aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It 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 ...

design, a chine is a longitudinal line of sharp change in the cross-section profile of the fuselage or similar body. The term

chine A chine () is a steep-sided coastal gorge where a river flows to the sea through, typically, soft eroding cliffs of sandstone or clays. The word is still in use in central Southern England—notably in East Devon, Dorset, Hampshire and the Is ...

originates in boatbuilding, where it applies to a sharp profile change in the hull of a boat.Angled chine, different from soft (rounded) chine In a

flying boat A flying boat is a type of fixed-winged seaplane with a hull, allowing it to land on water. It differs from a floatplane in that a flying boat's fuselage is purpose-designed for floatation and contains a hull, while floatplanes rely on fusela ...

hull or

floatplane A floatplane is a type of seaplane with one or more slender floats mounted under the fuselage to provide buoyancy. By contrast, a flying boat uses its fuselage for buoyancy. Either type of seaplane may also have landing gear suitable for land, ...

float, the longitudinal line of sharp change in cross-section where the bottom plane meets the sidewall is an example of a chine. 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.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" 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 The Lockheed A-12 is a high-altitude, Mach 3+ reconnaissance aircraft built for the United States Central Intelligence Agency (CIA) by Lockheed's Skunk Works, based on the designs of Clarence "Kelly" Johnson. The aircraft was designate ...

precursor of the

SR-71 Blackbird 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 the United States Air Force ...

, where they ran forward from the wing roots along the fuselage sides, into which they blended. The

Lockheed Martin F-22 Raptor The Lockheed Martin F-22 Raptor is an American single-seat, twin-engine, all-weather stealth tactical fighter aircraft developed for the United States Air Force (USAF). As the result of the USAF's Advanced Tactical Fighter (ATF) program, th ...

has chines along its nose section that align with its engine air intakes. The small horizontal surfaces forming a fillet between the forward wing root and the air intake is more usually called a

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.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 305. Aviation Supplies & Academics, ...

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. 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.

Stealth effect

Blending the chines into both the fuselage and the main wing avoids presenting

corner reflector A corner reflector is a retroreflector consisting of three mutually perpendicular, intersecting flat surfaces, which reflects waves directly towards the source, but translated. The three intersecting surfaces often have square shapes. Radar co ...

s or vertical sides to radars.Rebecca Grant (political expert
"The Radar Game"
Mitchell Institute, 2010 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. (An exception is the

Chengdu J-20 The Chengdu J-20 (), also known as ''Mighty Dragon'' (), is a twinjet all-weather stealth fighter aircraft developed by China's Chengdu Aerospace Corporation for the People's Liberation Army Air Force (PLAAF). The J-20 is designed as an air ...

, whose canards are mounted inline with its chines.)

Notes

References

{{reflist Aircraft configurations