New measurements further define performance polar with tape under the leading edge

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Oct 12, 2012, 8:52:05 PM10/12/12
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Until last Saturday, I had only one set of sink rate measurements for speeds below 60 KIAS with the 12mm wide, .025" thick tape located with the forward edge 45 degrees under the nose of the wing. Last Saturday, I took two additional sets of measurements over that speed range in 1 kt increments from 48 to 52 KIAS. This is a region in which a prominent notch always occurs in the large performance peak when a 2" wide tape is wrapped around the wing leading edge, as shown in Fig. 2 below.

Besides needing additional measurements to confirm and better define the performance boost from the narrow tape under the leading edge, there was the question of whether the lower surface only tape produced a similar notch. Fig. 1, below, shows the summation of all three sets of measurements for speeds below 60 KIAS. For 48, 49, 51 and 52 KIAS, there are only the two measurements taken last Saturday. For the other speeds, three measurements exist. In Fig. 1, the black curve is clean wing performance, as measured by Dick Johnson in 2006. The red curve is the average of all data points.

Conclusion, the performance boost from a full span application of the narrow tape under the wing leading edge is confirmed and better defined than before. Specifically, with two points each for 48 and 49 KIAS, a notch like that from the 2" wide tape (upper surface effect, Fig. 2) is seen to occur from the bottom surface effect too.

Independent measurements by Kiley and Shipp appear to this notch. With the lower surface tape, and after removing wax from the forward wing lower surface, they obtained the results shown in Fig. 3, below.

The airspeed of the notch from the top surface effect is very sensitive to airspeed. In Fig. 2, three measurements show the notch precisely at 49 KIAS. However, with a 15% reduction in all up weight, the notch moved up two knots to 51 KIAS. If the Kiley/Shipp data correctly show a notch, the, the difference in speed is probably due to the fact that their data are plotted vs. indicated speed, whereas mine are plotted vs. calibrated speed, which is slower than indicated. Also, there are differences in wing loading and somewhat in the position of the tapes.

I have two measurements for speeds above 60 kts. When these are plotted with the low speed data, the results shown in Fig. 4 and Fig. 5 occur.

Jim Hendrix

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