mocfly Posted July 10, 2013 Report Share Posted July 10, 2013 During my flight from Chattanooga to NJ yesterday I experienced what I can best define as a significant "shudder". Here is the background Departed Knoxville full fuel 2 passengers and plenty of baggage. Initial climb to 7500ft. with a cruise set at 5400rpm. Increasing clouds required a cimb to 9500ft. The flight progressed uneventful until about 4 hrs. where the 1st. shudder occurred. The initial shudder felt like something had become detached an hit the aircraft or there was a high speed miss. It last long enough for me to feel it but not long enough or hard enough to be concerned. It did however wake me up. The next event occurred after we had exited an area that had us in some pretty good precip. This occurrence lasted a little longer and felt strong enough to think that a prop blade was loose. From 5400 I reduced the rpm to 4600 and while the prop was ok and the rpm was steady the engine felt like it was running rough. This time i was concerned enough to start looking for nearby airport. Increasing to rpm to 5400 it was smooth as glass. This happened one more time before my descent into KCDW where the flight ended without any further problems. During my descent the engine responded normally with quick responses and all instrumentation in the green. After landing a walk around showed no abnormalities. My direction of flight was 060 with a 8-10kt wind from 260-270. Thoughts or Questions? Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted July 10, 2013 Report Share Posted July 10, 2013 stuck float? Link to comment Share on other sites More sharing options...
mocfly Posted July 10, 2013 Author Report Share Posted July 10, 2013 I'm not sure. How would one check if it is intermittant? I'm assuming that a stuck float on 1 carb would exhibit that type of engine behavior? Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted July 10, 2013 Report Share Posted July 10, 2013 In my case there was a hole in the float and that hole can catch on the bracket causing fuel starvation on one side of the engine, and a big time shutter. It could also function normally when it wan't caught on the bracket. The deteriorating float can also put debris in your carb. Link to comment Share on other sites More sharing options...
Rich Posted July 10, 2013 Report Share Posted July 10, 2013 Chris,----------Look at my last post in the topic " Float bowl debris (was resin nodules in gascolator" Seems like your engine may have had the same issues as mine.---------I removed the float bowls and included three pictures of the debris that was found. The debris found was intermittently blocking the main jet causing rough running and engine vibration. Changing RPM's, the debris would drop back into the float bowl only to be picked up again causing the problem to reoccur-----------I found the problem thanks to posters on our forum.-----Rich Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted July 10, 2013 Report Share Posted July 10, 2013 rubber debris from your hose change is another possibility. Link to comment Share on other sites More sharing options...
Roger Lee Posted July 10, 2013 Report Share Posted July 10, 2013 Hi Chris, First thing to check for this type of vibration is the carb bowl. Do it as shown in the maint. video and it will be fairly easy. A small piece of debris that doesn't fully block the jet will cause this exact type of vibration and or a small power loss. After that check all the wheel pants for tightness (they should not rock back and forth) and lastly check the stab for fore and aft free play. It should be solid with no play. The odds are in favor of a tiny fleck in the carb bowl. Link to comment Share on other sites More sharing options...
mocfly Posted July 10, 2013 Author Report Share Posted July 10, 2013 Guys, Thanks for the checks. I will go out to the airport and pull both carb bowls. Check them and then check the stab. Roger, What about pulling the gasolator? Link to comment Share on other sites More sharing options...
Roger Fane Posted July 10, 2013 Report Share Posted July 10, 2013 What do you mean by pretty good precip? Were you flying in heavy rain? Could be water was entering the air intake, and getting into the carbs. That could also cause some icing in the carbs as well, which cleared once the water source was gone. Link to comment Share on other sites More sharing options...
mocfly Posted July 10, 2013 Author Report Share Posted July 10, 2013 It was heavy enough that my daughter got a pretty good spray from the door seal. I thought about the carb ice scenario. Having experienced it before the same properties were not evident. Link to comment Share on other sites More sharing options...
Roger Lee Posted July 10, 2013 Report Share Posted July 10, 2013 Hi Chris, Water in the bowls could cause this too. Link to comment Share on other sites More sharing options...
mocfly Posted July 11, 2013 Author Report Share Posted July 11, 2013 Went to the airport and pulled the bowls off both carbs. No debris in the bowls but there were indications of the floats rubbing on the brass. Didn't pull the gasolator as it was safety wired and I dont have any with to re affix. I did drain the equivelant of 4-5 oz. of fuel and did not see anything. Pics of the right side carb. Stabilator nice and tight. During the event outlined I did not notice a reduction in rpm. After the first event I reduced the rpm. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted July 11, 2013 Report Share Posted July 11, 2013 Here's what mine looked like. Link to comment Share on other sites More sharing options...
mocfly Posted July 11, 2013 Author Report Share Posted July 11, 2013 I looked at the floats and didn't notice an abnormality like that. Link to comment Share on other sites More sharing options...
mocfly Posted July 11, 2013 Author Report Share Posted July 11, 2013 I guess the ride home with no chance of precip wil show if it was a contributing factor. Link to comment Share on other sites More sharing options...
Mike Posted July 11, 2013 Report Share Posted July 11, 2013 i would say carb ice .... had it once here in UK enough to stop engine on idle luckily over airfield at the time i then fitted a carb heat kit running of the engine coolant never had it again Mike Link to comment Share on other sites More sharing options...
Tom Baker Posted July 11, 2013 Report Share Posted July 11, 2013 Chris, what was the OAT when this happened? Also, I had a bad sparkplug do this once before too. Link to comment Share on other sites More sharing options...
mocfly Posted July 11, 2013 Author Report Share Posted July 11, 2013 Tom, OAT was around 60f. I will pull the plugs when I get back home and check them. Link to comment Share on other sites More sharing options...
Tom Baker Posted July 11, 2013 Report Share Posted July 11, 2013 Tom, OAT was around 60f. I will pull the plugs when I get back home and check them. I have always heard that temps in the mid 50's with visible moisture is when the Rotax will ice up. When I had the plug problem it was with a new set of plugs. I swapped them all out and the problem went away. I also had one sunk float about the same time. Link to comment Share on other sites More sharing options...
Jim Meade Posted July 11, 2013 Report Share Posted July 11, 2013 Does anyone know what kind of data logging (that any of us are likely to have in a FD) would collect any of this information for a postmortem? Link to comment Share on other sites More sharing options...
Brucegoose Posted October 30, 2013 Report Share Posted October 30, 2013 Hi there Chris, Had a similar shudder recently and just after the five year rubber replacement. What I noticed was a sharp drop on the EGT no.2. Took the RPM up to 5500 and the shudder went away. Once on the ground I lifted the cowl for a visual check, only to find the vent tube had been routed under the carb and the exhaust heat had melted a hole in it. Replaced the tube and routed above the carb and secured, test flew it and shudder gone. Maybe check your vent tube is not moving in flight, secured on the carb barbed fitting, and lastly for a hole. Kind Regards Bruce Link to comment Share on other sites More sharing options...
mocfly Posted October 30, 2013 Author Report Share Posted October 30, 2013 Bruce, That was actually one of the first things that I checked. After balancing the carbs, putting a new k&n air filter in and sealing up the holes in the air box I never experienced the problem again. I am almost convinced it was carb ice. I can't prove it. Link to comment Share on other sites More sharing options...
Jim Meade Posted October 31, 2013 Report Share Posted October 31, 2013 I've only had carb ice a couple of times and never in a Rotax as yet. In my experience, carb ice presented as a reduction in engine rpm (and loss of power) over time. When I applied carb heat, it resolved in the expected way - at first it got worse and then it improved as the ice was gone but the air was warm. When carb heat was turned off the engine ran normally. My gut feeling - call it an impression - is that your incident doesn't sound like the classic case of carb ice, but maybe your symptoms can occur and maybe it is different with Rotax. Just thinking out loud. Link to comment Share on other sites More sharing options...
Brucegoose Posted October 31, 2013 Report Share Posted October 31, 2013 Chris, If you had done that with the vent tube then I guess youre right about the icing. BTW temps constant winter and summer at 90F. Kind Regards Bruce Link to comment Share on other sites More sharing options...
FlyingMonkey Posted October 31, 2013 Report Share Posted October 31, 2013 I've only had carb ice a couple of times and never in a Rotax as yet. In my experience, carb ice presented as a reduction in engine rpm (and loss of power) over time. When I applied carb heat, it resolved in the expected way - at first it got worse and then it improved as the ice was gone but the air was warm. When carb heat was turned off the engine ran normally. My gut feeling - call it an impression - is that your incident doesn't sound like the classic case of carb ice, but maybe your symptoms can occur and maybe it is different with Rotax. Just thinking out loud. IIRC, the Rotax will vibrate and shudder when carbs are out of balance or one carb has restricted fuel flow, as the cylinders on that side get starved. It seems if one carb iced up before the other, it would cause the same symptoms. The two carbs as opposed to a single carb on most aviation engines could certainly cause different symptoms to carb ice. Link to comment Share on other sites More sharing options...
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