Time to wipe away the misconception about prop RPM and blade pitch angle.
Ok, I did my best here, so please don't make fun of my graphic
hehehe.
Flakbait and Downtown, I hope this will help to understand, let me know if my explanations are too confusing (because english is not my native language).
The whole system is working with the engine oil going into the system or out of the system. If ur oil system as a leack, you in trouble
The key components are the
Flyweight assembly, the
pilot valve, the
loaded spring and the
prop hub.
- Flyweight assembly: using centrifugal forces, the Flyweight varies directly with the engine speed. When the engine speed increases, the Flyweight moves outward and when the engine speed decreases, the flyweight moves inward.
- Pilot Valve: It is directing oil flow to the propeller. The pilot valve is attached to the fly weight. depending on the flyweight going inward or outward, the Pilot Valve will go up or down.
If the Pilot valve is going up, the oil is allowed to travel from the engine to the prop hub.
If the Pilot Valve is going down, the oil is allowed to travel from the Prop Hub back to the Oil Sump.
Prop Hub: it's lateral movements are allowing the bades to change their pitch angle.
When the oil flows into the prop hub, the cylinder is moving 'to the left'. A simple mecanical part is making the pitch angle of the blade increase.
When the oil flows out of the Prop Hub, a Loaded Spring makes the cylinder comes back 'to the right', making the blade angle transit to a smaller pitch (Fine pitch).
How it works :
- Flying along at constant RPM, you start to climb or you decrease the engine RPM. This results in an underspeed condition. Airspeed is reduced and, since the pitch of the propeller blades is too high, the engine starts to slow down. However, the instant this happens the Flyweights will droop, causing the pilot valve to move down. Then, oil flows from the propeller, reducing the pitch of the blades. This automatically increases the speed of the engine to maintain the former RPM setting.
- in a descent or engine power is increased: This causes an overspeed condition. Since the pitch of the prop blades is too low to absorb engine power, the engine RPM begins to decrease. But the instant this happens, the flyweights move out and raise the pilot valve. This in turn, causes oil to flow to the propeller, increasing the pitch of the blades. Engine speed then slows down to maintain the original RPM setting.
Advantages of a constant speed propeller :
- higher thrust output during take off
- increased rate of climb
- increased cruise speed
- better fuel economy
Geez, I hope all this makes sense for you guys. Flakbait it should help to decrease your misconception of prop RPM and blade pitch. Downtown, I wish it answered all your questions
)
have a great one... I need a beer after all this typing
------------------
Olivier "Frenchy" Raunier
AH Squad web site
http://home.cfl.rr.com/rauns/menu.htm SFRT main web site
http://www.sfrt.net [This message has been edited by SFRT - Frenchy (edited 07-22-2000).] Corrected a typo noted by Renfield
[This message has been edited by SFRT - Frenchy (edited 07-22-2000).]
