Cowl changes when going from FP to CS on a RV6

Vans mentions that changing from a FP to CS prop requires a different cowl (and spinner).

Anybody with direct experience on this change care to comment?

Set up

It must depend on the setup.
My hangarmate has a -6 that was originally built with a wooded FP prop with a 4" extension. He swapped to a CS hartzel and everything lined up perfect.

I completed this swap 10 hrs ago on my 0320 rv6. I have a fixed pitch cowling. I went from a catto 3 blade with a 4” spacer to a whirlwind rv200 with a 2” spacer for c/s props. The prop spinner to cowling gap is .43” vs the .25” that is in the plans. I have a conical mount and would get rubbing under high g loads. The .43” looks good and so far has not made contact with the cowling. I did have to cut the spinner hole out .5” all the way around to allow the tapered spinner backplate to fit.

You will be amazed at the performance difference. You won’t gain much top speed, but the takeoff acceleration and climb makes all the work worth the trouble and expense.

Thanks

I?m helping a friend with the engine and prop upgrade and hope to not have redo the cowl.

The original setup had a 2 1/4? spacer with a Sensenich FP prop. After a prop strike, we are installing a new Lyc IO360 with a BA CS...

I'm going with the new cowl

I'm in the middle of upgrading from Sensenich FP to Hartzel CS. I had hoped to reuse spinner and cowl. Forum search shows entries stating you can add spacers to the engine mounts to add a little clearance. I found that was not going to provide enough space. With the CS prop I went from the appropriate space to zero clearance. Too much to correct with washers on the engine mount in my mind. On the plus side, the current offering from Vans for cowling (prepreg) is an order of magnitude better in quality than my original gelcoat cowl.

There are variables that must be considered when switching from a fixed pitch to constant speed prop.
It is primarily related to the vintage of cowl that was used when the airplane was built.
Early cowls were sized to use a 4" prop extension with a fixed pitch prop.
Later cowls that worked with a F.P. or constant speed prop used a 2.25" spacer with the fixed pitch or a standard compact hub constant speed.

If you have a cowl that was using a 4" extension with a fixed pitch prop, you will need to do one of three things

- install a newer version cowl
- Use an extended hub style Hartzell prop (generally not approved for aero)
- Use a compact style hub prop with a 1.75" spacer (I am not what options are available for this)

If you currently have a 2.25" spacer on a fixed pitch prop, you should be able top switch to constant speed with no cowl fitment issues.

We have the 2.25 spacer. Thanks for the help.