Low test numbers on Standard Cirrus, what could it be?
Go and read all the Bickle and Johnson articles on how they went about going these tests. They had to go to a LOT of trouble to test performance accurately. Measuring the performance of a glider is not simple or easy. Johnson did very high tows usually on very calm winter mornings and he still found there were runs which were rendered unusable due to vertical air mass motion.
That said, one thing to take into account, especially with a Standard Cirrus is that Johnson discovered that the static system on this ship had fairly significant errors by design (many gliders do) and that this has to be taken into account when using the A.S.I. readings to calculate performance. Even if the A.S.I. itself is perfect it likely will still be giving readings that are significantly at variance with calibrated airspeed.
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