Lockheed L-2000
Encyclopedia
The Lockheed L-2000 was Lockheed Corporation
's entry in a government-funded competition to build the United States' first supersonic transport
(SST) in the 1960s. The L-2000 lost the contract to the Boeing 2707
, but that competing design was ultimately canceled for political, environmental and economic reasons.
In 1961
, President John F. Kennedy
committed the government to subsidizing 75% of the development of a commercial airliner to compete with the Anglo-French Concorde
then under development. The director of the Federal Aviation Administration
(FAA), Najeeb Halaby
, elected to improve upon the Concorde's design rather than compete head-to-head with it. The SST
, which might have represented a significant advance over the Concorde, was intended to carry 250 passengers (a large number at the time), fly at Mach
2.7-3.0, and have a range of 4,000 nmi (7,400 km).
The program was launched on June 5, 1963, and the FAA estimated that by 1990 there would be a market for 500 SSTs. Boeing
, Lockheed
and North American
officially responded. North American's design was soon rejected, but the Boeing and Lockheed designs were selected for further study.
could be managed throughout the entire speed range. Lockheed knew a variable geometry, swing-wing design could accomplish this goal, but felt it was too heavy; however, they preferred a fixed-wing solution. In a worst-case scenario, they were willing to design a fixed-wing aircraft using fuel for ballast.
Early designs followed Lockheed's tapered straight wing much like the type used on the F-104 Starfighter
, with a delta-shaped canard
for aerodynamic trim. The problem was that in wind-tunnel tests the shift in the airplane's C/L was substantial. A delta wing
was substituted which alleviated a portion of the movement, but it was not deemed sufficient. By 1962
, Lockheed arrived at a highly swept, bat-wing design featuring four engine pods buried in the wings and a canard. The improvement was closer to their goal, but still not optimal. By 1963, they extended the leading edge
of the wing forward a bit to eliminate the need for the canard, and re-shaped the wing into a double-delta shape with a mild twist and camber
. This, along with careful shaping of the fuselage, was able to control the shift in the center of pressure caused by the highly-swept forward part of the wing developing lift supersonically. The engines were shifted from being buried in the wings to individual pods slung below the wings.
132 in (335.2 cm) wide fuselage to meet aerodynamic requirements, allowing for passenger seating of five abreast seating in coach and a four-abreast arrangement in first-class seating. A typical mixed-class seating layout would equal around 170 passengers, with high-density layouts exceeding 200 passengers.
The L-2000-1 featured a long, pointed nose that was almost flat on top and curved on the bottom, which allowed for improved supersonic performance, and could be drooped for takeoff and landing to provide adequate visibility. The wing design featured a sharp forward inboard sweep of 80°, with the remaining part of the wing's leading edge swept back 60°, with an overall area of 8,370 ft² (778 m²). The high sweep angles produced powerful vortices on the leading edge which increased lift at moderate to high angles of attack
, yet still retained stable airflow over the control surfaces during a stall
. These vortices also provided good directional control as well, which was somewhat deficient with the nose drooped at low speeds. The wing, while only 3% thick, provided substantial lift due to its large area, which, aided by vortex lift, allowed takeoff and landing speeds comparable to a Boeing 707
. Additionally, a delta wing is a naturally rigid structure which requires little stiffening.
The plane's undercarriage
was a traditional tricycle type
with a twin-wheeled nose gear. Each of the two six-wheeled main gear utilized the same tires used on the Douglas DC-8
, but which were filled with nitrogen and to lower pressures.
To provide an optimum entry date into service, Lockheed decided to use a beefed-up turbofan
derivative of the Pratt & Whitney J58
. The J58 had already successfully proven itself as a high-thrust, high-performance jet engine on the top-secret Lockheed A-12
(and subsequently on the Lockheed SR-71 Blackbird.) Due to its being a turbofan, it was deemed to be quieter than a typical turbojet at low altitude and low speed, required no afterburner
for takeoff, and allowed reduced power settings. The engines were placed in cylindrical pods with a wedge-shaped splitter, and a squarish intake providing the inlet system for the aircraft. The inlet was designed with the goal of requiring no moving parts, and was naturally stable. To reduce the noise from sonic booms, rather than penetrate the sound barrier
at a more ideal 30,000 ft (9,144 m), they intended to penetrate it at 42,000 ft (12,802 m) instead. It would not be possible on hot days, but on normal days this would be achievable. Acceleration would continue through the sound barrier to Mach 1.15, at which point sonic booms would be audible on the ground. The plane would climb precisely to minimize sonic boom levels. After an initial level-off at around 71,500 ft (21,793 m), the plane would cruise climb upwards, ultimately reaching 76,500 ft (23,317 m). Descents would also be performed in a precise way to reduce sonic boom levels until subsonic speeds were reached.
By 1964
, the US Government issued new requirements regarding the SST Program which required Lockheed to modify their design, by now called the L-2000-2. The new design had numerous modifications to the wing; one change was rounding the front of the forward delta in order to eliminate the pitch-up
tendency. To increase high-speed aerodynamic efficiency, the wing's thickness was reduced to 2.3%, the leading edges were made sharper, the sweep angles were changed from 80/60° to 85/62°, and substantial twist and camber were added to the forward delta; much of the rear delta was twisted upwards to allow the elevons to remain flush at Mach 3.0. In addition, wing/body fairings were added on the underside of the fuselage where the wings are located, allowing a more normally-shaped nose to be used. To retain low-speed performance, the rear delta was enlarged considerably; to increase the payload, the trailing edge
featured a forward sweep of 10°. The new nose reduced the overall length to 214 ft (65.2 m) while retaining virtually the same internal dimensions. Wingspan was identical as before, and despite the thinner wing, the increased wing area of 9,026 ft² (838.5 m²) allowed the same takeoff performance. The airplane's overall lift-to-drag ratio
increased from 7.25 to 7.94.
During the course of the L-2000-2's development, the engine previously selected by Lockheed was no longer deemed acceptable. During the time frame between the L-2000-1 and L-2000-2, Pratt and Whitney designed a new afterburning turbofan called the JTF-17A, which produced greater amounts of thrust. General Electric
developed the GE4 which was an afterburning turbojet with variable guide-vanes, which was actually the less powerful of the two at sea level, but produced more power at high altitudes. Both engines required some degree of afterburner during cruise. Lockheed's design favored the JTF-17A over the GE-4, but there was the risk that GE would win the engine competition and Lockheed would win the SST contract, so they developed new engine pods that could accommodate either engine. Aerodynamic modifications allowed a shorter engine pod to be used and which utilized a new inlet design. This inlet featured minimal external cowl angles and was precisely contoured to allow a high-pressure recovery using no moving parts, and allowed maximum performance with either engine option. To allow additional airflow for noise-reduction, or to aid afterburner performance, a set of suck-in doors was added to the rear portion of the pod. To provide mid-air braking capability for rapid deceleration and rapid descents, and to assist ground braking, part of the nozzle could be employed as a thrust reverser at speeds below Mach 1.2. The pods were also repositioned on the new wing to better shield them from abrupt changes in airflow.
The additional thrust from the new engines allowed supersonic penetration to be delayed until up to 45,000 ft (13,716 km) under virtually all conditions. Since at this point the possibility of supersonic overland flight was still considered to be an option, Lockheed also considered larger, shorter-ranged versions of the L-2000-2B. All designs weighed exactly the same, with a new tail design, changes to the fuselage length, extensions to the forward delta, increased capacity, and variations in fuel capacity. The largest version featured capacity for 250 domestic passengers, while the medium version featured transatlantic capability with 220 passengers. Despite the fuselage length changes, there was no appreciable increase in the risk of the aircraft pitching upwards too far (over-rotation) on takeoff.
, the design took on its final form as the L-2000-7A and L-2000-7B. The L-2000-7A featured a re-designed wing and fuselage lengthened to 273 ft (83 m). The longer fuselage allows for a mixed-class seating of 230 passengers. The new wing featured a proportionately larger forward delta, with greater refinement to the wing's twist and curvature. Despite having the same wingspan, the wing-area was increased to 9,424 ft² (875 m²), with a slightly reduced 84° sweepback, and an increased 65° main delta wing, with reduced forward sweep along the trailing edge. Unlike previous versions, this aircraft featured a leading-edge flap to increase lift at low speeds, and to allow a slight down-elevon deflection. The fuselage, as a result of greater length, changes to the wing design, and attempts to further reduce drag, featured a slight vertical thinning in the fuselage where the wings were, a more prominent wing/body "belly" to carry fuel and cargo, a longer nose, and a refined tail. Since the airplane was not as directionally stable as before, the plane featured a ventral fin, located on the underside of the trailing fuselage. The L-2000-7B was extended to 293 ft (89 m), utilizing a lengthened cabin and a more pronounced upward-curving tail to reduce the chance of the tail striking the runway during over-rotation. Both designs had the same maximum weight of 590,000 lb (267,600 kg), and the aerodynamic lift-to-drag ratio was increased to 8:1.
Full-scale mock-ups of the Boeing 2707-200 and L-2000-7 designs were presented to the FAA, and on December 31, 1966 the Boeing design was selected. The Lockheed design was judged simpler to produce and less risky, but its performance during takeoff and at high speed was slightly lower. Because of the JTF-17A, the L-2000-7 was also predicted to be louder as well. The Boeing design was considered more advanced, representing a greater lead over the Concorde and thus more fitting to the original design mandate. Ironically, Boeing eventually changed its advanced variable-geometry wing design to a simpler delta-wing similar to Lockheed's design, but with a tail. If Lockheed had built its simpler design, it might have flown by 1971. With technical problems, delays, cost overruns, and environmental and economic questions, the Boeing SST was ultimately canceled on May 20, 1971 after the US Congress stopped federal funding for the SST program on March 24, 1971.
Lockheed Corporation
The Lockheed Corporation was an American aerospace company. Lockheed was founded in 1912 and later merged with Martin Marietta to form Lockheed Martin in 1995.-Origins:...
's entry in a government-funded competition to build the United States' first supersonic transport
Supersonic transport
A supersonic transport is a civilian supersonic aircraft designed to transport passengers at speeds greater than the speed of sound. The only SSTs to see regular service to date have been Concorde and the Tupolev Tu-144. The last passenger flight of the Tu-144 was in June 1978 with its last ever...
(SST) in the 1960s. The L-2000 lost the contract to the Boeing 2707
Boeing 2707
The Boeing 2707 was developed as the first American supersonic transport . After winning a competition for a government-funded contract to build an American SST, Boeing began development at its facilities in Seattle, Washington...
, but that competing design was ultimately canceled for political, environmental and economic reasons.
In 1961
1961 in aviation
This is a list of aviation-related events from 1961:-January:* January 3 – Aero Flight 311, a Douglas DC-3C, crashes near Kvevlax, Finland, killing all 25 people on board. An investigation finds that the captain and first officer both were exhausted for lack of sleep and drunk at the time of...
, President John F. Kennedy
John F. Kennedy
John Fitzgerald "Jack" Kennedy , often referred to by his initials JFK, was the 35th President of the United States, serving from 1961 until his assassination in 1963....
committed the government to subsidizing 75% of the development of a commercial airliner to compete with the Anglo-French Concorde
Concorde
Aérospatiale-BAC Concorde was a turbojet-powered supersonic passenger airliner, a supersonic transport . It was a product of an Anglo-French government treaty, combining the manufacturing efforts of Aérospatiale and the British Aircraft Corporation...
then under development. The director of the Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
(FAA), Najeeb Halaby
Najeeb Halaby
Najeeb Elias Halaby Jr. was a US businessman, government official, and the father of Queen Noor of Jordan.-Early life and ancestry:Halaby was born in Dallas, Texas. His father was Najeeb Elias Halaby Sr. a Syrian Christian, who emigrated to the United States from Syria in 1891...
, elected to improve upon the Concorde's design rather than compete head-to-head with it. The SST
Supersonic transport
A supersonic transport is a civilian supersonic aircraft designed to transport passengers at speeds greater than the speed of sound. The only SSTs to see regular service to date have been Concorde and the Tupolev Tu-144. The last passenger flight of the Tu-144 was in June 1978 with its last ever...
, which might have represented a significant advance over the Concorde, was intended to carry 250 passengers (a large number at the time), fly at Mach
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
2.7-3.0, and have a range of 4,000 nmi (7,400 km).
The program was launched on June 5, 1963, and the FAA estimated that by 1990 there would be a market for 500 SSTs. Boeing
Boeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
, Lockheed
Lockheed Corporation
The Lockheed Corporation was an American aerospace company. Lockheed was founded in 1912 and later merged with Martin Marietta to form Lockheed Martin in 1995.-Origins:...
and North American
North American Aviation
North American Aviation was a major US aerospace manufacturer, responsible for a number of historic aircraft, including the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F-86 Sabre jet fighter, the X-15 rocket plane, and the XB-70, as well as Apollo Command and Service...
officially responded. North American's design was soon rejected, but the Boeing and Lockheed designs were selected for further study.
Early design studies
Like Boeing, Lockheed had done a number of "paper studies" on various SST designs, starting in 1958. Lockheed sought an airplane with cruise speeds of around 2,000 mph (3,219 km/h) with takeoff and landing speeds that compared to large subsonic jets of the same era. They also desired a plane whose center of pressureCenter of pressure
The center of pressure is the point on a body where the total sum of a pressure field acts, causing a force and no moment about that point. The total force vector acting at the center of pressure is the value of the integrated vectorial pressure field. The resultant force and center of pressure...
could be managed throughout the entire speed range. Lockheed knew a variable geometry, swing-wing design could accomplish this goal, but felt it was too heavy; however, they preferred a fixed-wing solution. In a worst-case scenario, they were willing to design a fixed-wing aircraft using fuel for ballast.
Early designs followed Lockheed's tapered straight wing much like the type used on the F-104 Starfighter
F-104 Starfighter
The Lockheed F-104 Starfighter is a single-engine, high-performance, supersonic interceptor aircraft originally developed for the United States Air Force by Lockheed. One of the Century Series of aircraft, it served with the USAF from 1958 until 1969, and continued with Air National Guard units...
, with a delta-shaped canard
Canard (aeronautics)
In aeronautics, canard is an airframe configuration of fixed-wing aircraft in which the forward surface is smaller than the rearward, the former being known as the "canard", while the latter is the main wing...
for aerodynamic trim. The problem was that in wind-tunnel tests the shift in the airplane's C/L was substantial. A delta wing
Delta wing
The delta wing is a wing planform in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta .-Delta-shaped stabilizers:...
was substituted which alleviated a portion of the movement, but it was not deemed sufficient. By 1962
1962 in aviation
This is a list of aviation-related events from 1962:- Events :* Early 1962 – In Operation High Jump, the United States Navy McDonnell F4H-1 Phantom II fighter sets a number of world climb-to altitude records: 34.523 seconds to 3,000 meters , 48.787 seconds to 6,000 meters , 61.629 seconds to...
, Lockheed arrived at a highly swept, bat-wing design featuring four engine pods buried in the wings and a canard. The improvement was closer to their goal, but still not optimal. By 1963, they extended the leading edge
Leading edge
The leading edge is the part of the wing that first contacts the air; alternatively it is the foremost edge of an airfoil section. The first is an aerodynamic definition, the second a structural one....
of the wing forward a bit to eliminate the need for the canard, and re-shaped the wing into a double-delta shape with a mild twist and camber
Camber
Camber may refer to a variety of curvatures and angles:* Camber angle, the angle made by the wheels of a vehicle* Camber thrust in bike technology* In the steel industry, the concavity of rolls...
. This, along with careful shaping of the fuselage, was able to control the shift in the center of pressure caused by the highly-swept forward part of the wing developing lift supersonically. The engines were shifted from being buried in the wings to individual pods slung below the wings.
Later design studies
The new design was designated L-2000-1 and was 223 ft (70 m) long with a narrow-bodyNarrow-body aircraft
A narrow-body aircraft is an airliner with a fuselage aircraft cabin width typically of 3 to 4 metres , and airline seat arranged 2 to 6 abreast along a single aisle...
132 in (335.2 cm) wide fuselage to meet aerodynamic requirements, allowing for passenger seating of five abreast seating in coach and a four-abreast arrangement in first-class seating. A typical mixed-class seating layout would equal around 170 passengers, with high-density layouts exceeding 200 passengers.
The L-2000-1 featured a long, pointed nose that was almost flat on top and curved on the bottom, which allowed for improved supersonic performance, and could be drooped for takeoff and landing to provide adequate visibility. The wing design featured a sharp forward inboard sweep of 80°, with the remaining part of the wing's leading edge swept back 60°, with an overall area of 8,370 ft² (778 m²). The high sweep angles produced powerful vortices on the leading edge which increased lift at moderate to high angles of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
, yet still retained stable airflow over the control surfaces during a stall
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
. These vortices also provided good directional control as well, which was somewhat deficient with the nose drooped at low speeds. The wing, while only 3% thick, provided substantial lift due to its large area, which, aided by vortex lift, allowed takeoff and landing speeds comparable to a Boeing 707
Boeing 707
The Boeing 707 is a four-engine narrow-body commercial passenger jet airliner developed by Boeing in the early 1950s. Its name is most commonly pronounced as "Seven Oh Seven". The first airline to operate the 707 was Pan American World Airways, inaugurating the type's first commercial flight on...
. Additionally, a delta wing is a naturally rigid structure which requires little stiffening.
The plane's undercarriage
Undercarriage
The undercarriage or landing gear in aviation, is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land...
was a traditional tricycle type
Tricycle gear
Tricycle gear describes an aircraft undercarriage, or landing gear, arranged in a tricycle fashion. The tricycle arrangement has one wheel in the front, called the nose wheel, and two or more main wheels slightly aft of the center of gravity...
with a twin-wheeled nose gear. Each of the two six-wheeled main gear utilized the same tires used on the Douglas DC-8
Douglas DC-8
The Douglas DC-8 is a four-engined narrow-body passenger commercial jet airliner, manufactured from 1958 to 1972 by the Douglas Aircraft Company...
, but which were filled with nitrogen and to lower pressures.
To provide an optimum entry date into service, Lockheed decided to use a beefed-up turbofan
Turbofan
The turbofan is a type of airbreathing jet engine that is widely used for aircraft propulsion. A turbofan combines two types of engines, the turbo portion which is a conventional gas turbine engine, and the fan, a propeller-like ducted fan...
derivative of the Pratt & Whitney J58
Pratt & Whitney J58
The Pratt & Whitney J58 was a jet engine used on the Lockheed A-12, and subsequently on the YF-12 and SR-71 Blackbird aircraft. The J58 was a variable cycle engine which functioned as both a turbojet and a fan-assisted ramjet. The J58 was a single-spool turbojet engine with an afterburner...
. The J58 had already successfully proven itself as a high-thrust, high-performance jet engine on the top-secret Lockheed A-12
A-12 OXCART
The Lockheed A-12 was a reconnaissance aircraft built for the Central Intelligence Agency by Lockheed's famed Skunk Works, based on the designs of Clarence "Kelly" Johnson. The A-12 was produced from 1962 through 1964, and was in operation from 1963 until 1968. The single-seat design, which first...
(and subsequently on the Lockheed SR-71 Blackbird.) Due to its being a turbofan, it was deemed to be quieter than a typical turbojet at low altitude and low speed, required no afterburner
AfterBurner
The AfterBurner is a lighting solution for the Game Boy Advance system that was created by Triton-Labs.Originally, portablemonopoly.net was a website created to petition Nintendo to put some kind of light in their Game Boy Advance system...
for takeoff, and allowed reduced power settings. The engines were placed in cylindrical pods with a wedge-shaped splitter, and a squarish intake providing the inlet system for the aircraft. The inlet was designed with the goal of requiring no moving parts, and was naturally stable. To reduce the noise from sonic booms, rather than penetrate the sound barrier
Sound barrier
The sound barrier, in aerodynamics, is the point at which an aircraft moves from transonic to supersonic speed. The term, which occasionally has other meanings, came into use during World War II, when a number of aircraft started to encounter the effects of compressibility, a collection of several...
at a more ideal 30,000 ft (9,144 m), they intended to penetrate it at 42,000 ft (12,802 m) instead. It would not be possible on hot days, but on normal days this would be achievable. Acceleration would continue through the sound barrier to Mach 1.15, at which point sonic booms would be audible on the ground. The plane would climb precisely to minimize sonic boom levels. After an initial level-off at around 71,500 ft (21,793 m), the plane would cruise climb upwards, ultimately reaching 76,500 ft (23,317 m). Descents would also be performed in a precise way to reduce sonic boom levels until subsonic speeds were reached.
By 1964
1964 in aviation
For the year see 1964This is a list of aviation-related events from 1964:- Events :* Chilean President Jorge Alessandri grants the Chilean Navy the authority to operate all types of aircraft without restriction...
, the US Government issued new requirements regarding the SST Program which required Lockheed to modify their design, by now called the L-2000-2. The new design had numerous modifications to the wing; one change was rounding the front of the forward delta in order to eliminate the pitch-up
Pitch-up
In aerodynamics, pitch-up is a severe form of stall in an aircraft. It is directly related to inherent properties of all swept wings.-History:Pitch-up problems were first noticed on high-speed test aircraft with swept wings...
tendency. To increase high-speed aerodynamic efficiency, the wing's thickness was reduced to 2.3%, the leading edges were made sharper, the sweep angles were changed from 80/60° to 85/62°, and substantial twist and camber were added to the forward delta; much of the rear delta was twisted upwards to allow the elevons to remain flush at Mach 3.0. In addition, wing/body fairings were added on the underside of the fuselage where the wings are located, allowing a more normally-shaped nose to be used. To retain low-speed performance, the rear delta was enlarged considerably; to increase the payload, the trailing edge
Trailing edge
The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge rejoins. Essential control surfaces are attached here to redirect the air flow and exert a controlling force by changing its momentum...
featured a forward sweep of 10°. The new nose reduced the overall length to 214 ft (65.2 m) while retaining virtually the same internal dimensions. Wingspan was identical as before, and despite the thinner wing, the increased wing area of 9,026 ft² (838.5 m²) allowed the same takeoff performance. The airplane's overall lift-to-drag ratio
Lift-to-drag ratio
In aerodynamics, the lift-to-drag ratio, or L/D ratio, is the amount of lift generated by a wing or vehicle, divided by the drag it creates by moving through the air...
increased from 7.25 to 7.94.
During the course of the L-2000-2's development, the engine previously selected by Lockheed was no longer deemed acceptable. During the time frame between the L-2000-1 and L-2000-2, Pratt and Whitney designed a new afterburning turbofan called the JTF-17A, which produced greater amounts of thrust. General Electric
GE-Aviation
GE Aviation, a subsidiary of General Electric, is headquartered in Evendale, Ohio . GE Aviation is the top supplier of aircraft engines in the world, and offers engines for the majority of commercial aircraft. GE Aviation is part of the General Electric conglomerate, which is one of the world's...
developed the GE4 which was an afterburning turbojet with variable guide-vanes, which was actually the less powerful of the two at sea level, but produced more power at high altitudes. Both engines required some degree of afterburner during cruise. Lockheed's design favored the JTF-17A over the GE-4, but there was the risk that GE would win the engine competition and Lockheed would win the SST contract, so they developed new engine pods that could accommodate either engine. Aerodynamic modifications allowed a shorter engine pod to be used and which utilized a new inlet design. This inlet featured minimal external cowl angles and was precisely contoured to allow a high-pressure recovery using no moving parts, and allowed maximum performance with either engine option. To allow additional airflow for noise-reduction, or to aid afterburner performance, a set of suck-in doors was added to the rear portion of the pod. To provide mid-air braking capability for rapid deceleration and rapid descents, and to assist ground braking, part of the nozzle could be employed as a thrust reverser at speeds below Mach 1.2. The pods were also repositioned on the new wing to better shield them from abrupt changes in airflow.
The additional thrust from the new engines allowed supersonic penetration to be delayed until up to 45,000 ft (13,716 km) under virtually all conditions. Since at this point the possibility of supersonic overland flight was still considered to be an option, Lockheed also considered larger, shorter-ranged versions of the L-2000-2B. All designs weighed exactly the same, with a new tail design, changes to the fuselage length, extensions to the forward delta, increased capacity, and variations in fuel capacity. The largest version featured capacity for 250 domestic passengers, while the medium version featured transatlantic capability with 220 passengers. Despite the fuselage length changes, there was no appreciable increase in the risk of the aircraft pitching upwards too far (over-rotation) on takeoff.
Design competition
By 19661966 in aviation
This is a list of aviation-related events from 1966:-January:* The United States Armys helicopter assault-oriented 1st Cavalry Division begins Operation Matador to destroy North Vietnamese Army forces in Pleiku and Kon Tum Province, South Vietnam....
, the design took on its final form as the L-2000-7A and L-2000-7B. The L-2000-7A featured a re-designed wing and fuselage lengthened to 273 ft (83 m). The longer fuselage allows for a mixed-class seating of 230 passengers. The new wing featured a proportionately larger forward delta, with greater refinement to the wing's twist and curvature. Despite having the same wingspan, the wing-area was increased to 9,424 ft² (875 m²), with a slightly reduced 84° sweepback, and an increased 65° main delta wing, with reduced forward sweep along the trailing edge. Unlike previous versions, this aircraft featured a leading-edge flap to increase lift at low speeds, and to allow a slight down-elevon deflection. The fuselage, as a result of greater length, changes to the wing design, and attempts to further reduce drag, featured a slight vertical thinning in the fuselage where the wings were, a more prominent wing/body "belly" to carry fuel and cargo, a longer nose, and a refined tail. Since the airplane was not as directionally stable as before, the plane featured a ventral fin, located on the underside of the trailing fuselage. The L-2000-7B was extended to 293 ft (89 m), utilizing a lengthened cabin and a more pronounced upward-curving tail to reduce the chance of the tail striking the runway during over-rotation. Both designs had the same maximum weight of 590,000 lb (267,600 kg), and the aerodynamic lift-to-drag ratio was increased to 8:1.
Full-scale mock-ups of the Boeing 2707-200 and L-2000-7 designs were presented to the FAA, and on December 31, 1966 the Boeing design was selected. The Lockheed design was judged simpler to produce and less risky, but its performance during takeoff and at high speed was slightly lower. Because of the JTF-17A, the L-2000-7 was also predicted to be louder as well. The Boeing design was considered more advanced, representing a greater lead over the Concorde and thus more fitting to the original design mandate. Ironically, Boeing eventually changed its advanced variable-geometry wing design to a simpler delta-wing similar to Lockheed's design, but with a tail. If Lockheed had built its simpler design, it might have flown by 1971. With technical problems, delays, cost overruns, and environmental and economic questions, the Boeing SST was ultimately canceled on May 20, 1971 after the US Congress stopped federal funding for the SST program on March 24, 1971.
Specifications (L-2000-7A)
See also
Further reading
- Boyne, Walter JWalter J. BoyneWalter J. Boyne is a retired United States Air Force officer, combat veteran, aviation historian, and author of more than 50 books and over 1,000 magazine articles...
, Beyond the Horizons: The Lockheed Story. New York: St. Martin's Press, 1998. ISBN 0-312-19237-1. - Francillon, René J, Lockheed Aircraft Since 1913. Annapolis, Maryland: Naval Institute Press, 1987. ISBN 0-87021-897-2.