As I prepare to mount the upper cowling I want to know if & how my Catto prop spinner, specifically the “lampshade” flow guide portion of it, can be modified to work with my cowlings. If I need to make any minor adjustments or allowances for the prop spinner when installing the top cowling and mating it to the lower cowling, best to know now.
What I do know is that the current flow guide (“lampshade”) does NOT fit and will need to be modified. I’m pretty sure I mentioned in an earlier blog post that I had a good conversation with Mike Toomey on how he rolled his own spinners based more on Klaus Savier’s spinner design, again, specifically focusing on the flow guide portion of it.
From my conversation with Mike T. I came up with my inital plan on how to modify my flow guide to fit into my tight Melvill cowlings. My work today is a continuation of flushing out that possibility by creating a mockup of my proposed flow guide to A) test its fit with the spinner portion, and B) have it in place during the upper cowling installation to know my flow guide mod will work/fit.
Since the Catto ‘Hershey Kiss’ canard prop spinner is made with a hex pattern carbon fiber, I called Catto 2-3 weeks ago to see if I could get my hands on some. They obliged but we’ve been playing telephone/text tag with a good week-plus gap in comms to finalize price and quantity. Well, today I finalized the deal to have them ship me a couple yards of “their” CF to allow me to reconstruct a flow guide using their hex patterned CF.
Phase I of the flow guide mod is of course ensuring it will fit in the aft cowling opening. So I’ll reiterate that I feel this is a prerequisite/commensurate task early on in mounting the upper cowling.
I grabbed all the dimensions off the current flow guide for the middle opening and prop bolt hole studs and modeled them up in Fusion 360 CAD.
Once again the IT geeks got the best of me when, without thinking, I fired up my new mo-jamma 3D printer and promptly updated the firmware when I was prompted… then the issues began! Some of my previous Klipper firmware configurations apparently are no longer recognized in the latest version of Klipper so I am getting errors. I thought I had done enough research to clear them out, but then my model ended up printing about 1/4″ over the plate… a couple of times. After an hour+ of playing Johnny F- Around with that I called no joy and used the smaller new 3D printer. (Ugh!…. Geeks!)
My first test version of the bolt stud holes had the pattern just a hair in too close to the center and they all needed to be moved out just a skooch.
I moved all the holes out 0.017″, and reprinted the mockup. The new pattern worked a treat but I then discovered the holes themselves are just a hair too tight for a mockup. For actual installation they are probably perfect.
Here’s another shot of the #2 mockup with the correctly spaced bolt hole pattern.
I’ll add about 0.008″ to each hole just to give them a hair more clearance for getting this thing on and off, and press forward with the design. The reason I wanted to use the bigger 3D printer is that the new lampshade model may be too big for my smaller 3D printer. We’ll see, but I may be doing some more 3D printing troubleshooting tomorrow though.
I of course want to get this thing printed & complete so I can press forward with the upper cowling install!
I’ll also note that I had a good conversation with Marco as he was on his way to his hangar to do some brake line work on JT, his Long-EZ. His timing for calling was perfect and I had him grab a bunch of pics with various dimensions of his prop in relation to the aft cowling opening, exhaust pipes, etc. as references for me as I press forward in my cowl and exhaust pipe installs.