Looking for new baffles for this age airframe and engine had not proved fruitful, so the restorer built new side baffles and repaired the back and front but is still looking for other areas that need to be addressed.
Our baffle journey are talked about here and here.
The restorer found back baffles for the engine and spoke with the gentleman regarding side baffles some months back. They did not offer what we needed, so the restorer fabricated them himself.
Sis is a model 35 Bonanza and left the factory with an oil cooling duct inserted into the back baffle. They changed the design of the back baffle and the oil tank/ cooler with the release of the model A35.
While Bonanzas are still rolling off the assembly line, there are drastic differences between my Bonanza and the ones built today.
Some parts are easy to get like gas caps and wing attach bolts. Others, like engine baffles, require creativity.
Later model Bonanzas with larger engines have baffle kits available from various manufacturers.
As both the restorers are used to working with antique aircraft, a vintage airplane like Sis is a meld of both antique and modern.
Why are Baffles Necessary
Not much time was spent on baffles during flight training or ground school for that matter so watching the puzzle go back together has been a learning experience.
Baffles direct airflow through the engine compartment effectively. The placement of baffles pulls air from the top of the engine around the cylinder heads and engine case down through the engine compartment, eventually being pulled out through the cowl flaps adjacent to the exhaust mufflers below the engine.
The baffle and baffle seal work together to direct air through the engine compartment. High pressure above the engine and lower pressure below the engine ensure continuous airflow through the engine compartment.
Higher-performance airplanes, like Sis, have Cowl flaps that pull air from the bottom of the engine compartment out of the engine.
Pilots can monitor cylinder head temperatures while in flight. Before this, I knew temperatures were important, but I don’t remember ground or flight school discussing why.
Ill-fitting or missing baffles will increase cylinder head temperatures and can harm engine health.
The restorer did not have luck with baffles but did find someone who made seals for older Bonanzas like sis.
While some of the seals may not work on the Model 35, subsequent models had seals attached to the cowling rather than the supports as they are on Sis, the seals look much better than what was on there before.
We think the seals that were on Sis may be original, which is over 75 years old.
I can’t wait to see her engine performance with these new seals on!
Baffle Install
Back baffles went on first and are interconnected. While installing the restorer realized a fuel injection line was in tight tolerances to the back baffle and was corrected by modifying the area with a dremel to accommodate. The concern is that a high-pressure fuel line could be rubbed through if not corrected.
The front baffle had been repaired and painted, and new seals were installed and were next to be installed. Pulling the single piece through in front of the engine around the propeller was definitely a two-person job but doable. Once in place, the restorer was a bit irked that his paint job had become scuffed – oh well, that’s what touch-up paint is for.
As sunlight was drawing scarce, securing the fuel injection lines was the last task for the day. Sitting on top of the inter-cylinder baffle, the injection lines are held down with a clamp over each row of cylinders with a specific pattern on each side.
The next work day, the restorer picked up where he left off, installing the remainder of the back baffles.
Even during the reinstallation, the restorer was finding areas he was not happy with. The baffles have undergone extensive repairs to ensure their functionality for the time being and will be modified further after flying.
The original side baffles were beyond repair. The restorer used them to make a pattern for replacement side baffles.
Due to the location between the engine and the outside of the cowling, the side baffles, in particular, get a lot of vibration
As the front and back baffles need to be installed before the side baffles can be placed; the restorer knew modification would be needed.
In the last remaining moments of sunlight, holes were drilled, then fitted with clecos to allow the remaining holes to be drilled in the side baffles, where they will attach to the back and front baffles.
While working on the side baffle, the restorer mentioned he could not find one of the back baffles. He would search at his hangar while I was working on other projects at the house, and then we would continue to work on the side baffles while we searched for a serviceable lower back baffle.
The restorer made side baffles after he could not find anything – literally nothing at the time – for a 1947 Bonanza. While working on the installation, we did find a single left baffle on eBay for $200 in what the restorer called barely serviceable condition. That is more the realization that we are going about this slowly, but it will be exactly what we are looking for.
The side baffles the restorer made were out of an alloy that is less prone to cracking than the original alloy was.
As the baffles are custom to Sis, the restorer brought his Dremel to trim as needed around the cylinder heads and supports for a proper fit.
After fitting, tweaking, and fitting again, the baffle is ready to be installed.
Using holes already in place adjacent to the baffle, holes are drilled into the new piece and clecos are used to keep it in place while additional areas are attached. Clecos are used to keep pieces of metal together while drilling or riveting.
After the side supports are established, attention is drawn to the area around the cylinder heads. Clips are used to fasten the baffle to the valve cover screws.
The clips that were on the side baffle originally, like the baffle itself, were in poor condition. Patterns were made from the original clips. We still had to drill holes and trim excess material in some areas, but it felt more substantial than before we had started.
After the holes for the valve cover screws are punched into the clips, I put them onto the bolt and tighten them into place.
Holes are then drilled directly into the baffle where the clips attach.
After holes are drilled, clecos are used to hold the baffle in place temporarily before the final assembly with screws and Tinnerman nuts.
Since gaining momentum on the baffle project, the restorer is more optimistic about our timeframe. He would like to have Sis ferried to his hangar before the weather is too cold because of concerns with cold temperatures and the initial cylinder break-in.
After we finished work for the day, the restorer searched online for lower back baffles. He didn’t find anything, but he devised a game plan for continuing the search during business hours.
We are making progress every day, and Sis is getting closer to flying. Keep focusing on the little things and making consistent progress – it will happen!
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