Caravan PT6A-114 Prop Governor

lambo5oh · October 22nd, 2009, 13:11

Does anyone have a simple explanation of the prop governor system in its various modes of operation? Our manuals seem incomplete. References to other sources of information would also be appreciated.

lambo5oh · October 22nd, 2009, 13:30

More to the point, a description of the failure of each of the components, the prop governor, the overspeed governor, and the pneumatic Nf governor.

Alaska45 · October 25th, 2009, 01:20

First Post on JC for me, been a lurker for a few years. I dont have my C208 training material with me at the moment, so im going to try to remember C208 sim training...
The pneumatic governor is built into the primary prop governor unit as a safegaurd to protect the power turbine from overspeed in the event of a primary prop governor by limiting fuel flow to the flow divider. If the primary governor fails in cruise flight you will see the prop rpm redline at 1900RPM and a significant reduction of torque/gas generator rpm.
The overspeed governor is also a safegaurd to the primary prop governor and controls oil pressure to the the prop to maintain 1900 rpm in the event of a primary governor failure. The overspeed governor is checked at 1750 RPM before the first flight each day using the test switch.
It is unlikey to have see a failure of all three governors because the NF and Overspeed governors are a safegaurd to the primary governor.
So for a simple explanation to answer your question if the primary fails and then the Nf and Overspeed do not funtion, the prop and compressor rpm will exceed limits.

lambo5oh · October 25th, 2009, 16:46

Excellent! Now it is coming back to me. There are some percentage figures thrown in. I believe the overspeed governor kicks in at 4% above 1900(1976) and the Ng Gov will limit the prop to 2014(6%), or something close.

Thanks once again.

SpiraMirabilis · October 26th, 2009, 04:43

The prop governor keeps the RPM equal or less than 1900 RPM. The overspeed governor keeps the RPM less than 1976. The Nf (fuel topping) governor keeps the RPM less than 2090 by reducing the variable Py air to the fuel control unit and dropping Ng. The last one will cycle on and off.

October 22nd, 2009, 13:11	#1
lambo5oh Newbie Join Date: Oct 2009 Location: Honolulu Posts: 3	Caravan PT6A-114 Prop Governor Does anyone have a simple explanation of the prop governor system in its various modes of operation? Our manuals seem incomplete. References to other sources of information would also be appreciated.

October 22nd, 2009, 13:30	#2
lambo5oh Newbie Join Date: Oct 2009 Location: Honolulu Posts: 3	Re: Caravan PT6A-114 Prop Governor More to the point, a description of the failure of each of the components, the prop governor, the overspeed governor, and the pneumatic Nf governor.

October 25th, 2009, 01:20	#3
Alaska45 Newbie Join Date: Oct 2009 Location: Broomfield,CO and Anchorage, AK Posts: 29	Re: Caravan PT6A-114 Prop Governor First Post on JC for me, been a lurker for a few years. I dont have my C208 training material with me at the moment, so im going to try to remember C208 sim training... The pneumatic governor is built into the primary prop governor unit as a safegaurd to protect the power turbine from overspeed in the event of a primary prop governor by limiting fuel flow to the flow divider. If the primary governor fails in cruise flight you will see the prop rpm redline at 1900RPM and a significant reduction of torque/gas generator rpm. The overspeed governor is also a safegaurd to the primary prop governor and controls oil pressure to the the prop to maintain 1900 rpm in the event of a primary governor failure. The overspeed governor is checked at 1750 RPM before the first flight each day using the test switch. It is unlikey to have see a failure of all three governors because the NF and Overspeed governors are a safegaurd to the primary governor. So for a simple explanation to answer your question if the primary fails and then the Nf and Overspeed do not funtion, the prop and compressor rpm will exceed limits.

October 25th, 2009, 16:46	#4
lambo5oh Newbie Join Date: Oct 2009 Location: Honolulu Posts: 3	Re: Caravan PT6A-114 Prop Governor Excellent! Now it is coming back to me. There are some percentage figures thrown in. I believe the overspeed governor kicks in at 4% above 1900(1976) and the Ng Gov will limit the prop to 2014(6%), or something close. Thanks once again.

October 26th, 2009, 04:43	#5
SpiraMirabilis Old Skool Join Date: Jun 2006 Posts: 3,345 Blog Entries: 1	Re: Caravan PT6A-114 Prop Governor The prop governor keeps the RPM equal or less than 1900 RPM. The overspeed governor keeps the RPM less than 1976. The Nf (fuel topping) governor keeps the RPM less than 2090 by reducing the variable Py air to the fuel control unit and dropping Ng. The last one will cycle on and off. __________________ Yet Another Freight Puppy* Last edited by SpiraMirabilis; October 26th, 2009 at 04:44.

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