tim.jagenberg.info

Data Structure

A basic step is to understand the data and file structure. I’ll start from the small parts, joining them together to the final propeller.

On the very low level, there are basically two elements, the coordinates-file (*.dat) (representing the shape of the airfoil) and the polar-file (*.pol) (holding aerodynamic data).

Both are pretty independent. The first one is used for visualisation (the shape shown in the airfoil-section of the propeller editor) and the DXF-geometry export, the second is used for the analysis. As they are independant, it’s completly possible to use different airfoils-shapes for visualisation/geometry and for the actual analysis. (Might be use to aproximate one airfoil wich is badly calculated by XFOIL with another one with another one solving easier)

For easier handling the references to these two files are joined together in an airfoil-file (*.af). Using the airfoil-file, you can set up different coordinates/polars-combos, which can then be used at one or more stations in one or more propellers. (say you got different propellers using ClarkY with about the same working range of reynoldsnumbers you just need to create one airfoil-file, using the same polar- and coordinates-file every time at every station).

The last file is the propeller-file (*.prop) itself, defining different values (name, no. of blades, diameter and number of stations). For each station it contains the specific data (radius from hub, chord, angle, x-/y-offset) and a reference to the airfoilfile to be used at that station.

For convenience I usually store the references in the airfoil- and propeller-file relative to the BETPAT main directory, so same files can be used in different folders, or machines. (./airfoils/clarky-1000-3001000.af ./airfoils/coordinates/clarky.dat ./polars/clarky-1000-3001000.pol - the numbers represent the range of RNR, but this is free to everyones own preference).

Other files are used to store environment-values (*.env), the settings for one or more batch-analysis-jobs (*.ba), the results of a batch-analysis (*.csv - charater separated values) and the setting for one or more btach-polar-calcuation-jobs (*.bp).

step-by-step example

To get you familiar it’s probably best to play around with the included example propeller, found in ./userdata/TJ254-003/

• So go to the propeller-editor-tab and choose “load”, browse to the dir named above and open the propeller in there. Now browse through the stations using the arrows in the station-values-area, you’ll see how the values below and the airfoil-shape on the right change. On the right in the airfoil-area, you see the values of the airfoil-file used at the actual station.
• Go to the environment-tab, and change the velocity to 6 m/s. Pretty much anywhere in the program you’ll have to push “set” in order to make use of changed values (otherwise values won’t be used or might even get reset to the old ones), so do this now.
• Change to the analysis-tab and hit “analyse”. The propeller is analysed and the results are shown in the respective fields. The big are with the charts shows specific values along the blade, from hub to tip.