·:[ Darryl's Coot Building Journal ]:·
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Lake Union, Washington in the heart of Seattle is also at the heart of seaplanes. Visit the Lake Union Virtual Museum for more information:

After building new side baffles, front baffles, and rear baffles, the next step was to reinstall the whole thing.

First, here are a few “before” pictures. I took these in July 2007, while evaluating the airplane for purchase. No doubt they were in even rattier shape after an additional 225 hours of operations.

In this photo, notice the multiple patches on the side baffles. Pretty ratty, huh? When I bought the plane, one of my first thoughts was that I needed to build new baffling.

Here is the other side. Notice the beads RTV…

The horizontal bead of RTV was, in fact, the only thing that kept those two pieces of metal connected!

Check out the crack on this front baffle. Also, notice the ugly (dry, cracking) rubber seal along the cylinder.

Most of the top seals were in excellent shape. Not so for those front seals.

Okay…back to the future. The Yankee was in Dave Wheeler’s shop in Arlington getting a cylinder overhauled during the plane’s annual. Dave kindly permitted me to do the re-baffling re-installation myself.

Here is the preliminary installation (notice that one cylinder is missing in these photos):

And here are some photos after the final installation (and after the first test-flight):

Happiness!

Okay…I finished these things months ago, but have not finished writing them up. We previously examined the Yankee re-baffling project with new side baffles and new front baffles.

The two-piece rear baffle was in pretty good shape. Mostly, the cylinder shrouds had been rendered to almost toothless combs:

Following disassembly, cardboard patterns were carefully constructed for each piece:

As with the previous pieces, new blanks were cut from 0.032″ 6061-T6 sheet aluminum.

Here is one piece after putting in the bends. Notice the cylinder shrouds are longer than in the original, that was intentional. I curled the cylinder shrouds over forms made of wood, after hammerforming in the bead:

The other piece was slightly more complex because of multiple bends, requiring more planning in the order in which the bends were made.

The next step was to reassemble everything for riveting:

and actually riveting and reassembling the whole thing together:

The next step…re-install the fresh baffling.

Here is a Youtube video I came across of a Coot landing on and taking off from a lake.

This evening I’m going over Lycoming Service Instruction 1427B in anticipation of breaking in my Lycoming 0235 in the Yankee tomorrow, following the reconditioning of one cylinder. The document describes the engine break-in procedure in great detail, including ground testing the engine with a test club in place of the prop. On page 3 comes the warning:

WARNING: ENGINE TEST CLUBS MUST BE REPLACED WITH APPROVED FLIGHT PROPELLERS BEFORE FLYING AIRCRAFT.

Umm…right. Got it.

As suggested in the previous post, I did end up building new front and rear baffles for my Yankee. Here is the journey for the front baffles.

First, take a look at these dogs:

The first thing to notice is that the rubberized seals are in abominable shape. They are hard and crumbly. But there is more. Notice the big patch on the lower part of the left baffle. At the top of that baffle there is a big ol’ crack (click on the image and it becomes clear). See that bracket on the upper part of the right baffle? that bracket is just about cracked all the way through. Finally, the original steel staples used to hold in the seals have eaten away at the aluminum they contact. Yuck.

Here is the view from the back side:

The crack in the (now right) baffle is plainly visible. The upper seals are clearly very worn.

The first task was to make cardboard patterns from the baffles and cut out new blanks from 0.032″ 6061-T6 sheet aluminum:

The air duct tube on the passenger-side baffle is rolled into the original baffle. Therefore, I simply cut the original out and reused it in the new baffle:

New cylinder baffles were cut and shaped to closely correspond to the original. These were made longer than the original. Upon final fitting, a 45 degree bend will be put in the ends and the front and rear pieces will be safetied together:

And, of course, a new bracket was bent from 0.04″ stock (7075 T6 in this case):

A few bends later:

The next step was to cut out new seal material. I used a product called Cowl Saver™ from McFarlane Aviation:

I used Avex blind rivets with a sandwich of AN-960-6 washers on the aluminum side and AN-960-6L washers on the seal side for holding the seals on. Cherry rivets were used for holding metal parts together:

The next installment will be the rear baffles, followed by photos of the installation.

My Yankee is undergoing its annual, so that seemed like a good time for a new set of owner-made baffles for the plane’s Lycoming O-235 engine.

The two side baffles were in absolutely hideous shape. Take a look:

The rubberized seals are in good shape, but the aluminum is in really, really bad shape. take a look at the other side.

Patch after patch can be seen. See that little chunk below the red silicon stuff? That is, essentially, held together just by that bead.

The factory stock baffling is made from 0.032″ 5052-H34 sheet aluminum. This alloy’s biggest advantage seems to be its low cost. A better (and slightly more expensive) grade for engine baffles is 6061-T6. (This is what AA1/5 guru Ken Blackman uses for building new baffles.)

I had enough 0.032″ 2024-T3 in stock, but that grade, while stronger, is more brittle. The 6061-T6 is recommended over 2024-T3 by folks like (the late) Tony Bengalis for building engine baffling. I ordered a sheet from onlinemetals.com, which happens to be about 20 minutes from my place of employment in Seattle. I picked up the order several hours later.

The first thing was to drill out the rivets for the rubberized seal, and then make patterns out of heavy card stock:

Next, I used rubber cement to paste the pattern on the sheet of aluminum, and did all the center-punching for the holes, and drilled the strain relief holes for some of the bends. Being a cheapskate, I optimized the layout to save aluminum and used a jig saw to separate the two sides:

Next, I cut the basic shape on a band saw (and a bit on the jig saw when I ran out of throat on the band saw). After carefully dressing the entire circumference of each part, I drilled and debured the holes.

Each piece had two 90 degree bends with a generous 1/4″ bend radius. I formed a die on a belt sander from 1/4″ bar stock. I have a lousy 48″ sheet metal brake that could have been pressed into service (and I could have used my monster brake), but it was easier to use clamps on the edge of the bench and a block of wood with a mallet.

Here are the final pieces:

The next task is to rivet the rubber seals back onto the baffles. Here they are all Clecoed up and ready for some pop rivets:

Total construction time: About 6 hours, including to time to make the (reusable) patterns. I have another hour to go for the riveting.

I learned this afternoon that one of my cylinders has low compression and needs to be pulled. Since the rear baffle will have to be removed to pull the cylinder, I may just build a new rear baffle. Stay tuned.

Update: For connecting the seal to the baffle, I used Cherry Rivets (MSP-42) with AN-960-6L washers on the rubber and AN-960-6 on the aluminum side. The final products:

I upgraded the blogging software today. Leave a comment or send email if you notice anything wrong.

What did I do this past weekend? Here I am with Russ Milham, who was in the left seat flying my Yankee. He did a couple of touch and gos and then landed the third time. We then joined an American Yankee Association fly-in at the Spruce Goose Cafe.

Fellow Coot-builder, Doug, has posted this wonderful video of the late Peter Breinig building a Spencer AirCar in five minutes.

In the opening scene, Peter is looking through Private Pilot and finds an article titled, “Build Your Own Airplane.” But the airplane shown is not a homebuilt airplane at all. It is a 1971 American Aviation AA-1A (built a year after my AA-1 Yankee). On the other hand, the AA-1 series was developed by Jim Bede, and was originally to be a kit plane.

I had an aviation mission today. Namely, testing out a second-hand piece of avionics (a Narco NAV 121 VOR reciever W/CDI) that is going into the Traveler project. Today was a knock-out stunningly beautiful day here in the Pacific Northwest (on the heels of a nasty March), such that, 6 hours later, I still haven’t managed to wipe the smile off of my face.

Anyway, here is the video of the test:

Between us, Russ Milham and I have three engines to rebuild. I have a Franklin 165 (6A4-165-B3) to rebuild for my Coot, Russ has his Continental O300 to rebuild for his Coot, and we jointly own a Lycoming 0320 for our Traveler project that needs rebuilding.

We looked at commercially available engine overhaul stands (example) and found that they cost about $200 for a basic stand, and a little less for a kit. These are probably fine, but we wanted a stand that could be disassembled and stashed away when not in use—shop space is getting scarce! And we wanted a stand that can be used with a variety of prop flange bolt patterns, and had more than two holes for bolting the prop flange to the stand. I agreed to undertake the project.

This post shows the construction of the stand. Rather than providing technical drawings, I’ll explain things with text, measurements, and photos, which should be ample information for others to build a similar stand. Here is what the stand looks like completed:

Bill of materials:

1. One 7″ x 7″ x 0.125″ (11 gauge) mild steel sheet (prop flange plate)
2. Three 3″ x 3″ x 0.125″ (11 gauge) mild steel sheet (foot pads)
3. Three 1.25″ x 1.25″ x 0.25″ x 36″ mild steel angle (legs)
4. Two 0.125″ x 1″ x 72″ rectangle mild steel (cut into cross-braces)
5. One 1.5″ x 2″ x ~6″ block of steel or aluminum (shim fabrication)
6. Twelve 3/8″ x 1″ grade-8 bolt, washer, lock washer, nut set
7. Twelve 5/16″ x 1.25″ grade-8 bolt, washer, lock washer, nut set
8. As required, metal primer and paint

Legs: The legs are constructed as two nested pieces that are bolted together, so that the stand can be disassembled into a relatively compact form. The short leg pieces are about 5.5″ long and the long pieces are about 31″ long. The -3 legs are cut at a 55 degree angle. A single cut is made at 5″ from one end and the cut is toward the long end.

(Another view.)

Here is how I cut the angle using a metal cutting bandsaw. A piece of angle aluminum was put into the vice to hold the angle steel at a 45 degree angle in the saw’s vice.

…and the vice was rotated to 55 degrees:

This one cut, thus, sets the proper angle for the stubby legs (that are welded to the flange plate), and the long legs (that are welded to the foot pads).

Prop flange plate: The prop flange must bolt to the top of the engine stand. This requires machining plate steel, to turn a rectangular plate into a circle (although you could skip this, if you wanted) and machining slots for bolts. I used 1/8″ steel for the flange plate, which works perfectly fine. You can go thicker, but don’t go any thinner.

First a note about prop bolt patterns. There are three commonly-used prop bolt patterns for small aircraft engines. I recommend machining slots that will provide for all three patterns. The standards come from SAE AS127D, #1, #2, and #3. Numbers 1 and 2 are used on Lycoming and Continental engines and are 6-bolt patterns, and #3 is used on Franklin engines and is an 8-bolt pattern. The bolts for all three are 0.375 (3/8″) diameter, and the flange pilot (the central protrusion from the flange) is 2.249″ in diameter for all three patterns.

Here is a sketch of how the plate can be machined:

The face includes a 6-bolt pattern with a circle diameter of 4.375″ for #1 and 4.75″ for #2 patterns. The pattern also incorporates four (of eight) bolts for the #3 (Franklin) pattern, with a bolt circle diameter of 5.25″.

So here is are the holes:

• Two 3/8″ slots from 4.1875″ to 5.4375″ diameter (these are the horizontal slots that are used for all three patterns)
• Two 3/8″ holes at 5.25″ diameter at 90 degrees from the first two slots (two vertically aligned holes that are used for the Franklin prop pattern)
• Four 3/8″ slots from 4.1875″ to 4.9375″ diameter at plus and minus 120 degrees of the first two slots

Note that you can make the slots longer. For example the four slots can go from 4″ to 5″, without problems, but don’t make the holes much bigger that 0.375″ (3/8″). The bushing diameter on the prop flange is 0.623″, and the six or eight bushings are the only contact between the engine and the stand.

Here is the sequence of machining:

First, beginning with a 7″ x 7″ plate, bore a 2.5″ pilot hole in the center of the plate. I held the plate in a four-jaw lathe chuck and located the exact center:

Then a pilot hole was drilled, and a hole of about 1″ was drilled. A 2.25″ pilot was then bored into the plate:

Once the pilot hole is finished, the four-jaw chuck is replaced by a three-jaw chuck to hold the plate by the pilot hole. And the square plate is machined into a round plate:

(I started machining the corners and realized it was going to take awhile. So I switched to a thick cut-off bit and came in from the side. Slow the lathe down near the end to prevent the corners from flying too far.)

The next step is to machine slots and holes into the flange plate:

Tripod Assembly: The next step is to weld the short legs onto the flange plate:

(More views here and here.)

The long legs can then be fitted to the small tripod. The long legs are fitted to the inside of the short legs. I used a belt sander to round the outer angle of the legs slightl where they overlap the short legs. This allows them to nest snugly.

Using clamps to hold the legs in place, move the long legs up and down until the top of the stand is perfectly level. Don’t skimp here!

(Another view here.)

…and drill four 3/8″ bolts to hold the legs together:

Next cut three 3″ squares of 0.125″ steel, and weld them on.

Bracing: Next comes bracing. There are several ways to do this, so feel free to figure out your own way. I chose to add two “layers” of bracing, one near the top and one near the bottom. I cut three pieces of 1″ x 0.125″ rectangle for each. Here they are resting in place:

(Another view here.)

Since the angle of the legs is 90 degrees, but the legs are spread 120 degrees apart, shims are necessary between the bracing and the legs. I chose to saw the shims out of a block of aluminum I had sitting around. Use whatever works for you. Here is a shim being test-fitted.

Slight asymmetries in the angle at which each leg was welded to the prop flange plate necessitated custom shim thicknesses.

Now, use C-clamps to hold the whole thing together and drill holes for the 5/16″ bolts. Here is the entire thing assembled (before trimming of the shims) with 350 pounds of semi-static load (I was bouncing a bit). The stand is rock solid.

The next step was to trim the shims, and stamp a label where everything fits, so it can all be reassembled without difficulty.

Finishing: The last step is painting the stand. The top of the prop flange probably shouldn’t be painted or else you may end up scraping paint off of the prop bushings after a rebuild.

I brushed on RustOleum metal primer (here and here) and then sprayed on a RustOleum enamel textured white.

(Another view here.)

Here is the assembled stand:

Using it: Within a week of finishing the stand, Russ and I had mounted the engine on it and pulled cylinders, pistons, and connecting rods. Splitting the case comes next….

(Another view here.)