Approach - adjust/close cooling flap to avoid over-cooling the
engine.
Landing - close flap fully for landing.
Ground and Taxing - warm engine up if necessary
4.5 Touch and go’s and the risk of vapor lock
Problems with engine re-start can occur during hot days. This is
caused by overheated fuel in the engine compartment. Fuel starts
boiling at 70-80°C. Due to formation of bubbles an irregular fuel
supply occurs, and power loss including engine failure can occur
during take-off. This effect is called vapor lock.
To reduce risk of vapor lock, the T connection of the return line is
placed on the highest position of fuel hoses. Two temperature
sensors are installed inside engine compartment, one close to the
fuel line, so the pilot has information about these temperatures.
Temperatures over 60
o
C indicate yellow so attention is needed,
temperatures over 70
o
C generate a red indication, which causes
the risk of vapor lock. Recommendation is to turn airplane in the
wind and run engine at idle to reduce temperature or shut it down
to let it cool down. In hot environmental conditions, keep the oil
inspection door on the upper motor cowling open in flight, to
reduce this problem.
There is no risk of vapor lock during flight. After take-off the engine
compartment cools down to a temperature of about 20
o
C above
the outside air temperature. Rotax recommends using AVGAS fuel
in case of vapor lock issues.
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