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Archive for January, 2013

Started Making Cowl Modifications – 3 hrs

January 28, 2013 Leave a comment

Monday Jan 28, 2013

Now that the cowl is trimmed to the fuselage and the hinges are fitted I need to fix a few issues with the overall shape of the cowl. Specifically, the gap between the front face and the prop spinner bulkhead is not uniform. It is 0.25 at the top but about .55 along the bottom. Other builders have reported similar issues so I am not alone in this. Additionally, the outer edges of the nostrils don’t line up exactly either with the upper cowl overhanging the lower cowl slightly. So I need to do some fiberglass work to overcome these irregularities.

I started by making a foam ring segment to attach to the front edge. This foam ring started out a uniform .25 thickness and I glued it to the front surface of the prop opening with epoxy. After the epoxy set I sanded to the foam to taper it from essentially zero thickness to .25 for a relatively uniform wedge.

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Here is a photo with the foam attached and the cowl installed. You can see how it fills the gap and will result in a spinner gap that is much more uniform thickness at about 0.25 inch. Now I need to reinforce it with fiberglass and blend it into the existing cowl lines.

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The next step in the process is to lay down a layer of Rutan bidirectional cloth over the foam to give it strength. This step is kinda ugly but it leaves a strong surface that is close enough to the finished surface that I won’t have to build up a thick layer of filler over this large area. While I was mixing epoxy I also made a flox mixture and built up the lower cowl nostrils near the hinge pins to start to bring those into a shape that will blend in smoothly with the upper nostrils. Next step will be sanding to a rough stage for the next layer of epoxy with micro filler to get to a near finished profile if I am lucky. It will be more stages if I am not lucky. It’s just a matter of time.

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Categories: Cowling

Finished Fitting Cowl to Firewall – 11 hrs

January 26, 2013 Leave a comment

Saturday Jan 26, 2013

I continued to work on the cowl this week, fitting it to the fuselage. Some of this work I did in a few short session during the week but eight hours of it was completed today. This whole process is very iterative, requiring the cowl to go on and off the fuselage many times. I generally followed the Van’s instructions with a few tips I picked up on the web. I won’t describe every detail of this process but I will show the major stages.

In this photo I have the lower cowl taped in place so I can mark it for trimming. The first step is to mark and cut the lower edge under the fuselage and match drill the two short cowl segments to the lower hinges. Then I marked the sides for trimming.

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After trimming the sides and sanding the edges right up to the edge of the fuselage skin I drilled the vertical side edges to the hinges. Then I put the lower cowl on with the upper cowl overhanging the horizontal edges so I could mark a trim line for the lower cowl.

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With the lower cowl trimmed and sanded to the edge of the upper cowl along the horizontal edges I started installing the horizontal hinges. The plans say to allow the hinge to creep upward toward the aft end so here is my interpretation of that.

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In this shot the lower cowl has been match drilled to the horizontal hinges.

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Finally the upper cowl is match drilled to the horizontal hinges.

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Categories: Cowling

Match Drilled Upper Cowl – 3 hrs

January 17, 2013 Leave a comment

Thursday Jan 17, 2012

After futzing around with the upper canopy alignment and sanding the aft edge to the final, good-as-its-gonna-get shape I match drilled the upper cowl to the hinges.

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Here is a close-up of the aft edge. I have a gap of about .020 – .030 inch at this stage. It will be easy enough to sand a little more off when it comes time to paint to prevent chipping but that is a long time off. In the mean time, this gap is good. I installed the full size .125 aluminum hinge pins before I drilled the holes for the hinge rivets because I want the hinge aligned as close to nominal as I can get for this drilling. My theory is the hinge pins will be easier to install later if the eyelets are all aligned close to nominal during drilling. If I drilled with the .093 pins installed the alignment of the hinge halves could vary along the hinge line by the slop of the pin.

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Categories: Cowling, Finishing Kit

Cowl Hinges, Part 2 – 2 hrs

January 13, 2013 Leave a comment

Sunday Jan 13, 2013

Today I did some more work on the cowl hinges. I had to study the drawing a while to determine where to locate the vertical side hinges and how to trim them. The key came in understanding that the horizontal edges of the upper cowl along the sides are essentially good to go without trimming. I just need to sand them a bit to make them straight and true. That gave me the location of the horizontal side hinges and can align the upper edge of the vertical side hinges to that. I cut the left side hinge accordingly and match drilled it to the fuselage.

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I also fit the cowl portion of the upper hinges to the firewall portion of the hinges along the top. Because the hinges are bent into curves that follow the skin profile the gaps between the eyelets of the hinges are reduced to the point where you can’t easily slide the hinge eyelets together. To alleviate this the plans say to file the edges of the eyelets slightly to taper them to match the radials of the skin profile. So I did that and cut the hinge pins to length. I used the .090 pins included in the FWF kit but that leaves the joint pretty sloppy. I will probably try the .125 diameter pins although I know I will have to work to prebend the pins and taper the leading end to be able to get them in easily. I think the kit has enough .125 pin stock for the entire cowl.

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I also drilled three #40 holes inside the cowl nostrils to hold the upper and lower cowl halves together up front.

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Categories: Cowling

Trimmed Upper Cowl at Firewall – 8 hrs

January 12, 2013 Leave a comment

Saturday Jan 12, 2013

The prop extendsion that I ordered from Saber Manufacturing came in on Thursday and I need it installed to align the cowl so that seemed like a good place to start today. The extension is basically a spacer that places the prop at the correct distance from the flywheel for the cowl and spinner dome. This one is made specifically for the Catto 3-blade prop and is 2-1/4 inch thick aluminum with stainless steel inserts. It was kinda pricey but this one is recommended by Craig Catto and is very well made. Installation onto the flywheel was easy with no problems encountered.

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The spinner bulkhead was a different story. I expected it to slip right on but the bolt holes were too small to fit the stainless steel insert tubes for the bolts. It took me a while to discover that this spinner is made for an O-320 engine which uses 7/16 prop bolts, whereas the O-360 uses 1/2 inch prop bolts. You have to enlarge the holes in the spinner bulkhead for the larger bolts/inserts. After enlarging the six bolt holes to 3/4 inch with a unibit to fit over the IO-360 inserts and deburring everything I mounted the spinner bulkhead to the prop extension using the crazy expensive prop bolts ($16 each) that came with the extension from Saber. Because I don’t have the prop or crush plate installed I used some leftover PVC pipe to make spacers so I could snug up the bolts to clamp the spinner bulkhead firmly against the extension.

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Here is another view that clearly shows the stack up of parts.

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Another step necessary to align the upper cowl is to install the hinge strips along the upper flange of the firewall. I considered using 1/4 turn fasteners along the upper cowl to attach it to the firewall but ultimately decided to stay with the Vans stock hinge method. I like the ease of removing the 1/4 turn fasteners but I really like the clean, almost invisible seams of the hinge method. I also read of issues with puckering between fasteners with the 1/4 turns and don’t forget the additional cost (about $180) just for the upper firewall kit). I think there are techniques that can eliminate or minimize the puckering but it requires extra work and cost. So for this kit I am sticking with the stock design. After all, 1/4 turn fasteners can be retrofit later if the hinges turn out to be a pain.

I measured out and cut two pieces of the larger piano hinge material for the upper firewall flange per the instructions. I offset the hinge forward about 1/16 inch so the notches between hinge eyelets will be buried under the cowl and won’t be visible through the gap. With the hinges aligned and held by cleco clamps I match drilled through the firewall flange and the hinge.

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A long slot has to be cut in the lower cowl for the nose gear strut. At first I was struggling with finding the exact center of the cowl because there are no square edges on this thing to measure from but then it occurred to me I could use a plumb bob and locate the center relative to the two side walls. I put a long steel ruler on the floor to measure the width of the cowl and then adjusted the plumb bob to fall at the mid point of this width. I marked the cowl at that point and laid out the slot dimensions relative to that.

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I cut the slot a little under size for now. The plans call for a 1-3/8 slot but I cut it 1-1/4 in case I need to bias it a little one way or the other once I get it mounted to the fuselage and find out exactly where the strut falls relative to the centerline. I’m hoping everything will match up closely. I cut the slot with a cutting wheel on my electric cut-off tool and smoothed the edges with sand paper.

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Then I put the upper cowl on the fuselage and aligned it as best I could. I set a 0.20 inch gap between the front of the cowl and the back of the spinner bulkhead. I also put a small block of wood on the flywheel gear to raise the cowl to center the spinner bulkhead with the front opening in the cowl. Actually, I tried to bias the cowl about 1/8 inch below this point to allow for future settling of the engine on the mounts. I also checked side to side to make sure the cowl was level.

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In this picture you can see the gap between the cowl and the spinner bulkhead. No the gap is not uniform. As you can see it gets larger toward the lower edge of the cowl. Some of this will disappear when I attach the upper cowl to the lower cowl in the nostrils. The rest I will have to take out with epoxy and filler. This is really common with these pink pepto cowls.

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Before I aligned the upper cowl I drew a line on the fuselage skin two inches aft of the front edge of the firewall as a reference line. Then with the cowl placed on the fuselage and aligned as described above I drew a line on the cowl 2 inches forward of the reference line. This line should correspond with the forward edge of the firewall.

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I took the cowl off the fuselage and cut the excess material off the aft end based on my line. I was not brave enough to cut right to the line on the first try. In fact I cut about 1/8 inch shy of the line and sanded the edge smooth for the first test fitting. It took about 5 or six iterations on the fuselage, measuring, and sanding to fit to get it to where you see it now. I have 0.2 inch clearance between the spinner bulkhead and the cowl and the fit along the firewall edge is quite good. I used a 12-inch long block of wood with sandpaper attached to get a nice straight finished edge. This all took a fair amount of time since I was afraid to take large steps for fear of over trimming.

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Last but not least I cut the whole in the upper cowl for the oil filler access door. I left 3/8 inch overlap for the perimeter of the door and rounded the inside radii as you can see here. The edges were all well smoothed with sand paper as recommended in the plans.

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Categories: Cowling, Engine

Exhaust System Install, Part 1 – 1.5 hrs

January 8, 2013 Leave a comment

Tuesday Jan 8, 2013

Hot dog – my Vetterman exhaust system arrived in the mail today! This is a 4-to-2 crossover system with mufflers using 1.5 inch pipes. Larry Vetterman claims the 1.5 inch pipes provide as good or better performance than the conventional 1.75 inch pipes with less weight and a bit less crowding in the FWF section. Here are all the parts in the box (no they did not arrive loose in the box this way).

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I was anxious to get the exhaust installed so I can see if my throttle and mixture cable arrangements are acceptable. I was surprised how quickly the basic exhaust stack went on, however I still have to figure out how to orient the lower tail pipe sections and how to install the hangers that support those sections. You kinda need to install the lower cowling to get the optimum position for the pipes as they exit the cowl. It’s always the chicken and the egg problem on the FWF! Figuring out exactly what to do first is the big challenge. On the left side the muffler includes a heat muff that I don’t plan to use so the orientation is arbitrary. I will probably point the ports down so any moisture that condenses can run out easily.

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The right side heat muff will be connected to the port on the cylinder baffle and the air box on the firewall. It looks like there is plenty of clearance for that.

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Categories: Exhaust, Firewall Forward

Cowl, Part 2 – 1.5 hrs

January 7, 2013 Leave a comment

Monday Jan 7, 2013

Tonight I did some work cleaning up the cowl joints at the spinner overlap. Looking at the interior surfaces below you can see that the layup is very rough and irregular. The thickness varies a lot and there are ridges in several places that should not be there. No wonder the two halves of the cowl don’t want to mate together here.

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I took my dremel rotary tool with a drum sander and cleaned up the interior surfaces of the upper cowl and the exterior of the lower cowl. Hopefully this will help improve the fit at these joints.

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I also trimmed the oil filler access door to the finished dimensions and I marked the cowl opening underneath with 3/8 inch overlap around the perimeter. In addition, I ordered a hidden hinge from NonStopAviation.com today. At $40 it is pricey but it will save me time compared to making one from scratch and probably having to iterate a few times to get it right.

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Categories: Cowling, Finishing Kit