Model Airplane Rapid Design Toolkit
Python
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README.md

MAdesigner v2.0 - Model Airplane Rapid Design Toolkit

Project Description

MAdesigner streamlines the process of designing and creating built up model airplane wings. Structures are defined with higher level parameters like span, chord, airfoil, sweep, etc. MAdesigner takes your specification and automatically creates the detailed structures for you.

High Level Features

  • Supports distinct root and tip airfoils and automatically blends between them.
  • Supports separate root and tip chords, sweep, twist, and dihedral.
  • Automatic flap/aileron control surface structures and cutouts.
  • Supports multiple wing panels linked together (ex: a polyhedral glider wing)
  • Generates an STL (3d format) of entire finished wing structure including dihedral, twist, all stringers and stock, control surface cutouts, lightening holes. Useful for a final sanity check before sending parts to a laser cutter. It's also pretty and fun to look at your design!
  • Generates a FreeCAD model file so the entire logical design can be imported into FreeCAD and further manipulated. Ex: adding landing gear blocks, servo mounts, fancy wing tips, etc.
  • Creates nested laser cut sheets (svg file format) that can be loaded directly into your laser cutter and cut with minimal material waste.
  • Creates full size planes (svg file format) that can be printed on a large format plotted.
  • Written in python and fully open-source.

How to Install and Run

  • Install Python: http://www.python.org

  • Install required python libraries: numpy polygon2 svgwrite (Example for Debian or Ubuntu, as root or with sudo: apt-get install python-numpy python-pip python2.7-dev pip install polygon2 pip install svgwrite)

  • Download and install aura-props: https://github.com/AuraUAS/aura-props and run 'python setup.py install'

  • Download and install FreeCAD: https://www.freecadweb.org/ set/add an environment variable named PYTHONPATH to point to the path to FreeCAD.so (Linux) / FreeCAD.dll (Windows) file (In Ubuntu, using apt to install FreeCAD, FreeCAD.so should be in/usr/lib/freecad/lib/

  • Download madesigner from github: https://github.com/clolsonus/madesigner

  • cd to madesigner and run 'python setup.py install'

  • At a command prompt 'madesigner.py'

Low level features

  • Airfoils
    • Database of 1500+ airfoils
    • Smooth spline fitting through airfoil data points and resampling at a much higher resolution.
    • Proportional blending of airfoils
  • Cut outs
    • Flush/tangent stringer cutouts.
    • Best fit leading edge diamond cutout.
    • Best fit trailing edge cutouts supporting symmetric or triangle stock.
    • Spar cutouts with 'twist' built in for self aligning structures.
    • Simple round lightening holes.
    • Shaped lightening holes.
  • Add ons:
    • Optionally generate top or bottom build tabs to help with building alignment.

35,000' Overview

One of the most satisfying things in life is to create something yourself. From sewing to landscaping to flying a rocket to mars: designers pour their heart and soul and creativity into clever and interesting designs. Even with common well known items, it is still immensely satisfying to design and build (or even fix) it yourself.

In recent years we have made great strides in developing rapid prototyping tools. We have a variety of 3d design tools that have a dizzying array of features (often even more dizzying when you start trying to figure them out!) Once the design is drawn up in the computer, we now have a suite of tools from laser cutters, to CNC routers, to 3d printers which can create the actual parts accurately and quickly. All that remains is to assemble the parts and your design is finished.

More recently that has been a big push to "open source" the production of hardware. Others can summarize what this means better than I can, but "open source" fabrication includes open-source designs, open-source manufacturing machines, open-source 3d models. There is still a cost to physically produce a part and distribute it, but the goal is to apply community open-source development and improvement techniques to part design and production. The end goal is to lower costs and make the whole process more accessible and more possible for even us little guys. We give up some concept of "ownership" of the design and the tools to create and build it, but we gain far more in the end.

However, one of the big stumbling blocks to this whole process is the complexity and cost of the 3d computer design software itself. There can be a huge cost for advanced CAD software and also a huge learning curve to understand the software well enough to do anything useful with it.

MAdesigner is an experiment to help address the cost and complexity of the design portion of the process; focused primarily on the area of model aircraft which is one of my life long interests.

It will take some time to realize all the goals I can envision for this project, but I would like MAdesigner to reduce the time to design an entire model aircraft from scratch to just minutes. Select an airfoil, choose the basic layout of the model, tweak the scale and the dimensions, and then run the scripts. What should pop out are 3-view drawings; nested cut files for a laser cutter or CNC machine to make all the "hard" or "curvey" parts; full size plans; 3d cutaway models that you can spin around and look inside of; and even an assembly manual with practical build tips could all be fully automated.

Even though a basic "cookie cutter" design can be produced quickly, the designer can spend time up front adjusting their aircraft, engineering the structures, selecting materials, adjusting the lines and the proportions, personalizing it, making engineering trade offs, and ultimately making the design entirely their own.

Motivation

While are most airplane wings built as straight planks or straight sweeps even though we know that an elliptical design is the most efficient and most beautiful? The answer is that curved wings are very complex to design and build. Imagine every rib is a difference size with different cutouts for stringers and control surfaces. That is a nightmare with traditional tools, but MAdesigner makes this a breeze. First it generates all the exact rib cutouts for you, next it will layout the parts on a laser cut sheet, and finally it produces a full size plan to build on top of. Dream it, design it, build it!

Capabilities

Now let's come back to earth after seeing the 35,000' view. What are some of the actual capabilities available right now?

  • load any airfoil from the UIUC airfoil database.

  • do a smooth spline interpolation (fit) of the surface points that wraps around the nose of the airfoil in one continuous smooth curve.

  • resample the smoothed airfoil at any resolution

  • simplify a higher resolution sample with an adaptive fit algorithm that maintains a set error tolerance with a minimal number of points. This leads to smaller output files, faster cut times, while still maintaining as much precision as you like at any scale.

  • blend two airfoils together in any proportion. This is ideal for a wing panel that has one airfoil at the root and different airfoil at the tip. A series of airfoils (ribs) can be generated that incrementally and smoothly blend from the starting airfoil to the ending airfoil.

  • rotate an airfoil by any amount. This allows creating a wing with twist or washout by incrementally rotating each rib in the plan the correct amount to smoothly blend in the desired washout from root to tip.

  • scale an airfoil up or down to any size. There's no reason a designer couldn't smooth and resample an airfoil at a very high resolution and create full scale plans for a home built aircraft.

  • skin a layer off the airfoil. This is useful if you plan to sheet the wing (or a portion of the wing) with sheeting of some particular thickness. You can shave the exact amount off the core rib so that when the wing is finally sheeted, you are back to the exact dimensions you originally intended in your design. You can sheet all or individual portions of the upper and lower curves of your wing.

  • cut out a leading edge 'diamond' of some dimension. Kit and scratch builders will know what this is all about. It's a way to lock together the leading edge of the ribs, provide a starting point for sheeting the leading edge of the wing, and minimizes the amount of sanding you need to get back to the correct rounded airfoil shape. The diamond cutout algorithm tries to do a best fit of the diamond shape to the leading edge of your airfoil in order to maintain the original shape as close as possible while minimizing the amount of sanding required to finish the wing.

    In other words, for a fully symmetrical airfoil (like a NACA0015) the square leading edge stock will be rotated exactly 45 degrees. But in a flat bottom or semi-symmetrical airfoil, the square stock might be rotated 50-60 degrees for a better fit with the leading edge.

  • Cut in notches for stringers and spars. Any size notch can be cut. In addition, the cut out can be made relative to the top or bottom of the airfoil. The cut can be vertical (which would be appropriate for a spar) or a the cut out can be made tangent to the wing surface which might be appropriate for a supporting stringer.

    You can get a bit clever/creating by combining the cut out feature with the airfoil rotate feature and can cut the proper washout alignment right into the spar notch of your airfoil.

  • Add build support tabs to help align the rib correctly on your build surface. This is sort of the opposite of cutting out a spar notch combined with carefully selecting the height of the tab. These tabs are removed once the basic wing structure is framed together. Again, model airplane builders will know exactly what this feature is and why it's useful. Planes fly much better with accurately built wings that are straight and true.

  • Cut lightening holes into the ribs. Good for adding lightness to your design. Also good for precutting holes for wing alignment jigs or wing joiner tubes.

  • (TODO) better support of custom part labels (the text and the position)

Road Map

This is a personal hobby project so there is no hard time line for future development effort.

  • My next focus is on FreeCAD. FreeCAD offers a python library with a full suite of 3d cad functionality. I would like to use this to construct the structure geometry and then output in a format that can be imported into any CAD software for further manipulation.

  • I would like to extend the code to implement a fuselage structure so that more complete designs can be attained.

  • I would like to add some helper functions to autogenerate more of the internal structure based on larger user preferences. I.e. generate a D-tube wing structure on top of the given layout.

Frequently Asked Questions

Here's a quick FAQ (although no one has yet asked me any questions, so I'm just trying to anticipate what people might be thinking.)

Q: So why write python scripts to generate model aircraft designs?

Scripted design is a different mind set. Consider that if the scripts are setup well and I want to make a small tweak (like increase the wing chord size by a 1/2 inch, or try a slightly different airfoil), then in my script it is a small tweak, I rerun the script and out pops all the new cut files and new plans. If I wanted to make this change in a traditional cad program I might have to spend all evening making the same small change to a bazillion parts since everything is linked together and these small tweaks tend to have a large cascading effect. But you do give up the ability to visually manipulate the design. However, you can quickly run the script and view the output, so there is some visual feedback in the process.

Another reason is when you run up against the limit of what a tool like "profili" is able to offer you through it's gui interface, then what do you do? (a) do you live within the constraints of the gui? (b) use a scripting system that lets you steer off the roads and do your own clever/crazy things?

Q: Still that sounds like a lot of effort for something no one else will probably ever use.

Yes again, but this is project is a nice mental break from my daily grind. I'm having fun and teaching myself python at the same time. And besides, I always wanted to be an aerospace engineer when I grew up.

Q: Can your python design scripts do "xyz"

Yes it's python so you can add "xyz" feature yourself! Ok, but more seriously I am building up a core collection of basic design and assembly features. This is for fun so I'm not really taking requests, but if it's an easy thing to add or something that sounds interesting to tackle, I might be interested.