Preheating engines: Airplane engines versus auto engines

On 12/20/2007 9:15:15 PM, Dave wrote:

Watch this like a hawk on cold starts of any kind...15 secs is
marginal, 10 secs max preferred...

Will pay better attention to this. Thanks.

--
Peter

Preheating a car at +5C is just ridiculous if you are using the
proper
weight of motor oil. I might use a block heater if the temperatures
went below -20C, but not higher than that. Try using a good 10W30 oil
between +5 and -10, and perhaps a 5W30 below that. You won't damage
anything, and your engine will last longer than the body panels on the
car!

I use 5W30 year-round in my '01 Chevy. Runs just fine, and
it's what the manufacturer recommends for our climate. The tolerances
in these auto engines are now so small that anything heavier is not
only a waste of time but could be really bad in the cold.
Aircraft engines have much larger tolerances, mostly because
they're air-cooled and get a lot hotter, with clearances between
things like aluminum pistons and steel cylinders getting pretty tight
at high temps. Aluminum expands at twice the rate of steel, and while
some pistons have steel inserts cast into them to control that
expansion, they still expand a lot. Liquid-cooled engines can be built
much tighter. And auto engines have much smaller cylinders than
aircraft engines of the same HP and so the overall expansion is less.
Rings are either chomed steel or cast iron and will expand at around
the same rate as the cylinder, but they'll still get tighter from the
heat draining off the piston through them. They have a bit of
difficulty getting rid of that heat through the microscopic oil film
on the cylinder wall.
With larger tolerances, more oil escapes. With larger
tolerances, the arc of contact area is shorter. With larger
tolerances, things tend to strike each other harder. So heavier oils
are necessary to slow the oil's escape from bearings and so on,
heavier to lubricate the shorter contact arcs, heavier to dampen the
shocks of parts banging into other parts.
Piston scuffing often happens when an engine is driven to full
power too soon. Pistons get hot and cylinders are still cool,
clearances disappear. Scuffing can happen if the oil isn't reaching
the cylinders, and since it's usually thrown off the rods (some
engines have a squirt hole in the rod opposite), a really low idle
might leave the cylinders dry. Some two-strokes like the aircooled
Rotaxes must be warmed up thoroughly or they'll seize soon after
takeoff. Local guy learned that the hard way. Seized it twice before
someone clued him in.

Best things for folks who fly infrequently include installing
a preoiler and don't make short flights. The preoiler will fill all
the oil galleries and pressure will come up even before start. The
short flights leave water in the oil the eat the engine. The folks who
"run it up once in a while to keep it healthy" without flying it are
doing the worst damage by far.

Dan

A key to lubrication of any aircraft engine is how soon an oil fog can
be established in a crankcase. This takes a while - especially if the
oil is thick, as the bearing journal clearances are not that great and
the amount of oil thrown from them is minimal given starting oil
viscosity and the comparatively low crankcase activity at low rpm.
Most of the oil flow generated by that fixed volume oil pump ends up
blowing over the relief valve and dropping directly back to the sump,
giving the oil little access to the heat of the engine pistons and
cylinder heads. There are no features on the rotating machinery that
will centrifugally splatter oil blobs onto the cam surfaces. They
have to depend on previous operation for lubrication until the fog
gets more generally developed.

Oil viscosity can easily vary over a 100:1 range between moderately
cold start and normal operating values. The leakage from a journal
bearing will correspond inversely as that viscosity and directly as
the cube of the bearing clearance - which is also compromised by the
differential thermal expansion of aluminum vs steel.

Remember it isn't the bearings - it is all the expensive surfaces in
your engine that are starved in a cold start. And the operating
profile is almost always a full takeoff power after only a few minutes
of operation.

I do agree though that the OP didn't do any substantial damage to his
engine since it had been run so recently and since it has
Continental's bottom-of-the-crankcase camshaft.

On Thu, 20 Dec 2007 21:43:18 +0200, "gpaleo"
wrote:


Ï "Matt W. Barrow" Ýãñáøå óôï ìÞíõìá
...


"gpaleo" wrote in message
news:1198177392.30618@athprx03...
"Matt W. Barrow" wrote
news

"gpaleo" wrote in message
news:1198154485.901022@athprx03...
"Matt Whiting" wrote
news
................................................. ...............................
Perhaps with your extensive and pontifical experience you cold summarize
the findings of Shell, Chevron, and TCM of the percentage of wear that
occurs in the first 30 seconds of cold (ie, below 40 degrees) starts?


May I humbly pontificate that proper starting of engines (incorporating
the, appropriate for the temps and engine, oil) at 25F will NOT impact
their respective TBOs to any statistically significant degree.

Well, your holiness, no one said anything about TBO.


I see what you mean. I intended to convey the idea that no damage would
occur to the engine resulting from the cold-ish starts within the time
period to overhaul.
Do find some inner peace, my son ;-)) (the holy-ness kicking in).

I'm stuffed if I can see how the cold start will have ruined his
engine.
the traditional reason for warming an engine prior to flight is so
that the exhaust muffle is hot enough to deliver carby heat if needed
on climb out.
now if the engine is fuel injected....
all engines get some wear in the first 30 seconds until all the oil is
around the sliding surfaces but for heavens sake the engine us not
running under any load so the wear will be minimal!

humble little I only run an O-200 in a Wittman Tailwind. I can be
airborne in under a minute from a cold start my hangar is so close to
the runway end. if I do take off with a cold engine and I dont
encounter icing my worst worry is a little blowby spraying some oil
mist under the belly which resolves in very short time as the parts
come to working temperatures. I just stick some new oil in :-)

one of the hardest things for an owner is to develop enough experience
with hands on operation to know the *actual* relative importances of
the concepts of engine operation. from my experience gpaleo is bang on
the money ....and I'm an atheist :-).

when it is all said and done...
there is more said than done.

Stealth Pilot
Australia

On Thu, 20 Dec 2007 08:21:32 -0800 (PST),
wrote:

On Dec 20, 6:04 am, Denny wrote:
The biggest killer of aircraft engines is dry starts
from weeks/months of sitting between starts...


That's one, but there's another bad one: Short flights,
especially in cold weather. byproducts of combustion include water
vapor, and some of that squeezes past the pistons and rings when the
engine is cold (some when it's hot, too, but much less so) and this
vapor condenses in the crankcase and ends up in the oil. If the engine
doesn't get hot enough for long enough, the water isn't boiled off and
will mix slowly with the oil, breaking it down and combining with
sulfur and chlorine and nitrogen to form sulfuric, hydrochloric and
nitric acids. These don't belong in your engine. The stuff that's left
from these reactions forms sludge and clogs up hydraulic lifters and
cakes on the inside of the case and soon enough breaks off and shows
up as scary black guck in the filter. The acids cause dissimilar metal
corrosion between the crank and cam and their bearings, between the
aluminum piston and the steel cylinder and rings, and on valve stems.
Bad. Corroded valve stems break and the engine tries to eat the valve
heads and gets indigestion.
The oil in my little old Continental doesn't get above
120°F on cold days. There's a tank blanket that I need to buy or make
to get it up. I just finished rebuilding the thing to fix corroded
bearings and seized valve lifters.

Dan

as a matter of deep religious significance, once your engine is warm
start the clock and dont land until an hour is up at least.

in the depths of winter remember that some parts of the world need
global warming :-)

now to be serious...
squeezing past the rings probably contributes a millionth of one
poofteenth of a percent to the problem.
when the crankcase cools there is moist external air sucked into the
cavity of the case through the crankcase breather. the moisture
condenses onto the cold internal surfaces of the engine.
can you please factor that into the alchemy above? it probably does
the damage occurring between the poofteenth of your scenario and the
100%.

now if you really want scarey black gunk try taking off the oil
reservoir and cleaning it out.

honestly you must lay awake sleepless at night :-)

Stealth (the O-200 is king) Pilot

Peter, this thread has grown way too long and ****y for me to go check if
you already have received this info, so please excuse any duplication. Mike
Noel hit on an important factor that did not seem to be followed up on about
a difference between aircraft and automobile piston engines. See the papers
at http://www.tanisaircraft.com/articlesresearch.html .

Stan


"Peter R." wrote in message
...
This time of year here in the Northeast US I always preheat my Bonanza's
IO520 engine with a Tanis heater and an insulated cowling/prop cover as it
sits in an unheated t-hangar. The result is that the oil temperature at
startup is around 105 degrees F, even if the outside air temperature is as
low as -15 degrees F.

Monday night I arrived at my t-hangar to discover that at some point
during
the day the line person accidentally pulled out the plug connecting the
Tanis
heater to the small extension cord I use to extend the plug to the outside
of
the cowling cover, so the aircraft had not been preheating. Outside and
inside temperatures were both a cold 25 degrees F.

Given any other day, I would have plugged the aircraft back in and
scrapped
the flight but in this case I had an Angel Flight patient waiting in
another
city for my arrival and I was already late. Thus I made the painful
decision
to start up the aircraft and allow it to low idle until the oil heated
thoroughly. A small consolation is that the engine had been recently
filled
with fresh Exxon Elite oil. To my relief the aircraft started right up.

I know what I did has negative long term repercussions on my engine's
health
and I have already derived a tool to lock the two cords and prevent this
accidental unplugging from happening again. However, this leads me to
question the differences between aircraft engines and auto engines:

Why is it that here in the Northeast US seemingly no one preheats their
automobile engine before start-up in very cold temperatures? Is the
long-term
damage the same for both autos and aircraft engines? If so, why do you
suppose auto owners don't typically do this? Is it because that most auto
owners do not keep their cars very long?

--
Peter

Stealth Pilot wrote:

I'm stuffed if I can see how the cold start will have ruined his
engine.
the traditional reason for warming an engine prior to flight is so
that the exhaust muffle is hot enough to deliver carby heat if needed
on climb out.

That's pretty funny. A preheat has so little affect on the temperature
of the exhaust muff that it isn't even a consideration. Within 10
seconds of engine start, the heat of the exhaust pipe will be at roughly
the same value whether the engine was started at 20 degrees F or 80
degrees F.

Matt

Tauno Voipio wrote:
Matt Whiting wrote:
Tauno Voipio wrote:

Peter R. wrote:

--- clip clip --


Why is it that here in the Northeast US seemingly no one preheats their
automobile engine before start-up in very cold temperatures? Is the
long-term
damage the same for both autos and aircraft engines? If so, why do you
suppose auto owners don't typically do this? Is it because that most
auto
owners do not keep their cars very long?


Here in the north of Europe We'll pre-heat our cars if
possible, if the temperature goes below +5 C (whatever
it is in F, around 40?).

You can force an engine to start even at -30 C, but it
means that the poor thing runs some time practically
dry of lubrication.


Really? Where does all of the oil disappear to that was there when
the engine was shut down?

Matt

The lubrication is based on fluid between the metal
surfaces. When the oil thickens enough, it will not
get to the small spaces between the metal surfaces.


There was oil in those spaces when the engine was shut down and it
doesn't magically disappear. Most engines will run for some time with
no oil pressure and without damage.

Matt

Stan Prevost wrote:
Peter, this thread has grown way too long and ****y for me to go check
if you already have received this info, so please excuse any
duplication. Mike Noel hit on an important factor that did not seem to
be followed up on about a difference between aircraft and automobile
piston engines. See the papers at
http://www.tanisaircraft.com/articlesresearch.html .

Even more interesting is that Tanis leaves such obsolete information on
their web site. Take a magnet to a few car dealerships and see how many
engine blocks are cast iron these days...


Matt

On Dec 21, 4:45 am, Stealth Pilot
wrote:

squeezing past the rings probably contributes a millionth of one
poofteenth of a percent to the problem.
when the crankcase cools there is moist external air sucked into the
cavity of the case through the crankcase breather. the moisture
condenses onto the cold internal surfaces of the engine.
can you please factor that into the alchemy above? it probably does
the damage occurring between the poofteenth of your scenario and the
100%.

Nope. We have taken rocker covers off engines immediately
after a runup of a brand-new engine and found copious amounts of water
in them. The blowby of any cold engine is significant. If we briefly
run up an engine that has sat all night in a heated hangar and in our
very dry winter climate, we will find water on the dipstick every
time, with the engine at any point in its life. And the dipstick was
dry beforehand.
We operate on the western Canadian prairies where the air is
drier that where I grew up in south-central BC, which is the northern
tip of the Sonora Desert. We get little rain and snow here. Temps
reach -40C, more typically -20C, no fog and clear skies most of the
winter. It's REALLY dry, and any air sucked into these engines after
shutdown doesn't have enough moisture to make a couple of tears.

Dan