These thermal images
are from a Rotax 912 ULS
that was cold soaked and
sustained in a - 20 degree
Celsius environment. On the
left is the engine after a half
hour of preheat time. On
the right is after 5 hours of
preheat time.
Shaking Off the Chill
Preheating solutions for winter flying
BY TIM KERN
IT ISN’T JUST US; cold weather is uncomfortable for our airplane
engines, too. Not only do the metal parts shrink, but the oil also gets
“thicker” (more viscous) at low temperatures. Cold decreases power
available from the battery and increases the load on the starter motor,
even as it reduces the amount of oil available for lubrication. Cold oil
takes longer to coat surfaces, leading to higher wear at start-up and
during warm-up. In cold weather, everything works against you.
Even with multi-viscosity and more-stable synthetic oils available, cold-starting presents plenty of problems, and solutions run
from old-tech to modern, with some downright dangerous practices.
When I was in college, I would drain the oil from my car and
bring it into the dorm, placing it on the room’s heater overnight. In
the morning, I’d pour the heated oil back into the old Renault and
have a friend run the anemic starter motor, as I helped by turning
the crank at the rear of the car. If the engine started, I’d keep it warm
all day. If I parked during a class, I’d throw a blanket over the engine.
If I parked close enough to an outlet, I could avoid the mess of draining the oil by using a “trouble light” with a 100-watt bulb under the
sump. Later, I discovered the “dipstick heater” and stopped draining
the oil daily. Then spring came and I got rid of that car.
At the airport, a walk down the ramp in cold weather will reveal
a number of solutions: infrared-heated hangars, blankets and light
bulbs, counter stools with flaming cans of Sterno sitting under
engines (don’t do this!), dipstick heaters, guys with hair dryers
(okay) or heat guns (be careful), heat blankets, home-style electric
space heaters, and dedicated “proper aviation engine heaters” of several types. All raise the temperature of the engine and oil; not every
one is a good idea.
Assuming you run the proper oil for your
engine and climate, what else can be done to
make cold starts less destructive to the
engine and easier on batteries, starters, and
yourself? A cold battery delivers less power;
this can lead to starter damage, as well as
failure to start. For this reason, Teledyne
Continental Motors (TCM) advises, “Always
use an external power source when
attempting to start your aircraft engine in
cold weather.”
Of course, you can also warm your bat-
tery, too. If your battery is in the engine
compartment, an under-the-cowl heater will
heat the battery as well as the engine. For
batteries located elsewhere in the aircraft,
separate battery heaters are available from
Tanis Aircraft Products, Wicks Aircraft
Supply, and other aircraft supply houses,
WHAT TO CONSIDER
First, assess your environment. Whenever
you add heat to anything, there is the danger
of fire. (Is your hangar clean? Are you storing combustibles properly? Are your shop
rags properly managed?) Consider how
often you will need to preheat your engine.
Although you may need to preheat
