ATR45/75 power managment
 

Hello,
I am trying to understand ATR42/72-500 power plant especially EEC control function. I have several questions, so I will try to structure them one by one into posts. Any help is very appreciated, thank you.

Question one: What is expected torque (TQ) in CRZ and CLB power management modes where PL are set to RAMP (PLA 81deg) or to WALL (PLA 100deg). NP for these two modes is 82% RPM (at least for PL in NOTCH = PLA 67deg).

Please see attached picture from ATR75 FCOM:

https://cimg4.ibsrv.net/gimg/pprune....c86392213e.png
If you look at power curve for C (CLB) or D (CRZ) power management modes, then you can see, that at when PL is put to ramp 100% Power = 2750SHP shall be produced (sea level ISA temp). As Power is function of:

Power = Np * Torque

and nominal NP is 82% for CLB and CRZ modes, than TQ > 100% (~122%) will be produced! Is this really correct? I can see multiple problems with this including over stressing power plant components.

There is only one other possible explanation of picture as above and it is, that when moving in CLB or CRZ power mgmt mode PL from NOTCH position to RAMP position, NP is also increased from 82% to 100%, so Torque will not overshoot 100%.

Thank you for any help.

Question two: How EEC apply thermo dynamic limit for whole selected Power Management mode.

As for picture above, based on PLA/power curve, power to be generated is selected. Next step is to limit selected power to not exceed thermo dynamic limit of given mode (due to current air density and/or OAT):


https://cimg1.ibsrv.net/gimg/pprune....2a74a5c7ac.png


This results in torque to be commanded by EEC, as mentioned at table as follows:


https://cimg2.ibsrv.net/gimg/pprune....b1be748475.png

So lets take one example, for TO power management mode selected, PL in NOTCH (PLA 67deg, see picture above) with AC off, at 3000ft elev, OAT 30C, engine delivered torque shall be limited to TQ 85.2%,

What shall happen, when you will move PL from NOTCH to RAMP - what will be delivered Torque? I initially assumed, that, as you are already for given power management mode thermo dynamic limited (under given outside conditions) to get maximum 85.2% of Torque, engine will not produce anymore power! But as you can see bellow in table for GOA power (PL at RAMP) it does:


https://cimg8.ibsrv.net/gimg/pprune....9034fc3fed.png

At same 3000ft elev and OAT 30C you will still get 95.1% TQ.

To me it doesn't make any sense, except that RTO power limits are applied instead of TO! This would probably means, that when TO position is selected on Power Management rotary selection in flight, RTO power curve + limits is selected vs when the same happens on ground only derated TO power curve + lower limits are selected.

Or do I miss something else? Any help is very welcome.