More Filtered Airbox Work – 8 hrs

Sunday April 28, 2013

I worked mostly on the filtered air box this weekend but I also made a small doubler plate for the front left engine baffle section because I realized the gap to the engine there is too large to seal with RTV. I used a piece of scrape aluminum from the baffle trimmings and painted it red like the rest of the baffles. It is riveted on in this picture with the four unpainted rivets in the lower right corner.

 

So then on to the airbox again. I made the six aluminum retainers for the filter, aligned them to be flush with the filter cutout, drilled, dimpled and installed nut plates. This photo shows you how they fit with the filter.

 

I went out to Corona on Saturday to take my biennial flight review (I passed) and I stopped at ACS to pick up a few things including a 2 x 2 foot sheet of .032 alclad aluminum 2024-T3. From that stock I made a doubler plate for the .062 thick top mount for the FAB. You can see it on the left in this picture after I scuffed up the surfaces of the plates for bonding.

 

I want a uniform thin layer of ProSeal between these two plates so I made some small shims out of .016 thick aluminum stock and epoxied them down to the .062 thick plate as a first step for bonding. I allowed the epoxy to cure about 5 hours and removed all the excess with MEK and fine sand paper. Then I mixed up a batch of ProSeal and spread it out thin over the plates (but not on the shims). I put the two plates together and aligned them with clecos, then I removed the clecos and stacked a piece of plywood on top and added several gallon paint cans to press it down. After about 10 minutes I removed the paint cans and plywood and found that the two plates had shifted relative to each other. The ProSeal is like a lubricant and it allowed the top plate to flow because the table is not perfectly level. It was clear I need a way to maintain plate alignment while this cures.

 

I drilled holes in the plywood to allow clecos to pass through with clearance around each one and I drilled six holes in the table top so the cleco tips would not touch the table either. Now the clecos align the two plates in plane and the plywood just presses down on the plates for uniform pressure. You can see I put wax paper on each side of the plates stack to keep it from sticking to the table and the plywood.

 

Here you can see four gallon paint cans and a 10 lb bag of cat litter on top squishing it all down to apply pressure while this cures. It will take a couple of days to set up so I won’t find out until at least Tuesday if this was a success.

 

I also drilled the airbox top cover flange to the fiberglass shell this weekend – except for the part in front of the upward bend that is. The plans say to wait on that part until the vertical alignment of the top plate is set with the cowl opening. The bare fiberglass shell is kinda ugly so I sanded it and sprayed on a coat of white primer. An hour later I found a bazillion pin holes so I put on an additional coat of UV smooth prime because it fills the pin holes better than Stewart Systems primer.

 

I also carved the airbox foam block enough to fit it into the front air intake opening. This is in preparation for carving out a hole and laying up a fiberglass tunnel to the air box. I have to wait until the air box is assembled and back on the engine and aligned before I bond this plug in place and start carving.

 

This photo shows the approximate line around the intake scoop that I am considering cutting to make the scoop removable for easier cowling installation. The line will be at the top of the tape leaving just enough room for a ring of screws (probably six).

Filtered Air Box Construction – 1.5 hrs

Wednesday Apr 24, 2013

A couple of days ago I cut out a piece of .025 thick alclad sheet to fit into the bottom of the filtered air box fiberglass shell. That is because I have heard of cases where vibration caused the filter to literally rub through the fiberglass. The aluminum sheet just provides a harder surface against which the filter contacts so hopefully, if anything, the filter will wear and not the aluminum. I glued the aluminum sheet into the shell using ProSeal and tonight it was pretty well set up.

The evolution of the filtered air box continued tonight as I fit the top plate to the fiberglass shell. The top plate needs to bend upward near the air inlet so I cut two notches in the side walls and made a slight bend between those two notches so the top plate generally follows the angle of the fiberglass shell.

I flipped the top plate over and drilled four additional holes to attach to the top mount as well as hold the clips that restrain the position of the filter. I cut the raw stock for the clips and match drilled them to the top plate in the positions required to hold the filter just inside the cutout in the top plate. The filter actually sits flush against the top mount.

Here is the quasi-assembled air box with the filter installed.

Finished Riveting Engine Baffles – 6 hrs

Sunday April 21, 2013

There were lots of chores needing attention around the house this weekend so I only had time to do a few things on the airplane. At least I finished riveting all the rubber seal strips to the engine baffles with a little RTV on the surfaces to seal up air leaks. I’m glad to have this done. My hands are sore from squeezing all the pop rivets.

This view shows the aft side of the spinner area.

I also did some more trimming of the filtered air box top. It is now a little over 2 inches from the front edge to the inside edge of the inlet. That should be enough that the cowl can drop straight down without hitting the top cover. I am mentally struggling with how much gap to put between the air box and the inlet scoop. I am concerned about making the gap too small because of the threads I have read about FAB top plate cracking, perhaps caused by forces put on the FAB at engine startup due to relative motion between the FAB and the cowl. But a large gap may be harder to seal effectively. I also want to make the cowl as easy to install as possible and the FAB seal can be a major factor in that. I had a few questions I posted on the VAF forums so I am waiting to see what responses I get before proceeding.

I also sanded the exterior of the top cowl this weekend in preparation for applying a seal coat of thinned epoxy. No pictures of that.

Installed Alternator Blast Tube – 1.5 hrs

Wednesday April 17, 2013

Monday night I painted the blast tube duct for the alternator with some glossy high temperature rattle can paint. That was dry tonight so I riveted it to the alternator aft cover and installed the corrugated blast tube.

I re-installed the cover onto the alternator and routed the other end of the blast tube to the hole in the inlet ramp. Notice that the tube routes downward through a 180 degree bend and back up to the duct that directs the air into the cover and directly onto the cooling fins of the voltage regulator. This 180 bend is my trick to keep rain water out of the alternator. I drilled a small #40 hole at the low point of the bend in the corrugated tube. It will leak a little bit of air there but any rain water that gets into the blast tube from prop wash will collect at the low point and be ejected by this drain hole. It won’t prevent moist saturated air from entering the alternator but I have not heard of that being a problem.

Now I have two more blast tubes to figure out how to route; one for each P-Mag.

Started Filtered Air Box – 4 hrs

Sunday April 14, 2013

Today I started working on the filtered air box, also known as FAB. I am hoping this does not turn out to be as big of a project as the engine baffles but it didn’t take long to encounter the first problem. The Airflow Performance fuel injection kit came with a nice gold anodized FAB adapter plate that is pre-drilled to fit the clamping collar that attaches it to the servo. They even made it thicker (.090) than the standard top plate – I assume because of the many reports of the adapter plate cracking. I clamped the adapter plate to the air box top plate and mounted it to the servo for a check fit to the cowling.

First I found that the air box top plate is too long and interferes with the cowl but this was to be expected. So I cut an inch off the front end and tried again. This time nothing interfered and I was able to see the impact of the offset of the fuel servo from the centerline of the cowl. I could rotate the air box top plate to point directly at the cowl air inlet but there was only about 3/8 inch clearance between the air box top plate and the inside surface of the cowl along the side of the air box. I was not comfortable with that little clearance because of the relative motion that occurs at engine start up and shut down. So I began investigating options to slide the adapter plate sideways a bit to increase clearance. I want at least an additional 1/4 inch or a total of about 5/8. Unfortunately when I tried to slide the AFP adapter plate that far to the side two of the six holes that will mount it to the air box top plate have less than acceptable edge distances. After looking for options for a while I finally concluded that I need to make a new adapter plate that has the center hole offset by at least 1/4 inch and is wider to maintain hole edge distances. I used the AFP part as a template. In this photo you can see the new plate underneath the gold AFP adapter. I roughed out the new adapter with extra material on the near side for the mounting holes.

I sanded about 1/8 inch off the side of the AFP plate so I could slide it a little further and transferred the center holes for the fuel servo to the new adapter plate. Here is the new adapter plate mounted to the air box top plate. I used two holes to connect them temporarily with clecos. You can’t see it in this photo but I also trimmed about 1/4 inch off the inside edge of the top plate center cut-out on that same side to allow the air filter to sit flush against the adapter plate all around. This means the shape of the air filter will be slightly elongated on the left side compared to the standard oval race track shape. I don’t see any way this can cause a problem.

When I put the new setup on the engine for another fit check I measured a clearance right at 3/4 inch which is the thickness of the middle knuckle on my right middle finger (precision gauging). This is much more comfortable to me than 3/8 inch. This is a lousy picture looking in from the exhaust exit of the cowl but you can get the idea of the clearance along the side of the silver top plate. The clearance will decrease about 1/16 inch when I install the fiberglass air box.

As far as the new adapter plate is concerned, I made it from .062 alclad 2024-T3 stock. I considered using .090 stock like the AFP part but there are reports of even those cracking. I suspect the problem is also related to the stiffness of the rubber coupling between the FAB and the cowl inlet which puts loads on the FAB every time the engine is started but that is really a hypothesis. Another theory is the vibrations of the engine are causing fatigue failure. So my approach is designed to address both theories.  I plan to make a doubler out of .032 thick 2024-T3 alclad and bond it to the new .062 thick adapter with a thin layer (~.010) of Proseal. That will give me a total aluminum thickness of .095 for strength and the Proseal will add some damping to the plate to attenuate vibration response. I will also make the rubber coupling between the air box and the cowl snout as compliant as I can. Of course I will inspect the new adapter part regularly to look for evidence of cracking but I think this design approach gives me a good chance of avoiding the problem. We will see.

Cowling and Alternator Blast Tube – 5 hrs

Saturday April 13, 2013

The cowl surfaces are rather porous in the stock condition so the plans recommend that the surfaces be sealed with a thin layer of epoxy. But because the surface has tiny holes that the epoxy will not flow into naturally the epoxy should be thinned with acetone at about a 1 to 1 ratio. This morning I sanded the interior surface of the upper cowl and brushed on a thin layer as prescribed. The acetone slows down the curing process so it will sit a few days before I sand off the gloss in preparation for a coat of primer.

The instructions for the Plane Power alternator call for a blast tube to direct cooling air into the back opening of the alternator case. I did some research on this in the forums to determine how to mount the blast tube. The alternator is near the front of the engine so the standard place for the tube is in the right inlet ramp just behind the cowl nostril. I saw various ways of attaching the blast tube to the alternator, none of which I really liked. I also read of cases of alternator failure in rain conditions which is more likely to occur with the blast tube so near the air inlet of the cowl. So I decided to try to come up with a better way of mounting the blast tube to the alternator and reduce the risk of water blowing into the alternator case. I don’t know for sure that the water is a problem for the alternator but it seems like it can’t be a good thing.

To attach the blast tube to the alternator I designed a duct that I will rivet directly alternator rear cover. I removed the cover and built a mockup using  file folder paper. Then I made it from two pieces of .025 aluminum sheet epoxied and riveted together, mounting directly over the air inlets of the alternator. Here it is clecoed to the alternator rear cover with a blast tube installed.

Here is a side view showing how it is mounted to the cover. Air comes through the blast tube, turns 90 degrees and enters the alternator cover, exhausting out through the vents further forward on the alternator.

From the inside of the cover you can see the two square holes where the air will enter. I will give the epoxy a couple of days to fully cure then I will prime the duct and rivet it to the cover.

I will show you how I plan to address the water problem when I install this to the alternator.

Painted Engine Baffles – 6 hrs

Thursday April 11, 2013

I decided to paint my engine baffles this week. The alodine finish was OK but the parts lacked the finishing touch I was hoping for so I picked up several cans of  Ford red high-temp engine paint at the auto parts store. Now the baffles have a definite visual punch. I tried to find a gold color that would match the engine crankcase but had no luck. So I went with the strong statement of contrasting red. The color matches the ignition wires nicely. Compare this photo to the pre-painted photo on April 6th.

This view is from the oil cooler side. It looks kinda stunning.

And for good measure here is another shot from the right rear quarter.

Finished Fitting Seals – 4 hrs

Sunday April 7, 2013

I continued working on the baffle seals today finally getting to the cowl-mounted seal strips that seal up the gaps between the cowl and the inlet ramps. You start by sanding the inside surface of the cowl to get a smooth surface for the seal. Then I bent a 1/2 wide aluminum strip to match the inside profile of the inlets. Here is a view of the right inlet. The strips have to be fairly thick because they are only attached along the flat portion of the cowl. The stiffness of the aluminum strip provides pressure to hold the seal in place as it wraps around the curved portion of the cowl. I trimmed the left end of the strip after I took this picture.

As before I made a paper mockup of the seal to get a close approximation of the final shape for the rubber material. Here is the left seal after cutting the material, match drilling the aluminum strip to the cowl and the rubber seal and putting it back on the airplane for inspection. It seems to seal fit pretty well and I expect it to seat even better after a few hours of flight time.

Here is a view of the interface with the baffle seals on the inboard side around the ring gear.

More Baffle Seals – 6 hrs

Saturday April 6, 2013

Some of the seal pieces turned out to be pretty odd shapes. This is one example. I’m glad I mocked this up in paper templates before cutting away on the rubber sheet. You could waste a lot of rubber sheet experimenting to get a good fit.

My friend Scott came over to lend a hand this morning. We finished up all the rubber seals around the ring gear section.

Here is a dumb picture of me. Scott insisted that I don’t have enough pictures of myself working in the airplane in the blog.

Here is some detail of the rubber strip segments cut to fit around the inlet ducts. This was the hardest area to get a good fit.

Here is another view of the left inlet duct. Notice how the strips overlap.

And this is the right side…

And the right inlet duct near the ring gear…

We also worked on installing the control cable for the AFP fuel injection purge valve. I bought a 60 inch long cable from McFarlane for this. It runs from the valve through a hole in the baffle on the left rear side.

I made a special bracket to anchor the cable to the crankcase using some existing hardware. I wrapped silicon tape around the cable to allow it to be securely gripped by an adel clamp.

The cable exists the baffle through a snap bushing and then passes through the firewall through a stainless steel eyeball.

From there it is a direct run to the panel. The purge valve control is just to the right of the mixture knob. The control is a push to unlock cable so you have to deliberately push the button to move the control. Sixty inches was just barely enough. Two more inches would have been good but the standard sizes are in one foot increments and 72 inches would have been much too long.

Making Baffle Seals – 5 hrs

Thursday Apr 4, 2013

Tonight I finished cutting and fitting the rubber seal strips along the side baffles for the engine. The brown paper templates are gradually going away.