The Boeing 707
The Boeing 707 Overview
Development
During World War 2, Boeing was widely known for its military aircraft. The company had produced 2 main models that would prove to be a key role of the second World War. These were the B-17 Flying Fortress, B-29 Superfortess and the jet powered B-47 Stratojet and the B-52 Stratofortress After the second World War, Boeing was far behind its competitors in terms of aircraft development and manufacturing size. With the beginning of the Korean War, Boeing soon realized that they must develop jets that are suitable for both military and civilian use. Boeing studied numerous designs and soon settled on a new aircraft design that was called the "Boeing 367-80". The first prototype was powered by the Pratt & Whitney JT3C turbojet engine. The 367-80 was suitable for both military application as well as civilian use.The question of whether the 707 was to be a profitable plane for Boeing was very much debated, as the company had lost over 15 million dollars with its latest civilian aircraft, the Boeing 377 Stratocruiser. To make the 367-80 more suitable as a passenger transport aircraft, its width was extended to a total of 3.76m.
Testing
The first flight of the 707-120 took place on December 20, 1957 and the FAA certification was given on September 18, 1958. Both test pilots were awarded the first Iven C. Kincheloe Award for the test flights that eventually led to certification.
Design
Wings
The wings of the 707 are swept back at the angle of 35° and like all swept-wing aircraft, it had an undesirable tendency to perform a "Dutch Roll", which is the uncontrollable shaking of the aircraft's tail. Yaw dampers were developed by Boeing to minimize the effect of the Dutch Roll, however it could be de-actived. On one customer-acceptance flight, where the yaw damper was turned off to familiarize the new pilots with flying techniques, a trainee pilot's actions violently exacerbated the Dutch roll motion and caused three of the four engines to be torn from the wings. The plane crash-landed on a river bed north of Seattle at Arlington, Washington, killing four of the eight occupants.Engines
The 707 uses engine driven turbocompressors that supply pressurised air for the cabons. Many models of the 707 saw Engine no. 1 not fitted with a turbocompressor as it was not needed. Airlines such as American Airlines chose to install turbocompressors on all 4 engines to maximise the inflow of pressurised air into the cabin. The engine itself, the JT3D was a perfect pairing with the 707 as it was sleek and efficient at the time. It provided more than enough thrust and was fuel efficiente enough to enable the 707 to fly passengers over long distances without worrying about fuel.Later models were upgraded with newer and more powerful engines such as the JT8D-219 which provided the 707 to fly at faster speeds. These engine upgrades were usually completed on military models of the 707 and not civilian.
Operation
The only real rival in long-range flight was the de Havilland Comet. However, this was still not a proper threat to Boeing was the Comet had been the subject to numerous fatal accidents due to its poor design. It was also considerably slower than the 707. The Douglas Aircraft was the most preffered manufacturer for airlines as they had proved themselves to be reliable, efficient and fast. To stay competitive, Boeing made a decision to redesigne the interior of the 707's wings to help increase range and payload. The new version of the 707 was dubbed as the 707-320.
Pan Am was the first and biggest airline to operate the 707 and its popularity soon began to boom, both Pan Am's and Boeing's. Qantas became the first non-US airline to order and place the 707 into service in 1959. The 707 quickly became the world's most popular jetline of its time. Its popularity soon led to the development of newer, bigger airport terminals, runways, airline catering, baggage handling and other air transport infastructure. In essence, the 707 opened new doors to air travel and set the foundations of what we enjoy today.
As the 60's drew to a close, the 707 had fallen victim to its own success. It had now become too small to handle the increased passenger numbers and was also considerably less fuel efficient. An upgrade was, however, not feasable as the 707 had been designed in a way that did not allow any major modifications to the airframe and fuselage. Due to this design flaw, the 707 was abandoned by Boeing as the fuselage could not be lengthened and newer, bigger engines could not be replaced as the ground clearance would not have been enough. As a result of this, Boeing began to invest both time and money into the new 747.
Variants
Although Boeing's variants are usually numbered as 100s, 200s, 300s, etc., the 707 variants are most commonly numbered as 120s, 220s, 320, etc. The "20s" were Boeing's designation for its development aircraft.707-120
The 707-120 was the first variant of the 707s to be mass produced and had a longer and wider fuselage with greater wingspan than the 367-80. Its cabin had a full capacity of 189 passangers and was equipped with rectangular windows that were less prone to fracturing at high altitude flight than the de Havilland Comet. It was designed for transcontinental flight and often had to refuel for flights across the North At/pntic. It had 4x Pratt & Whitney JTC3C-6 engines that produced a total of 13,000lb of thrust each with water injection. The total takeoff weight was 247,000lb (112037kg). The maiden flight of the 707-120 was on December 20, 1957, while the first revenue flight operated by Pan Am was completed on October 26, 1958. An initial 8 orders were made in 1958, but the numbers soon increased 8 times over the course of the coming year. There was also a shortened version of the 707-120 produced that was called the 707-138. It was exactly 10ft (3.3m) shorter than the orignal design. This change was made possible by removing 5 panels from the front of the aircraft (each 1ft in lenght) and also 5 panels behind the wing.The 707-120B was a more powerful and efficient model that was powered by the Pratt & Whitney JTC3D-1 engine. The engines produced a total of 17,000lb of thust each and did not require water injection. This allowed Boeing to remove around 5000lb - 6000lb of unnecessary weight (2268kg - 2722kg). This engine was, however, once again replaced with the JT3D-3 which provided an extra 1,000lb of thrust from each engine.
707-220
The 707-200 was designed for high altitude flight and was equipped with a more powerul enngine; the Pratt & Whitney JT4A-5 which provided 15,800lb from each engine. Only 5 of these models were ever produced and 1 model was lost to a failed test flight. This version of aircraft was made obsolete with the arrival of the 707-120B.707-320
The 707-320 was the intercontinental version of the 707-120. It was initially powered by the JT4A-3 providing 15,800lb of thrust from each engine. The interior of the plane allowed for a total of 189 passengers as a result of a 80-in (2.03m) extention in the width of the fuselage. More extentions were made to the fin and the horizontal stabilisers, extending the 707-320's lenght and width even further. As a result, the 707-320 was able to increase its range by an extra 2,600km as the larger wing could be filled with more fuel. The wing modifications included outboard and inboard inserts, as well as a kink in the trailing edge to add area inboard. The takeoff weight was increased to 302,000lb (137,00kg), the heaviest 707 model produced at that time. Its first flight was on January 11, 1958 and a total of 69 707-320s were delivered through January 1963.707-420
The 707-420 is the identical to the 707-320, the only difference being the Rolls-Royce Conway 508 engines providing 18,000lb of thrust from each engine. The first announced customer was Lufthansa. BOAC's controversial order was announced six months later, but the British carrier got the first service-ready aircraft off the production line. The British Air Registration Board refused to give the aircraft a certificate of airworthiness, citing insufficient lateral control, excessive rudder forces, and the ability to over-rotate on takeoff, stalling the wing on the ground (a fault of the de Havilland Comet 1). Boeing responded by adding 40 inches to the vertical stabilizer, applying full instead of partial rudder boost, and fitting an underfin to prevent over-rotation. These modifications except to the fin under the tail became standard on all 707 variants and were retrofitted to all earlier 707s.
707-320B
The 707-320B had the JT3D turbofan engines with an improved, more refined aerodynamic refinements. The wing was modified from the -320 by adding a second inboard kink, a dog-toothed leading edge, and curved low-drag wingtips instead of the earlier blunt ones. The overall wingspan was increased by an extra 3ft (1m) which increased the total takeoff weight to 328,00lb (149,000kg). The first flight was made in June 1962 with Pan Am.707-320C
The 707-320C was equipped with a convertible passenger-freight configuration, which became the most popular version of the 707 ever produced. The 707-320C added a strenghtened floor and a new cargo door. The wing was fitted with three-section leading-edge flaps which allowed the deletion of the under fin. Despite the 707-320C being built for both freight and passenger transport, airlines removed the dividing panel between the cargo hold and passenger cabin for an increased capacity of travelers. This enabled the -320C to carry a maximum of 219 passengers, as opposed to the 189 on the -320 model. Only a few aircraft were ever used for pure freighters.
Specifications
Stay Tuned for upcoming updates. Subscribe My Youtube Channel, Follow Us on Twitter, Facebook and Instagram #Kasworld-Aero
Credit : Julie Singh
Sharing is Caring & Helping Eachother
