Talk:Chine (aeronautics)

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Definition : "A long, narrow horizontal surface attached to both the fuselage and the main wing is also called a chine or sometimes a strake."

Surface or fuselage extension ? The term "surface" leads to the idea of a thin lifting surface attached to the fuselage, like a strake.

"However chines have also been found to reduce lateral (roll) stability in some configurations, due to vortex effects."

Difficult to say "roll stability", as there is nearly no roll stability in aircraft, but usually a light instability giving a slowly diverging spiral mode. The vortices (assymetry ?) create roll excitations but do not modify the roll (stability or unstability) characteristics of the aircraft.

"The Grumman X-29 research aircraft featured a forward-swept wing with chines or strakes extending aft of the main wing and ending in a rear control surface."

This example enforces the strake-chine muddle ; the X-29 has no chines (following the definition of fuselage extensions).

"The chines of the Lockheed Blackbird series extend about 40% of the aircraft's length and contribute useful additional lift at supersonic speeds, and may be understood as enhancing the fuselage lift or as acting as a canard surface. In order to increase their lift contribution..."

That means chines are lifting, acting "like a canard surface". Once again readers look for and find a surface (a discrete wing). In fact the fuselage lifts, not exactly as a canard (usual meaning), but as a very low aspect ratio forward surface. "may be understood as enhancing the fuselage lift" : ok, with a reserve : the chines are the fuselage, not additional surfaces "enhancing the fuselage".

As a result, the definition would be "a fuselage with chines is a fuselage characterised in that etc..", in lieu of "Chines are surfaces attached to the fuselage etc...".

"Blending the chines into both the fuselage and the main wing avoids presenting corner reflectors or vertical sides to radars. 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.

Have you a citation of that (chines replacing canards)? it would be nice to add in "three surface" this last fighter configuration. Plxdesi2 (talk) 21:52, 25 April 2013 (UTC)

Much of the confusion over definitions and naming can be seen in the one article by Godfrey: He manages to refer to chines variously as extensions of the fuselage, extensions of the wing, acting "like canards" and as smaller surfaces we would nowadays call LERX. Miller similarly describes the X-29 extensions variously as chines or strakes. Wikipedia cannot make decisions about all this, we must just explain the word salad as best we can while remaining technically correct. I like to think my copy achieves this.

On two points you raise, the roll characteristic and the fifth-generation fighters, these both have/had inline citations. Someone else wrote those bits, with citations, in the previous article and I copied it all blindly across. On reading your post here I followed up the references and the fifth-generation fighters reference is inadequate so I replaced it with a citation needed tag (does the Chengdu even rate "fifth-generation"?). The roll citation is a 200-page e-book which I have not read so I cannot comment on it. — Cheers, Steelpillow (Talk) 10:59, 26 April 2013 (UTC)

Here's another interesting set of quotes on the YF-12A, these from Jones, L.S.; U.S. fighters, Aero (1975). "The sharp edge along the forward fuselage actually forms a lifting surface, as on a canard, thereby letting the fuselage itself generate aerodynamic lift." Then, "The leading edge of the forward lifting plane contains infrared sensors", i.e. the leading edge of the shortened chines used on this type. And on the SR-71, "The foreplane extends in an unbroken line to the nose". Are we to conclude that the forward fuselage is a "lifting plane" or even a "foreplane"? Surely not as such. Jones does not use the terms "chine" or "strake", but even so he shows the same cavalier disregard for words as Godfrey, as long as we can understand what he means. — Cheers, Steelpillow (Talk) 13:09, 26 April 2013 (UTC)

Roll stability : "Almost all full-scale airplanes exhibit an instability in which the airplane, when the controls are held fixed in level flight, gradually veers off into a diving turn or spiral. This instability, called spiral instability..." William H. Phillips, Chapter 4, flying qualities, A Career at NASA Langley Research Center. In Hoerner "Fluid dynamic lift", there are longitudinal and directional stabilities chapters, no "roll stability" chapter but "Lateral stability" (coupling of yaw/roll moments and lateral forces). In Raymer "Aircraft Design", there are "longitudinal static stability and control", and "lateral-directional static stability and control". Nowhere "Roll static stability and control". In Kroo, Desktop Aeronautics, Aircraft Design, the same : "Longitudinal stability" and "Lateral Dynamics". Roll moments exist, but roll stability doesn't ; this is a frequent misconception. Using the term roll stability is not "technically correct".

Jones analysis, fuselage = lifting surface, as on a canard, looks right. Fuselage = foreplane is excessive. Anyway, this aircraft is more than a simple Delta configuration. Not visually a 2 surface, but aerodynamically yes. Plxdesi2 (talk) 20:23, 26 April 2013 (UTC)

Chine - rear Chine

3 : "A long, narrow horizontal surface attached to both the fuselage and the main wing is also called a chine or sometimes a strake.[1] This article discusses this type of chine."

SR-71 fuselage has neither horizontal surfaces nor attached surfaces because the forward chines are the fuselage. The above definition excludes SR-71 typical example of chines.

"Rear Chine" Following the large previous definition, X-29 aft horizontal surfaces, vaguely looking like strakes, may be called "chines" ! - I think this volontary mixing (to respect and doing so continue authors/citations terminology muddle), preventing any clear understanding, is somewhat misleading. Plxdesi2 (talk) 19:34, 26 April 2013 (UTC)

As ever, we have no control over the words other writers use, we can only reference what they say. Wikipedia is an encyclopedia not a textbook. I know it is frustrating, but that's how it works. — Cheers, Steelpillow (Talk) 20:07, 26 April 2013 (UTC)

This does not fix the definition in contradiction with his typical very example. Plxdesi2 (talk) 20:33, 26 April 2013 (UTC)

In the case of the X-29, I had a quick search around. It seems that "strake" is more commonly used and Jones, writing before the aircraft flew, is not a strong enough example to change that. I see that someone has edited some articles accordingly, that is OK by me.

I think it useful to explain more clearly that some writers describe chines as long extensions of the wing, but if other editors feel that now is not the time to explain that, I'm not going to war over it. — Cheers, Steelpillow (Talk) 15:43, 27 April 2013 (UTC)

Seaplane

"In seaplane design, a chine is the longitudinal line of sharp change in hull cross-section, as in the chine of boat hull and having the same purpose - hydrodynamic lift and direction of spray."

A chine is a line, not a surface : it is the meeting of two surfaces (in the seaplane case, the meeting of planing bottom with lateral panel). A chine is not a planing surface, and there are a lot of planing dinghies without hard chines. I'am not sure that wording about "hydrodynamic lift and direction of spray" is useful in the introduction about (supersonic) aircraft chine. Plxdesi2 (talk) 09:30, 28 April 2013 (UTC)

I did muck up the prose a bit, but many more aircraft have had a chine on their fuselage and over a longer period of time (the first reference to an aerodynamic lifting chine shape I found in the flightglobal archive was 1970s - from 1909 til then its either fuselage longerons or seaplane hulls) so I think its best to get the explanation of the other sort out of the way early. GraemeLeggett (talk) 17:22, 28 April 2013 (UTC)

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