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A NASA report on winglets tested on a Beechcraft back in 1980. It has some nice plots of the before and after drag polars so one can see very clearly when winglets help and when they hurt.
From the summary
1. Adding the winglets increased the Oswald efficiency factor by 13 percent;
the increase in maximum lift-to-drag ratio was 11 percent.
2. Winglets left the maximum speed at 3962 m (13 000 f t ) density alti -
tude virtually unchanged. At lower altitudes, however, the maximum speed was
reduced. Cruise speed increased 8 knots (5.6 percent) at 3962 m and 51 percent
maximum continuous power.
3. An improvement in climb performance was obtained due to the installation
of winglets or 6 percent, a t 1524 m (5000 ft)and by a greater amount at higher altitude.
Rate of climb increased approximately 0.25 m/sec (50 ft/min:,
4. Winglets increased the fuel efficiency of the airplane for CL > 0.266.
5. Handling qualities were favorably affected by the installation of
winglets.
Chris Zavatson
N91CZ
360std
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