The Hartzell "diaphragm"/"bladder" prop (HC-1, HC-D) did not originally come with a governor. It instead had only a manual oil control valve. This meant that these props were not really constant speed props, but merely variable pitch props. The prop pitch can be adjusted from the cockpit, just like any constant-speed propeller -- however, since there was not a governor, changing the throttle position will also change the RPM. In other words, if you have the original setup, you're going to be regularly tweaking the prop control to keep the RPM where you want it. A lot of folks don't mind this, but if you'd like, you can add a governor to your bladder prop which makes it a real constant-speed. You're going to need:
-A Hartzell A-1-B Governor. You may only be able to find an A-1-C, which is what was used on the "Dome" props, but that's okay -- a governor shop can convert an A-1-C to an A-1-B fairly easily. As of November 2019, these governors are no longer available new from Hartzell. You'll have to find a used one.
-A Hartzell "T" drive. This bolts onto the pilot's side accessory drive pad on the back of your engine, allowing you to mount both the fuel pump and your new governor to that same accessory pad. My research indicates that if you have an E series Continental, you need a C-137-1B or C-137-3B "T" drive. If you have a GO-435 Lycoming, you need a C-137-2B. As of November 2019, these "T" drives are still available from Hartzell, but they are pricey. You are probably better off finding a used one and having it overhauled.
-A new/different Control Valve Link for the Oil Control Valve which sits on the top of the engine. My research indicates that E series Navions require part no. A-173-2. Super Navions (GO-435) require A-173-5. As of November 2019, these were still available from Hartzell and are not terribly expensive.
-Some miscellaneous hardware, including a new vernier control, which you'll find listed out in the instructions.
There are two sets of instructions for doing this. The most modern version is contained in Hartzell Manual 140, which is the latest version of the manual for these props, beginning in section 3-5. However, this version does leave out a few steps. You can find manual 140 here: https://hartzellprop.com/wp-content/upl ... R03-AW.pdf
There is also an old document from "back in the day" that detailed how to add this governor and T drive to the Bonanza, which is what it was originally offered for. You can find that, here: http://www.navioninfo.com/Gov-Tdrive.pdf I have found this very helpful. Keep in mind, these instructions were written eons ago, and they were written for the Bonanza. There are a few differences to note. Two that I can see right away:
-Both the HC-D2V20-7 and HC-D2MV20-7 propellers, and you probably have one of these, are merely later versions of the HC-12X20-7 which is what's discussed in this text. If you have one of those props, I'd follow the instructions for the HC-12X20-7.
-In step 26, the text discusses replacing the link on the valve assembly, and gives a part number. This PN is correct for the Bonanza, but not for the Navion! See "Control Valve Link", above.
We are currently in the process of doing this to my Navion, and I will report back with results/snags/etc.
One final note: If you have a "diaphragm"/"bladder" prop with a model number beginning with HC-1, it's time to seriously consider upgrading your propeller itself before adding a governor. See the pinned post on this board, "Hartzell Props for E Series - Identifying & General Info" for more information. However, if you have a bladder prop beginning with model number HC-D, carry on.