RV-3B Dave's in Colorado

[David Paule]

Started installing components on the dummy firewall. This was fun work. I had to balance a number of issues simultaneously, like filter removal and the routing for the various hoses. As of now, the remote oil filter, the gascolator, the sensor manifold, sensors, oil reservoir are all located. None of the hoses are on order yet. The dummy firewall is proving to be a very good idea.



I had initially thought that possibly both the remote oil filter and the gascolator could get hung from the engine mount on Adel clamps but it turns out that they are sort of comfortable on the firewall itself. Access appears awful but is actually better than it looks.

One note - the Airwolf remote oil filter assembly comes with the CH48109-1 filter. This takes approximately an inch and a quarter to remove. The CH48108-1 filter is very similar, slightly lighter and an inch and a quarter shorter. So the longer CH48109-1 is a decent stand-in for the shorter filter. If the long one fits, the shorter one can be replaced.

I noticed that at least one of the parts of the Airwolf remote oil filter assembly was quite poorly deburred. Nicely anodized but they left a sharp edge in several places. Be careful.

It’ll need to be relocated slightly downward from the position shown, maybe 4-5 mm.

The new Dynon sensors are just a bit too fat to permit the manifold to be mounted in its normal mounting position. I made a small bracket that you can’t see in the photo and placed it on it’s side. The sensors are on the cabin side of the firewall where there’s excellent access. That frees up some firewall space and keeps the sensors where the environment is a bit more benign. You can see some of the sensors on the dummy firewall, and some of the fittings might get changed.



Looking around for a decent place to attach the cabin heat valve, and well, there wasn’t any. But I’d built the firewall recess to allow the standard oil filter to poke into it along with the prop governor. Since that Lycoming filter adapter got replaced with the remote one, there was some room in the top of the recess, close to the aircraft centerline. It turns out to be a good location. You’re probably thinking that access will be awful but with some judiciously-placed access ports in the recess, it won’t be too bad.



Remember the governor lever is aft of the firewall? A worry. My mentor had a brilliant suggestion: route the control cable to it through the side of the firewall recess, just like the cabin heat valve’s control. Yes, I’ll need to spend some time with the access ports for sure. But doable.

When I shortened the oil dipstick, I had a stub left over. It was kicking around a workbench, looking like it really ought to be useful somehow. I’d thought it was stainless but it’s aluminum. Van’s sells several different colored round control handle balls and I had at least one of each on hand. Never know when they’ll come in handy…. A red one was fitted to the dipstick stub and now I have a great little brake fluid reservoir dipstick.



Dave

[David Paule]

Figured this would be a good time to update the various schematics.









Dave

[koupster]

Dave,
I've really enjoyed following your posts.
The dummy firewall is a ingenious idea.
I'm wondering about putting the Dynon sensors on the cold side of the firewall. A mechanical failure of a sensor could put hot oil or fuel in the cockpit.

[David Paule]

David, good thought. The latest Dynon sensors have improved mechanical strength and vibration resistance compared to the earlier ones, and the fuel and oil sensors both have restrictors in their supply lines. I think that the overall risk is low, and that there's at least some chance that if one does fail, it'll fail with a slow leak rather than a gusher.

And if that happens, my left foot will be in the puddle. At least it wouldn't be dripping on the hot exhaust pipes, as it would if I mounted it forward of the firewall.

Dave

[David Paule]

I made a mount for one of the under-cowling temperature sensors and it weighed about 20 grams. The second one weight under 4 grams, so it was worth doing. Sorry, no photo of that, but it was made from a piece of 1/8” 6061-T6 sheet. This one will go on the warm side of the baffles. The other one will go on the cold side and I’ll hold off on their attachments until further into the engine installation.

After mocking up the governor control, it was annoyingly evident that there was no way I could run the control through the side of the firewall recess. I made a control lever extension to bring the line of action forward and while the extension itself was fine, it made the total travel become greater than the control cable’s capability, so that didn’t work. This left some sort of way to carry the cable into the recess while not having its support in the recess. Here’s a picture of the mock-up of something that works.



No part of this assembly, except for the governor, is flight-worthy at this point, especially the hardware and the control itself.

One thing that was very necessary was to add some sort of access to the back of the recess. The access port started off well, using a 3/4” hole saw. The material is .020 grade 2 Titanium.



But cutting the outline out proved to be probably one of the worst jobs so far on this project. Turns out that the only tools I could apply were a nibbler, which didn’t work here, and a cut-off wheel on a die grinder. Well, attempting to make a groove and work it deeper was totally the wrong approach. The titanium formed around the cut-off wheel and then hardened. The spray of incandescent particles hid the marked line. This did not work.

But cutting through and then running the cut-off wheel along the line worked well enough. However, I did go past one of the corner radiuses a little bit and I had to patch that. This whole cut-out was not a fun job.

Cleaning up the cut edge was equally enjoyable. My Vixen file did make progress, but at a microscopic rate, and even at that it took a lot of force to make any change. I tried a sanding drum on the Dremel and surprisingly, that proved effective. It ran through drums at an alarming rate but did the job. You can see the corner error at the lower right.



Making this hole and the cover, not shown, took a day’s work session.

I later patched the corner error and added nutplates for the cover.

Dave

[rockitdoc]

Nice work, Dave. However, I am curious how you fixed the cut in the Ti. Welding that stuff is pretty tricky, but if anyone knows how.....

[David Paule]

Just riveted a patch on. Nothing fancy, Scott. Two -3 rivets on either side of the slit, and dimpled the holes.

Dave

[David Paule]

After learning how to attach coax cable to the BNC connectors used on the Delta Pop antennas and the TNC connectors used on the Dynon transponder and Trig com radio, I figured that this would be a grand time to see if the antennas fit on the airplane and if the cables fit their respective components. To my pleasant surprise, everything fits fine. Still not sure how that happened.

The cables and connectors were another skill to learn, and needed the usual new tool. Thanks, Steinair.com, for the and the BNC video which made the learning curve almost disappear. The TNC connector goes on the same way but with different dimensions, which are given in the manuals.



antennas above and below, the com antenna cable.



Remember that I’ll need to fit the fuel tank vent lines around the com antenna cable. Thanks to my mentor for reminding me; I'd forgotten. That's the transponder and its cable below.



All the engine control cables except for the throttle cable arrived. The throttle cable is a bit undefined since I can’t hang the carb on the engine just yet. This order, from McFarlane Aviation, included the

Prop governor cable,
Mixture cable,
Carb heat cable,
Cabin heat cable.

The first two are vernier-assist cables. The last two are basic Bowden cables. McFarlane sold me labeled knobs for these. The cabin heat cable goes through the firewall in the side of the firewall recess, so I drilled a hole for that, after first deciding how to fire-block the small hole. I’d had to ascertain that there’s enough access from the front of the firewall to install the cable on the valve. There is, but it won’t be a job that I’ll enjoy. Still, there's another way: remove the four cabin heat valve attach screws, which are inside the cabin on the recess, readily accessible, and then the valve can move around a bit for easier maintenance.

The stiffened governor cable attach bracket is ready to install now, too. I added a flange to stiffen it.

Here’s the Titanium foil overlay for the firewall insulation, with the Fiberfrax ceramic insulation that I’d previously cut to match the firewall resting on it. I’m in the middle of drilling holes in the foil.



The thin Titanium was easy to cut with shears - I think scissors might work but I didn’t want to dull them - and the edge was not particularly hazardous. I deburred the edges with a fine mill file. The recess hasn’t been cut yet, one of numerous operations still pending.

Drilling holes up to 3/16” is straight forward. I used a step drill to drill one of the 1/2" holes and that did not go so well. Nice hole but a monstrous burr, which I filed down. I'll try a punch next.

Dave

[terrye]

Dave,
Suggest you try Hougen hole saws for your firewall. Back them up with a piece of plywood. Worked excellent on my stock stainless steel firewall on my RV-9A.
https://hougen.com/cutters/sheet-met...olcutters.html

Have a look around on the website for the kits of multiple saws and mandrel. Available from the usual suspects.

[David Paule]

Hole saws work well, but these are 1/2" holes and they are not readily available here in that size. The ones you recommended don't go that small.

Thanks, though!

Dave