The blanket works very well if you go for a fly-in somewhere and you want the engine to reserve some heat for the return trip. I have used it a couple of times for that purpose. When handcranking you certainly appreciate every centigrade you can keep.
I think the mice or martens living under the hood find it very convenient … 
should of course be a genuine woolen blanket no plastic
Canuck wrote:
In relation to the blanket on the aircraft while it is in the hanger; The Reiff and Tanis systems can only put out so much heat… if it is really cold you need the blanket to keep the heat in while pre-heating.
Yes, the heat is on constantly 24/7. The blanket keeps the engine several degrees warmer. When it’s real cold, the heater is not enough. The blanket also keep the whole engine compartment hot and equalizes the temperature in the engine itself.
Edit. Keep the engine compartment hot of course .
Canuck is spot on for the reason.
However I wonder if anyone has produced a “blanket” which is so efficient that the engine remains “warm enough” for days?
Modern diesel cars achieve some of their great sales-data MPG by the method of not diverting any engine heat into the car heating system, for as long as possible They also use a lot of insulation around the engine. The combination of these hacks enables a better MPG figure to be obtained in the standard MPG tests, for marketing purposes. So… my 2 litre diesel VW takes about 10x longer to thaw my goolies than my 3 litre Toyota Soarer did. And, no, I am not installing the “improved” VW software 
It is also really obvious, from normal operations, that most of the heat loss from the aircraft engine is simple convection – not conduction or radiation. Just blocking the two big cowling holes reduces the heat loss by a factor of several times. When the plane is parked, the airflow reverses and the air enters at the bottom and escapes via those two holes. Very slow airflow but clearly effective. Similarly, if you park into even a slight wind, the airflow (this time flowing in the normal direction) cools the engine down really fast.
So it ought to be possible to make a really thick blanket which surrounds the whole cowling and makes the engine stay warm enough for days. I wonder if that has been tried? One challenge would be to keep it light and floppy so it can be carried in the back.
Peter wrote:
So it ought to be possible to make a really thick blanket which surrounds the whole cowling and makes the engine stay warm enough for days. I wonder if that has been tried? One challenge would be to keep it light and floppy so it can be carried in the back.
Given that a thermos can’t do that for water using a vacuum to prevent most conduction and convection, i really doubt any cover could. All they (or blankets) can do is make heating more efficient (or slow the rate of cooling) by helping retain more heat in the compartment.
I have a custom-made insulated blanket and use it for two purposes
1) to keep he heat in when pre-heating
2) to reduce the diurnal temperature fluctuation in the engine bay when parked outside – less changes in temperature should mean less condensation, right? if parked in the hangar, the temperature is fairly stable and so leaving the blanket on is just more convenient and makes the aircraft ready for pre-heating.
Given that a thermos can’t do that for water using a vacuum to prevent most conduction and convection, i really doubt any cover could. All they (or blankets) can do is make heating more efficient (or slow the rate of cooling) by helping retain more heat in the compartment.
The difference between an engine and a drink is that the coffee goes into the flask at something like +80C and you probably want it at +70C when you drink it, so the max desirable temp drop is small – example data.
Whereas an engine is at say +350F i.e. about +175C and it is quite fine for it to drop to 0C (for OK starting) or +20C (for instant starting).
Throw in the exponentially slowing decay and the engine problem is much easier than the thermos flask problem.
You may be right but it isn’t obvious to me. The factor likely to bugger this proposition is the need to be able to carry it in the back of the plane.
“One” could work out some figures with some typical materials and dimensions…
Peter wrote:
Modern diesel cars achieve some of their great sales-data MPG by the method of not diverting any engine heat into the car heating system, for as long as possible They also use a lot of insulation around the engine. The combination of these hacks enables a better MPG figure to be obtained in the standard MPG tests, for marketing purposes. So… my 2 litre diesel VW takes about 10x longer to thaw my goolies than my 3 litre Toyota Soarer did. And, no, I am not installing the “improved” VW software
And here I was thinking that diesel engines warm up slower due to higher thermal efficiency and bigger mass, so there isn’t any excess heat to “divert”.
I read all postings and think I understand the messages. However, Noe’s original question (" why would someone in a moderte climate put a blanket over his engine for overnight parking in a hangar? ") remains unanswered My only explanation (because I know people like that) is that the owners treat their aircraft like the children or pets they never had (or had a long time ago and since forgotten that children and pets and also aeroplanes can look perfectly well after themselves).
what_next wrote:
original question (" why would someone in a moderte climate put a blanket over his engine for overnight parking in a hangar? ") remains unanswered
Perhaps to keep the bird droppings off the paint. As I answered before there is no good reason other than the what ifs I thought up.
Centurion Flyer had a reasonable explanation of why he uses it.
Peter wrote:
However I wonder if anyone has produced a “blanket” which is so efficient that the engine remains “warm enough” for days?
I believe Ive seen studies done by either Aviation Consumer, Tanis or Rieff that show the effect of a insulation on the engine compartment and the cooling time. You might want to contact them. About it at least the last two.
Who wouldnt use cowl plugs when preheating in or out of a hangar? Why would anyone leave the cowl flaps open when preheating?
Regarding radiational cooling. There is a measurable amount of heat lost through the props. So it makes sense to put insulated prop covers on if your doing a turnaround which might last a few hours or if you want to preheat with Rieff or Tanis.
