FlyingMonkey Posted December 5, 2014 Report Share Posted December 5, 2014 I know that the carb heat on the Rotax 912 really causes minimal if any RPM drop. If I am doing a runup and pull my carb heat to full, I see nothing on the tach at all. I have an analog tach so it might not have the resolution of a digital EMS, but it doesn't seem to budge. IIRC correctly the drop is really only about 50rpm or so, so I just might not be able to see it... Is this pretty normal? With the cool, moist weather we are having here I don't want to get in a situation of needing carb heat and finding out I ain't got it. Link to comment Share on other sites More sharing options...
Tom Baker Posted December 5, 2014 Report Share Posted December 5, 2014 I know that the carb heat on the Rotax 912 really causes minimal if any RPM drop. If I am doing a runup and pull my carb heat to full, I see nothing on the tach at all. I have an analog tach so it might not have the resolution of a digital EMS, but it doesn't seem to budge. IIRC correctly the drop is really only about 50rpm or so, so I just might not be able to see it... Is this pretty normal? With the cool, moist weather we are having here I don't want to get in a situation of needing carb heat and finding out I ain't got it. Andy, for the CTSW what they call carb heat is really just an alternate air source. It pulls ambient air from inside the cowling. With this system you could even see a possible RPM increase instead of a decrease because of not pulling restricted air through the filter. Most small aircraft carb heat systems pulls heated air from around the exhaust manifold, and it has a significant temperature increase above what the CTSW uses. That is why they get a RPM drop, and your CTSW does not. The CTLS uses a different carb heat system than the SW. It pulls heated air from around the muffler. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 5, 2014 Author Report Share Posted December 5, 2014 Ah, that explains it, thanks Tom! I was trying to follow the carb heat cable to see what it does, but I was alone and could not both actuate the carb heat and check in the cowl for movement at the same time. Link to comment Share on other sites More sharing options...
FredG Posted December 5, 2014 Report Share Posted December 5, 2014 Andy, I also have no change in RPM (on Dynon panel) with the full application of carb heat. I have inspected the flap on the airbox/filter holder to ensure that it opens (to allow entry of warm unfiltered air from inside the cowling, as noted by Tom) when the carb heat knob is pulled. Fred 2006 CTsw E-LSA Link to comment Share on other sites More sharing options...
Anticept Posted December 5, 2014 Report Share Posted December 5, 2014 The LS models use the rotax airbox, which has the scat tubing (don't google that. I made that mistake a long time ago) and the changeover valves to pull carb heat from the muffler shroud. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 5, 2014 Author Report Share Posted December 5, 2014 Great, thanks guys. So I'm guessing there is really no good way to test carb heat function other than just visually inspecting the mechanism, and if it works normally assuming the heat will be there when needed? The Tecnam I trained in in 2009 had a 50-100rpm drop with full carb heat, it must have been pulling air from the muffler assembly instead of simply under cowl air. As a side note, for those who have needed carb heat in flight on a CT to correct roughness or an rpm drop, has it been quickly effective when applied? Link to comment Share on other sites More sharing options...
rookie Posted December 6, 2014 Report Share Posted December 6, 2014 Andy, I have the same experience with my CTsw. I talked with Eric Tucker about it when I was in school last fall. He thinks I should see a drop but I never do. For awhile it bugged me but after having two experiences with carb ice and carb heat worked fine I don't think about it any more. al Meyer Link to comment Share on other sites More sharing options...
Roger Lee Posted December 6, 2014 Report Share Posted December 6, 2014 A drop will only occur depending on the type of airbox/carb heat you have. The SW will almost never see a drop. The air introduced isn't hot enough. LS's may see approx. 25 rpm and some other aircraft engine systems none and up to approx. 50. The hotter the air introduced the bigger the drop. The hot air enrichens the mixture so the rpm drops. The better carb ice setup is the hot coolant one. It doesn't affect rpm or air flow and the carbs stay hot enough that ice can't form. Link to comment Share on other sites More sharing options...
Rich Posted December 6, 2014 Report Share Posted December 6, 2014 Roger, I picked up carb ice on the way to and from NC. I have the water jackets on my carbs. I noticed an air bubble in the overflow tube that goes from the main resivior tank to the overflow bottle. The plane had hoses removed when worked on by the Rotax mechanic prior to the trip. If there is air in the system, will it work itself out through the overflow tube? Link to comment Share on other sites More sharing options...
Anticept Posted December 6, 2014 Report Share Posted December 6, 2014 If there is air in the system, will it work itself out through the overflow tube? Going to answer in short: maybe. Now for the long response: liquid coolant systems all suffer from air problems in the systems. The overflow bottle does not exist because of coolant expansion and contraction. Fluids undergo very little of this, so little that for most calculations in physics, expansion coefficient of fluids are omitted. It's one of the defining characteristics of a fluid vs a gas. What the overflow bottle is for, is when gas inevitably forms in the coolant system and displaces coolant. This gas is composed of the coolant itself. When a fluid is pumped around a bend, it causes a pressure drop in the inside of the bend. Combined with the elevated temperatures, it begins to boil and causes a small air pocket. It will collapse on it's own when things cool down. We decrease this occurrence and severity by using large bend radii in hoses and turns when possible. Sometimes these bubble break loose. It goes through the coolant system to the overflow assembly, and out of the overflow bottle. That is why the line to the bottle is at the highest point in the system. Link to comment Share on other sites More sharing options...
Rich Posted December 6, 2014 Report Share Posted December 6, 2014 Anti, Thanks for that indept reply. It's very much appreciated. I felt the water jacket nipples, as Roger suggested, after a local flight a few weeks ago and they were hot. May be the situation cleard itself? I just cant be sure until the next long XC which will be coming up during the Sebring Expo. It just seems very unlikely to pick up carb ice with the jackets and the air filters exposed to cowl air. That was the first time it's happened and it was just after maintenance was performed. CHT's were all normal, so I guess coolant was flowing. This just has me puzzled. Link to comment Share on other sites More sharing options...
Brad Posted December 19, 2014 Report Share Posted December 19, 2014 On my CTLS, one day I did notice that there was an insignificant drop in RPMs when carb heat was applied. But, I recall about a 30 rpm drop in the past. When I mentioned the lack of the rpm drop to one FD service center, they said it was normal. It turns out it was not normal. I was able to rest one hand on the actuator behind the air manifold and activate the carb heat with the other only to discover that the cable was not functioning. When the carb heat knob was pushed in, the cable sleeve would move away from the actuator, but the actuator itself would not move. This meant that carb heat was being applied all the time (the cable could not shut it off). I manually repositioned the actuator to shut the valve and eventually brought it to FD. In order to access the actuator, they had to pull the engine. FD fixed the issue, but it broke again (although the issue is still the cable, the problem now seems to be somewhere other than at the actuator - I have not yet had the time for troubleshooting). It seems as though when the cable malfunctions, the actuator gets stuck with carb heat constantly applied. I need to get FD to look at it again, so in the meantime, I can't test my carb heat during run up and do not put it on for landing. Instead, if I happen to detect a potential carb icing problem, I'll activate it. Once activated it will then require a "manual reset". If you have a CTLS and don't see the rpm drop, you might just want to check this out and don't assume that the condition is normal. It you have a CTLSi, disregard everything I said and don't gloat... Link to comment Share on other sites More sharing options...
CT_MATT Posted December 19, 2014 Report Share Posted December 19, 2014 jbm3, I too had issues with my carb heat and it ended up being the cable/wire getting kinked (eventually broke) immediately behind the panel where there is a gap between the actuator handle and the cable housing. Mine was stuck somewhere between open and closed and caused some power loss until I was able to sort it out. This an easy thing to check to be sure (just pull the pilot side panel and you can see this connection). You may want to check this for peace of mind... Link to comment Share on other sites More sharing options...
Brad Posted December 19, 2014 Report Share Posted December 19, 2014 I hadn't thought to pull the panel, but will now. Thanks! Link to comment Share on other sites More sharing options...
Tom Baker Posted December 19, 2014 Report Share Posted December 19, 2014 On my CTLS, one day I did notice that there was an insignificant drop in RPMs when carb heat was applied. But, I recall about a 30 rpm drop in the past. When I mentioned the lack of the rpm drop to one FD service center, they said it was normal. It turns out it was not normal. I was able to rest one hand on the actuator behind the air manifold and activate the carb heat with the other only to discover that the cable was not functioning. When the carb heat knob was pushed in, the cable sleeve would move away from the actuator, but the actuator itself would not move. This meant that carb heat was being applied all the time (the cable could not shut it off). I manually repositioned the actuator to shut the valve and eventually brought it to FD. In order to access the actuator, they had to pull the engine. FD fixed the issue, but it broke again (although the issue is still the cable, the problem now seems to be somewhere other than at the actuator - I have not yet had the time for troubleshooting). It seems as though when the cable malfunctions, the actuator gets stuck with carb heat constantly applied. I need to get FD to look at it again, so in the meantime, I can't test my carb heat during run up and do not put it on for landing. Instead, if I happen to detect a potential carb icing problem, I'll activate it. Once activated it will then require a "manual reset". If you have a CTLS and don't see the rpm drop, you might just want to check this out and don't assume that the condition is normal. It you have a CTLSi, disregard everything I said and don't gloat... I had this with my airplane as well. The nut the holds the cable housing in place had come loose on the carb heat side of the cable end. It is a real bear to get to re-install and tighten. It also needs a little thread locker on it to keep it from coming loose again. Purple thread lock works good in this spot. Link to comment Share on other sites More sharing options...
Brad Posted December 19, 2014 Report Share Posted December 19, 2014 I had this with my airplane as well. The nut the holds the cable housing in place had come loose on the carb heat side of the cable end. It is a real bear to get to re-install and tighten. It also needs a little thread locker on it to keep it from coming loose again. Purple thread lock works good in this spot. My issue would have caused the same result, but was slightly different. The knurled end and nut were still in place, but the sleeve itself separated from its anchor at the end it the cable. Link to comment Share on other sites More sharing options...
paul m Posted December 20, 2014 Report Share Posted December 20, 2014 ..... If you have a CTLSi, disregard everything I said and don't gloat... This is me not gloating Brad. About to pick up my plane after its first annual from Dave. Sport upgrade went in. Looking forward to seeing if I notice any differences. Link to comment Share on other sites More sharing options...
Duane Jefts Posted December 21, 2014 Report Share Posted December 21, 2014 This is me not gloating Brad. About to pick up my plane after its first annual from Dave. Sport upgrade went in. Looking forward to seeing if I notice any differences. Would like to hear of any differences. Was the prop pitch changed? Link to comment Share on other sites More sharing options...
paul m Posted December 21, 2014 Report Share Posted December 21, 2014 Based on its performance pre the upgrade, I asked Dave to flatten it a little as I was barely getting 5500 WOT. Not sure if the Sport upgrade calls for any changes in and of itself. Will see if I can get some exact numbers for you. Link to comment Share on other sites More sharing options...
Roger Lee Posted December 21, 2014 Report Share Posted December 21, 2014 Hi Duane, Your parts are due here this week. As soon as they are on it would be a good idea to just double check the WOT at altitude. When are you due back? Link to comment Share on other sites More sharing options...
coppercity Posted December 21, 2014 Report Share Posted December 21, 2014 Based on its performance pre the upgrade, I asked Dave to flatten it a little as I was barely getting 5500 WOT. Not sure if the Sport upgrade calls for any changes in and of itself. Will see if I can get some exact numbers for you. I think you will be happy with the upgrade, we just completed one on a Jubilee and it seemed a noticeable difference in performance at our higher altitudes. Link to comment Share on other sites More sharing options...
Duane Jefts Posted December 22, 2014 Report Share Posted December 22, 2014 Hi Duane, Your parts are due here this week. As soon as they are on it would be a good idea to just double check the WOT at altitude. When are you due back? Leaving tomorrow (Monday) and back before the New Year I hope. Link to comment Share on other sites More sharing options...
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