refueling crews and equipment. Even though tests during 1943 and 1944 proved successful, the end of the war thwarted further development.
By 1946, when the Strategic Air Command (SAC) was activated at Bolling AFB, planners realized that in order for SAC to fulfill its global mission, in-flight refueling would have to be part of the program. The Air Materiel Command (AMC) contracted with Boeing Airplane Company to study transferring fuel by hose between two B-29s. The process called for the tanker and bomber to fly in formation at just under 200 knots and about 20 feet above and 75 feet behind, with the tanker above, ahead and to the left. A cable called a "contact line" with a 50 pound lead weight on the end trailed from the tanker; the receiving B-29 trailed a cable called the "hauling line" from its refueling receptacle. A grappling hook at the end of the hauling line caught the tanker's contact line during the crossover and a winch in the tanker wound in both lines. The tanker operator then attached the hauling line to the hose, another winch in the receiver aircraft pulled the hose out of the tanker. Once the hose nozzle was in place, it was locked with hydraulic toggles. A "contact made" signal was sent to the tanker and fuel transfer was started.
The process went through trials, and ultimately, the method proved successful. So much so, that the Air Force authorized 92 B-29s converted to hose-equipped tankers and another 74 modified to act as receivers. In June 1948, the 43d and 509th Air Refueling Squadrons, based at Davis-Monthan and Rosewell AFBs respectively, became the first air refueling units in the United States Air Force. The KB-29 was to become the work horse of the Air Force through the mid-1950s.
The sustain this new level of global flexibility at the outset of the Korean War, the Air Force needed air refueling procedures fitted for combat aircraft. The KB-29M tested the probe-drogue system. One KB-29 trailed refueling hoses from pods on both wing tips and one from a centerline position The remaining tankers had only one centerline hose. Fighter aircraft flew into position behind the tanker so that its probe could be inserted in the drogue at the end of the tanker's hose.
The system was good, but too limited. Boeing was hired to build an aerodynamically controlled, swiveling and telescoping arm known at the "Flying Boom." The boom was controlled by an operator positioned in the B-29s tail turret. The operator "flew" the boom nozzle by means of airfoils called ruddevators into a receptacle, usually atop the receiver's fuselage. The pilot stayed in contact by following a series of colored lights along the base of the boom to indicate "right," "left," "fwd," "aft," etc.
To meet the more powerful aircraft being developed, the KB-29s were phased out with the development of the more powerful KC-97 class of tanker-transporter. The primary improvements were speed and a better boom position to place the nozzle more precisely into the receptacle. Despite propeller problems, the KC-97 went on to set many records. But its most important contribution to air flight was its ability to refuel the short range aircraft such as the B-47 to serve as long-range bombers. It served the military warfighters well from 1956-1965.
The new replacement on the scene was the Boeing KC-135 jet tanker which was destined to dominate air refueling for the next 25 years and continues to play a significant role in air refueling through the twentieth century. Record-breaking flights were commonplace with the KC-135. They played an integral part in the SAC decision to keep a portion of its alert force airborne at all times. The mission of the B-52s was called "CHROME DOME." Missions averaged 24 hours in length and covered the southern route crossing the Atlantic, the Med and then return to the U.S.; the northern route up the eastern coast of Canada, across Canada west toward Alaska, then down the west coast of North America. This mission lasted seven years.
The other KC-135 historic achievement was its support of refueling missions in Southeast Asia. One of the most interesting accomplishments was the "Silent Refueling" missions of ARC LIGHT. Most missions consisted of between 18 and 30 tankers and an equal number of bombers. The entire process was accomplished without any form of vocal communication. Takeoff came by way of a green light from the tower. Tankers launched one minute apart with three minute spacings between formations. The tankers rendezvoused with the receiving B-52s by electronic beacon, often in bad weather, and usually at night. The tankers off-loaded about 12,256 gallons of fuel to each B-52, then returned to base. By 1972, there were 172 KC-135s flying from six bases. Monthly tanker sorties peaked at 3900 in support of fighter and bomber operations. From 1964 to the end of the war, KC-135s had flown 194,687 sorties, providing nearly 9 billion pounds of fuel in 813,878 refuelings. Truly representative of American mastery of the skies.
After nearly 25 years of service, the KC-135 was scheduled for a major modification to address metal fatigue in the wings and inefficiency of the J-57 engines. Even though tight budgets slowed down the reengineering effort, by 1990, a large portion of the fleet had been updated and return to service.
Responding to the need to be able to move air power into theaters of operation quickly, the Air Force looked to a concept known as ATCA - the Advanced Tanker/Cargo Aircraft. The demand for large cargo, as well as fuel transfer capabilities, led the military toward a wide body jet. McDonnell-Douglas had a DC-10 in operation. Work began on modifying this commercial aircraft to meet the military's specific needs. The most important logistical advantage to this aircraft was that the plane's components were interchangeable with the commercial DC-10. Since this plane was already used around the world, the Air Force could make use of an existing worldwide supply network.
Advantages over the KC-135 are notable. The KC-10 can be refueled using a universal receptacle atop the fuselage just aft of the cockpit. It can also refuel receivers using both the boom and probe-drogue methods on the same mission. With additional tanks added to the normal DC-10 tanks, the fuel capacity is nearly twice that of a KC-135 at 356,065. The boom area is also radically different. In the KC-135, the boom operator works in a prone position. In the KC-10, there is a small room with three seats and a large 26x54 inch window for the operator to see the receiver. A system of mirrors allows the "boomer" to monitor other aircraft in formation off the KC-10 wing tips. The boom is 10 feet longer than the KC-135s and features "fly by wire" flight controls and an increased fuel transfer rate of up to 1,500 gallons per minute. The KC-10 has served as an invaluable tool in the military forces. Perhaps too often , the tanker force goes unrecognized in the accomplishment of feats that attract media coverage to fighter aircraft. But, in the greater scheme of things, they have the satisfaction where it counts-from pilots who rely on them everyday to be there when they need refueling. And, they always are-refueling the forces.