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Is there a standard word or phrase, or several alternative commonly-used words or phrases, in the English-speaking aviation world to describe the angle between the longitudinal axis of the fuselage, and the flight path/ relative wind/ undisturbed free stream airflow?

Also, is one particular greek letter commonly associated with this angle in engineering texts and papers, much as "alpha" is commonly used to describe what the English-speaking aviation world usually calls "angle-of-attack"?

Basically the angle we are asking about is conceptually much like angle-of-attack, but modified to mean the angle-of-attack of the fuselage rather than the angle-of-attack of the wing.

Note: this question is asking about an angle that we would see when looking at the fuselage and flight path in a side view, as the aircraft flies with the wings level. This question is not asking about a yaw angle or sideslip angle.

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    $\begingroup$ If the fuselage is at a 0° angle to the relative wind, we would call it streamlined or maybe in the slipstream. Other than that, I can’t find any word or phrase to describe the angle itself. Interesting question, though. $\endgroup$
    – Dean F.
    Mar 29 '20 at 0:30
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    $\begingroup$ I think your answer is in bold above. $\endgroup$ Mar 29 '20 at 1:35
  • $\begingroup$ Your question is confusing (at least to me). Since the wing is generally fixed to the fuselage, would not angle of attack be sufficient to describe what you are looking for? Are you asking about deck angle corrected to relative wind (the difference between deck angle and angle of attack)? Or, are you asking about a measurable angle that would be comparable to yaw (called crab)? $\endgroup$
    – J Walters
    Mar 29 '20 at 11:12
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    $\begingroup$ I state that the angle of attack is usually measured on the fuselage because that is where the vane/probe/sensor is typically placed. All §25 and §23 jets that I am aware of, including Boeing, Airbus, Bombardier, and Cessna Citation models (these are the ones that I fly) have the vane placed on the forward fuselage. See for example the issues surrounding the 737 Max. The Quest Kodiak and certain light aircraft applications including various STC mods are the exception to the above and involve measuring the AOA on the wing. $\endgroup$
    – J Walters
    Mar 30 '20 at 16:38
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    $\begingroup$ A wing will not typically have a single "zero degrees" AOA, just as a propeller will not. Wings typically have a variable angle of incidence. An AOA system may be calibrated to aircraft performance, rather than a specific aircraft angle. The manufacturer will determine what reference is appropriate. According to Boeing's Aero magazine, "most commercial jet airplanes use the fuselage centerline or longitudinal axis as the reference line." $\endgroup$
    – J Walters
    Mar 30 '20 at 16:50
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It is just angle of attack.

Most anything can have an angle of attack. If you must be specific, you mention 'angle of attack of ...' Due to complexity of aerodynamics, most external elements of an airplane have their own local angle of attack. AoA sensors measure their angle of attack, and it is usually not even converted to 'wing' or 'fuselage'; it is dubbed 'indicated' or 'measured' and all limits are set with respect to that local AoA.

All these angles are usually designated as $\alpha$ (alpha), but with an appropriate index, which should always be explained in the nomenclature.

When we talk about airplane as a whole, usually the 'default' angle of attack is the one between the wind and the body frame (in the vertical plane). How body frame is defined depends on the aircraft designer, but normally X goes along the fuselage. Therefore, the angle of attack is exactly what you say: the angle between relative wind and the fuselage -- and not that of the wing (even though it is arguably more important).

Yet when we talk about aerodynamics, we may redefine the angle to mean 'angle of attack of the wing'. And even offset it to be with respect to zero lift. This is all fine as long as it's explicit. When we talk about just wing or airfoil, then the default angle of attack will be that of this object.

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  • $\begingroup$ I'm not sure this is entirely correct. See for example this link av8n.com/how/htm/aoa.html#sec-def-aoa . I think the default understanding of "angle of attack" in the aviation world refers to the angle between flight path/ relative wind/ free stream airflow and the mean chord line of the wing, though the phrase certainly has many other uses as well. $\endgroup$ Apr 3 '20 at 13:42
  • $\begingroup$ Two comments under answers to the related question aviation.stackexchange.com/questions/76799/… have also supported this viewpoint. $\endgroup$ Apr 3 '20 at 13:44
  • $\begingroup$ Maybe I need to ask another question asking "what is angle-of-attack"-- or maybe it already exists. $\endgroup$ Apr 3 '20 at 13:45
  • $\begingroup$ What if there is no wing? Or two wings? A body (say, a missilie) also has an angle of attack when it flies. AoA is a very generic term, and you can define it with respect to whatever body you like. The only crucial point is that it is body-to-relative-wind angle. When we consider the whole aircraft, we define AoA with respect to the aircraft, which in turn has a defined reference body axes frame. $\endgroup$
    – Zeus
    Apr 6 '20 at 0:25
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There is a term called "deck angle", which is the angle of the cabin floor, or deck, (and normally parallel to the longitudinal axis) relative to horizontal in a given flight condition. More or less the same thing as "pitch attitude". These however, don't cover your question because they are relative to the horizontal.

There is another term which I think fits, called "angle of inclination", which is the vertical angle of a streamlined body relative to the freestream. I dug up this NACA report that mentions it. This would be the closest term to define a fuselage's angle to the freestream.

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  • $\begingroup$ Or wing setting angle $\endgroup$
    – JZYL
    Mar 29 '20 at 19:40
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If you’re talking about the angle between the longitudinal axis and the relative wind rotated about the vertical axis, I’m not sure there is a term per se except for coordination of flight. The angle is not typically measured but of the angle is towards the inside of the flight path this is considered a slipping condition. When on the outside of the flight path, it’s a skidding condition.

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