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ananoman · September 15th, 2004, 23:58

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Why can't auto gas be used in high altitude aiplane engines? (even if the timing has been adjusted to prevent detonation)

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Most 'high altitude' engines are turbocharged and most available mogas STC's are for lower compression engines which are normally aspirated. But I am guessing that the reason you are looking for has to do with the vapor pressure of auto gas. At high altitudes, it will tend to evaporate due to the lower atmospheric pressure. This can cause all sorts of interesting fuel problems, but vapor lock would be the most common. Avgas is formulated to help avoid this, but it can be much more important to follow correct procedures when switching fuel tanks at higher altitudes. Some manuals specify using the electric boost pumps when switching tanks. At low altitudes it is usually no big deal if you omit this, but at high altitudes, you might get a suprise.

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You leave the mixture rich and turn the mag key to OFF. The engine keeps running, what's wrong?

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You either have a broken 'P-lead' or lots of carbon deposits in the combustion chambers.

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Where does the magneto get it's electricity?

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The magneto generates its own current. It is kind of a combined generator/distributor, which unlike a car, will allow the engine to run after a complete electrical failure.

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Who is ultimately responsible for the mechanical condition of the airplane?

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The owner/operator is responsible for keeping an aircraft in airworthy condition. The pilot is responsible for making sure it is safe for flight.

September 15th, 2004, 23:58	#22
ananoman Senior Member Join Date: Dec 2002 Posts: 916	Re: Today\'s Tech Trivia #4 [ QUOTE ] Why can't auto gas be used in high altitude aiplane engines? (even if the timing has been adjusted to prevent detonation) [/ QUOTE ] Most 'high altitude' engines are turbocharged and most available mogas STC's are for lower compression engines which are normally aspirated. But I am guessing that the reason you are looking for has to do with the vapor pressure of auto gas. At high altitudes, it will tend to evaporate due to the lower atmospheric pressure. This can cause all sorts of interesting fuel problems, but vapor lock would be the most common. Avgas is formulated to help avoid this, but it can be much more important to follow correct procedures when switching fuel tanks at higher altitudes. Some manuals specify using the electric boost pumps when switching tanks. At low altitudes it is usually no big deal if you omit this, but at high altitudes, you might get a suprise. [ QUOTE ] You leave the mixture rich and turn the mag key to OFF. The engine keeps running, what's wrong? [/ QUOTE ] You either have a broken 'P-lead' or lots of carbon deposits in the combustion chambers. [ QUOTE ] Where does the magneto get it's electricity? [/ QUOTE ] The magneto generates its own current. It is kind of a combined generator/distributor, which unlike a car, will allow the engine to run after a complete electrical failure. [ QUOTE ] Who is ultimately responsible for the mechanical condition of the airplane? [/ QUOTE ] The owner/operator is responsible for keeping an aircraft in airworthy condition. The pilot is responsible for making sure it is safe for flight.