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Know Your Aircraft: The Boeing KC-135 Stratotanker

Today on this “Know Your Aircraft” episode, let’s discover the Boeing KC-135 Stratotanker. 

The Boeing KC-135 Stratotanker is recognized as the most popular air to air refueling aircraft since its introduction to service in 1957. Built by the Boeing aircraft company, a staggering 800 units were produced in total. 

Designed for the United States Air Force, the KC-135 changed the landscape of air dominance when used to refuel bombers extensively during the Vietnam War. Its use expanded to include aerial refueling of the F-105 Thunderchief, F4 bomber, and the B-52 Bomber. It was subsequently also used by the Turkish, French, and Singaporean Air Force. 

The KC-135 Stratotanker is equipped with four CFM56 turbofan engines and has an impressive 322,500lb maximum takeoff weight. With a staggering cargo capacity of 83,000lbs, it can also be used for freight or transporting ambulatory patients during medical evacuations, with a capacity for up to 37 passengers. The standard crew consists of a pilot, co-pilot, and a boom operator located at the rear of the aircraft to facilitate the air refueling of other aircraft. 

In-flight refueling can be accomplished by the KC-135 using two methods, the ‘Flying Boom’ and the ‘Probe and Drogue.’ The ‘Flying Boom’ provides the fastest fuel transfer with up to 6,500lbs transferred per minute and is conducted by the Boom Operator situated at the rear of the Stratotanker. The operator navigates a gimballed telescope tube into a receptacle located near the front of the receiver plane.

The name ‘Flying Boom’ came about because small controllable aerofoils, hydraulically operated and controlled by the Boom Operator, are used to move the boom via aerodynamic forces. 

US Marine and US Navy aircraft use a different method known as ‘Probe and Drogue.’ The drogue, also known as a basket, is shaped like a shuttlecock and is attached to a flexible hose that trails from the aircraft’s rear. Once the hose is extended, the receiver pilot inserts a retractable probe into the basket to start the fuel transfer. 

There are significant advantages to aerial refueling, including significantly improved endurance, minimizing crew fatigue, and engine maintenance caused by multiple takeoff and landings. It also allows takeoffs with greater payloads by reducing the fuel load carried on departure. 

The replacement program for the KC-135 is now underway due to their age and significant maintenance costs. The first Boeing KC-46 Pegasus, the successor aircraft to the Stratotanker, was delivered in 2019, with 179 set to be delivered by 2027.

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