Davepar

Davepar

Well Known Member
I read in one of Van's handy FAQ articles that I could fit the cowl without the prop by mounting the spinner back plate to the starter ring gear with some 2-1/4" long spacers made from PVC. Now that I've read further into the spinner instructions, it looks like the back plate attaches differently with the constant-speed Hartzell prop I'm planning on using. The plate mounts to the back of the prop hub.

Is it still possible to use the 2-1/4" PVC pipe spacer trick? I'd like to start fitting the cowl soon, and haven't ordered the prop yet.

Thanks,
Dave
 
The instructions are the same for the C/S prop. I used them. I did find that the fit was not the greatest (too tight) and I did need to modify the cowl to compensate. I do recommend using the instructions, though. It is easier to fit the cowl without the prop on. I would allow for about an extra 1/8 to 3/16" spinner gap. Then just fill in with glass and resin if you need to.

Roberta

Here is a shot of the backing plate bolted to the engine and the upper cowl clamped to it. Use spacers about 1/8" shorter (or thicker wood blocks) so when the prop is installed, it is out slightly farther, increasing the gap by about 1/8".

cowl10zd.jpg
 
Last edited:
If I were doing it again, I'd make the PVC spacers 2-3/16" long. You're right, the spinner will be closer to the cowl by the thickness of the spinner backplate (1/16") with a C/S prop. I followed the plans and fit my cowl for a 1/4" gap; when I mounted the prop I had 3/16". That's with the spacers installed and no washers. If you just have to install the washers because they're shown in the plans, better make the PVC spacers 2-1/8". I'm perfectly happy with the 3/16" gap I ended up with, and really glad I didn't initially fit the cowl for a 1/8" gap.

Good luck-
Jim Percy
 
That is a slick trick Mark. Looks like you used some ABS that just fits inside the oil tube.

Thanks Jim. As Roberta suggested, I'm inclined to start with a larger gap. It's easier to add material than subtract it. Shooting for 3/16" sounds good.

Dave
 
A couple of notes in case somebody else tries this process:

1. The holes in the spinner back plate are larger than the prop bolts. You need to make sure the spinner back plate is centered. I drew some 1" circles on the back plate centered on each bolt hole and then centered the bolt heads in the circles.

2. The spinner back plate has a dish to it. The center is about 1/8" further aft than the edge. That may be the cause of the fitting issues mentioned above. While fitting, you have the back plate attached at the center. For a CS prop, the center is cut out and the edges are attached to the back of the hub.

I'll report back on the final fit in several months once I have the prop hung.

Dave
 
top to bottom fit

This is the typical fit that everyone starts with, and most people have to trim the cowling spinner disc at the top (you may need to reinforce from the inside), and build up the disc on the bottom. This is time consuming and fiddly. In addition, the top and bottom cowlings will need cutting and filling around the air intakes.

What I did (Sensenich) was to have a 1/8" clearance at the top of the top cowl and 1/4" and the bottom of the bottom cowl. In addition, the whole cowling was set about 1/8" lower than you'd expect.

This is mentioned in the instructions to allow for engine sag.

So... how did it work? After 10 hours, the clearance has evened out to about 3/16" top and bottom, and things look centered. As long as the engine doesn't sag much more, it's a perfect fit.

Vern Little
9A
 
Thanks Vern

Just to be clear, you sand material from the top of the cowl spinner ring and add epoxy/flox/micro to build up the bottom? Does sound like a lot of time....

Vern - I picked up a Trafficscope VRX pretty cheap on ebay. I will add that to the panel soon.

Thanks again for all the help.
 
floxing it up

I didn't use flox because it's hard to sand. I used layers of BID glass and micro to build up the lower cowl disc by about 1/4". This is quite a bit, of course, and takes some time.

Once I got the actual prop and extension, the fit was not quite right, so I had to adjust it cutting it down some more, then by slathering the cowling disc with micro, then weighting down a waxed board down on top of the disc to make everything co-planar.

Lots of time filling, sanding and fussing. Sometimes there are no shortcuts. At least it's easier than fitting the canopy.

One more thing, after painting, I applied some UHMW tape on the spinner disc to protect the paint and spinner backplate when taking the cowl on and off.

Vern, 10 hours, changing the oil!
 
I have a slight tilt, but not quite as much as in your picture. This sort of shows my situation:


I ordered the prop a week ago. Once that shows up, I'll fine tune the spinner/cowl fit, filling/sanding as needed.

Dave
 
You must log in or register to reply here.