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stevem

737 pitch and engine-out stability question

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Hello,

 

I've searched the forum for answers, but I haven't found one.  If there are forum threads addressing this, please let me know.

 

I fly the real plane... when applying thrust, the nose pitches up aggressively.  When reducing thrust, the nose drops aggressively.  This is true during the flare: when thrust is reduced to idle, one has to "pull, pull, pull" on the yoke to raise the nose.

 

But, in the PMDG simulation, the pitch really doesn't change much with thrust changes.  The simulation is far too easy to land.  In some cases, I don't even have to pull back to raise the nose.  If I tried this in real-life, the nose would smack into the runway, nosewheel first.

 

Additionally, with an engine failure, the real 737 yaws aggressively into the dead engine.

 

But, the PMDG simulation doesn't have much yaw at all with an engine failure.

 

Is there a patch, a modification, etc., to make the pitch and yaw be more reactive (i.e., aggressive) to thrust and engine-out situations?

 

Thank you!

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Because its a only a 40 quid game and fsx is about £10 now and made in 2006.

 

If i was you, i would hang about more in your level D sim at work than this. Thats what i would do lol

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Hello,

 

I've searched the forum for answers, but I haven't found one.  If there are forum threads addressing this, please let me know.

 

I fly the real plane... when applying thrust, the nose pitches up aggressively.  When reducing thrust, the nose drops aggressively.  This is true during the flare: when thrust is reduced to idle, one has to "pull, pull, pull" on the yoke to raise the nose.

 

But, in the PMDG simulation, the pitch really doesn't change much with thrust changes.  The simulation is far too easy to land.  In some cases, I don't even have to pull back to raise the nose.  If I tried this in real-life, the nose would smack into the runway, nosewheel first.

 

Additionally, with an engine failure, the real 737 yaws aggressively into the dead engine.

 

But, the PMDG simulation doesn't have much yaw at all with an engine failure.

 

Is there a patch, a modification, etc., to make the pitch and yaw be more reactive (i.e., aggressive) to thrust and engine-out situations?

 

Thank you!

Your supposed to sign your posts here, please.

 

Assuming you really do "fly the real plane", I would still question your comments about pitch. I've not flown a real 737, but I've flown 737 full flight sims frequently and I wouldn't describe the pitch response during thrust changes as agressive. You can apply full go-around thrust from level flight and the aircraft does pitch up but it's easily controllable, not agressive. The thrust change when you retard to idle during flare isn't anywhere near as much as for go-around either. What's missing in the simulation is pitching moment changes due to ground effect. They just don't happen in FSX, which only models the lift effects. In the real world as you enter ground effect you need to pull to counteract the pitch down trim change due to GE. That would happen even if you didn't reduce thrust. So you have to pull less to flare in the NGX, and of course in the real aircraft the forces are much higher than with a sim yoke or joystick. That is not PMDG's or Microsoft's fault. No commercially available controller can yet replicate those forces (one is in development).

 

As for patches, don't expect anything official. You can increase the thrust moment arm for yourself by editing then in aircraft.cfg, see under [GeneralEngineData], to increase the pitching effect if you wish, but you might make it unflyable in other conditions as the real problem is ground effect. Save the original as a backup of course.

 

As for asymmetric yaw, again FSX flight modelling is weak in lateral and directional axes. Not much to be done without rewriting the whole model externally. Again you could move the simulated engine thrust arms further outboard using the settings in aircraft.cfg to increase the asymmetric yaw, but the FSX aero model might not be able to cope with it.

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Isn't there a setting for the rudder that makes it act like an "auto-rudder"? Maybe monkey with those.

 

I don't really notice the pitch coupling anymore, but I did when I came to the 737 from a turboprop. It's not a huge amount of pitching, but it's noticeable. It shouldn't really require a "pull pull pull."

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I agree with Matt; and although I don't have 737 time like he has plenty of, I have flown many types over the years and never experience 'aggressive' pitch/power coupling. I don't recall the exact wording, but FAA certification includes dynamic stability. A mild pitch coupling is desired to ensure that recovery from flight near edge of the envelope is not impared by aircraft dynamics but assisted in a managable and predicable manner. As for asymmetrical thrust yaw in the 737, don't forget that the engines are relatively close-in to centerline compared to the length or the aircraft and that vertical stabilizer is huge. I imagine a 737 engine -out event is a lot less interesting than one in the C-414 light twin in which I have experience a couple engine shutdowns... real interesting flights.

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Kevin, thanks for letting me know about signing the message.  And, thanks for your suggestions about aircraft.cfg -- I'll try those.

 

Matt, I agree -- I don't notice the pitch/thrust reactions as much anymore as I did when I (like you) jumped from a turboprop (BE1900D) to the 737-800.  Back then, I thought it was a pretty massive difference in controllability (I slammed the plane into the runway pretty hard at MDW back in 2003 with my first landing, with a tailwind, and that's where I learned that the plane requires more pull force during the flare than the simulator indicated during newhire training).  I also think our current fleet of Level-D sims are more sensitive than the real plane.  That said, I'm trying to make my PMDG react more like our Level-D sims for proficiency-sake.

 

Dan, I thought you made an interesting comment about engine-out controllability in relation to light twins.  I've always actually thought that the 737 reacted a LOT like like twins... meaning, an engine quits, and the thing yaws pretty agressively.  You have to be on top of it, and you have to apply a lot of rudder.  Of course, I'm talking about a V1 cut, medium-weight airplane, 27K engines.  Maybe I just expect directional control to be easier than it is!  : )

 

Vernon said I should hang out in the Level-D at work more often... if only I could!  I get only one event per year, with no practice session.  You jump in cold, ready to do it all... V1 cuts, engine failures, high dive, all that stuff.  I try to be prepared for that, hence the PMDG sim.

 

So, thanks again for all your comments.

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Same as me at my work, except i'm a train driver in the UK and we get thrown emergency situations, defo makes you sweat lol

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Maybe I just expect directional control to be easier than it is!

 

Steve, it took me a long time to accept the poor fidelity inherent in PC-based simulation. I wouldn't touch MSFS stuff and used On Top for my instrument proficiency work for years. PMDG changed all that for me but not even the current products (737/777) can overcome PC limitations. My only 'real' simulator experience was years ago in a C-141 Starlifter analog Link, which had 6-axis motion but no visual and yet that took only milliseconds for my brain to accept the new reality. Sitting at a PC without any stimulus except sound and vision is like taking a shower with a raincoat on. My point, sorry for the wordiness, my point is that things that happen in events like asymmetrical thrust, pitch changes due to power/configuration changes, etc., are very difficult to simulate on a PC. I think PMDG has done an excellent job of capturing the 'numbers,' but the experience that we pilots have gained as we emptied that bag of good luck cannot be compared to what happens in FSX or any other PC-based simulator. Having said that, I have found that as a hobby I am having a lot of fun... and thank goodness. Early retirement left me grounded with a lot of time so the hobby has been a god send; however, it's not flying.

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My point, sorry for the wordiness, my point is that things that happen in events like asymmetrical thrust, pitch changes due to power/configuration changes, etc., are very difficult to simulate on a PC.

Actually they aren't difficult to simulate on a PC at all. It's all just forces and moments calculations. What you won't get in a PC sim is the motion cues to go with it. Also the flight controls aren't simulated very well in hardware. So realistic effects might be harder to deal with, especially engine out asymmetry. However pitch/thrust coupling should work correctly if the FDE is done right.

 

 

 


I also think our current fleet of Level-D sims are more sensitive than the real plane.  That said, I'm trying to make my PMDG react more like our Level-D sims for proficiency-sake.

The simulators shouldn't be too very far off flight test data, otherwise they wouldn't get Level D qualification. And no way should you be practicing manoeuvres in a desktop sim.

 

Are you for real? Your initial comment was that the real aircraft was very agressive in pitch due to thrust changes. Now some pilots are involved in the discussion and that's changed to the sim being too sensitive and you are trying to make the PMDG NGX like the sim so you can get more proficient flying it. Most pilots I know refer to the sim or the box. Not the Level-D.

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It's all just forces and moments calculations. What you won't get in a PC sim is the motion cues to go with it.

 

That's what I said when I gave PMDG kudos for getting the numbers right. It's not the motion but acceleration that makes a difference. The big boxes simulate acceleration to the extent possible. And we both agree, it is this that clouds any discussion on pitch/power coupling or asym thrust because in an airplane my seat of pants are giving me a lot of information... and missing that information makes PC simulation seem somehow not right. In my opinion.

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the ngx is an excellent model but cannot be expected to behave like the actual airframe.

 

For professionals - ngx is best used as a procedural trainer for entertainment purposes. Any requirement for more than that would require time in classroom and time on type in an approved synthetic trainer or better.

 

Again, don't expect a $20 dollar sim platform and a €60 aircraft to behave like a $XX, XXX, XXX aircraft operating in a dynamic world, which is essentially what you're asking for.

 

Brian Nellis.

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That's what I said when I gave PMDG kudos for getting the numbers right. It's not the motion but acceleration that makes a difference. The big boxes simulate acceleration to the extent possible. And we both agree, it is this that clouds any discussion on pitch/power coupling or asym thrust because in an airplane my seat of pants are giving me a lot of information... and missing that information makes PC simulation seem somehow not right. In my opinion.

Pitch-power is about right, but engine out response is under done. This may be deliberate, to make it easier for a desktop user. My point is there's no reason why a desktop sim can't get the asymmetry right from an aerodynamic model point of view. The only thing missing is the motion cue. But even in a full motion simulator this cue can't be achieved completely realistically.

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