[FSX] EPR 747F (CPA): Oscillating thrust during take-off and climb

[19AB67 16]

Hi folks, 

during my today's flight CPA17 VHHH-VOMM with Cathay Pacific's 747F B-LIC I experienced again with and only with EPR as primary thrust indicator an oscillating thrust while taking off and after some stabilsation again during my climb. (PMDG 747 V3 - FSX 3.00.8466)

1. The aircraft FMC was well prepared, the A/C not too heavy, TOW 255 tons only,

2. LNAV, VNAV armed, after 50% N1 I engaged TO/GA. 

3. EICAS displayed a TO2 EPR of 1.43

4. The throttles rapidly move back and forth so that EPR oscillates between 1.56 and 1.33. 

5. Similar during climb at FL270: EPR1.46 but oscillating between 1.58 and 1.32. 

6. On top  I witnessed that throttle levers were *not* in sync: In this occasion throttle lever of ENG1 moved forward (engine response accordingly) while the levers of ENG2-3-4 moved backwards. Their oscillation let the aircraft's nose wiggle, noticable on the ND as the dashed line of the path indicator waves like a dog tail. I checked by pushing E1234 that all levers *are* in sync, but to no avail. 

Huh...

A. What is going on?

B. What is my mistake? 

C. As somebody seen as well the out-of-sync thrust levers? 

Thanx in advance. 

[downscc 1,327]

My first suspect would be the panel state because you are describing something that is very unusual, illogical and not a known bug.

[19AB67 16]

On 03/11/2017 at 6:32 PM, downscc said:

My first suspect would be the panel state because you are describing something that is very unusual, illogical and not a known bug.

Hi Dan, 

I started with the PMDG Cold & Dark panel state in order to eliminate this possibility. 

1. 

Again, the pumping oscillation I only experience on the EPR-as-primary-thrust-indicator aircraft. 

On those we have to advance the throttle very slowly in order to avoid threspassing the limit in manual mode. 

Is the auto throttle working on EPR or N1 feedback? 

If it is EPR, its delicacy might be the reason ...

... or is it my hardware (Saitek X52 with throttle)? 

But in TO/GA it shouldn't be effective, should it? 

(I use A/T Manual Override = IN HOLD MODE ONLY. ) 

Have to check in my next flight what speed mode is shown -- does the throttle position switch off TO/GA? 

If I remember correctly, we need to push after activating TO/GA the throttle forward up to the limit. 

 

2. 

The diverging lever positions seems to be another issue, and I guess this one you find very strange. 

[downscc 1,327]

Sorry Andreas, I am not an engine expert.  If you have a RR or PW then EPR is the controlled variable.  I'm not sure of the best practice but according to Tutorial you advance N1 to about 50% (not EPR) then if all is okay hit TOGA.  You should not be trying to set takeoff EPR manually in most cases.

Your throttle, set to hold override only, will not effect thrust unless you are in hold.  I haven't flown the queen in a few days.... , but doesn't she revert to hold above 80 kts?  It is during this time that any throttle movement will disrupt the TOGA.

Pushing the throttle to the limit after pushing TOGA is just a simism, we do it because our throttle controllers are not motorized so this lines the controller up with the actual levers, and makes it easy to initiate a RTO by pulling the throttles to idle when above 80 kts.

[19AB67 16]

1 minute ago, downscc said:

doesn't she revert to hold above 80 kts?  It is during this time that any throttle movement will disrupt the TOGA.

Issue 1: So I need to push the throttle to calculated limit for this take-off before 80kts, yeah, this might do it. Will check, thank you! 

Issue 2 Not-in-sync-throttle-levers: Will try to capture settings, if I see it again.