new Maule pilot/owner, with question

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57NC
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new Maule pilot/owner, with question

Post by 57NC »

I've recently joined the rank of Maule pilot/owner, and looking forward to the adventure. I'm sure I'll have lots of questions along the way. Here's an initial one ...

This Maule (M-7-235) came equipped with a 120V oil sump heater. Do people just leave these plugged in full time during the winter? Is that ok? (The airplane is in a non-heated hangar).

Thanks.

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TxAgfisher
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Post by TxAgfisher »

There's a rule of thumb on this and it has to do with condensation - just can't remember which way is which!

I guess I need to know too since I now live in a state that has 4 real seasons!
TJ Van Matre

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Stinger
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Post by Stinger »

Leaving the oil sump heater plugged in all the time is when the condensation starts becoming a factor. Once the heat pad reaches it's thermostat temperature, it shuts off until it reaches the thermostat temp on the lower end at which point it turns back on. Constant heat/cool cycles introduces more chances of corrosion.

Overall, it'll depend on how often you fly (and the ambient temperature range.) Less time between flights doesn't give enough of an opportunity for corrosion to begin. As the time between flights increases, you're better off just using the oil heater prior to each flight. Just plug it in the day before you go and you'll be fine.

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Chris in Milwaukee
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Post by Chris in Milwaukee »

I recall the same. I only plug mine in when I plan to use it. Usually the night before, although I imagine a few hours beforehand is fine. I live on the frozen tundra, so I lean toward more time.
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Kirk
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Post by Kirk »

I disagree. Over the years, I have read a lot of articles and seen a few tests. The conclusion I came to was; leave it on all the time, or just turn it on as preheat before you intend to fly. Takes a long time to heat though.

I agree that wiring a sump heater to a thermostat that will only come on in colder weather could cause more condensation. The cycles of warm air and cold metal are bad.

I wouldn’t worry about the cycling of the sump heater itself causing that since the whole mass of the engine stays very warm and doesn’t cycle much. Helps to insulate it with an engine cover or sleeping bag. Sleeping bag is a good thing to have in the back anyway.

Just my opinion. There are others.

Here it what Reiff says about it, search the web for other tests or articles.

http://www.reiffpreheat.com/FAQ.htm#QA3

Kirk

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Stinger
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Post by Stinger »

Kirk wrote:I disagree. Over the years, I have read a lot of articles and seen a few tests. The conclusion I came to was; leave it on all the time, or just turn it on as preheat before you intend to fly. Takes a long time to heat though.

I agree that wiring a sump heater to a thermostat that will only come on in colder weather could cause more condensation. The cycles of warm air and cold metal are bad.

I wouldn’t worry about the cycling of the sump heater itself causing that since the whole mass of the engine stays very warm and doesn’t cycle much. Helps to insulate it with an engine cover or sleeping bag. Sleeping bag is a good thing to have in the back anyway.

Just my opinion. There are others.

Here it what Reiff says about it, search the web for other tests or articles.

http://www.reiffpreheat.com/FAQ.htm#QA3

Kirk
Keep on reading further down your linked page:

"The risk of corrosion may also depend on the type of preheater you have...

If you are using an oil sump heater alone, we recommend NOT leaving it on continuously unless the aircraft is flown frequently, and neither do the engine manufacturers. Any oil heater used alone will raise your oil temp more than it raises the top end. For example, ours raises the oil about 80oF over ambient, and the top end around 35. Since there is usually a lot of moisture inside your crankcase, we're afraid the oil heater will fill the case with warm moist air and condense water on the cooler top end parts."

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rev412
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use an engine cover

Post by rev412 »

My observation is that an engine cover makes all the difference. When I didn't have one, leaving the sump heater on resulted, sometimes, in condensation on the top of the engine. But with an engine cover, the entire engine compartment was toasty and the condensation happened inside the cover rather than on the engine.

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Post by Kirk »

Ah I see scrolling up we are talking about sump only not entire engine heat.

I do agree about using a cover. keeps the whole engine and compartment warm. If it’s warmer than the dew point, there should be no condensation.

Kirk

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TomD
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Post by TomD »

I think we had a long thread on this some time ago.

When I put my chemistry hat on, I seem to remember that there are two different measurements of humidity Relative vs absolute.

Relative is what we look at to determine if there is going to be fog at the time we take off or land and is a measurement as how much moisture can be contained by the air at a given temp (dew point). 100% is fog, but 100% could be 80F or 35F. There is far more H2O in 80F 100% Relative Humidity than 35F.

Absolute is the volume or mass of H20 per cubic ft or meter of air. 100% relative at 80F would have a much higher absolute than 100% Relative at 35F.

If you have borne with me this far I will get to the point.

Water on the surfaces of your engine parts is bad. Given.

However, the same number of water molecules in the air will react with metal more at a higher temp than a lower temp. So if you have a relative humidity of 70% at 32F and heat the air to 60F the same number of water molecules will be more"energetic" in contact with the metal parts of your engine which, if engine parts obey chemistry laws, will rust faster.

Seems to me reducing the absolute humidity would be more effective. Using a desiccant rig would seem to me a more effective means of limiting corrosion than heating the air within the engine.

The heater is great for warming the engine and oil to speed lubricant to moving parts on a cold morning. Maybe having both systems is the best answer.

The other side of the argument is there are more H2O molecules in contact with the metal when there is condensation and would compensate for the higher reaction energy in the heated vapor.




Thoughts?

Tom

Victor Gennaro
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Post by Victor Gennaro »

I have been using an Alien Turbo air heater for the last year in an unheated hanger in Sunny New Hampshire. I set it at 50 degrees and leave it on. It heats the engine compartment and recycles the air. No condensation.
It works very well. I take it off just before I pull the plane outside and it starts very well. It has not been expensive to operate. I thing it is better than the sump and cylinder ring system my old plane had. I purchased custom cowel plugs and it fits great.

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