Governer operation....

flyTotheSky · November 14th, 2006, 00:30

I've always been taught that when we move the prop control level in the cockpit that is adjusted the tension on the speeder spring which allows to select the desired RPM. However, I want to know more in depth as to why

I know that when the prop control is full forward that increases compression on the speeder spring and when it is pulled aft it dampens the compression on the speeder spring, atleast in McCauley systems. How does this corelate to changes in RPM settings?

Thanks

ananoman · November 14th, 2006, 01:42

If you search on here, you will find quiet a bit of info on this. What happens in the governor depends on what type of airplane you are flying, either a single or a twin. But, both systems use oil pressure to change the pitch of the blades on the prop.

In the twin, the front of the prop dome has a big spring and nitrogen pressure that is trying to feather the prop. The oil chamber is behind the hub and if you add oil, it will force the blades to a low pitch/high rpm setting.

The single has a large spring behind the hub, that is trying to force the blades to a low pitch/high rpm setting and an oil chamber in the prop dome. If you add oil to the prop on a single, it will go to a higher pitch/low rpm setting.

Knowing this, you can picture what goes on in the governor. It is geared to the crankshaft and the insides of the governor are always spinning around. At the very top of the governor is a pair of 'L' shaped flyweights that are controlled by the speeder spring. If the force exerted by the flyweights is in equilibrium with the speeder spring, the prop RPM is constant.

If you adjust the prop control in a single to a higher RPM setting, you are increasing the tension on the speeder spring and the flyweights will move inward. When this happens, they will push the pilot valve down and let oil out of the prop. This allows the spring behind the hub to push the blades to a lower pitch and the RPM will rise.

The opposite happens if you decrease the RPM. Now, you are decreasing the tension on the speeder spring and it the flyweights will move outward, raising the pilot valve, allowing oil to be pumped into the prop hub, moving the blades to a higher pitch/lower RPM setting.

ananoman · November 14th, 2006, 01:48

Read this. I think most of it deals with the props on a multi, but other than which way the oil moves, it is all pretty much the same.

http://www.avweb.com/news/pelican/182082-1.html

Looking4Lower · November 14th, 2006, 09:31

Quote:

Originally Posted by ananoman

Read this. I think most of it deals with the props on a multi, but other than which way the oil moves, it is all pretty much the same.

http://www.avweb.com/news/pelican/182082-1.html

Deakin has an outstanding series of articles on props, mixture, RPM and MP on avweb. It's required reading for anybody flying a constant-speed prop piston engine.

jawright · November 14th, 2006, 09:49

Dude, this article rocks!

flyTotheSky · November 14th, 2006, 14:57

Thanks guys, this is some great stuff!

jawright · November 17th, 2006, 12:35

Does anyone know where there's a good video that depicts the mechanisms inside the prop hub and governor at work?

November 14th, 2006, 00:30	#1
flyTotheSky Senior Member Join Date: Jan 2006 Location: LUK Posts: 379	Governer operation.... I've always been taught that when we move the prop control level in the cockpit that is adjusted the tension on the speeder spring which allows to select the desired RPM. However, I want to know more in depth as to why I know that when the prop control is full forward that increases compression on the speeder spring and when it is pulled aft it dampens the compression on the speeder spring, atleast in McCauley systems. How does this corelate to changes in RPM settings? Thanks

November 14th, 2006, 01:42	#2
ananoman Senior Member Join Date: Dec 2002 Posts: 916	Re: Governer operation.... If you search on here, you will find quiet a bit of info on this. What happens in the governor depends on what type of airplane you are flying, either a single or a twin. But, both systems use oil pressure to change the pitch of the blades on the prop. In the twin, the front of the prop dome has a big spring and nitrogen pressure that is trying to feather the prop. The oil chamber is behind the hub and if you add oil, it will force the blades to a low pitch/high rpm setting. The single has a large spring behind the hub, that is trying to force the blades to a low pitch/high rpm setting and an oil chamber in the prop dome. If you add oil to the prop on a single, it will go to a higher pitch/low rpm setting. Knowing this, you can picture what goes on in the governor. It is geared to the crankshaft and the insides of the governor are always spinning around. At the very top of the governor is a pair of 'L' shaped flyweights that are controlled by the speeder spring. If the force exerted by the flyweights is in equilibrium with the speeder spring, the prop RPM is constant. If you adjust the prop control in a single to a higher RPM setting, you are increasing the tension on the speeder spring and the flyweights will move inward. When this happens, they will push the pilot valve down and let oil out of the prop. This allows the spring behind the hub to push the blades to a lower pitch and the RPM will rise. The opposite happens if you decrease the RPM. Now, you are decreasing the tension on the speeder spring and it the flyweights will move outward, raising the pilot valve, allowing oil to be pumped into the prop hub, moving the blades to a higher pitch/lower RPM setting. __________________ My observation is that those with an extreme knowledge deficit have a real hard time believing that anyone else knows something they don't. That's why the knowledge deficit never goes away. - tgrayson

November 14th, 2006, 01:48	#3
ananoman Senior Member Join Date: Dec 2002 Posts: 916	Re: Governer operation.... Read this. I think most of it deals with the props on a multi, but other than which way the oil moves, it is all pretty much the same. http://www.avweb.com/news/pelican/182082-1.html __________________ My observation is that those with an extreme knowledge deficit have a real hard time believing that anyone else knows something they don't. That's why the knowledge deficit never goes away. - tgrayson

November 14th, 2006, 09:49	#5
jawright Senior Member Join Date: Feb 2004 Location: in search of the elusive "BowieGoat." Posts: 424	Re: Governer operation.... Dude, this article rocks!

November 14th, 2006, 14:57	#6
flyTotheSky Senior Member Join Date: Jan 2006 Location: LUK Posts: 379	Re: Governer operation.... Thanks guys, this is some great stuff!

November 17th, 2006, 12:35	#7
jawright Senior Member Join Date: Feb 2004 Location: in search of the elusive "BowieGoat." Posts: 424	Re: Governer operation.... Does anyone know where there's a good video that depicts the mechanisms inside the prop hub and governor at work?

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