Over the last week or so, I have been working on my induction inlet for both front and rear engine. The design of it comes from my day long visit with Dave Anders, of worlds fastest RV-4 fame. He has written many articles for Kitplanes and is very upfront about the science he uses. One of his articles, “Optimizing Air Induction,” will certainly give you all the information you need to design your inlets.
I used his articles as well as “Best Bell,” by Blair to design my inlet. I am pretty new to 3D modeling/CAD so it took me a while to get it right, but I was able to design an elliptical shaped inlet that blended into a Kuchemann A30 airfoil on the exterior. From the articles, I have read, and the advice I received rom Dave, this seems to be the best approach.
I had my solid model 3D printed in a plastic/carbon fiber material. This gave me something to hold in place and look at to verify that it was what I wanted. This part was not exactly the right material to use as my actual inlet, so I needed to make one out of higher temperature material that was lighter.
I wet sanded my 3D printed part and got rid of the inevitable rings/steps of a 3D printed piece. Using wax and PVA, I ensured that the 3D part would release from a layup. Then I used this part to make a 3 ply splash. Once released, my 3 ply splash made the perfect mold shape to make more inlets.
It was then just a matter of re-enforcing the splash and creating flanges around it to allow a sealing surface for the eventual vacuum bagging. I am hoping that I can get some nice carbon fiber inlets by using the vacuum bagging process. Without vacuum, I am sure that the carbon wouldn’t stay in the curves of this inlet.
I couldn’t help myself after the mold was ready. I needed to make a part. So I did a 2 ply glass inlet using wet layup techniques. There are most certainly some flaws in the part, especially since doing this layup was kind of on a whim. I didn’t even take the time to figure out the right shape to cut the glass to ensure proper ply overlap, etc. I just went for it with scraps.
A little more finesse with the layup process and I will have 2 inlets, one for each engine, ready to integrate into the cowlings. Oh, and I will have a mold if anyone needs one.
Here is the time-lapse video of working on the inlet mold.