Prop movement ?

[JorisVdB 0]

I'm doing a flight to Mustique Island (near Trinidad & Tobago), and when I shut down after parking the Cat, I wonder whether you can move the prop or not with the engines off on the real Catalina.

I've seen this before on other add-on prop aircraft, but I don't see it on the Catalina X now.

If it doesn't works this way in the real world Cat, I don't need the feature, but it'd be nice if it's included in a future patch if it actually works on the real Catalina...

[Finn 873]

You can´t...

This is an excerpt from the beta forum:

The prop blades was moved to fullfine (low pitch) position by flyballs inside the propellerhub, very much like the speedcontrollers found on stationary steamengines.

To move them into coarse position (high pitch) engine oilpressure was used. The balance between the flyballs and the oilpressure determined prop blade position.

Inside the propellerhub was a socalled governor, wich consisted of the flyballs and a springloaded valve setting the oilpressure to counter the flyballs, wich was moved by the centrifugal force of the propeller.

Thhis valve was set by moving the propeller levers. The higher the oilpressure (remember engine oilpressure, but boosted by a small mechanical boostpump), the more the prop blades moved towards high pitch. The higher the pitch of the blades the more air the prop would "grab", and thus the lower the RPM for a given engine power setting.

If the engine failed, rpm would decrease. Engine oilpressure would drop and the prop blades would move towards full fine in an attempt to keep rpm.

To feather the prop blades, the pilots wold press the feather button. The feather button is an electrical switch that powers an electrical feather pump.

This would apply oilpressure into the governor and thus move the baleds towards high pitch - feathered position. Once the blades reached full feathered position, a pressure sensing switch will turn off that featherpump. The feather button is held by a solenoid, wich also is turned off by the same pressure sensing switch and thus pops out again when the prop blades has feathered.

As Yiu can see - no oil pressure - no prop blade movement. You can move those propeller levers as much as You like, but when then engine is stopped, there is simply no pressure to move the blades apart from that supllied by the feather pump.

more...

Problem is that some people mix up Variable pitch and constant speed propellers.

In variable pitch propellers You move propeller balde angle directly with an mechanical link.

What determaines RPM is still engine power more or less.

On a constantspeed propeller You don´t set anything directly, but rather "tells" what RPM You like the propeller to rotate with.

Let´s say You set the propeller lever to a certain setting that balances the flyballs and the oilpressure at 2500 RPM (Engine RPM !!)

If You now increase engine power, then the flywheels will start moving further out and and open the valve for the oil pressure.

The resultant higher oilpressure will move the blades towards high pitch until balance is restored inorder to keep the set RPM.

This governing of RPM is only effective within a certain RPM range. Thats why, if You have set RPM to 2500 RPM and then reduces engine power, that

at some point the RPM will drop anyway. At that point the blades has reached their low pitch position.

Now imagen what happens when the engine fails...

RPM starts to drop, engine oilpresuure is probably still present, but as the rpm drops, so does the flyballs. The flyballs starts to close the valve inorder to try to keep the set RPM. This causes the blades to move toward low pitch. When the engine is dead it will probably still rotta due to the windmilling effect of the propeller that now has reached it´s low pitch position.

At this position the propeller causes alot of drag, so the pilot presses the feather button, wich will start the feather pump, increasing the oilpressure and therfore starts to move the blades towards hgih pitch and stops there.

Now on the ground, if the props are standing still, there will be no oilpressure to move the blades to high pitch, and there will be no rotation to cause the flyballs to open the valve.

If the props are stopped and the blades are feathered, starting the engine will make the flyballs move out due to centrifugal forces and open the oil valve nad at the same time moving the blades into low pitch. From then on the governor will start govern thr RPM again.

Buttom line - If there is no rotation and/or no oil pressure, there is no means to move the blades.

Finn

[JorisVdB 0]

Sorry Finn, should have known it as a betatester . Just got the Cat down safely at night on one engine, on the water...I was glad when I shut down the remaining engine.

I don't have a clue what the cause could be, though. The rpm dropped to about 1,100, with manifold pressure remaining at a reduced level, as was the oil temperature, following a short in-flight fire...opening the cowl flaps helped, it appears...

But it's one heck of an aircraft, both in real life and in the sim. Thanks again, Finn and the rest of the crew!