Concerning governor masking of carb ice.

[jibboo]

Whilst explaining the phenomenon of carb ice i say:

1. Low pressure and vaporization of fuel lower temp in the
venturi

2. If the right conditions exist (high humidity, close temp/dew
point spread) moisture in the air may freeze

3. When the throttle valve is closed (low MAP) it may stick to
the ice and not open any wider when power is applied

NOW if i got that right

I cannot seem to understand how the governor can mask the signs of carb ice by rolling on the throttle more...

To maintain constant RPM wouldn't the throttle valve have to open more?

Thanks to anyone with more knowledge on the subject than myself!

[homeguard]

with regard to (2) it would be more correct to say; that the water vapour within the air may condence into liquid and freeze within the venturi around the area of the throttle butterfly ............

With a fixed pitch propellor any reduction in manifold pressure will become apparent with a reduction in RPM. Therefore as ice builds within the venturi we observe a reduction in RPM.

A constant speed propellor of cause will not reduce RPM because of venturi ice. The propellor governor is a mechanism within the propellor assembly and put simply responds to RPM not manifold pressure. Therefore the signs of the build up of venturi ice are less obvious to the pilot with regard to the RPM. But, you will have clues just the same by observing the manifold pressure gauge.

[ROB-x38]

G'day jibboo
To maintain constant RPM wouldn't the throttle valve have to open more?
No. This is where a CSU / variable pitch prop differs.

To maintain a constant RPM the blade angle would reduce (go to a finer pitch), reducing the 'drag' on the blades and maintaining the RPM set within the governer. A reduction in RPM would only be observed once the blades had reached the fine pitch stop (blade angle can't reduce any further), and a loss of power would result in a drop in RPM.
I cannot seem to understand how the governor can mask the signs of carb ice by rolling on the throttle more...
The governer has no control over the position of the throttle butterfly. It's only purpose is to maintain the RPM set by the pilot (with the blue pitch lever), which it does by altering the angle of the blades.

Hope that makes some sense. If not i'd suggest a search re: variable pitch props, CSUs, governers etc...

Cheers