![]() ![]() For the propeller, instead of making a crude simple flat blades like other designs I have seen, I decided to go all-out and engineer a propeller that uses real-world propeller design features, such as an elliptical blade planform and using multiple NACA airfoil profile transitions along the length of the blades. I already over-engineered the handle to be an ergonomic design, and I over-engineered the pull cord gear teeth as well. Sources: PickPik and Wikimedia Commons I want to make a pull-copterĪs I wrote in my article about ergonomic handle design, my objective is to 3-D print an over-engineered pull-copter, a toy that drives a propeller when you pull a cord through a handle, to make the propeller fly into the air. For example:Įlliptical planform blades (left) and truncated elliptical blades (right). (In the case of the Spitfire, the decision to give it an elliptical wing had less to do with induced drag and more to do with being roomier near the wing root than a straight tapered wing, allowing the aircraft guns to be completely internal.)While elliptical-wing aircraft are a thing of the past, modern propeller blades are still made with elliptical planforms, or approximately elliptical planforms, and sometimes the rounded end of the ellipse is truncated. Because the advantages to elliptical wings are often negated by other design considerations (such as wingtip washout to improve stall characteristics), it is more economical to fabricate tapered wings with straight edges, so this is how wings are designed nowadays. It is possible to create an elliptical lift distribution over the length of a wing without actually having an elliptical planform, by adjusting the airfoil shape and angle of attack. Another advantage to an ellipse is that the wing tip is quite small, which reduces drag from induced wingtip vortices. The optimal and most efficient wing planform shape to distribute lift and minimize induced drag, theoretically, is an ellipse. It is also inversely proportional to aspect ratio (the ratio of wing length to airfoil average chord length). Induced drag depends on the planform shape of the wing. Induced drag has nothing to do with the drag created by surface area, surface roughness, or thickness of the airfoil. Of all the kinds of drag that a wing or propeller blade experiences, induced drag is an unavoidable price for lift. However, with all curved edges, elliptical wings are expensive to construct. In the case of the Spitfire, the gentle taper of the ellipse near the wing root also provided more room to mount weapons internally than a straight-taper wing, while providing an overall thinner, low-drag cross-section. Elliptical wings have the most uniform theoretical distribution of lift and therefore the least induced drag. The most famous aircfaft with such wings is probably the Supermarine Spitfire fighter aircraft from World War II. This method is how I do all my aircraft wings and airfoils and it produces perfect surfaces.You don't see aircraft with elliptical wings anymore. If you have to locate the airfoil on a plane other than the Main X,Y or Z planes you can use the 'Move' function to do so, usually before scaling. You can also save out the airfoil (preferably the 'unit' sized one) as a block and import it into other models. Then you can then create a surface or solid and scale that to reach the exact size airfoil you need for the different locations of your wing or prop. If needed you can edit this spline, typically at the trailing edge, if needed. You then start a sketch on same plane as curve and then 'Convert' the curve into the current sketch which will give you a spline. This method will give you a curve that is a perfectly smooth, not facteted, airfoil. Note that the airfoil data you import from a website will only contain 2 data sets, one for X dimension, and one for Y dimension, simply copy that data into Excel and add a third column for Z dimension (all zeros) to use in SW. This allows you to import (from a website) the actual NACA airfoil coordinates and generate a 'Unit' sized airfoil. If you are using Solidworks (or maybe other 3D CAD) to generate the airfoils, the best way to do it is to use the 'Curve thru X,Y,Z Points". ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |