Constant Speed Props

ozziecat35

4 out of 5 great lakes prefer Michigan.
I'm moving from the lowly C-172 world into the glorious PA-44 Seminole land and just can't grasp the concept of the internal workings of constant speed props. I get that the Prop Control levers change the pitch using oil pressure and fly weights, etc, but what I can't visualize is,

a. what's really happening inside the spinner and the actual mechanics at play

b. the prop pitch itself and high RPM & low RPM (feather)

I looked at the Seminole MX Manual earlier in the Tech. Talk forum but couldn't find anything that was making it click for me. Does anyone have a good resource to turn my light bulb on?

Thanks in advance!
 

ozziecat35

4 out of 5 great lakes prefer Michigan.
So by moving the Prop lever , you are directly controlling the governor, and in turn the amount of oil pressure being allowed in (ie more oil pressure, lower pitch/higher RPM) or vise versa?
 

Matt13C

Well-Known Member
I'm moving from the lowly C-172 world into the glorious PA-44 Seminole land and just can't grasp the concept of the internal workings of constant speed props. I get that the Prop Control levers change the pitch using oil pressure and fly weights, etc, but what I can't visualize is,

a. what's really happening inside the spinner and the actual mechanics at play

b. the prop pitch itself and high RPM & low RPM (feather)

I looked at the Seminole MX Manual earlier in the Tech. Talk forum but couldn't find anything that was making it click for me. Does anyone have a good resource to turn my light bulb on?

Thanks in advance!
Here is a good article.

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

pierre

Well-Known Member
the prop control sets the pressure of the speeder spring. the speeder spring pressure is like a "desired rpm" setting. any time the rpm differs due to a change in power or prop loading an underspeed or overspeed condition will occur in the governor. more or less oil is directed to the hub changing the blade pitch until the desired rpm is achieved which will allow an on speed condition to be re established. the governor always tries to be on speed. when feathered, all the oil is allowed out of the hub and the spring, gas pressure, and centrifugal forces all act to move the blades to feathered
 

ozziecat35

4 out of 5 great lakes prefer Michigan.
This is all helping, thanks guys. Any chance you have pics that compare Props at high RPM vs Feather settings? My head is not wrapping around that visual no matter how hard I try...I know this should be a simple item too.
 

shdw

Well-Known Member
This is all helping, thanks guys. Any chance you have pics that compare Props at high RPM vs Feather settings? My head is not wrapping around that visual no matter how hard I try...I know this should be a simple item too.

http://www.faa.gov/library/manuals/aircraft/media/FAA-H-8083-32-AMT-Powerplant-Vol-2.pdf

Check out page 7-9, topic title Propeller Governor. This sections information, along with the included pictures should straighten you out.

On a side note, keep in mind that oil into the system only flattens your pitch on a multi. Because, when the engine dies and you lose oil pressure, you go to feather. On a single you don't want that, so the process is reversed: Oil in will increase pitch.
 

gotWXdagain

Highly Visible Member
First, you have to understand the purpose of a prop governor. What makes a constant-speed setup so much better than a fixed-pitch setup? Obviously, if it didn't have a benefit, the complexity wouldn't be justified. Find the benefit of a constant speed prop, and you will find the trailhead on the road to your answers ;)
 
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