Cowl intake ducts 2

October 23rd, 2011

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.

Posted in Cowl

Cowl intake ducts

September 18th, 2011

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!

Posted in Cowl

Starter & alternator cables

August 14th, 2011

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…

Posted in Electrical/Panel, Firewall Forward

Current sensor spacers

July 23rd, 2011

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…

Posted in Electrical/Panel, Firewall Forward

Exhaust pipe supports

July 10th, 2011

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.

Posted in Firewall Forward

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