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-   -   Atr72-500 (https://www.pprune.org/tech-log/634242-atr72-500-a.html)

barrichello72 22nd Jul 2020 15:04

Hello folks i have a couple of questions for the ATR gurus out there!
as far as i know the propeller is hydro mechanically operated with oil pressure from a PEC fed through an EHV or Electro Hydraulic Valve housed in the the PVM, to the pitch change mechanism. The pitch change mechanism uses supply pressure and metered pressure to move a servo piston in the actuator mechanically connected to the shanks. To decrease the pitch, metered pressure is fed into the decrease side of the actuator, opposing the ever present supply pressure and moving the blades to a lower pitch, higher Np; on the contrary increasing the supply pressure and dumping the metered pressure allows the supply pressure to increase the pitch and decrease the Np. With the CL in AUTO the reference NP is controlled by the setting of the PWR MGT rotary selector and by the setting of the PL - in the takeoff notch.
what does the PEC controls: the metered pressure or the supply pressure or both?
Where does the supply pressure come from - the HP pump on the propeller RGB or the electrical feathering pump?
when the PL is retarded to FI at the top of descent with the CL in AUTO the PVM will reduce the blade angle in the attempt to maintain the Np: the reason behind that is that as the power is reduced and the airplane slows down, in order to maintain the most efficient angle of attack, the blade angle must be decreased as the relative wind becomes more vertical, resulting in a decrease in induced drag and thus in an increase in Np, is that correct?
many thanks

Maisk Rotum 22nd Jul 2020 16:46

Yep. A ground school instructor who taught me Vickers Viscount technology said if asked a question like this said " It works just fine and lasts a long time"

barrichello72 22nd Jul 2020 17:25

Well imho that gentleman shouldn’t have been an instructor, cos there is a huge difference between how deep your knowledge is and how good/willing you are to share it.
thanks for your no-input anyway

PS i truly envy you for having flown such an iconic plane!!! In a positive way of course! More admiration than envy!

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