Are Jab engines prone to icing?

[Old Koreelah]

A few years ago the magazine had an article about icing by Daffyd LLewelyn. (I can't find it now, but he specified a proper carby heat system should deliver a large and rapid temperature rise.)

 

I can undertand this is needed to rapidly melt ice accumulating in the carby throat.

 

My carby heat installation takes air from around the muffler. When I switch to heat, the temp probe upstream of the carby shows only a small rise in temperature. It probably would not comply with Daffyd LLewleyn's specs. Seems that the muffler does not heat the air as much as I'd expected. To take hot air from further up the exhaust system would require major surgery.

 

Dedicated aero engines like Jabiru often have heated intake tubes, but presumably for other reasons.

 

I doubt heat could conduct up the tube and across a rubber mount to melt carby ice.

 

Has anyone any experience of Jab engines icing up?

 

 

[airangel]

A few years ago the magazine had an article about icing by Daffyd LLewelyn. (I can't find it now, but he specified a proper carby heat system should deliver a large and rapid temperature rise.)I can undertand this is needed to rapidly melt ice accumulating in the carby throat.

My carby heat installation takes air from around the muffler. When I switch to heat, the temp probe upstream of the carby shows only a small rise in temperature. It probably would not comply with Daffyd LLewleyn's specs. Seems that the muffler does not heat the air as much as I'd expected. To take hot air from further up the exhaust system would require major surgery.

 

Dedicated aero engines like Jabiru often have heated intake tubes, but presumably for other reasons.

 

I doubt heat could conduct up the tube and across a rubber mount to melt carby ice.

 

Has anyone any experience of Jab engines icing up?

YES, they ice

 

 

[jetjr]

Due to the location of the carb, above muffler can and tight behind sump, icing is supposed to be minimized. But they sure do ice in right conditions. Carb heat also works well, removing ice effectively. Also its a good way to richen mixture if needed. Hot air, same fuel.

 

There is a screw in electric heater available used in Europe.

 

Your directing hot air not conducting heat itself.

 

 

[turboplanner]

They do, have had one ice up in the circuit.

 

 

[Deskpilot]

They do, have had one ice up in the circuit.

Me to, then couldn't restart the motor. Called Mayday for glide approach, and just made it.

 

 

[Sapphire]

Carby temp guages should be mandatory. The carby in my plane iced up at the sight of a popsicle-depends where they are mounted in relation to the engine and airflow.

 

 

[Vev]

I have experienced carby Ice only once in over 600hrs in Jabs ... upon refection the condition were there, and I shouldn't have been a surprise. I simply went through the process and pulling on the carb heat and fuel pump and things came back to normal ops within 20 sec.

 

However when the lean burn kit was in place a few years ago there seemed to be more reports of carby ice in Jabs. Despite a number of service bulletins, I did come across many owners (including schools) still running on lean jets. I think the first AD was in 2007 and a second bulletin later in the year (mainly to stop detonation) ... it was resent again in 2009 to try and get owners to upgrade their jetting. I wouldn't be surprised to learn that many of these reports (still) would relate back to the lean jetting kits released in 2004.

 

I have a rule for myself .... 26 needs heat. That is, anything <2600 rpm pull on the carby heat.

 

Cheers

 

Vev

 

 

[Gnarly Gnu]

Do you run Avgas or Mogas Vev?

 

 

[Keenaviator]

Apparently mogas is more prone to carby ice than avgas - something to to with volatility or boiling point?

 

 

[bushpilot]

Our 3300 motors are more prone to icing than our 2200s. Most instances to date have been straight and level at relatively high altitudes (7K or above) and cleared within seconds of applying carby heat. The trick is to recognise it - and respond quickly..

 

 

[blueline]

Had carb ice in a Jab but I seem to get it more often in an C150 I also fly. Like Bushpilot says get it early and no problem.

 

 

[Vev]

I mostly run a cocktail of both Mogas (98) and 100LL avgas in my Jab ... I do this as 98 acts as a diluent on the lead content of 100LL and the lead has a synergistic interaction with the mogas and bumps the octane levels above the sum of the two parts. This reduces the overall lead depositions and takes advantage of the double dose of the additive treatment in 98 to keep things clean as well keep the octane levels up.

 

I agree that the laten heat of evaporation with mogas is slightly higher, however I really wouldn't get too excited about about its endothermic (or exothermic) values in relations to carby ice .... I have more of a concern with vapour lock, albeit it has a fair dose (99%) of the isooctane contained in Avgas and is somewhat remote in terms of vapour lock with a 50/50 blend.

 

Cheers

 

Vev

 

 

[Gnarly Gnu]

Apparently mogas is more prone to carby ice than avgas - something to to with volatility or boiling point?

Now how about that - I have heard the exact opposite claimed! As I don't run Avgas I don't have an informed opinion on this.

 

 

[Keenaviator]

My experience with my c150 was that it was more prone to carby ice on mogas. Yes, it had a mogas STC.

 

 

[Old Koreelah]

I mostly run a cocktail of both Mogas (98) and 100LL avgas in my Jab ... I do this as 98 acts as a diluent on the lead content of 100LL and the lead has a synergistic interaction with the mogas and bumps the octane levels above the sum of the two parts. This reduces the overall lead depositions and takes advantage of the double dose of the additive treatment in 98 to keep things clean as well keep the octane levels up.

What proportions, Vev? (Tell us your secret recipe!).

 

I recall one post last year which cautioned against mixing, in case of incompatible additives.

 

 

[Vev]

No secret recipe mate ... close enough to a 50/50 blend works fine..

 

All of the additives are compatible enough ... I would worry more about getting a dose of ethanol as this stuff needs a wide berth all round.

 

Cheers

 

Vev

 

 

[facthunter]

I always felt that avgas , by evaporating quicker than mogas would make the carb run colder. Having the fuel evaporate is better for the engine all round though and is one of the reasons I prefer to run it (avgas).in a carburetter equipped engine. ( exc. the rotax 912) Just pour some on your hands and see how much colder it gets, or leave the lid of the container loose, and have it evaporate . Both fuels will ice . Have the right technique at all times. The C-150 engine will ice more ( 0- 200 Continental) but has a good carb heat set-up. If there is any doubt .. use it, and always check it is OFF when going around. Nev

 

 

[jetjr]

Jabiru carb heat setup is a bit different to others in that the air is always filtered. There really isnt much performance lost when running carb heat and can be used all the time if needed. When performing carb heat checks almost nil rpm drop is seen on 3300. Gives good control of high EGT if they run hot at certain rpm.

 

It is very effective for deicing just have to pick up when its happening. Mine gives plenty of warning in flight but on the ground taxiing can run rough and quit quite quickly. In winter its on until just before run ups.

 

Dont use it for take off or on landing of course

 

 

[Old Koreelah]

Thanks for that jetjr. Where does a standard Jab take the hot air from?

 

If I can't heat the air enough from the shroud around the muffler I will have to pull hot air from around exhaust pipes. The problem is that the gate is way back behind the firewall next to the air filter box. If I cover one or more header pipes the air is only flowing while the carb heat gate is open. The rest of the time the header pipe is likely to get very hot and conduct that heat back to the head.

 

 

[facthunter]

if you shroud the muffler or exhaust pipes in some areas for providing hot air for the carb heat, you should not really shut it off, but bypass it somewhere else so as not to overheat the areas shrouded. ie it is either going to the carb or somewhere else. The trouble with the shrouds, the air from there is normally NOT filtered. Nev

 

 

[Jabiru Phil]

Have had carby ice a few times now. My method is as taught, run up and Magneto test and check for carby ice at run up rpm, if ice present revs will drop and then increase when heat is turned off. If ice is present I leave the heat on during the taxi or backtrack.

 

I have noticed a couple of times whilst touring, that if the revs start to drop off, the first reaction is to give more throttle, however after a couple of adjustments of the throttle and the revs are still dropping, applying heat rectifies the problem

 

My experiences.

 

 

[jetjr]

Jab have shield covering most of the top rear of the muffler can, a spigot for the scat hose is on top left. Facing rear a little

 

Air can enter from both ends of this shield, it sits maybe 10mm off the can and is held there by screw hose clamps around the whole muffler. Plenty of heat.

 

 

[Captain]

I had a temp probe fitted into the carb on my 3300 in a 230 and had a constant readout & alarm warning through a Dynon 180.

 

It was interesting to monitor, as often when I expected icing it would be fine and then the temp would get low at times when you would swear that it would be OK.

 

But carb heat always gave an instant rise in temp.

 

I would recommend a carb temp probe to anyone who has a facility in their dash to locate a readout.

 

 

[Thirsty]

I've had icing in a jab as well. Engine starts to run roughly for no apparent reason the first thing to do is put on carb heat. If the rough running goes away it was probably carb ice.

 

I'm pretty sure the jabs run unfiltered hot air. The carb heat fitting on the airbox directs the hot air behind the filter.

 

 

[Old Koreelah]

I had a temp probe fitted into the carb on my 3300 in a 230 and had a constant readout & alarm warning through a Dynon 180.It was interesting to monitor, as often when I expected icing it would be fine and then the temp would get low at times when you would swear that it would be OK.

 

But carb heat always gave an instant rise in temp.

 

I would recommend a carb temp probe to anyone who has a facility in their dash to locate a readout.

Good idea. My probe is just inside the air box, and this may explain the slow change when the heated air is applied. Must mount it closer to the throat.