Are Jab engines prone to icing?

[Guest Maj Millard]

Jetjr, That setup for carb heat you discribe works well, and is the same as had been fitted to Lightwings for years, and quite a few other aircraft as well............................................................Maj...

 

 

[Captain]

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.

OK.

 

It was a simple job to drill the side of the carby and tap it.

 

The location and outcome is shown if you search the thread on the build at J230 at YSWG.

 

But the temp sensor probe needs to be a short one so as not to restrict the carby throat.

 

Regards Geoff

 

 

[Sapphire]

Some carbys have a hole already drilled. If not it's important to put in right spot as indicated by mfg. Otherwise you are just reading ambient air.

 

 

[Old Koreelah]

OK.It was a simple job to drill the side of the carby and tap it.

 

The location and outcome is shown if you search the thread on the build at J230 at YSWG.

 

But the temp sensor probe needs to be a short one so as not to restrict the carby throat.

 

Regards Geoff

Sorry about the delay replying, Captain. What temp does your probe read in normal flight? I presume it would be pretty close to zero. Do you often check carby temp, and do you notice changing conditions affecting the reading?

 

 

[Dieselten]

My Jabiru 2.2L engine ices fiercely on Mogas (BP Ultimate 98-octane) in winter and less so - but will still ice up - on Avgas. I learned to recognise symptoms (rising level of vibration to the point where the instrument-panel is hard-to-read) and use carb-heat very early on and it has done me no harm at all.

 

 

[Old Koreelah]

Sounds like the best engine monitoring instrument is your hearing.

 

 

[Yenn]

A temp probe in the air box is next to useless. The temp s critical at the venturi, where pressure are lower leading to a drop in temperature. You would need some means of getting humidity readings or an airbox probe to start to be any use.

 

 

[Old Koreelah]

I agree, Yenn. I have gauges for humidity and ambient air temp, which give some general warning of icing conditions, but I need to move my remote probe closer to the action. Ideally I should remove the carb, drill a hole and glue the sensor just downstream of the butterfly valve. It's a huge job to remove the Bing, so next best thing is to glue or clamp the probe to the outside of the exit side of the carb. Surely the alloy will conduct the temp changes. What do you think?

 

 

[poteroo]

Used mogas for many years in the Continental 0-470 engines in my C180 and C182, also for 12 years in the 0-300 in my C170 - all by STC- and found they were all more prone to icing than with avgas 100/130. The old avgas 87 we used to enjoy,(sigh), never caused any grief at all. Strange though, that all the myths about fuel vapourisation with mogas never happened to me - and we operated often in 45c with a heat soaked engine.

 

Couldn't say conclusively whether mogas 98 is better or worse than avgas 100/130.

 

But, we do suffer with lots of icing here on the coast. Our schools special rule is - do your engine run-up last, and leave the carby heat ON for 30 secs before you enter the runway and apply power. Some checklists have the engine run-up 1st - followed by sveral minutes of pre-takeoff checks. This is guaranteed to create some fun by the time you get to applying take-off power.

 

happy days,

 

 

[Old Koreelah]

Strange though, that all the myths about fuel vapourisation with mogas never happened to me - and we operated often in 45c with a heat soaked engine.

This thread was meant to help me with icing, but I have discovered that vaporisation is also a hazard. I'll be ducting cooling air to my fuel pump, which needs it more than most Jab engines, because the metal shield I installed to prevent fuel leaking onto the hot muffler also shields it from cooling air. Whoops.

 

 

 

Good idea, poteroo.

 

 

 

Operating a flying machine, even a simple little one, is complex enough without the added hassles of icing and vapourisation. My next project will have fuel injection, liquid cooling, and computers to look after the details.