Ramblings about flying for fun and profit.

Category: Aircraft Maintenance Page 3 of 5

Repairing and maintaining an airplane.

Swift Maintenance

My time at home in April was split between catching up on the usual home and office duties and working on the interior of the Swift. I bought a new Garmin SL-30 communications radio for the plane along with a new Comant CI-121 VHF communications antenna and RG-400 cable to connect the two. About a month ago we had a nice warm day, so I decided to go out and work in the hangar and to start the new radio installation. First I took the old unit out, a big box com/nav unit that had long outlived it’s usefulness. The next step was to remove the old antenna and install the new one, then route the new cable along the same path that the old cable used. Stripping paint from the rear of the cockpit of a Globe Swift.

I won’t say what I found when I removed the old antenna other than to say that it hadn’t been installed using the best practices. In order to correct the workmanship and install the new antenna correctly I would have to install a doubler under the antenna. That would involve stripping the ugly yellow/tan paint away from the area below the antenna before doing the riveting. Stripping the paint in just a small area and then painting a new color wasn’t a good idea, so now I was looking at stripping the ugly old paint in the aft area of the cockpit and repainting the whole thing. Now I needed to remove the shoulder harness installation, the electric pitch trim motor and lines and the rear windows. This list is not getting shorter!

Aircraft Engine Pre-Heat

I mentioned my engine pre-heater in my last post and received a request to explain it in a little more detail. Engine manufacturers and engine overhaul facilities such as Mattituck strongly recommend pre-heating the engine whenever the temperature is below 20° F. and some sources recommend pre-heating when the temperature is below 32° F. However, all the sources I checked agreed that pre-heating before starting in cold temperatures will significantly reduce wear to the engine.

Ben Visser, Staff Research Engineer, Shell Oil:

“Preheating your engine makes a world of difference. It heats the oil so the oil is thin enough to flow through the engine and properly lubricate all of the critical wear surfaces. Preheating also heats the metal parts in the engine. That’s important because aluminum crankcases have a higher coefficient of thermal expansion than iron crankshafts. This means as your engine cools down, the clearance is reduced. And as a result, you may not have sufficient oil film thickness for proper hydrodynamic lubrication at very cold temperatures. In other words, the wear rate is going up. If you’re using [an electric] heater, make sure it’s a system that heats the whole engine, not just the oil.”

I made a small pre-heater for my plane that forces hot air into the engine compartment from below, allowing the warm air to heat the oil sump and then to flow up around the cylinders and out the front of the engine, using the reverse of the route used by the cooling airflow during flight. Home-made aircraft engine pre-heater.

I bought all of the materials for my pre-heater from one of the local home improvement centers like Home Depot. The heat source is a small portable ceramic heater. The sticker says it is a Ceramic Safe-T-Furnace, Model HC-441W (made in China, of course). It has a built-in fan and a plunger-type safety switch on the bottom that will shut the unit off if it tips over. There are both fan speed and heat controls on the front, though I just set both of them to their maximum settings and leave them there. I also have a piece of tape on the bottom of the unit holding the safety switch depressed. As you can see in the photo, the unit is tipped slightly forward and the tape keeps the unit from shutting off.

square-to-round adapter

I used a square to round flange adapter similar to this larger version and tapped it to the front of the ceramic heater to use as a transition to the round ducting, then attached a length of dryer duct to the adapter to direct the heat upward. The duct is a very flexible expandable metallic tubing that is easily molded to any shape that you might need.

I used the pre-heater with bare tubing for a little while, then decided that the unit was transferring too much of it’s heat through the thin-walled ducting, so I bought some self-adhesive insulation and wrapped that around the duct leaving the last 6″ or so uncovered so that it could be squeezed into an elongated oval in order to fit up into the cowl. The adhesive on the insulation wasn’t staying attached to the uneven surface of the duct, so I wrapped the whole duct with aluminum tape that is used by HVAC installers.

I also use 2-3 layers of blankets and carpet remnants over the engine compartment to help reduce heat loss. When I intend to go flying, I plug in the unit, make sure that the fan is operating and then go about my preflight duties. If it’s really cold, I will often make a trip to the local coffee shop for a few minutes and give the unit about an hour to work it’s magic. By the time I return there is a noticeable flow of hot air coming out of the front of the engine and the blankets/carpet over the top of the engine compartment are warm to the touch. The engine always turns over easily during start and the oil pressure indicates quickly.

Aircraft engine pre-heater.

I don’t know how much the pre-heater cost to make. I do know that I bought more material than I needed for the project because smaller quantities were not available. Two people could probably build units and split the costs. I did notice the other day that you can buy the flexible ducting with insulation already attached. Bigger heaters will, of course, pump out a larger volume of hot air and will do the heating job a bit quicker, but they would also need a larger diameter duct to move the air.

I’m sure other people have made more elegant and more professional-looking pre-heaters, but this one works for me and it seems like it will last for quite some time. It looks like the temperatures are starting to trend higher now, so maybe by the end of the month I’ll be able to put it away for the summer.


Update:I first posted this article on the evening of March 8th after a beautiful, clear day with temperatures in the low 50s (F). It is now 8 am on the morning of March 9th and I am looking at a thermometer indicating a temperature of 22° F with 5″ of new snow on the ground. Maybe I won’t put the heater away this month…

Big Tow Little Tow

Airline tow vehicle hooked to a Boeing 747.

Traffic was backed up a little as we were leaving Tokyo the other day which meant we had to to wait in line on the parallel for our turn to take off. We happened to stop just abeam a parking apron where a maintenance crew was readying a 747 for tow. They were using one of the big tugs that can lift the nosewheel off the ground and capture it in a cradle. This makes it very easy to maneuver the aircraft from one position to another and gives a very smooth ride if the plane is full of passengers. The tug also has auxilliary electrical power capability. You can see the yellow power cord coming from the tug, looping around the steering cylinders at the rear of the nosewheel strut and connecting to the plane. It’s not obvious what the other line is that is coming out of the nosewheel well, but it is probably the cloth streamer attached to the end of the nosewheel pin. The pin is inserted into a hole in the nosewheel retraction mechanism to prevent the gear from retracting. I have seen these tugs moving 747s around at what seemed like 30 knots. It was probably not that fast, but it was definitely faster than a brisk walk. For those of you who may be curious, the ANA on the side of the tug stands for All Nippon Airways. If you have really good eyes, you can see the letters NCA on the underside of the aircraft nose. That’s a Nippon Cargo Airlines 747-400 freighter, not the private plane of the National Cheerleaders Association. (Amazing the things you find with a Google search.)

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