Past Talks : September 2019

“KC135 Operations, 1969 – 73” by Jack Froelich

Regular attendees at SOFFAAM talks will remember Jack Froelich’s entertaining talk on Caribou operations in Vietnam, so would have expected an enjoyable evening. We were not disappointed – the in-flight refuelling tankers of the USAF do not have a glamorous profile, but Jack’s lively delivery and copious illustrations brought these long-lived jets to life.

He started with a brief description of the evolution of the tanker requirement to provide support to the long range strategic bombers being developed after the Korean War. Early tanker aircraft included the KB50 (a modified B29) and the KC97 – a modified Stratofreighter that first introduced the flying refuelling boom. The limitations of these propeller-driven aircraft in support of the early jet fighters and high-flying B-52 bombers led to the search for a jet tanker. The KC135 was it, a fast sleek jet developed from Boeing’s remarkable Dash-70 prototype that also led to the widely used 707 airliner. Jack showed us a brief video of the Dash 70 being barrel-rolled at an air display by the renowned test pilot “Tex” Johnson.

Jack flew the KC135 with the 99th Bomb Wing of Strategic Air Command (SAC). They spent seven days at a time on Quick Reaction Alert (QRA) and would take off with the bombers when they exercised. The initial model, entering service in 1957, was the KC-135A, powered by four Pratt and Whitney J57 turbojet engines. You needed a certain fatalism to fly these early models, said Jack, as they were always at maximum weight at take-off and had few of the aids expected by civilian pilots, such as anti-skid, thrust reversers and an autopilot. In particular, the engines used water injection at take-off to increase power. “You were out of luck if the water supply failed at under 1000 feet.” Water injection cooled the burning fuel, so that some remained unburnt, giving the charateristic black smoke trail behind the jet pipes. Even with water injection, you needed all the runway to take off, which was apparenly USAF philosophy in the nuclear support mission.

During their nine year support to operations in Vietnam, the KC-135A tankers few 813,000 refuelling sorties. This compares with the 18,000 sorties flown in the Persian Gulf. The main customer for the KC-135 was the B-52D, recognisable from its black underside. These aircraft had a tail gunner as well as pilot, co-pilot, two navigators and electronic warfare officer (EWO). These crew members all had ejection seats, of which the navigators’ seats ejected downwards. Additional observers often flew in the B-52, but on the rare occasion when they had to abandon the aircraft they would have to wait until the navigator had left and then drop down through the gap left by his departing seat.

The USAF is unique in using the flying refuelling boom, since all other western air forces use the British-developed “probe and drogue” system. The flying boom is operated by a crew member, who is responsible for guiding it into the refuel receptacle on the receiving aircraft. The boom is manoeuvred by two small winglets and also can be exended by up to 15 feet. Once engaged in the refuelling receptacle, the boom is locked in place, needing an axial disengaging force of 600 lbs. The main advantage of this system is that it enables much higher fuel transfer rates compared with the probe and drogue, a key requirement for the demands of strategic bombers.

The high break-out force of the boom was an advantage when refuelling fighter aircraft, such as the Republic Thunderchief, since if the receiving aircraft was damaged and losing fuel, the tanker could “tow” it a long distance home, refuelling it constantly as required. Jack reminded us that Republic used to name all its products with the “Thunder” prefix and said that the F-105 was universally known as the “Thud” after a Native American character called Chief Thunderthud in ”Howdy Doody” –  a popular children’s TV show at the time.

The USAF deployed the Douglas B-66 Destroyer in the Electronic Countermeasures (ECM) role in Vietnam. As this aircaft had been derived from the US Navy’s A3 Skywarrior, it had retained the Navy’s flight refuelling probe arrangement. KC-135 tankers had to be equipped with a drogue attachment to the flying boom to refuel these types, which precluded the use of tankers so fitted from refuelling other US fighter types. Another occasional customer for fuel was the high-flying SR-71, based in Okinawa. Jack showed us a picture of this phenomenal aircraft refuelling from a specialist variant of the tanker, named the KC-135Q. This variant was needed because the SR-71 used JP7, a specially-developed fuel with high flash point and high thermal stability to cope with the SR-71’s Mach 3 cruising speed.

A completely different task for the KC-135 was its modification, known as “Luzon”, to the airborne radio relay mission. These aircraft would fly in long (eight-hour) orbits over the Gulf of Tonkin, with the specific task of re-broadcasting signals from US aircrew who had ejected over the sea. This was an invaluable aid for the rescue services, since the range of the aircrew radio beacon was relatively limited.

Finally, Jack reminded us of the need for celestial navigation in those days before the satellite-provided Global Positioning System (GPS). Sun and star sights would be taken through a periscope, resulting in such accuracy that Jack was sure he was never more than 100 miles off course. It was always easy to navigate towards Hawaii, he said, as (like the Japanese in their attack on Pearl Harbour) you just had to home in on the island’s radio broadcasts. Other aids to navigation were LORAN and doppler, but these were never popular with navigators. Later models of the KC-135 were equipped with GPS, so that they no longer needed specialist navigators.

Once again, Jack has delivered a fascinating talk in his inimitable style. He told us he is developing another, on his later career. We have made an advanced booking!