PMDG 737 flight model question

[jcomm 5,943]

@Greazer @ All,

I share your admiration for the Zibo, and for some aspects of what can be done with XP's flight dynamics which, just like MSFS, are under active development, so, the near future will probably reveal new aspects of what can be achieved on both platforms.

Regarding your observation of what could be expected from a considerable deflection of the yoke on a flaring 737, at idle thrust, I believe there are so many variables in play that it's complex to make a definite assumption about what is the correct and expected outcome...

I'd say I like the feel of the 737 in MSFS too, for instance when it comes to x-wind effects compared to how most aircraft, the Zibo included, react to a mid x-wind on landing...

Both excellent flight simulators, both with excellent addons that can make each SHINE ! Taking all into consideration, all of the pluses and the minuses, MSFS is presently my preferred, so, I tend to close my eyes to some of it's irritating limitations in aspects more directly related to flight dynamics...

As a glider pilot I can tell you that due to their aerodynamics, gliders are well capable of ballooning if you pull the stick, just prior to touchdown, or even after being in contact with ground, and even at full spoiler deflection, actually one of the reasons some end up broken due to porpoising 😕

At least you @Greazer, have always had what I consider an acceptably unbiased approach to the platforms you use ... You criticize them all 🙂 just as I uninstall them all 🤣

Edited February 27 by jcomm

[lwt1971 7,424]

On 2/26/2024 at 3:31 AM, Stearmandriver said:

Zibo is a great freeware project and so I never like to say anything negative about that project, but if we're comparing flight models... Well, there's no comparison.

There are so many things in the PMDG that are so good, but most people will never even know about unless they can recognize it from the real airplane.  

The PMDG 737 flight model is very good.  Their engine out / V1 cut performance is the best I've seen in any sim aircraft.  

I know people like to nerd out on the Zibo and for freeware it IS incredible... But it's definitely not the same level.

I'm not an IRL pilot, but having used the Zibo on XP and now the PMDG 737 on MSFS, 100% agree (with you and other IRL pilots who've chimed in here) about the PMDG flight model being on a different level, especially when hand flying. Zibo is great for what it is of course, especially given that it's free.

Re: the specific issue being discussed, just from a plain physics 101 point of view it just makes sense that when coming in with enough energy/momentum then even at idle thrust the bird can climb a bit on excess flare. Like someone else said above, idle thrust does not mean the aircraft is instantly transformed to a state of zero/minimal energy.

Re: the side topic of PMDG not getting their LNAV updated (i.e. RNP support etc), like mentioned on another thread, it certainly seems to be in the works and in testing per RSR's recent answer to a forum question about this, and it could release with the first 777 variant, or subsequent one, or some time during the 777 releases as a fixpack (https://forum.pmdg.com/forum/main-forum/general-discussion-news-and-announcements/282945-03feb24-737-pc-xbox-news-777-beta-updates-trolling-a-meltdown-and-more-for-your-weekend-update#post283110)
 

Edited February 27 by lwt1971

[ha5mvo 256]

34 minutes ago, lwt1971 said:

I'm not an IRL pilot, but having used the Zibo on XP and now the PMDG 737 on MSFS, 100% agree (with you and other IRL pilots who've chimed in here) about the PMDG flight model being on a different level, especially when hand flying.
 

Would you be so kind and elaborate how did you determine it's on "a different level?" (you've heard so on youtube won't count).

Did you test its pitch\power curve at different weights? perform Airspeed Unreliable checks? How about turn rates?

 

[threexgreen 3,143]

7 hours ago, Greazer said:

Pilot is late to flare 737 and pulls back quick on yoke.

Does the aircraft suddenly climb immediately?

No! Because of Idle thrust. There is slightly lesser hard landing.

If this was Pmdg 737 it would have ballooned up!

Zibo would not do that. 

The aircraft isn't climbing because it's being flown onto the runway in a continuous descent, regardless of thrust or how quickly the pilots pulls on the yoke. I really mean no offense, but physics and flying an aircraft are more complex than your argument of idle thrust.

If you land the PMDG 737 like in the video it is not going to climb. If you think there is a problem though, I would suggest posting a video demonstrating what you mean, otherwise we'll just keep going in circles.

[nrunning24 151]

I can't believe we have gone 1.5 pages of people with no real world 737 piloting experience using cockpit YouTube videos to tell the real 737 pilot that he is wrong about the flight model....  I mean what are we doing here.

[El Diablito 328]

9 minutes ago, nrunning24 said:

I can't believe we have gone 1.5 pages of people with no real world 737 piloting experience using cockpit YouTube videos to tell the real 737 pilot that he is wrong about the flight model....  I mean what are we doing here.

Please tell me this isn't true? lol

[Fiorentoni 4,257]

11 minutes ago, nrunning24 said:

I can't believe we have gone 1.5 pages of people with no real world 737 piloting experience using cockpit YouTube videos to tell the real 737 pilot that he is wrong about the flight model....  I mean what are we doing here.

I've seen worse here on Avsim. Not sure if that cheers you up 😄

[ha5mvo 256]

28 minutes ago, nrunning24 said:

I can't believe we have gone 1.5 pages of people with no real world 737 piloting experience using cockpit YouTube videos to tell the real 737 pilot that he is wrong about the flight model....  I mean what are we doing here.

You need to understand a simple truth, and yes, I have been flying airplanes in the real world and teaching others to do so for more than 20 years now but this doesn't mean a thing in this context.

The simple truth is that in the real world you fly by the seat of your pants - this applies across the board, from a cessna 152 to a jumbo 747. It is something you can never achieve neither on a multimillion level -D simulator and certainly not on a desktop one. So what you're left with is something to correctly fly by the numbers. Those numbers remain the same regardless of whether you are a type rated pilot or a complete amateur.

Granted, 99.9% of the users will use the sim flying from A to B on autopilot following the magenta line....In this scenario the FM is of little importance. For those who wish to simulate abnormals, an accurate FM is quite crucial.

[Stearmandriver 2,309]

9 hours ago, Greazer said:

 

Pilot is late to flare 737 and pulls back quick on yoke.

Does the aircraft suddenly climb immediately?

No! Because of Idle thrust. There is slightly lesser hard landing.

If this was Pmdg 737 it would have ballooned up!

Zibo would not do that. 

That landing wasn't a result of idle thrust (he had just pulled to idle as he tried to flare, and he should not have since he was slow, but the power is just rolling back as he touches down).  He was obviously slow.  If you're slow, popping the yoke back isn't going to do anything, since the wing doesn't have any excess performance to give you.  If you're 10kts fast and do that, you'll get a very different response.

You can see this in the PMDG; if you're at ref or ref-5, you're not going to find any balloon or float capability.  You are, in fact, probably going to plant it just like this video.

One thing to check might be your assistance settings in the sim; if you have any of them on, they interfere with the PMDG flight model in severe ways.  Sometimes they get turned back on as a surprise from a sim update.

If that's not it, and you're really seeing a severe balloon, you're simply too fast.  If you think you're on speed, you've probably got something wrong in the FMC perf init that is causing the plane to think it's heavier than it is, and give you a ref speed higher than is actually required.

Balloons are much more about excess speed than they are about excess thrust.

[Stearmandriver 2,309]

7 hours ago, g-liner said:

Remember it’s the poster you’re quoting that nearly got banned from the PMDG forum for pointing out some of the failings in the 737.

Oh not nearly; I'm banned.  😁

If the PMDG has an Achilles heel, it is definitely their current LNAV flight guidance and inability to handle RF segments.  But taken in total (flight model, engine perf, single engine perf, systems modeling and depth and range of failures etc) it's hard not to see the PMDG 737 as one of the best-simulated (if not the best) aircraft in the sim.

The behavior of those running the company is a different story 😉.  But I don't see that as really related to the performance of their sim aircraft.

Edited February 27 by Stearmandriver

[Mike_CFII_MEL 789]

As timing would have it, here we a have a few level D sim landings. 
 

 

 

 

 

I believe if one also looks at the FCOM you'll find that it states the aircraft may float but makes no mention of climb out.

[Stearmandriver 2,309]

1 hour ago, Mike_CFII_MEL said:

I believe if one also looks at the FCOM you'll find that it states the aircraft may float but makes no mention of climb out.

That's because the FCOM is speaking to presumably qualified pilots who understand the importance of energy management and flying on-speed.  Excess energy can absolutely result in a balloon, and this is in fact one of the leading ways that pilots accomplish a tail strike.

[Mike_CFII_MEL 789]

4 hours ago, Stearmandriver said:

That's because the FCOM is speaking to presumably qualified pilots who understand the importance of energy management and flying on-speed.  Excess energy can absolutely result in a balloon, and this is in fact one of the leading ways that pilots accomplish a tail strike.

Naturally excess energy is possible based on pilot error, but if conditions are right the PMDG should not climb when one pulls back on the yoke and yet it does. If anything with ground effect one can float. 

Edited February 27 by Mike_CFII_MEL

[Stearmandriver 2,309]

48 minutes ago, Mike_CFII_MEL said:

Naturally excess energy is possible based on pilot error, but if conditions are right the PMDG should not climb when one pulls back on the yoke and yet it does. If anything with ground effect one can float. 

What do you mean, when conditions are right?  In what conditions are you seeing the PMDG do this, that you think the real airplane wouldn't?

Like I say, a mishandled balloon or bounce is one of the leading causes of a tail strike.  I mean, I've had to take the controls from an FO and go around - from idle thrust - because of a severe balloon.  In the actual airplane.

I don't understand why folks who have only flown the sim variety think that this can't happen??  You can be on-speed at ref +10 or 15 (for wind additive) and balloon for sure...

[DD_Arthur 1,068]

15 minutes ago, Stearmandriver said:

I don't understand why folks who have only flown the sim variety think that this can't happen??  

Don’t you know? We 1g comfy chair pilots will always know better than you mere pro’s….