Beta Range

[Hueyman]

Ok so, it becomes more and more clear.

For example, in my simulator, I set everything like that :

The prop angles varies from 86.1 ° ( Fully feathered ) to -11 ° reverse.

Now, when I start up the PT-6, with prop lever fully forward, when the prop slowly going out of feather ( as the engine oil press is rising, to fine the pitch of the blades against the spring and counterweights forces ), it goes to -0°30', which is the β angle.. then, when the cond. lever is at Low Idle, I get aroud 1350 RPM ( with 52% Ng ) and the prop pitch only start to coarse when the Np comes close to 2150-2200 RPM ( Max nominal rpm for that Hartzell prop, when the RPM lever is full forward ).

Some incomprehension now. When I see a PT6 engined plane starting up from the side view of the prop, I can see the blades slowly flattening while speed increases ( getting out of feather angle ) , but then it comes to a stop ( visually, the low flight pitch stop of 9°30', and it create tractive thrust ( the only flat pitch is on the extreme tip of the blades )? The drawn I posted earlier in this thread ( " Flight Idle " )could be that stop. It doesn't get lower than that, near the 0° WHY ? I can reach in the simulator those 9° to get tractive thrust, if I bring the Prop Lever back a bit ( on ground, just after start up for example )

In flight, when you are at cruise speed of 115 Knots, power 80% and Np 2200 RPM, if you fully retard Power lever, the pitch will flatten to keep those 2200 RPM, then it will come to a low pitch stop, and from this moment the Np will start to decrease, and will eventually re-increase up to 2200 RPM if you pitch nose down, and gain some airspeed ( then the pitch will coarsen again ). Now, how you can come into the flat pitch angle ( -0°30' ) while you don't have to lift the power lever to go into reverse, just by pulling it against Idle stop ?

If I set the flight idle stop to -0°30', then if my plane has low airspeed, the Np will fall below the max RPM set of 2200 RPM, and slowly reach those -0°30', and NOW the prop disc will act like a big airbrake, and I'll be able to start my impressive dive at -7000 ft/min without going over 120 IAS, but if the plane goes up to around 130 IAS, and the relative wind makes the prop gaining speed by windmilling, the pitch will coarsen again, and it will get out of Bêta range

And in flight, what is the range where the RPM Lever can actually be used to change prop speed ? I know max is 2200RPM, full low ( aft detent ) is feathered, but on the full aft stop, that is something like 1300 RPM or so ? Can't find anything on it, even with the 650+ pages manual of the PT6A-27 I have in front of me..

You guys have to admit it's MUCH MORE complex than the simple explanation " Bêta is flat pitch " or " It's anything that is not Alpha range "..

Hasta later