Old 18th Feb 2021, 15:00
  #5 (permalink)  
Join Date: Oct 2017
Location: Bressuire
Posts: 415
However, what happens if the prop is cycled (not suggesting it should be) whilst on the ground and the throttle is at idle? Will there be an increase in pitch and therefore a further drop in prop rpm or will the rpm remain the same?
The blue prop lever, when put to the fully forward position, applies a spring pressure to its design maximum onto the bob weight leverage which in turn closes off engine oil pressure. The prop is held in the fully fine position by additional springs in the prop hub. Counter to this the oil pressure is used to oppose the hub springs to coarsen the prop which then in turn reduces the engine speed. However with the throttle at idle the oil pressure is at a minimum and by design will not be sufficient to push the oil valve open. If this could happen it would coarsen the prop and possibly stall the engine. With the lever full aft the power lever spring pressure will be at the minimum but will still be sufficient to prevent the low oil pressure overcoming and opening the oil valve and finding a path to the prop.

The manufacturer states the optimum power (usually an RPM indication) above idle which provides the system sufficient effect to exercise the bob weights allowing the oil to pass and operate the prop mechanism. This check is done prior to take off after the engine has been warmed. The manufacturer will also state the minimum RPM change when operating the prop lever during the check.

Last edited by Fl1ingfrog; 19th Feb 2021 at 11:53.
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