Boeing 707

The 707 was based on the 367-80 (the "Dash 80").

The six-abreast cabin

During and after World War II, Boeing was known for its military aircraft. The company had produced innovative and important bombers, from the B-17 Flying Fortress and B-29 Superfortress, to the jet-powered B-47 Stratojet and B-52 Stratofortress, but its commercial aircraft were not as successful as those from Douglas Aircraft and other competitors. As Douglas and Lockheed dominated the postwar air transport boom, the demand for Boeing's offering, the 377 Stratocruiser, quickly faded with only 56 examples sold and no new orders as the 1940s drew to a close. That venture had netted the company a $15 million loss.[6] During 1949 and 1950, Boeing embarked on studies for a new jet transport and saw advantages with a design aimed at both military and civilian markets. Aerial refueling was becoming a standard technique for military aircraft, with over 800 KC-97 Stratofreighters on order. The KC-97 was not ideally suited for operations with the USAF's new fleets of jet-powered fighters and bombers; this was where Boeing's new design would win military orders.[7]

As the first of a new generation of American passenger jets, Boeing wanted the aircraft's model number to emphasize the difference from its previous propeller-driven aircraft, which bore 300-series numbers. The 400-, 500- and 600-series were already used by their missiles and other products, so Boeing decided that the jets would bear 700-series numbers, and the first would be the 707.[8] The marketing personnel at Boeing chose 707 because they thought it was more appealing than 700.[9]

The project was enabled by the Pratt & Whitney JT3C turbojet engine, the civilian version of the J57 that yielded much more power than the previous generation of jet engines and was proving itself with the B-52. Freed from the design constraints imposed by limitations of late-1940s jet engines, developing a robust, safe, and high-capacity jet aircraft was within reach for Boeing. Boeing studied numerous wing and engine layouts for its new transport/tanker, some of which were based on the B-47 and C-97, before settling on the 367-80 quadjet prototype aircraft. The "Dash 80" took less than two years from project launch in 1952 to rollout on May 14, 1954, then first flew on July 15, 1954.[10] The prototype was a proof-of-concept aircraft for both military and civilian use.[10] The United States Air Force was the first customer, using it as the basis for the KC-135 Stratotanker aerial refueling and cargo aircraft.

Whether the passenger 707 would be profitable was far from certain. At the time, nearly all of Boeing's revenue came from military contracts. In a demonstration flight over Lake Washington outside Seattle, on August 7, 1955, test pilot Tex Johnston performed a barrel roll in the 367-80 prototype.[11] Although he justified his unauthorized action to Bill Allen, then president of Boeing, as selling the airplane with a 1 'g' maneuver he was told not to do it again.[12]

The 132 in (3,400 mm) wide fuselage of the Dash 80 was large enough for four-abreast (two-plus-two) seating like the Stratocruiser. Answering customers' demands and under Douglas competition, Boeing soon realized this would not provide a viable payload, so it widened the fuselage to 144 in (3,660 mm) to allow five-abreast seating and use of the KC-135's tooling.[13] Douglas Aircraft had launched its DC-8 with a fuselage width of 147 in (3,730 mm). The airlines liked the extra space and six-abreast seating, so Boeing increased the 707's width again to compete, this time to 148 in (3,760 mm).[14]

Early 707-120 in Boeing livery. This aircraft, N709PA, would later crash in 1963 as Pan Am Flight 214.

The first flight of the first-production 707-120 took place on December 20, 1957, and FAA certification followed on September 18, 1958.[15] Both test pilots Joseph John "Tym" Tymczyszyn and James R. Gannett were awarded the first Iven C. Kincheloe Award for the test flights that led to certification.[16] A number of changes were incorporated into the production models from the prototype. A Krueger flap was installed along the leading edge between the inner and outer engines on early 707-120 and -320 models.[17][18] This was in response to de Havilland Comet overrun accidents which occurred after over-rotating on take-off. Wing stall would also occur on the 707 with over-rotation so the leading-edge flaps were added to prevent stalling even with the tail dragging on the runway.[19]

The -320 and -420 are 8 ft (2.4 m) longer than the initial -120; later 707s were powered by JT3D turbofans.

The initial standard model was the 707-120 with JT3C turbojet engines. Qantas ordered a shorter-bodied version called the 707-138, which was a -120 with six fuselage frames removed, three in front of the wings, and three aft. The frames in the 707 were set 20 in (510 mm) apart, so this resulted in a shortening of 10 ft (3.0 m) to a length of 134 ft 6 in (41.0 m). With the maximum takeoff weight the same as that of the -120 (247,000 lb (112 t)), the -138 was able to fly the longer routes that Qantas needed.[18] Braniff International Airways ordered the higher-thrust version with Pratt & Whitney JT4A engines, the 707-220. The final major derivative was the 707-320, which featured an extended-span wing and JT4A engines, while the 707-420 was the same as the -320, but with Conway turbofan engines.

Though initially fitted with turbojet engines, the dominant engine for the Boeing 707 family was the Pratt & Whitney JT3D, a turbofan variant of the JT3C with lower fuel consumption and higher thrust. JT3D-engined 707s and 720s were denoted with a "B" suffix. While many 707-120Bs and -720Bs were conversions of existing JT3C-powered machines, 707-320Bs were available only as newly built aircraft, as they had a stronger structure to support a maximum takeoff weight increased by 19,000 lb (8,600 kg), along with modifications to the wing. The 707-320B series enabled nonstop westbound flights from Europe to the West Coast of the United States and from the US to Japan.

The final 707 variant was the 707-320C, (C for "Convertible"), which had a large fuselage door for cargo. It had a revised wing with three-sectioned leading-edge flaps, improving takeoff and landing performance and allowing the ventral fin to be removed (although the taller fin was retained). The 707-320Bs built after 1963 used the same wing as the -320C and were known as 707-320B Advanced aircraft.

In total, 1,010 707s were built for civilian use between 1958 and 1978, though many of these found their way to military service. The 707 production line remained open for purpose-built military variants until 1991,[20] with the last new-build 707 airframes built as E-3 and E-6 aircraft.

Traces of the 707 are still found in the 737, which uses a modified version of the 707's fuselage, as well as the same external nose and cockpit configurations as those of the 707. These were also used on the previous 727, while the 757 also used the 707 fuselage cross-section.

The 707's wings are swept back at 35°, and like all swept-wing aircraft, display an undesirable "Dutch roll" flying characteristic that manifests itself as an alternating combined yawing and rolling motion. Boeing already had considerable experience with this on the B-47 and B-52, and had developed the yaw damper system on the B-47 that would be applied to later swept-wing configurations like the 707. However, many pilots new to the 707 had no experience with this instability, as they were mostly accustomed to flying straight-wing propeller-driven aircraft such as the Douglas DC-7 and Lockheed Constellation.

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, a brand new 707-227, N7071, destined for Braniff, crash-landed on a river bed north of Seattle at Arlington, Washington, killing four of the eight occupants.[21]

In his autobiography, test pilot Tex Johnston describes a Dutch roll incident he experienced as a passenger on an early commercial 707 flight. As the aircraft's movements did not cease and most of the passengers became ill, he suspected a misrigging of the directional autopilot (yaw damper). He went to the cockpit and found the crew unable to understand and resolve the situation. He introduced himself and relieved the ashen-faced captain, who immediately left the cockpit feeling ill. Johnston disconnected the faulty autopilot and manually stabilized the plane "with two slight control movements".[22]

Tex Johnston recommended Boeing increase the height of the tail fin, add a boosted rudder, as well as add a ventral fin. These modifications were aimed at mitigating Dutch roll by providing more directional stability in yaw.[23]

• 
  An early JT4A turbojet
• 
  A later JT3D low-bypass turbofan

The 707 uses engine-driven turbocompressors to supply compressed air for cabin pressurization. On many commercial 707s, the outer port (number 1) engine mount is distinctly different from the other three, as this engine is not fitted with a turbocompressor. Later-model 707s typically had this configuration, although American Airlines had turbocompressors on engines 2 and 3 only. Early 707 models often had turbocompressor fairings on all four engines, but with only two or three compressors installed.[24]

The JT3D-3B engines are readily identifiable by the large gray secondary-air inlet doors in the nose cowl. These doors are fully open (sucked in at the rear) during takeoff to provide additional air. The doors automatically close with increasing airspeed.

The 707 was the first commercial jet aircraft to be fitted with clamshell-type thrust reversers.[25]

Omega Air's 707-330C testbed for the 707RE program takes off from the Mojave Airport, 2007.

Pratt & Whitney, in a joint venture with Seven Q Seven (SQS) and Omega Air, selected the JT8D-219 as a replacement powerplant for Boeing 707-based aircraft, calling their modified configuration a 707RE.[26] Northrop Grumman selected the -219 to re-engine the US Air Force's fleet of 19 E-8 Joint STARS aircraft, which would allow the J-STARS more time on station due to the engine's greater fuel efficiency. NATO also planned to re-engine their fleet of E-3 Sentry AWACS aircraft. The -219 is publicized as being half the cost of the competing powerplant, the CFM International CFM56, and is 40 dB quieter than the original JT3D engines.[26]

The 707-020 (720) is 9 ft (2.7 m) shorter than the 707-120.

Announced in July 1957 as a derivative for shorter flights from shorter runways, the 707-020 first flew on November 23, 1959. Its type certificate was issued on June 30, 1960, and it entered service with United Airlines on July 5, 1960. As a derivative, the 720 had low development costs, allowing profitability despite few sales.

Compared to the 707-120, it has a length reduced by 9 feet (2.7 m), a modified wing and a lightened airframe for a lower maximum takeoff weight. Powered by four Pratt & Whitney JT3C turbojets, the initial 720 could cover a 2,800 nmi (5,200 km; 3,200 mi) range with 131 passengers in two classes. Powered by JT3D turbofans, the 720B first flew on October 6, 1960, and entered service in March 1961. It could seat 156 passengers in one class over a 3,200 nmi (5,900 km; 3,700 mi) range. A total of 154 Boeing 720s and 720Bs were built until 1967. Some 720s were later converted to the 720B specification. The 720 was succeeded by the Boeing 727 trijet.

Boeing 707-120 edit without “eyebrow windows”

The 707-120 was the first production 707 variant, with a longer, wider fuselage, and greater wingspan than the Dash 80. The cabin had a full set of rectangular windows and could seat up to 189 passengers.[41] It was designed for transcontinental routes, and often required a refueling stop when flying across the North Atlantic. It had four Pratt & Whitney JT3C-6 turbojets, civilian versions of the military J57, initially producing 13,000 lbf (57.8 kN) with water injection. Maximum takeoff weight was 247,000 lb (112,000 kg) and first flight was on December 20, 1957. Major orders were the launch order for 20 707-121 aircraft by Pan Am and an American Airlines order for 30 707-123 aircraft. The first revenue flight was on October 26, 1958;[42] 56 were built, plus seven short-bodied -138s; the last -120 was delivered to Western in May 1960.

John Travolta's 707-138: a -120 shortened by 10 ft (3.0 m)

The 707-138 was a -120 with a fuselage 10 ft (3.0 m) shorter than the others, with 5 ft (1.5 m) (three frames) removed ahead and behind the wing, giving increased range. Maximum takeoff weight was the same 247,000 lb (112,000 kg) as the standard version. It was a variant for Qantas, thus had its customer number 38. To allow for full-load takeoffs at the midflight refueling stop in Fiji, the wing's leading-edge slats were modified for increased lift, and the allowable temperature range for use of full takeoff power was increased by 10°F (5.5°C).[43] Seven -138s were delivered to Qantas between June and September 1959, and they first carried passengers in July of that year.

The 707-120B had Pratt & Whitney JT3D-1 turbofan engines, which were quieter, more powerful, and more fuel-efficient, rated at 17,000 lbf (75.6 kN), with the later JT3D-3 version giving 18,000 lbf (80 kN). (This thrust did not require water injection, eliminating both the system and 5000–6000 lb of water.) The -120B had the wing modifications introduced on the 720 and a longer tailplane; a total of 72 were built, 31 for American and 41 for TWA, plus six short-bodied -138Bs for Qantas. American had its 23 surviving -123s converted to -123Bs, but TWA did not convert its 15 -131s. The only other conversions were Pan Am's five surviving -121s and one surviving -139, the three aircraft delivered to the USAF as -153s and the seven short-bodied Qantas -138s (making 13 total 707s delivered to Qantas between 1959 and 1964[43]). The first flight of the -120B was on June 22, 1960, and American carried the first passengers in March 1961; the last delivery was to American in April 1969. Maximum weight was 258,000 lb (117,000 kg) for both the long- and short-bodied versions.

The 707-220 was designed for hot and high operations with more powerful 15,800 lbf (70.3 kN) Pratt & Whitney JT4A-3 turbojets. Five of these were produced, but only four were ultimately delivered, with one being lost during a test flight. All were for Braniff International Airways and carried the model number 707-227; the first entered service in December 1959. This version was made obsolete by the arrival of the turbofan-powered 707-120B.

The stretched -320, powered by JT4A turbojets

The 707-320 Intercontinental is a stretched version of the turbojet-powered 707-120, initially powered by JT4A-3 or JT4A-5 turbojets producing 15,800 lbf (70.3 kN) each (most eventually got 17,500 lbf (77.8 kN) JT4A-11s). The interior allowed up to 189 passengers, the same as the -120 and -220 series, but improved two-class capacity due to an 80-in fuselage stretch ahead of the wing (from 138 ft 10 in (42.32 m) to 145 ft 6 in (44.35 m) ), with extensions to the fin and horizontal stabilizer extending the aircraft's length further.[44] The longer wing carried more fuel, increasing range by 1,600 miles (2,600 km) and allowing the aircraft to operate as true transoceanic aircraft. The wing modifications included outboard and inboard inserts, as well as a kink in the trailing edge to add area inboard.[18] Takeoff weight was increased to 302,000 lb (137,000 kg) initially and to 312,000 lb (142,000 kg) with the higher-rated JT4As and center section tanks. Its first flight was on January 11, 1958; 69 turbojet 707-320s were delivered through January 1963, the first passengers being carried (by Pan Am) in August 1959.

A BEA Airtours -420, powered by Rolls-Royce Conway low-bypass turbofans

The 707-420 was identical to the -320, but fitted with Rolls-Royce Conway 508 (RCo.12) turbofans (or by-pass turbojets as Rolls-Royce called them) of 18,000 lbf (80 kN) thrust each.[45] 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 yaw 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 in (100 cm) 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. The 37 -420s were delivered to BOAC, Lufthansa, Air-India, El Al, and Varig through November 1963; Lufthansa was the first to carry passengers, in March 1960.

The -320B, powered by JT3D turbofans

The 707-320B had the application of the JT3D turbofan to the Intercontinental, but with 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.[18] These wingtips increased overall wingspan by 3.0 ft. Takeoff gross weight was increased to 328,000 lb (149,000 kg). The 175 707-320B aircraft were all new-build; no original -320 models were converted to fan engines in civilian use. First service was June 1962, with Pan Am.

The 707-320B Advanced is an improved version of the -320B, adding the three-section leading-edge flaps already seen on the -320C. These reduced takeoff and landing speeds and altered the lift distribution of the wing, allowing the ventral fin found on earlier 707s to be removed. From 1965, -320Bs had the uprated -320C undercarriage allowing the same 335,000 lb (152,000 kg) MTOW. These were often identified as 707-320BA-H.

The 707-320C, a convertible passenger–freight configuration

The 707-320C has a convertible passenger–freight configuration, which became the most widely produced variant of the 707. The 707-320C added a strengthened floor and a new cargo door to the -320B model. The wing was fitted with three-section leading-edge flaps which allowed the removal of the underfin. A total of 335 of this variant were built, including some with JT3D-7 engines (19,000 lbf (85 kN) takeoff thrust) and a takeoff weight of 335,000 lb (152,000 kg). Most -320Cs were delivered as passenger aircraft with airlines hoping the cargo door would increase second-hand values. The addition of two additional emergency exits, one on either side aft of the wing raised the maximum passenger limit to 219. Only a few aircraft were delivered as pure freighters. One of the final orders was by the Iranian Government for 14 707-3J9C aircraft capable of VIP transportation, communication, and in-flight refueling tasks.[46]

The 707-700 was a test aircraft used to study the feasibility of using CFM International CFM56 engines on a 707 airframe and possibly retrofitting existing aircraft with the engine. After testing in 1979, N707QT, the last commercial 707 airframe, was restored to 707-320C configuration and delivered to the Moroccan Air Force as a tanker aircraft via a "civilian" order. Boeing abandoned the retrofit program, since they felt it would be a threat to the Boeing 757 and Boeing 767 programs.[47][48] The information gathered from testing led to the eventual retrofitting of CFM56 engines to the USAF C-135/KC-135R models, and some military versions of the 707 also used the CFM56. The Douglas DC-8 "Super 70" series with CFM56 engines was developed and extended the DC-8's life in a stricter noise regulatory environment. As a result, significantly more DC-8s remained in service into the 21st century than 707s.

The 707-620 was a proposed domestic range-stretched variant of the 707-320B. The 707-620 was to carry around 200 passengers while retaining several aspects of the 707-320B. It would have been delivered around 1968 and would have also been Boeing's answer to the stretched Douglas DC-8 Series 60. Had the 707-620 been built, it would have cost around US$8,000,000.[49] However, engineers discovered that a longer fuselage and wing meant a painstaking redesign of the wing and landing-gear structures. Rather than spend money on upgrading the 707, engineer Joe Sutter stated the company "decided spending money on the 707 wasn't worth it". The project was cancelled in 1966 in favor of the newer Boeing 747.[50]

The 707-820 was a proposed intercontinental stretched variant of the 707-320B. This 412,000-pound MTOW (187,000 kg) variant was to be powered by four 22,500-pound-force thrust (100 kN) Pratt & Whitney JT3D-15 turbofan engines, and it would have had a nearly 10-foot (3.0 m) extension in wingspan, to 155.5 feet (47.4 m). Two variations were proposed, the 707-820(505) model and the 707-820(506) model. The 505 model would have had a fuselage 45 feet (14 m) longer than the 707-320B, for a total length of 198.6 feet (60.5 m). This model would have carried 209 passengers in mixed-class configuration and 260 passengers in all-economy configuration. The 506 model would have had a fuselage 55 feet (17 m) longer than the 707-320B, to 208.6 feet (63.6 m) in length. This second model would have carried 225 passengers in mixed-class configuration and 279 passengers in all-economy configuration. Like the 707-620, the 707-820 was also set to compete with the stretched DC-8-60 Super Series models. The design was being pitched to American, TWA, BOAC, and Pan Am at the time of its proposal in early 1965.[51] The 707-820 would have cost US$10,000,000.[49] Like the 707-620, the 707-820 would have required a massive structural redesign to the wing and gear structures. The 707-820 was also cancelled in 1966 in favor of the 747.[50]

RAAF 707-320C

The militaries of the US and other countries have used the civilian 707 aircraft in a variety of roles, and under different designations. (The 707 and US Air Force's KC-135 were developed in parallel from the Boeing 367–80 prototype.)

The Boeing E-3 Sentry is a US military airborne warning and control system (AWACS) aircraft based on the Boeing 707 that provides all-weather surveillance, command, control, and communications.

The Northrop Grumman E-8 Joint STARS is an aircraft modified from the Boeing 707-300 series commercial airliner. The E-8 carries specialized radar, communications, operations and control subsystems. The most prominent external feature is the 40 ft (12 m) canoe-shaped radome under the forward fuselage that houses the 24 ft (7.3 m) APY-7 active electronically scanned array side looking airborne radar antenna.

The VC-137 variant of the Stratoliner was a special-purpose design meant to serve as Air Force One, the secure transport for the President of the United States. These models were in operational use from 1962 to 1990. The first presidential jet aircraft, a VC-137B designated SAM 970, is on display at the Museum of Flight in Seattle. Two VC-137C aircraft are on display with SAM 26000 at the National Museum of the United States Air Force near Dayton, Ohio and SAM 27000 at the Ronald Reagan Presidential Library in Simi Valley, California.

The Canadian Forces also operated the Boeing 707 with the designation CC-137 Husky (707-347C) from 1971 to 1997.

Boeing 717 was the company designation for the C-135 Stratolifter and KC-135 Stratotanker derivatives of the 367-80. (The 717 designation was later reused in renaming the McDonnell Douglas MD-95 to Boeing 717 after the company merged with Boeing.)[52]