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Carb Ice and Governor


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Hi,

I'm reading through the R44 manual and I have a question about a note in here about carb ice. It says "A pilot may be unaware of carb ice formation as the governor will automatically increase the throttle and maintain constant manifold pressure and RPM." I understand that the ice is going to make the hole in the carb smaller and make it seem like the throttle is closing, so therefore the throttle needs to open. My question is why wouldn't there be a raise in manifold pressure. I'm thinking more throttle higher manifold pressure. I'm guessing it is because the ice is counteracting any increase in throttle, so in actuality the engine doesn't "know" the throttle is increasing. Am I correct?

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Correct.

The manifold pressure gauge is reading pressure at the cylinder port area which is well down stream from the carb. Ice up the intake area and effective airflow to the cylinder is reduced..(engine makes less power)... governor opens throttle to increase air to the cylinder.

Edited by apiaguy
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  • 3 weeks later...
thanks a lot!

 

When flying along the governor does not usually turn the throttle at all, unless in turbulence or making large collective changes. So, if youre buzzing along and you feel the throttle turning in your hand slowly, just reach down and pull full carb heat. If its icing up, it might cough or shudder for a second, if not, it hurts nothing and you can re-set the carb heat it to an appropriate level.

 

 

Unless you are in very very cold temps, when in doubt, pull full heat and pull it now !

 

Goldy

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When flying along the governor does not usually turn the throttle at all, unless in turbulence or making large collective changes. So, if youre buzzing along and you feel the throttle turning in your hand slowly, just reach down and pull full carb heat. If its icing up, it might cough or shudder for a second, if not, it hurts nothing and you can re-set the carb heat it to an appropriate level.

 

 

Unless you are in very very cold temps, when in doubt, pull full heat and pull it now !

 

Goldy

 

Here you go:

 

The pilot probably noticed the throttle moving trying to maintain RPM, then he noticed it was difficult to maintain RPM, first pull full carb heat...then look for a spot to set it down if need be.

 

 

 

During the afternoon of Friday January 30th, a company R-44 helicopter was involved in a crash near Grande Cache, Alberta.

 

The two occupants survived. Madden Sarver and Klint Sarver (pilot-in-command) were flying up the ridgeline of a mountain when Klinton noticed a reduction of power in the R-44. The carbureted engine appeared to be producing less power than usual and when collective was reduced the RPM was barely maintained.

 

Klint felt that he didn't have sufficient power to make it to the valley floor so he elected to land in a small clearing surrounded by trees.

 

Due to what is thought to be carb ice, a landing was not able to be made successfully on the sloped terrain and the aircraft ended up on it's right side.

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