The Boeing 720 was a bit of an unusual aircraft in the Boeing lineup. For a start, it was the only one not to follow the Boeing naming strategy of the 7X7 that began with the 707 and persists to today. And it was more than just a variation on the 707.
The Boeing 707 was the plane that changed aviation. Developed from the Dash 80 prototype, it brought competition for the DC-8 and paved the way for mass acceptance of jet air travel. In just two years following its launch, the 707 had become the fashionable way to travel, but sales were slow.
To encourage more orders, Boeing sought to develop specific variants of the 707 for different customers. For Braniff, for instance, Boeing built the 707-220, a variant designed for hot and high operations to South America. The long-range 707-300 was designed for Qantas, while the Rolls-Royce powered 707-420 was preferred by BOAC and Lufthansa.
In July 1957, Boeing announced a derivative that was designed to fulfill a niche for United Airlines. The 707-020 would be a shorter aircraft, designed to take on shorter routes from shorter runways. After input from launch customer United Airlines, Boeing decided to rename this derivative the 720. According to Boeing,
The 707 was designated the 720 when it was modified for short- to medium-range routes and for use on shorter runways. Engineers reduced the fuselage length by 9 feet (2.7 meters), changed the leading edge flaps and later installed turbofan engines. Boeing built 154 720s between 1959 and 1967. Its short- to medium-range role was later filled by 727s and 737s.
A very different plane
Boeing states that, although the 720 was outwardly almost identical to the 707, under the surface, it was a completely different beast. Its structure was much lighter, and it carried much less fuel than the 707. This gave it a lower gross weight, better takeoff performance and a higher top speed.
Other differences included an improved wing, with a greater sweep and reduced drag. The rearmost overwing emergency exit was removed on both sides, although two overwing exits remained an option for high-density configured models.
Initially, the 720 was powered by four Pratt & Whitney JT3C turbojets. These pushed out 12,500 pounds of thrust and gave the aircraft the power to fly 131 passengers in two classes to a range of 2,800 NM (5,200 km).
However, the more popular engine option was the JT3D turbofan, which delivered 18,000 pounds of thrust. This gave the 720 the ability to fly 156 passengers to a range of 3,200 NM (5,900 km). Aircraft with the turbofan option were designated the 720B.
A rare bird
The 720 entered service with United Airlines on July 5th, 1960. American Airlines joined with its own 720 on July 31st the same year. The first turbofan 720B was flown by American Airlines in March 1961. Other notable operators included Lufthansa, Eastern Air Lines, Northwest Airlines and Western Airlines.
In the 1970s, the first 720 ever built was renamed ‘The Starship’ and was used as a private charter jet for rock bands, including Led Zeppelin. One 720 was flown by remote control and deliberately crashed in 1984 as part of an FAA and NASA test project.
The turbofan-powered 720B was by far the more popular variant. Boeing sold 89 702Bs and 65 of the turbojet-powered 720. But in 1960, just four years after the type was launched, Boeing cannibalized the future of this plane with the introduction of a direct competitor, the 727.
The last 720 was flown by Pratt & Whitney in 2010, with its last operational flight taking place on September 29th. That plane is now on display at the National Air Force Museum of Canada.
Did you ever fly on the 720? Let us know in the comments.