The following screenshots with a few comments show some of the detail of the complete engine model:
- The engine assembly consists of a radial compressor, vaned diffuser, combustor, turbine, interstage guide vanes, power turbine, speed-reducing gearbox, fuel/lubrication system, and a propeller. The left half of the assembly is the turbo-compressor and right half, the turbo-prop.
All of the V0.13 turbo-compressor components were imported to the V0.17 file using copy/paste (CTRL C/CTRL V). For some reason, some of the components imported in their proper location but without any placement property. This may be a bug or something I did incorrectly in V0.13.
- - Picture1_Top&Side-View.jpg (161.55 KiB) Viewed 7183 times
- The engine is organized as a series of Part sub-assemblies in the model tree which makes it quite handy to isolate sub-systems when modelling by toggling visibility.
All new bodies were created using the global axes and planes rather than feature faces as I had done in V0.13. Since many of the bodies are axisymmetric no datum planes were necessary. As a result the model is much more stable with any changes to correct errors.
The exception was the lubrication tubing for which I used the tubing faces to locate pads and to create revolves for any bends. (Just don't screw-up or you are back to square one!) Although, this approach is quite tolerant to changes in the tubing configuration as it is being routed around components.
The exhaust ducting sheet metal was a bit tedious to create using Pads and Revolves.
The propeller was created from a series of PartDesign>AdditiveLofts using cross-section airfoils of a model airplane propellor design found on the internet.
- - Picture2_Front&Side-View.jpg (194.87 KiB) Viewed 7183 times
- Some of the detail of the internal components are exposed through the transparent housings in this screenshot. I remember struggling with the complexity of the combustor in V013. It would be much easier now with V0.17.
Note the detail of the main housings containing the diffuser, guide vanes, and turbine nozzles. These were created with Part>lofts (V0.13) and PartDesign>AdditiveLofts and PolarPatterns (V0.17). The same process was used with the turbine wheels.
All fasteners are included. Fortunately the design is metric so I was able to use the Screw_Maker_2.0 macro, however, it does not function properly in V0.17. I created them in a V0.16 and copy/pasted them into the V0.17 file with out any problems. The bolt patterns were created with Part/Polar Arrays.
- - Picture3_Front-View,Internals.jpg (231.3 KiB) Viewed 7183 times
- The rotor on the left is the turbo-compressor and on the right is the power turbine and gearbox. Ball bearing assemblies are shown in red. Note the preload spring on the turbocompressor bearings to prevent ball skidding on startup. The power turbine and gearbox use wave springs (imported from McMaster-Carr) for preload. A tolerance ring on the inboard bearing of the power turbine accounts for any misalignment.
The gears were created from the Gear>InvoluteGear workbench and modified in PartDesign bodies using BaseFeature links. They are 15 deg helicals.
- - Picture4_Rotor-Turbo-Compressor,Power-Turbine,Gearbox.jpg (171.03 KiB) Viewed 7183 times
- All of the tubing for the lubrication system was created using PartDesign>Pads and Revolves with datum lines as axes. I was able to use faces rather than sketches in V0.17. Quick & easy!
The lubrication fluid is a combination of jet fuel and turbine oil with the exception of the dry sump gearbox which uses only oil. This simplifies the system since the turbine bearing lube can be dumped and burned off in the turbine exhaust.
- - Picture5_Lubrication-System&Schematic.jpg (212.19 KiB) Viewed 7183 times
It was most interesting to me to see how far FreeCAD has advanced since V0.13. Several of the components that I struggled with or could not do at all in V0.13 (somewhat due to inexperience probably) were easily completed in V0.17. Such great progress!
The turboprop section required 181 sketches and 58 bodies. File is 28.8 Mb and got a bit slow during modelling toward the end unless most of the parts were made nonvisible.
I cannot attach the file due to size and obvious copyright restrictions. With a little searching you can find several YouTube videos of these minature engines in operation.
OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.13375 (Git)
Build type: Release
Branch: master
Hash: 2bfea410fce1434fec0f853b032549aa2cd3c47e
Python version: 2.7.14
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.1.0
Locale: English/UnitedStates (en_US)
