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I know about induced drag, parasite drag, form drag, skin drag, wave drag, and interference drag. But I don't encounter the term profile drag often, and I can't find a good definition of it.

Is profile drag the same thing as form drag? If not what is it?

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    $\begingroup$ And exactly what type of drag is RuPaul? $\endgroup$ – TomMcW Mar 30 '17 at 17:58
  • $\begingroup$ It's the observation that when you run code under a profiler to measure its performance, the very act of measurement causes it to run slower, or "drag". $\endgroup$ – hobbs Mar 31 '17 at 7:48
  • $\begingroup$ @hobbs lol no kidding $\endgroup$ – Pugz Apr 1 '17 at 1:27
  • $\begingroup$ Yet another breakdown for drag. $\endgroup$ – mins Apr 1 '17 at 20:57
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    $\begingroup$ @mins Threre are so many different types of drag that trying to understand is really becoming.... [ok, did anybody not see this pun coming?] $\endgroup$ – TomMcW Apr 1 '17 at 23:23
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The composition of total Drag as it is shown below:

enter image description here

enter image description here

Thanks to DRAGBUSTERS... This document can solve this question, and analyses the drag in detail.

Profile Drag Definition: Profile Drag is the drag incurred from frictional resistance of the blades passing through the air. It does not change significantly with angle of attack of the airfoil section, but increases moderately as airspeed increases. Taken from here.

Definitions of profile drag as they are in dictionaries:

The portion of the wing drag that is due to friction and turbulence in the fluid and that would be absent if it were nonviscous

The part of the drag on an aerofoil or aircraft which arises directly from its profile and from skin friction (i.e. the part not attributable to lift).

By reading this...(in fifth par.)

Form Drag Definition: Drag which depends on the shape of the aircraft, is called form drag.

The following definition has been taken from here.

Profile Drag or, sometimes called form drag, is the drag caused by the separation of the boundary layer from a surface and the wake created by that separation. It is primarily dependent upon the shape of the object. Form or pressure drag is caused by the air that is flowing over the aircraft or airfoil.

And finally, the most commonly types of drag encountered are,

Parasitic Drag, composed of

Form Drag, which is the result of the aerodynamic resistance to motion due to the shape of the aircraft,

Skin Friction Drag, which is due to the smoothness or roughness of the surfaces of the aircraft, and

Interference Drag, which may occur where surfaces with different characteristics meet (e.g. wing and fuselage)

Induced Drag, which is a secondary effect of the production of lift,and

Wave Drag which comes into play when shock waves are developed close to the surface of the aircraft in transonic and supersonic flight.

Taken by this Skybrary Article which describes very nicely the types of drag.

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    $\begingroup$ Herein lies the conundrum. I posted the question after having read most of those articles. They each give s different definition. Your first example basically gives the definition of skin drag. Your second example first appears to define skin drag, then changes and defines it as the sum of skin and form drag. The third is actually defining form drag, not addressing profile. The fourth says it's another name for form drag. And Skybrary never mentions profile at all. So my question is still not answered. $\endgroup$ – TomMcW Mar 30 '17 at 20:21
  • $\begingroup$ Why would induced drag flatten at low speed? Those two plots look very wrong near the Y-axis. Apart from that your answer is spot on. $\endgroup$ – Peter Kämpf Mar 30 '17 at 21:10
  • $\begingroup$ Thank you for your comments, the answer is revised, with new content. Hope this helps now. If you need anything else, or if something is wrong, please let me know. $\endgroup$ – Lidakis Emmanuel Mar 30 '17 at 22:26
  • $\begingroup$ Ok, I think the flowcharts are going to be the key to understanding it. +1 for those. Can you look at the other definitions in your answer? Some seem to conflict with the chart and should probably be edited out. For example, it's clearly not synonymous with form drag and one of the definitions says exactly that $\endgroup$ – TomMcW Mar 30 '17 at 23:20
  • $\begingroup$ Yes of course, there is a sense of contradiction between the definitions, but at the same time, if you see the second flow-chart, imho, the definition is not actually completely wrong, but it depends on the perspective of taking a UNIT(profile or form, or all together), for a measurement, and of course it depends on the perspective of 2D and 3D. I am going to make an edit on this, to look right,but if you still think that is not correct please point me out, the section, that you think, needs an edit. $\endgroup$ – Lidakis Emmanuel Apr 1 '17 at 11:22
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I have seen this term wrongly used.

The right definition refers to the drag of an aerodynamic 2D profile. Essentially, friction drag and form drag, ignoring the induced drag being a 3D phenomena.

However, in some papers I have seen the use of this term as equivalent to the form drag itself, not being restricted to a 2D phenomena.

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    $\begingroup$ A 2D object as viewed from what angle? From the direction of the airflow or orthagonal to it? $\endgroup$ – TomMcW Mar 30 '17 at 23:13
  • $\begingroup$ Essentially a cut of the wing perpendicular to its length axys. $\endgroup$ – Trebia Project. Apr 1 '17 at 7:38
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I share your confusion about those many sources of drag.

In the end, many of them describe similar things. When doing a performance calculation, it is extremely important to add all drag sources and to do this for every one only once. Drag estimation requires meticulous bookkeeping. Therefore, I would distinguish only two types of drag:

  1. Viscous drag, where the flow is slowed down by friction. The result is a force parallel to the local surface, and viscous drag is its component parallel to the flow direction at infinity.
  2. Pressure drag, where the local lift vector is tilted away from the vertical (in reference to the flow direction at infinity).

Profile drag is a muddle because it adds both types, but only part of them. This makes proper bookkeeping harder. As Trebia Project writes, profile drag is the drag in 2D flow and neglects both interference and lift-related components. But when designing an aircraft, profile drag is easy to get at - just look it up or run a calculation.

Profile drag includes the full friction component of the unswept wing without engine and real-world effects (so no drag from flap gaps, pylons, flap track fairings, rivet heads ...), the pressure drag from incomplete pressure recovery and wave drag in supersonic flow. It excludes the lift-related drag (induced drag) in subsonic flow, the pressure drag stemming from interference and the drag increase in the slipstream of a propeller. All these drag sources need to be added and be kept free of drag that was already considered in the profile drag data.

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  • $\begingroup$ So that's why I don't run across the term often, because the components of profile drag are accounted for by the other terms? $\endgroup$ – TomMcW Mar 30 '17 at 23:24
  • $\begingroup$ @TomMcW: Yes, the same drag is called friction drag plus form drag or whatever expression the author picks. Profile drag has its justification because it can be looked up easily during early design and the expression should occur most often in this context. $\endgroup$ – Peter Kämpf Mar 31 '17 at 12:36
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The total drag acting on an aircraft in flight is the sum of:

  • Profile drag
  • Induced drag
  • Interference drag

Profile drag can be further separated into:

  • Form drag
  • Skin friction drag

Form drag is produced whenever the streamline airflow passing over an aircraft separates from the surface and becomes turbulent. An example of extreme form drag is the effect of a flat plate placed at right angles to the airflow:

enter image description here

Skin friction drag is a function of the layer of air closest to the surface. As air flows over a wing, the roughness of the surface and the viscous property of the air itself slow it down. Much like other fluids, the more viscous the air, the greater its retardation. At the surface, the air particles adhere to it and their relative velocity is reduced to zero:

enter image description here

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Profile drag is the combination of form drag and skin friction as it results from the cross-sectional area, or profile, of the aircraft, presented to the relative airflow.

Principles of Flight | ATPL - Lesson 6 Part 2 - 7:34

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