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Cowl, Oil Door, Exhaust, etc. – 9 hrs

February 17, 2013 Leave a comment

Sunday Feb 17, 2013

It’s been a very busy weekend. I didn’t have as much time as I wanted to work on the airplane because I had to replace and paint some base molding that was damaged by a water leak recently but I got quite a bit done anyway. First, I trimmed and sanded out the epoxy and microlight filler layups I placed a few days ago in the outer nostrils of the air intakes to make flanges. As you can see it turned out pretty well. Not ready for paint but good for a first cut. The rest is just making it prettier.

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I also sanded the epoxy layer I added to the inside of the oil door. This is ready to prime and seal, then I will rivet in the latches.

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Another recent mini-project has been the lower cowl brace which I primed and assembled yesterday. Here are the parts ready for installation.

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I called Clint at Vetterman Exhaust last week and asked him about the unused heat muff in the exhaust system. Since I plan to use only one heat muff the other will not have forced air. I read somewhere that if left uncooled it will get very hot and could damage the cowl. Clint recommended three options; 1) duct air to the muff to cool it, 2) take the outer shell off the muff to allow air flow around the muffler, or 3) replace the muff with a bent sheet of aluminum alclad that wraps only half way around the muffler. I chose option 3 as you see in the photo below. With half the shell open the muffler should not overheat and the aluminum shell will act as a thermal shield to protect the mixture cable which is right behind it.

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Installing the lower cowl brace was a pain in the neck but as you can see in this picture I got it in. I also bent and fitted the final hinge wires for the lower hinges. These wires have long “handle” extensions that overlap the center brace and then poke through holes in the lower brace to retain them. You can see them if you look carefully on either side of the brace. Something else I did was rivet the cowl hinges to the sides and bottom of the fuselage.

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With the lower cowl and cowl brace installed I was ready to finalize the positions of the exhaust pipes. As you can see above, the pipes come fairly close to the cowl, engine mount tubes, and the edge of the fuselage. Each exhaust pipe has a slip joint right in front of the muffler that allows the aft section of the pipe to be rotated to “aim” the joggle for best fit and clearance. I tweaked the pipe alignment about as much as I could and when I thought I could get it no better I decided it was time to lock it down. The aft section of each pipe is locked to the front section with a split collar with  1/4 inch diameter internal pin. You have to drill a 1/4 inch hole through the joint for the pin and then clamp it together with an AN3 bolts and lock nut. I mustered my courage and drilled. In this next photo you can see the clamp installed one of the slip joints.

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The next few photos are just to illustrate the exhaust pipe supports and clearances to various critical components like control cables and fuel lines. It is hard to see in two dimensional pictures but everything seems to have reasonable clearances. The forward supports for the exhaust pipes connect to engine sump bolts. There is also a horizontal support that ties the two pipes together.

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In this view you can see the right side.

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I recently ordered a longer fuel line (part number VA-139) because the “standard” one that came with the kit would not reach to the AFP fuel servo inlet. As it is, the VA-139 is just barely long enough.

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This photo gives you an idea how much clearance the throttle cable has to the engine mount and exhaust. I also ordered a 46.5 inch long throttle cable from Vans because the standard 44.5 inch cable was a little tighter than I liked under the panel. The 46.5 inch cable allows for a more slack routing.

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This photo gives a good view of the mixture cable and it’s clearance from the exhaust. I may put a fire sleeve around the mixture cable to further protect the rubber seals from the heat.

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Back on the cowl I drilled holes in the hinges for bonding. These holes will improve the strength of the bond according to Vans. I used a 3/16 drill because the 1/4 inch holes recommended in the plans looked too big to me. Since the extra holes are called “optional” in the plans I figure I have some latitude here.

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Finally, I started work on hinge pin covers for the horizontal cowl hinges. I sketched six round patches on a piece of 8 oz Rutan cloth. These sketches are about 2.5 inches in diameter which will give some margin for 2-inch cover plates.

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I placed this between two pieces of plastic drop cloth, poured in some epoxy, and rolled it out to make prepreg cloth. After I cut the round patterns out with a roller knife I applied packing tape over the hinge pin access area and laid up three layers of prepreg on each side. I will let this cure to make stock for 2-inch access covers.

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Oil Access Door and Lower Cowl Brace – 5 hrs

February 13, 2013 Leave a comment

Wednesday Feb 13, 2013

I sanded the fiberglass layup on the inside of the oil access door and I am pretty happy with how it looks at this point but the epoxy layer over the foam is pretty thin so I decided to apply an additional layer of epoxy/micro to give me a little stronger structure and a layer I can sand out smooth. I was afraid of cutting through the glass layer without it.

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So here is the epoxy/micro layer I applied over the original layup. I will let this set up and sand it out tomorrow or Friday.

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I also started building the lower cowl brace which is unique to the nose gear models. It secures the two sections of cowl that straddle the nose gear tube since you have to cut a big slot down the middle of the cowl. The slot is extra long on the 3-blade prop version which I am building. These are the individual parts that I predrilled with all the holes I can drill before actually fitting it to the cowl and nose gear structure.

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This next photo is after fitting it. What a huge pain working under the fuselage with barely any room to stick my hands in there, especially with the exhaust in the way also. It would have been easier to do this before the exhaust pipes were installed but I wanted to determine how to orient the pipes with the cowl installed so it is the old chicken and the egg problem. Now I need the rivet these parts together and maybe prime them before the final installation.

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This photo shows the brace attached to the lower fuselage, nose gear structure, and cowl. I used free running nuts for the fit up but the final install with use lock nuts. At least I should be able to do the final installation without the cowl in place. That should make it easier.

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Another task I started tonight is to add flanges to the outer nostril seams between the upper and lower cowls. Stock from the factory they just butt up against each other. I want an overlapping flange so forward air pressure does not blast directly into this joint causing it to spread apart. I taped the surfaces I don’t want epoxy to stick to and mixed up some epoxy/flox and put down a thick layer. The flow should strengthen the epoxy. I gently applied a layer of peal ply to smooth out the inner surface for less sanding.

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Here you can see that the cowl is facing nose down so the epoxy does not flow out or create runs. We’ll see how it looks tomorrow.

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Categories: Cowling, Lower Cowl Brace