If you are able to show me bubbles of pistons rising through denser, cooler cylinder heads then I will believe that metals can heat via convection!
What part of the convection process do you not comprehend, when putting two hot air scat hoses from a combustion heater in the bottom of the cowl, to warm the engine? That's convection.
Heating metal to metal is conduction, and one doesn't need "bubbles" to transfer heat by conduction.
When preheating via a sump heating pad, one invokes the principles of conduction, convection and also radiation.
In most circumstances in the real world, one method of heat transfer is not present without the other.
You'll find that during engine operation, the upper spark plug in the horizontally opposed recip engine tends to be the hotter plug, which is why the lower plugs tend to be more susceptible to fouling. You'll also find that most light airplane pressure cowl assemblies run cowl inlet air across the top of the cylinders first then exhuast it through the bottom of the cowl; hottest part on top, to lowest on the bottom. Conductive heating, convective cooling.
Shut down, and one doesn't vent the engine through the bottom. Fly your 206 to a desert location and expect to leave during the heat of the day, it's a good idea to vent that cowl. You won't find it in the aircraft handbook, but one can open the oil filler door and oil check door, to vent the cowl best, because heat rises, and the doors are on the side and top of the cowl; this helps vent heat, which makes the follow-on engine start a little easier on a hot day.
This is probably why they say -12C (or whatever) without qualifying it according to oil type used, which makes the -12C (or whatever) an obvious farce if stated as a straight unconditional figure for a given engine type.
Probably? I'm always impressed by uneducated guesswork.
You have the manufacturer data before you. Elect to disregard it at your peril. What part of "required" escapes you? It it a difficult definition, or simply something not found in the UK lexicon?
[QUOTE]This kind of stuff should have been documented by now.[/QUOTE
It has been, ad nauseum. Hence manufacturer guidelines on operation.
It is the arrogant unwillingness of the manufacturers to get stuck into some proper research and documentation (and I fully understand why they behave like this - the above legal reasons) which has given rise to countless theories on engine management.
On the contrary, it's your arrogant unwillingness to buy the company and change the procedures, as you seem to know so much better than the folks who designed, manufactured, and built the engines. With your expertise, you could easily replace the legal department, engineering department, and serve as customer service to tens of thousands of operators who hungrily await your counsel. That you've failed to do so can only be a testament to your arrogance, can it not?
No?
Interesting that it's a testament to the "arrogance" of the manufacturer, then.
More interesting is the fact that the manufacturer has the legal right and responsibility to make those guidelines, requirements, and recommendations whereas you...do not.
I have a 60W greenhouse tubular heater resting inside the bottom cowling of my Moth (and switched on), which keeps my Gipsy engine warm enough to start no problem all Winter. Works for me!
It works until a float sinks, the carb floods, and avgas drips on the light or fills the cowl with vapor. It works until the light finally blows, or a short occurs, or something else happens to cause a fire. It happens.
For each type of oil there will be a low temperature below which it doesn't flow well enough to get around a (particular design of) engine fast enough, before it gets a chance to warm up. This behaviour should have been studied (they have been making these things since the 1950s, essentially) and documented, but nothing has been done.
It has been done, actually, and is well known. Oil flow rates and viscosity is only a part of the picture, however. You'll note that the manufacturers (the ones who know less than you, remember) specify heating the entire engine. Not just the oil. It's an engine preheat. Not an oil preheat. Warming the oil is only part of the process, only one of the reasons for the preheat, as we've already discussed. Your disbelief lies in your ignorance of the matter, but doesn't change the fact.
Personally I just test the igniters, press the start button and watch the ITT......
Turbine cold weather starts: the biggest hazard with cold weather starts in a turbine is a low battery Two solutions are to use a battery heater, and to use external power for the start. Low battery causes hot starts, hung starts, and slow starts, all of which can cause burner can damage and other thermal injury. Even if they never show up as a high ITT. One can do severe damage to an engine and never have it exceed ITT start or takeoff limits, most commonly during a very slow start or a hung start. The high temperatures aren't reaching the ITT probes as the gasses aren't passing through the engine due to the low speed or stagnated airflow: the damage is done prior to the probes.
Some turbine engines do have cold weather limitations, which must be observed. Turbines do make cold weather starts easier, but also present additional hazards.