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Archive for February, 2013

Started Trimming Baffles – 1.5 hrs

February 28, 2013 Leave a comment

Thursday Feb 28, 2013

Tonight I began trimming the engine baffles starting with the inlet ramps. Initially I installed the stock ramps then I tried to mount the lower cowl to the fuselage. It wouldn’t go on of course because the inlet ramps interfere with the cowl but I could get a general idea where to trim. I used snips to gradually trim the forward and outboard edges of the two ramps until I could just barely get the cowl hinges in line and the pins installed. Then I laid out trim lines on the ramps per the instructions. In the photo below you can see some of the minor trim cuts on the left inlet ramp and the lines I drew for the side and forward cuts.

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And this is the right side inlet baffle. Same deal here.

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Categories: Engine Baffles

Hinge Riveting Revisited – 1.5 hrs

February 25, 2013 Leave a comment

Monday Feb 25, 2013

Tonight I am documenting some lessons learned regarding the bonding and riveting of hinges to the cowl. My thoughts are prompted by two problems I discovered tonight; first I could not put the top and bottom cowl together, and second I could not get the hinge pins installed. I discovered that even a small amount of epoxy squeeze-out where the mating hinge eyelets fit will keep the two hinge sides from fully mating and that will prevent the hinge pins from going in. I spent the better part of two hours cleaning excess epoxy out of the nooks and crannies around the hinge eyelets. In three or four place there was even epoxy inside the eyelet. Even after cleaning out around all the horizontal side hinge eyelets I found that the hinge pins are much tighter now than they were with just clecos installed. They may loosen up a bit in time but I really liked how easily they went in before bonding and riveting. So based on my own experience here are the lessons I learned.

1) Don’t use flocked cotton in the epoxy. It is fibrous and does not flow out well in small gaps so it causes some buildup under the hinges which in turn causes the hinges to not sit flush against the cowl. It is hard to apply the epoxy in a uniform thin layer so there are inevitable “lumps’ of epoxy in places. Even small buildups under the hinge cause eyelets to shift relative to each other slightly and that causes the hinge pins to tighten. If I could do it over again I would use a small amount of West Systems Microlight – just enough to keep the epoxy from running like water. The microlight is so fine that I think it will flow out of the gaps under the hinge leaving only a very thin layer and eliminate the buildup problem and the tight hinge pins.

2) Apply a very small amount of epoxy to the hinge faces only and avoid build up on the edge nearest the eyelets.

3) After four or five hours when the epoxy has partially set but is still flexible clean up excess epoxy around the eyelets. It is much easier to remove at this stage than after it fully hardens.

I hope this helps someone. I can’t guarantee your results but this is what I would do if I could go back 48 hours.

 

Categories: Uncategorized

Riveted Cowl Hinges – 8.5 hrs

February 24, 2013 Leave a comment

Sunday Feb 24, 2013

It took more time than I expected this weekend but I finally bonded and riveted all the hinges onto the cowl. This included machine countersinking all the holes on the outside of the fiberglass cowl for the rivet heads. This is a bit tricky since the surfaces are curved and the radii change so I checked the depth of every countersink. That took hours. I also sanded the mating surfaces on the cowl and scuffed up the mating surfaces on the hinges with coarse sand paper to give the epoxy something to bite into. And before applying the epoxy I cleaned all surfaces with acetone. Applying the epoxy was challenging. Too much and it squeezes out into the spaces between hinge eyes; too little and the bond is weaker. I completed the lower cowl on Saturday and the upper cowl on Sunday. The only clecos that remain are for the oil access door.

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Here is a closeup of the flush rivet heads on the outside surface of the upper cowl. I used flocked cotton fiber in the epoxy to give it more strength and to add viscosity. I put clecos in every other hole first, then riveted the remaining open holes. Next I removed the clecos and finished riveting the rest of the holes.

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I was out in Corona flying on Saturday and stopped by Aircraft Spruce to pick up some supplies including some all metal lock nuts I needed for the control cable brackets.  I took the FI servo off the sump and installed those nuts so this is good to go now. I also picked up some 1/2 inch fire sleeve. I used a short piece of that to cover the mixture cable where it is closest to the left exhaust pipe/heat muff. It just covers the non-articulating part of the cable as well as the rubber boots that keep out moisture. You can see it in the view below.

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You can see it better in this view taken directly below the engine looking up. This also gives a better representation of how far away the cable is from the exhaust. I secured it with a high-temp zip tie near the mounting bracket. The other end is completely free.

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Categories: Control Cables, Cowling

More Oil Door Work – 4 hrs

February 21, 2013 Leave a comment

Thursday Feb 21, 2013

The next step in the evolution of my oil access door is making the latch buttons flush to the skin. The KM610-32 camlock latches are designed for a skin thickness of .032 but the fiberglass door is about .064 thick. So the stock latch buttons are about .032 recessed from the door surface. They are fully functional of course but they look a little odd and are less aerodynamic than they could be. So I made two round discs from some .032 stock aluminum sheet to bond to the tops of the buttons. Since I don’t have a lathe and I could think of no way to punch out perfectly round discs I just rough cut a circle with a little extra margin to the desired diameter and drilled a .093 hole in the center. Then I mounted it to my dremel tool using the cutting disc mandrel, spun it up to high speed and used a piece of sand paper on a block of wood to sand the edge into a nice round disc 0.75 in diameter. I bonded one of these to each of the latch buttons with epoxy. I used epoxy to fill the center holes also.

After it all cured I sanded the surface of the door to make the buttons perfectly flush. To add the finishing touch I put saran wrap over the buttons ( as mold release) and filled the gaps around each one with epoxy/microlight filler. When that cured I sanded the surface flush again, removed the latches, and carefully enlarged the holes with sand paper for a nice uniform gap around each button. Here is how it looks now. I think it will look very good when it is painted. Am I wasting too much time on this?

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The cowl horizontal hinge side pins need access covers for removal. I molded some fiberglass stock for the covers but I also need some larger stock for the backing plates. So tonight I laid up some 3 x 3 inch squares on the sides of the cowl where the access holes will be drilled. When these cure I will peel them off and trim to fit the interior of the cowl to hold the nutplates for the covers. For your reference, it has been so cold in the garage lately that it has been taking two days for the epoxy to cure up hard unless I rig up a light to put a little heat on the subject.

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Categories: Cowling

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

More Oil Access Door Work – 12 hrs

February 10, 2013 Leave a comment

Sunday Feb 10, 2013

I continued working on the oil access door this weekend. This thing is taking more time than I expected, but I am going beyond the plans with the hinge, latches and now the stiffener. I received two KM610-32 latches from B&B Aircraft Supplies on Thursday so I was eager to install them. I wanted the KM610-64 latches which are designed for a .064 thick door but I could not find a source for less than $36 each. So I took the -32’s (designed for a .032 door) from B&B for $10 each. You can see in this photo that I mounted the two latches facing outward about 2/3 of the way from the hinge to the opposite edge. The door has a slightly smaller curvature radius than the cowl and placing the latches here pulls the door down snugly against the cowl all around. It also supports the door near to the center so it should minimize bow-out under pressure in flight. You can’t see it in this photo but I cut the holes in the opposite side for the buttons. I checked out the door operation and it works as expected.

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To prevent the latch from wearing away the fiberglass along the edge I epoxied a couple of strips of thin stainless steel as wear plates along the inside edge. The thickness of these turned out to be an issue I did not expect. Due to variations in the thickness of the fiberglass and latch placement tolerance I found the steel strip needed to be about 0.020 thick for the forward latch to give a snug fit when latched with the button full flush. For that strip I actually cut the end off of a stainless steel putty knife which was .020 thick. For the other latch the strip needed to be significantly thinner or else the latch would not close fully and the button would not be flush. For that strip I used some .004 thick stainless steel I had on hand (luckily). They were both scuffed up on the back side and epoxied down with West Systems.

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To minimize bowing that can cause the door to lift or even pop open during flight I decided to reinforce it with additional fiberglass. Some builders have made a new door out of aluminum but I want to try the fiberglass route first. I cut some 1/4 inch foam into a pattern that fits around the latches and up to the hinge. I epoxied that piece to the interior of the door with it latched in place on the cowl to maintain the proper curvature. When the epoxy was set I sanded the edges at about 45 degrees to taper them down to the surface of the door. I also made a new spacer for the hinge that includes a tab for securing the hinge pin. This will allow me to remove the pin and the door if desired.

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Next I laid out some strips of fiberglass cloth between two pieces of 2 mil plastic drop cloth, added some epoxy and rolled it out to impregnate the cloth. I cut strips of the prepreg and laid them on the foam so the edges covered the tapered edges of the foam down to the door. I was careful to keep the prepreg cloth away from the latches and edges of the door because I don’t want to bond those up. This is only two layers of cloth at this point. I can add more later if it’s not stiff enough. By evening the epoxy was pretty hard and I made sure the latches were not stuck.

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While waiting for epoxy to cure this weekend I also worked on the engine baffles. I plan to mount my oil cooler on the rear of the baffles so to prevent cracking (which many builders have reported) I made some custom stiffeners for the #4 cylinder baffle. I used 1x1x.125 angle to reinforce the rear edge and horizontally across the baffle. I tied the horizontal angle into the vertical angle with a .125 thick doubler. I also made a new doubler for the screw that attaches to the cylinder. That doubler is actually an angle that attaches to the horizontal angle to reduce local bending in the baffle.

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I also started drilling holes in the hinges that will bond to the cowl. These “optional” holes help strengthen the bond joint by increasing the area for epoxy adhesion to the hinges. This view is along the aft edge of the upper cowl.

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Categories: Cowling