Low test numbers on Standard Cirrus, what could it be?

On Thursday, 11 August 2011 02:59:20 UTC+1, akiley wrote:
Hi All,

I'm fairly new to soaring, but thought it might be fun to test our clubs Standard Cirrus to see if it was getting advertised L/D. I jumped in with not enough understanding of all the factors that effect performance, other than reading how Dick Johnson does his tests.

I took a tow to 6000 agl on a calm early morning when ground temps were about 70f. I raised the gear, closed both vents and flew one minute legs after I stabilized the IAS at 40, 50, 60 and 70 KIAS. Then I turned in the opposite direction and flew the series again. I video taped the gauges and got an IGC file from SeeYou/iPaq.

I did NOT factor temps and didn't compute calibrated airspeed. My average of both directions at each speed gave me: 26 L/D at 40 KIAS, 26.5 at 50, 28 at 60, and 25 at 70. These numbers seem to be very low for a Standard Cirrus. Johnson's results were in the neighborhood of 35 L/D. It had no bugs, wing root tape, and yes, the gear was up.

Any comments or ideas other than sending me back to school? ... Aaron

Why not making it simple (and more accurate and realistic) and use SeeYou to analyze your IGC file which can give you the glide ratio in every segment? Granted it will give you glide ratio over the ground which is fine if there is no wind or if you average the up wind and down wind legs (avoid cross wind as suggested).

Ramy