Cowl to Spinner Gap

[mikeyj350]

Hey guys, I know this is a common subject on the forums here but I didn't find anything on this specific problem. I'm working 47-6 Step 11/12. I've fitted the cowl to this point following the plans exactly, with the exception of I'm using SkyBolts instead of hinges around the perimeter of the firewall. Both the upper and lower cowl halves seemed to fit perfectly, and with the 1/8" spacers taped to the front face of the cowl, everything lines up great.

The problem came with the step saying remove the 1/8" spacers taped onto the front. Upon reinstallation of the lower cowl, it is now MUCH closer to the spinner bulkhead than with the 1/8" spacers, and it seems pretty well-set in that position. I can pull and flex the cowl aft and upwards, and with a fair bit of force I can hold it in the desired 1/8" spacing position. As soon as I let go though, it goes back to its "happy" position of only 1/32"-1/16" gap. In contrast, with just the upper cowl skybolted into place, the gap is fine.

I've already trimmed the split line for the lower cowl and have traced that line onto the top cowl, but haven't cut the top cowl yet in case there is some more adjusting I'll need to do.

Am I worried about nothing? Build on and it will fix itself? Do I need to go back and re-trim my firewall line a bit more to get the extra clearance so it sits correctly without the spacers taped into place? Any ideas from folks who may have been here would be great... thanks!

[ecurington]

I don't think you have anything to worry about, but also don't think it will fix itself. You are just into fiberglass work, or as some call it fiberglass ""ell. Because you have not fitted the top cowl seems you still have the option of trimming the cowl to firewall gap and that may be easiest.

I discovered the same problem after my entire cowl was fit and ended up sanding almost 1/8" off the front of the cowl. Because of the extensive sanding mine required building up the back side of the cowl where it met the spinner. Regardless, the gap fit turned out well. So you have options, work it now or work it latter. Either way its work.

Remember, anything can be done with fiberglass. I just takes time.



Eulice Curington
N104EW Painting

[Pittsartist]

I messed around for ages trying to deal with this on my cowls - then I finally decided to just grind a slit all around the bit of the cowl just behind the spinner. Made a 5/16 thick ply ring and gaffer taped to the rear of the spinner backplate and then simply fibreglassed the cowl back into the correct place. Took about 20% of the time spent messing above and produced a much better result.

You really need to have at least 1/4" gap - especially if you intend pulling a few G's . Also bear in mind that the Engine can rotate (in the crankshaft axis) against the torque by as much as 3/8" measured on the fuel servo

[rleffler]

There is more than one of us that has fallen into this trap. If there is any tension or torque on the cowl is being trial fitted, you pay for it as soon as you make that back cut. The cowl is long enough that you don't notice until its too late.

Like Eulice mentioned, you'll have to sand down the front. But before you start sanding add a few layers of glass on the inside. You may end up sanding down to the new glass layers depending on how much material you need to take off.

I'm not sure if I posted any of my photos on my build site. It did set me back a few days to remedy the issue. Now that it's painted, you can't tell the difference anymore.

[Carl Froehlich]

Look at the Hartzell prop manual. It gives you some options on adding washers on the spinner bolts. This will move the spinner out enough for what you need.

Note - the prop says where it is, the washers just space out the spinner back plate.

Carl

[clutch22]

Originally Posted by Carl Froehlich

Look at the Hartzell prop manual. It gives you some options on adding washers on the spinner bolts. This will move the spinner out enough for what you need.

Note - the prop says where it is, the washers just space out the spinner back plate.

Carl

What Carl said sounds like it might be a good solution for you.

I just want to throw out there that I also opted for a .25" gap. I think it looks perfectly fine and I wanted to allow for engine movement and sag over time and perhaps make it a little easier to pull the cowl on and off.

[N427EF]

I just want to throw out there that I also opted for a .25" gap.

Good advice and if you have any pressure between the spacers and the spinner plate, it will reduce to less than 1/4" as soon as you remove them.
My first RV-8 I wanted to keep it as small as possible, 1/8th and it looked very good until you need to take the cowl off.
You'll thank us later if you go with a larger gap.

[Rupester]

In my experience, it's better to have that gap a little too wide than a little too narrow. Mine is 1/4" and it looks just fine ... have never had an "RV Looker" ask about the gap or observe it was wider than normal.
FWIW ... free advice is worth what you pay for it.

[Bill Dicus]

Mine on the RV-8 is 9-10/64. Looks good and have had no contact between spinner and cowl with maximum positive and negative G' during phase one. Lord mounts seem stable with no change in last 10-15 hours good luck with yours...

[rvbuilder2002]

Originally Posted by Carl Froehlich

Look at the Hartzell prop manual. It gives you some options on adding washers on the spinner bolts. This will move the spinner out enough for what you need.

Note - the prop says where it is, the washers just space out the spinner back plate.

Carl

Adding spacer washers would move the spinner closer to the cowl.