Matt's RV-7 Project » Propeller

Mounted dummy prop hub

Matt — Mon, 25 Jan 2010 01:01:59 +0000

I primed the spinner backplate and doubler, then riveted them together:

I had to buy these spacers from Van's for five bucks each, since the dimensions aren't shown on the plans (and I don't have a lathe either).

Using hardware-store bolts, I attached the spinner backplate to the dummy prop hub. The plans call for an AN960-416 here, but I think they must have meant -616 for a 3/8" bolt.

Another view:

Then I bolted the backplate and hub to the engine crankshaft. There's only enough clearance to turn the captive prop bolts about one flat at a time, so this part took a little while. Removing the prop to replace the alternator belt is going to be annoying.

I plugged the oil passage to keep moisture out of the inside of the crankshaft. The hole isn't threaded, but I managed to find a plug that fits somewhat snugly and used fuel lube to seal it.

Just for grins, I threw the top cowl on there just to see how it looks. Pretty cool:

Oh wait, I forgot about this part… I may need to finish the top skin before I can work on the upper cowl attachment stuff. Argh.

Back to wiring I guess…

Prop hub and spinner backplate

Matt — Sun, 17 Jan 2010 23:40:30 +0000

Another month without much work on the airplane. I have an excuse, though: it's been really cold in my garage!

I have a whole list of wiring chores left to complete, but I need to take a break from running wires through the fuselage before I go cross-eyed. I thought I might work on some firewall-forward tasks for a while, which will actually help with wiring in a roundabout way; before you can do much wiring forward of the firewall, you need to finish the baffles, which means you need to fit the cowl, which means you need to fit the spinner (the pointy bit on the very front of the airplane), which means you need to fit the propeller. Plenty of work to do there.

The plans suggest making a spacer out of wood or PVC to stand in for the propeller, but since the consequences of getting the cowl/spinner gap wrong are so ugly to contemplate, lots of folks end up using a real prop instead. However, instead of using my very expensive propeller as a fitting template, I had the idea to use a junked prop hub instead – that way there's no questions that the dimensions will be right.

I put out a call for an unairworthy Hartzell prop hub to use for fitting the cowl and spinner, and received the following hunk of grungy aluminum from a generous forum member (thanks, Joe!). It's only the rear half of the hub, but that's all I really need anyway. It is the older C2YK model instead of the C2YR that I have, but the critical dimensions for spinner-fitting are the same.

A little solvent and elbow grease cleaned it up pretty well. The key metric here is that we want to avoid leaving a big grimy smear on the clothing of any wives who happen to be walking through the garage. It just seems like everything will go so much more smoothly that way.

Digging into the pile of remaining airplane parts, I pulled out the rear spinner bulkhead and its associated doubler ring.

As I expected, the spinner bulkhead is noticeably dished, although it appears to be otherwise true and symmetrical. This appears to be a common occurrence, so I will probably just ignore it.

With some hardware-store bolts, I temporarily attached the doubler to the bulkhead:

…then drilled and clecoed the holes for the rivets that will eventually attach these two pieces together:

If you have a Hartzell prop like I do, you need to cut out a significant portion of the spinner bulkhead. I transferred the shape of the hole in the doubler ring:

Initial cuts were made with my air nibbler, which is great for this kind of work. Going slowly and carefully, I was able to get within 1/8" of the line.

Then it was time to file, file, file. The corners look lumpy here, but that's how the cutout needs to be in order to clear the prop hub.

More filing and finish work… I made plenty of aluminum shavings.

I spent a lot of time making sure all the edges were well and truly deburred.

I need to prime these parts before I rivet them, but it's way too cold and dark outside to do that, so it will have to wait on the weather.

Also: What are these?! I haven't looked at the plans for over a year, I think… ever since I got to the step that said something like "Now might be a good time to think about wiring and an electrical system, if you want one."

And speaking of the spinner backplate… I realized that this piece will literally be moving the fastest of any of the parts that I've fabricated: in addition to however fast the plane is moving through the air, the perimeter of the 13" diameter spinner will also be doing about another 100 mph as the crankshaft is turning at 2700 RPM. Neat.

Propeller arrived

Matt — Mon, 15 Sep 2008 02:00:54 +0000

Eight and a half weeks after placing the order, the propeller arrived. It is a thing of beauty. Heavy, expensive beauty.

The box is like eight feet long and weighs ninety pounds. With it sitting like this, there's barely any room to walk. Or store empty beer bottles.

I dragged it over by the wings, and raised it up on some boards so the cardboard doesn't soak up moisture from the concrete garage floor.

For reference, here's the current status of the fuselage:

And the rest of the garage… what a mess.

Ordered propeller

Matt — Thu, 10 Jul 2008 14:21:22 +0000

Last night I sent Van's a big chunk of change for a propeller – specifically, a Hartzell C2YR-1BFP/F7497-2. That's an aluminum constant-speed prop with a pair of 72" blended-airfoil blades specifically designed for the two-place RV's, and will look something like this.

I kind of wish I'd ordered the prop sooner, since it has a 12-16 week lead time and I find myself with the following chicken-and-egg scenario: In order to finish the FWF plumbing and wiring I kind of need to have the baffles in place, for which I need to have the cowl fitted first, which means I need the prop to fit the cowl. Actually I guess that's a whole series of chickens/eggs. Theoretically you can fit the cowl without the prop if you make some kind of spacer, but even Van's suggests you wait for the real thing to arrive if you have a constant-speed prop like I will. Apparently there's something different about how the spinner is mounted…? We'll see.

Meanwhile, I suppose I will continue to work on interior fuselage systems, when I have time.