Using a propane forced air heater to pre heat

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Scott MacKie

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Are the forced air propane area heaters like those sold at the Depot suitable for preheating? I'm thinking some kind of high temp hose clamped to the heater and stuck into or under the cowling. Just to raise the temps from say 30 to 50 or so, prestart.

Anyone done this? Or is it stoopid?
Thanks
 
you will get a variety of opinions on this, I will tell you that 30 degrees in not that cold for a start. usually that type of forced air heat through the cowling only heats up parts of cyl, not very efficient. having said that, a lot of planes i see on the ramp gets quickly heated that way by the FBO, they do use something like a Red Dragon which i am guessing is far more powerful than what you are thinking

Edit: From Lycoming - https://www.lycoming.com/content/operating-cold-weather

In cold weather, preheat is another factor that must be considered prior to starting the engine. There are specific guidelines in Lycoming service instructions which establish when preheat should be used, but how much, or the method of preheat is generally left to the good judgment of the pilot or maintenance person doing the preheating. Use of the heated dip stick is not recommended by Lycoming, although most other methods are considered to be satisfactory. For most Lycoming models, preheat should be applied anytime temperatures are at 10˚ F or lower. The exception to this rule is the 76 series models that include the O-320-H, and the O/LO-360-E. These engines should be preheated when temperatures are below 20˚ F. It is recommended that these guidelines be followed even when multi-viscosity oil is being used. In addition to hard starting, failure to preheat the entire engine and oil supply system as recommended may result in minor amounts of abnormal wear to internal engine parts, and eventually to reduced engine performance and shortened TBO time.
 
I prefer using an electric heater. I'm not so sure I want potentially corrosive, water-saturated exhaust gas blowing over my engines. Some sort of air-to-air heat exchanger system using the propane heater might work well.
 
We use an Aerotherm DEUCE, it does the job in our moderate climates. When I use it I cover the cowl with an old comforter to help minimize heat loss.
 
We have a construction heater modified to preheat. It has a thermal cutoff that kicks in too often. Not enough airflow when consticted.

Food for thought. The units made to preheat are built differently.
 
Our group uses a 100,000 BTU kerosene powered torpedo heater hooked up to a large tube and duct that blows air up through both cowl flap openings. In colder weather we run it for about 10 minutes or so and the engine heats up nicely. From the looks of the age of the heater and duct work I would say this has been the practice for far longer than I have been an owner.
 
So, lessee. Specific heat capacity of aluminum is about 900 J/(kg*C). My little engine is about 90kg, let's assume it's all aluminum (it isn't). I wanna raise it from -5C to +5C, so delta t of 10. 900*90*10=810kJ. A little electric heater is 1500W. Let's assume no losses (there are). That comes out to 9 hoursminutes...
 
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GeorgeC said:
So, lessee. Specific heat capacity of aluminum is about 900 J/(kg*C). My little engine is about 90kg, let's assume it's all aluminum (it isn't). I wanna raise it from -5C to +5C, so delta t of 10. 900*90*10=810kJ. A little electric heater is 1500W. Let's assume no losses (there are). That comes out to 9 hours...
Click to expand...
Whoa whoa whoa facts and science have no place on POA.

And made my head hurt for a Friday evening
 
GeorgeC said:
So, lessee. Specific heat capacity of aluminum is about 900 J/(kg*C). My little engine is about 90kg, let's assume it's all aluminum (it isn't). I wanna raise it from -5C to +5C, so delta t of 10. 900*90*10=810kJ. A little electric heater is 1500W. Let's assume no losses (there are). That comes out to 9 hours...
Click to expand...

Science, I didn't check your numbers, but it sounds pretty good to me.

I like these little guys, up to 3 times the heat of a 1500W electric heater, no electricity. A little imagination and it could work.

Big Buddy Portable Heater (mrheater.com)
 
Like the turtle and the hare.... slow and steady is far better for it that a quick blast... I want the internals of my engine toasty too...

The Reiff and Tanis are great I hear, but I just have a sump heater however with a cowl and prop cover the cylinders are in the 80s...

I’d be happy maybe w a quickie when it’s in the 30s but colder than that the whole things getting warm before I clear prop... overly cautious maybe... she also would technically fly on one set of mags...

I just don’t think a blast type unit is going to do all that much to really get the thing truly preheated... just my take...
 
GeorgeC said:
So, lessee. Specific heat capacity of aluminum is about 900 J/(kg*C). My little engine is about 90kg, let's assume it's all aluminum (it isn't). I wanna raise it from -5C to +5C, so delta t of 10. 900*90*10=810kJ. A little electric heater is 1500W. Let's assume no losses (there are). That comes out to 9 hours...
Click to expand...

You sure that isn't 9 minutes (no losses)?
Caveat: it's early, only 1 cup coffee so far
 
focal_plane said:
You sure that isn't 9 minutes (no losses)?
Caveat: it's early, only 1 cup coffee so far
Click to expand...

Hmmm, this is why I always had to show my work.

GeorgeC said:
So, lessee. Specific heat capacity of aluminum is about 900 J/(kg*C). My little engine is about 90kg, let's assume it's all aluminum (it isn't). I wanna raise it from -5C to +5C, so delta t of 10. 900*90*10=810kJ. A little electric heater is 1500W. Let's assume no losses (there are). That comes out to 9 hours...
Click to expand...

Specific heat AL 900J / (kg*K) K = Kelvin Since 1 degree of change Celsius equals 1 degree change Kelvin and we are doing a delta here, then we can use Celsius to figure the difference.

Engine = 90 kg

Change in temp from +5C to -5C = 10C

So (900 J/(kg*C)) * 90 kg * 10 C = 810 kJ

So how long will it take 1500 W to produce 810 kJ?

E(J) = 1000 * P(kw) * t(s)

810,000J = 1000* 1.5 kw *t

810,000 / (1000*1.5) = t

t = 540 seconds = 9 minutes ( assuming perfect heat transfer to the engine which is impossible)


9 minutes does make more sense than 9 hours though.
 
Ugh, thanks. Math is hard, let's go shopping.

I wonder what the real world losses are like. Guess I need to time it and measure the temp rise...
 
GeorgeC said:
Ugh, thanks. Math is hard, let's go shopping.

I wonder what the real world losses are like. Guess I need to time it and measure the temp rise...
Click to expand...

Bah, don't worry about it. It was late, but the short answer makes more sense. I think the Tanis is less than 1,000 watts and it can heat an io 550 from 20f to 70f in less than 2 hours.

It's important people remember with these calcs that the heat transfers in all directions, so the actual time will be much longer.
 
Bill said:
We use an Aerotherm DEUCE, it does the job in our moderate climates. When I use it I cover the cowl with an old comforter to help minimize heat loss.
Click to expand...
I use the same Aerotherm model. It does not have the same heating ability of the newer more powerful versions, but I use a movers blanket over the cowl, plug up as much of the openings with the sponges, put gun socks over the propeller blades, and put a ratty car cover to act as a tent over the cowl compartment. I usually feel comfortable waiting 1 hour when outside temps are around 30F. Will wait a little longer if below 30F. The oil just before start up is flowing nicely on the dipstick and the CHTs are usually 50-80ish F.
And if you start the heater first thing when you arrive, install the sponges and tent afterward and then do your preflight and fueling while the heating is going on, you are not waiting very long before you have completed your heating cycle before departure.
 
Small forced propane heater: i have a Mr Heater Hero battery powered unit, 35000 btu. I put it on a crate with block on one side to tip the front up to match the open cooling flaps of my bird. I have a cheap harbor freight blanket I drape over the cowling and with little wind it works well. I also have 2 cheap hair dryers and if electricity is available they work well too and can be placed inside the cowl flaps next to the nose wheel. I got both of them for under $20.

I don't preheat above 30F, but I do warm up at the lowest idle possible, and I may to face away from the wind until the cylinder heads warm up some.
 
GeorgeC said:
I wonder what the real world losses are like. Guess I need to time it and measure the temp rise...
Click to expand...
The losses are enormous. The air is tepid by the time it exits the duct. Either need to insulate the duct or get a bigger heater. Or give up for another year because it's almost spring.
 
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