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

On Aug 11, 10:07*am, akiley wrote:
On Aug 11, 1:31*am, (Alan) wrote:



In article writes:
Hi All,

I'm fairly new to soaring, but thought it might be fun to test our clubs St=
andard Cirrus to see if it was getting advertised L/D. *I jumped in with no=
t enough understanding of all the factors that effect performance, other th=
an reading how Dick Johnson does his tests.

I took a tow to 6000 agl on a calm early morning when ground temps were abo=
ut 70f. *I raised the gear, closed both vents and flew one minute legs afte=
r I stabilized the IAS at 40, 50, 60 and 70 KIAS. *Then I turned in the opp=
osite direction and flew the series again. *I video taped the gauges and go=
t an IGC file from SeeYou/iPaq.

I did NOT factor temps and didn't compute calibrated airspeed. My average o=
f 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 Cirr=
us. *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

* Well, doing it in both directions probably didn't have much effect, since
you were doing it with airspeed, not groundspeed.

* The suggestion that you do it for a greater time, such as 500 feet of
altitude, seems good. *Since you don't have an engine vibrating the altimeter,
you need to tap it to ensure it isn't lagging behind from minor friction.