Matt's RV-7 Project

Started baffle seals

Matt — Mon, 28 Nov 2011 02:00:25 +0000

I started fabricating and fitting the rubber strips that seal the baffles to the cowl. These allow the engine to move independently from the cowl, while preventing the incoming air from escaping past the baffles. In effect, the whole top of the engine becomes a plenum chamber with the top cowl as the lid, and the cooing air is forced down through the engine cylinders.

Before I got the tools out, I did a bunch of thread-reading on VAF, then went to the airport and looked under the cowl of as many RV's as I could find (five). It turned out that every one of airplanes I encountered had its baffle seals done in a different way, but it was interesting to see which ones fit well and which ones had leaks. In the end I came away with some good ideas that I'll try to put into practice.

In places where the baffles are curved, I used multiple overlapping strips to avoid wrinkles that could cause leaks. Each one overlaps its neighbor in such a way that the incoming airflow will tend to flatten it against the baffles and top cowl – sort of like bird feathers. The fastener holes are 3/8" from the edge of the baffles, spaced approximately every 1 1/2". Eventually the rubber seals will be riveted to the metal baffles with large-head blind rivets.

Since the seal material (rubberized fabric) comes rolled up, it has a natural curve to it. I took advantage of this by cutting parallel to the axis of curvature and orienting each piece of material so it naturally wants to bend inwards.

A leather punch is about the best way to put the fastener holes in the rubber strips. The rubber doesn't drill well with a normal twist bit, but the punch makes a clean hole without tearing.

Looking into the cowl inlet during a test-fit. I purposefully left the rubber strips overly long so I could trim them to fit later. The forward end especially will need some work, since there will also be a separate set of rubber strips attached to the lower cowl.

I managed to fit rubber seals to all the outboard and aft cylinder baffles before I got tired. The prop hub and flywheel will have to come off again in order to do the crankcase baffle seals anyway, so this is a good stopping point.

Finished baffle riveting

Matt — Mon, 14 Nov 2011 01:00:58 +0000

After trimming the baffles to their final shape, I finished riveting together all the parts that I had been leaving clecoed together for fitting purposes. First I made some doublers out of scrap to reinforce the outboard corner of the #3 cylinder baffle:

Here's what it looks like riveted together:

Another view. I'm not sure if reinforcement is strictly necessary here, but it was easy enough to do and adds almost no weight.

Here's the previously-seen #1 cylinder baffle, newly riveted to the starboard side crankcase baffle.

Closeup view of the joint… flush rivets towards the front where the rubber seal material will go:

And now the #2 cylinder baffle, also riveted to its corresponding crankcase baffle. I later used RTV to fill those visible gaps where the parts come together.

A view of the #2 cylinder baffle from the aft side. The angle reinforcement piece has almost no rivets through it, since it will primarily be secured by the screws that hold the air filter retaining ring.

All the baffles are now riveted together permanently, and back on the engine temporarily:

It's a bit hard to see in a photo, but there are substantial gaps between the forward baffles and the nose of the crankcase that will have to be caulked up when I put them on for good. You can also see some of the RTV previously mentioned.

The plans tell you to rivet little tabs to the forward cylinder baffles where they overlap the aft ones, to make a sort of expansion joint. I wanted these to be removable without drilling out rivets, so I sized the holes for #6 screws instead.

Screw heads are flush on the inside to accommodate the rubber seals:

I cut the tabs slightly oversize so they would seal up the tooling hole that's visible in the previous photo:

One small step at a time…

Heater duct cover plate

Matt — Sun, 13 Nov 2011 21:00:10 +0000

The #3 cylinder baffle, as supplied from the factory, has a big round hole cut in it. You're supposed to attach a hose flange here and connect a scat hose to pick up air for the cabin heat… problem is, that only works for a vertical induction engine, and mine has horizontal induction. So I had to fabricate a cover plate to make the hole go away.

I put a bead of RTV between the baffle and the cover plate to keep air from leaking past. I'll have to wait till I buy the heat muff to figure exactly where I'm going to relocate the heater air supply.

Finished baffle trimming

Matt — Sun, 13 Nov 2011 17:00:33 +0000

After a seemingly never-ending process of measuring, marking, trimming, and test-fitting, I finally have the forward baffles trimmed to fit the cowl inlet ducts.

I ended up totally re-making the center crankcase baffles from new parts. It was really tough to figure out the proper shape here, so I'll post plenty of photos.

The key thing here is to try for a nice smooth transition up the side of the inlet ducts to the inside surface of the top cowl. This is highly dependent on how you shape your inlet ducts so there is a feedback effect as you work on the shape of the various parts.

Close-up of how the parts join together just behind the spinner:

All the various baffle parts are cut about 3/8" behind the aft edge of the cowl opening:

A view from the other side:

I bent the forward edges of the crankcase baffles inward to help the rubber baffle seal material bridge the gap:

Trimming the outboard baffle on the #2 cylinder was fairly easy. I already made the corresponding modifications to the outboard #1 cylinder baffle in a previous work session.

I had to grind away more baffle material in front of the #1 cylinder to make room for the back of the flywheel:

A view with the cowl on… the gap between the crankcase baffle and inlet duct looks huge due to the camera angle. In real life it's between 3/8" and 1/2".

Same area on the left side. This photo shows where I still need to do some fiberglass work to square up the face of the cowl behind the spinner… that can wait till next summer, though.

Looking in through the spinner cutout. This is the best photo I could get of how the crankcase baffle runs up the side of the inlet duct towards the apex of the cowl. It's almost impossible to see in real life – you mostly have to figure it out by sticking your hands in through the inlets and feeling around. Naturally this makes trimming the baffles a long and tedious process.

On to the next step…

Cowl intake ducts 2

Matt — Sun, 23 Oct 2011 22:00:50 +0000

Had a bit of a work interruption recently due to a painful injury that knocked me off my game for a couple weeks, but I'm back on top now. So, remember those great-looking cowl intake duct closeouts I made last time? Yeah, about that… it seems that it would have been a good idea to check the fit with the flywheel installed before I got all crazy with the fiberglass. Grinding away a week of work was no fun at all.

I traced the line of the crankcase baffles onto the cowl so I'd know where to build the shape back up:

With the inboard ends of the inlet ramps cut further back, the cowl fits over the engine like it's supposed to:

Here's another problem area I've been putting off dealing with. I had to cut the lower cowl farther forward in order to allow it to clear the engine air filter when it's being installed and removed, and in doing so I lost space for the third attachment screw.

I cut the upper cowl to match and sanded the edge straight. For now I'll just live with only two screws on each side of the spinner here. If it causes problems down the road, I'll come up with a fix. In retrospect, it was a bad idea to follow the plans and drill all three holes early on… I should have drilled only a single hole at the very front, and left the others for after I had the cowl trimmed to fit the baffles.

At least the inlet ducts are fine at the outboard ends. I trimmed the forward cylinder baffles to fit the inlet ramps using the paper clip method.

I built up the new inlet duct closeout shapes I wanted using floral foam. This time made sure to leave clearance around the flywheel, and to allow a more natural transition of the crankcase baffles as they run across the inlet ducts and up to the apex of the cowl.

I laid up three plies of glass over the foam:

Then I followed up with the usual sand-and-fill process. Once again, this looks like hell, but it's fairly smooth to the touch.

Here's a view looking inside the cowl to show just how close the flywheel comes to the cowl and inlet ducts. There's a gap of about 1/2" all the way around, now that I properly shaped the fiberglass to fit.

Now I guess I'm back where I was a month ago, except this time the cowl fits properly. I guess that's progress, of a sort. Oh well – if this was easy, everybody would be doing it.

Cowl intake ducts

Matt — Mon, 19 Sep 2011 00:30:31 +0000

The baffles have been fitted to the cowl, but the cowl isn't finished yet. I still have to attach the intake ducts to the inside – these will help the air enter the cowling volume and slow down before flowing through the engine.

I put the cowl on the airplane, then reached in through the inlets and traced the position of the baffles onto the inside of the upper cowl:

The lines make it fairly straightforward to locate the ducts on the cowl. I also trimmed back the lips of the cowl inlets slightly in order to make them symmetrical.

I drilled and clecoed the ducts to the cowl to temporarily hold them in place:

Then I glued the ducts in place using epoxy and flox:

I used more flox and microballoons to fair the ducts into the cowl. Even though you can't see this area from outside the airplane, the oncoming air sure can, so I figured a smooth transition would help cut down on cooling drag.

This area was particularly interesting… the cowl is relieved here to clear the #1 cylinder on the bigger 200 hp engine, which prevents the intake duct from fitting properly. I used a heat gun to reshape the corner of the duct, and filler to bring it all together.

The space between the cowl surface and the intake duct forms a tunnel between the high and low pressure parts of the cowl, which is known to cause a loss of cooling air and resulting high cylinder head temperatures. Many folks end up closing off one end or the other in order to force the air to go through the cylinder fins and oil cooler, where it will do some actual work. I figured I might as well go ahead and make this modification now while it's easy.

I started by cutting some endplates out of balsa, and coated the soon to be hidden surfaces with epoxy to make them resistant to oil and water.

Then I glued them in place on the inner face of each intake duct "tunnel".

Once the wood was glued securely, I laid up some glass over the top to provide the real strength and close up the remaining gaps. Hmm, since wood is composed of fibers that are made of carbon, do you suppose I can get credit for this as a "custom carbon fiber part"?

As I went along, I wiped down the inside surface of the cowl with whatever unused epoxy I had left over in each batch. Eventually the entire surface will get an epoxy coat to seal it, so I figured why let perfectly good glue go to waste.

Finally, I squeegeed on a coat of filler to smooth the edges of the glass layup on the endplates, and sanded it all smooth. It looks like hell, but it's smooth to the touch, which is the point. This might be overkill, but when you stick your hand in and feel around for how I did the baffles (which is something all builders do) hopefully you'll say "hey, craftsmanship!" Not to mention, maybe all this effort will make the airplane 0.001 knots faster… every little bit helps.

Next: Trimming the baffles to fit the cowl, again!

Starter & alternator cables

Matt — Mon, 15 Aug 2011 01:00:52 +0000

I got the big cables run for the starter and primary alternator. Here's an overview shot, and I'll walk you through the details below:

I played around with several different variations of cable routing before I found a configuration I liked, which took several hours. Then I had to take it all apart, cut the cables to the proper length, and install the terminal ends with my crimping tool in the vise. This is 4 AWG wire in this photo.

Good thing I didn't forget to install the current sensor on the alternator cable before I crimped on the ends. Proper clocking of the terminals is important here too.

Young Ryan from work stopped by for a visit, and I put him right to work. An extra set of hands is… handy!

We made a spike catcher diode for the starter contactor out of a 1N5400 I had laying around. The anode connects to ground through one of the mounting bolts, and heatshrink insulates it all.

Here begins the tour. The starter cable leaves its contactor and heads towards the right side of the firewall (left in this picture). The alternator cable comes off the big current limiter, goes through the current sensor, and continues on in the same direction. You can also see the much smaller alternator field wire, which comes in from the top and parallels the whole works. Adel clamps are everywhere, holding the big cables securely.

This may be my crowning achievement in adel-clampery. Three clamps on the same bolt hold both the starter and alternator cables to the engine mount, and another adjacent pair holds the alternator current sensor. If you've ever dealt with adel clamps, you can imagine how fun it was to install all of this.

The two cables meet up at another set of clamps on the starboard gear socket:

Then they turn the corner and run in parallel through space up to the engine. I left a bit of slack to accommodate relative movement between the engine and the fixed components.

The wire bundle is clamped to the #3 cylinder induction tube and then runs forward from there.

The wiring runs along the top of the oil sump towards the front of the engine. It's hard to see, or even to photograph properly, but the exhaust pipes are nowhere near the wires – the pipes are at least three inches outboard, not visible in this photo.

Adel clamps attached to convenient sump bolts bring the wires around the corner and back around towards centerline. There's adequate clearance between the wires, oil sump, and prop governor line, and the wires are secure enough to avoid chafing.

The alternator cable then splits off and does a 180 back towards the alternator. A clamp on the bolt that holds the prop governor line in place keeps the cable from flopping around and rubbing against the nearby fuel hose.

This is a view of the same area, looking upward from below:

I put a knife splice joint and a service loop in the alternator field wire, and used plenty of heatshrink to support the wire where it goes into the (needlessly huge) plastic field connector. This seems like a prime location for a wire to fatigue and break, so I tried to secure things as well as I could.

Later on, I potted the connector with RTV to further secure the wires:

Meanwhile, the starter cable continues across to the port side of the engine, behind the starter itself (removed for this photo).

Note the clamping arrangement needed to bring the starter cable around the spine of the engine and then back up to clear the mixture bellcrank assembly. This is heavy 2 AWG wire, so you can't just bend it out of the way and hope it stays there, you have to bolt it down.

Around the back of the starter it goes, then bends forward to the starter terminal post:

From the front it looks like the starter cable must surely be rubbing on something back there, but from below you can see there's plenty of clearance between the wire and the starter housing:

No conflicts here:

I also had a rare burst of foresight, and brought out the air duct to check for interference with the starter cable. No problem here either:

It's good to have the two heaviest wires on the airplane installed for good. Just one of a million details left to do before this thing is finished…

Current sensor spacers

Matt — Sat, 23 Jul 2011 21:00:53 +0000

I'm using Amploc brand Hall effect sensors (most easily found as a GRT accessory) instead of shunts to measure alternator current in my airplane. You pass the bus wire through the middle of the sensor, which is a bit less than an inch in diameter:

The wire doesn't have to be centered inside the sensor, but I still wanted to come up with a way to secure it and make it look nicer. This just looks sloppy to me:

I went up to Airparts and bought some 1" diameter nylon rod, then turned it down on my lathe so it would exactly fit the inside diameter of the current sensors. Having a lathe is great, even if I am only barely competent at using it.

With a bit chucked in the tailstock, I center-drilled the nylon to fit the diameter of the wire. After I took this photo, I parted off what I needed and cleaned up the ends a bit.

Voila, now it's a perfect fit:

I made one spacer with a 3/8" hole to fit the #4 wire from the main alternator, and another one with a 5/16" hole to fit three turns of #10 wire for the secondary alternator. With a Hall effect sensor, running multiple turns of wire through the sensor gives you a current reading that's multiplied by the number of turns, which your engine monitor then divides back down to give you the true current value. This is a handy way to increase the accuracy of the measurement, as long as your EFIS supports it, which mine does. Since these are 100A sensors, three turns of wire from the 20+ amp standby alternator should be just about right.

I glued the spacers into the sensors with E6000. Nylon is resistant to most glues, but I'm hoping this stuff will grab hold of the roughed-up surface.

Next: Off to Oshkosh for a week…

Exhaust pipe supports

Matt — Mon, 11 Jul 2011 00:30:04 +0000

One of the million little things surrounding the engine that I've been needing to figure out is the exhaust pipe supports, sometimes also referred to as exhaust hangers. These are made from two pieces of stainless tubing that are each flattened at one end, joined by a piece of rubber fuel hose that's clamped in between. Here is the single page of xeroxed handwritten instructions that was included in the kit, so you can get an idea of the end goal:

The idea is that these will support the cantilevered exhaust pipes, while also providing some amount of shock absorption. I temporarily used clear vinyl hose while fitting them, so I could see how the separation between tubes was working out. You don't want the tubes to touch, since it would negate the vibration-absorbing properties of the hose; you also don't want them to be too far apart, since the hose will collapse when the airstream tries to push upwards on the exhaust. I shot for a gap of 1/4"-3/8" per advice from Larry Vetterman.

To help prevent the hose from slipping, I roughed up the ends of the tubes with a file, and lightly expanded the tube mouths with my flaring tool.

I put the lower cowl on so I could move the pipes around on their ball joints to center them in the cowl outlet and get 3/4" of clearance all around:

It's hard to photograph the exhaust hangers since there's so much other stuff in the way. It's also hard to install them when there's so much other stuff in the way! My throttle cable was in the way of one of them, and since there's no way to move it, I had to anchor the exhaust supports to the engine differently from how it's shown in the drawing.

A view from the floor, looking up at the bottom of the engine, while fitting the transverse support tubes. The exhaust hangers are supposed to go straight up, but with the throttle cable in the way I had to angle them inward to provide adequate clearance.

Closeup of the top end – little steel tabs attach the tube ends to convenient bolts on the oil sump:

This photo of the finished transverse support also shows how I had to bend the tabs on the pipe clamps to get the angles I needed:

I wish I could have supported the pipes farther aft, but this was as far back as I could get the clamps to go without causing the starboard support to hit the throttle cable, or creating a big gap between the tubes that made the hangers too floppy. Longer tubes would have helped here – perhaps I'll make some replacements someday, but for now we'll see how these work.

Oil cooler plumbing

Matt — Sun, 03 Jul 2011 01:12:43 +0000

The firewall forward kit came with a pair of hoses for the oil cooler, but they were the wrong length and I wanted to use a different type of hose anyway. I wish I would have thought to delete them from the order and save some money, but oh well. Anyway, to figure out the correct length to order a set of replacement hoses, I used some plastic ice maker tubing of a convenient diameter. I played with different hose routing and fittings, and decided that a 45-degree fitting was needed on the bottom, and a right-angle fitting worked best on top.

Once I had the lengths, I called up Precision Hose in Tulsa and ordered two Stratoflex 124J hoses with integral firesleeve, with #8 fittings, 13" flare to flare. They cost darn near a hundred dollars each, but they are just as nicely made as everything else I've ordered from PHT.

Notice how much longer the ones from the FWF kit are. Even if they'd been the right size, I'd have also had to buy and install a separate firesleeve on each of the factory hoses anyway. My rule is to always use firesleeve on important hoses forward of the firewall that carry flammable fluids.

The top hose carries oil from a 45-degree fitting on the engine (necessary to clear the oil filter adapter) to a 90-degree fitting on the oil cooler:

There's over an inch of clearance between the hose and engine mount all the way around. The bend is a little tighter than I'd like, but it seems like it will work.

It's hard to photograph the bottom hose, which returns oil from the cooler back to the engine:

From certain angles it looks like the hose rubs against the prop governor bracket, but if you look at it from the starboard side you can see that there's enough clearance. These parts don't move relative to one another, so anything over a quarter inch is plenty.

The blue aluminum fittings shown in the photos above were installed hand-tight, and only for fitting purposes. For the real deal I wanted to use steel fittings (black) since best practice favors the use of steel over aluminum here.

I drew some temporary guide lines on the oil cooler to help me figure out how to clock the fittings when I tightened them for good. Trying to clock pipe fittings to the right angle can be a frustrating challenge sometimes.

When tightening the oil cooler fittings, it's important to use a wrench on the boss that surrounds the fitting, rather than torquing away on the fragile oil cooler body:

I installed the steel fittings with Loctite 567 thread sealant, and tightened them two full turns past hand-tight:

One more test fit to make sure the fittings were clocked at the right angle, and then I put the oil cooler and hoses on the shelf for later. The next time I install them on the airplane, it will hopefully be for all time!

While I was at it, I riveted the missing nutplate to the angle on the rear baffle where the oil cooler brace attaches. Go ahead, try to guess how I squeezed the rivets on that nutplate in the foreground:

Just kidding, I totally drilled out the rivets holding the angle to the baffle, attached the nutplate on the bench, and then riveted it all back together. Doh, should have done a little more planning ahead.

Oil cooler brace

Matt — Wed, 22 Jun 2011 01:00:13 +0000

When we last saw the oil cooler, it still needed a brace to strengthen the inboard corner and keep the baffle from cracking under load. I happened to have some 3/8" OD, 0.058" wall 4130 tube on hand, so I cut off a chunk and commenced to turn it into an oil cooler brace.

First I hammered the ends flat, which is easier said than done when you're talking about thick-walled tube with a small diameter. I put John Henry on the MP3 player while I did the 30-minute blacksmith power workout.

Heat helped me bend the ends to the correct shape. It took about twenty iterations of heat / adjust bend angle / force-cool with compressed air / carry over to airplane / test fit / repeat.

Once I got it pretty close, I drilled the attachment holes and proceeded to fine-tune the fit so the fasteners would line up exactly.

After much tweaking, I finally got it to fit perfectly. Success! (pay no attention to the temporary hardware shown in this photo)

Once I had the right shape, I polished off the worst of the hammer marks:

Then I heated the ends red-hot and let them cool down slowly to room temperature… one end at a time, obviously, since I had to keep the burning hot metal in the vise.

The intent is for this this to anneal the metal and relax the stress risers caused by hammering and bending it to a new shape. The better to prevent cracks, or at least that's the idea.

After annealing, I cleaned and scuffed the part, then shot a coat of primer followed by two coats of enamel. In between coats I let it sit under the heat lamp to really bake on the finish.

The topmost screw on the rocker cover – seen here from outside the baffles – is where the brace attaches to the cylinder head.

I had no luck sourcing the correct aircraft-grade machine screw (MS51957-85, stainless, 1/4-20 thread, 1.5" long) from any of the usual mail order places, but surprisingly enough was able to find it locally at a surplus aircraft hardware place on my lunch break. I must be living right this week. Here it is next to the original factory screw:

Luckily the cylinder casting is tapped all the way through, so the longer screw protrudes on the inboard side of the head as if it was a stud, and the brace attaches with a nut and lockwasher. On the baffle end, I'll rivet on a nutplate the next time it's convenient.

Even with temporary hardware, this brace seems to do a great job of removing that last bit of play in the oil cooler mounting. After this I probably really could drag the airplane around by the oil cooler, and now I even have a place to attach the chain!

#4 cylinder baffle & oil cooler mount

Matt — Sun, 12 Jun 2011 01:00:41 +0000

The oil cooler is attached to the baffles behind the #4 cylinder, at the left rear corner of the engine. (I did briefly consider mounting it elsewhere, but I couldn't find a place that it would fit) Unfortunately, the plans are especially vague about exactly where to position the oil cooler on the baffle, leaving you up to your own devices to make it fit. Also, the thin sheet metal baffles are really not strong enough to be hanging an oil cooler from, which is widely known to eventually lead to cracks. Many builders add reinforcement to the baffles to better support the weight of the oil cooler, which is yet another thing you have to design and build on your own. This will be a long post showing how I fit the oil cooler and built up the baffles to support it.

The CB-705B brace is a prepunched part that forms a box at the top of the #4 baffle, and adds some stiffness to it. Its rear flange is supposed to share some rivets in common with the oil cooler doubler ring. They don't give you any guidance on where to position it vertically, but I think this is how they want you to install it: (rear baffle removed for illustration purposes)

The problem with this is that positions the oil cooler so low that almost half of it is blocked by the cylinder fins. For an RV-8 with its narrow cowl this is your only option, but in a side-by-side RV there is room to mount it higher for better cooling airflow.

My solution was to cleco the aft flange on CB-705B to the next row of prepunched holes on the oil cooler doubler. This allows the doubler, and thus the oil cooler opening in the baffle, to move upwards a substantial amount.

Obviously the aft flange on CB-705B now blocks an equivalent amount of the oil cooler opening, but there's a solution for that.

Test-fitting the oil cooler to make sure everything is going to fit. You want to mount it as high as you can to get the most airflow through it, but you don't want it to get so high that it hits the inside of the cowl. There is also a constraint related to the clearance between one of the mounting bolts and the diagonal engine mount tubes. And, you don't want to put the rectangular opening so close to the edge of the baffle that you run into edge distance problems.

It's typical to have to grind away a portion of the flange where my finger is, to get the proper clearance between the oil cooler and the engine mount.

Drilling the doubler to the rear baffle locks in the oil cooler position. The sharp-eyed will noticed that I drilled a hole for a third bolt in the middle of the outboard corner. Since the oil cooler has a hole for a bolt there, I figured why not use it…

The three clecoed holes in the CB-705B flange will be used – the rest of the flange will be cut off.

If you are working on this part of the baffles right now, this photo contains enough information for you to position your CB-705B:

I riveted a piece of 0.040" angle to the top of the horizontal part of CB-705B. It picks up the row of rivet holes along the top of the oil cooler doubler. It's all one big puzzle that you have to figure out how to fit together, while you're also designing the pieces.

Lots of work between the last photo and this one. I built a number of reinforcement pieces to be attached to the baffles, which I'll detail below. Here's the master shot of all the parts that will be riveted together to form the #4 cylinder baffle and oil cooler mount:

From left to right, this is the aft cylinder baffle, 0.063" spacer, and oil cooler doubler ring. These are all kit parts, no bespoke items yet. Note that the outboard top corner of the doubler ring is substantially ground away to fit the inside of the cowl.

I used a unibit and air nibbler to make the rectangular opening in the aft baffle, using the doubler ring as a template. A complex pattern of dimpling is required to accommodate the different rivets that are flush on one side or the other. The small piece of angle picks up the two inboard bolts on the oil cooler, and will become the attachment point for a diagonal brace later on (a future project).

Another view of the aft baffle and doubler ring. Flush rivet holes everywhere – be careful to pay attention to which way each one faces!

I used a piece of 1/8" angle to stiffen the corner where the aft baffle and outboard side baffles meet. I had to file a radius on the apex of the angle (not visible in this photo) to get it to nest into the bent flange in the corner. The holes where the oil cooler bolts come through are just barely far enough from the angle web to install the nutplates – careful measuring is required here. Note the countersunk holes on the aft side of the 0.063" spacer where it faces the dimpled holes in the aft baffle.

The leftmost and rightmost pieces in this photo are designed to stiffen the side and rear baffles by providing a load path from the oil cooler to the forward mounting screw. This shown more clearly in one of the photos below, keep reading.

This is what 705B looks like after it's trimmed to fit the cowl, and after the bottom flange has been truncated and a new flange riveted to the top. I also added an extra little tab on the left side to tie it into the cylinder baffle.

Here's a final fit test to make sure everything is going to work. It all seems to line up, thank goodness.

I used a hacksaw, rotary file, and scotchbrite drums to notch the oil cooler flange where it comes close to the engine mount. No clearance problems now, but probably no more warranty either!

It took hours to rivet the whole thing together. Many of the rivets are hard to get to, and you have to pay careful attention to the order you install things so you don't block access to any of the holes.

Another view from the side:

Here's how the stiffener pieces on the outboard side work:

And a closeup of the triangular, joggled attachment at the aft end. The two blind rivets here are the only ones in the entire #4 cylinder baffle, believe it or not – I managed to squeeze or buck all the rest.

Top view:

A view from the inside. Note how the horizontal part of CB-705B is even with the top of the oil cooler opening. That turned out pretty well – not sure why Van's didn't just design the part that way.

Nutplates on the corner stiffener. Some of these rivets were an absolute pain to set properly. It wasn't my best or prettiest riveting work, but it's adequate.

Back side, showing the doubler ring. Rivets are flush where the oil cooler flanges go.

Test-fitting the oil cooler to the completed baffles. I cut and ground a bunch of AN970 large-area washers to spread the load on the cooler flanges, which are made of some very soft type of aluminum and don't seem very strong. Later on I'll prime and paint the steel washers to keep them from rusting where I cut through the cad plating.

I turned some spacers on my lathe to fit around the bolts and prevent the oil cooler flanges from bending.

The inboard side has one long bolt (with spacer) and one short bolt where the rear flange was ground away. The lower hole doesn't get a bolt since the cylinder fin would be in the way on the forward side.

Believe it or not, it's possible to install and remove this whole huge thing with the oil cooler still attached. With the baffle screwed into the cylinder head, the oil cooler mounting is very solid.

Plenty of clearance between the inboard flange and the engine mount – the plans call for a minimum of 1/2", and I have between 5/8" and 3/4".

Mounting the oil cooler up high allows more of the face to be exposed to the local airflow, which should help with oil temperatures in the summer.

The only part of the oil cooler mounting arrangement that's not as stiff as I'd like is the inboard side, which flops around a bit when shaken. This is only natural, since there's no good way to attach anything to the cylinder between the case and the head. Later on I'll rectify this by running a brace from the flange on the inboard side of the oil cooler to a convenient screw on the cylinder head.

I dabbed a bit of zinc chromate on an area of the oil cooler where I lightly gouged it while trying to fit the short bolt on the inboard side. Got to protect this expensive and vital piece of machinery.

That's it for the oil cooler mounting, for now anyway. A friend once told me, "Keep adding stiffness to the baffles until you can attach a chain and tow the airplane around by the oil cooler." While it may not be quite that strong, it's definitely a lot better than if I'd stuck with the flimsy factory design. Hopefully by putting in the extra effort now, I'll have saved myself some heartburn down the road.

Finished intake air duct

Matt — Sun, 05 Jun 2011 01:00:39 +0000

The FWF portion of the airplane seems to involve doing a lot of work that advances things incrementally, but rarely reaches a "finished" state that lends itself to an interesting blog post. Thus, I've been working on various things for the last month that I haven't been doing a good job documenting. Time to get some of these pictures off the camera…

The flanges at the top of the intake air duct are riveted to some fairly thin fiberglass. This seems like an area where cracks could eventually develop, so I laid up a series of glass strips on the outside to reinforce it. After sanding the edge and cleaning up the holes, the air duct now has a "belt" around the top to help strengthen it.

I drilled a 3/16" hole at the low point of the air duct, to let water drain out in case the airplane gets rained on while parked outside. The engine won't be happy (and probably won't even start) if the intake is choked with water.

I countersunk the rivet holes on the inside of the duct (an angle drill once again proves invaluable here) and also dabbed a bit of epoxy/flox over the alternate air door rivets to encapsulate them and hopefully prevent cracking.

A couple coats of grey primer did wonders for the air duct's cosmetic appearance. It's still lumpy and covered with patches, but at least now it's all the same color.

Before riveting the flanges to the duct, I roughed up the mating surfaces and spread epoxy/flox between them, and allowed it to cure overnight while clecoed together. Same basic idea as with the cowl hinges.

Then I riveted the flanges to the duct, using countersunk closed-end rivets with small washers on the outside to prevent crushing the fiberglass. Van's sent me the wrong rivets initially, which caused another work stoppage while I got that sorted out.

Finally, the air duct is finished and ready to go on the airplane. But I won't install it permanently until I get the starter and alternator wiring sorted out, as it would just be in the way.

Air duct patches

Matt — Mon, 02 May 2011 01:00:00 +0000

The engine air duct had a big section cut away to make it fit next to the alternator, and also a couple smaller holes that I ground away before realizing that it's a better idea to cut the vestigial mounting lugs off the starter instead. These all need to be covered over, starting with the two smaller ones for reasons of finger-access. I laid up two plies of 8-ounce glass tape on the outside, let that cure, then followed up with two more plies on the inside. (that was probably overkill, three would likely have been enough here)

The larger opening at the end of the duct is big enough that it needed a form to hold the glass in its proper place while the glue dried. I glued a chunk of styrofoam in there to act as an in-place mold, and then sanded it to the desired shape.

I laid up three plies of glass on the outside:

When it's cool like it has been lately, I use a lamp as a directed heat source to help the epoxy cure faster:

Once the layup on the outside was dry, I poured acetone into the air duct and swirled it around until the foam was all dissolved, leaving only the fiberglass behind. Magic! Then I laid up a single ply of glass on the inside, to give it a bit more strength and to smooth out the rough surface left by the fairly coarse foam. This was tricky to do, as I had to reach my arm down from the wide end of the air duct and get glue all over my sleeve in the process. (if my wife is reading this, yes I did remember to change clothes first)

Once this is all dry, I'll sand off any rough edges – then there's just a few more chores before the air duct is finished.

Alternate air door

Matt — Mon, 02 May 2011 00:00:30 +0000

The factory provides parts to build an alternate air door, which can be opened in an emergency to provide an auxilliary source of air to keep the engine running if the normal engine air filter is blocked by ice, snow, debris, a bird strike, or something else. I don't particularly like the design, since it's kind of hokey and it is a one-shot deal that requires removal of the cowl to reset it, meaning you can't test it before takeoff. But, after several rounds of making cardboard prototypes I couldn't come up with a better one that would a) fit within the restricted space available, and b) not increase the risk of having the engine ingest metal parts if any part of the alternate air door assembly were to fail (talk about the cure being worse than the disease). Some people have omitted the alternate air door entirely, but I decided it would be a good idea to just install the factory kit as provided. Every certified airplane has to have one, after all, and most of the requirements in Part 23 exist for a reason.

I cut a hole in the side of the air duct in the specified location, and match drilled holes through the steel mounting ring. Per the plans, I angled it 10 degrees clockwise relative to the top of the air duct.

Using hand seamers, I folded the retaining tab at the top of the ring:

Then I crimped the forward end, which provides a stop for the door when it reaches the closed position:

The door itself is a piece of 0.063" alclad that pivots around a screw and is actuated by a pull cable. This is the open position:

And here's the closed position. It took a bit of grinding to get it to close securely and move without interference.

The surface of the air duct is not flat all the way across, so you have to build it up to match the mounting ring. I mixed up a big batch of epoxy and flox and laid down a fillet, trying to as much as possible to squeegee the excess material away from where I didn't want it to go – this stuff is tough as nails and therefore hard to sand.

Here's the end result of the first round of sanding. I wish Van's would modify their mold to have a flat-topped bump on the side for this thing – sure would be a lot easier (and lighter!) to do it that way.

As I did other stuff with fiberglass this weekend, I'd use the leftover epoxy from each work session to mix up some microballoons that I'd apply to the alternate air door here and there, just to make it look less nasty. I know it will be hidden under the cowling, but I would like it to at least be a little bit professional looking.

I installed the pop rivets and polished the heads smooth to keep them from hanging up the door, or pushing it outwards and causing a gap, aka an air leak.

Here's the finished product, minus the cable that will be installed later once I figure out where to put the cockpit control for it. It's pretty ugly right now, but it will look better with a coat of paint.

Tool interlude

Matt — Mon, 04 Apr 2011 02:00:22 +0000

I went to fire up my drill press the other day, and absolutely nothing happened. I figured it must be the switch, which is a really low-quality plastic thing, but tested okay on my ohmmeter. So, I tore the thing apart trying to diagnose the problem.

Long story short, it actually was the switch – it was just making intermittent contact, and when I tested it the first time, it gave the false impression of being okay. But while I had the machine disassembled trying to pinpoint the problem, I managed to crack one of the cheaply-made pot-metal drive pulleys. Argh!

Since the cost for replacement parts was going to be about $50, and the whole drill press cost me less than $250 to begin with, I thought hard about just junking it – after salvaging the motor and chuck, of course – and buying a better-quality drill press to replace it. But after pondering it further, I decided I really want my next drill press to be a floor-stander, and I just don't have the space for one of those right now. So, fifty bucks and a few days later, I had a new switch and pulley in my mailbox.

Here's what the drive mechanism on this model of drill press (Delta DP350) looks like. The pulleys on the motor and spindle are actually split into two halves, and control of the spindle speed is effected by varying the spacing between the pulley halves, thereby changing the effective pulley radius as seen by the belt. It's partially clever and partially hokey. On the one hand, this is the only low-end variable-speed drill press that doesn't require you to stop the machine and change belts to alter the spindle RPM; on the other hand, the low-end speed is too fast to use with a fly cutter, the special belt is expensive to replace, and the speed-change mechanism sometimes gets bound up. By the way, getting the collar and snap ring back onto the motor shaft while compressing that big spring was a fun chore.

All back together and working again. One thing I will say for this drill press, it does have a very good depth stop (which I hardly ever use), the chuck is easy to adjust, and it generally seems to run true. It's just too bad about all the cheap internal parts. Hopefully by the time it breaks again, I'll have more space for a bigger and better model.

In other tool-related news, I bought a lathe! I've wanted to get one for a while, and when I saw that somebody in town was selling a Sherline 4400 on Craigslist, I couldn't resist.

I got a pretty good deal, if I do say so myself. In addition to the basic lathe itself, I got a three-jaw chuck for the headstock, both a 1/4" Jacobs chuck and a 3/16" Albrecht chuck for the tailstock, a dead center, a live center, a lathe dog, a steady rest, a milling vise, and a collection of carbide cutting tools. And probably some other stuff that I don't even know how to recognize yet!

I have scant experience using a lathe, so this will be fun to learn on. I doubt I'll do anything fancy with it, but it should be great for making tubular spacers and the like. However, one thing I didn't like about the lathe when I got it was the fact that with speed knob dialed all the way down to zero, you don't have any indication that the power is switched on. I figured it would be bad to start messing with the chuck while accidentally leaving the lathe in a state where it could unexpectedly start turning, so I took apart the motor control box to see if I could rig up some kind of reminder lamp.

I bought a 120VAC neon bulb from Radio Shack, mounted it in the plastic cover, and connected it downstream from the power switch. I used high strength loctite to secure the mounting nut on the lamp, so it can't work its way loose and fall down onto the speed control board and cause a short.

Voila, an obvious red light now reminds me to shut off the power before adjusting the lathe.

The lathe will get put to work soon to turn out some spacers for the oil cooler mounting bolts. Meanwhile, I have been working quite a bit on reinforcements to the baffles where the oil cooler will be attached, but I still have some work to do before I'm satisfied with the design.

The old paper clip trick

Matt — Mon, 14 Mar 2011 01:00:47 +0000

Once the baffles are roughly trimmed far enough to generally fit under the top cowl, you then have to trim them further so you get a nice even gap all the way around the engine. I used the "old paper clip trick" to figure out what to trim and what to keep. I didn't invent this method, but here's how it works…

You start by putting a whole bunch of paper clips on top of the baffles. The jumbo size seems to work best.

Then, very carefully put the top cowl on, and push it down onto the paper clips. Here's a view of what's happening inside, looking in from the oil filler door:

This is another view looking aft from the spinner opening:

Then you carefully remove the cowl, and if you're lucky you're left with an impression of the inside face:

Mark a line the desired distance down from the top of the paper clips – without bumping them out of position! – and proceed to trim, file, and deburr.

Then, repeat a dozen more times! Seriously, I did this for hours, tweaking the fit a little more each time. The baffles came off and went back on many many times, which I didn't bother to take pictures of. But the finished product looks something like this:

Not a very interesting picture, I know. So here's a shot of the whole airplane with the cowl on, which is more fun to look at:

Baffle trimming

Matt — Tue, 08 Mar 2011 01:00:17 +0000

It's finally time to start fitting the baffles to the top cowl. The upright baffle parts all start life being extra-tall, and then they get trimmed down so they end just short of the top cowl. You don't want too small of a gap between the fiberglass cowl and sheet metal, which could cause the shaking engine to damage the cowl; you also don't want too large a gap because it prevents the rubber air seal material from doing its job.

But, since the cowl isn't transparent, how do you know where to trim without a lot of tedious trial and error? I used a method suggested by someone else, which begins by using wood strips to elevate the top cowl some known distance above its usual position:

After making sure the gap is even at each corner, you then reach through the gap to trace the contour of the top cowl onto the baffles.

It just happened to work out that a popsicle stick is just the right length to give me a 3/8" offset from the inside cowl contour. I notched the end to locate the tip of a sharpie, then used this contraption to draw a line on the baffles inside the cowl.

This is a picture looking in one of the cowl inlets, showing the line I traced. This worked pretty well and wasn't too difficult, other than requiring some painful contortions to get the pen onto every corner of the baffles while working in a limited space.

After removing the top cowl, I retraced the wobbly line so I could see it while cutting:

Then I removed all the baffle parts (quite a chore).

This is the first time in quite a while that the engine has been baffle-less:

The bandsaw made quick work of the initial trim cuts. I stayed outside the line, since there is some error inherent in this process, and I didn't want to cut off too much too quickly.

Everything goes back on for fitting, for the nth time:

After only one cut, it almost fits! Still a little trimming left to do in the aft corners, where I had a hard time making sharpie marks.

Here's a view into the right inlet, with the top cowl in place. I'll have to trim the cylinder baffles down a lot further once I glue the upper inlet ducts in place, but that will come later. For now, I'm glad I haven't attached them yet, since they would just be in the way.

Next: Yet more trimming…

Cylinder 1 baffle

Matt — Sun, 06 Mar 2011 01:00:28 +0000

It's relatively easy to remove and replace the engine baffles when they're still individual pieces clecoed together; it's tougher to do it when the various pieces are assembled into big unwieldy shapes. I am trying to design for future maintenance as much as possible, so I am trying to ensure that the baffles can all be removed without drilling out any rivets. In certain places this might require using screws where rivets are specified – we shall see. I know that the finished baffles are all going to have come off at least once before the airplane flies, since there is already at least one airworthiness directive on the cylinders that will need to be addressed.

With that in mind, I tested my ability to remove the baffles attached to the #1 cylinder as a complete unit – cylinder head baffle, inlet ramp, and crankcase baffle all clecoed together. With the flywheel removed, it's just possible to twist and turn it enough to get it off the engine and put it back on. So, all the parts you see here will eventually be riveted together as a single assembly.

I riveted the stiffener angle and the various brackets to the inlet ramp. Some rivets could be squeezed, and some had to be driven. Surprisingly, considering I haven't used the rivet gun in ages, none of them look too bad. Note the use of flush rivets between the three screws that will eventually attach an air dam in front of the #1 cylinder.

Then I riveted the cylinder baffle and corner gusset to the inlet ramp With careful planning, these rivets can all be squeezed if you do it in the right order. You can see where I used some red RTV between the mating parts to fill some gaps that would otherwise be air leaks.

I'll wait to rivet the crankcase baffle until I finish fitting the baffles for good, since not having it permanently attached makes it a lot easier to remove and reinstall the baffles… and unfortunately there's still a lot more of that to come.

Left crankcase baffle

Matt — Mon, 28 Feb 2011 03:55:22 +0000

Well, this is a fine mess… there's no room on the left inlet ramp for the brackets that are supposed to attach to the left crankcase baffle:

Adding insult to injury, I accidentally trimmed off too much of the crankcase baffle while I was trying to get it to fit, resulting in a too-large gap behind the cowl inlet:

I spent a day scratching my head and testing various ideas to make this all work, before I finally came up with something that I was happy with. I started by making two brackets and a filler piece:

Here's how the two brackets are attached to the inlet ramp. Each one picks up one of the rivets in the other bracket that runs longitudinally on the bottom side. You can also kind of see how I ground away the edge of the air filter retaining ring to make it clear the crankcase baffle.

The funny-shaped bracket tucks under the baffle and attaches on the back side:

Another view of the same area:

The filler piece rivets to the baffle and erases my trimming mistake:

It all basically works together, and I verified that there is still just enough room to remove and reinstall the air filter and bracket. Stupid air filter, making things entirely more complicated than necessary, again.