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Topic-icon Engine Preheater

  • MARY MCMAHON's Avatar Topic Author
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6 months 3 weeks ago #1563

Having always operated in temperate climates I have no knowledge of preheaters. I'm going to be spending some time in cold climates occasionally and was looking into purchasing an electric preheater. Does anyone have suggestions or words of wisdom?

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6 months 3 weeks ago #1564

Hi Mary, This article will answer provide you with a broad base of winter operating tips.
Tips for getting started for winter flying
By Steve Ells
"The lower the ambient temperature, the higher the volatility of the fuel must be, or starting aids, such as engine heaters or primers must be used,"
—Chevron Aviation Fuels Technical Review
Winter is a good time to fly. The cooler denser air provides more lift and the engine makes more power than is possible during warm weather months. The sun's rays are less direct so there's less thermal lifting which translates into a smoother ride and less violent storms. All those factors contribute to the enjoyment of winter flying. But all these benefits come at a cost.
Aircraft engines need to be pre-heated before each winter start. Snow and ice need to be completely removed from wings, and controls must be checked for complete range of travel prior to every launch. Although it's not a necessity pre heating the cabin will pay big dividends in comfort and in the reduction of window fogging.
Engine Preheat
There's a vast difference between the computer controlled temperature regulated automobile engines of today and the air-cooled and pilot-controlled engines in our light airplanes. The engine in even the least costly automobile will spring to life in the dead of winter with a twist of the key. Not only that the engine is almost instantly tractable. Our air-cooled aircraft engines won't and aren't. No, our airplane engines have more in common with our grandfather's Model T engine than one of today's automobile engines—they have to be ministered to and nursed into action especially when temperatures are at or below freezing.
How Cold is Too Cold?
Both Lycoming and Continental Motors make suggestions about pre heating. Continental Service Information Letter SIL 03-1 says to preheat whenever an engine is exposed to temperatures at or below 20 degrees Fahrenheit (7 Degrees C) for two hours or more. The letter specifies wind chill degrees.
Lycoming Service Instruction 1505 says preheat must be applied any time temperatures drop to 10 degrees F (-12°C) except for the O-320-H and LO/O-360-E series -76 engines which must be preheated at 20 deg F (-6°C) and below.
These pre heating publications are also spell out the necessity of switching to a thinner oil or a multi-grade oil at colder temperatures.
However, many engine shops and experienced cold weather operators think the manufacturer's recommendations aren't good enough. They recommend pre heating whenever temperatures approach freezing (32 °F/0°C).
Here's why. Air cooled airplane engines consist of a forged steel crankshaft and other steel reciprocating parts. The crankshaft is held in position in bearing shell halves that are clamped between two semi-flexible aluminum case halves. The expansion rates of these major components are very different; aluminum expands and contacts at approximately twice the rate of steel. Steel is dense and heavy especially compared to the thin and light metal of the case halves; therefore the crankshaft takes longer than the case does to "grow" to its "in-service" dimension after an engine is started and begins to warm up to its standard operating temperature.
This also holds true for the cylinder walls which are steel and the pistons which are aluminum. During cold temperatures clearances between parts are reduced which ratchets up the likelihood of rubbing and scuffing wear between parts. If power is applied too soon after a cold start engine damage is more likely. Limit power increases prior to seeing 75 °F (24 °C) on the oil temperature gauge. A cold start and the rapid application of power following the start will cause more wear than hundreds of warm weather starts.
I Can Get It Started
There are pilots who insist that the factory pre heat temperatures recommendations are B.S. and cite instances when they have started their engine without pre heat at much lower temperatures. Remember that liquid fuel does not burn; only fuel vapors burn. And it's true; certain techniques will work. Their tools include shooting a lot of fuel into the cylinders with the primer pump coupled with pulling the prop through during priming. This "loosens the oil" and attempts to get fuel vapors to all the cylinders. Following this pre-start process, as soon as the engine starts carburetor heat is applied. Carb heat aids in fuel vaporization. However, these tools don't always work. Sometimes one or two plugs fire then nothing more. Since one of the byproducts of combustion is water vapor this water vapor will sometimes freeze on a cold spark plug, "frosting" that spark plug during a very cold start. The only solution for frosted plugs is to remove the plug to dry it out or to apply heat.
The "prime and pull" method of starting a cold engine comes at a cost. Fuel that isn't vaporized is drawn into cylinders as a liquid where it dilutes the lubricating oil on the cylinder walls. This accelerates cylinder wall wear.
If power is applied too soon after a cold engine start the pistons, having expanded more quickly than the cylinders, will contact the cylinder walls, especially if the lubricating oil surface has been compromised. This causes what's called piston scuffing.
Piston scuffing is just one of the problems that can occur during a cold engine start. Another is oil circulation; cold oil is thick and slow to flow. Pre heating aids in fuel vaporization, speeds the circulation of lubricating oil, enables quicker more efficient starts, lessens problems due to divergent expansion rates of metals, and lessens stresses on starter and the battery.
Pre Heat Tools
Reiff and Tanis offer engine preheat systems. Their pre heaters consist of a number of discrete heating elements that are attached to cylinders, and to other parts of the engine. Tanis puts a heat pad on the engine case; Reiff doesn't. They both put heaters on the oil sump. Tanis systems have been around since 1973 and for decades was the system most used by commercial operators. Bob Reiff founded his company in 1998 and has established itself beside Tanis as a major player in the piston engine pre heater business.
Tanis stresses the importance of pre heating each cylinder head and sells a variety of different cylinder head heating elements; there's one for every need. All Tanis systems also include heating pads that are affixed to the oil pan and engine case. Tanis systems are available for both 115 and 230 VDC power.
Reiff Preheat systems also come in a wide variety of configurations—HotStrip, HotBand, Standard, Turbo and TurboXP—as well as an oil cooler option that covers many different applications and airplane types. Reiff doesn't install heating elements on the cylinder heads; instead it offers individual cylinders heating elements—50 or 100 watt sizes—that are bonded onto stainless steel bands that are installed around the steel barrel at the base of each cylinder.
A report on the Reiff company website for its top-of-the-line Turbo XP system that uses a single 100 watt heaters on each cylinder and two 100 watt heaters on the oil sump cites it as being capable of raising the temperatures of the oil and cylinders of a O-540 engine from a starting temperature of 21°F (-6°C) to 100°F (38°C) and 77°F (25°C) respectively in three hours. The same report cites the Standard system—one 50 watt heater on each cylinder and one 100 watt heater on the oil sump—as capable of raising the temperatures on the same engine under the same conditions to 57°F (14°C) and 73°F (23°C) respectively. The Standard system does fine; the Turbo XP system just does it faster.
Naturally each of these two companies disputes the other's methods; for instance the Tanis site contains a thermal picture of an engine after pre-heating with its and the Reiff system showing that its system is much better able to heat the cylinder heads. Reiff counters with a statement that its cylinder heating bands are not installed "in" the engine—that they are "on" the engine. This may sound a little bit nit-picky but one reason Tanis has developed three different styles of head heating elements is because its original heaters screwed into the threaded boss in each cylinder head that's now needed for a modern engine monitor probe.
Installation approval
There's some confusion about approvals to install engine heaters. The FAA has issued a letter saying that since engine heaters is not used in flight nor are they tied into other aircraft systems that installation can be approved by an airframe and powerplant (A & P) mechanic if the manufacturer's installations instructions have been adhered to and signed off as a minor alteration that only requires a maintenance record entry.
However, Reiff makes the point that FAR 21.303 says that only parts manufactured under a FAA-issued Parts Manufacturing Approval (PMA) may be legally installed on a certified aircraft. Reiff parts are manufactured under a PMA. Tanis Pre heater parts also have PMAs and many of its systems are approved under what's known as a Supplemental Type Certificate (STC). STCs guarantee that Tanis pre heat system installations will be accepted by even the most rule-bound FAA or country's regulatory personnel.
Other Pre Heat Options
If electrical power or a portable generator is available other preheat options include oil pan pad heaters such as the the Safe-Heet from McFarlane, the E-ZHeat, and the Design Logic. All of these are thermostatically controlled. AeroTherm sells a series of self-contained electrically-powered heaters that utilize an internal fan to blow the heat into the engine compartment. The AeroTherm units are equipped with temperature controllers.
The Red Dragon heater is a propane-burning system with a fan that blows heated air through ducting and flexible tubing into the engine compartment. The fan is powered by either 12 VDC (from the airplane battery or a car battery) or 110 VAC.
If don't have electrical power or want a truly portable system you have a couple of options. The first is the Northern Companion heater which consists of a small, rugged multi-fuel stove, a stainless steel firebox and the tubing required to duct heat under the engine cowling. The stove, which can double as a survival tool, burns avgas, auto gas, kerosene, diesel and jet fuel and produces around 20,000 BTUs. The unit packs into a 6 inch by 17 inch package and weighs less than 7 lbs. Current cost is $635.
Another option is a Coleman Catalytic heater. During my time in Alaska these small compact heaters were a favorite among small airplane owners because they didn't produce an open flame, they put out between 3,000 and 5,000 BTUs, and they didn't require any external power. Although they are no longer in production, I found one within a few seconds on eBay.
All pre heaters especially the heaters that depend on convection to move heated air will do a much more thorough job when an insulated engine cover such as the ones by Bruce's, AircraftCovers, PlaneCover or KennonCovers is installed.
Over the last decade there has been a back and forth discussion about whether or not to leave an engine pre heater on all the time, or whether it should only be turned on a few hours prior to flight. The only-before flight school cites evidence they say illustrates that constant heat causes internal engine corrosion. When asked about leaving one of its heaters on continuously Doug Evink, President and CEO of Tanis Aircraft Products said, "We've have never tested to determine what the effects are of leaving one of our heaters on continuously. However, we do know that it won't cause any adverse conditions."
Evink did say that one of the things that will cause water to condense inside an engine is over-heating the oil. When this happens water vapor in the oil escapes only to then condense on colder internal engine parts such as the camshaft or lifter bodies. This, he explained is why the Tanis oil pan heating element is designed to provide oil temperatures of 100 to 110°F. The Safe-Heet system from McFarlane Aviation utilizes a heating pad on the oil sump. McFarlane seems to support Evink by offering a heating pad temperature controller. The controller allows owners to keep its oil pan heater on all the time yet still avoid corrosion by cutting the heat back so there's only enough to keep the oil limber. Prior to a flight the heat output is increased to get the rest of the engine up to a safe starting temperature.
Mobile phone-controlled switching such as the unit by Switchboxcontrol.com and the RCS unit sold by AeroTherm makes it easy to turn on and off electrical pre heaters from the office or from home as long as there's a cell network nearby. Reiff sells a cell phone controlled (GSM networks only) on-off switch to its customers for a very reasonable price.
Instruments and Cabin
Pilots, passengers, and flight instruments also fare better if pre heated. The best option is an overnight stay in a heated hangar, if possible. But if that option isn't in the cards, putting a small ceramic-type heater on the floor of the airplane during the engine pre heating session will reap big rewards. Gyro instruments especially work much better when they are at normal operating temperatures. Very inexpensive 110 VAC heaters with tip-over shut off switches are available in every local hardware store.
Protect Yourself
Always guard against carbon monoxide—that insidious silent, odor free killer—poisoning during winter flying with a carbon monoxide detector. Almost all light airplane cabins are heated by air that's been routed around the engine exhaust system or air heated by circulation around a combustion heater. Because the heat is provided by combustion there's always the possibility of a leak with will allow CO in to the cabin. AeroMedix sells portable CO detectors that are suitable for aviation. Guardian Avionics (formerly CO Guardian) sells a wide variety of panel-mounted detectors.
Now get out there and enjoy that good winter flying.

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5 months 3 weeks ago #1604

Hi Mary I just read Steve's info on pre-heaters. It was a good read and gave all the reasons why you should have it in the cold country. I fly in Minnesota so I use pre-heat. 4 of my past/current aircraft have Tanis heaters. 2 of which I have installed. 15 years ago I had a partner on a Piper Aztec and he did not want to install heaters on them so I used torpedo heaters and put them in the cowling. I was not crazy about that but worked fine other than waiting long enough to fly. Every Tanis that I had worked great. I left plugged in anytime the ambient temp went below 50 degrees F. 7 years ago when I installed my engine on my Bonanza I did research on different heaters and decided to go with Tanis again. I installed and because I was also installing a JPI that took the probes I called Tanis for technical help and as it turns out the were local. (I did not know because I only called the 800 number) They came out and changed out the parts with the ones that would work with my JPI. (BTW I did not think about mentioning me installing the JPI that took the inserts for the cylinder head heaters - my bad) I currently have a Seneca III and was already installed. Love the Tanis heaters and if needed I will reinstall them again.

Good luck with your decision and if already made one sorry for the late response. I am new to this organization and just flipping though this web site.

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  • Lydell L. Newby II
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5 months 2 weeks ago #1617

I work really closely with the Tanis people. We install more of them than any other system. And I just installed a system on my overhauled IO360. Everyone that has them love them. Go to www.tanisaircraft.com and Doug has a whole site of videos, information and testing graphs regarding his systems. Our shop is about a mile from Tanis so we have really good access to the equipment and literature. Up here in Minnesota you either have a heated hangar or a Tanis system... or both!
Happy New Year.

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5 months 2 weeks ago #1618

Lydell are you at KANE (Blane)? Do you have a shop there? And if so what is the name of the shop? BTW I used to fly out of KANE now at 21D (Lake Elmo)

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  • Lydell L. Newby II
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5 months 2 weeks ago #1619

Yup. I’m at Twin Cities Aviation and we have moved the maintenance shop to the Lynx Hangar over on the north side of the field.

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