hevansrv7a
Well Known Member
I have posted regarding dehydrators before but I thought perhaps it would be best to isolate the subject and to offer some evidence that I think reasonably supports my assertion that we should use one.
Facts include:
1. Humidity is relative. This means that hotter air can hold a greater quantity of moisture in vapor form. It also means that there is for any air that contains some moisture, a dew point that is usually lower than ambient. That's often reported by automated systems at airports, for instance. See https://en.wikipedia.org/wiki/Dew_point
2. The byproducts of burning avgas include large quantities of carbon dioxide and hydrogen dioxide AKA water. That's because gasoline is mostly carbon and hydrogen. See
https://en.wikipedia.org/wiki/Gasoline
"Energy is obtained from the combustion of gasoline by the conversion of a hydrocarbon to carbon dioxide and water. The combustion of octane follows this reaction:
2 C8H18 + 25 O2 → 16 CO2 + 18 H2O"
The water produced by burning avgas is in vapor form because the exhaust is hot.
3. All piston engines but especially loose ones such as our air-cooled ones allow some of the exhaust to pass down past the rings into the internal spaces of the engine. We have crankcase vents for a reason.
4. The dew point of the moist air inside the engine that has reached operating temperature and then is shut down is almost certainly higher than the ambient temperature at the destination airport.
My own Logical Conclusion:
You will wet the inside of your engine every time you fly it and then stop it for more than an hour or so (actual ambient conditions control the cooling rate, actual interval). More exactly, when the engine cools it will reach the dew point long before it reaches ambient temperature and the necessary consequence is that there will be liquid water inside your engine. Again.
My Evidence that the Dehydrator Works:
While my new engine was waiting to be installed in my unfinished airplane it had clear plastic water absorbing "plugs" where the upper plugs would go. They were filled with a material that I think is the same silica gel that comes in little packets with packaged electronics. Anyhow, the beads contained some indicator beads which are blue when dry and pink when fully wet. My plugs gradually changed from blue to pink. I then purchased and began using the dehydrator that I still use. Within a few days, the indicator plugs in the engine changed back to blue and stayed that way. I interpret that as a direct indication of the humidity inside the engine. The particular dehydrator that I use is just a much bigger version of those plugs that came with my engine plus an air pump that is commonly used for aquariums. It blows ambient air into the jug full of beads and then the dried air comes out the other side and goes up the oil vent pipe into the engine. A slight positive pressure is maintained inside the engine and the dry air escapes via the exhaust pipes.
I am agnostic as to which device should be used. I am happy with mine. Some friends saw mine and built their own and those work the same. Some manufacturers use a mechanical device which is like the dehumidifier for a house's basement. I'm of the opinion that those will work, too.
Facts include:
1. Humidity is relative. This means that hotter air can hold a greater quantity of moisture in vapor form. It also means that there is for any air that contains some moisture, a dew point that is usually lower than ambient. That's often reported by automated systems at airports, for instance. See https://en.wikipedia.org/wiki/Dew_point
2. The byproducts of burning avgas include large quantities of carbon dioxide and hydrogen dioxide AKA water. That's because gasoline is mostly carbon and hydrogen. See
https://en.wikipedia.org/wiki/Gasoline
"Energy is obtained from the combustion of gasoline by the conversion of a hydrocarbon to carbon dioxide and water. The combustion of octane follows this reaction:
2 C8H18 + 25 O2 → 16 CO2 + 18 H2O"
The water produced by burning avgas is in vapor form because the exhaust is hot.
3. All piston engines but especially loose ones such as our air-cooled ones allow some of the exhaust to pass down past the rings into the internal spaces of the engine. We have crankcase vents for a reason.
4. The dew point of the moist air inside the engine that has reached operating temperature and then is shut down is almost certainly higher than the ambient temperature at the destination airport.
My own Logical Conclusion:
You will wet the inside of your engine every time you fly it and then stop it for more than an hour or so (actual ambient conditions control the cooling rate, actual interval). More exactly, when the engine cools it will reach the dew point long before it reaches ambient temperature and the necessary consequence is that there will be liquid water inside your engine. Again.
My Evidence that the Dehydrator Works:
While my new engine was waiting to be installed in my unfinished airplane it had clear plastic water absorbing "plugs" where the upper plugs would go. They were filled with a material that I think is the same silica gel that comes in little packets with packaged electronics. Anyhow, the beads contained some indicator beads which are blue when dry and pink when fully wet. My plugs gradually changed from blue to pink. I then purchased and began using the dehydrator that I still use. Within a few days, the indicator plugs in the engine changed back to blue and stayed that way. I interpret that as a direct indication of the humidity inside the engine. The particular dehydrator that I use is just a much bigger version of those plugs that came with my engine plus an air pump that is commonly used for aquariums. It blows ambient air into the jug full of beads and then the dried air comes out the other side and goes up the oil vent pipe into the engine. A slight positive pressure is maintained inside the engine and the dry air escapes via the exhaust pipes.
I am agnostic as to which device should be used. I am happy with mine. Some friends saw mine and built their own and those work the same. Some manufacturers use a mechanical device which is like the dehumidifier for a house's basement. I'm of the opinion that those will work, too.
