Talk:Drag curve

Drag or L/d

Is the author talking about Drag polars or Lift/Drag polars, there is a mighty difference, though they portray some of the same data. I think the article should clarify the differences and cover Drag polars, Lift polars and L/D polars.Petebutt (talk) 12:17, 17 June 2012 (UTC)

Drag polar is the name used by aerodynamicists to describe how Cl varies with Cd, whether by a diagram or an equation. Drag polars do not use angles of attack explicitly, though drag curves and lift curves do. This is covered in the opening para. I've reverted the title, since this sort of plot/ equation is the subject of the article.TSRL (talk) 14:03, 17 June 2012 (UTC)

OK , much clearer now, thanks.Petebutt (talk) 01:40, 18 June 2012 (UTC)

Why called polar plot?

It is not polar coordinates, so why is it called a polar plot? 2600:1700:4CA1:3C80:2536:CFC6:40D7:3026 (talk) 23:02, 22 August 2020 (UTC)

Under the heading Drag polar#The drag polar you will find the following explanation: "If, in a wind tunnel or whirling arm system an aerodynamic surface is held at a fixed angle of attack and both the magnitude and direction of the resulting force measured, they can be plotted using polar coordinates. When this measurement is repeated at different angles of attack the drag polar is obtained. Lift and drag data was gathered in this way in the 1880s by Otto Lilienthal and around 1910 by Gustav Eiffel, though not presented in terms of the more recent coefficients. Eiffel was the first to use the name drag polar." Dolphin (t) 08:34, 23 August 2020 (UTC)

It does seem a silly name, since while they could be plotted in polar coordinates, no one does so any more. They are also known as drag curves, which is less confusing. cagliost (talk) 13:44, 14 May 2021 (UTC)

Do the colors and the Reynolds numbers match?

The better performing polar is shown in blue, but the Reynolds number is less than for the red poplar. This does not match my experience. — Preceding unsigned comment added by Adventure50 (talk • contribs)

Thanks- you're right. My error, made 9 years ago is now corrected.TSRL (talk) 18:58, 1 May 2021 (UTC)

Requested move 14 May 2021

The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion.

The result of the move request was: page moved. cagliost (talk) 13:46, 25 May 2021 (UTC)

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Drag polar → Drag curve – Both names are acceptable, but "Drag curve" is clearer, since they are not in fact polar plots cagliost (talk) 13:49, 14 May 2021 (UTC)

• Support. Rreagan007 (talk) 18:31, 16 May 2021 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Merger proposal

The following discussion is closed. Please do not modify it. Subsequent comments should be made in a new section. A summary of the conclusions reached follows.

The result of this discussion was Merge. cagliost (talk) 09:36, 27 May 2021 (UTC)

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We have a separate article Drag curve (gliders), which is about the sink rate of unpowered gliders. But this seems like just a special case of aircraft in flight, and indeed this article contains a section on Glider polars. OK to merge? cagliost (talk) 13:47, 14 May 2021 (UTC)

Agree we should merge them, though Drag curve (gliders) does not seem to contain much new material; wind speeds are implicit in airspeed. I've not checked the refs to see if they have anything new to say. The list of links should be dropped: if they are relevant they should be in the text.TSRL (talk) 22:34, 25 May 2021 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Power required inverse of sink rate?

Is the power required graph just the mirror image of the glider sink rate graph? cagliost (talk) 09:50, 28 May 2021 (UTC)

As a first approximation, the power required in straight, level flight is equal to the weight of the aircraft multiplied by the sink rate (vertical speed) in steady gliding flight.

However, this first approximation is based on the assumption that the drag at true airspeed V₀ in gliding flight is the same as the drag at V₀ in straight & level flight. This is a reasonable assumption providing the sink rate as a fraction of true airspeed V₀ is so low it can be assumed to be zero.

If the sink rate as a fraction of true airspeed V₀ is not zero it means the flight path in steady gliding flight is inclined at an angle θ below the horizontal; and the lift on the aircraft is equal to the weight of the aircraft multiplied by cosine θ.

In straight and level flight the lift on the aircraft is equal to the weight of the aircraft. If the lift on the aircraft is less than the weight (such as when it is equal to the weight multiplied by cosine θ) then lift-induced drag is less than in straight, level flight. So when accurately accounting for the sink rate and the variation in induced drag, there is no simple relationship between sink rate and power required. (There is a relationship but it must take account of aspect ratio and Oswald efficiency number.) Dolphin (t) 03:23, 29 May 2021 (UTC)