Second Porous Membrane Measurement (6/2/2009)

On this date, I had an opportunity to take more performance measurements using parachute fabric (ripstop Nylon) for deturbulator membranes. On tow, the air went smooth at 2500 feet agl, so I stayed on until 6000 feet. The smooth air beneath me would be enough to fly one minute at speeds 37, 40, 45, 50, 51, 52, 60, 65 and 70 KIAS. Based or the good data taken on 5/22/2009 and on 12/1/2007, I expected very good performance at 51 or 52 kts. But that was not to be. Below, in red, are the results:

From 40 to 60 kts, everything was flipped upside down. Upon landing, I inspected the fabric deturbulator membranes and found them to be very tight, noticeably tighter than before. So, considering that everything was the same as when the 5/22/2009 measurements (below) were taken, I attributed this inverted behavior to excessive tension in the membranes.

Right away, I recognized something familiar. When Jeff Baird flew the second flight in the Johnson test series on 12/13/2006 (below), these speeds were flipped upside down too. Then, in the very next flight, the data in the same speed range flipped over and he recorded extreme performance for the first time (second image below).

Note: The data point indicated by the red arrow is a bogus manual data point. The red curve shows data from the flight data recorder and is more reliable.

Jim Hendrix
Oxford Aero Equipment

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