Carby Heat Check

[Whack777]

I'm flying a 2.2 Jab and am just wondering how much variation in rpm others are getting when applying carby heat during the runup. I'm not sure I'm getting any variation at all.... is this normal?

 

Regards

 

Wayne

 

 

[Geoff]

Yes Wayne you don't get much rev drop if any even at full revs its minimal. have accidentally left it on in a touch and go. Then you will see a 200 to 300 rev drop and quiet a drop in power, not enough to stop the plane from flying just enough for you to notice something different.

 

 

[BigPete]

G'day Wayne,

 

My experience has been no drop in revs if no ice in carb. ;)

 

I have only found ice when doing the run up after taxiing to the rup up point when motor started from cold. :;)1:

 

Although I apply carb heat every 8 minutes or so in ice type conditions - I have never found it (ice) once the motor is hot. ;)

 

Only 100 to 150 rpm drop - (motor usually runs a little rough) so keep a good eye on it or you may miss it - revs will come back once ice is gone.

 

If your mixture/carby is adjusted well there may be no difference in rpm with heat applied if there is no ice.

 

hope this helps :)

 

regards

 

 

[glenns]

Same for me I would struggle to find any drop in revs.

 

 

[Guest brentc]

A Jab aviator who recently flew up to Darwin experienced severe Carby Ica coming into Alice Springs airport. Cruising at 8,500ft, 8 degrees temp at 2,800rpm in crystal clear blue skies, the engine started to run rough to the point where he thought it was going to stop. He put on the carby heat and about 30 seconds later it came good again.

 

I don't get a drop in RPM when I pull mine on that I've noticed.

 

 

[glenns]

I have had a similar response, flying back from Bundy when collecting the aircraft I put on carby heat as a precautionary measure about 30 minutes into flight at around 4500 ft and experienced an increase in RPM in about 10 seconds.

 

 

[Guest brentc]

To complicate things a little more, I remember reading quite some time ago in Flight Safety magazine that you shouldn't use carby heat unless you are actually experiencing carby icing as by adding carby heat you could actually change conditions and bring on carby icing. Food for thought.

 

 

[Yenn]

I get a drop of about 30rpm when I do pre take off checks. It is more evident as an increase of revs when the heat is turned off than as a drop with heat application.

 

 

[Whack777]

Thanks Guys... Interesting. So if there is no variation during the run up, there is really no way of knowing if it's even working or not at that point.

 

 

[Guest Fred Bear]

I know this does not answer your specific question Wayne but here is some good reading:

 

http://www.casa.gov.au/fsa/2004/dec/32-33.pdf

 

 

[slartibartfast]

Good article Darren.

 

This is why I am fitting a carb temp gauge. I have experienced quite a bit of icing, and I reckon knowing what is going on in the carb is invaluable (or at least worth $180).

 

Ross

 

 

[Guest JRMobile]

Last year flying to Broken Hill in winter I had 3 carby ice incidents, all on the ground during taxi or warm up and again last weekend. But generally no drop in RMP during checks.

 

"I have experienced quite a bit of icing, and I reckon knowing what is going on in the carb is invaluable (or at least worth $180)." Ross, can you give us some more info on this temp gauge please?

 

Cheers

 

John

 

 

[slartibartfast]

Sure John. Garry Morgan is supplying mine, but I think he is getting it from Aircraft Spruce. There's a few on this page with more info.

 

That's all I know. When we talked about gauges, it sounded like a really good idea to include it.

 

Ross

 

 

[Guest Fred Bear]

Ross, they are an excellent extra and why not all aircraft have them is beyond me. For the usual reason of they are not legally required I guess. It was a good article. I have had that one a while. Should have posted before. Might create another thread. It's out there this time of year (icing) and if you are not aware it is happening it can be fatal. I am a believer in giving 30 sec bursts of carb heat at 2800RPM in these conditions. Would be interested in knowing more about what Brent has mentioned about inducing icing when using carb heat when there are no symptoms of icing.

 

 

[jetboy]

no more than 50 rpm at runup (2000 rpm)

 

I think the discussion re inducing formation of ice is more related to flying with partial heat applied, in my years of GA flying all manuals and teaching advises against this: it should be on or off, and if clearing ice the engine stumbles a bit then full heat should be held.

 

Certified A/C need to produce a rise in intake temp something like 40 deg C which is probably why the rpm drop is more severe.

 

Discussion on the fulltime electric carb body heaters sold in UK is interesting, but for peace of mind I'd like both.

 

Ralph

 

 

[Yenn]

Time of year doesn't matter. Here in Qld we can experience carby ice in the heat of summer with our high humidity.

 

 

[Guest brentc]

Sorry My bad on that one, I was indeed referring to the use of 'partial' carby heat which could bring on icing conditions. Quite obviously pulling it right on wouldn't cause ice.

 

 

[Guest Fred Bear]

No worries Brent. Just wanted to clear it up as I was not sure but I have never done it half way. I was taught all or nothing. So you are quite correct. So a burst of all, full carb heat every once in a while at say 2800rpm will not hurt right?

 

 

[Guest brentc]

Personally I can't see why not. I have done that on the odd occasion myself when I've got a hunch that something isn't quite right. On the odd occasion you might find an airframe vibration could be caused by carby ice.

 

 

[Whack777]

So what we are left with so far is:

 

1. In a Jabiru with 2.2 engine, you can't necessarily confirm your carby heat is working or not by applying it at runup. (Because you don't necessarily get a variation in rpm)

 

This is interesting because I always looked for an rpm drop at runup in GA aircraft - What Ralph said above might explain the reason.

 

Talking to our local cfi, he suggested that if you apply carby heat in flight at a higher power setting you will probably notice a drop in rpm then. (and then I guess you then know that your carby heat is working)

 

2. When using carby heat it's all or nothing

 

which I think is commonly taught

 

The exception might be if you have a Carby temperature guage.

 

3. Icing probability can occur at any Outside Air Temperature (in degrees C) up to about +38.

 

- Serious icing at any power most likely between -3 and +17

 

- Serious icing with descent power likely from -5 to +27

 

from the graph in the article in Flight Safety Australia Nov Dec 2004;

 

http://www.casa.gov.au/fsa/2004/dec/32-33.pdf

 

Thanks for your input everyone. Been a good learning exercise and refresher for me.

 

Regards

 

Wayne

 

 

[rick-p]

My Jab 2200 doesn't have carby heat as such and I don't get carby ice. Reason, the manufacture's of my aircraft designed the installation in such a way that there is always warm air around the carby which such prevents carby ice.

 

In my Skyfox the 912 has iced up on take off in the middle of summer, of course under idle conditions, right dewpoint etc.

 

My old Auster Gypsy Major can run with carby heat on all the time and should be used at times on takeoff.

 

Rick-p

 

 

[BigPete]

Quite cool here in Echuca this morning (5 deg.) - went for any early flight before the day turned ugly. ;)

 

Quite a long taxi from back hanger to warmup point. Had quite a lot of carb ice - it took a fair while before the revs dropped, around 10 - 12 seconds and a drop of around 100 revs (from 1600 rpm. :;)1:

 

When the motor increased revs (ice gone) - it came back to 1700 revs. This took another 10 or so seconds.

 

Because the unsealed taxi ways were closed, I had to enter and backtrack along the main runway. I again checked for carby ice (and had some) :;)1: when I lined up on the keys.

 

A very heavy dew was on the ground and this would have been the main reason for the ice build up.

 

Once the motor is warm (in the air) I have never had carb ice :) - but in ice type conditions I always apply carb heat every 10 minutes or so. I always apply carb heat if decending power off/reduced.

 

regards

 

 

[Guest Teenie2]

Folks

 

Just for interest sake,to attain FAA certification the carby heat must be able to raise the inlet air temp by 90 degrees F,and I'm pretty sure the PFA has similar requirements .

 

Jaycar electronics has battery powered digital thermometers that could be used at a lot less than $180.

 

 

[jcamp]

Where should the sensor go in a Bing Carby? Does anything sticking out between the slide and the butterfly cause problems.

 

Given the temperature, vibration and electromagnetic environment in the engine bay, cheap domestic grade electronics may be problematic.

 

 

[Captain]

Here is where mine is located jcamp.

 

I exchanged info with a few guys in the UK & US who have them in the same location before I tapped into the carb.

 

The sensor came from Dynon.

 

It works well & you'd be surprised how cool is the result from the venturi action in the carbie (latent heat & all that jazz).

 

Hope this helps

 

Geoff

 

(The website is having trouble replying to my photo upload request. I'll insert it as soon as it lets me)