Area rule
Encyclopedia
The Whitcomb area rule, also called the transonic area rule, is a design technique used to reduce an aircraft
's drag
at transonic
and supersonic
speeds, particularly between Mach
0.75 and 1.2.
This is one of the most important operating speed ranges for commercial and military fixed-wing aircraft
today, with transonic acceleration being considered an important performance metric for combat aircraft, necessarily dependent upon transonic drag.
At high-subsonic flight speeds, supersonic
airflow can develop in areas where the flow accelerates around the aircraft
body and wing
s. The speed at which this occurs varies from aircraft to aircraft, and is known as the critical Mach number. The resulting shock wave
s formed at these points of supersonic
flow can bleed away a considerable amount of power
, which is experienced by the aircraft as a sudden and very powerful form of drag
, called wave drag
. To reduce the number and power of these shock waves, an aerodynamic shape should change in cross section
al area as smoothly as possible. This leads to a "perfect" aerodynamic shape known as the Sears-Haack body
, roughly shaped like a cigar but pointed at both ends.
The area rule says that an airplane designed with the same cross-sectional area distribution in the longitudinal direction as the Sears-Haack body generates the same wave drag as this body, largely independent of the actual shape. As a result, aircraft have to be carefully arranged so that large volumes like wings are positioned at the widest area of the equivalent Sears-Haack body, and that the cockpit, tailplane, intakes and other "bumps" are spread out along the fuselage and/or that the rest of the fuselage along these "bumps" is correspondingly thinned.
The area rule also holds true at speeds higher than the speed of sound
, but in this case the body arrangement is in respect to the Mach line for the design speed. For instance, at Mach 1.3 the angle of the Mach cone formed off the body of the aircraft will be at about μ = arcsin (1/M) = 50.3 deg (μ is the angle of the Mach cone, or simply Mach angle). In this case the "perfect shape" is biased rearward, which is why aircraft designed for high speed cruise tend to be arranged with the wings at the rear. A classic example of such a design is Concorde
. When applying the supersonic area rule, the condition that the plane defining the cross-section meet the longitudinal axis at the Mach angle μ no longer prescribes a unique plane for μ other than the 90 degrees given by M=1. The correct procedure is to average over all possible orientations of the intersecting plane.
The area rule was discovered by Otto Frenzl when comparing a swept wing with a w-wing with extreme high wave drag working on a transonic wind tunnel at Junkers works in Germany
between 1943 and 1945. He wrote a description on 17 December 1943, with the title “Arrangement of Displacement Bodies in High-Speed Flight”; this was used in a patent filed in 1944. The results of this research were presented to a wide circle in March 1944 by Theodor Zobel at the “Deutsche Akademie der Luftfahrtforschung” (German Academy of Aeronautics Research) in the lecture “Fundamentally new ways to increase performance of high speed aircraft.”
Subsequent German wartime aircraft design took account of the discovery, evident in the slim mid-fuselage of aircraft such as the Messerschmitt Me P.1112
, P.1106
, and the indisputably wasp-waisted Focke-Wulf Fw 1000x3 type A long range bomber, but also apparent in delta wing designs like the Henschel Hs 135. Several other researchers came close to developing a similar theory, notably Dietrich Küchemann
who designed a tapered fighter that was dubbed the “Küchemann Coke Bottle” when it was discovered by U.S. forces in 1946. In this case Küchemann arrived at the solution by studying airflow, notably spanwise flow, over a swept wing
. The swept wing is already an indirect application of the area rule.
, a pioneer of supersonic
flight, developed the supersonic area rule in publications beginning in 1947 with his Ph.D. thesis at the California Institute of Technology
.
Richard T. Whitcomb, after whom the rule is named, independently discovered this rule in 1952, while working at the NACA
. While using the new Eight-Foot High-Speed Tunnel, a wind tunnel
with performance up to Mach 0.95 at NACA's Langley Research Center
, he was surprised by the increase in drag due to shock wave formation. Whitcomb realized that, for analytical purposes, an airplane could be reduced to a streamlined body of revolution, elongated as much as possible to mitigate abrupt discontinuities and, hence, equally abrupt drag rise. The shocks could be seen using Schlieren photography
, but the reason they were being created at speeds far below the speed of sound, sometimes as low as Mach 0.70, remained a mystery.
In late 1951, the lab hosted a talk by Adolf Busemann
, a famous German aerodynamicist who had moved to Langley after World War II
. He talked about the difference in the behavior of airflow at speeds approaching supersonic, where it no longer behaved as an incompressible fluid. Whereas engineers were used to thinking of air flowing smoothly around the body of the aircraft, at high speeds it simply did not have time to "get out of the way", and instead started to flow as if it were rigid pipes of flow, a concept Busemann referred to as "streampipes", as opposed to streamlines, and jokingly suggested that engineers had to consider themselves "pipefitters".
Several days later Whitcomb had a "Eureka
" moment. The reason for the high drag was that the "pipes" of air were interfering with each other in three dimensions. One could not simply consider the air flowing over a 2D cross-section of the aircraft as others could in the past; now they also had to consider the air to the "sides" of the aircraft which would also interact with these streampipes. Whitcomb realized that the Sears-Haack shaping had to apply to the aircraft as a whole, rather than just to the fuselage. That meant that the extra cross-sectional area of the wings and tail had to be accounted for in the overall shaping, and that the fuselage should actually be narrowed where they meet to more closely match the ideal.
The area rule was immediately applied to a number of development efforts. One of the most famous was Whitcomb's personal work on the re-design of the Convair F-102 Delta Dagger
, a U.S. Air Force jet fighter that was demonstrating performance considerably worse than expected. By indenting the fuselage beside the wings, and (paradoxically) adding more volume to the rear of the plane, transonic drag was considerably reduced and the original Mach 1.2 design speeds were reached. The culminating design of this research was the Convair F-106 Delta Dart
, an aircraft which for many years was the USAF's primary all-weather interceptor.
Numerous designs of the era were likewise modified in this fashion, either by adding new fuel tanks or tail extensions to smooth out the profile. The Tupolev Tu-95 'Bear'
, a Soviet
-era bomber
, has large bulged landing gear nacelles behind the two inner engines, increasing the aircraft's overall cross section aft of the wing root. Its airliner version
has been the fastest propeller-driven aircraft
in the world since 1960. The Convair 990
used a similar solution, adding bumps called antishock bodies
to the trailing edge
of the upper wing. The 990 remains the fastest U.S. airliner
in history, cruising at up to Mach
0.89. Designers at Armstrong-Whitworth took the concept a step further in their proposed M-Wing, in which the wing was first swept forward and then to the rear. This allowed the fuselage to be narrowed on either side of the root instead of just behind it, leading to a smoother fuselage that remained wider on average than one using a classic swept wing.
One interesting outcome of the area rule is the shaping of the Boeing 747
's upper deck. The aircraft was designed to carry standard intermodal container
s in a two-wide, two-high stack on the main deck, which was considered a serious accident risk for the pilots if they were located in a cockpit at the front of the aircraft. They were instead moved above the deck in a small "hump", which was designed to be as small as possible given normal streamlining principles. It was later realized that the drag could be reduced much more by lengthening the hump, using it to reduce wave drag offsetting the tail surface's contribution. The new design was introduced on the 747-300, improving its cruise speed and lowering drag, with the side effect of slightly increasing capacity on passenger flights.
Aircraft designed according to Whitcomb's area rule looked odd at the time they were first tested, (e.g., the Blackburn Buccaneer
), and were dubbed "flying Coke bottles," but the area rule is effective and came to be an expected part of the appearance of any transonic aircraft. Later designs started with the area rule in mind, and came to look much more pleasing. Although the rule still applies, the visible fuselage "waisting" can only be seen on a few aircraft, such as the B-1B Lancer
, Learjet 60
, and the Tupolev Tu-160 'Blackjack'
— the same effect is now achieved by careful positioning of aircraft components, like the boosters and cargo bay on rockets; the jet engines in front of (and not directly below) the wings of the Airbus A380
; the jet engines behind (and not purely at the side of) the fuselage of a Cessna Citation X
; the shape and location of the canopy on the F-22 Raptor
; and the image of the Airbus A380
above showing obvious area rule shaping at the wing root, which is practically invisible from any other angle.
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
's drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
at transonic
Transonic
Transonic speed is an aeronautics term referring to the condition of flight in which a range of velocities of airflow exist surrounding and flowing past an air vehicle or an airfoil that are concurrently below, at, and above the speed of sound in the range of Mach 0.8 to 1.2, i.e. 600–900 mph...
and supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
speeds, particularly between 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...
0.75 and 1.2.
This is one of the most important operating speed ranges for commercial and military fixed-wing aircraft
Fixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...
today, with transonic acceleration being considered an important performance metric for combat aircraft, necessarily dependent upon transonic drag.
Description
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
airflow can develop in areas where the flow accelerates around the aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
body and wing
Wing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...
s. The speed at which this occurs varies from aircraft to aircraft, and is known as the critical Mach number. The resulting shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
s formed at these points of supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
flow can bleed away a considerable amount of power
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
, which is experienced by the aircraft as a sudden and very powerful form of drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
, called wave drag
Wave drag
In aeronautics, wave drag is a component of the drag on aircraft, blade tips and projectiles moving at transonic and supersonic speeds, due to the presence of shock waves. Wave drag is independent of viscous effects.- Overview :...
. To reduce the number and power of these shock waves, an aerodynamic shape should change in cross section
Cross section (geometry)
In geometry, a cross-section is the intersection of a figure in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc...
al area as smoothly as possible. This leads to a "perfect" aerodynamic shape known as the Sears-Haack body
Sears-Haack body
The Sears–Haack body is the aerodynamic body shape with the lowest theoretical wave drag. Aircraft designed to operate at high subsonic or supersonic speeds have their cross-sectional areas designed to match as closely as possible the proportions of Sears-Haack body.By Whitcomb's area rule, the...
, roughly shaped like a cigar but pointed at both ends.
The area rule says that an airplane designed with the same cross-sectional area distribution in the longitudinal direction as the Sears-Haack body generates the same wave drag as this body, largely independent of the actual shape. As a result, aircraft have to be carefully arranged so that large volumes like wings are positioned at the widest area of the equivalent Sears-Haack body, and that the cockpit, tailplane, intakes and other "bumps" are spread out along the fuselage and/or that the rest of the fuselage along these "bumps" is correspondingly thinned.
The area rule also holds true at speeds higher than the speed of sound
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....
, but in this case the body arrangement is in respect to the Mach line for the design speed. For instance, at Mach 1.3 the angle of the Mach cone formed off the body of the aircraft will be at about μ = arcsin (1/M) = 50.3 deg (μ is the angle of the Mach cone, or simply Mach angle). In this case the "perfect shape" is biased rearward, which is why aircraft designed for high speed cruise tend to be arranged with the wings at the rear. A classic example of such a design is 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...
. When applying the supersonic area rule, the condition that the plane defining the cross-section meet the longitudinal axis at the Mach angle μ no longer prescribes a unique plane for μ other than the 90 degrees given by M=1. The correct procedure is to average over all possible orientations of the intersecting plane.
Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
between 1943 and 1945. He wrote a description on 17 December 1943, with the title “Arrangement of Displacement Bodies in High-Speed Flight”; this was used in a patent filed in 1944. The results of this research were presented to a wide circle in March 1944 by Theodor Zobel at the “Deutsche Akademie der Luftfahrtforschung” (German Academy of Aeronautics Research) in the lecture “Fundamentally new ways to increase performance of high speed aircraft.”
Subsequent German wartime aircraft design took account of the discovery, evident in the slim mid-fuselage of aircraft such as the Messerschmitt Me P.1112
Messerschmitt Me P.1112
-Specifications :...
, P.1106
Messerschmitt Me P.1106
The Messerschmitt P.1106 was an intended improvement to the Messerschmitt P.1101. It went through several redesigns; the first version had a T-tail with cockpit faired into the vertical stabilizer, the later design having a V-tail with the cockpit moved slightly forward. In both cases the wings...
, and the indisputably wasp-waisted Focke-Wulf Fw 1000x3 type A long range bomber, but also apparent in delta wing designs like the Henschel Hs 135. Several other researchers came close to developing a similar theory, notably Dietrich Küchemann
Dietrich Küchemann
Dietrich Küchemann CBE FRS FRAeS was a German aerodynamicist who made several important contributions to the advancement of high-speed flight...
who designed a tapered fighter that was dubbed the “Küchemann Coke Bottle” when it was discovered by U.S. forces in 1946. In this case Küchemann arrived at the solution by studying airflow, notably spanwise flow, over a swept wing
Swept wing
A swept wing is a wing planform favored for high subsonic jet speeds first investigated by Germany during the Second World War. Since the introduction of the MiG-15 and North American F-86 which demonstrated a decisive superiority over the slower first generation of straight-wing jet fighters...
. The swept wing is already an indirect application of the area rule.
United States
Wallace D. HayesWallace D. Hayes
Wallace D. Hayes was a professor of mechanical and aerospace engineering who made numerous fundamental contributions to the understanding of supersonic flight and supersonic aircraft design....
, a pioneer of supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
flight, developed the supersonic area rule in publications beginning in 1947 with his Ph.D. thesis at the California Institute of Technology
California Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...
.
Richard T. Whitcomb, after whom the rule is named, independently discovered this rule in 1952, while working at the NACA
National Advisory Committee for Aeronautics
The National Advisory Committee for Aeronautics was a U.S. federal agency founded on March 3, 1915 to undertake, promote, and institutionalize aeronautical research. On October 1, 1958 the agency was dissolved, and its assets and personnel transferred to the newly created National Aeronautics and...
. While using the new Eight-Foot High-Speed Tunnel, a wind tunnel
Wind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
with performance up to Mach 0.95 at NACA's Langley Research Center
Langley Research Center
Langley Research Center is the oldest of NASA's field centers, located in Hampton, Virginia, United States. It directly borders Poquoson, Virginia and Langley Air Force Base...
, he was surprised by the increase in drag due to shock wave formation. Whitcomb realized that, for analytical purposes, an airplane could be reduced to a streamlined body of revolution, elongated as much as possible to mitigate abrupt discontinuities and, hence, equally abrupt drag rise. The shocks could be seen using Schlieren photography
Schlieren photography
Schlieren photography is a visual process that is used to photograph the flow of fluids of varying density. Invented by the German physicist August Toepler in 1864 to study supersonic motion, it is widely used in aeronautical engineering to photograph the flow of air around objects...
, but the reason they were being created at speeds far below the speed of sound, sometimes as low as Mach 0.70, remained a mystery.
In late 1951, the lab hosted a talk by Adolf Busemann
Adolf Busemann
Adolph Busemann was a German aerospace engineer and influential early pioneer in aerodynamics, specialising in supersonic airflows...
, a famous German aerodynamicist who had moved to Langley after World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. He talked about the difference in the behavior of airflow at speeds approaching supersonic, where it no longer behaved as an incompressible fluid. Whereas engineers were used to thinking of air flowing smoothly around the body of the aircraft, at high speeds it simply did not have time to "get out of the way", and instead started to flow as if it were rigid pipes of flow, a concept Busemann referred to as "streampipes", as opposed to streamlines, and jokingly suggested that engineers had to consider themselves "pipefitters".
Several days later Whitcomb had a "Eureka
Eureka (word)
"Eureka" is an interjection used to celebrate a discovery, a transliteration of a word attributed to Archimedes.-Etymology:The word comes from ancient Greek εὕρηκα heúrēka "I have found ", which is the 1st person singular perfect indicative active of the verb heuriskō "I find"...
" moment. The reason for the high drag was that the "pipes" of air were interfering with each other in three dimensions. One could not simply consider the air flowing over a 2D cross-section of the aircraft as others could in the past; now they also had to consider the air to the "sides" of the aircraft which would also interact with these streampipes. Whitcomb realized that the Sears-Haack shaping had to apply to the aircraft as a whole, rather than just to the fuselage. That meant that the extra cross-sectional area of the wings and tail had to be accounted for in the overall shaping, and that the fuselage should actually be narrowed where they meet to more closely match the ideal.
Applications
F-102 Delta Dagger
The Convair F-102 Delta Dagger was a US interceptor aircraft built as part of the backbone of the United States Air Force's air defenses in the late 1950s. Entering service in 1956, its main purpose was to intercept invading Soviet bomber fleets...
, a U.S. Air Force jet fighter that was demonstrating performance considerably worse than expected. By indenting the fuselage beside the wings, and (paradoxically) adding more volume to the rear of the plane, transonic drag was considerably reduced and the original Mach 1.2 design speeds were reached. The culminating design of this research was the Convair F-106 Delta Dart
F-106 Delta Dart
The Convair F-106 Delta Dart was the primary all-weather interceptor aircraft for the United States Air Force from the 1960s through the 1980s. Designed as the so-called "Ultimate Interceptor", it has proven to be the last dedicated interceptor in USAF service to date...
, an aircraft which for many years was the USAF's primary all-weather interceptor.
Numerous designs of the era were likewise modified in this fashion, either by adding new fuel tanks or tail extensions to smooth out the profile. The Tupolev Tu-95 'Bear'
Tupolev Tu-95
The Tupolev Tu-95 is a large, four-engine turboprop-powered strategic bomber and missile platform. First flown in 1952, the Tu-95 entered service with the former Soviet Union in 1956 and is expected to serve the Russian Air Force until at least 2040...
, a Soviet
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
-era bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
, has large bulged landing gear nacelles behind the two inner engines, increasing the aircraft's overall cross section aft of the wing root. Its airliner version
Tupolev Tu-114
The Tupolev Tu-114 Rossiya is a turboprop-powered long-range airliner designed by the Tupolev design bureau and built in the USSR from May 1955....
has been the fastest propeller-driven aircraft
Fastest propeller-driven aircraft
A number of aircraft have claimed to be the fastest propeller-driven aircraft. This article presents the current record holders for several sub-classes of propeller-driven aircraft that hold recognized, documented speed records. Fédération Aéronautique Internationale records are the basis for this...
in the world since 1960. The Convair 990
Convair 990
The Convair 990 Coronado was a narrow-body jet airliner produced by the Convair division of General Dynamics, a "stretched" version of their earlier Convair 880 produced in response to a request from American Airlines. The 990 was lengthened by 10 feet, which increased the number of passengers from...
used a similar solution, adding bumps called antishock bodies
Anti-shock body
An Anti-shock body is a pod positioned on the leading or trailing edge of an aircraft's aerodynamic surface to reduce wave drag at transonic speeds .-Wing trailing edge:...
to 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...
of the upper wing. The 990 remains the fastest U.S. airliner
Airliner
An airliner is a large fixed-wing aircraft for transporting passengers and cargo. Such aircraft are operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an aircraft intended for carrying multiple passengers in commercial...
in history, cruising at up to 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...
0.89. Designers at Armstrong-Whitworth took the concept a step further in their proposed M-Wing, in which the wing was first swept forward and then to the rear. This allowed the fuselage to be narrowed on either side of the root instead of just behind it, leading to a smoother fuselage that remained wider on average than one using a classic swept wing.
One interesting outcome of the area rule is the shaping of the Boeing 747
Boeing 747
The Boeing 747 is a wide-body commercial airliner and cargo transport, often referred to by its original nickname, Jumbo Jet, or Queen of the Skies. It is among the world's most recognizable aircraft, and was the first wide-body ever produced...
's upper deck. The aircraft was designed to carry standard intermodal container
Intermodal container
An intermodal container is a standardized reusable steel box used for the safe, efficient and secure storage and movement of materials and products within a global containerized intermodal freight transport system...
s in a two-wide, two-high stack on the main deck, which was considered a serious accident risk for the pilots if they were located in a cockpit at the front of the aircraft. They were instead moved above the deck in a small "hump", which was designed to be as small as possible given normal streamlining principles. It was later realized that the drag could be reduced much more by lengthening the hump, using it to reduce wave drag offsetting the tail surface's contribution. The new design was introduced on the 747-300, improving its cruise speed and lowering drag, with the side effect of slightly increasing capacity on passenger flights.
Aircraft designed according to Whitcomb's area rule looked odd at the time they were first tested, (e.g., the Blackburn Buccaneer
Blackburn Buccaneer
The Blackburn Buccaneer was a British low-level subsonic strike aircraft with nuclear weapon delivery capability serving with the Royal Navy and the Royal Air Force between 1962 and 1994, including service in the 1991 Gulf War...
), and were dubbed "flying Coke bottles," but the area rule is effective and came to be an expected part of the appearance of any transonic aircraft. Later designs started with the area rule in mind, and came to look much more pleasing. Although the rule still applies, the visible fuselage "waisting" can only be seen on a few aircraft, such as the B-1B Lancer
B-1 Lancer
The Rockwell B-1 LancerThe name "Lancer" is only applied to the B-1B version, after the program was revived. is a four-engine variable-sweep wing strategic bomber used by the United States Air Force...
, Learjet 60
Learjet 60
The Learjet 60 is a mid-size cabin, medium range business jet aircraft manufactured by Bombardier Aerospace in Wichita, Kansas, USA. The Learjet 60 is powered by two Pratt & Whitney Canada model 305A turbo fan engines producing 4,600 total pounds of thrust. The manufacturer notes the range of the...
, and the Tupolev Tu-160 'Blackjack'
Tupolev Tu-160
The Tupolev Tu-160 is a supersonic, variable-sweep wing heavy strategic bomber designed by the Tupolev Design Bureau in the Soviet Union. Although several civil and military transport aircraft are larger in overall dimensions, the Tu-160 is currently the world's largest combat aircraft, largest...
— the same effect is now achieved by careful positioning of aircraft components, like the boosters and cargo bay on rockets; the jet engines in front of (and not directly below) the wings of the Airbus A380
Airbus A380
The Airbus A380 is a double-deck, wide-body, four-engine jet airliner manufactured by the European corporation Airbus, a subsidiary of EADS. It is the largest passenger airliner in the world. Due to its size, many airports had to modify and improve facilities to accommodate it...
; the jet engines behind (and not purely at the side of) the fuselage of a Cessna Citation X
Cessna Citation X
The Cessna Citation X is a long-range medium business jet aircraft. The Citation X is powered by two Rolls-Royce turbofan engines and is built by the Cessna Aircraft Company in Wichita, Kansas. It is the fastest production civilian jet in the world. The Citation brand of business jets encompasses...
; the shape and location of the canopy on the F-22 Raptor
F-22 Raptor
The Lockheed Martin/Boeing F-22 Raptor is a single-seat, twin-engine fifth-generation supermaneuverable fighter aircraft that uses stealth technology. It was designed primarily as an air superiority fighter, but has additional capabilities that include ground attack, electronic warfare, and signals...
; and the image of the Airbus A380
Airbus A380
The Airbus A380 is a double-deck, wide-body, four-engine jet airliner manufactured by the European corporation Airbus, a subsidiary of EADS. It is the largest passenger airliner in the world. Due to its size, many airports had to modify and improve facilities to accommodate it...
above showing obvious area rule shaping at the wing root, which is practically invisible from any other angle.
See also
- Anti-shock bodyAnti-shock bodyAn Anti-shock body is a pod positioned on the leading or trailing edge of an aircraft's aerodynamic surface to reduce wave drag at transonic speeds .-Wing trailing edge:...
- Sonic boomSonic boomA sonic boom is the sound associated with the shock waves created by an object traveling through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion...
- Sound barrierSound barrierThe 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...
- Supersonic aerodynamics
External links
- Aerospaceweb.org: Area rule explained
- Aerospaceweb.org: Whitcomb Area Rule and Küchemann Carrots
- DGLR document
- German patent search system - look for Patent DE 932410 filed March 21, 1944
- NASA 2004: Overuse increases drag but still reduces boom heard on the ground
- PBS.org - See Image 4 for an extreme example: fuselage before wing
- The Whitcomb Area Rule: NACA Aerodynamics Research and Innovation
- Whitcomb, Richard T.: A Study of the Zero-Lift Drag-Rise Characteristics of Wing-Body Combinations Near the Speed of Sound. NACA Report 1273, 1956.
- Contemporary reporting and explanation of area rule