Continuous Heater and Dehumidifier good or bad?

[J0nathan225 189]

My after shutdown procedure is opening the oil door and unscrewing the dipstick to let hot air escape while I pull the aircraft into the unheated hanger.  I then cover the cowling with a blanket and plug in my EZ sump heater and my Engine Saver.  I keep the heater plugged in 24/7 as well as the dehumidifier which cycles as needed. Wondering if this is better or worse than letting the engine cool and only pre-heating a few hours prior? 

 My thought process; I'm HOPEFULLY creating an desert like atmosphere inside the engine and keeping the dew point spread large.  

[carusoam 11,978]

Continuous heating has several problems...

It could be good...

It could end disastrously...

It takes being a weatherman of micro-climates to know....

The last thing you want to do... is heat up a moist environment inside the engine... but not enough to drive the moisture out...

Temperature increases the rate of oxidation... 

So... instead of a little rust... you accidentally get a lot of rust... 

 

Dehumidifiers take the microclimate aspect out of it...

PP thoughts only, not a weatherman...

Best regards,

-a-

[larrynimmo 287]

I use this kind of heater by the left cowl (cylinder 2) and I lay a sleeping bag over the entire cowl closing off both inlets.   This keeps the upper engine about 70 degrees.  The coldest area is the lower oil pan.  Any condensation created should happen directly on the oil surface and should be quickly disapated as the engine warms up.   I rarely go more than 5 days without running my plane.  These heaters introduce very little heat and are completely automatic and explosion proof....but overly expensive.  Nothing like starting up a warm engine

[tmo 523]

I only blow dry air in via the dipstick on a permanent basis. I also leave desiccant in open containers in the cabin (baggage compartment and both footwells).

When the temperature warrants it, I'll pre-heat the engine by blowing warm air up via the cowls during preflight; might also warm up the cabin some.

In due course I might end up with a remotely controllable setup to start the pre-heat as I drive to the airport, too scared of possible fires with the current setup.

I do not plan on any permanent heating setup for the engine, ever.

If I ever build my own hangar, I might consider a heat pump and heated floor. But that will probably mean I have to live there...

[GeeBee 895]

I use an Aerotherm Deuce to continuously blow hot air when needed with a thermostatic control. By keeping the engine above ambient, you are preventing condensation. Aviation Consumer did a test and found out the same thing. Once the temp goes below 70, I remove the desiccant device and use only hot air and keep the entire engine at 90 degrees. This is not an unknown phenomena. If you keep a "Golden Rod" in your gun safe, it is the same principle. I would not use heat bands to effect this as they are too concentrated on the cylinders. A hot air machine or a pan heater seems to work the best for this method.

 

http://www.reiffpreheat.com/Article-Fiorentini-ContinuousPreheating.pdf

[J0nathan225 189]

On 10/27/2020 at 8:28 AM, GeeBee said:

I use an Aerotherm Deuce to continuously blow hot air when needed with a thermostatic control. By keeping the engine above ambient, you are preventing condensation. Aviation Consumer did a test and found out the same thing. Once the temp goes below 70, I remove the desiccant device and use only hot air and keep the entire engine at 90 degrees. This is not an unknown phenomena. If you keep a "Golden Rod" in your gun safe, it is the same principle. I would not use heat bands to effect this as they are too concentrated on the cylinders. A hot air machine or a pan heater seems to work the best for this method.

 

http://www.reiffpreheat.com/Article-Fiorentini-ContinuousPreheating.pdf

Hmm I like the temperature output.  I think with my blanket, sump heater, and space heater setup I only keep the firewall forward at ~70-90 degrees. Great article though!

[larryb 671]

I have also instrumented my engine with RH and temperature measurements. My results duplicate the referenced article. As temperature is increased RH decreases. Using a Reiff heater, blanket over the cowl, and a thermostat I have my setup maintain a constant 90 degrees F year round. The oil fill cap is left off when the airplane is home and inside. This is in a relatively dry California climate. I maintain around 10% RH when the plane is in Truckee and around 30% when the plane is in San Jose. In a humid environment this might not work as well and active dehumidification might be required. Actually measuring the humidity is key, and avoids any guesswork.  

 

What is interesting is that right after flight RH is typically 60%. I have seen it at 100% after taxiing without flight, such as bringing the plane back to my hangar after avionics work at my home field. After a day or so at 90 degrees F the RH drops to the stable long-term values.

[J0nathan225 189]

I may purchase an Aerotherm. The sump heater + blanket isn't getting up to the 90-100+ where I'd like to be. 

[jetdriven 4,408]

8 hours ago, larryb said:

I have also instrumented my engine with RH and temperature measurements. My results duplicate the referenced article. As temperature is increased RH decreases. Using a Reiff heater, blanket over the cowl, and a thermostat I have my setup maintain a constant 90 degrees F year round. The oil fill cap is left off when the airplane is home and inside. This is in a relatively dry California climate. I maintain around 10% RH when the plane is in Truckee and around 30% when the plane is in San Jose. In a humid environment this might not work as well and active dehumidification might be required. Actually measuring the humidity is key, and avoids any guesswork.  

 

What is interesting is that right after flight RH is typically 60%. I have seen it at 100% after taxiing without flight, such as bringing the plane back to my hangar after avionics work at my home field. After a day or so at 90 degrees F the RH drops to the stable long-term values.

Yes, as temp increases, RH decreases. But the total grains of water per cuft increase.  More water more corrosion.  Short story, warmer humid air is corrosive.

[larryb 671]

Yes, as temp increases, RH decreases. But the total grains of water per cuft increase.  More water more corrosion.  Short story, warmer humid air is corrosive.

The only water that matters for corrosion is the water on the surface of the metal which makes a little micro battery. Water trapped in the air is not available for corrosion and therefore a good thing.

[MikeOH 776]

1 hour ago, jetdriven said:

Yes, as temp increases, RH decreases. But the total grains of water per cuft increase.  More water more corrosion.  Short story, warmer humid air is corrosive.

This is what I was reasoning out.  But, I'm not up on what really causes corrosion.  Does the moisture have to condense?  I suspect, but don't know for sure, that it does not.  To your point, the coldest places on earth have VERY low humidity.  Seems like hot and humid (e.g. Florida) is not ideal!

[MikeOH 776]

2 minutes ago, larryb said:

The only water that matters for corrosion is the water on the surface of the metal which makes a little micro battery. Water trapped in the air is not available for corrosion and therefore a good thing.

Do you have a cite for that?  Not trying to be a jerk; honestly, I'm not sure how the chemistry really works.  What you stated is the 'argument' I've always heard, but...

[carusoam 11,978]

Moisture on the surface is the obvious give away...

Realistically... high RH can even lead to moisture condensing on the surface...

Really realistically... high RH itself is enough to support the oxidation process...

Sure... O2 is required as well...

To test....   Put your metal samples out in a room, run the RH up to 80%....

If the samples are sensitive to moisture in the air and the O2 in the air will find the metal’s surface and begin rusting overnight...

 

If you wear glasses... come in from outside on a cold day... and see how much moisture keeps condensing on the lenses... what a pain in the butt...

RH lower than 50% seems to be much better for metals than above 50%...

Rust uses water as a catalyst to combine O2 with the metal’s surface...

The more catalyst there is around, the more often O2 and metal can become one...

 

PP thoughts only, not an oxidation/reduction chemist...

Best regards,

-a-

[PT20J 2,266]

From the Tannis FAQ (https://www.tanisaircraft.com/faq-frequently-asked-questions)

• Resistance heat cannot create moisture. Moisture is always present inside your engine and specifically within your oil.  Use of our system will NOT result in corrosion because a Tanis preheat system keeps all of the metal parts that are above the oil level above “dew point” and as a result condensation cannot occur on these parts. Tanis preheat systems are not to be cycled on and off as this could cause the engine to go through “dew point” (timers and thermostats are not to be used).

The Reiff FAQ has a lengthy discussion on the subject (http://www.reiffpreheat.com/FAQ.htm#QA3)

From Mike Busch in 4/1/2019 (April Fool?) AOPA Pilot (https://www.aopa.org/news-and-media/all-news/2019/april/pilot/savvy-maintenance-crimes-and-misdemeanors)

• I’m frequently asked whether it’s OK to leave an engine-mounted electric preheater plugged in continuously. Both Continental and Shell have published warnings against leaving such preheaters on for more than 24 hours prior to flight. Their concern is that heating the oil pan will cause moisture to evaporate from the oil sump and then condense on cool engine components such as the camshaft, crankshaft, or cylinder walls, resulting in accelerated corrosion of those parts. In Continental engines, the starter drive adapter is particularly vulnerable. Tanis did a study on this some years back, and published a white paper that said, in essence, it’s OK to run an electric preheater 24/7 provided the engine is hooked up to an electric dehydrator system (e.g., Engine Saver, Black Max, EICU), but that if the crankcase contains moist air then it’s best not to plug in the preheater until six hours or so before you plan to go flying.

Skip

 

[GeeBee 895]

That is why I use hot air and keep the whole engine compartment and the whole engine warm, that way there is no where for condensation to occur.

 

 

[steingar 2,288]

I'm in the same boat as @larrynimmo.  I use the same product in the same way.  My thinking is if you could keep your airplane in a heated hangar I'm pretty certain you would.  So I keep my engine in a mini heated hangar.  I don't really worry about humidity, never have and have never had a problem with an airplane engine corroding in 20 years.

[DXB 2,053]

20 hours ago, jetdriven said:

Yes, as temp increases, RH decreases. But the total grains of water per cuft increase.  More water more corrosion.  Short story, warmer humid air is corrosive.

It's RH matters for corrosion, not absolute water content in the air.  At less than 60% RH, there is minimal corrosion irrespective of temp or atmospheric pollutants.  Heating an engine uniformly in the winter should be effective, unless you're also heating an adjacent moisture source.  

[larrynimmo 287]

10 hours ago, DXB said:

It's RH matters for corrosion, not absolute water content in the air.  At less than 60% RH, there is minimal corrosion irrespective of temp or atmospheric pollutants.  Heating an engine uniformly in the winter should be effective, unless you're also heating an adjacent moisture source.  

And that’s why a sump heater is not a good choice...as moisture in the oil will evaporate off the warmed oil and create an atmosphere of 100% relative humidity in the cavity of the engine.  By air heating the heads....the way I do it....the upper engine is too warm for internal condensation to form...as the oil will be cooler.  If condensation dies form, it should be on the cool oil surface.  If you don’t fly too often though, you have to assume that there is some water in the oil, and when you fly, it needs to be long enough for it to vent off...and your oil needs to achieve close to 180 degrees to accomplish that

[GeeBee 895]

Personally a sump heater is not my choice, however, oil has a tremendous amount of latent heat. Once heated it would conduct that heat to warm the entire engine. The only question is there sufficient BTU to overcome the heat loss as it radiates off the engine. If there is more input than loss, the entire engine should stay warm. If the sump heater is activated after a run, and it has sufficient BTU input, I don't see the engine cooling down enough to effect condensation.

 

[larrynimmo 287]

5 minutes ago, GeeBee said:

Personally a sump heater is not my choice, however, oil has a tremendous amount of latent heat. Once heated it would conduct that heat to warm the entire engine. The only question is there sufficient BTU to overcome the heat loss as it radiates off the engine. If there is more input than loss, the entire engine should stay warm. If the sump heater is activated after a run, and it has sufficient BTU input, I don't see the engine cooling down enough to effect condensation.

 

It is all “relative”. So are temperature variations.   If the oil is kept at 80f and the upper engine is 75 degrees...that 75 degrees is cool enough that moisture laden air would condensate.

when you shut down the hot engine at 180 degrees, moisture is easily suspended in the warm air...as the air is cooled water vapor will condensate.

in the already “cold” engine with only a sump heater, you are creating a “steam room effect”. If there is enough moisture that it drips, it will drip into the oil, then evaporate again as it warms continuing the cycle.

[GeeBee 895]

Well I think you can prove it to yourself. Get a double boiler use oil instead of water. Heat up the oil above the dew point and with nothing in the the upper pan.  Any water condensate in the upper pan?

 

[larrynimmo 287]

47 minutes ago, GeeBee said:

Well I think you can prove it to yourself. Get a double boiler use oil instead of water. Heat up the oil above the dew point and with nothing in the the upper pan.  Any water condensate in the upper pan?

 

A double boiler does not really have a common vapor cavity as an engine would have.. it would be the moisture from the oil that would condensate on the walls, parts and top of the engine...take a pan of water with a glass top...heat the water without boiling it...the glass (as long as it is cooler will collect water droplets on the inside and drip down again

[larrynimmo 287]

3 minutes ago, larrynimmo said:

A double boiler does not really have a common vapor cavity as an engine would have.. it would be the moisture from the oil that would condensate on the walls, parts and top of the engine...take a pan of water with a glass top...heat the water without boiling it...the glass (as long as it is cooler will collect water droplets on the inside and drip down again

Perhaps a steamer with a lower pan would be a better test

[GeeBee 895]

It is really simple. No condensate is going to form as long as the metal temp is above the dew point.

 

[larrynimmo 287]

1 hour ago, GeeBee said:

It is really simple. No condensate is going to form as long as the metal temp is above the dew point.

 

That is true, but are we talking about the dew point inside the engine or outside the engine.  Almost no matter what, when an engine cools down after operating, water vapor that is in the engine atmosphere will condense on the relatively cooler metal parts and drip into the oil.  Unless you circulate dry air through the engine, most of the time the cavity will hang in the 100% relative humidity state unless heat is applied after fully cooling off