Carburettor Air Heating

[skippydiesel]

Saw an interesting installation last weekend. Have read about it but not actually seen befor. A coolant heated "ring" installed (in this case) between carburettor and inlet manifold on a Rotax 912ULS.

 

Wondering ;

• How effective at preventing carbi ice can such an add on be ?
  
• Should it be befor the carburettor, rather than after?
  
• Would it generate enough heat to degrade the performance of the engine (like alternate air leaving carbi heat on)
  

[Thruster88]

Saw an interesting installation last weekend. Have read about it but not actually seen befor. A coolant heated "ring" installed (in this case) between carburettor and inlet manifold on a Rotax 912ULS.

 

Wondering ;

• How effective at preventing carbi ice can such an add on be ?
  
• Should it be befor the carburettor, rather than after?
  
• Would it generate enough heat to degrade the performance of the engine (like alternate air leaving carbi heat on)
  

Not,yes,unlikely.

Why do people spend good money to add wieght and complexity to their aircraft in search of a solution to a problem that probably doesn't exist?

[IBob]

Where the 912 installation is taking air from under the cowl, icing is less likely. Where it is taking air from outside the cowl, given the 'right' conditions, icing is a real possibility.

[skippydiesel]

Where the 912 installation is taking air from under the cowl, icing is less likely. Where it is taking air from outside the cowl, given the 'right' conditions, icing is a real possibility.

 

Hi IBob - in this installation the carb air was being drawn from outside the cowling.

 

In my installation the air the carbi's are"breathing" is usually about 10 degrees above OAT.

[IBob]

Hi Skippy, if I've got it right, that would give you approx 3.5% drop in air density? However, I doubt the relationship between that and engine HP is anything like linear.

My installation has a NACA scoop on the top of the fairing. There was a 30mm gap between that and the actual airbox intake. The airbox has a temp sensor and I noticed that in a hard climb airbox temperature was rising, which meant air was being taken from under the cowling instead of via the scoop.

I fixed this by reducing the gap between the scoop and the airbox intake (while still leaving a gap for drainage).

 

The Savannah airbox has a butterfly valve setup that allows air to be drawn from over the muffler, and we do use it here: I've never had icing, but a mate has, and apparently it was very unpleasant, causing the engine to run violently rough.

[onetrack]

I'd have to opine a coolant heated ring between carburettor and manifold would have so little effect on the intake mixture, you wouldn't even notice it in operation.

If it was a coolant-heated intake manifold - well, they've been around for 100 years and they have been proven to offer advantages as regards smoothness of operation, and improved fuel economy.

 

There's a very intensive 1920 study on a heated manifold on a 6 cyl automotive engine, that's available on the 'net. Their testing was extensive and thorough.

But the testing was all about improving throttle response and fuel economy in the early days of motoring, when the engineers were still coming to grips with manifold designs, mixture flow patterns, and fuel droplet size.

 

The HR Holdens were fitted with a coolant-heated manifold, which improved throttle response, made for a smoother-running engine and which also improved fuel economy under most conditions.

In high ambient temperature conditions, the advantages of a coolant-heated manifold are minimal.

 

As regards intake icing in aircraft engines, if there was a good reason for fitting coolant heating arrangements to aircraft engines intakes, to counter icing, it would have been done 90 or 100 years ago.

I don't recall any aviation engine that has ever featured an intake design fitted with coolant heating, but perhaps I've missed it.

[FlyBoy1960]

I knew I had a photo of it somewhere, this was taken roughly 2004 but I forget which aircraft it was on. If you look closely at the photo and I am sorry that I don't have an enlarged copy you will see a heating ring which operates on hot water from the radiator between the carburettor and the carburettor mount. Thinking back now this has the carburettor stabilisation bracket which I sent photos of a week ago when we were talking about the Savannah carburettor throttle linkage. Also notice the drip tray on the bottom of this photo just made out of a piece of stainless steel sheet. It had an angle on it so if fuel overflowed it would go away from the engine towards the side of the cowling. This was on a very early sting aircraft imported into Australia which I helped assemble at the airfield. Just walking past to be in the right spot that the right time. I don't know if they are still using them because I have not seen another sting in maybe 15 years

 

[skippydiesel]

FlyBoy - the photo shows exactingly what I saw last Saturday. Initially I could not work out what all the extra small tubing was for - then the "penny dropped".

 

Your photo also shows the same location of the heated ring - between carb & inlet manifold. Hence my question about location location.

[facthunter]

One track, nearly every Lycoming has it. The intake goes up through ports that pass through the "HOT" sump oil.

In general you WILL lose power with any effective form of carb heat and some will be unfiltered air. Others may be through ducts which reduce flow.( MP).

Being above Icing temp doesn't mean NO ice. The expansion of the air and evaporation of fuel can cause ice at up to say 25 C. Near port individual injectors make a large difference to the likelihood of intake icing barring Rhime ice (impact) on the air intake screen or filter. Nev

[Downunder]

To me, coolant heated carbs are a bit self defeating.

As the colder the OAT, the colder the coolant will be in most circumstances.

The opposite of what you generally want......

[facthunter]

There are stipulated performance requirements for Carb heat systems. A lot wouldn't come close. Carb heat from exhaust system won't be very adequate if applied when the engines, idling either. You must be able to completely get rid of any ice, fairly quickly. Nev

[derekliston]

I fitted electric carb heating. Doesn’t affect power in any way because it is heating the butterfly and not the intake air!

[skippydiesel]

I fitted electric carb heating. Doesn’t affect power in any way because it is heating the butterfly and not the intake air!

Interesting - Engine? Heating system maker? Your observation of efficacy?

[Old Koreelah]

There are stipulated performance requirements for Carb heat systems. A lot wouldn't come close. Carb heat from exhaust system won't be very adequate if applied when the engines, idling either. You must be able to completely get rid of any ice, fairly quickly. Nev

From memory, a proper carb de-icing system is supposed to increase intake air temp. by about 50C within half a minute. Mine only raises temperature by about 20C (and not very quickly) because it takes air from a shroud around the muffler; an easy build, but not very effective.

It's not easy to build a decent collar on a Jab exhaust pipe, so I wonder if air taken directly from the back of one ram-air duct would do the job?

 

As OT points out, coolant-heated intakes have been around for yonks; my Starke-Stammo had a neat oil-heated setup for it's long intake ducts.

I recall a well-respected LAME telling me he likes to keep his carb heat slightly open on his Jab.

[derekliston]

Interesting - Engine? Heating system maker? Your observation of efficacy?

There are a couple of different options available. I think my one came from x-air. It works well, simpler and lighter than the traditional hot air system. I am at Warwick in Qld, so really rarely have to use it, only know that it works from indicator light and increase in power consumption.

[Blueadventures]

There are a couple of different options available. I think my one came from x-air. It works well, simpler and lighter than the traditional hot air system. I am at Warwick in Qld, so really rarely have to use it, only know that it works from indicator light and increase in power consumption.

Also you can feel it soon after turning on. Draw about 5.6amps.

[derekliston]

Also you can feel it soon after turning on. Draw about 5.6amps.

I like it, no change over airbox, no exhaust shroud, no scat hose, like I said, simple!