Reading SGS 2-32 Polar Curve

To read the L/D curve, solo, the plane will have a best L/D of about 35 at a speed somewhere between 52.5 and about 56 MPH. The curve is fairly flat up there. L/D read from the left side scale, airspeed read on the horizontal axis.

To read the VS (vertical Speed) curve, for this same speed range, the VS will be roughly 2.1 to 2.4 feet per second (read from the Right side vertical scale). As you indicated, hard to tell from the VS curves exactly where best L/D occurs since they truncate the vertical and horizontal axis of the plot. Must be why they also show the L/D curves on the same chart.

I believe you would use the VS curve to draw the polar as you are use to seeing it. Complete with airspeed going all the way to zero (so you can more quickly do graphic analysis) and sink rate going all the way to zero. Lopping off the unobtainable portions of this graph allows a manufacturer to show a "flatter" polar, making you think the plane will not increase its sink rate rapidly as you increase the airspeed.

Hope this is more helpful than my previous reply.

Steve Leoanrd

Helpful. Am I correct in assuming this L/D curve is interpreted differently than a polar curve? And therefore the apex of the curve is the best L/D, not a line touching the curve beginning at the origin?

How do I compensate for wind? If I have a 15 mph headwind, what becomes my best L/D?

On Tuesday, March 15, 2016 at 5:04:14 PM UTC-5, runner4065 wrote:
Helpful. Am I correct in assuming this L/D curve is interpreted differently than a polar curve? And therefore the apex of the curve is the best L/D, not a line touching the curve beginning at the origin?

How do I compensate for wind? If I have a 15 mph headwind, what becomes my best L/D?

Correct. On the L/D curve, max L/D is the apex of the curve. On the "polar curve" as you describe (horizontal and vertical speeds), best L/D is a line drawn through the origin, tangent to the polar curve.

To see what affect wind has, you can take the existing chart, extend the airspeed to the left to find the zero airspeed, and the vertical speed down to zero vertical speed, and use this origin. It will be "upside down" from what you are use to, but you should be able to work with it, drawing tangents to find speeds to fly for various winds and anticipated climb rates.

Steve Leonard