RV-6-7-9 Firewall Recess

[DanH]

Question for 6-7-9 finished/flying owners: Do you really need the deep firewall recess? Could you get by with less depth, or no recess at all, and still accommodate your prop governor or other accessory?

Not suggesting you change it on your flying airplane, merely if you found it necessary.

[skypilot737]

I have a fixed pitch prop (actually ground adjustable ) so no recess required. It did make a handy place to attach the fuselage rotisserie though during the build.

[Desert Rat]

I was thinking about this the other day as I was hanging the engine; Since I'm going with a 390 with fwd governor it really isn't necessary, but it sure gives more knuckle room back there to accommodate a straight spin on oil filter.

I don't see much value in getting rid of it, whether the engine configuration requires it or not.

Curious what you have in mind that's causing you to ask the question?

[wirejock]

Mine is an "A" model with the elasomeric gear
Throttle cable goes through the recess. IO-360-M1B. CS prop with rear mounted governer. There is 3/4" between the oil filter and firewall.

[Ralph Inkster]

Could manage with a shallower recess, but than I would have to
1- fabricate a replacement cover plate myself
2- modify the firewall inner lower heater diffuser box
Besides, the recess is a good place to set sockets & wrenches when man handling things on the back of the engine.

[rvbuilder2002]

It is necessary to accommodate a governor for a constant speed prop if mounted on the rear of the engine. It could be a bit shallower for the governor but that would just make it more challenging doing the control cable hook up, etc. it is not absolutely necessary for clearance on the oil filter but there is just barely enough room to get a standard filter installed or removed with the amount of clearance because of the length of the threaded nipple.
Years ago some people would cut the nut portion off of the back of the filter when they had no recess, so that they didn’t have to struggle with getting it installed and particularly removed because of the mess that can cause. There was probably some variation in the amount of clearance depending on whether you had a Dyna focal or conical mount. Though I don’t know any specifics regarding a difference between the two. If using some of the newer filter options that are much smaller than the standard aircraft engine filter it would not be a factor.

[DanH]

So far it sounds like it is not required, but it is convenient.

Humor me....consider only the minimum required, and assume there will actually be more.

[agent4573]

PCU5000 governor doesn't require the recess to fit. The straight oil filter adapter requires just a small relief in order to have room to get the threads started. If I had a 90 degree filter adapter I wouldn't need a recess at all.

[azrv6]

Picture of the recess and governor on my RV6 (mid 1990's vintage build). The attach point of the control cable to the governor extends slightly back into the recess. In this picture the oil filter is off. The 48110 is easy to install/remove with the recess. Without the recess, the oil filter nut would be in the way.

[Stevea]

Like Scott says, a shallower recess would work, but it makes installing the governor cable attach hardware just a "bit" more challenging. Would also make installing/removing the oil filter tougher too, since the oil filter on my setup has a nipple on it.....so it gets "longer" when unscrewing from the filter adapter.