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RV-6-7-9 Firewall Recess

Is the deep firewall recess really necessary?

  • I need the standard recess.

    Votes: 23 46.9%

  • I could get by with half the depth.

    Votes: 11 22.4%

  • I don't need the recess at all.

    Votes: 15 30.6%
  • Total voters
    49
  • Poll closed .
DanH

DanH

Legacy Member
Mentor
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.
 
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recess

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.
 
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?
 
Recess

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.
20221220_103315.jpg
 
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.
 
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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.
 
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.
 
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.
 
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.


IMG_3450.jpg
 
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.

IMG_0697.jpg
 
Regarding that firewall recess part……. on my used RV6 kit that I purchased from the second (or third?) builder, the firewall recess was already installed, but it was upside down in accordance with plans. So I ordered a new one. Apparently, this is one of the few prepunched parts on an early RV6. I drilled out the upside down one and clecoed the new one in, and surprisingly, all the holes lined up. Then I thought - gee I wonder how that could be with the original one install backwards. I took the original recess and oriented it correctly, and all the holes still lined up. I wouldn’t have needed to buy a new one…… Bottom line, if anyone needs a SS firewall recess part because they goofed theirs up, I have a spare. Let me know if you need it.
 
A shallower recess may be possible at the expense of governor hook-up issues but there's no downside to the deeper recess. There's nothing on the cabin side that would benefit from the shallow recess. At least for me. If you have something that could use that space then you have a trade-off to balance.
 
MarkW said:
RV-9 fixed pitch and 90 degree oil filter adapter.
No need for the recess.
Click to expand...

Ditto for my 9.

Comment:
Question
why change it?
Answer
Think about a single piece firewall! No need to rivet and seal that center section if there is no need for a recess.
 
RVbySDI said:
Ditto for my 9.

Comment:
Question
why change it?
Answer
Think about a single piece firewall! No need to rivet and seal that center section if there is no need for a recess.
Click to expand...

And it would probably greatly simplify the installation if there was a desire to add firewall insulation ;)
 
rvbuilder2002 said:
And it would probably greatly simplify the installation if there was a desire to add firewall insulation ;)
Click to expand...

With or without insulation, it would eliminate four lap seams and eight holes.

Thanks guys, I have what I needed to know.
 
While not totally necessary on all installations it sure makes life easier if you have a recess. Maintaining those aircraft without any recess is always a hassle.

Plenty of people have used stainless steel cooking bowls or baking dishes to make the desired size recess. They work well.
 
I didn't have a choice but to not have the recess - being tall, I installed the rudder pedals as far forward as I could, then found the recess wouldn't fit when I tried to install it...:eek:
 
Not needed

I thought about making a flat plate cover but didn't have any stainless around so I used it. Van's should include a flat option.

I have a couple of the control cables exiting in the recess. It does provide a little more space to start a bend in the cables.

Not applicable to the recess but, I used the 90 Degree adapter for the oil filter. Much easier to change oil!!
 
Ok, tell me what you think about this...
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You would have to follow up with a top cover panel to close off the F-782C cabin heat diffuser for the RV6/7/9 builders. Page 34A of the 7 plans.
 
airguy said:
Hydroformed?
Click to expand...

Yes, homebuilt, proof of concept. Eliminates eight open holes and four seams, which are not fire friendly.

This one is an inch deep, but it could be deeper. An inch clears oil filters.

Best I can tell, only a few prop governor models might need a deeper recess. I've been looking for governor dimensions, for confirmation, without much luck. The PCU5000 is less than 6' long and if I understand correctly, would work with no recess at all. See posts #6 and #8.

Ralph Inkster said:
You would have to follow up with a top cover panel to close off the F-782C cabin heat diffuser for the RV6/7/9 builders. Page 34A of the 7 plans.
Click to expand...

Thanks Ralph. Fundamentally, that just requires adding a top on the box.
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I have a fixed-pitch O-360 6A with a 90degree oil filter adapter. With that configuration, the recess is not required or particularly useful.
 
Me Too

RV-6,O-320, fixed prop. I like the recess because it gives me a little more finagling space when changing the oil filter. Half depth would work about as well, I think. I like Dan’s hydroformed part because it looks cool and it seems it would be easier to clean spilled or leaked oil out.
 
I blew a bubble recess for a project today. Made two extra. One inch deep, maybe a fuzz more. Replaces the box recess, eliminates a bunch of seams and rivets. Want one? Send a PM, $100 plus shipping.
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Recess

Love it. Much easier.

Just a heads up to 7A builders. Check the drawings. One cable goes through the recess. Probably specific to the A model with Elastomeric Gear and IO-360-M1B. I bet it could go through just below the recess as well.
 
WingsOnWheels said:
I have a fixed-pitch O-360 6A with a 90degree oil filter adapter. With that configuration, the recess is not required or particularly useful.
Click to expand...

It does hold the center mounting block for the rudder pedals.... At least on the 6-6A. Not correct! see next two posts.
 
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gasman said:
It does hold the center mounting block for the rudder pedals.... At least on the 6-6A.
Click to expand...

Not on a -6 with the stock setup--the center block is supported by the F-6118 angle which is riveted to the LH center vertical stiffener on the firewall. The recess can be there or not; doesn't affect F-6118. See attached plan snip below.

Would be interesting to see how yours is set up, if not on the F-6118 angle.

Capture.JPG
 
Dan, nice job with that bubble recess! If you wanted to take that a few steps further, would be nice to mold all the stiffening ribs into the firewall to eliminate the aluminum angles and their associated rivet holes.

hg
 
hgerhardt said:
Not on a -6 with the stock setup--the center block is supported by the F-6118 angle which is riveted to the LH center vertical stiffener on the firewall. The recess can be there or not; doesn't affect F-6118. See attached plan snip below.

Would be interesting to see how yours is set up, if not on the F-6118 angle.

View attachment 47917
Click to expand...

I did alter mine. I wanted the blocks up another 3/4 of an inch and forgot what I fastened it to....... 23 years ago.
 
wirejock said:
Just a heads up to 7A builders. Check the drawings. One cable goes through the recess. Probably specific to the A model with Elastomeric Gear and IO-360-M1B. I bet it could go through just below the recess as well.
Click to expand...

I'll make up a tubular fitting which points as needed. Might hammerform the baseplane a little. For a control cable, a tube fitting pumped full of FireBarrier is bulletproof.

This style steel ball fitting would probably work, and there is always the classic grommet with SS shields.
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Recess

DanH said:
I'll make up a tubular fitting which points as needed. Might hammerform the baseplane a little. For a control cable, a tube fitting pumped full of FireBarrier is bulletproof.

This style steel ball fitting would probably work, and there is always the classic grommet with SS shields.
.
Click to expand...

Yep. That works perfect. Nice work.
 
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