« Archives in January, 2012

Cowl Fitting 3

6 hours.

Another day, another run at the cowl. First thing was to get the cowl-side top hinges on so I could drill the top cowl to them. This is one of those times where fit is critical, because an error here multiplies itself all over the place.

This is the arrangement I came up with to lock the hinges in place as best I could. On the relatively flat part, I used the 1/8″ aluminum pin that came with the hinges to minimize the slop, driving it in until it couldn’t get past the curved parts on the outboard end. With this set up, I measured 1″ back from the center of the hole on the firewall flange which put the hole right in the middle of the hinge meat. These things are going to take a crapload of vibration, so it’s important that the fastener loads are spread as well as possible.

With the top cowl in place, I drilled where I’d marked. I was doing three on each side until I got down to the tight-radius bend, where at that point, it really didn’t matter, because nothing was going anywhere with most of the clecos in place.

Like so.

With all these guys drilled, I made the hinge pins from the .090 stainless steel provided in the kit, with 90 degree bends at the center ends, and some loops to zip-tie together. The plans say FA about securing these, so I consulted VAF again, and was given several options, one of which was the above solution. Simple, elegant, safe. I like it. I also had to taper the outboard ends of the pins so they could find their way into the eyes of the hinges. Getting them to go all the way down the length of the hinge is kind of a chore, but after a few tries, I got the knack of it, and now they insert and remove pretty easily, and the cowl doesn’t move around at all.

After that, I figured what the hell, I’ll try to fit the lower cowling. This didn’t work out so well, because it’s really big, really awkward, and I need to make cutouts for the landing gear. The idea is you’re supposed to suspend the thing below the top cowl, make everything fit, then drill the hinges. The prop is a bit of an obstacle, but it’s not too bad, what’s vexing me right now is the cutouts for the landing gear. I don’t want to eyeball it and take off too much fiberglass, because I don’t want to have to build it back up later. As usual, it’s always easier to remove material than to put it back. I might need some help on that one, but once that’s done, fitting and trimming the lower cowl shouldn’t be too hard. I also have to do the oil door, which I might get into this week. with the lower cowl on, the oil door is the only access to the area inside the cowl.

Cowl Fitting 2.

6 hours.

First thing was finishing up drilling the top cowl hinges, then it was on to the cowl itself.

I finished measuring the line 2″ back from the firewall all the way around the fuselage. My original plan was to just mark the ends of the lines with red electrical tape, which you can see in this photo, but after some thought, it turned out to be a stupid idea. Electrical tape flexes like crazy, and a closer examination from a different angle showed the tape line to be wavier than an acidhead’s dorm room. What I did have was a flexible plastic ruler, which allowed me to mark the ends of the 2″ lines all the way around and still conform to the shape of the fuselage. Once I had a good line, I laid the edge of the red tape on it, which gave me a tactile cue for measuring back onto the cowl itself. 2″ back from the red tape is where the edge of the firewall is, so that got marked on the cowl, and the same process repeated, but this time with masking tape. Masking tape flexes less, and doesn’t seem to bother the fiberglass cutter on the Dremel too much.

Here’s the Pepto-pink cowl with the tape line marked, ready to have the extra bit trimmed off the end. I had to clamp a couple of blocks to the bench to keep it from jumping around, but once that was set up, I cut off the overhang on the cowl. There wasn’t much. With 1/4″ of clearance between the spinner and the front of the cowl, there was just about that much overhang from the cowl aft of the firewall edge. Once the cowl was marked, I put the hinges back on

This is right after trimming off the excess. What followed this was a lot of iterations of sanding and shaping, trying to keep the 1/4″ of clearance up front, but maintain a nice even 1/32 gap all along the cowl edge. You leave this gap for paint. If you don’t, when you put the parts back toghether, the thickness of the paint makes them not fit anymore, and the paint gets chipped, and nobody wants that.

The 1/4″ gap up front is pretty important. The engine is on rubber mounts, so it’s going to flex a little when it starts and shuts down, so you want to keep the spinner clear of the cowl. In this shot, it’s still a little high, I want to have the spinner about 1/16″ to 1/8″ above the cowl to account for when the engine sags after the first few hours of flight. I guess the rubber mounts do this. Go fig.

Apparently, the pink cowl is thinner than the old green cowl Van’s used to provide. The plans have you putting .032 shims between the hinges and the firewall because the old cowl used to stick up significantly. The pink one, or at least this one, required no shims at all. It’s either flush with the top deck skin or just slightly above it, just enough to catch a fingernail on. That can be sanded flush without thinning the material significantly.

All in all, a non-suck day.

Cowl fitting 1

1.5 hours

Took a crack at the top cowl hinges. Didn’t turn out too bad, either. The hinges that attach the cowl are beefy 1/8 hinge, but they follow the contours of the firewall, so you have to replace the 1/8″ aluminum hinge pin with the .090 stainless pin that Van’s supplies. Makes getting them into the eyes with your arm jammed in the oil door easier, supposedly.

Left side drilled.

I also found another neat trick on the Interwebs. Walter Tondu’s RV-7A site shows how to align the cowl to the spinner using a couple of quick-grip clamps. Much easier than some of the methods I’ve seen out there.

I got the right side clecoed on, but not drilled yet. Maybe I’ll tackle that in the morning.

Right side

I also filled out the spec sheet for my PCU500x governor. Good thing I ordered the Van’s bracket. I think I still have the old Cessna bracket around somewhere, but I doubt it will be of much use. If the Van’s bracket doesn’t work, I’m going to have some fun making up a new one. From steel, no less.

Prop and cowl.

4 hours.

Prior to any fun stuff with the prop, I clecoed on the forward top skin. I did put clecoes in from upside-down along the front in a couple of places, But I think I’m going to take them out, because as somebody on VAF wrote, you’re trying to match the cowl to the skin, not the firewall flange.

So, remember that fancy purple custom spinner on my prop?  Turns out there isn’t a really good way to mock that up, short of scoring a junk Hartzell C2YR or C2YK rear hub half.  Here’s why:

The stock spinner is  a flat disc that can be mounted to the prop flange with six bolts, at the end of 2 1/4″ spacers.   This one mounts to the back of the prop hub using a 7/8″ spacer between it and the hub, to get it clear of the hub itself.   No place to attach bolts for the prop flange.

Here it is again from the side.

Measured from the back of the prop flange, It’s a little under the 2 1/4″ spacer length called for in the factory setup.

So a command decision was made to just hang the prop on the engine and fit the cowl based on the real deal instead of the mockup. This is acceptable, lots of guys have done it to no ill effect, other than it being an obstacle in the shop. However, with the blades set to vertical, it’s not in the way all that much. Initially I was going to see if David could help me hang the prop, but then I remembered, hey… I have an engine hoist. The installation guide in the prop manual recommends using a sling to position the prop anyway, so the hoist got yet another use.

I wrapped some blue masking tape around the blade roots to protect them from the straps, enhancing the plastic wrapping the prop shop put on the blades when I had it resealed a few months ago.   This gave me a pretty decent setup to get the prop hub flange lined up to the crankshaft flange.

This is where it got interesting.    The actual installation has you putting six studs in the prop flange, torquing them, then installing the prop to those via castle nuts with spring pins through them.   I don’t have that option.  You can see from the top pic that my prop came with the studs, castle nuts, and spring pins installed already, so the process became this:

Get the prop lined up as nicely as possible
Get all the studs started
Keep hand-turning each one a couple of turns until after an eon, the prop seats on the crankshaft flange.

This took a while, and they’re not torqued down at all. The whole point of this is to fit the cowl.

The top half of the pepto-pink cowl came down from the rafters to be sat atop the engine (from which I had previously removed the baffles in their current state), and I have to tell you, the pink/metallic purple combination is striking and eye-catching, in the worst way possible.

Next is

To do list: Cowl fitting.

I’ve added a new category to this chronicle, which is currently approaching Stephen King’s ‘Dark Tower’ series in its span and scope. And horror. Don’t forget the horror.

Anyway, I think it might be helpful to post the occasional list of things to do in preparation for a task or to collect all the fiddly bits that make the difference between a phase of the project being completed.

(Ya think, genius? Where was this 7 years ago?)

(Hey, look through the blog, there are a few, they just didn’t get their own category before, now pipe down and let me finish.)

So, for fitting the cowl, it looks like I’ve got the baffles about as roughly assembled as they’re going to get, barring a couple of things on the aft left one that need a good riveting.

1. Prep the prop: Extricate the spinner from the back of the hub and make it available to line up the upper cowl.

2. Make some 2 1/2″ spacers out of PVC to simulate the depth of the prop hub between the flywheel and the spinner plate.

3. Acquire a set of suitable bolts to anchor the spinner backplate to the spacers and flywheel.

4. Get upper cowl down from rafters.

5. Cleco or rivet (not sure which) the top deck skin on.

That should cover it, for now. If I need to add more, I’ll update later.

Baffles 3.

7 hours.

Spent a good portion of the day iterating the front inboard baffles. This is where it gets weird: I used the IO-540 baffles from the RV-10 kit as a template to modify the baffles that came with my kit. Pretty straightforward, except that the hole for the governor is going to be very interesting.

The process here was pretty simple: Trace the outline of the 540 baffles onto the 360 baffles supplied with the kit, then cut away the excess. The 540 baffles sit a little farther back on the engine, behind the bulge for the governor drive gear and governor pad. I had already spent a good bit of time yesterday trimming the left front baffle to fit using more or less the same method, except I screwed it up a little. I didn’t leave any metal crossing over the centerline of the engine to link the two halves up. No big deal, that’s what spare .032 and platenuts are for.

Since the right baffle sits a little bit more aft, I needed to cut down the bottom of it about 7/8″ and cut the forward part straight back. It turned out OK, but left about 1/2″ of difference at the top from the left side. This is not problematic either, really, since a good chunk of that material has to be removed for the cowl fitting.

I’ll also have to extend the sides out to just past the ring gear on the flywheel, since the front baffles are now mounted too far aft.

I got my replacement #4 cylinder baffle parts, so I worked on those for a while. I”m not going to tackle the oil cooler until I’ve trimmed the baffles down for cowl fitting.

Speaking of which, that happens next. I have to get the spinner off the prop, make some 2 1/2″ spacers, and get my spinner put on the engine so I can line up the cowl. We’re about to head back into fiberglass land, folks. Yay! The entire world will be covered in pink dust. Like a Chtorran invasion site.

Baffles again.

1.5 hours.

The front baffles from the O-360 kit don’t fit at all. No surprise there, the front of my engine is more like the six-cylinder O-540 that goes on the RV-10, the Harmon Rocket II, and which a couple of gnarly dudes have shoehorned into an RV-7 like mine.

This is the problem. This big piece of meat right behind the flywheel (the toothy thing on the left) is where the governor mounts. Putting the front baffles between this and the flywheel didn’t give me nearly enough clearance between the baffle and the flywheel to make me happy, so I’m glad I ordered the front baffles from the O-540 kit from Van’s.

Here’s another shot. The floor baffle needed a good chunk trimmed away to accommodate that big flat boss below the governor pad. I have no idea what that is, other than a place to mount an air conditioning compressor, and that’s so not going to happen. I read the TCDS’s on this engine today and this fat little bastard weighs in at roughly 40lbs more than its conventional cousins, so I’m not about to start bolting on more heavy things up front.

The right baffle went on OK with some trimming, but it’s a no go: It puts the line of the baffle wall right down the centerline of the governor, which necessitates the O-540 baffle for that side too. The io-390 guys all had to make new ones, which I might do, but I can use the pattern of the 540 baffles to help out with that, and there are also pdf’s on the io-390.com site.

So that’s where it’s at. The #1 and #3 side baffles are done, but I have to put the supports on the floor baffles. Then, when my new parts come in, I can finish the rough install before fitting the cowling and trimming all the baffles to final shape.

More baffles.

7 hours.

Apparently, 7 hours is enough time to royally screw up a cylinder baffle. Case in point:

The #4 cylinder baffle holds the oil cooler on the aft section of the baffle. The way this is supposed to work is that the baffle is made largely of 4 pieces: There’s the part that connects to the #4 cylinder head, the part that holds the oil cooler, the part that covers the inboard part of the crankcase, and the stiffener that holds parts 1 and 2 together and gives it some beef so the oil cooler doesn’t rip the baffle apart in all the vibration. The plans call out a distance of 3/8″ from the outboard edge of the baffle where it joins parts 1 and 2. Fun fact: If you stick to this dimension, you don’t get enough room between the drill-through holes of the oil cooler doubler and the angle on part 1, which means you can’t install platenuts. Part 4 has pre-drilled holes which supposedly line up with the holes in the oil cooler doubler. The plans then say “keep the oil cooler as high as possible for maximum efficiency.” Well, that’s neat and all, but if you do that, you get out of alignment with the predrilled holes, and everything’s a mess.

Another important safety tip is to leave cutting out the big rectangular hole for the oil cooler airflow until AFTER the whole mess is drilled. Long story short, I wound up making a huge mess, with holes drilled way outside acceptable parameters for edge distance, a rectangular opening about 1/4″ off from where it should be, and a generally bad day. So I have to order new parts from Van’s and call it a lesson. Also, the plans say to follow the callouts on drawing OP-27A. I don’t have that one, I have drawing OP-27, which is probably the same thing, but I have to check.

So after setting that aside, I went on to see if I couldn’t screw up the #3 cylinder baffle as well. Lo and behold I did not.

This one clecoed together nicely. IN the above photo, you can see the flange for the cabin heat intake. A little piece of screen goes between this and the baffle to keep the grasshoppers out of your cabin heat muff attached to the exhaust pipes.

Here are the two sections of the #3 baffle in an intermediate state of completion. Notice on the lower right, the cutout looks a lot like a Lycoming valve cover. The two doublers there are where it screws to the cylinder heads. One thing you have to do to get these things to fit right is to trim away the excess gasket squeezing out from under the valve covers.

Another shot of the #3 aft section. You can see the bug screen sandwiched between the flange and the baffle, as well as the tab that mounts to the crankcase. Bit of fun, that. In order to get to this part with a screwdriver, you have to dismount the oil fill tube from the engine. Nothing else will work, not even my miniature ratched screwdriver. That’s fine, I just have to remember to safety-wire the oil tube again before I run the engine.

A test fitting. This is a pain. Install, figure out where the baffle rubs on the crankcase, uninstall, grind down baffle, repeat.

From the back. See how deeply buried that mounting tab is? It’s hard to see, but there’s a piece of black PVC tape covering the hole for the oil fill tube.

I also started messing around with the center mount bracket, which requires a little bit of moving the injector lines around to keep clear. This steadies the middle of the baffle in back and connects both #3 and #4 baffles together at the center.

Next is to continue on with the #1 baffle, whichever one connects to the one I just built, because I can’t do squat on the other side until I get the new parts for #4.

What does “baffled” mean?

3 hours.

Came home from work and tucked into the baffles. This setup is basically a box of aluminum that goes around the engine, forcing the air from the cowling intakes down through the cylinders to cool the engine. It was so nice to get back into metal work, after months and months of wiring, but it wasn’t without difficulty.

The plans have you start on the aft left baffle, which is where the oil cooler mounts. You have to cut a rectangular hole in the aftmost outer piece to accommodate the airflow though the cooler and a doubler that supposedly reinforces it against the stresses of having a big chunk of aluminum bolted to it.

The plans say to mount this doubler 3/8″ inboard of the edge and as high as you can for greater airflow efficiency. 3/8″ is a lie. If you do that, you don’t have enough edge distance between the edge of the hole and the angle of the part that attaches to the #4 cylinder, and that’s bad. So do 5/16″. Unfortunately, I have a couple of exploratory holes in the baffle trying to get this right. It’s a little uglier than I’d like, but I’m not trying to win any beauty contests with the baffles. If everything goes right, you’ll never see them.

This shot shows the baffle on the bench being match-drilled

Looks like I’m going to have to cut away another 1/4″ of metal on the left side there to clear the airflow to the cooler.


Here are some pics from the last couple of weeks.  I’ve recovered my server-side image processing script, so I promise more photos in the future.

This is the mess before I cleaned it all up.

Flap actuator and servo reinstalled (Yay!)

Fuel pump reinstalled, lines secured.

This is me working on the endless process of dressing cables and zip-tying everything.