Source: 2025 Q1 Beartracks, Brooks Cone
I wrote an article last issue on a Patrol that I started in 2017 and am nearing completion on. I talked about the theme of efficiency, utility, reliability and maintainability that drove decision making of the build. At that time the FAA paperwork had been submitted for its airworthiness inspection.
I signed off the condition inspection on January 2nd, the FAA performed the airworthiness Inspection on January 21st and the first flight was on February 22nd. The Patrol has about 7 flight and 10 hours on her now as of this writing.
I knew that the FAA’s inspection of my Patrol would be broad in nature rather than detail oriented. I wanted and needed an inspection with detail, so I hired an A&P with IA in November to inspect it. The inspection lasted about 3.5 hours. With a mirror and flashlight in hand he looked at everything and wrote discrepancies down on a tablet. I studied what he did and how he “thought” as he looked around. At the end of it I had 75 items to fix, a builder tutorial of how to inspect, and a higher standard to rise up to. That was just what I, an untrained amateur who builds alone at home, needed. In the subsequent weeks as I worked on his list, I kept discovering my own items and so the number of items to fix nearly doubled. I am convinced I would not have appreciated a judgmental eye on my build if a DAR inspection
was combined with an evaluation for an airworthiness certificate. I suppose the way I had it done gave me a measure of protection from failure and confidence in more than just “passing”.
The first flight was done on Saturday morning, February 22nd. The temperature was 17F and it lasted about 40 minutes with the objective to run the engine hard for break-in. I’ve got good cabin heat, low CHT’s and very good oil temp control. My oil system has a shutoff valve to the cooler controlled in the cockpit. I have outstanding control of oil temp. The break-in schedule after the first flight was interrupted by my ADS-B performance report saying it’s inoperative.
My Patrol resides in mandatory ADS-B airspace, and so flights #2 and #3 were dedicated to making it operational. Break-in continued on Flights #4-7, providing 9 more hours on the engine.
When we break-in an engine the question we all ask is “Will it run too hot?” My CHT’s were normal from the first takeoff. With 65% confidence I say CHT’s were not hot because of time and care spent on crafting two firewall forward items – Sealing the baffling, and the design of the cowl exit.
Air that enters the top cowl is for engine & oil cooling. Air that leaks and dodges any cooling fins is wasted drag and reduces the pressure differential across the cooling fins, so I decided to plug them all up. A flash light in a dark hanger strategically positioned below the cylinders reveals all the leaks. Most of them are found around the base of cylinders. I have a friend at the airport. His name is Wayne. Wayne is a super inquisitive, and enthusiastic builder who is at the airport every day . I’m just kind of average but am further along so we help each other out. Life is better when humans collaborate. Occasionally Wayne uses good words that describe a situation. Three that come to mind are “Rat Hole”, “Sticktion” and “MVP”. Sticktion is the sticky friction we overcome when we initiate movement. After things get going, the stickiness of high resistance is reduced. MVP describes a part or assembly that is Minimally Viable…a Minimally Viable Product. An MVP is not pretty but gets the job done and keeps the build moving along. We’ll make it pretty later on.
Now about rat holes. Cars have rat holes and manufacturers don’t like them. My grandma’s basement fruit cellar had them. The average Lycoming baffling installation has rat & mice holes too. They are found in places like corners, at the cylinder base and inner cylinder baffle. Lots of air passes through them without cooling. When a rat hole is plugged, the cooling improves and drag is reduced. So I search out and seal up baffle joints and small stuff with ahigh temp silicone product called Permatex Ultra Black gasket maker. I think the black Permatex looks better than the red stuff but that works too. Some spots are difficult to reach, so I fill a small syringe with Permatex. A 12” piece of tubing pressed onto the syringe nozzle helps apply it there. Another tool I used was a tongue depressor.
My flashlight easily exposed four rat holes the size of my thumb. They got a piece of fiberglass impregnated with Permatex. I place plastic sheathing onto the top of my workbench, then put down a small piece of fiberglass cloth. I squirt some sealant onto the cloth then fold the top of the plastic over it so the sealant and cloth are sandwiched by the plastic. Then I press the sealant into the weave with a putty knife. It should be mess free. When the cloth is fully impregnated with sealant, I cut the patch to final size with scissors, remove the plastic and plug the rat hole by stuffing it with hemostats.
In conclusion, my Patrol is flying, I’m breaking in the engine, and have cool temperatures that I think is due to tight baffling, and the engine cowl design. Next quarter I’ll share how I incorporated the tunnel and cowl exit, and share with you how my engine break-in went.