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Frequently Asked Questions about Polar Explorer

Running Polar Explorer

Glider Definition in Polar Explorer

Polar Explorer's Calculations

Running Polar Explorer

Q What versions of Windows will Polar Explorer 2.2 run under?

A You can run Polar Explorer directly on Windows 3.1 to Windows XP.

Q Can I run Polar Explorer under Mac OS X or Linux?

A Although at the time of this writing I haven't tested this, I believe that you can do this through DOSBox DOS-emulator. You can download free DOSBox for Mac OS X, Linux and a bunch of other operating systems from http://dosbox.sourceforge.net/download.php?main=1

Q Can Polar Explorer be displayed in a window when in graphics mode?

A Although Windows (especially XP) doesn't support DOS graphics mode in a window natively, there is a way to do this by running Polar Explorer through DOSBox DOS-emulator. You can download free DOSBox from http://dosbox.sourceforge.net/download.php?main=1
After installing DOSBox, do the following:

  • Copy the shortcut to DOSBox from the Windows Start menu to the desktop.

  • Right click on the DOSBox shortcut and select Properties.
  • Click on the General tab.
  • In the top text box type PE22 DOSBox.
  • Click on the Shortcut tab.
  • In the Target text box insert the full path to the Polar Explorer Program File (PE22.EXE) after the path to the DOSBox program and before the -conf. For example:
    "C:\Program Files\DOSBox-0.63\dosbox.exe" "C:\PE22\PE22.EXE" -conf "C:\Program Files\DOSBox-0.63\dosbox.conf"
  • Delete the contents of the Start in text box.
  • As a finishing touch, you can click on Change Icon... and select POLAR.ICO from the folder containing Polar Explorer.
  • Click on OK.
  • Double click on the PE22 DOSBox Icon. This will launch Polar Explorer as a proper Windows program and enable both text and graphics modes to run in a window.

Q Can I print or capture the graphics display from Polar Explorer?

A If you are running Polar Explorer under Windows 98 or earlier (with or without DOSBox) you can use <Shift>+<Print Screen> key combination or <Alt>+<Print Screen> when you have the desired graph on screen. This will send the screen graphics into the Windows clipboard, from which you can then insert it into any image editing program (such as MS Paint) or directly into Word.
If you are using Windows 2000 or Windows XP, you can use <Alt>+<Print Screen> only when running Polar Explorer through DOSBox.

Q Can I set Polar Explorer's graphic display with to white background?

A You can do this by selecting Options | Force mono graph (Yes) and then Options | Colors | Graph | Inverse.

Q Can I export Polar Explorer's graphs to an Excel spreadsheet?

A In order to do this, do a Table print to a text file (selected under Printing options). Then import the table from the text file into Excel and use it to recreate the graph.

Glider Definition in Polar Explorer

Q How is a glider defined in Polar Explorer?

A A glider is defined by a few geometric parameters (e.g. wing span, wing area), aerodynamic parameters (e.g. aspect ratio correction factor), and anywhere between 3 and 30 points on the polar curve. The polar curve can be a speed - sink polar, or one of 3 different variations of a CL-CD (lift coefficient - drag coefficient) polar. Once entered, the polar curve can be converted from one type to any other.

Q In what units of measure should a glider polar be entered?

A Any combination of supported units of measure is permitted (Options | Units). For instance, you can enter speed in m/s and sink in fpm.

Q If a glider is entered in one set of units, can it be converted to another?

A Unit conversion in Polar Explorer is very simple, and you can convert glider data from one set of units to any other set of units through Options | Units. The results of the conversion are instantly shown on the screen.

Q How does Polar Explorer approximate a polar curve?

A It draws a smooth piece-wise double parabolic curve through every V-W or CL-CD point on the polar curve.

Q Can Polar Explorer process irregular polars?

A Polar Explorer goes to great lengths to accommodate and correctly process almost any possible and impossible glider polar. If a polar has dents, knees or bulges, Polar Explorer will take them all into account when calculating the speed-to-fly, cross country speed, circling performance, etc.

Q How long does it typically take to enter a new polar?

A For instance, if you have a table with 20 points on a speed polar, it should take 5-10 minutes to enter the points and iron out unwanted irregularities.

Q Do I have to enter the glider data every time I run Polar Explorer?

A No. The data defining a glider can be stored in a glider library. One library can store up to 500 gliders, and you can use more than one library.

Q Does Polar Explorer come with some glider examples already entered?

A It already comes with a fairly large library of polars (see Polar_Explorer_Short_Guide.pdf). Most of the polars are based on flight measurements by DLR institute in Germany and Richard Johnson in U.S.A. There are also some factory polars.

Q What can be done with the gliders that are already in the library?

A Any glider in a library can be: renamed, edited, deleted from the library and copied to another library. (The same can be done to any sheet in the sheet library.)

Polar Explorer's Calculations

Q What kind of performance can Polar Explorer calculate?

A It can calculate the following performance curves, shown here grouped into five categories:

  • Basic performance:

    • Speed - sink polar.
    • Speed - glide ratio.
  • Cross-country performance:
    • Speed-to-fly - rate of climb.
    • Speed-to-fly - rate of climb + glider sink rate (for direct use on a speed ring).
    • Rate of climb - average cross-country speed.
    • Updraft velocity - average cross-country speed.
  • Climb performance:
    • Updraft velocity - rate of climb.
    • Updraft velocity - optimum bank angle.
    • Updraft velocity - optimum circling speed.
  • Circling performance:
    • Circling radius - horizontal speed.
    • Circling radius - sink rate.
    • Circling radius - bank angle.
  • Lift coefficient versus drag coefficient curves:
    • CL - CD viscous for Re=1,000,000.
    • CL - CD viscous for Re that varies with CL.
    • CL - CD total for Re that varies with CL.
    • CL - CD induced.

Q Which parameters can be varied in the performance calculations for any given glider?

A Any combination of the following parameters can be varied:

  • Glider parameters:

    • Wing loading.
    • Surface contamination (bugs).
  • Environmental parameters:
    • The model of the atmosphere (standard or custom).
    • altitude (within the limits of the atmosphere model).
    • horizontal wind speed and angle.
    • vertical wind (vertical air movement between updrafts).
  • Updraft (thermal) parameters:
    • The shape of the vertical velocity profile.
    • Fixed or variable diameter (variable means that the thermal diameter increases when the maximum updraft velocity increases).
    • Thermal diameter, when fixed diameter is selected.
    • Ratio between the diameter and the maximum updraft velocity (Dia/Wmax) when variable diameter is used.
    • Coefficient of updraft drift (Cud) as defined by the Generalized Speed-To-Fly Theory. Cud determines whether the updrafts are drifting freely with the wind, are stationary, or somewhere in between. See Generalized_STF_Theory.pdf  for details.
  • Cross-country tactics parameter:
    • McCready speed ring setting.

Q What is the accuracy of Polar Explorer calculations?

A It normally calculates only a certain number of discreet points on the performance curves, and then draws a smooth curve through those points.
The calculation precision can be adjusted by the user. There are three available levels: low, medium and high. The higher the precision, the higher the number of calculated points on a curve, and the lower the margin of error. Of course, the time needed for calculations increases with higher precision, which nowadays should not be a problem.

Q What is the accuracy of Polar Explorer graph display?

A Graph display precision can be set separately to low, medium, high, or straight-line. It is independent of the calculation precision, and it determines how the program shows the curves on the screen. When the precision is higher, the performance curves are drawn more accurately, and therefore slower.
Straight-line graph precision causes the program to draw straight line segments between the calculated points of the performance curve. That way you can see the exact points that were calculated. (This doesn't apply to all curves, because some are calculated differently.)

Q When are results shown in equivalent airspeed (EAS) and when in true airspeed (TAS)?

A Horizontal speed (V) and vertical speed (W) can be both shown either as EAS or as TAS by setting the V equivalent and W equivalent parameters on the main sheet to Yes for EAS or No for TAS.

Q Can results of the calculations be shown in different units?

A The results can be shown in any combination of units that are available in the Options | Units window.

Q Does Polar Explorer account for the changes in Reynolds number?

A Polar Explorer approximates the Reynolds number influence on the viscous drag coefficient through the Reynolds number exponent that is a part of glider definition data.

Q How is the custom atmosphere model defined?

A It is defined by setting the values of pressure and temperature at zero altitude, and giving the temperature at up to 5 more levels. The laps rate in each segment is assumed constant. The gas constant for air can also be modified to simulate the effect of humidity.

Q How is circling performance calculated?

A Polar Explorer can calculate circling performance in 4 different modes:

  • optimum mode - circling is optimized in such a way that the rate of sink is minimized for any given radius of circling

  • lift coefficient reserve mode - circling is calculated for a constant CL that is at a specified level below CLmax
  • speed reserve mode - circling is calculated in such a way that the circling speed always exceeds the minimum speed for that particular radius by a specified margin
  • constant speed mode - circling is calculated for a specified constant horizontal speed.

Q How is climb performance calculated?

A Polar Explorer first calculates the optimum circling performance (see above). Then, it determines the circling radius for which the maximum rate of climb is achieved. Polar Explorer does this for different thermal strengths, so the climb rate varies from 0 to the maximum desired climb rate.

Q How does Polar Explorer calculate average cross-country speed?

A It calculates it by varying climb rate, or by varying thermal strength and calculating the corresponding climb rate. In addition to altitude, glider performance and wing loading, it takes into account horizontal wind, updraft movement (drift), vertical movement of the airmass between the updrafts and the McCready speed ring setting.

Q Can I use Polar Explorer to plan or analyze a cross-country flight?

A You can use Polar Explorer to get the following information:

  • The optimum glider configuration for the expected weather conditions: wing span (if applicable) and wing loading;

  • Expected average XC speed and the distance that can be covered
  • Speed-to-fly tactics, especially in wave lift for which McCready theory is incorrect.
 

Copyright Branko Stojkovic