Article by Douglas Ritter
This article appeared in the January 1993 issue of Code One Magazine.
Print friendly version of this article (text only)
An F-16 carefully closes on a KC-10 tanker from below. As the fighter nears, a long boom extends down from the rear of the KC-10. The fighter pilot flips a switch and the receiver door atop his fuselage drops in. Stabilizing his approach about seventy-five feet behind the KC-10, the pilot throttles back to match his speed with the tanker's. The fighter pilot nudges the throttle forward and his jet inches closer while staying aligned with the end of the boom.
The pilot makes only minute control inputs. Guided by lights beneath the tanker, the fighter pilot maneuvers into position. As the end of the boom passes from sight, the boom arm swings overhead so close the pilot could reach up and grab it were it not for the canopy. The boom operator in the rear of the tanker looks down at the fighter and guides the end of the boom into the receptacle behind the cockpit. As soon as the end of the boom is lined up with the connector, the boom operator forces it home into the receptacle, locking into the fighter. The F-16 pilot hears a thunk behind his head and another air-to-air refueling operation is underway.
Pumps whine as jet fuel flows through the hollow boom into the F-16 at the rate of 200 gallons per minute. In just under seven minutes, nearly 10,000 pounds of fuel are transferred and the thirsting fighter is topped off. A quick thumbs-up, a slight spray of fuel at disconnect, and another aerial refueling is completed. The boom instantly retracts and raises out of the way. The F-16 backs off. The pilot flips a switch and the fuel receptacle door closes. The F-16 slips to the side to allow the next fighter its turn at the pump.
Day or night, good weather or bad, aerial refueling keeps our military aircraft in the air, extending their endurance, range, and payload and vastly increasing their effectiveness. When duty calls at the far reaches of the globe, aerial refueling allows a rapid response. Without aerial refueling, the face of modern combat would be changed. Most strategic and tactical air missions could never be undertaken.
The importance of aerial refueling was reemphasized during the Gulf War. Getting the warplanes and their support equipment and personnel as well as ground combat troops, equipment, and supplies to the Middle East required an extraordinary aerial refueling effort on short notice. The first group of deployed F-15s required seven refuelings during their fifteen-hour flight direct to Saudi Arabia from Langley AFB, Virginia. Once in theater, aerial refueling continued to play a critical role. Without it, the F-117A stealth fighter would have run out of fuel before it could drop its bombs with impunity. Many aircraft returned to refueling points with barely any fuel left. When the exigencies of the war ate into a fighter's planned fuel reserve, tankers picked up the slack. As one tanker pilot boasted during the war, "Fighter jocks buy drinks for tanker crews; not the other way around."
Fighter crews weren't the only ones dependent on aerial refueling during the war. Large command-and-control aircraft, like the E-3 AWACS and the E-8 Joint-STARS, also depended on these flying gas stations to stay aloft so they could provide the continuous mission control and reconnaissance our forces required. Cargo aircraft, including the giant C-5 Galaxy, used aerial refueling to speed delivery of their cargo and to increase their loads. And bombers, like the venerable B-52, used refueling so they could carry maximum bomb payloads over long distances from remote bases.
Fuel is a necessary evil in aircraft. It's a heavy energy source that consumes space. Fighters like the F-16 trade fuel capacity for performance and payload. For short-range air defense, the tradeoff works just fine. To fly long distances, however, designers resort to auxiliary fuel tanks in various configurations. With rare exceptions, pilots would choose not to carry auxiliary fuel tanks in combat, whether for air-to-air or for tactical missions. The tanks increase fuel consumption, reduce ordinance payloads and G limits, and tend to reduce top speed of the aircraft. Dropping the tanks before combat solves these problems, but the practice is wasteful and involves other compromises. Even with extra tanks, a fighter could never cross the vast oceans by the most direct route without running dry. The only practical answer is to pick up extra fuel along the way.
By refueling in the air, aircraft can go the distance. Fighters can also stay lean and mean or carry maximum combat payloads. Aerial refueling makes a big difference in what the F-16 can do and how it gets it done. Fuel is a precious commodity, but in the midst of combat, survival often requires the pilot to sacrifice it. Getting safely back to base may require an aerial refill. Maj. Ron MacKenzie of the 336th Aerial Refueling Squadron of the AF Reserve remarks that "during Desert. Storm it was not unusual to hear pilots yelling for gas." More than one combatant made contact practically flying on fumes.
Even long-range bombers like the F-111 often need tankers to complete their missions, especially when other countries don't permit overflights. The successful F-111 raid on Libya could never have been accomplished without air-to-air refueling. This situation repeated itself during the Gulf War. Flying out of European bases, bombers denied overflight permission had to fly lengthy, indirect routes to stay over international waters.
During operations in the Persian Gulf, USAF KC-135s and KC-10s completed over 85,000 aerial refuelings. They offloaded to receiver aircraft over 1.2 billion pounds of fuel, about 190 million gallons. These figures don't include USAF C-130 tankers, Navy tankers, or foreign tankers. "People at home saw all these photos of sleek fighters during the war," remarks TSgt. Phil Stidham of the 336th, a KC-135 boom operator during Desert Storm, "but they never saw the tankers. Few people realize that not one sortie, with the exception of maybe some B-52 sorties, was flown without tanker support."
The history of refueling aircraft in flight goes back to 1918 when a Navy Reserve pilot, Lt. Godfrey Cabot, snagged gasoline containers from his biplane with a grappling hook. However, the first recorded air-to-air refueling took place in 921 when Wesley May, a barnstorming stuntman, strapped a five-gallon gas can to his back and stepped from the wing of his Lincoln Standard to the wing skid of a Curtis JN-4. He unstrapped the can and emptied its contents into the Jenny's fuel tanks.
Aerial refueling developed in fits and starts from its gutsy beginnings. In July of 1923, the Army Air Service, predecessor to the Air Force, conducted the first successful air-to-air refueling that used a hose to refuel one aircraft from another. Later that year, two Air Service lieutenants, John Richter and Lowell Smith, used aerial refueling to fly their de Havilland DH-4B for thirty-seven hours and over 3,200 miles over southern California. They were refueled fifteen times from another DH-4B, receiving seventy-five gallons of fuel through a hose as well as oil and other supplies. The lieutenants went on to demonstrate practical applications of the new capability by flying non-stop from the Canadian border to Tijuana, Mexico, covering the 1,300 miles in twelve hours with two refuelings. An accident the following month abruptly ended their cycle of experimentation.
Aerial refueling development was renewed about five years later. On New Year's Day 1929, a Fokker C-2 trimotor nicknamed "Question Mark" (because no one was sure how long it might remain aloft) began a record-setting flight. The first refueling took place over the Rose Bowl as Georgia Tech edged California eight points to seven. Two Douglas C-1 biplanes used as tankers kept Question Mark aloft for seven days before a failing engine on the Fokker brought it back to the ground. During the flight, the aircrews transferred 5,660 gallons of fuel, 245 gallons of oil, as well as meals, water, batteries, and other supplies.
Despite the achievement, development in the United States languished. The British conducted experiments with some success, but through World War II, long-range strategic missions and aerial refueling were greeted with skepticism by most of those in command. With few exceptions, little further development was done even though a great need existed. Doolittle's famous bombing raid on Tokyo from a precarious launch from an aircraft carrier is but one glaring example of the difficulties that had to be overcome because there was no way to refuel in the air.
After the war, the long-range requirements of the Strategic Air Command renewed interest in aerial refueling. Development progressed rapidly, culminating on 22 March 1949 when "Lucky Lady II," a specially outfitted B-50A bomber, landed at Carswell AFB in Texas after completing the first non-stop around-the-world flight. The mission took ninety-two hours and covered nearly 24,000 miles. Fuel was dispensed from KB-29 tankers, a modification of the B-29 bomber. Air-to-air refueling was here to stay.
These early tankers used a cumbersome refueling system in which the receiver aircraft would grapple a contact line trailed by the tanker and then winch in the refueling hose to make the connection. The system worked fine in relatively calm air during the day. But making a connection in turbulence or at night was tricky.
During the Korean War, a probe-and-drogue system was developed. In this system, still used today, the tanker unreels a refueling hose from the rear or from wing pods. At the end of the hose is a funnel-shaped drogue, a basket that resembles an oversized shuttlecock. The drogue stabilizes the trailing hose and provides a lead into the connector at the end of the hose. The receiver aircraft is fitted with a probe that extends out from the side of the fuselage or from the leading edge of the wing. The pilot guides the probe into the drogue to make the connection.
While this arrangement was a major improvement over its predecessor, it still had drawbacks. Early versions of the probe-and-drogue receiving equipment were bulky (especially for fighters) and fuel transfer rates were slow. The probe-and-drogue method also placed a high workload on the pilot of the receiving aircraft because the early drogues were not very stable and tended to wander in tight circles. Successfully hooking up took much practice and training.
These drawbacks were addresses by a new refueling concept used by today's Air Force - the flying boom. In this concept, a crew member in the rear of the tanker controls a telescoping rigid boom into a receptacle on the receiver.
The boom operator literally flies the boom into place using small airfoils, called ruddervators, near the boom's end. Guided by colored lights on the underside of the tanker, the pilot has only to maintain a position behind and below the tanker. The first KB-29s were outfitted in 1950 with the flying boom, which was installed in the old rear gunner's turret. Modifications to B-50 bombers as receivers for the boom-equipped tankers commenced simultaneously.
By the early 1950s, with most fighters equipped with either refueling receptacles or probes, the first large-scale overseas deployments began. In July 1952, KB-29s supported the deployment of fifty-eight F-84Gs of the 31st Fighter Escort Wing from Turner AFB, Georgia, to bases in Japan. Three months later, seventy-five F-84Gs flew from Bergstrom AFB in Texas to Misawa Air Base in Japan. These deployments and others proved the practicality of sending large numbers of fighters overseas from bases in the United States.
The slower, prop-driven KB-29s, however, soon became outpaced by the jet fighters. So the aging B-50 was pressed into service as a tanker in 1955. A small jet engine was added on each wing of the bomber to increase the KB-50s speed to better match the jet's. Three refueling hoses were fitted to the bomber, one from the fuselage and one each from a pod mounted under each wing. This crowded arrangement (the wings of the B-50 tanker sported four large radial engines, two refueling pods, and two jet engines) allowed three receivers to refuel at the same time.
The KB-29s were also being replaced with new Boeing KC-97s. While these versions of the Stratofreighter retained their cargo capability, their rear doors were replaced with a boom operator's station derived from that of the KB-29. With no turret to use, the boom was moved forward on the fuselage. The boom operator laid prone, face down, to view the receiver through a viewing window. (KC-97 boom operators enjoyed one of the few positions in the military in which lying down was part of the job description.) The upper-deck fuel tanks and boom equipment on the KC-97 could be removed if necessary and the tanker quickly converted to a freighter. Two improved models of the KC-97 offered greater payload capacity and flexibility. In January 1957, three B-52s, supported by ninety-eight KC-97s stationed along the route, flew around the world in forty-five hours and nineteen minutes. The lead aircraft, christened Lucky Lady III, was commanded by Lt. Col. James Morris, the copilot of Lucky Lady II's around-the-world mission in 1949. The bombers more than halved the record set by Lucky Lady II only eight years previous, and they did it with three aircraft to boot.
As the Air Force converted to an all-jet fleet of warplanes, the gasoline-fueled, prop-driven tankers became anachronisms. A new tanker was needed to better match the capabilities of the B-52 and the newer, faster fighters. In the early 1950s, Boeing began developing a new airframe, the KC-135, that could serve as both an Air Force tanker and as the company's first civilian jet transport. The prototype first flew in July 1954. (Contrary to popular misconception, the 707 airliner and the KC-135 are not two versions of the same aircraft.) The first KC-135A entered service in 1957 and it remains in service today.
Propulsion on the early models of the KC-135 was supplied by four Pratt & Whitney turbojet engines. Its cruise speed was over 500 mph at 30,000 feet. Range, of course, depended upon how much fuel was offloaded. The aircraft had an unrefueled range of over 9,000 miles. With 24,000 pounds of fuel to transfer, the aircraft had a mission radius of about 3,500 miles. With 120,000 pounds of fuel, the radius was reduced to just over 1,000 miles.
The KC-135 uses the time-tested refueling boom and operator's panel from the KC-97. The boom operator still lays face-down in the center of the aircraft. The aircraft also has stations for two observers or instructors, one on either side of the boom operator. Large mirrors around the periphery of the windows extend the operator's view. The KC-135 carries its fuel in twelve wing and nine fuselage tanks, which together hold over 200,000 pounds of fuel. While no refueling hose is fitted to refuel probe-equipped aircraft, a special nine-foot adapter hose and drogue can be attached to the boom on the ground.
Over the years, KC-135s have given a good account of themselves. But the old turbojets used a lot of fuel and were noisy and expensive to maintain. In recent years, engine upgrades have extended the life of the tankers and increased performance, lowered the noise level, and reduced maintenance costs. The Air Force fitted their tankers with higher thrust high-bypass turbofan engines to create the KC-135R variant of which 295 are now in service. Air National Guard and USAF Reserve aircraft received 18,000-pound-thrust Pratt & Whitney turbofans taken from scrapped late model 707s. These aircraft are now designated KC-135Es.
To date, 163 have been converted. The differences in performance are dramatic. For example, the R model is twenty-five percent more fuel efficient, can offload fifty per cent more fuel, and costs twenty-five percent less to operate than the original version. Today the fleet retains 633 KC-135 tankers. Service life extensions will keep the KC-135s in the air well into the next century.
By the early 1970s the Air Force needed a larger, more capable tanker transport with increased cargo payload, range, and refueling capability. It examined the larger civilian aircraft available and selected a derivative of the McDonnell Douglas DC-10-30 tri-jet in 1977. The first KC-10 Extender was put into service in 1981. The aircraft retains almost ninety percent commonality with its civilian counterpart, easing maintenance and logistics costs. The wing tanks and tanks installed under the main cargo deck can hold 365,000 pounds of fuel, nearly twice the capacity of the KC-135. Unrefueled range is 11,500 miles. A center-mounted hose and drogue improves mission flexibility. An inflight refueling receptacle behind the cockpit allows refueling by a KC-135 or another KC-10. Sixty KC-l0As were delivered before the production line closed in 1987.
While the most common location for the refueling receptacle has been on the centerline of the main fuselage somewhere behind the cockpit, not all Air Force fighters use this location. The F-111's receptacle is offset a bit to the left of the centerline. The F-15's connection is outboard of the left engine inlet in the upper body of the wing root strake. The A-10's receptacle is located in its nose, just forward of the leading edge of the canopy.
From the pilot's perspective, some aircraft are easier to refuel than others. By all accounts, the F-16 is the easiest fighter in the Air Force inventory to refuel. One pilot with experience in many different types of aircraft says the F-16's sophisticated fly-by-wire controls and flight control computers make aerial refueling "a piece of cake." Pilot training seems to support the statement. Students transitioning into the F-16 are introduced to midair refueling very early in their training. In other fighters, much more flight experience is required.
The A-10 is at the opposite end of the ease-of-refueling spectrum The Warthog's top speed is just about as fast as the tanker's slowest refueling speed. Tanker pilots relate that the most common request from A-10 pilots is to slow down. The A-10 can sometimes barely break through the wake off the rear of a KC-135, and the slight changes in airflow from movement of the boom are enough to destabilize the approach if the pilot isn't careful. An A-10 pilot describes making contact as "one of the most rewarding moments in my flying. The worst was over; I could relax a bit." Any relaxation vanishes at disconnect, when the pilot is momentarily blinded by fuel spray on the canopy from the forward-mounted receptacle.
The F-4 and F-15 are not quite as difficult to refuel in the air as the A-10, though they still require considerable more effort than the F-16. But refueling is always a tense and relatively difficult flight regime. Every aircraft has its individual refueling idiosyncrasies. Each flies differently behind the tanker and interacts differently with the boom. Thus, aerial refueling trials are an important part of any aircraft's development flight testing and validation.
Refueling operations are generally quite safe today, though accidents can happen. A pilot's nightmare is bringing home part of the boom. A pilot can do this if he exceeds the limits of the boom's travel or if he encounters unexpected turbulence. The most dangerous situation occurs if the pilot gets too high and too close to the tanker before the boom can disconnect. This position prevents the boom operator from retracting the boom or from raising it out of the way on disconnect. In rare instances when the boom fails to disconnect, the only choice left is to perform a "brute force disconnect." The receiver puts out the brakes and breaks off the boom just above the dry break valve, as designed. Sometimes the pilot or boom operator makes a mistake during approach or break-off and the boom and the receiver make contact in the wrong place. Such contact can result in scraped paint, a scratched canopy, a broken antenna, or a slight dent in the fuselage. Occasionally more serious damage occurs.
In some instances, a pilot may prefer being locked onto the boom to be towed. During the Desert Shield deployment, for example, a KC-135 towed an F-4 part way across the Atlantic when the fighter experienced partial power loss. During the Gulf War, a fighter with serious fuel leaks caused by battle damage was towed by a tanker pumping fuel in as fast as it was leaking out. While tankers can't tow a powerless aircraft, they can dramatically slow the rate of descent of a disabled aircraft.
Most people may think that tankers just fly around in safe areas during wartime, never getting too close to danger. The Gulf War disproved this notion. On numerous occasions, tanker crews flew into the combat zone to rescue aircraft low on fuel. In some cases, tanker crews braved antiaircraft fire. A flight of two KC-135s led by Maj. Herb Otten of the 452nd Air Refueling Wing was orbiting in Saudi Arabia near the Israeli border awaiting a return strike force of F-16s when an AWACS advised that the F-16s were low on fuel and that one had sustained serious battle damage. Despite lack of fighter cover, Otten flew north into Iraqi air space to meet the fighters before they ran out of fuel. The tankers eventually had to fly almost 100 miles north into Iraq before they made contact with and successfully refueled the fighters.
"One of the vital lessons of our experience over there was the vulnerability of tankers," explains Col. Bill Sherer, the commander of the 161st Air Refueling Group of the Arizona ANG. Sherer was coincidentally in Europe on an air refueling mission when Desert Shield began. He flew one of the first missions of the tanker "air bridge." Sherer notes that flying close to enemy lines, or sometimes into enemy territory, opened a lot of eyes. "In years past at exercises like Red Flag, our tankers would orbit outside the exercise area and refuel either side's aircraft as necessary," Sherer continues. "It was like the game King's X: everyone was safe from attack when refueling. Now we are treated as the high-value assets we really are. If we get shot down, our side loses its fuel supply, and probably loses the war. So now when we go on exercises, we practice evasive maneuvers. We work much closer with our fighter cover when we have it. Fighter crews have a vital interest in our protection."
Briefings during the war took on a new meaning as initial expectations of tanker losses as high as twenty percent were revealed to crews. Strict rules of communication went into effect; nearly all refueling was completed in silence. Much of the refueling was done at night, lights out. Tactics and situations were constantly evolving and changing and crews had to adapt and react quickly. "In most regards, our training stood us in good stead," says boom operator SSgt. Ty Warren. "The basics of refueling are the same no matter what you may encounter. We just did what we had practiced to do."
However, piloting tankers outside the immediate war zone was rarely as easy as it is during peacetime. The lack of navigation facilities and ground radar-assisted air traffic control over wide areas required pilots and navigators to earn their keep. "The crowded skies meant that you had better be where you were supposed to be when you were supposed to be there," explains Capt. T. J. Bain, a KC-135 navigator of the 161st Aerial Refueling Wing. "If you were not, you would quite probably be in another aircraft's airspace. And no one on the ground was there to keep you separated."
The large numbers of aircraft flying in formation was also a new experience for many tanker pilots. Tanker cells commonly had three, six, or even more tankers plus receivers flying in formation. MSgt. Maggie Evans, a KC-135 boom operator of the 336th, remembers one mission in particular during Desert Storm. "We were the tenth and last tanker in a cell with nine KC-10s and we had a total of seventy receivers with us." Formation flying is demanding and requires considerably more concentration for longer periods than many pilots are used to. This type of flying is now practiced more often.
The lessons gleaned by the tanker community from the Gulf War will serve in the future. The emphasis is on new and expanded roles, new tactics in diverse operating environments. As military aviation moves toward the next century, aerial refueling will continue to provide the means to project military power to the far reaches of the globe.
Under the current restructuring, ANG and USAF Reserve units contribute almost half of the Air Force's peacetime aerial refueling mission. Control of the significant majority of the tanker force passed to the Air Mobility Command, headquartered at Scott AFB, Illinois, when it was formed last June. From a single command center at Scott, tanker assets worldwide are scheduled for airlift, strategic, and tactical needs. No matter when or where a need for rapid deployment of personnel, supplies, combat equipment, or aircraft arises, these tankers and their crews will be the ones that make it possible. Or as one airman says, "We provide the legs, to carry the muscle, to deliver the punch."