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Carb ice


Terry
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Hi there

 

- Just joined. I have owned a Corby Starlet for around 7 years now, and have around 550 hours in this aeroplane. Came into power flying by way of gliding, and before that G.A.

 

Interested in hearing from other A/C owners with VW installations who have experienced carb ice. I had an issue yesterday and although the carb heater did the trick, without that carb heat, I would have found myself flying a not very efficient glider quite quickly. It was all quite dismaying.

 

Its quite "parky" here in the South Island at the moment - around 5 c, and relative humidity around 65%., and although I've flown the aeroplane frequently over the winters I have owned her, I have never experienced anything quite like yesterday. It all ended well, but I'd prefer it didnt happen again.

 

The carb is a Stromberg, mounted above the engine, and the heads on the this engine are dual ports.

 

best wishes

 

T

 

 

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The Australian authorities publish this:- http://www.atsb.gov.au/media/56519/carb_icing.pdf and if you look at the conditions you report for yesterday, ie 5degrees and 65% RH your in the serious icing potential for any power setting part of the graph (ie worst potential). If you were up around or close to clouds where the RH is 100% then you are well inside the Serious icing potential any power setting........

 

Generally you determine icing potential by knowing Temp and dewpoint, using your relative humidity of 65% for 5degrees infers that the difference between temp and dewpoint is around 6degrees and I don't believe dewpoint is ever negative degrees celcius, but Im no expert on this, other than to say it appears you got icing were by all accounts we likely all might have seen it no matter what we fly.....

 

Andy

 

 

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The longer the inlet tracts the more probability of icing.. It is a natural thing where you have what constitutes a refrigerator your carby) evaporating A FLUID and expanding a gas adiabatically. Your hot air must be more than capable of melting the ice, and an engine affected by ice loses power and doesn't put heat into the exhaust system so it will cool the exhaust fairly quickly. Better to use it while the engine is still delivering power, to prevent rather than cure Air a bit warmer will hold more moisture so ambient temp is not entirely the cause... You could get icing at 20 degrees C. Good luck. Nev

 

 

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I had a moment a few weeks ago, flying north in the Hunter Valley. The only cloud in the sky was the plumes above Bayswater Power Station's cooling towers. As my route took me directly over them, I used these as an aiming point, but drifted right so that I missed them by about a kilometer, passing over Lake Liddell. At this point my engine tone changed and it seemed to struggle for breath for a few seconds before recovering. I can only put that down to the build-up of carby ice as I passed through a local spike in humidity downwind of the cooling-tower plumes.

 

 

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Thanks to all. Really appreciate your replies. I have flown in what I though were similar conditions, and the aeroplane has never missed a beat, but perhaps the humidity was higher yesterday. I know VW's have the reputation of being more prone to carb ice, and perhaps yesterday I found out the limits. Great to know however that my carb heater works(!) very well indeed.

 

Its quite nippy here at the moment (I live in North Canterbury) and we have had sleet during the day. Snow is quite low on the surrounding hills, so the Corby might just have to stay all tucked up in its hanger until things improve.

 

Once again, thanks for your advice and taking the time to reply.

 

regards

 

Terry

 

 

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Thanks to all. Really appreciate your replies. I have flown in what I though were similar conditions, and the aeroplane has never missed a beat, but perhaps the humidity was higher yesterday. I know VW's have the reputation of being more prone to carb ice, and perhaps yesterday I found out the limits. Great to know however that my carb heater works(!) very well indeed.Its quite nippy here at the moment (I live in North Canterbury) and we have had sleet during the day. Snow is quite low on the surrounding hills, so the Corby might just have to stay all tucked up in its hanger until things improve.

 

Once again, thanks for your advice and taking the time to reply.

 

regards

 

Terry

Terry, not sure why you would not fly just because of this ? The Carb Heat is there for a purpose - to be able to fly safely in these conditions !

 

 

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Hi there

 

Thanks to all for your replies. Firstly, to Gnarly Gnu, yes I have considered replacing the carb with fuel injection and I had an engineer point out to me the "bits" on the VW heads where these can be fitted. For most of the year however, carb ice isn't an issue (although it might be a tad chilly here from time to time, generally, Canterbury enjoys relatively low humidity). I do use carb heat over summer, but most of the time I apply it to confirm that it still works! Well, that's a slight exaggeration, because I always use carb heat in any sort of descent/power reduction, and of course on base and finals. At anytime of year.

 

And to Nev, on the day in question, there was around 2/10ths - cumulus as I recall. And it was a lot higher than the altitude I was flying at.

 

And to Ian R. Well, I proved that the carb heater works. Very well indeed as it happens. I would have ended up doing a forced landing if it hadn't have been working. I guess its just nice to know that it doesn't need to be mandatory and to be on permanently to go out there and safely commit aviation. There is the reduction in power when the carb heat is used, plus again, the increased fuel burn. I believe its better for the control to be used as needed.

 

Really appreciating the conversations. And hope its a damn sight warmer on your side of the Tasman than it is here right now. Still, the forecast for the morning here is fine and frosty, and the Corby just loves that thicker air. Take-off runs are shorter, the engine seems to produce more power, and although she's a draughty wee thing, and you need to be well bundled up, visibility will be unlimited, and all will be well with the world. Can't wait.

 

Safe flying to you all

 

Terry

 

 

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A sensor to measure the temp of the carby body wouldn't be a major cost. It would be a lot colder than ambient. The whole length of the manifold is heated by tapping of some of the exhaust in the car installation with the VW. Nev

 

 

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I flew an RF5 with Limbach conversion many years ago.

 

Was taking off on a morning when there had been fog about. Got about 1000' AGL when there was a humongous backfire.

 

I thought I had done major damage and returned to airstrip post haste.

 

There was a ring of ice crystals around the air filter and the engine wasn't damaged...unlike my nerves!

 

Kaz

 

 

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I now fly with a carb body temperature gauge, and use varying amounts of carb heat to maintain at least +5 degrees. My setup has both hot and cold air going through the air cleaner with the carb heat able to go from full cold to full hot or anywhere between. By a lucky coincidence, the SU carby has a blanking plug in the ideal position between the jet and the throttle spindle, and the port is the exact size and thread to accept a VDO temperature sender. A smear of heat conducting grease ensures that it reads actual body temperature. It has been a revelation since fitting this gauge to see just how cold the carby can get in relatively warm outside conditions.

 

 

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I fitted a remote sensor into a small hole I drilled downstream of the butterfly in my Bing. After all the effort, the damned sensor gives crazy readings and will have to be replaced.

 

A previous VW-based engine had a neat oil-cooler box mounted on top of the engine. The Zenith carby fed thru this box, cooling the oil and heating the mixture as it set off down those long VW induction tubes. Never a hint of icing.

 

 

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I've had it happen a few times, in the jabiru and lately in the Piper... it is disconcerting the first time or 2 but I think as Andy pointed out, having an idea of the temp and RH helps to be on the alert for the first sign of engine sputter.

 

 

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I get plenty of carby ice during warm up on the ground but none as yet during flight with the Jab. Used to get lots in flight with the 0200 in the C150 and that was disconcerting.

 

Laurie

 

 

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Terry

 

 

 

I had a hole drilled and tapped into the bing on my J230 to take a sensor that was screwed then sealed into place.

 

 

 

It worked well & gave really useful early indications of icing (from memory I think I alarmed it on the Dynon at 4 C in accordance with the Cessna Carb icing graphs).

 

 

 

If interested, the location & associated data can be seen if you search the thread J230 @ YSWG at and around post # 185.

 

 

 

Regards Geoff

 

 

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Here are a few more Carby Icing Probability Graphs. Consider them and use care when applying them, but they may help. I have always used the bottom one to get an indication of likelihood before flying on a suss day, but around central NSW it has never proven to be as bad as that graphs predicts in the Bing on my J230.

 

 

 

 

 

 

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Interesting stuff carb ice !! When I picked up my Auster from Redcliffe it was really bad on icing. Had to use carby heat quite extensively including on reduction of power at top of climb - quite a warm environment but high humidity. Here at Camden it very rarely needs to be used at all - although per normal practice I always have it on hot while descending and prior to landing. I have also had quite a few instances of it in an old Piper Cherokee 180 I fly. Some are worse than others.

 

 

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Remember - if you pull on carb heat - leave it on until after the engine improves. Your engine might run even worse for a moment or three while it ingests all the melting ice, but then it should clear.

 

Pilots have gotten into trouble by pulling heat on, the engines stumbles further, then they take the heat off fearing it isn't having the desired effect. IT IS, you just have to have faith. Run your engine on the ground one of those type of days with the cowls off. You will be astonished at the amount of water forming on the intake tubing.

 

 

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Some of the aircraft I've flown e.g Tecnam Eaglet have no Carby heat (Rotax) Why would that be?

Because their carby intake is inside the engine cowl and it is alleged that they will not suffer from carby icing because of the heat generated inside the engine bay by the engine.

 

 

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