Wednesday, August 27, 2014

Jenny 3D Printed Aircraft Being Dialed In

With 55 hours of design time on the computer model for my planned 3D printed Jenny aircraft I think I finally have the model dialed in to starting construction.  A lot of the sub-assemblies for the aircraft were a real puzzle to figure out how to make. The design for the model had to work and not throw the general shape of the aircraft way out of wack with the effort. So I thought I would show you the progress with this posting about this portion of the project.

The model is looking very complete now with a lot of the littler details added from the first time I posted about the project. In this image you can see the addition of seats, wing king posts and more detailing in the aileron assemblies. With the king posts in the model I plan on adding all of the wires that you would see on a real plane.  These wires criss-crossed at each of the wing struts, up to the king posts and even inside the fuselage between each vertical support.  I will just have to see how difficult it will be to add this level of detail in the model.  Hopefully I can make it all work and give the model that much more realism in the effort. 

The landing gear on the model was quite an effort to design as well for the model.  I wanted to keep the look as close as possible to the real plane and yet not make it a pain in order to assemble or 3D print. The wheels will be printed in four parts each.  This way I will be able to get the white tires and red wheel covers put together easily.  This is simply a matter of printing the parts as though they are halves of a tire split down the center line.  Like a bagel would be cut for breakfast and gluing them together using plastic modeling glue.    

The landing gear is mounted using cylinder and pin mounts that are attached to the upper portions of the assembly.  You can see these mounts (in blue) in the image above just under the fuselage. 

 The axle for the landing gear is shown here in close up with one of the front wheels.  The oblong hollow protrusion on the top of the axle is the receiving mount for the lower portion of the right landing gear.  It took some doing to get all the landing gear parts to line up correctly to make this portion of the model work and look proper. The wheels are glued to the axle with a printed .10 diameter protrusion on the end of the axle.  I will have to make sure that I do some testing of this portion of the axle to make sure that the strength needed is designed into this portion of the assembly.  Would hate to find out that it would fail after I get the model all put together.  

Another brain teaser for the model was the engine and exhaust.  This took a number of hours to figure out how to design using actual photos of a real Jenny Aircraft engine.  The exhaust is pretty close to the real thing so I am happy with my efforts on this portion of the model.  There were several different variations that I found on different planes for the exhaust.  Some had the exhaust tip tipped down, others were straight back to the rear of the plane and still others were tipped up with an extension that would route the exhaust up over the top wing.  I went with the straight back version as it was the simplest to design. 

Here you can see the seats and mounts along with the windshields for the cockpits.  The engine sticking out of the left front cowling looks good in this image as well.  In the model as in the real plane the engine and exhaust stick out of both sides of the aircraft.  I had to mirror the parts for the exhaust in this portion of the assembly to make it look right. 

I started printing some of the pieces of the top wing as you can see from the photo above.  These ribs are only 2.5 inches long and .10 inch thick.  The notches in the spar (the long piece in the photo) match up to the ones in the ribs so there is no guess work when it comes time to assemble the parts of the wing. 

Here is the layout of one of the rib and strut assemblies.  It took me a little while to realize that the simplest thing to do with this portion of the assembly was to combine these parts into one piece for strength, ease of assembly and ease of 3D printing.

Here is the completed 3D print of one of the rib/strut assemblies.  Only two of these parts are needed for the wing assembly and printing one only takes around 30 minutes to complete.  Turned out very well and will make the wing assembly nice and strong when it is mounted into the model.

These two wing/strut parts are different versions of the same part.  The one on the left I printed first.  The upper portion of the top rib is called the king post.  This was used in the real aircraft to attach mounting wires to strengthen the upper wing.  After I had printed two of these parts I realized that the wing skids (the lower loop on the bottom rib) for each of these parts was missing from my model.  So I had to reprint the parts again (the part on the right) to make the model correct.  As before the parts turned out very well and give the model the correct look.  The last rib/strut part is good sized being nearly 7 inches long and 4 inches wide. Will be fun to see the model come together now with the design portion of the project nearing completion. I'll keep you posted once I get enough parts printed and some of the wing assembled.  Enjoy the photos.

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