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low n' slow
7th Jan 2008, 00:13
Hi all!
I had a discussion with a colleague that argued that it didn't matter if the EAI was on for takeoff or not, as regards to performance limited takeoff mass.
His argument was that the same torque is extracted and thus the performance will be the same.

I argued that because the EAI is powered from the 115 V frequency wild AC generator, connected to the AGB, this will become a part of the total torque readout as the AGB applies drag to the prop shaft. The torque that will be sensed (also for CTOT purposes) will then be a combined readout of both prop and AGB produced torque and therefore the actual power produced at the props will be less than if EAI had not been switched on.

I convinced myself and my colleauge, but I've tried to proove this to myself and I have so far been unsuccessful. Could anyone confirm that what I'm argueing is correct?

Regards/ LnS

barit1
7th Jan 2008, 03:44
To my best recollection (24 yrs ago in SF340 flt test) the AC wild freq generator is on the Prop Gear Box (Gearcase), not the core AGB which has a DC starter-generator.

Thus the indicated torque (measured at the PGB input axis) must drive both the prop AND the AC generator; In other words the power at the prop is reduced by the amount of the generator power when it is loaded, assuming equal indicated torque. Whether this is a significant figure I'll leave to someone with more current knowledge of the system.

low n' slow
7th Jan 2008, 10:11
Ofcourse it's on the PGB! How silly of me.... :\
So in essence I was correct that the torque readout in cockpit will be a compound of both gearbox and propeller drag with engine anti ice on.
The question of how much the gear box drag will be is also interesting. Not for calculation purposes (someone has allready calculated those charts for us) but more for my peace of mind.

Thanks Barit1!
/Lns