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12 Things to Know About Cold Weather Start Procedures in GA Aircraft
21 December 2015
It’s cold out there. Winter days are often the best flying days, but it can be a pain to get your airplane started when it’s freezing outside. In addition, starting a cold-soaked engine can cause excessive engine damage in just the first minutes after engine start - damage that may not be evident initially but will significantly decrease your engine life. Preheating your aircraft engine will save you a lot of money on engine maintenance, as well as battery and starter wear and tear. Here are a few facts about cold weather operations in small general aviation aircraft:
It’s not (just) about cold oil. According to
this avweb.com article
, cold oil isn’t really the main problem at all, at least not until the temperature gets below -18 degrees Celsius. While cold oil is more viscous than warm oil, the more important problem is the expansion and contraction of the engine’s different types of metal. Aircraft engines include many different types of metals - aluminum, steel, etc. - with different expansion coefficients. When heated or cooled, aluminum expands or contracts quicker than steel, so when the aluminum crankcase contracts more easily than the steel crankshaft (like in cold temperatures), you have little or no clearance between the two, causing metal-on-metal grinding, which isn't good.
When not fully charged to begin with, a cold battery can mean a weak start, causing a pilot to crank on the starter more than he should in an attempt to start the engine. In a less-than-fully-charged battery, the chemical reaction is slowed when the temperature is cold which causes it to perform as if it has a lesser charge. This makes it more difficult to start an airplane that has a cold battery, and the continued cranking will be tough on the starter. Warming up the battery can reduce the demand on the battery and on the starter.
Starting a cold engine can give it the equivalent of 500 hours of cruise wear and tear, according to
this article on planeandpilot.com.
that preheating your aircraft engine is required when the engine temperature is below +10°F/-12°C.
that preheating be done whenever the engine has been exposed to temperatures at or below 20° Fahrenheit for two hours or more.
Lycoming also advises opening the cowl flaps, if necessary, during the preheating process, in order to reduce damage to nonmetal parts like hoses and wires.
Preheating in increments of 5-10 minutes is best, in order to heat slowly and prevent overheating of nonmetal parts.
When it comes times to start the engine, if it’s a carbureted engine, prime only when you’re ready to engage the starter. Allowing too much time to pass between priming and engaging the starter, or over-priming, can cause fuel from the primer to pool at the bottom of the carb heat box, presenting a fire hazard.
After start, keep the engine at idle while the oil temperature and pressure increase to their normal operating ranges. Surges or fluctuations in engine RPM are an indication that the engine is still too cold and takeoff should not be attempted.
Engines can be preheated with installed electrical heaters or forced air heaters, or by leaving the aircraft inside of a heated hangar for hours before the flight.
When using a forced air preheating system, Continental suggests that you should direct preheated air directly to the oil sump, oil filter, external oil lines, oil cooler, coolant radiator and cylinder assemblies for a minimum of 30 minutes
According to Continental, "Attempting to start your engine with a partially discharged aircraft battery may result in damage to the starter relay, possible engine kick-back resulting in a broken starter adapter clutch spring."
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