Always too fast in descent

[Jetstream96 20]

I don't hit F1, just let the NGX work as designed. The fact that the VC throttles aren't at idle isn't a bug, it's the way flight idle N1 is achieved in the NGX. The N1 is correct. If you hit F1 to force the throttles closed you get an artificially low N1.

I knew this is related to the way PMDG bypasses the FSX limitation. The interesting thing is that when I hit F1 above FL290 N1 goes down only momentarily (and then goes back to the original N1), but below FL290 throttles actually stay at idle upon hitting F1.

 

Anyway this trick works for me so it may worth a try if nothing else works.

 

Btw I set the A/T Override to "never". Not sure if this matters.

[kevinh 409]

I knew this is related to the way PMDG bypasses the FSX limitation. The interesting thing is that when I hit F1 above FL290 N1 goes down only momentarily (and then goes back to the original N1), but below FL290 throttles actually stay at idle upon hitting F1.

 

Anyway this trick works for me so it may worth a try if nothing else works.

 

Btw I set the A/T Override to "never". Not sure if this matters.

Only PMDG can say which is the intended value for N1 at idle. I have no idea, but I tend to leave it alone. A few percent N1 near idle should not make much difference to thrust.

 

A/T Override settings will only affect things if the hardware throttle input has been left above idle or is prone to noise.

[MrGreen 0]

Only PMDG can say which is the intended value for N1 at idle. I have no idea, but I tend to leave it alone. A few percent N1 near idle should not make much difference to thrust.

 

So would you recommend me not to bind F1 to the reverser detent then? I like it as an insurance in case the hardware-throttles happen to stay at a >0% level, hitting F1 will make it go 0 so autobrakes etc applies. But I don't want to break the simulation.

 

 

I did a flight yesterday with cost index 50 (descent speed 296/.792, if I remember correctly) and I never had to use drag (until touchdown ). I did however do the F1 "trick" during the descent to shave off a few % of N1. 

 

I'm not sure if the F1 thing actually had any effect, and I feel it is harder for the aircraft to keep a low ECON SPD in descent compared to 280+.

 

Maybe I have unrealistic expectations, but it feels like I shouldn't have to use drag during long parts of the descent (5000-10000ft) if my planning is correct and there are no unexpected changes during the descent (new speeds, different routing, sudden changes in weather). Am I wrong?

[pcubine 143]

What am I doing wrong here?

I don't think you are doing anything wrong. The 737-800NGX will pick up speed during descent if the vertical profile is maintained. I do two things to try and keep the speed under control. Press F1 at FL290. Enter tailwinds in the descent forecast no matter what PFPX says. I set the tailwinds at 180 degrees opposite the direction of the STAR. If a STAR if heading 245 degrees I set the winds at 065 degrees increasing the velocity of the tailwinds as the plane descends. It might not be real world but it keeps the NGX under control. In fact thrust is usually required during the descent.

[kevinh 409]

So would you recommend me not to bind F1 to the reverser detent then? I like it as an insurance in case the hardware-throttles happen to stay at a >0% level, hitting F1 will make it go 0 so autobrakes etc applies. But I don't want to break the simulation.

I don't see how binding the reverse detent to F1 can create a problem. You can't break the simulation like that. If pressing F1 helps the descent then that's good too.

[Driver170 42]

I never knew about pressing F1 at FL290 ? So do i need to place my thrust levers to idle after a vnav des ?

[skelsey 765]

I normally place the TLs in the idle detent prior to the start of a descent just so they're in more or less the right place later on, but that's all.

 

You don't need to press F1 at FL290. If you do, you will get a lower N1 (and thus a steeper descent) but this is unrealistic as it is effectively circumventing PMDG's simulation of Flight Idle.

[Driver170 42]

I normally place the TLs in the idle detent prior to the start of a descent just so they're in more or less the right place later on, but that's all.

 

You don't need to press F1 at FL290. If you do, you will get a lower N1 (and thus a steeper descent) but this is unrealistic as it is effectively circumventing PMDG's simulation of Flight Idle.

 

Thanks simon. I always place my TL after reaching cruise. So is this a FSX limitation where PMDG has done something to flight idle?

[skelsey 765]

Exactly -- as I understand it, PMDG's flight idle simulation effectively moves the thrust levers off the backstop slightly (I imagine there must be an FSX limitation that prevents commanding a higher N1 without thrust lever movement).