Plane & Pilot
Tuesday, November 1, 2005

Aircraft And Engine Preheat Is A Big Deal

Pilots need to stay warm during the winter months. Your airplane deserves the same consideration.

Aircraft Engine Preheat Is A Big DealYour engine needs preheat. Starting a cold engine can give it the equivalent of 500 hours of cruise wear and tear, according to engine authorities. Assuming no other potentially catastrophic damage occurs, this single event easily could raise the hamburger price to a healthy four-digit value.

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Aluminum is an amazing alloy that has given engineers the ability to design all-metal aircraft structures, their engines and components without the power loading requirements of the space shuttle. The metallurgical properties of this material provide the basis for the preheating argument. It’s important to understand that aluminum responds more rapidly and to a greater degree to thermal change than most other engine metals. Under cold conditions, the operating tolerances between these dissimilar metals are compromised, possibly to the point of being nil. This will have significant consequences during startup. The closer we can move toward normal operating temperatures prior to start for both the metals and the proper grade of lubricating oil, the more likely an engine will make TBO.

Aircraft operation without electrical power, although not impossible, can increase the overall degree of flight difficulty. Starters, instruments and avionics all require electron enthusiasm to be motivated. A fully charged wet battery may be immune from freezing to a temperature of minus-95 degrees F, but once depleted to 25%, it will freeze at approximately 10 degrees F. Because a cold storage battery’s chemical reactions are slowed, the situation becomes equivalent to using a battery of lower capacity. Although voltage may be normal, you may not have enough amperage for multiple engine starts. Keep in mind that a cold battery, especially one not placed on the firewall, may take hours to fully charge in flight.

When the thermometer dips, cockpit knobs, selectors, displays, switches, mechanical instruments and housed cables are all subject to condensation buildup and changes in tolerance. Freezing temperatures may seize mechanical actions or short delicate circuits. Lubricants will become more viscous, creating undesirable resistance. At some point, electronic components may refuse to power up.


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