Chine (aeronautics)

Last updated
Chined fuselage of an SR-71 Blackbird Lockheed SR-71 Blackbird.jpg
Chined fuselage of an SR-71 Blackbird
The front view of the A-12 showing forebody shaped into chines A-12 Nose View.jpg
The front view of the A-12 showing forebody shaped into chines

In aircraft design, a chine is a longitudinal line of sharp change in the cross-section profile of the fuselage or similar body. The term chine originates in boatbuilding, where it applies to a sharp profile change in the hull of a boat. [note 1] In a flying boat hull or floatplane float, the longitudinal line of sharp change in cross-section where the bottom plane meets the sidewall, is an example of a chine.

Contents

On some supersonic aircraft a chine extends sideways for some distance, with a very sharp edge blending in with the main wing leading edge root. [note 2] The rest of this article is concerned with this type of chine.

Configuration

A chine can in aerodynamic terms act as a long extension of the wing root along the fuselage. Such chines first appeared on the Lockheed A-12 precursor of the SR-71 Blackbird, where they ran forward from the wing roots along the fuselage sides, into which they blended. [1]

The Lockheed Martin F-22 Raptor has chines along its nose section that align with its engine air intakes. [2] The small horizontal surfaces forming a fillet between the forward wing root and the air intake is more usually called a leading edge root extension (LERX) or leading-edge extension (LEX).

Forward chines effects

Large chines along the forward fuselage can have a significant effect on aircraft lift, drag, longitudinal balance and directional stability.

Effect at high Mach numbers

The chines of the Lockheed Blackbird series extend about 40% of the aircraft's length and contribute useful additional lift at supersonic speeds. The chines may be understood as enhancing the lift generated by the forebody by acting as a low aspect ratio canard surface. [3] In order to further increase this lift contribution, the forward fuselage is set with a positive incidence relative to the wing.

The chine lift increases with the square of the Mach number, helping counterbalance the rearward shift in the lift of the main wing in supersonic conditions. If a tailless (Delta) wing is trimmed for safe subsonic flight, at high speeds it gains excess trim drag in pitch and becomes excessively stable resulting in poor manoeuvrability. The destabilising effect of a forward surface is provided by the chines where it is needed most, at high Mach numbers.

Effect at low airspeeds

Forward chines also act as leading edge root extensions (LERX) at low speeds and high angles of attack, generating a vortex flow over the inboard wing to stabilise the airflow and increase its speed locally, thus delaying the stall and also providing additional lift.

Directional effect

The chines also increase directional stability, by reducing the adverse effects of crosswinds or yaw on the forward fuselage. Unlike a conventional fuselage, the chines allow the crossflow to travel smoothly over their profile and beyond, avoiding the side forces due to flow separation and stagnation. Again the effect is stronger at higher speeds, and reduces the size of the vertical stabilisers (tail fins). The YF-12A lacked the foremost section of the chines seen on the SR-71 and consequently needed extra vertical tail surfaces.

Lateral effect

The improved crossflow behaviour also benefits lateral characteristics by reducing yaw-induced roll, especially during landing and takeoff of delta-winged aircraft. This in turn helps reduce roll-yaw coupling and any tendency to Dutch roll. However chines have also been found to reduce lateral stability in some configurations, due to abrupt asymmetric vortex breakdown effect. [4]

Stealth effect

Blending the chines into both the fuselage and the main wing avoids presenting corner reflectors or vertical sides to radars. [5] This has led fifth-generation jet fighter designs to replace low-stealth canard surfaces with chines, when helping to generate vortex lift over the main wings.[ citation needed ] (An exception is the Chengdu J-20, whose canards are mounted inline with its chines.)

See also

Notes

  1. Angled chine, different from soft (rounded) chine
  2. NASA-AIAA-98-2725 Impact of fuselage cross-section on the stability of a generic fighter uses "chined-shaped fuselage cross section, chined forebody, fuselage with ... included chine angle" expressions. NASA CR 189641 and AIAA 2008-6228 use "Chine forebody and Chine fuselage"

Related Research Articles

Lockheed SR-71 Blackbird Supersonic reconnaissance aircraft in service with US Air Force 1964-1998

The Lockheed SR-71 "Blackbird" is a long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft developed and manufactured by the American aerospace company Lockheed Corporation. It was operated by both the United States Air Force (USAF) and NASA.

Delta wing Triangle shaped aircraft wing configuration

A delta wing is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (Δ).

Flying wing

A flying wing is a tailless fixed-wing aircraft that has no definite fuselage, with its crew, payload, fuel, and equipment housed inside the main wing structure. A flying wing may have various small protuberances such as pods, nacelles, blisters, booms, or vertical stabilizers.

Leading-edge extension

A leading-edge extension (LEX) is a small extension to an aircraft wing surface, forward of the leading edge. The primary reason for adding an extension is to improve the airflow at high angles of attack and low airspeeds, to improve handling and delay the stall. A dog tooth can also improve airflow and reduce drag at higher speeds.

Lockheed L-2000 Proposed US supersonic airliner design

The Lockheed L-2000 was Lockheed Corporation's entry in a government-funded competition to build the United States' first supersonic airliner 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.

Grumman X-29 1984 experimental aircraft family by Grumman

The Grumman X-29 was an American experimental aircraft that tested a forward-swept wing, canard control surfaces, and other novel aircraft technologies. The X-29 was developed by Grumman, and the two built were flown by NASA and the United States Air Force. The aerodynamic instability of the X-29's airframe required the use of computerized fly-by-wire control. Composite materials were used to control the aeroelastic divergent twisting experienced by forward-swept wings, and to reduce weight. The aircraft first flew in 1984, and two X-29s were flight tested through 1991.

High-lift device

In aircraft design and aerospace engineering, a high-lift device is a component or mechanism on an aircraft's wing that increases the amount of lift produced by the wing. The device may be a fixed component, or a movable mechanism which is deployed when required. Common movable high-lift devices include wing flaps and slats. Fixed devices include leading-edge slots, leading edge root extensions, and boundary layer control systems.

Republic XF-103 Cancelled American military plane project of the 1940s-1950s

The Republic XF-103 was an American project to develop a powerful missile-armed interceptor aircraft capable of destroying Soviet bombers while flying at speeds as high as Mach 3. Despite a prolonged development, it never progressed past the mockup stage.

Airplane Powered, flying vehicle with wings

An airplane or aeroplane is a fixed-wing aircraft that is propelled forward by thrust from a jet engine, propeller, or rocket engine. Airplanes come in a variety of sizes, shapes, and wing configurations. The broad spectrum of uses for airplanes includes recreation, transportation of goods and people, military, and research. Worldwide, commercial aviation transports more than four billion passengers annually on airliners and transports more than 200 billion tonne-kilometers of cargo annually, which is less than 1% of the world's cargo movement. Most airplanes are flown by a pilot on board the aircraft, but some are designed to be remotely or computer-controlled such as drones.

Flight mechanics are relevant to fixed wing and rotary wing (helicopters) aircraft. An aeroplane, is defined in ICAO Document 9110 as, "a power-driven heavier than air aircraft, deriving its lift chiefly from aerodynamic reactions on surface which remain fixed under given conditions of flight".

The United States Air Force Stability and Control Digital DATCOM is a computer program that implements the methods contained in the USAF Stability and Control DATCOM to calculate the static stability, control and dynamic derivative characteristics of fixed-wing aircraft. Digital DATCOM requires an input file containing a geometric description of an aircraft, and outputs its corresponding dimensionless stability derivatives according to the specified flight conditions. The values obtained can be used to calculate meaningful aspects of flight dynamics.

General Dynamics F-16XL

The General Dynamics F-16XL is a derivative of the F-16 Fighting Falcon, with a cranked-arrow delta wing. It was originally conceived as a technology demonstrator, later entered in the United States Air Force's (USAF) Enhanced Tactical Fighter (ETF) competition but lost to the F-15E Strike Eagle. Several years after the prototypes were shelved, they were turned over to NASA for additional aeronautical research. Both aircraft are currently stored at Edwards AFB.

Vertical stabilizer

A vertical stabilizer, vertical stabiliser, or fin, is a structure designed to reduce aerodynamic side slip and provide directional stability. They are most commonly found on vehicles such as aircraft or cars. It is analogous to a skeg on boats and ships. Other objects such as missiles or bombs utilize them too. They are typically found on the aft end of the fuselage or body.

Stabilizer (aeronautics) Aircraft component

An aircraft stabilizer is an aerodynamic surface, typically including one or more movable control surfaces, that provides longitudinal (pitch) and/or directional (yaw) stability and control. A stabilizer can feature a fixed or adjustable structure on which any movable control surfaces are hinged, or it can itself be a fully movable surface such as a stabilator. Depending on the context, "stabilizer" may sometimes describe only the front part of the overall surface.

Vortex lift

Vortex lift is that portion of lift due to the action of leading edge vortices. It is generated by wings with highly sweptback, sharp, leading edges or highly-swept wing-root extensions added to a wing of moderate sweep. It is sometimes known as non-linear lift due to its rapid increase with angle of attack. and controlled separation lift, to distinguish it from conventional lift which occurs with attached flow.

Canard (aeronautics)

A canard is an aeronautical arrangement wherein a small forewing or foreplane is placed forward of the main wing of a fixed-wing aircraft or a weapon. The term "canard" may be used to describe the aircraft itself, the wing configuration, or the foreplane. Canard wings are also extensively used in guided missiles and smart bombs.

Tailless aircraft

A tailless aircraft has no tail assembly and no other horizontal surface besides its main wing. The aerodynamic control and stabilisation functions in both pitch and roll are incorporated into the main wing. A tailless type may still have a conventional vertical fin and rudder.

Wing configuration Describes the general shape and layout of an aircraft wing

The wing configuration of a fixed-wing aircraft is its arrangement of lifting and related surfaces.

Strake (aeronautics) Flight control surface

In aviation, a strake is an aerodynamic surface generally mounted on the fuselage of an aircraft to improve the flight characteristics either by controlling the airflow or by a simple stabilising effect.

Leading edge

The leading edge of an airfoil surface such as a wing is its foremost edge and is therefore the part which first meets the oncoming air.

References

  1. David Godfrey (30 August 1973), "Blackbirds from the skunk works", Flight International : 383
  2. "F-22 Raptor Manufacturing". globalsecurity.org. 7 August 2011. ...the F-22's chine, a fuselage edge that provides smooth aerodynamic blending into the intakes and wings.
  3. Forebody lift is about 17 to 20 % of total lift. AIAA 2008-6228 report, p.15 fig. 8
  4. Chambers, Joseph R. "Modeling Flight." NASA, 2009, p.143.
  5. Rebecca Grant (political expert) "The Radar Game" Archived 2012-06-09 at the Wayback Machine Mitchell Institute, 2010