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Engine N1 Idle % in Flight

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All:I don't know if this is right or wrong, but after installing SU2, N1 at idle during flights (specifically descents) is in the mid 30's, instead of low 20's. This makes for descents where the airspeed is hard to manage.Is this right, or should N1 at idle in flight be in the low 20's?Note: when I'm on the ground, it's definitely around 20% N1.Thanks,James

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Shaun:I've certainly familiar with this in turboprops (I work for Rolls-Royce Indy), but I haven't heard of this in turbofans.Are you sure about this?James

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N1 will windmill to a higher RPM. Flight idle should be 72% N2. Not simulated. Approach idle a bit higher (do not remember). Purpose of flight/approach idle is to prevent flame out. Turboprop is a different story. Guess you talk about ground and flight fine pitch? Ground fine pitch in air = crash.eker

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Eker, that's absolutely NOT true. Flight idle will indeed be in the 30's for N1. They are also not to prevent flameout but to provide enough power for operation of pressurization during flight and anti-icing operations if necessary (idle is also raised when using it) and approach idle is specifically higher to give a better acceleration margin when doing a go-around (lower idle setting would require too much time for the engines to spool up).There ya go!Iz

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Hi Iz :-)I am talking about N2 not N1. There was a couple of flame outs first year of operation - when flying through heavy rain on approach. Solution was a redesign of nose cone and we reprogrammed the EEC for a higher flight idle and approach idle at the same time.Here we go!!:-)eker

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"we" are a medium size airliner company - technical mainbase ENZV -( a little research and you will find...)More detailed -I got a diskette from CFMI at my office and I joined my old tech colleagues at nightshift and "we" :-) reprogrammed EEC`s- and still loading new software. "We" are now up mod status 22 (or 24?) ;-)eker

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Ah yes, I see you guys all the time at EHAM. Sometimes parked next to us at the C-terminal ;)Anyway, as I'm new to the 737NG, having never flown the previous gen 737s, I've just been wondering: Do you really have to put the ignition on for every takeoff and landing, technically? These new CFM's are state-of-the-art engines (certainly compared to the rest of the airplane) and I wonder if this procedure is simply a commonality thing where pilots that also fly previous gen aircraft won't forget it.The auto-relight feature on the CFM56s is not dependent on the ignition switch, if I recall correctly.Any ideas about this?

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Yes there is a kind of auto ignition feature that kicks in if in danger of flameout - low N2 RPM I guess? Keeping the procedure with ignition on is probably a kind of double safety.Our pilots fly a mix of 400/500/NG all day - so have the same procedures makes sense.eker :-)

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Yes, absolutely it makes sense.But coming from the 757 (and we don't have any previous gen 737s), I'm just a little spoiled in that respect that the 757 is a much more automated aircraft than the 737NG and putting those ignition switches on every time for a takeoff, landing and your anti-ice, it seems, well, a bit 'primitive'. A simple 'auto' setting on the knob would do wonders. I don't think the A320 guys with CFM56s flick those switches all the time ;)

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"I don't know if this is right or wrong, but after installing SU2, N1 at idle during flights (specifically descents) is in the mid 30's, instead of low 20's. This makes for descents where the airspeed is hard to manage. Is this right, or should N1 at idle in flight be in the low 20's?"Idle speeds on the real aircraft are based on N2, not N1, James ;-) With N2 at carefully controlled values (in flight, approach and on the ground), the resultant N1 speed is a consequence of airspeed, air density, airflow through the engine and other variables (and is probably of no consequence... unless the fan is locked up/not spinning at all :-)).In the PMDG sim, it was decreed that the correct relationship between N1 and N2 could not easily be achieved in all phases of flight, so basically engine speeds are all based on N1 (with N2, I recall, at a fixed ratio). This has led to some compromises. However, I don't think that faulty airspeed management is a consequence of this (I'm just wondering if you are flying in still air or do you have headwinds/tailwinds? SU2 has the provision to programme winds into the FMC to allow for the effects of tailwinds/headwinds during descent).Hope this helps.Cheers.Ian.

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Hi,I have noticed the flight idle N1. With me it is always in the mid 30's (ground idle is in the low 20's). This makes it difficult to descend and slow down at the same time. I need to do this often. When I arrive at my home airport EHAM, I often have to slow down from 250 to 220 knots while descending from FL070 to 3000 feet.I am wondering if the N1 setting is correct. Can anyone confirm that this the same as in a real 737. I have never seen this behaviour, or at least the effects of this, on other FS aircraft.Only if the behaviour and its effects are as in the real world, I am willing to live with it. Since the speed brakes aren't very effective (this seems also to be the case in the real world), I will have to explain to my ATC why I am speeding up during my descend. If real world behaviour is different, or if the effects are a bit overdone in the PMDG , I am looking forward to some way to patch this behaviour (tweak the airfile or something like that).Kind regards and thanks for helping,Jacques de BeursThe Netherlands

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