Spinner to cowling fitup

219PB · #1 07-24-2019, 08:50 AM

I have a question for the masses. I recently installed my constant speed spinner on my RV-6A. The spinner is centered on the cowling and the gap is about .200" all around. I know that this is on the tight side. My problem is that the OD of the cowl is larger than that of the spinner. There is about 3/8" of frontal area exposed on the cowling. If my spinner was 13 3/4" in diameter, it would be looking great.

Is this a common occurrence? I am leery about just building up the inside of the cowling and sanding down the outside. Would be very difficult to get an even transition, especially with the honeycomb filler inside the cowling.

Any ideas?

Bill Boyd · #2 07-24-2019, 02:37 PM

Can't help so much with the overall profile issue, but I can assure you .20" is not likely too small of a gap. I'm fitting my 10 cowl now and the plans call out 1/8" spacers taped to the cowl front in 3 places to give the offset behind the spinner.

0.125" spacers plus a ply of Gorilla Tape securing them is less than .2" thickness - so if the idea generalizes to the -6, you're good to go. I could go measure the gap on my -6A but I'm at work.

I'm not sure there's much you can easily do to profile the cowl to the spinner, going smaller, because of the honeycomb.

Cowl fitment underway last night with 1/8" spacers taped in place behind spinner:

219PB · #3 07-25-2019, 06:54 AM

Anyone have a recommendation for a company that can provide a custom spinner?

Carl Froehlich · #4 07-25-2019, 10:02 AM

Paul,

I have seen RVs with such a problem and they all shared the same issue, during cowl fit the front of the cowl was not trimmed enough to achieve a perfect circle. While I note your statement that the cowl extends equally around the spinner you may want to check - the cowl sides are a complex curve and measuring is not straight forward. Get a piece of thin plywood and make a perfect 13? circle and see how that looks on the cowl nose.

That said, the cowl nose will still be a little larger in diameter. Here most builders have the spinner such that it is a little high on the nose. The idea is it will be about center after the engine mounts sag a little. My experience is this sag is very small, so recommend no more than 1/4? bias.

On your custom spinner question the answer is if you really want one then you will need to make a mold and lay it up yourself.

Carl

Larry DeCamp · #5 07-25-2019, 04:12 PM

Consider the Dave Anders felt seal on the prop extension. You can leave whatever gap your aesthetic value / engine sag dictates. The lower cowl pressure is sealed better than a close spinner/cowl gap.

Ted RV8 · #6 07-25-2019, 04:27 PM

First set mine up with 1/8” cowl to spinner clearance.

It makes things a lot harder when removing and installing the cowls when doing maintenance. I run two layers of black electric tape on the rear spinner edge as a cushion when removing the cowls. Still hurt the paint trying to install the cowls doing maintenance.

New Hartzell composite prop and polished spinner set up with more clearance and it sure makes cowl removing and installing a lot easier.

Thinking of doing Dave’s felt seal this winter.

Oh and don’t forget to remove the tape from the spinner before firing the engine. Whips around pretty good!

Bavafa · #7 07-25-2019, 06:27 PM

Quote:

Originally Posted by Ted RV8

First set mine up with 1/8? cowl to spinner clearance.

It makes things a lot harder when removing and installing the cowls when doing maintenance. I run two layers of black electric tape on the rear spinner edge as a cushion when removing the cowls. Still hurt the paint trying to install the cowls doing maintenance.

New Hartzell composite prop and polished spinner set up with more clearance and it sure makes cowl removing and installing a lot easier.

Thinking of doing Dave?s felt seal this winter.

Oh and don?t forget to remove the tape from the spinner before firing the engine. Whips around pretty good!

Plus 1 for this.

While making the gap as little as possible would aesthetically make it very nice, it will make the removal and installation of bottom half much harder. This becomes even more important if the plane has been painted.

Ted,
I am using a laminated piece of paper (8.5x16) that has a round cut to fit under or above the spinner. I used this during cowl removal to protect the paint.

gmcjetpilot · #8 07-27-2019, 09:53 AM

It likely is not as bad as you think and no one will notice... the parts are standard Van's made on molds... Post a pic so the peanut gallery can judge it... Ha ha.

Comment made about getting the cowl and spinner centered is good. However any mismatch will be most notable at the top. Bottom of cowl and spinner joggle will be less noticeable. Also as said above some trim cowl so spinner is high for engine sag. I suppose you could shim out sag later... I did on my RV-4 with conical mounts.