The spinner is the little nose cone that covers the propeller hub. It is not just ornamental, it plays an important part in smoothing the air flow over the cowling and guiding the air into the intakes on either side. The construction is fairly simple: A fiberglass party hat reinforced by a rear bulkhead and a forward bulkhead that sits about midway within the spinner. How it got the name spinner shall remain forever a mystery :)
The rear bulkhead is delivered by Vans without the cutout. Airplanes with fixed pitch props don't need the cutout, but for those of us with constant speed propellers -- well, we have more work to do. Cut a hole in the bulkhead to allow the propeller hub to protrude into the spinner cavity.
Now test fit the spinner and bulkhead and drill out the mounting screw locations. This takes a bit of measurement and calculation to get even spacing, but this step has gotten a lot easier since PI was discovered.
The next step is to cut out the openings for the propeller.
This is the front bulkhead bolted to the prop hub.
On a constant speed propeller, the blades twist to change their pitch during normal operation. Internally, hydraulic pressure moves the blades in one direction, while a big spring pushes the blades back. Without the engine running, there is no hydraulic pressure so the spring pushes the blades back against their stops. In the this step I will need to twist the prop blades to do the final fitting of the blade cutouts on the spinner, but the spring is really strong so I need some kind of leverage. A couple of pieces of wood and two C clamps later I have a big lever. The last part of the fitting is iterative: twist the blade until it contacts the spinner cutout, then make the cutout bigger. Repeat.
Here is where I run into the first problem with the propeller installation. I get the prop mounted on the enginge and the prop bolts are lightly seated. Great. Now I realize that these prop bolts need to be torqued to 65ft/lbs. There's barely enough room for a thin wrench between the rear of the spinner and the flywheel/ring gear. There is just no way that my torque wrench was going to fit in there. There are probably expensive torque wrench extenders that I could buy, but I didn't find anything suitable after a quick look online. This is where cheap tools are really valuable -- there is no need to feel bad about re-purposing them. Carol found a $3 dollar combination wrench in some kind of bargain bin and I was able to cut off the end I needed and weld on a 3/8" socket adapter. A new tool is born! Carefully measuring the extension allows an appropriate adjustment to be made to the final torque value using a ratio of total torque arm length to extension length.
So here we are with the propeller mounted and torqued. Next, the prop bolts were safety wired.
It's a little bit hard to see what is going on here, but after the prop was mounted I wanted to see how the propeller tracked blade to blade. A dial indicator is set up to measure the relative position of one blade and then the prop is turned 180 degrees to compare it to the other. The two blades were virtually identical in their track, but one of the blades was .01" longer than the other. I think I can live with that.
Almost finished now, the final step is to paint the spinner and then put it on your head. Check.
All assembled, including a whole bunch of painted screws.
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