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jgoggi

EPR/N1 at thrust HOLD during takeoff run

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Hi, I tried a takeoff with the PW4056 engines. Is it correct that, when thrust HOLD engages at 80 knots, the EPR values remain correctly fixed at the takeoff green reference, while the N1 still continue increasing (like it did erroneously with the GE engines before the latest update)? I guess that, since I see that also the N2 values increase during HOLD mode, the EPR remains constant, right? Unfortunately I see on the Aerowinx PSX simulator that this does not happen, that is N1 remains constant as well during HOLD mode...

Thanks.

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James,

This is actually correct behavior.  EPR is calculated by the EEC using Probes and has no true relation to N Speeds through moving air.  As the aircraft accelerates and decelerates the EEC will Maintain EPR in Normal mode and adjust N1speeds as necessary for changing P2/T2 on the inlet probe and turbine exhaust probes adjusted for Temp.  Perfectly normal behavior for PW4056.  Now if the N1 speeds are changing on the ground when not moving that would be a different issue.

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On ‎21‎/‎10‎/‎2017 at 7:26 PM, Jet Tech said:

 As the aircraft accelerates and decelerates the EEC will Maintain EPR in Normal mode and adjust N1speeds as necessary for changing P2/T2 on the inlet probe and turbine exhaust probes adjusted for Temp.  

Thanks, Paul. The only thing that does not convince me is that N1 is not just "adjusted", but has a continuous and constant increase until the A/T takes control again at 400 ft, as it happened with the GE before the latest update...

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Hey James,

Well then,  Challenge Accepted :biggrin:   Find TO2 Departure a small bit of Sim Video that illustrates very nicely this phenomenon with the PW4056.  Remember now, GE's are controlled by N1 so it wouldn't make sense for N1 to change on the controlling parameter.

 

 

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Hi Paul, thank you very much! I spent hours trying to find a video on the net that could show that behaviour, but could not find any... Now I am convinced ;-)

Thanks again.

 

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Hello,

Interesting topic. Definitely something unusual with the TO thrust management.

At Narita, planned TO thrust setting was TO+56°C and N1 of 99,9%. During accel, N1 went as far as 101,9% then settled back to 101,2% during initial climb prior to reach THR RED height. That was with the GE variant.

Best regards

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6 hours ago, alex98 said:

Hello,

Interesting topic. Definitely something unusual with the TO thrust management.

At Narita, planned TO thrust setting was TO+56°C and N1 of 99,9%. During accel, N1 went as far as 101,9% then settled back to 101,2% during initial climb prior to reach THR RED height. That was with the GE variant.

Best regards

Full names on all posts in the PMDG forums please.

This is off topic, James was specifically discussing the relationship between EPR and N1 as in a RR or PW.  You have a question about the behavior of N1 on a GE.... apples and oranges.  Was 101.9% above the amber line?

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Further, that abnormal N1 increase in GE engines has been fixed in the latest update, did you install it?

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On 08/11/2017 at 7:11 PM, downscc said:

Full names on all posts in the PMDG forums please.

This is off topic, James was specifically discussing the relationship between EPR and N1 as in a RR or PW.  You have a question about the behavior of N1 on a GE.... apples and oranges.  Was 101.9% above the amber line?

Hello,

I dont know what went wrong with my profile signature but I have my full name there.

My bad, I misunderstood the subject of the topic. Nonetheless, my 747 is up-to-date and I still see an increase in thrust during takeoff roll on all engine variants.

Best regards

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Do you see GE engines increase in N1 from 80 knots to 400 ft? In that case please check first that your throttle hardware is properly calibrated, or try just with the keyboard keys.

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3 hours ago, jgoggi said:

Do you see GE engines increase in N1 from 80 knots to 400 ft? In that case please check first that your throttle hardware is properly calibrated, or try just with the keyboard keys.

Hi James,

Yes that's exactly whats happening. I do not use any separate throttle hardware, only a joystick. It is properly calibrated but I will try with the keyboard next time. When ready to takeoff, I usually advance throttle to appr. 70%N1 then press TOGA and when the blue line of the physical position of my throttle handle appears I go full throttle and leave it there till TOD. Is that correct? I have the A/T MANUAL OVERRIDE option to IN HOLD MODE ONLY. Don't know if that is relevant.

Best regards

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Yes, Alex, that's correct. Please, try only with the keys, having your joystick unplugged from the usb port (CTRL+SHIFT+G or click spot for TOGA switch), and see if N1 increases after the thrust mode goes into HOLD. Then please report. Thanks.

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6 hours ago, alex98 said:

when the blue line of the physical position of my throttle handle appears I go full throttle and leave it there till TOD

I suspect this is contributing to your issue. Because you have the manual override set to "in hold mode only," it's possible that noise from your joystick while it's in hold mode during takeoff is causing the N1 to increase to full power. Also, any bump of your joystick while it's in hold mode will cause it to go to full power. Two things you can try (other than what James advised above): advance the throttles only to the point where they agree with the N1 setting the A/T is commanding or temporarily set the override to "never" and see whether the issue is still present.

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9 hours ago, alex98 said:

I have the A/T MANUAL OVERRIDE option to IN HOLD MODE ONLY. Don't know if that is relevant.

This is only useful if you have throttle hardware. Without it, I'd set it to NEVER.

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3 hours ago, wsmeier said:

I suspect this is contributing to your issue. Because you have the manual override set to "in hold mode only," it's possible that noise from your joystick while it's in hold mode during takeoff is causing the N1 to increase to full power. Also, any bump of your joystick while it's in hold mode will cause it to go to full power. Two things you can try (other than what James advised above): advance the throttles only to the point where they agree with the N1 setting the A/T is commanding or temporarily set the override to "never" and see whether the issue is still present.

 

33 minutes ago, scandinavian13 said:

This is only useful if you have throttle hardware. Without it, I'd set it to NEVER.

Hello Walter and Kyle,

Thank you for your insight I will try and report.

Best regards

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