Engine Pre-Heaters/Preheating Techniques

[n86121]

Even owning an airport I have been on tie down doe 25+ years.

Our hangars in Washington DC go for quite a premium!

I am also (too) busy, so also having to drag a heavy airplane in and out of a hangar each time would make flying even less spontaneous.

Lastly, modern paint, interior materials, and avionics are simply not affected by weather as much as they used to be 30 years ago. Almost not at all. At least not mid latitudes. What's your experience in Arizona?


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Years ago, I dug into this topic, and here are my two cents:

There are I guess two reasons to preheat.

1. Engines are so expensive, we want to extend their operating life

OPERATION - One of the many reasons a regularly operated engine is happiest is that all of its internal surfaces get re-coated with a thin film of oil. When they sit, the oil slides off, leaving internal metal bits exposed to corrosion.

OIL TYPE - One of our based pilot characters years ago was Bud Soucy. He had been an aerospace engineer with Temco Vought in WW2. He was quite a character. Bud once ran an experiment painting unfinished metal with each type of aviation oil, then leaving it out to see what would happen. No theories, just an empirical test.

What he found was straight 80 or 100 stuck to and kept the surface coated, ...with no corrosion..., while ALL the others drooled off faster, leaving the metal to rust.

I have used straight 100 summer and 80 winter ever since.

PRE HEATING - Any pre heating over any extended time will vaporize moisture from the warm bits to condense onto the cold bits. Moisture doesn't disappear.

We had a 210 that kept heating all the time, despite my warnings, and found his cylinders kept corroding.

Interesting to note Tanis patented an airflow thing, which actually makes more sense, IF the intake air is dry.

PRE-OILERS? - I even looked into pre-oilers. Small electric pumps that would pre-pressurize oil in the engines. Not a bad idea, but what I found was perhaps 50% of the engine is oiled by splashing oil around, so pre-oilers wouldn't do much in those areas.

INTERNAL CLEARANCES WHEN COLD - Again, best thing is to still have a thin film of oil, instead of 'dry starting.' Rumor has it initial dry contact between surfaces does 'the most' wear. All the methods of trying to get oil in as fast as possible are trying to avoid this fundamental issue.



2. Ease of starting

There are two considerations here:

A. Thick oil circulates slowly and is hard for cold batteries and starter motors to spin, and

THINNING THE OIL - By heat or lower viscosity rating will help it circulate more easily.
The best thing is an engine that still has oil on its surfaces from the last time it ran. See 'OPERATION' above.

COMPRESSION RATIO - TURBO? - My turbo's compression ratio is slightly lower compression than non-turbo. 7.5:1 vs 8.5:1, I believe. This must make it a bit easier to spin.

(Early Lotus motors could be as high as 12.5:1, famous for blowing up starter motors!)

B. Finding the right fuel air mixture to start.

See my other recent posting about my universal starting technique.
Works every time!

CONCLUSION

A. Straight oil to keep a thin film on the internal bits longer
B. Regular periodic flight to A. boil off moisture in oil and K. keep an oil film on engines
C. Keep battery charged (I have a solar trickle charger I setup on tie down)
D. Use my magic starting technique (see other post)

Easy peast, no worries, no problems, ...mon