Chapter 23: Engine Cooling Baffles
Step 7: Engine Cooling Baffles
(In work)
(Updated 9/19/2011)
A More Effective, Updraft Cooling Concept
The problem:
It’s my opinion that the Cozy IV cowl ingests air that doesn’t do real work. Air stagnates in the upper cowl and around the accessory case. Air fills the wing roots. It swirls and stagnates. Why have air in the wing roots at all? Its volume and pressure contributes nothing to flowing air through the cylinder fins. Worse, air leaks out the gaps between wing roots and the center spar, and where cowls are attached to wing roots.
A New Concept:
For a cooling system to work effectively and efficiently, ALL cooling air must be doing real work. ALL cooling air needs to go through the cylinder fins. My concept is to fabricate a contained plenum under the cylinders. With this configuration, all cooling air is contained to the space & volume under the engine. The air cannot migrate into the wing roots or along the firewall. The air cannot leak out through the gaps between the wing roots and the strakes. To make this plenum, the forward baffles will be extended downward along the accessory case to seal off the entire front of the engine. The cylinder head baffles will be extended downward to the lower cowl cheeks. A sump baffle will be installed left to right under the engine. A diffuser installed in the lower cowl will join the sump baffle. The aft baffles will be built per plans more or less. I'm also going to relocate the oil cooler into this high pressure plenum.
There will be a bulkhead installed into the lower cowl, 11 inches from the firewall. The top edge of this bulkhead will accept the bottom edge of the sump baffle. A diffuser is also glassed into the lower cowl. It expands from the NACA opening at the firewall to the opening in the lower cowl bulkhead. The top of the diffuser carries the slope of the NACA ramp to the bottom of the sump baffle. The sides of the diffuser curve outward like the bell of a trumpet to the sides of the lower cowl. The lower cowl will still be easy to put on and take off. As the lower cowl is raised into position, the sump baffle will seat into a C-channel lined with silicon baffle strips on the top of the diffuser bulkhead.
Why do I want to do this? I've found over the years that most Cozy IV flyers have cooling problems. They spend the first year or so trying to improve their updraft cooling. I am running a larger engine. More horsepower, more heat. I want my cooling to work first flight and every flight. I've had this concept in my head for over 8 years now. It's time to build it and see if it works.
Cylinder Barrel Baffles
These are 6 of the 8 cylinder barrel baffles that wrap around the barrel fins. As you'll see later, the other two barrel baffles are riveted to the aft baffles. They are sized to leave a 120-degree opening on the bottom of the cylinder and a 2-inch exit gap at the top of the cylinder. The bottoms of the inner barrel baffles are bolted together with the inter-cylinder closeout plates that block off the area between the cylinder barrels and the crankcase. The tops of the barrel baffles are held together with threaded rod straps
A top interI had to make the top baffles in two pieces. It was the only way I could get the baffles to fit into place on the engine. The top baffle plate is shown in the second picture. It spans across the inner cylinder barrel baffles and to the barrel bases. The tops plates are made from 0.065 aluminum. These need to be stiff because they help hold the inner cylinder baffles against the barrel fins. The strap is shown in the third picture. It is bent up in such a way as to block off the space between the last fin and the barrel base. The little finger on the strap fills the gap between the cylinder bases and the crankcase. The straps are made from 0.025 aluminum. They are held to the plate with a screw and nutplate. The bottom inter-cylinder baffling plate is shown in the fourth picture. They are exactly like the top plates except that the straps are riveted to their plates. (I guess I could have made the bottom plates as one-piece. But it was easier to bend up the 0.025 strap than it would have been to bend 0.060. Plus, it was easier to copy and fabricate from the top plates.) For now, each top and bottom plates are being held together by a threaded rod running between the cylinder barrels. I will replace the rod later with a long, AN-3 bolt once I determine the length needed. The plans mention using safety wire. But I'm going to use long, AN-3 bolts.
Forward Baffles
The Vans kit provides three baffles that form the forward baffling that goes across the top of the engine. These are pictures of the outer right panel that fits around cylinder #4. It comes with the metal tab that wraps under the cylinder head fins. It is meant for round cylinder heads. It took all of 5 minutes to bend and reshape the tab to fit around my square cylinder head. The baffling kit does not come with any baffles to cover the cooling fins on top of the cylinder. I made the one shown here in the pictures. I used paper templates, then transferred the pattern to metal, then cut and shaped the metal. I riveted it to Vans panel. Notice that I am using some black lining material. It is my intent to line all baffles with 0.025 high temperature silicon material. The purpose is to seal the gaps between the baffles and the edges of the fins and to keep the baffles from vibrating and chafing. I'm using some tool shelf liners for trials while I'm building the baffles. I'll RTV the silicon material in place once all the baffles are fabricated.
Inner Cylinder Barrel Baffles
The first picture shows the parts needed to baffle between the cylinder barrels. The four inner cylinder baffles are shown in the top row. The bottom inter-cylinder baffles are in the middle row. The top inter-cylinder baffling plates and straps are on the bottom row.
The inner cylinder barrel baffles wrap around the barrel fins. (Sorry, no picture.) An A&P friend is allowing me to use his metal bending brake and rollers. The rollers make quick work of curling the baffles to fit around the barrel diameter. I used a vice to curl the ends around a 9/16th inch rod.
Inter-Cylinder Head Baffles
The inter-cylinder head baffles are one-half of the baffling needed to force cooling air through the cylinder heads. (The "other half" is the outer baffles attached to the front and aft baffles.)
The first picture shows one of two inter-cylinder head baffles that get installed onto the top of the cylinder heads. The second picture shows how it is inserted between the cylinder heads. These are made from 0.025 aluminum. It took me a while to figure out how to bend the metal. I scrapped a few of them before I got it right. The top baffles will be held into place with RTV and with safety wire to the bottom baffles.
Trimming the Baffles
I decided to trim the forward baffles and the outer cylinder baffles before starting the aft baffle. As mentioned before, the Vans baffles are too large and too tall. My top cowl would not fit over them. So I removed the Vans baffles and started with templates instead. I made some templates from scrap metal and scrap cardboard. I installed these templates on the engine, then installed the top cowl. Using small squares of cardboard, I reached under the cowl and butted the cardboard squares against the inside of the cowl. This gave me the shape of the inside surface of the cowl. One by one, I transferred the templates to each baffle panel. I drew the outline of the template onto the panel, then subtracted the amount of gap indentified in the plans. I think I'm using 3/4-inch gap on the outer cylinder baffles and 1/2-inch everywhere else.
These picture show I trimmed that right outer baffle. The first picture shows a cardboard template attached forward of the #4 cylinder. The little cardboard squares are butted to the inside of the cowl, then taped to the template. These give me the shape of the top part of the cowl and the shape of the cylinder blister. The second picture shows the template traced onto the Vans baffle. It's important that the template use the same bolt holes as the baffle panel so you can orient the template properly. I traced the outline of the template onto the baffle panel. I removed the template and traced a new line 1/2-inch below the template line. I cut off the excess material with the bandsaw.
I used this same technique on the other baffles. This next picture shows the trim template for the right forward inner baffle. The left forward baffle has already been trimmed. Don't be alarmed at this picture. The Vans baffles are not high enough to reach the very top of the cowl near the centerline of the engine. The final picture shows the trim template for the outer cylinder baffles.
Aft Baffles
(In work)
I'm experimenting with making the aft baffle in two pieces instead of the three pieces mentioned in the plans. I have no patterns, so I must template the whole thing. Picture 1 shows a stick installed horizontally between two known reference points on the engine. Picture 2 shows me measuring the distance between the reference stick and the bottom cowl in half-inch increments. Picture 3 shows the measurements transferred onto a template. Picture 4 shows the template installed onto the engine. Again, I used little cardboard squares taped in place to give me the exact contour of the lower cowl. I also taped little squares against the crankcase housings and around the alternator bracket. I will worry about the hole for the alternator later. I transferred the template outline to the baffle plate and drew a new line 1/2-inch above it. Picture 5 shows one half of the aft baffle in place on the engine. Woohoo!!
Next Steps
Make attachment bracket for the left side aft baffle, make cylinder #1 head and barrel baffles, then attach them to the left side aft baffle.