The Aircraft of MDT: KC-135 Stratotanker

Welcome to the twelfth regular installment of The Aircraft of MDT. In this series we are taking a look at some of the aircraft that you may spot flying to and from Harrisburg International Airport.

The KC-135 Stratotanker was the United States’ first jet powered tanker aircraft. Prior to its adoption in 1957, the U.S. Air Force’s primary tanker was the piston-engined KC-97 (also called the Stratotanker). The KC-97 served a vital role from the time it entered service in 1950, but it was not ideal for fueling jet aircraft. The fighters and bombers it typically served had to lower their speed and altitude in order to accommodate the relatively slow tanker. The jet-engined KC-135 solved this problem. Also, because the KC-135 operated on the same type of fuel that it was supplying to other aircraft, there was no need to keep the two supplies segregated. This change, along with its larger size, meant that the KC-135 could carry a fuel load more than three times the volume of the KC-97 (31,000+ gallons compared to 9,000 gallons).

Aft view of a KC-135. Note the boom control surfaces
extending above the tailplane.

The KC-135 Stratotanker was built by Boeing and is a sibling to their premier jetliner, the 707. The KC-135 is not a derivative of the 707; instead, both aircraft are derived from the 367-80 prototype that Boeing built in the early 50s. When the 135 was in development, it was known internally as “Model 717,” a designation that would later be used publically for the airliner that started life as the McDonnell Douglas MD-95.

The KC-135 Stratotanker employs a “flying boom” fueling system. This system uses a rigid boom that is lowered from the aft center of the tanker. The boom has flight control surfaces near its tip that allow it to be maneuvered by an operator aboard the tanker. Watching from a small window, the boom operator steadies the boom and extends it to mate with a receptacle on the receiver aircraft. Not all aircraft fit for aerial refueling are equipped for a flying boom system. The most common alternative system is the “probe and drogue,” in which a flexible hose with a cone-shaped drogue is lowered from the tanker, and the receiver aircraft positions itself to insert an extended probe. The boom on the KC-135 can be fitted with a drogue adapter that allows it to refuel aircraft of this type. In addition, some KC-135s have been outfitted with under-the-wing drogue refueling pods.

The KC-135 carries more than just fuel, too. It has an upper deck that can be outfitted to carry up to 83,000 pounds of passengers and cargo, depending on the fuel load. KC-135s have also been used by NASA. They have served as a platform in various research endeavors, and, until it was replaced in 2004, the KC-135 (minus the tanker equipment) functioned as NASA’s infamous “Vomit Comet.” Flown in parabolic arcs, the plane simulated weightlessness for astronaut trainees. One of the specially modified tankers was used to film scenes of weightlessness for the movie Apollo 13.

A KC-135 conducting touch-and-go maneuvers at MDT.

A total of 732 KC-135s have served the United States Air Force since 1957. That record makes it one of only six fixed-wing military aircraft (including the C-130) to have served for more than 50 years with their original operator. It is estimated that the fleet of KC-135s could potentially continue flying until 2040, but, since some of the aircraft would be more than 80 years old at that point, the Air Force has initiated a plan to replace them much sooner. In February 2011, a tanker based on the Boeing 767 was selected to fill the role of the 135. The new tanker, called the KC-46, is scheduled to enter service in 2017.

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Parking Garage at MDT

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The Aircraft of MDT: A-10 Thunderbolt II

Welcome to the eleventh regular installment of The Aircraft of MDT. In this series we are taking a look at some of the aircraft that you may spot flying to and from Harrisburg International Airport.

Although the only military aircraft with a permanent home at Harrisburg International Airport is the EC-130J, others are still a common sight. Several factors contribute to the preponderance of military air traffic at MDT: the size of the runway, the presence of the Pennsylvania Air National Guard base, and proximity to Joint Base Andrews. Some military craft come with business at the Guard base, but most come to practice “touch-and-go” maneuvers, in which the plane begins a landing, but then takes off again without ever coming to a complete stop.

One of the military aircraft you may see on the ground or in the sky around MDT is the Fairchild-Republic A-10 Thunderbolt II “Warthog.” The A-10 is a twin-engine, single seat jet used by the United States Air Force for close air support, attacking ground targets in support of nearby troops.

An A-10 Thunderbolt II parked at MDT

Named for the World War II era P-47 Thunderbolt, a fighter that served in a close air support role, the A-10 Thunderbolt II is the first U.S. Air Force aircraft designed and built solely for CAS. The USAF began planning for a new attack aircraft in the mid 1960s. By the early 70s, there were two prototypes competing to be that aircraft, the Northrup YA-9A and the Fairchild-Republic YA-10A. Ultimately, the Fairchild-Republic design won the contract, and production of the A-10 began shortly thereafter. The Air Force received its first A-10 in 1976 and 714 more over the ensuing eight years.

The A-10 can carry a wide variety and large quantity of air-to-ground and air-to-air weaponry, but its primary armament is the 19 foot long 30mm GAU-8 Avenger rotary cannon. The GAU-8 weighs in excess of 4,000 pounds when fully loaded and fires at a rate of 3,900 rounds per minute. When fired from 4,000 feet, 80% of the rounds fired from the GAU-8 will strike within a 40-foot diameter circle. The Avenger cannon was developed for the A-10, and the A-10 is still the only aircraft that carries it.

Its close air support role demands that the A-10 fly in hostile territory at relatively slow speeds and low altitudes. As such, it is built to be extraordinarily hardy. The cockpit is surrounded by a 1,200 pound “bathtub” of titanium armor to protect the pilot from projectile weapons. All of the A-10’s fuel tanks are self-sealing, protected by fire-retardant foam, and designed to be isolated from the rest of the fuel system in the event of damage. All of the aircraft’s flight systems have redundant hydraulic backups and mechanical systems to fall back on in case both the primary and secondary hydraulic systems are disabled. In a worst-case scenario, the A-10 is designed to be flyable even when missing one engine, one elevator, one tail, and half of one wing.

One of the A-10s most distinctive features is its aft section, with its large engines and twin-tail configuration. With the engines placed high off the ground and behind the wing, the chance of foreign object damage is reduced when operating from damaged or otherwise sub-standard runways. The engine placement also supports faster turn-around time in combat. The wings on the A-10 are closer to the ground than they would be if the engines were mounted underneath them, making them more accessible to ground crews. Also, because the engines are out of the way, they can be left running while the aircraft is serviced and rearmed. The twin-tail also provides dual benefits. The most obvious is redundancy, but channeling the engines’ exhaust over the tail planes and between the vertical stabilizers reduces the A-10s infrared signature, making it harder to hit with surface-to-air heat-seeking missles.