The T6b uses a PT6-68 engine which has a variable pitch, constant speed, feather, and non-reversible prop system. There is only one lever in the cockpit which regulates Torque and the Power Management Unit (PMU) whenever is on (PMU switch on, under normal operations) would regulate the pitch of the propeller in order to keep the propeller at a constant speed 2000 RPM (the Reduc Gear Box lowers it from about 30k RPM to 2k)

Here is the manual for the P&W PT6 series I found online: https://mikeklochcfi.files.wordpress.com/2018/08/training-pt6a-60-series.pdf or you can google "pt6 60 series manual"

Under the Propeller system (page 216 pdf), I believe the PMU On mode is referred to as the "governor governing mode".

  • "When the engine output power is increased, the power turbines tend to speed up. The flyweights in the CSU sense this acceleration. The flyweights go into an overspeed condition because of the increase centrifugal force and force the control valve to move up and restrict oil flow to the propeller dome. The feathering spring increases the propeller pitch (more towards feather position) to maintain the selected speed"

First, What makes the Flyweights spin up? There is no blue lever in this plane. I read from other designs that flyweights are on top of a disc sometimes, what makes it spin though? I don't see how the engine spooling up is connected to the flyweights. The counterweights on the other hand are spinning because are connected to the spinning hub, but the Governor in which the flyweights are is not spinning I think. In the picture, the flyweights are the yellow u-shape bars above the Pilot Valve

I also have a second question regarding this propeller system I posted separatelly. Thank youenter image description here

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    $\begingroup$ I see where your confusion is... Yes, the CSU does NOT spin, but there is a 90 degree gear and vertical shaft running into the CSU that spins these flyweights. I don't have time for a full answer right now, but look at the diagram on 11.5 and you see a crude representation of these gears. $\endgroup$ Oct 18, 2022 at 22:25
  • $\begingroup$ Sir, I found it thank you. Yes I see now there are a couple of gears that are connected coming from the main turbine shaft. I posted another question about this topic, you could find it in my profile Im sure. Id def appreciate the help please $\endgroup$ Oct 18, 2022 at 23:46


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