In reply to:
If your plane is going to be sitting outside the battery heater would make most sense.
You may well be right in terms of EASE OF STARTING, but I’d respectfully disagree regarding the advisability of doing so.
The engine takes a pretty decent beating when it it started when it’s cold-soaked. It’s a matter of widely varied opinion as to just-how-cold-is-how-bad… but the experts I’ve read agree that it’s healthier to start a warmer engine.
F.E. Potts, author of the excellent on-line book Guide to Bush Flying - Concepts and Techniques for the Pro, quotes Mike Bush, the Cessna Pilots Association’s engine specialist, claiming that “one cold start at the lower temperature extremes can cause as much wear as 500 hours of normal cruise operation… This takes into consideration the metal-to-metal contact between the piston and cylinder walls caused by the uneven expansion of the aluminum pistons and steel cylinders as the engine goes rapidly from very cold to very hot”. Of course, he’s talking about temperature extremes, but I think that the point is valid at any temperature below freezing, albeit to a lesser extent. [How much less? Don’t know. Just figure it pays to be conservative here.]
As an aside… what is it with the name “Mike Bush” and airplanes? The “Mike Bush” quoted above may or may not be the http://www.avweb.com/articles/temp_authors.html#mbusch>Mike of AVweb (different spelling); there’s a Mike Busch at Cirrus (head of the Air Safety department), and Michael Bush, one of our COPA members.
By the way, I heartily recommend Potts’ book - sadly, because of repeated copyright violations, he has pared down the free online offering, although the book can still be purchased in print form. However, chapter titled Preheating Equipment and Methods is, thankfully, still available. This is the source of the quote above.
In the Cirrus, I say preheat the engine with the cylinder bands and sump heater; the engine will radiate enough warmth to keep the battery happy. That’s the best of both worlds. Anyway, that’s my opinion on preheating and cold-weather starts, for whatever it’s worth.