Rich Posted October 19, 2014 Report Share Posted October 19, 2014 Good morning, Friday, flying from PA to NC I encountered a 150 RPM loss at 4500 MSL under a haze level about 1,000 feet above. OAT at the time was 60*F Altimeter setting 29.78 Cruse RPM set at 5250. There may have been some rising moisture. At cruise the RPM dropped slowly from 5250 to 5100. I advanced the throttle to wide open but couldn't get more than 5200. I left the setting at WOT and gradually the rpm started to return to 5400. It took about three minutes.I reduced the throttle setting back to cruise and there were no more issues. I probably had some ice forming but my 912ULS is equipped with the carb water jackets that keeps the carb body warm at all times. I guess its possible to have ice form in the carbs, even with the water jackets. Has anyone with the same set up had this occurrence or known of this happening? Link to comment Share on other sites More sharing options...
Anticept Posted October 19, 2014 Report Share Posted October 19, 2014 Our carbs are not immune to ice, and we've seen it first hand. Are your water jackets working? Link to comment Share on other sites More sharing options...
2FlyAgain Posted October 19, 2014 Report Share Posted October 19, 2014 According to Dean Vogel during the Rotax Service training course this summer, the Rotax 912 is most likely to experience carburetor ice when the ambient temperature is around 60 F and there is visible moisture present. If you are like me, you probably wouldn't think of carb ice at 60 F... or at least not at first. He didn't discuss the effect of water jackets on the carbs. Link to comment Share on other sites More sharing options...
Anticept Posted October 19, 2014 Report Share Posted October 19, 2014 According to Dean Vogel during the Rotax Service training course this summer, the Rotax 912 is most likely to experience carburetor ice when the ambient temperature is around 60 F and there is visible moisture present. If you are like me, you probably wouldn't think of carb ice at 60 F... or at least not at first. He didn't discuss the effect of water jackets on the carbs. This is due to fuel vaporization, which absorbs a lot of heat, then the effect of the venturi or throttle plate further restricting the passage, and it drops the temperature to freezing very quickly. Link to comment Share on other sites More sharing options...
Tom Baker Posted October 19, 2014 Report Share Posted October 19, 2014 The temperature drop can be as much as 70°f. That is why you can have carb ice with outside temperatures as high as 90°f. Link to comment Share on other sites More sharing options...
Dan Kent Posted October 20, 2014 Report Share Posted October 20, 2014 Rich, I have the same water jackets and live in a very high humidity area and have never encountered this. Also, I was under the impression that carb icing was more likely at lower rpm (partially closed throttle plate) than at near WOT, like you were at. Link to comment Share on other sites More sharing options...
2FlyAgain Posted October 21, 2014 Report Share Posted October 21, 2014 This is due to fuel vaporization, which absorbs a lot of heat, then the effect of the venturi or throttle plate further restricting the passage, and it drops the temperature to freezing very quickly. It makes sense that fuel vaporization is going absorb heat and in the process cool some thing nearby (e.g. water vapor, metal surfaces, etc.). For the sake of argument, I am willing to accept that this effect can be as large as 70 F. What I am curious about then, is why is the Rotax 912 reportedly less susceptible to carb ice at say 35 to 40 F. Is it that the colder air contains less moisture which means less potential ice to foul the carburetor? Thanks! Link to comment Share on other sites More sharing options...
Anticept Posted October 21, 2014 Report Share Posted October 21, 2014 It makes sense that fuel vaporization is going absorb heat and in the process cool some thing nearby (e.g. water vapor, metal surfaces, etc.). For the sake of argument, I am willing to accept that this effect can be as large as 70 F. What I am curious about then, is why is the Rotax 912 reportedly less susceptible to carb ice at say 35 to 40 F. Is it that the colder air contains less moisture which means less potential ice to foul the carburetor? Thanks! Exactly. The area that is most prone to icing is 70 degrees and mid to low power settings, according to Eric Tucker. I've heard that 40 degrees can be a bad temperature to be at as well, but I am not so sure. Maybe at wider throttle settings for extended periods of time since there is a lot of vaporizing fuel, and the moisture is going to want to stick to something as freezing air can't hold much at all. Link to comment Share on other sites More sharing options...
Rich Posted October 21, 2014 Author Report Share Posted October 21, 2014 Had to be ice as the drop was gradual. WOT cleared it after a few minutes. I was surprised. Having the water jackets may minimize but I guess does not negate the possibility of carb ice. Link to comment Share on other sites More sharing options...
Rich Posted November 1, 2014 Author Report Share Posted November 1, 2014 Same scenario on the way back to PA. with a lower OAT and a higher Alt. setting OAT 48*F RPM 5250-5270 3500 MSL Alt setting 30.6 At RPM drop> applied full throttle> cleared sooner than on the way down>left the RPM setting at 5300 and no more issues. I,m hoping it was only carb ice and nothing more serious. Link to comment Share on other sites More sharing options...
Runtoeat Posted November 1, 2014 Report Share Posted November 1, 2014 Rich, I experienced carb icing this summer while flying over North Central PA. Temp at altitude was 65 F. and cruise RPM was 5400. Link to comment Share on other sites More sharing options...
Tom Baker Posted November 1, 2014 Report Share Posted November 1, 2014 Same scenario on the way back to PA. with a lower OAT and a higher Alt. setting OAT 48*F RPM 5250-5270 3500 MSL Alt setting 30.6 At RPM drop> applied full throttle> cleared sooner than on the way down>left the RPM setting at 5300 and no more issues. I,m hoping it was only carb ice and nothing more serious. If that float you pictured in the other thread was heavy, it could be the cause of the RPM loss. A slightly heavy float might not keep enough pressure on the float needle, and the float bowl might fill up with excess fuel. Going to full throttle will use more fuel possibly lowering the fuel level in the float bowl. Link to comment Share on other sites More sharing options...
Rich Posted November 1, 2014 Author Report Share Posted November 1, 2014 Tom, I don't think that was the issue. On the way to NC I had flipped the float so the rough area was on the top. The bad float was not worn down to the foam inner core but was coming close. The new float was shipped from Lockwood to NC where I replaced it. I had the same issue on the return to PA with the new float installed. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted November 1, 2014 Report Share Posted November 1, 2014 Rich, I experienced carb icing this summer while flying over North Central PA. Temp at altitude was 65 F. and cruise RPM was 5400. Such reports give more insight if you include the dewpoint or dewpoint spread. Link to comment Share on other sites More sharing options...
Runtoeat Posted November 1, 2014 Report Share Posted November 1, 2014 CT, Don't recall but thinking dew point must have been close to ambient of 65 F. I was dodging rain coming out of big puffy scattered. Couldn't go higher due to ceilings. Two days prior to this, I was going over same area of North Central PA but had lower ambient of 45 F and higher ceilings of 9500' but still large puffy with rain/snow showers. No icing noted on this leg of the trip while at 7500'. Link to comment Share on other sites More sharing options...
Roger Lee Posted November 1, 2014 Report Share Posted November 1, 2014 The Bing 64 variable throat carb is less susceptible than a standard carb, but it is by no means immune. Link to comment Share on other sites More sharing options...
Tip Posted November 1, 2014 Report Share Posted November 1, 2014 Is it possible that many of us are seeing carb ice due to the ethanol we are using? Link to comment Share on other sites More sharing options...
Doug G. Posted November 1, 2014 Report Share Posted November 1, 2014 Why would that be? Link to comment Share on other sites More sharing options...
FastEddieB Posted November 1, 2014 Report Share Posted November 1, 2014 Why would that be? Also curious, since ethanol is used in some antifreeze! Link to comment Share on other sites More sharing options...
Doug G. Posted November 1, 2014 Report Share Posted November 1, 2014 Not sure if Heet is ethanol or methanol, but, of course, It is used for absorbing water in fuel. I would think, if anything, ethanol would minimize icing. But, the examples given seem to be dependent on atmospheric moisture, not anything in the fuel. Link to comment Share on other sites More sharing options...
Jim Meade Posted November 2, 2014 Report Share Posted November 2, 2014 The MSDS on HEET says it is methanol. http://www.prairielandelectric.com/msds/inbookmsds/HEET.pdf Link to comment Share on other sites More sharing options...
Runtoeat Posted November 2, 2014 Report Share Posted November 2, 2014 As others here indicate, our Rotax engines are not immune to icing, given the proper conditions. Prior to this and due to what I had read about the 912ULS "rarely" icing up, I had let my guard down and was not vigilant for the signs of carb icing. My friend, who is very experienced, was vigilant and sensed the engine loosing power and told me to see if application of carb heat would add some RPM's. It did. I will now try to be on the lookout for carb icing at all times but especially when ambient temps are in the 60 to 70 F range with moderate to high humidity/low dew point spreads. Tip, interesting you ask about methanol in our Mogas. Due to my cross country flight, I was burning 100% 100LL fuel when I experienced icing. Link to comment Share on other sites More sharing options...
Doug G. Posted November 2, 2014 Report Share Posted November 2, 2014 No scientific evidence, but I don't believe ethanol has an impact on carb icing. Link to comment Share on other sites More sharing options...
Rich Posted November 2, 2014 Author Report Share Posted November 2, 2014 RTE, I believe you have carb carb heat as you stated applying it. I have the water jackets that warm the carb body. I would like to know if anyone, who has the water jackets, experienced carb ice. CT, I don't remember the exact temp/dew point spread but it wasn't close to where I wouldnt fly. I just got the report, checked my closest wx, temp/ dew point and it was not a factor. I never get a temp/dew point spread while at altitude and didn't know you could ask and receive it. Link to comment Share on other sites More sharing options...
Tip Posted November 2, 2014 Report Share Posted November 2, 2014 My earlier post was a question not a statement. But a quick google search found this, "The key problem is that ethanol absorbs water from the atmosphere. In fact, fuel with 10 percent ethanol absorbs up to 50 times more water than standard gasoline. Older gas tanks found in many classic cars vent to the atmosphere, increasing the likelihood that moisture will be absorbed into the gas tank at a rapid pace." And our fuel tanks are open through the vents. Link to comment Share on other sites More sharing options...
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