Compare Polars

Was just thinking it would be fun if there was a website (or software) that you could overlap polars of multiple gliders at the same time to compare them? Does this exist?

Thanks!
WC

There is a spreadsheet that allows comparison of quite a few polars he https://www.gliding.com.au/assets/docs/Polar10.xls

On Friday, December 22, 2017 at 11:28:11 AM UTC-5, Tony wrote:
There is a spreadsheet that allows comparison of quite a few polars he https://www.gliding.com.au/assets/docs/Polar10.xls

Thanks Tony, I'll have some fun playing with this!

-WC

On Friday, December 22, 2017 at 8:28:11 AM UTC-8, Tony wrote:
There is a spreadsheet that allows comparison of quite a few polars he https://www.gliding.com.au/assets/docs/Polar10.xls

It is a really good ap....too bad it is not up to date and does not include some of the newer models.

On Friday, December 22, 2017 at 11:28:11 AM UTC-5, Tony wrote:
There is a spreadsheet that allows comparison of quite a few polars he https://www.gliding.com.au/assets/docs/Polar10.xls

This is interesting data to me, but I open it up, and look at the "gliders" table of the raw data, and I cannot make any sense of what I am seeing.

What is "G/F" ... and then after that looking across the table, look at the first line, for an ADSH-25e ... yes, pretty high-performance sailplane ... but it says the units are "mps" (surely meters per second ?) ... but then the first entry is of 80? 80 what? 80 m/s ... yowsa, that's ≈ 160 kts!

and at "80" the value in the table is is 0.62 ... what is that? If that were the sink speed in m/s then the L/D would be 80/0.62 = 129 ... no way! So what are the numbers?

Can somebody explain WTF I am looking at here?

At this point I should mention that I really have been looking for these data. and I am an applied mathematician/scientist by trade and have been studying risk tradeoff optimization in speed-to-fly problems, this is also basically the same problem as optimal handicapping in disguise.

Is there interest in discussion of these issues? I could point out some issues where the current methods aren't entirely right or complete, that do have pretty straightforward solutions.

One other point I would make ... for all calculational purposes, you want to reduce the polef data to a fitted function of some sort, and boy ... are polynomials convenient for this purpose in this case. The standard "McCready Speed to Fly" just assumes the polar from best L/D on up is fitted with a quadratic, after trivial calculus and a little algebra the speed-to-fly is computed by solving the quadratic equation. This is easy to generalize to better fits.

And when you see this, and go through just a little math, what you see you want for the polar are stated minimum sink and best-L/D speeds & sinks, and then at least one, preferably 2 or 3 data-points at higher speeds ... and you don't need anything more than that.

The reason minimum sink and best-L/D are so important to defining the polar should be intuitively obvious, but there's a mathematical reason too ... these provide additional important equation constraints on the fitted function

minimum sink is of course s'(h) = 0

best L/D means that s(h) = h / s'(h)

where h is the horizontal speed (that what's really the independent variable in a polar, NOT airspeed, although at the very high L/Ds of gliders the differences between these two is negligible) s(h) is the sink rate at horizontal speed h, and ' means first derivative.

Forth these two "special" points you get two constraint equations, not one. Playing around with real polar data it takes a 5 to 6 order polynomial to really fit one well, and for manipulating all the ensuing calculations it is the coefficients of that polynomial that is wanted.

Also, I don't see listed gross weights for these test data? That is important ... to do ballast corrections etc.

The help page seems clear enough

Cell H21 says 80 is the speed in kph at which the sink rate is measured.
Cell F19 says .62 is the sink rate in mps

The glider weight is included in the wing loading column.

I don't have much interest in discussing failings in these calculations because I'm pretty happy to have the spreadsheet as it is.

OTOH, if you have energy to put more gliders into the data set, that would be interesting.

ok, I'm not getting the "cell says", perhaps not so up on xls spreadsheets etc. I am working with the CSV exported data...

what is the "wing loading column?" Is that G/F? What units?

what are the units for the rows where the units are specified as "kts?" Are the airspeeds all in kph for all rows, sink rates in mps or kts as stated?

Ok, the .csv thing explains your problem.

The .xls file is not just a spread sheet, but rather a workbook of sheets that work with Excel.

Without that, I can see your frustration and can offer no help.

You are kind of in a dark hole of your own digging.
Suggest you stop digging and find a copy of Excel.

On Fri, 22 Dec 2017 16:06:55 -0800, stu857xx wrote:

Ok, the .csv thing explains your problem.

The .xls file is not just a spread sheet, but rather a workbook of
sheets that work with Excel.

Without that, I can see your frustration and can offer no help.

You are kind of in a dark hole of your own digging.
Suggest you stop digging and find a copy of Excel.

Choices:
1) Buy a copy of MS Office / Excel
2) get a hooky copy of Office/Excel
(may be OK, may contain malware unless you know and trust the source)
2) Download and try Libre Office
This is a free/open source office suite that provides the same
functionality as MS Office. There are versions for Windows, OSX and
Linux

I use Libre Office on Linux systems for all my spreadsheet and word
processing needs. By and large it 'just works' for spreadsheets including
Microsoft XLS spreadsheets, but might have problems if these include VBA
macros. I've never needed to load a MS spreadsheet with VBA macros so
can't comment about that.


--
Martin | martin at
Gregorie | gregorie
| dot org

On Friday, December 22, 2017 at 4:33:36 PM UTC-8, Kiwi User wrote:
On Fri, 22 Dec 2017 16:06:55 -0800, stu857xx wrote:

Ok, the .csv thing explains your problem.

The .xls file is not just a spread sheet, but rather a workbook of
sheets that work with Excel.

Without that, I can see your frustration and can offer no help.

You are kind of in a dark hole of your own digging.
Suggest you stop digging and find a copy of Excel.

Choices:
1) Buy a copy of MS Office / Excel
2) get a hooky copy of Office/Excel
(may be OK, may contain malware unless you know and trust the source)
2) Download and try Libre Office
This is a free/open source office suite that provides the same
functionality as MS Office. There are versions for Windows, OSX and
Linux

I use Libre Office on Linux systems for all my spreadsheet and word
processing needs. By and large it 'just works' for spreadsheets including
Microsoft XLS spreadsheets, but might have problems if these include VBA
macros. I've never needed to load a MS spreadsheet with VBA macros so
can't comment about that.


--
Martin | martin at
Gregorie | gregorie
| dot org

Open Office is another decent free one if you don't use spreadsheets enough to purchase a program.
Jim