How does the Oudie N/SeeYou determine glide ratio?

[Jack Derrickson]

Greetings,

An American aircraft firm will be conducting test flights of a new sailplane design in the coming month, and I have a few questions about how the Oudie N IGC handles glide ratio data. How does the Oudie determine glide ratios during flight? Does it calculate the variometer reading by comparing actual performance against the selected polar? If testing is performed early in the morning when the air is relatively calm (with multiple flights averaged), would the glide calculations be accurate enough to generate a polar from plotted points?
Is it possible to access detailed glide ratio information after a flight for analysis? Could the Oudie be used to generate a polar directly, and if not, might this be a feature in the future, allowing pilots to combine multiple flights and/or selected segments to create a polar?
Apologies for the number of questions. I am simply trying to find the best way to accurately generate polars for new designs, as well as for existing designs that have never had a proper polar documented.

Best regards,
Jack N. Derrickson

077, 847, and P4

[Rick Sheppe]

Hi Jack -

Looking at a glide ratio on an instrument (any instrument) isn't the best way to determine the performance polar.  After all, the instrument is presenting some achieved glide ratio, averaged over time or distance, in real thermic conditions.  Not very closely related to the polar.

The best way to measure a polar is to make long glides at constant airspeed in still air, using a Flight Recorder with a 1-second logging interval.  If the plot of the altitude versus time shows little noise, then a sink rate for that airspeed can be  calculated.  You'll discover that you have to throw away a lot of data due to noise, especially at speeds close to best gliding speed.

-Rick