Q & A
What should be
preheated to give a safe start?
At temperatures from
20°F down to O°F the primary concern is
the cylinder. If the cylinder heads are warm the
engine will start easily, fuel will vaporize, spark
plugs will fire without frosting and the valve
guides will lubricate properly.
If cylinder heads are not
heated the engine will be more difficult to crank
due to the choke in the cylinders. One other
unexpected result is that upon starting, the piston
size will grow at a rate faster than the cylinder
diameter (due to differential expansion), causing
scuffing and rapid wear, until the temperatures
equalize.
At temperatures below
O°F there are additional problems that
need to be addressed. The aluminum crankcase* needs
heat to provide proper fit for the bearing surfaces
that it supports.
(At -11°F one popular
engine may have no crankshaft bearing clearance at
all.) The valve lifters in the crankcase need to
have oil flowing through tiny orifices and through
the push rods in order to lubricate the valves.
Accessories and oil lines in the engine compartment
will need heat. The breather line should be warm
enough to melt out ice that has formed in
it.
* Aircraft crankcases are
the center structure of the engine - not the 'oil
pan'. On an aircraft, the 'oil pan' is called a
sump.
The oil in the sump will need
a small amount of heat at these temperatures. (Even
15W50 needs heat at 0°F and below.)
At very low temperatures
(-20°F and below), the lead acid battery
will also need to be warmed in order to produce a
start and to recharge for the next battery
usage.
THE TANIS PREHEAT SYSTEM
ADDRESSES ALL OF THESE PROBLEMS.
TANIS gives safe and reliable
starts down to -30°F. (We make special order
systems good down to -65°F.) No 'one element'
preheater can do this. The TANIS Preheat System
always heats the cylinder heads in piston
engines, as well as the crankcase, screens, and oil
sump. TANIS Preheat Systems have several
heaters to warm the parts of the engine that need
heat.
Why heat the cylinder
heads?
All TANIS Preheat Systems for
piston engines heat the cylinder heads. Other
heaters heat the cylinder base and claim the same
benefits, but don't work as well. Cylinder head
heat is important for several reasons.
A. A start with cold cylinder
heads may not have lubrication to the rocker arms
for several minutes.
B. Oil to this area of the
cylinder comes through the small pin holes in the
pushrods. If the top end of the cylinder is cold
then oil can't flow here.
C. Change in the diameter of
the top end of the cylinder (called choke) occurs
here. Preheating here helps reduce it.
D. Combustion occurs here.
Cylinder heads must be warm to allow fuel to
vaporize and ignite.
E. Piston growth that occurs
here on a cold start. Preheating here helps reduce
this. (The piston doesn't travel past the base of
the cylinder.)
F. Spark plug frosting occurs
here on cold starts. Preheating prevents
this.
G. Valve guides may not have
lubrication for several minutes when starting with
cold cylinder heads.
How does a TANIS
Preheat System heat the cylinder
heads?
The TANIS Preheat System
heats the cylinder heads using one of several
heaters.
'I don't fly much in
really cold weather, I only need a little heat for
my oil.'
If the aircraft is really not
flown in cold weather, it probably doesn't even
need oil heat. Modern aircraft oils such as 15W50
flow very well down to about O°F so oil heat
doesn't even help at these temperatures. Oil heat
isn't necessary until temperatures drop below zero.
Preheating is needed for other reasons. What the
engine really needs is a little cylinder heat. 'Oil
only' preheaters being marketed today don't give
the cylinder heat needed even at mild temperatures
- much less in conditions below zero!
How does the TANIS
Preheat System heat crankcase and engine
oil?
Will warm oil make my
engine start better?
Actually, no. Any improvement
in starting will be from heat losses from the oil
warming the cylinder heads and induction system. It
is possible to have warm oil in an engine and have
no lubrication once the engine starts due to poor
bearing clearance caused by the cold crankcase.
There may be warm oil in the sump but no
lubrication to the valves due to the restricted
pushrod holes. Oil heating preheaters often
overheat the oil causing carbon formation and
breakdown of the oil. Heating an engine in this way
may even accelerate moisture accumulation in the
oil. The TANIS Preheat Systems avoid this by using
only the amount of heat necessary on the oil sump
area and keeping the top end of the engine warm
using other heaters.
"I want to use
an engine gauge that shows all the cylinder temps -
will this work with the TANIS Preheat
System"?
Yes, there are several ways
to do this. The most simple and least expensive is
to use spark plug washer thermocouples with the
engine gauge. The TANIS Preheat System can use the
thermocouple wells, and factory installed CHT gauge
can remain in place. There are two minor problems
with doing this. The CHT gauge will read about
80°F - 100°F higher than the temp sensed
at the thermocouple well. (This is usually
acceptable since the pilot is mostly interested in
trends.) The other problem is that the washers make
changing the spark plugs somewhat more difficult.
Another choice is to order a TANIS Preheat System
with dual purpose probes which will heat as well as
read cylinder temperature. This option is the more
expensive and can add to the cost of the preheater
and analyzer installation. TANIS also has
thermocouples that install on existing TANIS
Preheat Systems which are inexpensive.
Before doing either, one
should consider whether the temperature of each
cylinder head really needs to be seen, or if EGT
indication will do just as well. If the aircraft
has a factory installed temp gauge, this was
determined to be the correct one during flight
testing and will give reliable information. Any
change in engine condition will produce a change in
EGT indication long before a change in CHT will be
seen. At least two manufacturers make engine
analyzers which sense only EGT.
"What about 'shock
cooling"?
Some people want multiple CHT
systems to avoid cooling the engine suddenly on
descent. The way to handle this is to avoid large
power changes in flight and to refuse steep
approach clearances. The gauge only allows the
pilot to observe what is already happening. A gauge
on one cylinder will show the same thing. To choose
a multiple CHT system over a cylinder warming
preheater is to accept the largest 'thermal shock'
the engine can experience in hope of avoiding minor
temperature changes. Pilot technique can avoid
'shock cooling'. No technique can avoid the damage
caused by starting a cold cylinder.
Will continuous use harm
my engine?
No. There are over 26,000
TANIS Preheat Systems in the field, most of which
are used continuously every winter. We know of one
'cold country' engine overhauler that won't
warranty engines unless they have a TANIS Preheat
System. If an engine is mistreated by running with
too low an oil temperature in the winter, or by too
long an oil change interval, heating the engine in
any way may recirculate moisture that has collected
in the oil. TANIS service bulletin #4 discusses how
to operate an engine properly under these
conditions.
How much do I save by
using a TANIS Preheat System?
A cold start can be the most
destructive thing done to a new engine. How much
does an overhaul cost for the engine? The TANIS
Preheat System costs less than l% of an overhaul
and can easily add 10 times this amount to engine
life. Where else can you get that kind of return on
your money? It also saves the time that would be
wasted waiting to start a cold engine.
How long do TANIS
Preheat Systems last?
Properly cared for, they will
out last the engine. We have known of one customer
who used one system for over 5000 hours of engine
operation. Parts to repair damaged systems are also
readily available.
Why don't you have a
thermostat?
The TANIS Preheat Systems are
designed to operate without them. We have matched
the wattage of the systems to the heat losses in
the engine. This is not only the most simple method
of heating but also the most reliable. Every
thermostat is rated in 'cycles until failure'. What
this means is that every thermostat will fail at
some point. If a thermostat is used, the heater
design must be 'oversized' so it will be able to
heat the engine with the element operating part of
the time. When the thermostat fails there will be
either no heater at all or else it will run wide
open and over heat everything. One 'oil only'
heater we tested normally runs at 440°F on its
start up. Should its thermostat fail to the 'on'
position, it would destroy something!
Some things to
check...
There are other heaters on
the market which list for a lower price than the
TANIS Preheat System. Several things may be true of
these heaters.
*Although advertised
as FAA approved, not all other heaters actually
have FAA approval.
*Some heater manufacturers
advise illegal installation procedures which
could void insurance. (For example, some advise
that neither a mechanic nor a log entry is
needed for the installation.)
*Added time and difficulty
of installation on some heaters brings their
cost up considerably.
*Some heaters will not
operate with a failed unit, and no replacement
parts are available.
*Some heaters are sold as
a 'one-size-fits-all' unit, but they may not fit
the aircraft.
*Some heaters heat only
part of the engine, which could be harmful to
the engine.
On the other
hand...
The TANIS Preheat System
offers quality and integrity.
*The TANIS Preheat
System is manufactured under an FAA-PMA and is
specifically FAA approved for each aircraft.
*The TANIS Preheat System
is easily installed and requires only a log
entry when installed by an A & P
mechanic.
*The TANIS Preheat System
will operate with a failed element, and
replacement parts are readily available.
*The TANIS Preheat System
is designed and approved for particular airframe
and engine combinations.
*The TANIS Preheat System
will heat the entire engine, which gives a safe
preheat and start.
Are some
thermocouples better than
others?
All thermocouples are
accurate enough to run aircraft CHT systems.
Variations are caused by using different locations
to sense the cylinder temperature. For the best
data as referenced in the engine operating specs,
use the well tip. On multi-cylinder gauge systems
where relative data is used to compare one cylinder
against another, all cylinders should be sensed
from the same reference points. For example, to use
five spark plug washer thermocouples and one
adapter thermocouple would be a 'worst case
scenario'. The adapter and the washers could
possibly read as much as 140°F apart when the
cylinders were actually the same temperature. A
system using six probe type well tip thermocouples
such as the TANIS TAS100T preheater / thermocouples
would be the best. A system using five TANIS
TAS2144 thermocouples and one adapter thermocouple
would be good for comparing cylinder to cylinder.
A. Spark plug washer
thermocouple
The spark plug washer
thermocouple was used to sense temperature on older
engines without thermocouple wells when they passed
certification. When installed on engines with
thermocouple wells, spark plug washer thermocouples
will read the same as the well tip at idle with the
aircraft not moving. In certain flight conditions
(like high power climbs) the spark plug washer will
read 80°F-100°F hotter than the well tip.
The spark plug washer is also subject to damage
when the spark plugs are removed carelessly.
B. Thermocouple well
tip
This is the best place to
sense engine CHT, and is the place the engine
manufacturer used to pass FAA certification. The
'red line' temperature for the cylinder is based on
this point. The factory cockpit gauge senses
temperature here. The TANIS TAS100T heater element
/ thermocouple senses temperature here.
C. Thermocouple well
threads
Adapter thermocouples sense
temperature of the thermocouple well threads. This
thermocouple has been developed for after market
CHT gauges in order to avoid replacing the factory
CHT gauge. The thermocouple is in the threaded
device that holds the factory thermocouple probe in
place. It does not sense the well tip temperature
but the temperature of the threads. With the engine
at idle and the aircraft not moving it will read
the same as the well tip. In certain flight
conditions, such as high speed cruise, these
adapter thermocouples may read as much as 40°F
cooler than the thermocouple well tip. The TANIS
2144 thermocouple (made to adapt an existing TANIS
Preheat System to a multi-cylinder gauge system)
also senses temperature at this point. These are
less expensive than the TAS100T
thermocouples
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