Polar Data Spreadsheet

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Lenticular
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Joined: Tue Aug 01, 2017 7:29 am

Polar Data Spreadsheet

Post by Lenticular » Tue Jun 15, 2021 7:18 pm

Hi,

I noticed there are several dead links in this post: viewtopic.php?f=1&t=9878

...so I am creating a new spreadsheet that generates polars from known data (min sink, best L/D, and a known 3rd value in the high-speed flight regime).

I'm stuck at finding the (x,y) of the tangental point that touches the polar curve, but otherwise everything is calculating and plotting correctly (it already plots the polar and the zero MC tangent line), and calculates the glide ratio.

It allows for entry of general sink speed, with the idea being to be able to find best speed to fly when encountering general sink for a given glider. This is missing from many polar calculators.

Yet to add is effect of ballast/water on glide ratio/speeds. This will likely require a second table with data for maximum mass, then linear interpolation for intermediate weights.
G-ZULU /// LTN
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Bre901
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Re: Polar Data Spreadsheet

Post by Bre901 » Tue Jun 15, 2021 8:21 pm

You might want use the data points that I have computed for XCSoar or LK8000 (parabolic polars)
viewtopic.php?f=32&t=17820 (the link to the most recent data is at the end of the thread)

The data points are for the (dry) mass specified in the files.
If you want to adjust for ballast, the correction factor for both V and Vz is the square root of the mass ratio
CN: MPT — CondorUTill webpage: https://condorutill.fr/

Lenticular
Posts: 140
Joined: Tue Aug 01, 2017 7:29 am

Re: Polar Data Spreadsheet

Post by Lenticular » Wed Jun 16, 2021 3:06 am

Bre901 wrote:
Tue Jun 15, 2021 8:21 pm
You might want use the data points that I have computed for XCSoar or LK8000 (parabolic polars)
viewtopic.php?f=32&t=17820 (the link to the most recent data is at the end of the thread)

The data points are for the (dry) mass specified in the files.
If you want to adjust for ballast, the correction factor for both V and Vz is the square root of the mass ratio
Thanks!

I compute the polar data from known parameters, which seems to be similar to your method? I neglect ballast for now, and so the polars are only good for dry ships. I require min sink speed, best L/D speed, and the fastest speed for which known data exists.

I used the Diana2 for the test data I computed. Here is the polar as computed by my spreadsheet (I'm still working on a tidy spreadsheet! This one is a mess from testing).

Image

One feature I've added is the computation for optimum speed-to-fly when encounting heavy sink. It computes the optimum speed through recursive calculation (to increase speed, the basic aircraft sink rate also increases to attain that speed). Approximately 30 iterations are required.

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G-ZULU /// LTN
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