The Light Weight Engine Houtekietstraat 11
B-8540 Deerlijk, Belgium
EFFECTIVITY
page 48
ALL
19-3-2019
If the temperature rises above 95°C and the pilot notices, the performance most be reduced.
However the cooling system is relatively slow and the changes are measured slowly. If the
pilot reduces power shortly before 100°C (212°F), the temperature may still rise bove 100°C
(212°F). In that case, when action has been taken by the pilot, no danger is to the engine.
Water boils at 100°C (212°F) ?
The above statement is right at MSL (sea level
– 1013 hg). If the cooling system is without
pressure, the water can boil at 90°C or 80°C depending on the altitude! If the pressure is
increased in the cooling system, the water will only boil at higher temperatures. Clear water
boils at 1.4 bar at just over 110°C. Frost protection (additives) in the water does not freeze at
0°C. The frost additives also ensure that the water does not boil until higher temperatures are
reached. Depending on thge pressure (The D-Motor sealing rings are fit for maximum 1.2
Bar pressure) and the proportion of the frost additive, water will boil at 115°C to more then
130°C.
When the manual states ‘water boils at 100°C (212°F), D-Motor means : common sense
(taking altitude, duration, OAT, etc under consideration) !
Biggest risk for the D-Motor engines
, bubbles or no bubbles …
The biggest risk for the D-Motor engines is not running 10°C higher then allowed. The D-
Motor engine will not be damaged by this. The greatest risk to damage is caused by
cavitation. The steam ‘bubbles’ in the water occur when the pressure drops to far and the
temperature rises to high. Vibrations of components or housing walls intensify the effect. The
pressure in the water also drops where the water flows at high speed, i.e. around corners or
trough constrictions. In addition, there are ‘hotspots’ in the engine where the temperature can
be a lttle higher locally. Eg. Near the exhaust valve.
Cavitation ?
Even at to low temperatures cavitation may occur. If, for example, the engine
gets warm while climbing, the water expands and goes into the overflow tank. At high
altitudes (without a thermostat) and reduced power, the water cools down considerably.
Perhaps even below 60°C. At that moment the pressure in the cooling system can drop
below 1 bar and the water can boil at lower temperatures and form steam bubbles at the hot
spots. So water temperature to low at high altitudes can be harmful.
What is the normal, warning and danger water temperature for the D-Motor engines ?
It is all about the difference between Temp IN and Temp OUT ! eg. Rotax and Lycomming
only pushes its water trough the cilinder head chamber, they do not cool the cylinders, so
comparing the water temperature of eg. Rotax with the D-Motor limits is of no use !
The best practise for cooling the D-Motor engines is to keep the Temp IN and Temp OUT
close to each other (+/- 10°C). Temp IN is measured on a other place then Temp OUT !
When the three coulor code is installed in the cockpit, a pilot should see if the temperature
rises above 90°C, and act! Eurocopter voids warranty if temperature is logged more then 15
