A-10 Refueling From a KC-97L

Two Fairchild Republic A-10As refuel with a Boeing KC-97L Stratotanker (S/N 53-355) of the Texas Air National Guard. (U.S. Air Force photo) Click image to enlarge.

In this picture a pair of Fairchild A-10As are being refueled by a KC-97L. I am unaware of the exact date of this picture, but the A-10 first flew on 10 May 1972 and the KC-97 was retired in 1978 so the picture must have been taken somewhere in that window.

The Strategic Air Command took delivery of its first KC-97 on 14 July 1951. The main production version of the KC-97 was the KC-97G of which 592 were built. By 1958 SAC operated 780 KC-97s, but the 1957 introduction of the KC-135 meant that the -97s days were numbered. The piston powered KC-97 was too slow for the new generation of fighters and too small for the newly introduced B-52.  The KC-135 was an all new design that was more than fast enough to keep up with the fighters and had sufficient offload to support the B-52. In 1958 SAC began to decommission its KC-97 fleet.

In April of 1961 the Air National Guard received its first KC-97 from SAC. The mission of the KC-97 under the guard was to refuel the Tactical Air Command’s fighters. During refueling with fighters the KC-97 was required to fly as fast as possible while its receiver flew on the edge of a stall. Often times the refueling had to be conducted in a shallow dive (toboggan) so that the tanker could maintain a minimum speed required by the fighter. Surplus General Electric J47 jet engines were available from decommissioned KB-50 tankers and they were added under the wings of the KC-97E/Fs. The upgraded aircraft was redesigned the KC-97L. Each J47 produced 5,800 lbs of thrust which drastically increased the performance of the KC-97 and gave it enough extra speed to keep up with fighters of the day.

Just as the KC-97 was too slow for fighters of the day, the KC-135 was too fast for the A-10. Refueling between a heavily laden A-10 and KC-135 produced a situation where the A-10 did not have enough thrust to fly at the KC-135’s minimum flying speed. When refueling A-10s, the KC-135 was limited to a maximum gross weight of 250,000 lbs and even then it was often required to lower its flaps to 20º or 30º. The KC-97L and A-10 were a perfect match due to their similar flying speeds.

Sources:

• http://books.google.com/books?id=C04zANFFmzgC&pg=PA58&dq=kc-97l&as_brr=3&ei=OBoHSo6zI4vKNdv-tYUC#PPA56,M1
• KC-97 Stratotanker. (2009, April 19). In Wikipedia, The Free Encyclopedia. Retrieved 19:12, May 10, 2009, from http://en.wikipedia.org/w/index.php?title=KC-97_Stratotanker&oldid=284815953

Image Source:

• http://www.nationalmuseum.af.mil/shared/media/photodb/photos/051128-F-1234P-025.jpg

KB-29P – Heated Ruddevators

The boom of the KB-29P featured electrically heated ruddevators so that ice would not accumulate on the control surfaces. Click image to enlarge

This article from the June 1950 edition of Popular Science discusses the electrically heated ruddevators of the newly designed boom fitted to a KB-29p. Heated ruddevators were dropped from future boom designs, presumably due to the different refueling altitude that the KC-97 and KC-135 operated at. Note the B-50 being refueled in the bottom right picture. If anybody has information on the history of heated ruddevators (which booms featured them), please let me know through the comments.

Boeing developed the rigid flying boom system to improve on the hose and drogue in-flight refueling (IFR) system. 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.

Sources:

• http://books.google.com/books?id=Fy0DAAAAMBAJ&printsec=frontcover&source=gbs_summary_r&cad=0_0#PPA107,M1
• http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2555

DHC-4 Caribou Refueling an OV-1B Mohawk

A OV-1B Mohawk is refueled by a CV-2B Caribou during refueling trials. Click image to enlarge.

In this Vietnam War era picture, a de Havilland Canada DHC-4 Caribou serves as a tanker for a Grumman OV-1 Mohawk. One OV-1B was experimentally fitted with a midair refueling probe for ferry flights, but this scheme was not adopted.

In 1964 an Army Caribou was used in the Army’s testing of airmobile concept. Caribou “CV-2B” 62-4187 (c/n # 129) assigned to the 11th Air Assault Division was fitted with a external refueling unit (hose-drogue), internally in the cargo bay.

George Nelson (the Caribou pilot) and Bob Loudermilk (the Mohawk pilot) supplied the following information:

The project was initiated to flight deliver the OV-1 to SE Asia after the Air Force refused to tanker the flight. The OV-1 was the only aircraft that wouldn’t fit in an Air Force cargo plane without extensive tear down and resultant long rebuild on the other end. The idea was to launch a CV-2B from California with the jerry-rigged refueling system and a bladder of jet-fuel. The OV-1 would follow to catch-up part way to Hawaii and refuel. The CV-2B would double back to California and a second CV-2B would meet the inbound OV-1 from Hawaii for a second and last refueling. Both would recover in Hawaii. After Hawaii, the OV-1 with its 600 gal. internal fuel capacity and 2 300 gal. drop tanks could island hop the rest of the way to SE Asia. To test the theory we were going to do the above procedures starting from Key West, Fla and recovering in Seattle. It was scuttled just before that attempt. After the system was proven, the project was cancelled.

After manufacturing the box the refueling pod (borrowed from an F-100) sat in, and mastering the mating of the pod’s hydraulic servicing ports to the CV-2B’s hydraulic connections behind the pilot’s seat, then using safety wire and a nail to stop the pod’s ram air turbine from spinning every time hydraulic pressure was applied to the system, we ground tested the transfer as some of the pictures show. The CV-2B had to run both engines to deliver enough hydraulic pressure to turn the fuel pump fast enough to make it work. This heated up the hydraulic fluid so a thermometer was placed in the reservoir tank so it could be monitored from the cockpit.

Bob seem to recall a fuel bladder forward of the pod that provided the bulk of the fuel. The buddy pod held only 300 gallons or less and would not have been sufficient for refueling en-route. I don’t remember the method of getting the fuel from the bladder to the pod. Possibly a simple transfer pump?

The OV-1B Mohawk used, s/n 62-5868, had the Side Looking Airborne Radar antenna and internal sensor equipment removed and two 300 gallon drop tanks installed instead of the normal 150 gallon tanks. The refueling probe was “borrowed” from a Navy A-4 and plumbed directly into the main fuselage tank. Fuel could then be transferred to each drop tank upon replenishing and back to the main tank later as needed. Bob doesn’t remember of any other probe kits installed on other OV-1’s.

Bob and George flew the system dry a couple of times just to make sure the refueling receptacle would stabilize enough to use and the drogue could be pulled back into the Caribou hydraulically. Testing was done at Fort Benning at 13,000 feet to reduce the chance of sparking between the drogue and probe, all crews were on oxygen. We probably transferred fuel 10 or 15 times and topped off my tanks totally on a couple occasions. The airspeeds we used were dictated by the indicated airspeed the CV-2B (George remember 100kts) could maintain at higher altitudes. I remember having a rather sluggish feeling wallowing behind the CV-2B. There was concern also of an overrun of the drogue and getting it in the propeller blades. The OV-1B had no speed boards to stop forward movement so the only way to rapidly slow was to idle the thrust levers and walk the rudders side to side.

This was NOT a deployable system. It was a test of feasibility only. The fuel transfer was slow due not only to the reduced flow caused by the overtaxed CV-2B hydraulic system but the small piping leading into the main fuel tank of the OV-1 and to the drop tanks. The hose drum reel had no responsiveness to it. Ideally as you engage it with the probe it should slowly retract 5 or 10 feet to give a little leeway on aircraft positioning. Instead, the lack of response caused the hose to droop and sometimes snap like a black snake whip. Exciting. Fortunately, no one was hurt, no equipment damaged and we proved our point.

It was also possible to refuel the OV-1B  from a KC-130F tankers. The OV-1B and KC-130F are compatible for air refueling when the KC-130F air refueling system is modified by incorporation of a high drag paradrogue canopy. The high drag paradrogue canopy utilized during this evaluation is suitable for service use. Successful probe-drogue engagements were made at airspeeds from 135 to 190 KIAS at altitudes varying from 5,000 to 15,000 ft. The optimum airspeeds and altitude for air refueling are 155 to 160 KIAS at 10,000 ft. Correction of the following deficiencies in the OV-1B were desirable for improved service use: low refueling transfer rate, inability of fuel quantity indicating system to indicate full fuel load with 300gallon drop tanks installed, and lack of TACAN for tanker rendezvous. Army pilots flying the OV-1B participating in operational AR flights with the KC-130F must be qualified in formation flying, familiar with procedures outlined in the Air Refueling NATOPS Manual and this report, and certified to be qualified by an air refueling instructor pilot.

The Grumman OV-1 is an armed military observation and attack aircraft, designed for battlefield surveillance and light strike capabilities. It is of twin turboprop configuration, and carried two crew members with side by side seating. The Mohawk was intended to operate from short, unimproved runways in support of Army maneuver forces.

Sources:

• http://www.faqs.org/docs/air/avbtsv1.html#m5
• http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=AD0468088
• http://www.dhc4and5.org/USA_10.html

Image Source:

• http://www.ov-1mohawkassociation.org/images/fullsize/coleman_g_mohawk_pics/Ov1_Refueling.jpg

Lockheed X-35 Refueling

Lt. Col. Paul Smith holds the X-35A Joint Strike Fighter steady in behind a 418th Flight Test Squadron KC-135 tanker during the X-35A's first refueling mission. (Photo by Judson Brohmer) Click image to enlarge.

The X-35 was an experimental aircraft developed by Lockheed Martin for the Joint Strike Fighter Program. It was declared the winner over the Boeing X-32 on 26 October 2001 and went on to enter production in the early 21st century as the F-35 Lightning II.

The ability of the X-35 to conduct air refueling was crucial for the accelerated test program to remain on schedule. Without the ability to receive fuel in flight the aircraft would be forced to hot pit frequently which would waste valuable time.

This photograph was taken in the Edwards Air Force Base test range on 7 November 2000.

Source:

• Jenkins, D. (2001). Lockheed secret projects. St. Paul: Zenith Imprint.(LINK)

Image Source:

• http://www.af.mil/shared/media/photodb/photos/021105-O-9999G-090.jpg

KC-97Gs refueling F-100Ds

In August 1964 these former Strategic Air Command KC-97Gs -- by then assigned to the Illinois Air National Guard's 126th Air Refueling Wing out of O'Hare International Airport -- refueled Air National Guard F-100D Super Sabres in the first non-stop trans-Atlantic deployment of guard fighters to Europe (U.S. Air Force photo) Click image to enlarge.

In this picture depicting a coronet operation, probe equipped F-100Ds are being refueled by a formation of KC-97Gs. This exercise was one of many that helped prove the speed at which TAC fighters could be deployed with the help of SACs tanker fleet. Note the nose high attitude of the F-100s which helps illustrate the incompatibility of the KC-97 and fighters.

Image Source:

• http://www.amc.af.mil/shared/media/photodb/photos/090216-F-0304D-004.jpg

KB-29P Boom Operator’s Station

The boomer in the KB-29P operated his equipment from a station in the converted tail turret of the bomber. Click image to enlarge.

The Boom Operator’s station in the KB-29P was in approximately the same location as where the tail gunner would sit in a conventional B-29. A large hemispherical Plexiglas bubble provided a generous view of the refueling operation. The boom was mounted beneath the operator which made the job of effecting a contact more difficult. Subsequent aircraft would be configured with the boom mounted above the operator so that he could more accurately sight down the boom.

Boeing developed the rigid flying boom system to improve on the hose and drogue in-flight refueling (IFR) system. 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.

Source:

• http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2555
  

Image Source:

• http://www.amc.af.mil/shared/media/photodb/photos/090216-F-0304D-002.jpg

KB-29P Refueling a RB-45C

A KB-29P from the 91st Air Refueling Squadron, Barksdale Air Force Base, La., puts Strategic Air Command's long reach into practice by refueling an RB-45C of the 91st Strategic Reconnaissance Wing. ( U.S. Air Force photo) Click on image to enlarge.

Image Source:

• http://www.amc.af.mil/shared/media/photodb/photos/090216-F-0304D-001.jpg

History of aerial refueling: Fueling the fighters

by Mark L. Morgan
Hq. Air Mobility Command History Office

This is the fourth article in a series of articles highlighting the history of aerial refueling and the important role aerial refueling has played in American military history.

Strategic Air Command entered the 1950s on a roll. It operated a growing fleet of tanker aircraft, and the first jet bombers — commencing with the B-47 Stratojet — were coming on line.

The combination of tankers and bombers made SAC a truly global strike force, with mission duration only limited by crew endurance. However, one question remained: what was the proper role of SAC’s small escort fighter force?

During World War II, fighters, such as the legendary P-47 Thunderbolt and P-51 Mustang, escorted bombers over their targets. However, the postwar jet-propelled fighters, such as the F-80 Shooting Star and F-84 Thunderjet, used fuel at a much higher rate and were, therefore, range-limited. They could no longer escort the bombers.

To be sure, the Air Force regularly transferred fighter units overseas, particularly after the outbreak of the Korean War on June 25, 1950. The standard method involved using U.S. Navy or Navy contact vessels — primarily World War II-era escort aircraft carriers — to physically ship the aircraft. This took weeks, and — more often than not and despite protective efforts — upon arrival the fighters required extensive maintenance because of salt air exposure and corrosion.

The answer was simple: find a way to extend the range of fighter aircraft. Initial efforts included projects with the names of Tip-Tow, Tom-Tom and FICON (for “Fighter Conveyor”). These did not involve actual in-flight refueling, but instead involved literally “towing” fighter aircraft, albeit under rather unusual circumstances.

Project Tip-Tow employed a modified B-29 and two F-84Ds, which attached to the bomber at either wingtip through a clamping device. Project Tom-Tom, tested in 1953, was similar and involved the coupling of RF-84F reconnaissance aircraft to the wing tips of a modified B-36. The FICON proposal involved the actual carriage of a modified RF-84F in the bomb bay of a B-36, slung beneath a trapeze.

During testing, flying the fighters in close proximity to large bombers and hooking up proved supremely challenging, even in perfect weather. A fatal crash involving the Tip-Tow B-29 and one of the F-84s in April 1953 reinforced this and led to the cancellation of Tip-Tow. Doing such hook-ups operationally, possibly in combat and most likely at night and in bad weather, made the efforts even more risky. Fortunately, advances in air refueling of fighters made all three of these difficult and complex “towing” methods superfluous.

As during the early development of SAC tankers, the United Kingdom’s Flight Refueling Limited, or FRL, led the way. The company fabricated external drop tanks with integral refueling probes, suitable for using with the probe and drogue system. On Oct. 22, 1950 — barely four months after the start of the Korean War – U.S. Air Force Col. David C. Schilling used this system to make the first non-stop, air-refueled flight by a fighter across the Atlantic Ocean.

Colonel Schilling commanded the 62nd Fighter Squadron and later the 56th Fighter Group in the European Theater during World War II. In July 1948 he led the F-80s of the 56th Fighter Wing from Selfridge Air Force Base, Mich., across the Atlantic to the Royal Air Force installation at Odiham, England. Accomplished under the title of Fox Able One (“Fighters Atlantic, Operation No. 1”), Schilling’s pilots went over via landings and fueling stops at Bangor, Maine; Goose Bay, Labrador; Bluie West 1/Narsarsuaq, Greenland; Meeks Field, Iceland; and RAF Stornaway, the Hebrides. Because of stops and the weather, the 16 fighters took 10 days to get to Europe.

In October 1950, using aerial refueling, Colonel Schilling made the trip in the reverse direction in an incredible 10 hours and 8 minutes.

After launching from RAF Manston in two modified F-84Es, Schilling and Colonel William Ritchie refueled from FRL-operated Avro Lincoln bombers/tankers over Scotland and Iceland. Unfortunately, one of Ritchie’s probes sustained damage during the contact over Iceland. Unable to take on fuel, he literally ran out of gas and ejected. Fortunately, he was quickly rescued.

With the Korean War well underway and its high demand for fighter aircraft, the Wright Air Development Center at Wright-Patterson Air Force Base, Ohio, designed additional external drop tanks with fixed refueling probes and dispatched them to the theater. Republic Aviation, the manufacturer of the Thunderjet, concurrently started delivery of the F-84G with a refueling receptacle in the leading edge of the left wing compatible with SAC’s boom-equipped KB-29Ps.

On July 6, 1951, the first combat air refueling of fighter-type aircraft took place over Korea. Three RF-80As launched from Taegu with the modified tip-tanks and rendezvoused with a tanker offshore of Wonsan, North Korea. Through in-flight refueling, the RF-80s effectively doubled their range, which enabled them to photograph valuable targets in North Korea.

The big test came with plans for the movement of an entire fighter wing to the Korean theater. On July 4, 1952, 60 F-84Gs launched from Turner AFB, Ga., and flew the 1,800 nautical miles to Travis AFB, Calif., non-stop. Refueled en route by 24 KB-29Ps over Texas, this served as the rehearsal for the main event, designated Fox Peter One.

Organized by Colonel Schilling — who now served as the commander of Turner AFB’s 31st Fighter Escort Wing — Fox Peter One kicked off on July 6 when the first of the 31st FEWs three squadrons of F-84Gs headed west from Georgia to Travis. Throughout the following three days, each squadron refueled from KB-29Ps over Texas.

At 1,860 nautical miles and with no alternate landing sites or divert fields, the flight from Travis AFB to Hickam AFB (Territory of Hawaii), was the longest of the trans-Pacific flight. All of the fighters made it and then island-hopped the rest of the way to Yokota Air Base, Japan, via Midway Island, Wake Island, Eniwetok, Guam, and Iwo Jima. The arrival of the last aircraft in Japan on July 16, less than two weeks after leaving Georgia, marked Fox Peter One as a resounding success.

The following October, the 27th FEW from Bergstrom AFB, Texas, replicated the route and in-flight refuelings and relieved the 31st FEW. The 27th FEW’s commander was Col. Donald Blakeslee, another famous World War II pilot and ace.

More record flights followed, including Operation Longstride in October 1953, which saw Colonel Schilling’s wing — now designated the 31st Strategic Fighter Wing — dispatch eight F-84Gs to Nouasseur Air Base, French Morocco. The aircraft covered 3,800 miles in 10 hours and 20 minutes, thanks to in-flight refueling by brand-new SAC KC-97s in the vicinity of Bermuda and the Azores.

Concurrently, Col. Thayer S. Olds, commander of Turner AFB’s 40th Air Division, led 20 F-84Gs of the 508th SFW to RAF Lakenheath, England. Three of the fighters landed at Keflavik, Iceland, because of mechanical problems; however, the remaining aircraft successfully hooked up with the orbiting KC-97 tankers and made it to England in one flight.

In 1957, SAC’s fighter units transferred to Tactical Air Command or were inactivated as part of a reorganization of Air Force strategic and tactical assets. However, they set the standard; by the end of the 1950s, trans-oceanic flights became commonplace. The Air Force never bought another fighter aircraft without in-flight refueling capability; a capability which proved its worth a few years later when Vietnam heated up.

Source:

• http://www.amc.af.mil/news/story.asp?id=123144488

U.S. military aerial refueling: extending ‘the reach’

by Mark Morgan
Hq. AMC History Office

This is the third article in a series of articles highlighting the history of aerial refueling and the important role aerial refueling has played in American military history.

On Aug. 6, 1946, the world’s largest bomber took to the air from the Consolidated-Vultee plant on the south side of Lake Worth, west of Fort Worth, Texas. The huge, six-engine B-36 was a wartime design, built for non-stop round-trip flights from the United States to Germany in the event of the loss of bases in England.

The first B-36 production models entered service with Strategic Air Command in late 1948. The B-36 was big enough to carry the large nuclear weapons of the time and carried enough fuel – more than 183,000 pounds — to make the 10,000-mile round-trip flight to Europe and back.

However, the B-36 lacked speed and maneuverability and, during the early 1950s, the aircraft became highly vulnerable to enemy jet fighter aircraft. Fortunately, the Boeing Airplane Company had the B-36’s replacements in development: the jet-propelled B-47 and B-52. However, these new aircraft — unlike the B-36 — needed air refueling to hit targets in the Soviet Union. At the time of their development, no aerial refueling aircraft existed.

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.

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.

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.

Based on the Model 377 “Stratocruiser” trans-oceanic airliner, the KC-97 featured a unique double-bubble fuselage with plenty of space available inside for fuel, cargo and passengers, combined with the wings and engines of the Boeing B-50.

The first prototype YC-97A transport served with the Military Air Transport Service during the Berlin Airlift in 1949 and went into full production that same year. In 1950, Boeing introduced the KC-97 variant, equipped with the flying boom system.

Dubbed the “Stratotanker,” the KC-97 quickly became the most numerous SAC tanker, with more than 800 built. The first aircraft went into service with the 306th Air Refueling Squadron at MacDill AFB, Fla., in 1951. By 1953, SAC operated almost 30 air refueling squadrons with 502 tankers, with the majority of the squadrons flying KC-97s. Nearly every B-47 wing had a KC-97 air refueling squadron assigned to it. When B-47s deployed overseas, their tankers went with them, enabling the mass deployment of entire wings of bombers to bases in Europe and the Far East under Operation Reflex.

However, even the new KC-97 operated with several limitations. While a single KC-97 could adequately refuel a B-47, it took two or more to refuel a B-52. Additionally, it took a long time for a fully laden KC-97 to get to its cruising altitude. This forced SAC to deploy its tankers for extended periods to locations in Alaska and Canada, strategically located along the routes the bombers would use to get to their targets. With adequate warning, the KC-97s would get to altitude in time to service the bombers coming from the United States.

However, speed disparity between the KC-97 and its receivers provided the biggest problem. During aerial refueling, the bomber had to slow down and drop to the KC-97’s altitude. Once the aircraft connected, the tanker went into a dive, allowing the bomber to maintain enough speed to stay in the air. As the receiver took on more fuel, it grew heavier, which made the maneuver — known as “tobogganing” — even more difficult. When done in poor or marginal weather, the experience proved even less enjoyable for the aircrews. Once the two aircraft completed the refueling, the jet bomber had to climb back up to its cruise altitude, which burned a lot of the fuel it had just taken on.

Fortunately, a suitable replacement for the KC-97 was already on the way. And this aircraft, still in operation to this day, would feature jet propulsion.

Source:

• http://www.amc.af.mil/news/story.asp?id=123138375

Air refueling development lags

by Ellery D. Wallwork
Headquarters AMC History Office

This is the second in a series of articles highlighting the history of aerial refueling and the important role aerial refueling has played in American military history.

After the success of the Question Mark’s Jan. 1929 aerial refueling flight, and the operational shortcomings of the spring 1929 Army war-game maneuver, the U.S. Army Air Corps spent little time thinking about aerial refueling. This was not to say that nothing was done with the air refueling concept through the 1930s, but most was accomplished thanks to civilian aviators. The Question Mark also rekindled Britain’s interest in air refueling.

From 1930 until 1937, the Royal Air Establishment at Farnborough conducted a series of air refueling experiments. The Royal Air Force looked at air refueling not so much as a way to extend an aircraft’s reach, but more to help lighten take-off weights to reduce wear and tear on the aircraft and grass airfields. They also looked at it as a way to supplement the narrow bomber size restrictions being considered by the League of Nations — less fuel on take-off, meant more bombs could be loaded on the aircraft.

These experiments began with the Question Mark’s techniques (improved by U.S. barnstorming efforts) of the dangle-and-grab method. To accomplish this, the tanker aircraft would feed out a hose that someone in the receiving aircraft reached out and grabbed.

In September 1934, Flight Lieutenant Richard Atcherly introduced his newly patented looped-hose aerial refueling system.

This new technique put most of the operational effort on the tanker crew. Both the tanker and receiver trailed cables with grapnels on the ends. The receiver flew a straight line, while the tanker crossed its path from behind allowing the grapnels to catch. The receiver then reeled in the cables, along with a hose from the tanker. Once the two aircraft were connected with about 300 feet of hose, the tanker pilot would then maneuver to a higher position and let gravity take care of rest.

These experiments continued until 1937, but by then, even the Royal Air Force had decided that air refueling offered a limited application at best. Aircraft technology had surpassed any perceived need for air refueling. Before this date, the standard aircraft were bi-planes (although monoplanes had started becoming more frequent) using “doped” linen fabric and fixed landing gear, with only a little consideration given to aerodynamics.

By 1933, two American corporations built the first all-metal, low-wing monoplanes — the Douglas DC-1 and the Martin B-10 bomber. These aircraft, each about 17,000 pounds, had retractable landing gear, cowled engines, and high-lift devices to improve take-offs. They also used the new controllable pitch propeller. These advances didn’t do much for payloads, but they doubled the DC-1’s and B-10’s airspeed and operating range over their contemporary aircraft.

British commercial interests, however, soon returned to the idea of air refueling. Companies began looking at “flying boats” to connect the widespread British Empire, and they hoped air refueling would improve their operation.

Sir Alan Cobham and Flight Refueling Limited, or FRL, further refined the looped-hose system. In 1939, from Aug. 5 to Sept. 30, Imperial Airways took advantage of the first commercial air refueling operations. The company flew Short S.30 flying boats for weekly mail service flights between Southampton, England, and New York City. FRL used two obsolete Handley Page HP.54 Harrow bombers as tankers — one at Gander, Newfoundland, and the other at Rineana, Ireland. These air refueling operations were not intended to extend the flight times, but to allow the flying boats to take off with minimal fuel and more mail. Imperial Airways flew 15 of these transatlantic missions before the outbreak of World War II.

World War II offered many examples of how air refueling could be used. For example, Britain depended on shipping to stay alive, and aircraft technology provided only limited support. Bomber operational ranges early in the war meant they were not very useful in helping to suppress the German submarine threat. Still, in wartime, many innovations are examined and tested. During World War II, air refueling was among them.

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

Source:

• http://www.amc.af.mil/news/story.asp?id=123133645