@Archer-181, flame is only part of the problem, even with catalytic oxidation there will be fuel vapours potentially forming an explosive mixture. Both can be made safe with a proper design, but for liability/insurance purposes you’ll need it certified in some way.
There are reusable hand warmers with no combustible substances, e.g. the ones with supersaturated solution of sodium acetate where you trigger crystallisation, which releases heat. They produce about 275 kJ/kg, so theoretically you need ~15 kg of the stuff to warm up the engine by 30°. That’s not too bad, but for an efficient heat transfer you’ll need a relatively thin pad, which will then have to be large enough to accommodate that quantity of substance (roughly 1 m² or a bit more if the pad is 1 cm thick). For a good heat transfer you’ll also need to keep this pad in tight contact with the engine. Theoretically, in a liquid-cooled engine, you may be able to fill the cooling system with the stuff, but then you’ll need to keep the system free of nucleation centres, which means polished walls, no sharp edges and no materials that could release particles into the system (e.g. no rubber hoses).
On second thoughts, a ridiculously simple solution is a big hot water bottle. Water gives 4.2 kJ/kg·K – two and half times as much as oil – and even the strictest airport security probably won’t mind you taking a bucketful of hot water to the aircraft.
I was considering one of those a while back
@slowflyer
Where do you measure the temperature and how long do you (and others on this forum) preheat usually? Thanks!
@cessnatraveller
I did infrared measurements on several parts of the engine, like cylinders, oil sump and any other structure i was able to reach without removing the cowling. The above presented temperatures represent an average of all the mentioned structures.
Based on the recent temps around zero degrees centigrade I usually start the heater first thing when arriving at the aircraft, do my preflight and then wait another ten minutes, so in total it adds up to 25-30 minutes heating time. That usually gives me a confident feeling and the oil temps quickly reach the green after startup.
Maybe it is voodoo, but i do feel better by applying heating below 10 degrees centigrade as it does not add significantly to my preparation time.
Remote control would be nice but is not possible as mentioned beforehand
@Sir_Percy, according to seller’s claims, this device violates the laws of physics. Burning 0.1 L fuel oil per hour will produce about 1000 W of heat power, not 5000 W as claimed.
@slowflyer
Thanks again! Same here, I also do it from +10° and lower. However I let my blower run for 1:30 to 2:00 hrs.
I think I need to get an infrared device for the temperatur measurement in order to bring my heating time down to what I really need.
You are absolutetly right this
guy states a more reasonable 0.64 l/h
Anyway, the intersting part is that they offer the same heater that is used as a car heater in a neat package for a very decent price.
The quality and correctness of the specification has to be proven …
For the case at home base where 220V is available, I have had good experience with Reiff. They make a plate that is glued to the oil pan as well as rings that tighten around the cyl heads. A couple Watt options are available.
I won’t start the engine, unwarmed, when the ambient temp is <4°C. Clearly there are varying opinions on what that number should be, so to each his own. I have the heater connected permanently in the hanger through an SMS-operated power switch. I also have a Canada-sourced engine, spinner, and prop covers. I turn on the switch from home and the engine and compartment is nicely warmed when I arrive at the (unheated) hangar an hour or two later.
On the “road”, a power source would of course need to be considered, either at-airport or taken along.
Given the typical nasty / adversarial airport-political scene in European GA (the impossibility of plugging anything in, prohibition on any heating devices, etc) I reckon if there was a problem with starting just below +4C then we would be seeing it, with thousands of engines getting trashed rapidly – because that’s exactly what most people do for several months of the year.
I am not saying there isn’t a problem; just that we would hopefully see some obvious manifestation of it.
If one could plug something in, it would be really easy, because just bolting something like a 100W resistor onto the sump might be sufficient.
Especially if you plug the cowling holes, and better still put a blanket around the engine cowlings.
The pool of oil in the sump would absorb the heat nicely. I reckon one could distribute several hundred watts that way, without creating a hot spot.
