Sympoms of icing

[Bruce Tuncks]

Some years ago, on a cold morning, I had descended from 8,000 ft down to 2,000 ft at partial throttle, foolishly without using carby heat. Then when I opened the throttle again all was normal for about 30 seconds at which time the engine gave a big "bump" which frightened hell out of me. Then the engine ran normally again.

 

I later figured that there had been ice in the carby which melted and the water got sucked into a cylinder. And I learned that the carby heat system is there to be used if there is any chance of icing.

 

Recently, a club member asked me about his experience, again with a Jabiru engine. He had done a similar descent , this time to get under cloud, and when he opened the throttle again, there was no response from the engine. He barely had enough power to maintain altitude, but after about 2 minutes, the power returned and the throttle worked normally again.

 

I could see nothing wrong with the throttle linkage and concluded that ice had literally frozen the throttle.

 

Funny how the 2 engines showed such different symptoms to icing. Mind you, I can't prove that either of these really was icing.

 

 

[Yenn]

Long descent with partial throttle is one of the easiest ways to get carbie ice. I used to fly a C150 that would ice up in that configuration even when the ground temp was in the 30's. I used to reckon if there was a cloud in the sky i needed carbie heat at anything less than full throttle.

 

I have had what must have been carbie ice in a 503 engined Thruster. I put it down in the paddock next to my house rather than continue over tiger country. It just coughed and spluttered. I couldn't find anything wrong and it started and ran OK on the ground.

 

I had an engine failure at T.O. in a C150 and a bit later a pilot put a twin through the hedge taking off. I stopped OK. Both put down to carbie ice.

 

 

[skippydiesel]

Years ago I did a few hours of flying in BC Canada. Took an instructor along with me, as I was very unfamiliar with the area. Learnt that in Canada, all pilots are trained to use carbi heat prior to and during, all significant reductions in power. When I flew GA, I adopted this measure but now that I am RAA and I fly an aircraft without carbi heat. I do worry on occasions that icing may impact my engine. In 8 years of flying my Rotax 912 uls motivated aircraft I have never knowingly encountered ice. I am careful to make power reductions gradual, in an attempt to minimise carburetor icing conditions.

 

 

[jetboy]

I've had icing with a Bantam B22 / Rotax 503 on a warm but humid day, gentle cruise under the cloudbase back to base and seemed to reduce power

 

trouble with this was no carb heat system but I got in OK with a higher than normal throttle setting.

 

C150 had a few "possible" events but always trained to use full carb heat at any sign of roughness and always on descent for landings.

 

zenair 701 with Jabiru 2200 no problems in flight but it has a good heat system and I use it like the cessna one.

 

I have had many instances of icing during the initial warmup phase especially cool mornings where there is dew on the grass airfield. The idle starts slowing and continues to slow even after throttle increse which can be fixed with carb heat otherwise the engine will stop.

 

 

[skippydiesel]

.......................I have had many instances of icing during the initial warmup phase especially cool mornings where there is dew on the grass airfield. The idle starts slowing and continues to slow even after throttle increase which can be fixed with carb heat otherwise the engine will stop.

Yep! you have reminded me of the only time I knew I had encountered carbi ice - Early morning departure from Condobolin in a Cessna 172. Symptom - engine ran normally at low RPM but refused to increase RPM for magneto checks. Had no idea what the problem was. Started to go through list of engine checks...... Applied carbi heat - chug chug followed RPM rise. The light went on CARBI ICE! and I hadn't even left the ground.

 

 

[Jaba-who]

Jab engines seem to have a vast array of symptoms to carb icing. (Though they are not alone there either ) have friends who have described typical gradual loss of power, rough running after heat on, sudden missing without prodromal change.

 

I have had only one where I suspect it happened.

 

Same sort of scenario as BT described. Long descent at lower power ( although it wasn't at very low or idle. )

 

Descent was only a couple of thousand feet and was not a particularly cloudy day but was in the tropics (Cairns area ) so humidity was usual moderately high.

 

Levelled out at about a thousand and back to normal power (2900

 

rpm) few minutes later a single miss in the engine then normal. I waited for a bit before applying carb and nothing happened so didn't bother. About ten minutes later another miss. Applied full carb heat but still nothing different.

 

Another few minutes later a single miss then normal again. Ran on carb heat for about 20 minutes and then off. No change no further misses. Since then nothing abnormal.

 

No real definitive proof but couldn't put it down to anything else.

 

 

[408059]

I hadn't had the Cassutt Racer long and was down at Moruya on the Southern Coast of NSW. It was 20+ degrees and very humid. I had done my usual pre-takeoff checks including using the carbie heater and lined up but had to wait 10-15 minutes before there was a slot in the traffic to get away. The break in the traffic appeared and I took off on 05 taking me out to sea. At 300 feet ASL the engine stumbled and all but died. I was well outside of gliding distance to the beach. There was more than a few tense moments before the engine came good at 150 foot or so above the waves. I learn't from the event that the old Stromberg carbie on the Continental C85 engine was very susceptible to carbie icing, that humidity can cause icing in warm temperatures, and to use the carbie heater just prior to taking off as a matter of routine. So bad was the Stromberg that if there was dew/frost on the ground then I knew I was in for carbie icing, which in Cooma was a daily winter condition.

 

Steve