In this tutorial, we will discuss how to apply pre-cone and how to alter the construction and feather axes to change how the propeller blades are built and rotated. The construction axis, defined by Construct X/C, is how the blade airfoils are placed relative to one another by a chord percentage. For example, a value of 0.0 will align all airfoils at their leading edges while a value of 0.25 will align the airfoils at the quarter-chord location. The feather axis, in contrast, controls where along the blade root chord the feather axis passes through the blade. The entire blade will shift along the root chord direction relative to a fixed feather axis.
In this tutorial, we will discuss how to alter the Propeller diameter, alter the number of blades, and set the blade collective pitch or feather. In addition to these basic operations, we will also discuss propeller orientation, propeller rotation, and how feather or 3/4 pitch work with the blade twist.
You can change the visual and functional representation of the Propeller in OpenVSP by altering the Design Mode from “Blades” to “Disk” to “Both”. Choosing “Blades” mode allows the full 3-D propeller model to be shown in the workspace including all surfaces, caps, and tessellation as defined in the design or Blade curves. “Disk” mode changes the visual representation to that of an actuator disk with the same diameter as the Propeller. “Both” will display both the full 3-D model and the actuator disk. As you’ll notice, “Blades” mode can begin to update slowly as more control points are added to the model due to the highly complex parameterization of the Propeller component. In fact, your model may quickly become unwieldly if there are too many points and the propellers are nested with other Parents. However, there is a simple way of making multiple changes to the Propeller at once without waiting for an update each time. Changing the Propeller to “Disk” mode removes the need to visually update the propeller model with each parameter change and enables you to alter almost any parameter instantly. In this way, you can very quickly alter the design as intended and then get back to work. Once your changes are complete, change the Design Mode back to “Blades” and the 3-D model will appear with your updates.
We will note here that the Design Mode is useful in determining which type of propeller/rotor/disk run you would like to choose in VSPAERO. “Blades” mode enables the Rotating Blades option while “Disk” mode enables Actuator Disk. Whichever of these modes is chosen, the other will be greyed out and deactivated to avoid attempting to run with incorrect geometry inputs. This will be covered in more detail in the VSPAERO tutorial sections.
The Propeller component is perhaps the most complex OpenVSP geometry there is to date. This stems from the fact that there are countless variations of the methods used to design propellers, rotors, proprotors, fans, turbines, compressors, windmills, vanes, etc. and while the most fundamental purpose of each of these is to push or turn air (or other fluidic mediums), the assumptions and even the nomenclature associated with them vary. It is very difficult for a single parameterized model, however complex, to capture the intent behind each of these applications. The OpenVSP Propeller component has been parameterized in such a way that whatever the application, the designer may either directly alter the given parameters or determine a translation between intent and implementation. This tutorial provides a brief introduction to this powerful component and lays out a path for the training content that follows. In this Subject you will learn how to alter the overall shape of the rotor by changing the number of blades, the diameter, and the blade feather or 3/4 pitch while also diving into the individual curves that will define the blade profile as well as how to alter the airfoil or section distribution. Additional tutorials are provided that demonstrate the propeller folding parameters and how to alter the tessellation for export to other tools such as CFD grid generators.
Custom airfoil files may be used to define the shape of your cross-section. Apply these section types by choosing “AF_File” from the type dropdown menu and clicking the “Read File” button. This will allow you to browse for the AF or DAT file of your choice. OpenVSP will spline the points to generate the airfoil shape. By default, the baseline thickness to chord ratio will be calculated and set for the chosen section. However, you may also alter the thickness to chord if you wish, creating a new airfoil based on the original profile. Note that the camber line is conserved in this case. Detailed information about the AF file format can be found on the OpenVSP Wiki File Formats page. Many airfoil files and coordinates can be found on the UIUC Airfoil Database.
