KB-29M / KB-29MR / KB-29P / YKB-29T - Flying Fortress
Just after Pearl Harbor, the U.S. Army Air Forces began working on an air refueling solution. With the help of Hugh Johnson, the man who had been in charge of FRL's Gander operations, they studied three primary concepts. First, planners looked at launching B-17 Flying Fortresses from Midway Island against Japan, with the idea of using modified B-24 Liberators as tankers. Second, they considered using B-24s from Hawaii with tanker support from U.S. Navy seaplanes. The third concept called for B-17s to tow fuel-laden gliders to serve as tankers. Testing -- using a variation of the looped-hose method -- began in the summer of 1943 at Eglin Field, Fla. A B-17E served as the receiver and a modified B-24D as the tanker. The successful tests extended the B-17's range (with three tons of bombs) from 1,000 to 1,500 miles.
The problem now was how would the country's taxed manufacturers build the equipment for squadrons of B-24 tankers and B-17 receivers? Added to this dilemma was the time required for the aircraft modifications and crew training. Additionally, by mid-1943, Boeing began rolling out the B-29 Superfortress. The B-29 had a combat radius of 1,500 miles and carried twice the bomb load of the B-17.
In 1944, the U.S. Army Air Forces began studying the feasibility of equipping B-29s with an air refueling capability. The engineers at Wright Field, Ohio, determined it was possible to modify the aircraft, but the 1,500-gallon capacity of a B-24 tanker only extended the B-29's range by 830 miles. At the same time, the British developed plans to convert 600 Lancaster bombers to serve as tankers in the Pacific, serving 600 Lincoln bombers. However, before any air refueling plans to support the bombing mission reached fruition, Allied forces began seizing islands within striking distance of Japan.
The U.S. Army Air Forces also looked at a possible refueling method for smaller fighter aircraft. A contractor, All American Aviation, equipped and tested a specially modified P-38 Lightning and a B-24 tanker. In the test, the B-24 suspended an external fuel tank on a cable. The P-38 was to catch that cable, securing it into a device mounted on the forward fuselage. The fighter would then descend to the tank which was to lodge into the securing device while the cable broke away. A nitrogen bottle fired to force the fuel into the fighter before ejector springs released the tank. The tests proved highly unsuccessful, and in March 1945, the Army Air Forces cancelled the method as unsound.
While air refueling was not used operationally, World War II led the U.S. Army Air Forces to examine its potential. These studies and the testing of new equipment showed what air refueling could offer to future contingency operations.
In January 1948, former bomber commander and the first U.S. Air Force chief of staff, Gen. Carl A. "Tooey" Spaatz, identified in-flight refueling as the young service's highest initial priority. Two months later, Air Force personnel from Wright-Patterson AFB, Ohio, visited Britain's Flight Refueling Limited, evaluated the company's loop-hose air refueling system design, and bought two examples. The Air Force also ordered 40 additional sets and acquired manufacturing rights for the system.
Upon arrival in the states, the two refueling systems went to Boeing's Wichita, Kan., plant for installation in B-29s. The subsequent conversion program resulted in the production of 40 KB-29M tankers and 40 B-29MR receivers. On June 30, 1948, SAC activated its first two KB-29M squadrons: the 43rd Air Refueling Squadron at Davis-Monthan AFB, Az., and the 509th Air Refueling Squadron at Walker AFB, New Mexico.
The introduction of dedicated tanker aircraft and crews allowed SAC to extend the range of its B-29 and B-50A bombers. Concurrently, SAC and the Air Force made the decision to equip all future bombers with an in-flight refueling capability. However, the loop-hose system proved unwieldy and difficult, particularly in bad weather. With a two-and-a-half-inch diameter refueling hose, the FRL-developed system transferred fuel at a rate of only 110 gallons per minute. With new high-speed, high-altitude jet bombers coming on line, capable of operating at night and in bad weather, it quickly became apparent something better was needed.
Interestingly enough, Boeing already had a better system in mind. The company developed a "flying boom," which featured a telescoping pipe with fins at the nozzle end. The fins were termed "ruddervators" because they functioned as both rudders and elevators. The boom operator, sitting in the B-29's converted tail turret, literally flew the boom into a receptacle on the upper fuselage of the receiver aircraft. This design allowed more positive control of the air-to-air refueling operation and, with the boom's four-inch diameter, it offered much faster fuel transfer. Because this system used a pump to transfer fuel, its transfer rate increased to more than 4,600 pounds per minute.
The boom refueling system worked exceptionally well for refueling bomber aircraft. The Air Force responded by ordering more than 100 B-29s fitted with the flying boom system, designated the KB-29P. The first KB-29Ps went into service with the 97th Air Refueling Squadron at Biggs AFB, Texas, on Sept. 1, 1950.
In the meantime, training continued with the KB-29Ms, including periodic attempts at record-breaking flights. For example, in 1948, from Dec. 7 through Dec. 9, a 43rd Bombardment Group B-50A, commanded by Lt. Col. Michael N. W. McCoy, flew from Carswell AFB, Texas, to Hawaii, dropped a practice bomb, and then returned to Carswell. The flight was made possible by KB-29Ms assigned to the 43rd and 509th Air Refueling Squadrons. The Air Force followed up with a non-stop, around-the-world flight. Again, the 43rd Bombardment Group got the call, although the first attempt on Feb. 25, 1949, came to a quick end when the B-50A "Global Queen" sustained engine problems and landed at Lajes Air Base, Azores.
The next day, the back-up plane, the "Lucky Lady II," commanded by Capt. James Gallagher, launched from Carswell. The aircraft returned to Texas on March 2, having completed a 94-hour-1-minute flight of 23,452 miles with four in-flight refuelings. Afterwards, Gen. Curtis E. LeMay, SAC commander, told the news media the obvious: SAC could now deliver an atomic bomb anywhere in the world, and tankers made it possible.
Subsequently, SAC converted its KB-29Ms to a probe and drogue system, using another design pioneered by Flight Refueling International. It featured a refueling hose mounted on an electrically-driven reel inside the tanker, with the receiver aircraft taking on fuel through a fixed refueling probe. While initially tested with bombers, the design later proved particularly useful with fighter aircraft.
Although SAC was convinced of the merits of the flying boom system, the Royal Air Force, the US Navy, and Tactical Air Command still saw advantages in the probe and drogue system. TAC transformed the British system of using only one drogue per tanker into a system of three drogues per tanker allowing refueling of three receivers simultaneously. This system made aerial refueling fast and flexible, and it was readily accepted by fighter pilots of all services as the preferred refueling method.
In 1952 this system was proved operational when KB-29A equipped with wing tip and tail hose and drogues ferried F-84Es to Japan and Korea. OPERATION HIGH TIDE, which saw the first aerial refueled strike missions, began in May 1952 when twelve F-84Es flew non-stop from Japan to bomb targets in North Korea. In the same year, aerial refueled FOX PETER operations began flying F-84s non-stop across the Pacific.
Boeing developed the rigid flying boom system to improve on the hose and drogue in-flight refueling (IFR) system, with 129 aircraft concertd to this KB-29P configuration. The boom, mounted at the aft-most portion of the KB-29P, was fitted with two small wings that allowed the boom operator to maneuver the boom. The pilot of the receiver aircraft, guided by the boom operator and light signals on the tanker belly, flew behind and below the tanker for refueling. Once in position, the boom operator "flew" the boom into the refueling receptacle, and the KB-29P flight engineer began fuel transfer. The flying boom system became the most common method for IFR and was used on KB-50s and KC-97s. It is still used on the USAF's modern tankers -- the KC-135 and KC-10.
The Boeing YKB-29T was a modification of KB-29M S/N 45-21734 fitted with two additional refueling hoses, one on each wingtip. This gave the aircraft a total of three refueling hoses and served as the prototype for the KB-50D. The triple hose tanker could refuel three fighters and was more efficient for small aircraft during the early days of in-flight refueling.
The Tactical Air Command had been trying officially ever since 1949 to get funds to develop in-flight refueling, using the probe and drogue, which wts and is preferred by fighter pilots of all services, including the Navy, which officially adopted the system for its special uses. The Tactical Air Command [TAC] history is/replete with references to its efforts to eliminate the flying boom system from its aerial refueling operations and TAC's desire for the probe and drogue system.
In 1957 TAC historians recorded the following: "TAC's KB-29 tankers, in the process of being phased out, appeared in the inventory until November 1957. Subsequent to the date the last single boom tanker was transferred out of the command, KB-50s became TAC's exclusive aerial refueling vehicle. Utilizing three drogues from which three separate receiving aircraft could receive fuel simultaneously, the KB-50 proved to be much more efficient refueler than the KB-29. All the aerial refueling squadrons had thqjr full complement of aircraft by the end of 1957." TAC clearly wanted to maintain its own complement of tankers for its fighters, and the advantages of multipoint probe and drogue refueling were recognized.
However, the B-29's aging airframe and limited fuel offload capability definitely made it an interim tanker (although the last B-29s didn't retire from SAC until November 1957). In the meantime, Boeing came up with an improved tanker aircraft, the KC-97.
|Join the GlobalSecurity.org mailing list|