Baseline polar for performance testing

Figure 15. Baseline Polar for Performance Testing on Standard Cirrus #60

Preliminary sink rate measurements have been performed to establish a baseline for measuring performance gains with SinhaFCSD. Sink rates were measured for three test flights. Data scatter from vertical air motion was reduced by dropping a few points that were clearly out of bounds and averaging the three resulting polars. The result is shown in Fig. 15 where the red curve is the average. The black curve is from Standard Cirrus #267 (N5CC) as reported by Dick Johnson.

The difference in these curves is due to the fact that in these tests only the ASI is calibrated, not the Pitot/static system. Since total ASI system calibration is not necessary for performance comparisons on the same glider, and since I do not have a trailing bomb of known quality, it was decided to proceed using ASI instrument calibration only. Total system calibration will be done later when #60 is tested by an independent party.

To verify that the deviation from Johnson's, and Bikle's polars (not shown), is due to the Pitot/static system, correction data reported by Johnson for #267 was applied to the baseline polar for #60. The result is shown in Fig. 15 as a broken purple line. It is expected that correction data measured on #60 will bring the baseline polar more in line with the black curve.

The aircraft configuration for these and future test flights is as follows:

• All up weight = 728 lbs
• Wing loading = 6.8 lbs/sq ft
• All control surface gaps sealed with tape on hinge side, mylar on other side
• Tail boom inspection ports open
• Canopy/fuselage gap not sealed
• Standard wing tips
• Soft wing tip skids in addition to standard skid pads
• Tail wheel instead of standard skid
• Pilot relief tube extending 1/4th inch through gear door
• Drag rake installed on right wing with connecting tube taped to trailing edge, under wing fillet and down fuselage side