Pre-heating in 0degF weather

[nyoung]

Hi All. I saw a thread on POA a few weeks ago about pre-heating. I live/fly in Chicago, but am fortunate to have a heated hangar, so I do not have to deal with preheat that often.

Yesterday, I flew to OSH to visit the EAA museum (well worth a Sunday afternoon flight if you live in the area). It was 1degF when I landed and got colder as the day progressed. So I thought I would share my preheat experience.

I asked the FBO to put my Cherokee 180 (Lycoming O-360) in a hangar, and they agreed, but ultimately were not able to do so because their tug could not handle the wheelpant on the Cherokee. Kind of odd, but whatever...

We were at the Museum for about 1.5 hrs, so the plane sat outside for maybe 2.0 hrs in the 0degF temps. No cowl cover, plugs, or Tanis. The engine was completely cold to the touch, so I suspect it was completely cold-soaked.

I have started my plane at 15degF without preheat, and it did not care for the experience, so I was certainly not going to attempt 1degF without preheat. Fortunately, the FBO had a 115k BTU heater, and so we fired that up and aimed the flexi-nozzles into the cowling. I babysat the plane because the heater was VERY hot, and I was worried about bubbling the paint or worse melting the fiberglass. It ended not being an issue, and after only 10 minutes of preheat, the engine had definitely warmed a bit and started no problem.

In contrast, I have a RedDragon preheater that runs on a tank of propane (same as a charcoal-less grill). It usually takes about 30 minutes to get the engine warm enough to start.

Anyway, being as we are in the middle of winter, I thought I would share my experience in case it helps anyone.

 

[jtheune]

When you tested the engine temp was it by felling the outside of the casing? Did you check the oil temp on the dipstick? What did the engine oil temp guage say? I would think that 1.5 to 2 hours in 0 degree temp would not coal soak a engine but could be wrong.

 

[gismo]

Supposedly, the main problem with a quick high BTU pre-heat is that it will warm the cylinders up quickly but leave the crankshaft and main bearings cold enough to be tighter than they should be when starting. I think the heat should be applied for a minimum of 20 minutes to get everything warmed up a bit.

And my latest pre-heat story:

Last weekend I left the plane with the big FBO at DuPage. On Sunday a few hours before I expected to depart I asked the FBO what it would cost to put the plane in a warm hangar for a couple hours and was quoted $50. That seemed a bit high given that I'd already paid their ramp/overnight fee so I got them to plug in my electric heaters using cords I had left in the nose baggage compartment. When I got ready to start I discovered that only one of the heaters had been operating. My guess is that they didn't push the plug on the right engine all the way into the extension cord (it's inside the cowling and a bit difficult to do). The oil and cyl temps on the right engine were right at 20 F, the temp I consider minimum for starting so I fired up the (warm) left engine and then started the right one with considerable difficulty. "Fortunately" DUATS had lost my IFR flight plan so the cold engine had plenty of time to warm up while I was dealing with that. I was surprised how difficult it was to start the cold engine even though it was still at 20F. The OAT was below 10 F at the time and no doubt contributed to the starting difficulties.

 

[gismo]

When you tested the engine temp was it by felling the outside of the casing? Did you check the oil temp on the dipstick? What did the engine oil temp guage say? I would think that 1.5 to 2 hours in 0 degree temp would not coal soak a engine but could be wrong.

I think it can if there is a wind blowing and the cowl openings aren't plugged. Those cooling fins can transfer a lot of heat with 0F air blowing over them.

 

[jesse]

Supposedly, the main problem with a quick high BTU pre-heat is that it will warm the cylinders up quickly but leave the crankshaft and main bearings cold enough to be tighter than they should be when starting. I think the heat should be applied for a minimum of 20 minutes to get everything warmed up a bit.

And my latest pre-heat story:

Last weekend I left the plane with the big FBO at DuPage. On Sunday a few hours before I expected to depart I asked the FBO what it would cost to put the plane in a warm hangar for a couple hours and was quoted $50. That seemed a bit high given that I'd already paid their ramp/overnight fee so I got them to plug in my electric heaters using cords I had left in the nose baggage compartment. When I got ready to start I discovered that only one of the heaters had been operating. My guess is that they didn't push the plug on the right engine all the way into the extension cord (it's inside the cowling and a bit difficult to do). The oil and cyl temps on the right engine were right at 20 F, the temp I consider minimum for starting so I fired up the (warm) left engine and then started the right one with considerable difficulty. "Fortunately" DUATS had lost my IFR flight plan so the cold engine had plenty of time to warm up while I was dealing with that. I was surprised how difficult it was to start the cold engine even though it was still at 20F. The OAT was below 10 F at the time and no doubt contributed to the starting difficulties.

When I rented one of those DA-20s at KFCM--there was *absolutely* no way it would start with a OAT of about 25 degrees and below. Plug in the tannis heater for about 20 minutes and it'd start instantly.

 

[Trapper John]

Supposedly, the main problem with a quick high BTU pre-heat is that it will warm the cylinders up quickly but leave the crankshaft and main bearings cold enough to be tighter than they should be when starting. I think the heat should be applied for a minimum of 20 minutes to get everything warmed up a bit.

Actually, the colder it is, the more clearance the bearings have. But that's not necessarily a good thing, though...


Trapper John

 

[SCCutler]

When I rented one of those DA-20s at KFCM--there was *absolutely* no way it would start with a OAT of about 25 degrees and below. Plug in the tannis heater for about 20 minutes and it'd start instantly.

Man, I love my Tanis; plug that sucka in for a while, and everything that matters is toasty-warm, and it starts like a spring day.

 

[ScottM]

Man, I love my Tanis; plug that sucka in for a while, and everything that matters is toasty-warm, and it starts like a spring day.

I agree I have a reiff heater on the oil pan and around each cylinder. It is great, as long as the battery is not dead.

For the first time that happened to me today. Went upload a new gps database. Everything was fine for about 10 minutes and then I heard a change in the sound of one of the electric gyros, the gps display started to flash and that was pretty much the end of the battery.

Pulled the plane out and jumped it. Let it charge back up the battery for a while, taxied over to get fuel and it started right away again. Took off and flew for 2.4 hours.

 

[timwinters]

Pulled the plane out and jumped it. Let it charge back up the battery for a while

That can be really, really hard on an aviation battery. The plates are much thinner than car batteries and don't tolerate high rate charging very well.

Don't ask me how I know...but if you must...I ruined a battery this way once.

 

[nyoung]

When you tested the engine temp was it by felling the outside of the casing? Did you check the oil temp on the dipstick? What did the engine oil temp guage say? I would think that 1.5 to 2 hours in 0 degree temp would not coal soak a engine but could be wrong.

The engine oil temp gauge was pegged to the left. The engine felt very cold to the touch. No different than the airframe. But I do agree with you... it is possible the oil in the crankcase was still above zero. It would be pretty difficult to tell (via touch) the difference between 0 and 20 deg.

Also, I could only feel the cylinders via the cowling inlets and the oil access door, so I was not able to feel the bottom of the case.

 

[nyoung]

<snip> The oil and cyl temps on the right engine were right at 20 F, the temp I consider minimum for starting so I fired up <snip>

That has been my experience too. I have started the plane many times in temps just below freezing... with no problems.

The one time I tried at 15degrees, it started, but required a lot more cranking than normal. It also died shortly after starting, requiring a restart, which is quite a rare occurrence for the engine in my plane.

 

[gismo]

Actually, the colder it is, the more clearance the bearings have. But that's not necessarily a good thing, though...


Trapper John

That's not what I've read.

From the Tanis website:

Because the engine was designed and assembled at room temperature, its clearances between parts can shrink dramatically when the severe cold of winter jets in. At temperatures as low as -11 degrees Fahrenheit, one popular engine can completely lose crankshaft bearing clearance. No wonder they turn over hard when they're cold! Even warm oil can't help when there isn't any bearing clearance.

And from Mike Busch (The savvy aviator):

The real culprit in cold-start damage is the fact that our aircraft engines are made of dissimilar metals with radically different expansion coefficients. The crankcase, pistons and cylinder heads of your engine are made from aluminum alloy, while the crankshaft, camshaft, connecting rods and cylinder barrels are made from steel. When heated, aluminum expands about twice as much as steel. Likewise, when cooled, aluminum contracts about twice as much as steel. And, therein lies the problem.
Consider your steel crankshaft, which is suspended by thin bearing shells supported by a cast aluminum crankcase. As the engine gets colder, all of its parts shrink in size, but the aluminum case shrinks twice as much as the steel crankshaft running through it. The result is that the colder the temperature, the smaller the clearance between the bearing shells and the crankshaft. That clearance is where the oil goes to lubricate the bearings and prevent metal-to-metal contact. If there's not enough clearance, then there's no room for the oil, regardless how high the oil pressure gauge reads.
How significant is this problem. Well, take the TCM IO-520-series engines used in many Beech and Cessna singles and twins, for example. The IO-520 overhaul manual lists the minimum crankshaft bearing clearance as 0.0018 inch (that's 1.8 thousandths) at normal room temperature.
What happens to that clearance when you start cooling the engine down? TCM doesn't say. But tests performed in 1984 by Tanis Aircraft Services in Glenwood, Minn. (where it gets mighty cold) indicated that an IO-520 loses 0.002 inch (2.0 thousandths) of crankshaft bearing clearance at -20°F. An engine built to TCM's minimum specified bearing fit at room temperature would actually have negative bearing clearance at -20°F-in other words, the crankshaft would be seized tight!
You've probably noticed how difficult it is to pull the prop through by hand before starting in cold weather. Now you know why. It's not that the oil is thick (because if you use multivis oil, it's not). It's that the clearance between the crankshaft and bearings is tighter than normal. If it's cold enough, you might not be able to pull the prop through at all.
Start an engine in this condition and you're likely to experience accelerated bearing wear and possible damage to the crankshaft journals in the first minute or two of engine operation. If bearing clearances are small enough, it's even possible for the bearing shells to shift in their saddles-a so-called "spun bearing-misaligning the oil feed holes and starving the bearing from lubricating oil

And from Reiff:

Propane fired forced air heaters produce high BTU's. Heat transfers quickly to the cylinders via the cooling fins, so if all you want is to warm your cylinders quickly this is the way to go. Warm cylinders are all you need if your only goal is to get the engine started. However, if your goal is to both get the engine started AND to avoid damage and wear to the engine from cold starting, then the entire engine and the oil needs to be uniformly heated. To do this you need to preheat long enough to allow the heat to conduct throughout the entire engine. You may do this with a propane heater, but the typical 15-20 minute blast of hot air will not do it. Some propane heaters are portable and can be powered from a battery, so you can take it with you when you travel and it can be used in remote locations. However, they weigh 15 lbs or more (plus the LP tank) and take up baggage space. Some flights are not allowed to carry propane.

 

[Tim]

come on up I will give you a class on preheat for a small fee

 

[gprellwitz]

And from Reiff:

Some propane heaters are portable and can be powered from a battery, so you can take it with you when you travel and it can be used in remote locations. However, they weigh 15 lbs or more (plus the LP tank) and take up baggage space. Some flights are not allowed to carry propane.

How a propane heater can be powered from a battery, I'm not sure. But if it's not able to be powered from a battery, I know I'd be VERY uncomfortable toting that propane along in the cabin! Would anyone else be comfortable doing that? Wouldn't that violate some reg on transport of hazardous materials, too?

 

[jmaynard]

How a propane heater can be powered from a battery, I'm not sure.

The heater needs a blower to push the heated air. That blower could conceivably be battery powered. I agree, though: I'd be very uncomfortable hauling the tank in my airplane.

 

[flyingcheesehead]

We were at the Museum for about 1.5 hrs, so the plane sat outside for maybe 2.0 hrs in the 0degF temps. No cowl cover, plugs, or Tanis.

Get thee some cowl plugs!

I bought cowl plugs for the club a couple of years ago, and I've noticed a dramatic improvement in heat retention during the winter. Duh, I know, but it makes me much less nervous about the heat situation while I'm away from the home drome. It also helps the engine retain heat from the Tanis heater. (You should get one of those, too!) Where even an hour in 0ºF made me very nervous before, now I can park the plane, unplugged, in very cold weather for a few hours and still feel warmth on the cylinders when I go to remove the plugs for startup.

There's a thread about cowl plugs here. After looking at the options, I went with Ron Levy's recommendation of Ground Tech at http://www.planecover.com/ and you'll see in Post 16 that I was happy with the buying experience and the product. There's a picture attached too.

Two years later, still a happy customer. Plugs are still in great shape, really no signs of wear at all. I'll definitely be looking to them for cowl plugs again when I have my own plane.

 

[stingray]

The heater needs a blower to push the heated air. That blower could conceivably be battery powered. I agree, though: I'd be very uncomfortable hauling the tank in my airplane.

I used to use one of the throw away bottles of propane and used a small 12 volt fan and duct work. took very little room and started the plane once. Throw the bottle away and you do not have to haul it unless you are going to a place that does not have a "Walmart".

Now I just carry a long extension cord, you can always find a place to plug in.

Dan

 

[wsuffa]

I was surprised how difficult it was to start the cold engine even though it was still at 20F.

My experience, too. Worse with a single as the battery is also weaker.

The real issue for me is battery issues. I'm simply not flying it enough (especially in the cold weather). I guess I'm going to have to put a trickle charger on it as the Solargizer just isn't enough. Real risk of ruining the battery (as noted by Tim).

 

[Trapper John]

That's not what I've read.

From the Tanis website:



And from Mike Busch (The savvy aviator):




And from Reiff:


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I'd really like to see the results of these tests. I guess properties of materials are somehow magically different for aircraft engines...


Trapper John

 

[Dean]

Man I love my Rotax, no need to pre-heat, a shot of primer and hit the starter. But what do expect from an engine company that builds mainly snowmobile engines. And some say just because it flies, it doesn't qualify as a real airplane, whatever that means.

 

[nyoung]

Man I love my Rotax, no need to pre-heat, a shot of primer and hit the starter. But what do expect from an engine company that builds mainly snowmobile engines. And some say just because it flies, it doesn't qualify as a real airplane, whatever that means.

I haven't been on the board for that long... What are you flying and which Rotax?

I had a 377 Rotax in an '82 Moto-Ski snowmobile. For the amount of care I put into it, it was amazingly reliable.

 

[Geico266]

I am reminded of a "hanger story" I have heard about bush pilots up north. They would land for the night, drain the oil out in a bucket and put it on the stove at night to keep it hot. In the morning the would add the hot oil back in the engine and take off. That was their "pre heat".

Can any of you cold weather pilots confirm this practice?

 

[Dean]

I haven't been on the board for that long... What are you flying and which Rotax?

I had a 377 Rotax in an '82 Moto-Ski snowmobile. For the amount of care I put into it, it was amazingly reliable.

I started out with a C-150, then went to a C-172 and now with the way the economy is, I have a Challenger CWS with a 503 DCDI, fun and cheap to fly.

 

[Tim]

I am reminded of a "hanger story" I have heard about bush pilots up north. They would land for the night, drain the oil out in a bucket and put it on the stove at night to keep it hot. In the morning the would add the hot oil back in the engine and take off. That was their "pre heat".

Can any of you cold weather pilots confirm this practice?

Not quite how they did it but close. They also preheated the engine. I doubt anyone has done it that way in 50 years.

 

[bbchien]

Get thee some cowl plugs!

Go to a Lowe's or Home Depot. Buy the LARGEST natural sponges you can buy. Trim 'em to fit the cowl intakes.... remember to put 'em in and take 'em out. You can go TWO hours with a blanket over the cowl and the plugs in and still not have cold soaked oil. BTDT.

 

[kgruber]

Not quite how they did it but close. They also preheated the engine. I doubt anyone has done it that way in 50 years.

They also diluted the oil with gas.

 

[gkainz]

My uncle worked on the Alaska pipeline back in the early beginnings of its construction. Not airplanes, but he said they never shut the equipment down, and did oil changes while it was running. One guy drained out the old while one guy poured in the new...

 

[GMascelli]

Of course there is always the DIY preheater....http://www.youtube.com/watch?v=_5bK_ivwXs4

I would add a four or six inch duct fan to this set up if I could find one that would handle more then 140*