Talk:Drag coefficient

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[edit] Question

Very nice, very well explained, but, how the hell does someone determine the drag coefficient? Where it comes from?

Actual drag coefficients are determined through wind tunnel testing, although computer simulation can come very close. — orioneight (talk) 16:50, 27 April 2006 (UTC)
The nutshell version is that somebody probably saw that certian shaped objects move at different speeds and wanted to figure out why.—Preceding unsigned comment added by [[User:{{{1}}}|{{{1}}}]] ([[User talk:{{{1}}}|talk]] • [[Special:Contributions/{{{1}}}|contribs]])

[edit] Unclear combination of metric and imperial

The article changes from imperial to metric measurements half way through - could be clarified - Cd measurements are given for the cars in both, meaning that they differ by a factor of 10.7. —Preceding unsigned comment added by [[User:{{{1}}}|{{{1}}}]] ([[User talk:{{{1}}}|talk]] • [[Special:Contributions/{{{1}}}|contribs]])

This statement is absolutely ridiculous. As an Aero student, I can assure you that the Cd value is entirely unitless, and the reference area determines the units of the answer (as does, if one is observing the entire drag equation, velocity and density).

Cd can be obtained through a method called dimensional analysis. This method allows comparison of scaled conditions that are similar enough to represent the actual scale. It also reduces the amount of parameters that need to be considered to fully understand a given condition.

[edit] Cw

I just added that Cw is another way to write drag coefficient, based on http://www.vectorbd.com/peugeot/archive/General/2003/Mar/0063.html, the only source I could find. Correct me if I'm wrong. DirkvdM 07:48, 13 September 2006 (UTC)

[edit] nomenclature

It would be nice to describe what each variable represents and how it is determined, especially the area "A". —Preceding unsigned comment added by 129.107.97.131 (talk • contribs)

That is explained on the main drag equation page. I don't think we should duplicated it all here, so I have added another link right after the formula. Meggar 01:17, 27 November 2006 (UTC)

[edit] Cd vs. Cdmin

It'd be a good idea on the aircraft section to make sure you differentiate between Cd and Cdmin, since the Cd min values given in the reference page are valid only for certain types of flight... besides all that, there's also the question of whether or not it's set up for Cdi or Cdo...

(edit began here, previous segment was unsigned) Cd really needs to be entirely separated in this article. It is very inconsistent in that it is combining Cd and Cd(induced) far too often. It might also be beneficial to state that the Cd itself has no meaning outside of Cd*ref area. That value is the 'equivalent flat plate area' and Cd is initially derived from Flat plate area/reference area, not magically created or tested for.

Mentioning the derivation of Cdo, which is done either using 'wetted area'*'aerodynamic cleanliness' or by individual parts being summed up, and the aerodynamic interference being introduced.

Cdi, induced Cd through lift, is ENTIRELY different, and needs to be clarified as such. This is why a vehicle like an indy car, which has an extremely low aerodynamic cleanliness value, has such a high Cd(a very high negative lift keeps the car on the ground). Lift induces drag via the equation: Cd=Cdo+(Cl^2/pi*AR*e). e is the wing (lifting surface) effiency factor, and AR is the Aspect ratio of the plane, Span^2/wing area. 164.107.199.93 05:54, 24 January 2007 (UTC)Jason Mead

Cars don't have the same induced drag as air vehicles because they are much closer to the ground. The ground effect doesn't allow as much of a vortex to occur, and the induced drag would be lower than expected.

[edit] Found comment

I just found this comment in the article —Ben FrantzDale 16:38, 26 April 2007 (UTC):

In the section on drag coefficients, the entries for "hollow semi-sphere opposite stream" and "hollow semi-sphere facing stream" may need to be swapped. In the table entries, "hollow semi-sphere opposite stream" = 1.42 and "hollow semi-sphere facing stream" = 0.38. This is inconsistent with the next two table entries for "hollow semi-cylinder opposite stream" = 1.20 and "hollow semi-cylinder facing stream" = 2.30. So, either the hollow sphere or the hollow cylinder entries need to be swapped.
Peter d. Vangel vangel@stcc.edu

[edit] Why is drag equation and coefficient of drag on different pages???

These 2 articles should be merged; I see no reason why the 2 pages are separate. The two topics are about the same thing, except it makes it more inconvenient by having another link to the drag equation page. "drag equation" should be redirected to the "drag coefficient" page Subheight640 23:08, 24 June 2007 (UTC)

They really aren't the same subject, in the same way that Ohm's law,Electrical resistance, and Resistor are different articles. There was some talk about that on the Drag coefficient page. If after some carefull concideration you still believe it should be merged, then some merge suggestion tags will be needed. Meggar 04:54, 25 June 2007 (UTC)

[edit] Automobile drag coefficients

I moved a substantial portion of the material that was in this article to a new one entitled Automobile drag coefficients. Rracecarr 18:42, 31 August 2007 (UTC)

The automobile-related talk is also now moved to the new page. Meggar 19:36, 31 August 2007 (UTC)

[edit] Accuracy

I think that the article should be clearer that the equation given does not work in all scenarios. The larger the velocity the more the drag becomes linear, and thus deviates from the quadratic dependence of the given equation. —Preceding unsigned comment added by Moto Perpetuo (talk • contribs) 05:41, 17 January 2008 (UTC)