Boeing - 720
The Boeing 720 was a development of the Boeing 707 and was intended to compete with the Convair 880 in the medium range market segment then being served by turboprop and piston engine aircraft.
The 720 model designation is reputed to have been changed from its original 707-020 designation at the behest of United Airlines President W.A. Pat Patterson who at the presentation of the initial 707 mock up had stated that he would never buy an aircraft from Boeing with the designation 707, and then went on (for more pragmatic reasons) to order the DC-8. The DC-8 however was too large for many of United’s services, and they became the launch customer for the 720 placing an order for 11 in November 1957. The 720 differed significantly enough from the 707 to require a separate type certificate, but utilised the same fuselage as the 707-100, which was shorter overall than the 707-100 at 37.9m. Utilising the same wing as the707-100 the 720’s wing included an aerodynamic enhancement in the form of an extended inboard wing leading edge which raised the Vne to Mach 0.91 and improved fuel burn, it also featured Kruger leading-edge flaps on the outboard sections of the wing to deliver the take off and landing performance required for the smaller airports the 720 was intended to serve. The 720 was also lighter than the 707-100 due to a shorter fuselage and the reduced requirement for environmental systems and passenger amenities.
As a result the 720 had a lighter undercarriage which yielded a further weight reduction. The 720 was powered initially by Pratt & Whitney JT3C-7 or JT3C-12 turbojets the later producing an additional 4.8kN on take off due to the provision of water injection.
A total of 64 720s were produced before production shifted to the 720B model, brought about the availability of the Pratt & Whitney JT3D and the emergence of the Convair 990 which threatened make inroads into one of Boeings major customers American Airlines. The 720B was used to counter Convair not only with its improved performance but with pricing driven by the intent of ensuring dominant market share.
The 720B had a considerably enhanced performance compared with the turbojet powered 720. Operational empty weight was increased by 3.6%, which was ameliorated by a 2.1 % heavier maximum take off weight, but the maximum structural payload was increased by 31%. In operational terms a 720B at a take of weight of 99,800kg could carry a payload of 9070kg a distance of 6428km compared with 5218km for the turbojet 720.
American Airlines ordered 13 720Bs with the first revenue flight in March 1961 and had 10 720s converted to 720Bs .Other operators included Northwest Orient (17), Continental (8), Lufthansa and Pakistan International with 4 each, and Western, who received 27 aircraft, the last of which was delivered on September 20 1967 and was also the final production 720. Production of the 720B ran to 99 aircraft and in June 2006, according to Flights ACAS database only 3 were operational, with 2 being used as engine test beds in North America and 1 in service as a corporate aircraft in the Lebanon.
