Peteolero, you're making constant speed props way too hard.
http://youtu.be/Z9M_KuP-fbI
When you're doing say, a 1700 RPM run-up and you've got the prop control full forward, you've requested an RPM the prop can't get to with available power. So you are pumping oil through the fine pitch tube, because the spring is holding it open, and the fly-weights aren't being thrown out hard enough by centrifugal force to close it.
The spring is holding the fine pitch tube open and that prop is being held solidly at the finest pitch by engine oil pressure. The prop therefore is essentially not acting as a constant speed prop, but it's acting like a fixed pitch fine/climb prop, because it's being held there by force.
That's what's happening at run-up RPM. You've applied enough power to speed it up but you haven't reached the point where the flyweights will match the spring yet, and the fine pitch valve is open and making sure the prop stays at low pitch. So it's essentially fixed pitch, because oil pressure is holding it there.
As you add throttle, the flyweights start to move out but they still haven't been balanced by the spring and you're still pumping oil to hold that prop fixed at low/fine pitch.
So for run up, it's behaving just like a fixed pitch climb prop.
Now later...
When you push the throttle up to full power, at some point in adding power, the centrifugal force on the flyweights equals the spring force and the prop is turning as fast as it'll go because that's where the prop control is set. Full forward. Redline. It was adjusted by the mechanic to limit RPM there.
Any additional power now added will throw the flyweights out harder and overcome the spring, and open the coarse tube and start pushing the blades more coarse/bigger angle, to try maintain the RPM the mechanic set "full forward" on the prop control to be.
Continue to add power, they'll continue to dig harder. Until you run out of throttle. Once the prop is at an angle that holds that RPM, the flyweights will be balancing the spring again and no oil will flow. Static state. Full throttle, redline.
Okay now we are sitting here at full throttle throwing rocks into our tail and overheating the engine for a while and suddenly a big gust of headwind comes along.
(Or we are flying at any setting of the prop control and we dive, adding airspeed over the prop so the engine power plus the wind is more power than is needed to spin the prop at the RPM we selected)...
The prop now accelerates a bit, and the flyweights go out again from being spun harder, and overcome the big spring and let some more oil flow through the coarse tube, the blades dig a little harder and we find an equilibrium again between the flyweights and the spring after the prop returns to the RPM set by the control. Oil stops flowing and the prop holds this new coarser pitch while this big steady state hypothetical gust is blowing. Flyweights balance the spring and no oil flows.
Headwind dies , prop slows a bit, flywheels come back in a bit, spring wins and we open the fine tube a bit. Prop moves toward a finer pitch and speeds up. Flywheels go back to balanced with the spring and oil stops flowing and the RPM is back where we set it.
Obviously in flight this is happening constantly unless it's super calm out. And even pitch changes to the aircraft will change the airspeed over the prop and change how hard it needs to dig or not dig to maintain a particular RPM. And the flyweights and spring will keep finding equilibrium.
Now we go to land. We pull the throttle back and the flyweights aren't being spun outward as hard. The spring wins and the fine tube is opened until we find equilibrium again. The RPM remains constant for a while as we slowly pull back the power and manifold pressure drops.
Eventually we reduce the engine power enough (plus air flowing over the prop from being in flight) that the flyweights stay in and the spring is stronger. We're back to pumping oil constantly to hold the prop at the finest pitch possible. And the RPM starts to fall. We are essentially a fixed pitch climb/fine prop again, unless we dive harder or add engine power.
What is not discussed in the video or above is how the prop control actually sets the desired RPM. There really are two things pushing on the spring. The flyweights and engine oil pressure as set by the prop control. The flyweights by themselves aren't enough. The spring is big and powerful.
I don't know if they'll let anyone in the shop but worth asking to see the guts of on at Rocky Mtn Propeller if you're up at KEIK sometime. They're really simple devices. Just flyweights and oil pressure fighting with a spring to move a piston that has two valve openings in it. You'll notice with the engine shut down on the ground your prop is at the finest pitch or close to it. The spring was winning at shutdown.
(Turboprops and some aircraft do this differently and their blades will often be full coarse on the ground when there's no power wing applied. But we're talking about what's on most piston singles like our 182s. Just flyweights and oil pressure fighting a big tough spring.)
