Freezing temperatures don’t mean your club’s operations have to cool down as well. It is important to make sure every member of your club knows how vital a properly preheated aircraft is. This month we will take a look at how your club can make sure everyone is doing their part to protect your engine and other systems during the colder months.
Warming up to Preheating
There are a lot of great systems on the market to get your aircraft flight ready in the winter months. Some are permanently installed on your engine and others are meant to be removed before flight. The system you select depends on your club’s needs and the region you fly in. We won’t go into the specifics of all of the systems on the market in this article, that would end up being more like a book if we did. Instead, we will focus on how you can set up a standard operating procedure to ensure that every member of your club is properly preheating before start up-every time. First, let’s look at why preheating is so important.
What is the big deal?
A common belief is that the risk to starting a cold engine is that the oil is so viscous that it can’t properly circulate through the engine, causing excess wear. This can be true if you are using single weight oils, but multi-viscosity oils commonly in use today have excellent flow even at 0 degrees F. The real risk comes from the fact that your engine has dissimilar metals working in close proximity to one another. As those dissimilar metals get colder they shrink at different rates, which causes space normally occupied by a protective film of oil to completely close off, resulting in metal on metal contact. Attempting to start an engine in this state without properly preheating can cause the equivalent of 500 hours of wear in the span of a few minutes. This is why it is important to have a good preheat before every start in colder temps.
Cold or Cold-Soaked?
How cold does it have to be before a preheat is mandatory? Like most things in aviation, it depends. Let’s start by checking with the manufacturers. Continental and Lycoming both have temperatures below which a preheat is mandatory, but they go about it in different ways. Lycoming in Service Instruction 1515 mandates preheating when an engine’s internal temperature has been allowed to drop below 10 degrees F. Similarly, in Service Information Letter SIL 03-1 Continental requires preheat when an engine is exposed to temperatures below 20 degrees F for more than two hours. Lycoming is talking about a cold-soaked engine while Continental is taking the more cautious route and mandating a preheat even on a cold engine.
While these mandates provide a good starting point around which to build a preheat procedure, it is a good idea to err on the conservative side when dealing with your club’s own precious engine. A general rule of thumb is that preheating is necessary whenever the ambient temperature has dropped below the freezing level and has remained there for more than four hours. For those of us who keep their airplanes outdoors or in unheated hangars, this means we’ll be preheating for most of our winter flights.
The cold doesn’t just affect your engine, however. Gyros, radios, electrical contacts, and other vital systems all need time to warm up before working their best. Setting up a small space heater in the cockpit usually does the job. Make sure you use a heater that is safe for the cockpit. Some heaters require a three foot space away from any objects-try doing that in a lightplane cockpit. Supply companies like Aircraft Spruce sell plug-in cabin heaters designed for this purpose.
Before your next club meeting, write up a standard operating procedure for how you want club members to perform the preheat. Having pictures of the correct setup will be helpful in avoiding potential damage to your engine compartment and cockpit. It is also a good idea to have all of the equipment needed to perform a proper preheat organized in your hangar or in a dock box by your plane. A handy tool to know how your preheat is an infrared thermometer, just point it at your cylinder heads or at the oil pan under the cowl and you will have an instant read out of how warm things are getting. Make sure you have a plan in place as well for preheating your aircraft while away from home base. Combustion heating is a great way to quickly warm up your engine but exercise caution when requesting it. It may be the line person’s first time heating up your particular type of aircraft, and expensive parts can be melted accidentally.
Save yourself a trip
A great way to make preheating less of a chore is to invest in a SMS switch so that club members can engage the preheat system from the comfort of home. These switches can be purchased commercially and many of them have multiple ports that can be controlled independently allowing you to heat up your engine the night before and the cabin a few hours ahead of your planned flight. Obviously, you will need to make sure whoever flew the plane last has plugged in and positioned all of the heating elements correctly.
A word of caution about using installed preheating systems is that they can cause excess condensation inside your engine. It is best to limit engine block preheating to 24 hours at most. The problem here is that most plug in heating systems do not heat up your entire engine uniformly. An oil pan heater for example can cause moisture from the oil sump to evaporate and condense on unheated engine components like the camshaft or cylinder walls. Only using the preheat for a brief period before flying is a great way to avoid corrosion problems. Notice we said before flying and not before running the engine. Performing a short ground run or taxiing the aircraft around the ramp does not adequately warm up the engine and can cause crankcase moisture to increase. Your best protection against engine moisture is to go flying!