Icing?

PGT

Well-Known Member
About 180 nm into a XC in a C152 the RPM gauge was starting to decrease but not gradual decrease, it was more of a sudden ~200 rpm drop that was very noticeable. It did this about every 20 seconds or so. I applied carb heat for it a bit and eventually it stopped. Applying carb heat there was no big change in rpm (dead giveaway?). When I took the carb heat out the engine got a big boost which to me would be the now water raising compression in the cylinders. Now the temp was 5 C, I was cruising at 5,500 at 70% power (around there) and no visible moisture; it was hazy and 8sm visibility. A low had just passed earlier in the day.

On the way back, this time about 150nm into the flight, it did the same thing but conditions were much better. I was up at 6,500 and no front in the area. Same thing, increase throttle/mixture and add carb heat got it to stop.

Was I picking up some carb ice from being up that high with lower temps and being powered back? I was thinking that was the case.
 

flyinguitar

Well-Known Member
Yep, it's carb ice. I've had that happen on a beautiful clear day with low humidity. Carb ice will often produce that surging drop and rise in RPM you described. Get's your heart pumping, doesn't it?
 

Holocene

Well-Known Member
When I took the carb heat out the engine got a big boost which to me would be the now water raising compression in the cylinders.
:confused:

Normally, the application of carburetor heat will quickly melt any ice that may have been present in the carburetor throat. It is in those very first few seconds that you may ingest water into the cylinders, not after you shut it off.
 

FrankieFlyCRQ

Well-Known Member
About 180 nm into a XC in a C152 the RPM gauge was starting to decrease but not gradual decrease, it was more of a sudden ~200 rpm drop that was very noticeable. It did this about every 20 seconds or so. I applied carb heat for it a bit and eventually it stopped. Applying carb heat there was no big change in rpm (dead giveaway?). When I took the carb heat out the engine got a big boost which to me would be the now water raising compression in the cylinders. Now the temp was 5 C, I was cruising at 5,500 at 70% power (around there) and no visible moisture; it was hazy and 8sm visibility. A low had just passed earlier in the day.

On the way back, this time about 150nm into the flight, it did the same thing but conditions were much better. I was up at 6,500 and no front in the area. Same thing, increase throttle/mixture and add carb heat got it to stop.

Was I picking up some carb ice from being up that high with lower temps and being powered back? I was thinking that was the case.
Oh you scaredy cat! :D

J/k good job buddy, it seems like you handled the situation pretty well, your training kicked in and you handled business! :rawk:
 

PGT

Well-Known Member
Thanks, you SoCal pilots wouldn't know anything about icing :sarcasm: ;)

:confused:

Normally, the application of carburetor heat will quickly melt any ice that may have been present in the carburetor throat. It is in those very first few seconds that you may ingest water into the cylinders, not after you shut it off.
I don't know, the engine got a huge boost when I turned the carb heat off, I'd say probably greater than usual.
 

SFCC/UND

Well-Known Member
I though a quick mag drop could be a sign of mag problems, and a slow drop in rpm would be a icing problem.
 

Maurus

The Great Gazoo
Thanks, you SoCal pilots wouldn't know anything about icing :sarcasm: ;)



I don't know, the engine got a huge boost when I turned the carb heat off, I'd say probably greater than usual.
You might have been increasing the throttle when the ice started to form to correct for a gradual drop in RPM. Once you turned off the carb heat, the RPM jumped higher than you were expecting as a result of the increase in the throttle.
 

PGT

Well-Known Member
You might have been increasing the throttle when the ice started to form to correct for a gradual drop in RPM. Once you turned off the carb heat, the RPM jumped higher than you were expecting as a result of the increase in the throttle.
Could be, don't quite recall but I do remember reducing the throttle a lot on the trip because the throttle creeps up in this plane.
 
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