PPRuNe Forums - β Range

Hello everyone.

I know one thread is already open here, and I already posted there. But as the whole thread is globally explaining this quite simply, at least much simpler than how it's actually work, I thought it would worth to start another one.

Ok, I am not a CPL operating a turboprop plane, just a PPL flying little reciprocating planes. But, I'm very interesting in learning the deep and complex side of the thing, how it works, and also because I'm creating a plane for a simulator, which use that " system ".

Ok, I know the operating principle is different according to engine brands, fixed/free turbines, even airframes sometimes... so, let's take this example for the medium sized PT6A series, here the well known Pratt & Whitney Canada PT6A-27.

I have as much documentation as I can ( thanks MX Trainer for your PT6 training PDFs ) and the 780+ pages of the PT6A-20 maintenance manual.

The last interrogation I have now, is :

On some installations ( called on maintenance manual as " STOL " or " Non STOL " applications ) the PCL or PLA ( Power Control Lever or Power Lever Assembly ) can directly control prop blade angle in forward operation, down against the idle gate PCL position ( so this is STOL installation ) while other rigging don't allow pilot to control blade pitch on ground ( or low speed flights ) via forward movements of the PCL ( so in both case, not reverse range )

In the maintenance manual, I read :

" The installation for Non-STOL applications is identical to the STOL reversing propeller installation except that a special propeller cam is used. This cam has a different curved slot configuration for the Low-idle position up to the Take-Off position of the power control lever travel (refer to Figure 1-13-2 for a detail of the Non-STOL cam). The reversing position of the propeller control cam is the same as that for STOL applications except that the Bêta range of the STOL application is limited to that part of the control range from Lo-Idle to Reverse. Movement of the cockpit power control lever from Lo-Idle to Take-Off position, therefore, has no direct effect upon propeller pitch. "

So, is this the reason why I have the feeling that some installations allow the pilot to directly control blade angle ( against the feedback Bêta ring, actuated by Bêta valve ) while taxiing, WITHOUT pulling PCL back in reverse range ?

Here what I mean, on this video : from 03:15 to 03:30

I hear the prop sounds is different when the pilot advance PCL and sounds is returning like before when he pulls them again... another notice : the yellow-orange warning lights on the warning panel, something like " low pitch " are illuminating when PCL are retarded and switch off when he push them :

And on this Twotter, at 03:20, we can hear and see the Np decreasing when they push PCLs up to take off power... decreasing because PCL are directly controlling blade angle THEN the Ng is rising ( Ng slower to rise than blade action movements, inducing drag and so Np drop ? )