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Posted by tspeer | Nov 05, 2017 @ 07:36 PM | 845 Views
The attached report presents the results of flight tests of a full-scale sailplane, the Lark IS-28B2. Appendix B describes the method for calibrating the pitot-static system, and Appendix D describes the methods for analyzing the performance data and estimating the performance under standard atmospheric conditions.

The typical method of testing the performance of a sailplane is to make a series of straight-line glides at different airspeeds, recording the speed, rate of descent, and altitude lost in a given time. From these measurements, a curve of descent rate vs airspeed can be made, and the speeds for best lift/drag ratio and minimum sink determined. The biggest drawback of this approach is the need for very calm conditions over the entire area used for the testing. Since the plane flies in a straight line, it necessarily covers a significant amount of ground, even when different runs are made in opposite directions.

This report develops a method for testing sailplane performance in turning flight. One advantage of measuring the performance in a turn is the aircraft stays in the same airmass throughout the test. This makes it easier to find and stay in a region of calm conditions so lift or sink do not affect the results.

The performance in turning flight is also relevant to flying in thermals, and the report shows how this can be used to determine the smallest or weakest thermal needed to maintain altitude.

Turning flight measurements are particularly applicable to measuring the performance of radio controlled models, because the craft can stay in close proximity to the pilot. All of the necessary data can be collected onboard a model using today's instrumentation and electronics.