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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)reply
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)reply
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)reply
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)reply
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)
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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.
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)reply
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.
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)reply