N1 difference

[Copper. 78]

Something is not set right on the pneumatic panel. Probably a pack or bleed switch in the wrong position.

+1

[kevinh 409]

can anyone explain the discrepancy between the 2 N1 engines

 

This is related to the way PMDG have modelled bleed corrections to N1 command. It's come up before in the forum. They aren't looking at the bleed and pack switches as they should. It appears that they are looking at whether the packs are running and applying a correction to the associated engine's N1 command. It always assumes the engine is the bleed source. This works ok till you try a bleeds off takeoff.

 

So it's a limitation of the current simulation. Can't be fixed without a model update.

[Driver170 42]

This is related to the way PMDG have modelled bleed corrections to N1 command. It's come up before in the forum. They aren't looking at the bleed and pack switches as they should. It appears that they are looking at whether the packs are running and applying a correction to the associated engine's N1 command. It always assumes the engine is the bleed source. This works ok till you try a bleeds off takeoff.

 

So it's a limitation of the current simulation. Can't be fixed without a model update.

 

Thank you for that kevin.

 

Its certainly not my configuration, i always do a takeoff review and always check my essentials. Everything was setup right!

[pcubine 143]

Its certainly not my configuration, i always do a takeoff review and always check my essentials. Everything was setup right!

Vernon

 

In the NGX world, bleeds off is not correct. If you want the N1 for the two engines to agree as shown in your screenshot the bleeds must be on. Maybe your setup is correct for the real world but it not correct for the NGX world which is the one we live in when preparing the NGX for flight. Go to bleeds on.

[Driver170 42]

So its not possible for a bleeds off then?

[pcubine 143]

So its not possible for a bleeds off then?

Vernon

 

I have no idea. I have always switched to bleeds on once I have started the engines. Try a bleeds off take off and see what happens.

[Driver170 42]

Everything was fine i suppose just the difference in N1 by 1 %

[codechris 9]

A bleeds off take-off is certainly possible.

 

However, what was the reason why you had the APU on during take-off? I can only think of one scenario off the top of my head

 

Also, just noticed your new signature Vernon. I couldn't be any less surprised that you are a beta team for FS2Crew.

[kevinh 409]

A bleeds off take-off is certainly possible.

 

However, what was the reason why you had the APU on during take-off? I can only think of one scenario off the top of my head

 

Also, just noticed your new signature Vernon. I couldn't be any less surprised that you are a beta team for FS2Crew.

The APU is on for a bleeds off takeoff. It supplies air to one pack.

So its not possible for a bleeds off then?

It's possible to do from a procedural point of view, you just won't quite have the same N1 on both engines. It might be better to just switch the packs off for takeoff. That way the NGX won't compute any bleed correction for the engines. Then your performance will be right, though the cabin won't be getting any air. Simply turn the packs on after reducing to climb power.

[Driver170 42]

Also, just noticed your new signature Vernon. I couldn't be any less surprised that you are a beta team for FS2Crew.

 

Ha, thanks! Couldn't turn the opportunity down.

 

 

It's possible to do from a procedural point of view, you just won't quite have the same N1 on both engines. It might be better to just switch the packs off for takeoff. That way the NGX won't compute any bleed correction for the engines. Then your performance will be right, though the cabin won't be getting any air. Simply turn the packs on after reducing to climb power.

 

Is a packs OFF takeoff even approved? Never seen that procedure in the FCOM?

[pcubine 143]

Ha, thanks! Couldn't turn the opportunity down.

Congratulations.

[Driver170 42]

I feel really special : D

[kevinh 409]

Is a packs OFF takeoff even approved? Never seen that procedure in the FCOM?

I don't see any reason why it shouldn't be approved but I've no idea whatever it is or not.

[Driver170 42]

Helios disaster ? Maybe thats why

You notice TOPCAT has AIR CON off or on option!? Is this effectively BLEEDS OFF

[Spin737 102]

So I did some switch flipping while I was prepping my last flight.

 

If you force the pack in to HIGH by turning off a bleed, you can cause the split. You can also cause the split by having one pack on.

 

Also, even with both PACKS MELd, you'd still have both switches on, if I'm reading the procedure correctly.

 

Edit: the procedure is weird. It looks like you have to infer that only one PACK switch is on and in HIGH.