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kabekew

Revived "passengers vomiting in VNAV mode" thread

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(MODS, I know you deleted my previous thread about this because I didn't 'sign' my post, so I'm going to sign this three times which is hopefully enough -- but really you and I know you deleted it because you don't like bug reports. And that's fine, but first, deleting the bug reports doesn't fix the bug, and secondly we're all loyal users here and just want to improve your product! So please don't see this as an insult to your awesome product -- I'm just trying to be helpful!)The bug is the current autopilot uses pitch exclusively to achieve speed, which is not realistic. In the real world, and the real 738 there is a balance between pitch and throttle. Currently, the PMDG relies way too much on pitch. This means if ATC assigns a slower speed, the current PMDG autopilot will violently pitch up into a 3-4g climb to slow down as fast as possible. To recreate this, climb out at normal FMC speed (probably around 296 kts) around 15,000, then hit spd intv and dial in 280 kts (to simulate ATC instructing you not to exceed 280kts) and notice how the autopilot violently pitches upward. In the real world this would cause passengers to scream and/or vomit.I posted this bug on another thread and it was deleted. And that's fine -- MODS can delete this thread again, but killing the messenger won't fix the bug. I've seen the autopilot violently pitch upward into a 7700fpm climb and that simply is not realistic for any 737.Again, PMDG, you can delete this thread and ban me for reporting this problem, but that will not increase your sales, and by ignoring this issue I think will just turn people away.Please fix this, PMDG! Put in limits in climb/descent rate, and if you're calculating g forces please limit it to something more realistic. The real 737NG does not pull 4g's+ in a climb like the current build sometimes does,(EDIT) also in the climb, the autopilot should never level off to build up speed as it currently does. The minimum climb rate for a jet is 1,000 fpm which is expected by ATC and listed in the AIM.(Signed)Gabriel Keewaydin--Gabe Keewaydin

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In LVL CH or VNAV, climbs are conducted with power set to the thrust limit and pitch for speed. I'm not sure why you would want to reduce power to reduce speed in a climb - it would be better to convert than kinetic energy into gravitational potential energy and thereafter, using the excess power to increase climb rate. Even in a Cessna 172 would you pitch for speed.

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Gabe-We appreciate when our customers come here and help us identify things that can be improved or fixed.When you have spent some time here- you will find that this is the case. I'm not sure why- but you seem pretty paranoid that we might ignore someone coming to use with a legitimate issue. We *almost* never do. We do ignore jerks, self-important grandstanders, and anyone who seeks to draw attention to themselves by acting like the back end of a horse.So- my suggestion to you is that you keep the tone of your posts civil, and conversational. Your post above is more intent on being insulting than factual.Your earlier attempt at this thread was deleted in compliance with forum guidelines because you failed 8 times to comply. Ignorance of the rules is not an excuse- but rather than delete BOTH of your threads I elected to leave the other one and throw a warning in there to help you assimilate AND, I thought the conversation was interesting and might lead someplace. (I was right- and rather than telling us that we delete posts that report bugs- perhaps you should thank Ryan for spending his friday evening trying to validate your post... See? No reason to be paranoid here...)So, bottom line: Act like a reasonable person and we'll treat you in kind. Act like a self important pompous putz- and we'll just delete/ignore.Now- as to your post here: Your understanding of VNAV logic and what our VNAV logic is accomplishing are not accurate. (There is always danger in being so specific in your wording...) All the same, I'll have one of the fellows take a look at your report- and if he is able to weed through all of the insults in your post without growing tired- we'll see if we can't figure out why you are seeing something that appears incorrect to you.Who knows- it might actually lead someplace! (See? No reason to be paranoid here....)

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(MODS, I know you deleted my previous thread about this because I didn't 'sign' my post, so I'm going to sign this three times which is hopefully enough -- but really you and I know you deleted it because you don't like bug reports.
Gabe, I'm pretty sure you have something valuable to add to this forum, like your previous topic for example in regard to the FMC peculiarity. I too see that issue and am grateful for your input.However, you need to take a step back, and refrain from accusations. PMDG do have a policy in regard to signed posts. It's existed on this forum for a long time and is nothing to do with the topic of conversation, or bug reports. Do a search and you will see that PMDG are keen to fix bugs when they are identified, and verified.Re the pitch issue...The only pitch issue I have seen, is in the 600/700, in regard to takeoff. If My speed doesn't match the bug speed before I engage the autopilot, then rather than a smooth pitch change when the AP is engaged, I see a sudden jerk up in pitch.

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Martin-I've seen this aggressive pitch change in the 600 and 700 as well. Obviously, good operator technique dictates have thing airplane in trim and stable- as you suggest. That being said, we are going to see if we can get some data from the sim to see if the airplane responds as aggressively in this circumstance- perhaps it will lead to adjustment. Perhaps it won't.. hard to say at the moment.

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Thanks Robert, very much appreciated. smile.png By the way, is the following worth investigation...

In the real aircraft gear would give you more drag than that and the engine goes to app idle AFTER 3 green lights, not when gear is commanded down like in the NGX.
Sorry to add to your workload.

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Martin-No. The drag value is based on official values already...The approach idle was tweaked some in SP1 based upon a review of data from the simulator. Our contacts up at test flight agree with the SP1 version as it stands now. (You will notice I am not taking a position... I am trusting the experts here.)We've gotten feedback from a number of NG crew- and their feedback is rather "goldylocks." (Too little, too much, just right, in even quotients...)

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I have noticed that the B737NGX can pitch up aggressively sometimes I have started (ish) to work out when it’s most likely to happen so I sometimes switch off VNAV and set the climb speed myself – this is something that I have seen pilots do at the airline I work for, I shall ask them if they do it for the same reason.I guess like so many aircraft the Boeing 737 can have a lot of spare power, especially when there is a lighter load but I do agree there should be something done to stop this fantastic little aircraft from trying to climb like the ‘Space Shuttle’!Kimberly Richmond-Jones Angel.gif

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I have noticed that the B737NGX can pitch up aggressively sometimes I have started (ish) to work out when it’s most likely to happen so I sometimes switch off VNAV and set the climb speed myself – this is something that I have seen pilots do at the airline I work for, I shall ask them if they do it for the same reason.
When do you find it normally happens Kimberly?Do the pilots at your airline switch to FLCH or VS?If it's climbing too fast, you can always switch to CLB2 of course.

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Just one observation in this...the minimum rate of climb or descnt. Is my understanding that 500ft is the minimum rate that should always be commanded in order to comply with atc. And thus the autopilot should always command this even when it's pitching up or down to adjust speed. I too have noticed a levelling off on times. From my side of the world I generally always observe a a slow down in climb as acceleration occurs, but not as significant as is seen in the ngx, likewise for descent. So there may be some value in the ops post regarding pitch and speed.

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I have to agree, just as I was reading this in a VNAV climb. For no real reason it thrust the stick back and the aircraft shot up to 2500 fpm. This seems to happen in turbulence and may be the pitch variant of the roll problem in turbulence. I've got the roll problem fixed with FSUIPC but the reaction in pitch would make all the PAX never want to fly with me again. No wonder why the random load gives me so few!I to would like to get to the bottom of this one.

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Original PT/BRCreio que consegui entender o que estão falando, o afundamento, ou levantamento abrupto do nariz quando alteramos VS.Talves seja o caso de iniciar a modificação da atitude de neutra para positiva ou negativa de uma maneira mais progressiva.Bem, me desculpem se não for esse o problema, tenho grandes dificuldades de comunicação, os tradutores nem sempre funcionam como desejamos.Uma certeza eu tenho, nenhum passageiro abriu a porta da cabine para jogar o saco de vomito em mim !Translated by GoogleI believe that I could understand what they are talking, subsidence, or abrupt withdrawal of the nose when we change VS.Maybe the case is starting to change the attitude of neutral to positive or negative in a more progressive.Well, excuse me if this is not the problem, I have great difficulty communicating, the translators do not always work as desired.I have a certainty, no passenger opened the cabin door to throw the bag of vomit on me! LOL.gifJoão Alfredo

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I have noticed this, but in my case it only happens when 1)I have realistic autopilot turned off because I have just cleanly reinstalled the Ngx, and the plane isn't properly trimmed or 2)when I have real weather chosen in FSX and the wind suddenly changes direction (since I don't have fsuipc). But I don't think a real ng would be faced with these condition anyway.

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Yes, I think some of you are experiencing the sudden wind shift issue. Which is an FSX bug, nothing to do with the NGX.The registered version of FSUIPC fixes the issue. Wind smoothing set, and turbulence suppression on.This isn't the issue I was talking about.

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Sorry, I'm still blinded by how marvellous this product is, and that's in light of the fantastic other products PMDG has produced before it!!! It is after all a non-professional, personal PC based application, not a $25M tool for airline pilot training, not to degrade the superior attention to detail PMDG has obviously invested. I've spent over 25,000hrs on FS (often to my chagrin) and the NGX takes the cake thus far!

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Yes, I think some of you are experiencing the sudden wind shift issue. Which is an FSX bug, nothing to do with the NGX.The registered version of FSUIPC fixes the issue. Wind smoothing set, and turbulence suppression on.This isn't the issue I was talking about.
Well ... not quite.I'm running ASE and registered FSUIPC with wind smoothing and turbulence suppression. If you don't disable turbulence in FSX, you'll still get turbulence effects which will cause the NGX to pitch up and down occasionally, producing vertical speed changes of 2000-3000 fpm.It is probably necessary to disable turbulence in FSX too as it was written by some guy on these forums.Bad thing is: your flight will then be boring since there's not going to be *any* turbulence effect.So: either put up with the pitching up/down (which can be minimized, but not totally removed), or face an overly smooth flight at all times.

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Well ... not quite.I'm running ASE and registered FSUIPC with wind smoothing and turbulence suppression. If you don't disable turbulence in FSX, you'll still get turbulence effects which will cause the NGX to pitch up and down occasionally, producing vertical speed changes of 2000-3000 fpm.
It works with REX weather Dave.FSUIPC works perfectly for me in combination with REX weather.I haven't disabled turbulence in FSX.I never get the 2000-3000 fpm issue you do. However, despite having turbulence suppression on in FSUIPC... I still get some turbulence.Have you looked at the thread on the forum, regarding FSUIPC and ASE settings? It's obviously a lot more complex with ASE than REX weather.I do have ASE but not installed, i think I'll stick to REX weather then if ASE is so naughty.
So: either put up with the pitching up/down (which can be minimised, but not totally removed), or face an overly smooth flight at all times.
Nope, not for me with REX and FSUIPC.I have wind smoothing at something like 8 seconds per knot as I recall, and turbulence, variance and gusts suppressed.

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Here's a screenshot I made that illustrates this bug:wuforq.jpgNote a 4200 fpm climb at FL320! This is on autopilot in VNAV, plane loaded with passengers and fuel. It's trying to bleed off a mere .03 mach and it pitches way up from about 1300fpm to 4200 (actually I saw it go to 4800 briefly until it "stabilized" at 4200).This just isn't realistic. Yes, it can certainly "physically" achieve that by yanking back on the yoke, but the r/w 738 autopilots just don't behave that way. Please, PMDG, show this to a r/w pilot and he'll verify they never see 4200fpm climb rates at FL320.(To reproduce this:1. Plan any flight, say 75% pax and cargo loading, 20K lbs fuel, and climb to FL390 at normal FMC speeds (probably achieving mach .78 once transitioning to mach)2. Around FL320 hit SPD INTV and dial in .75 mach to simulate the very realistic ATC command to "reduce speed to mach .75 for spacing."3. Note the autopilot pitch up...way up...in a high g climb (I calculated on the order of 1.5-2g's just counting seconds and change from 1300fpm to 4800fpm over about 5 seconds).4. Note the unrealistic climb rate while it attempts to IMMEDIATELY bleed off all of .03 mach!The correct behavior should be that it uses more throttle than it currently does, instead of pitch, to achieve the desired airspeed. It's mainly to keep g forces on passengers (and stress on the airframe, I'm sure) to a minimum.)

Just one observation in this...the minimum rate of climb or descnt. Is my understanding that 500ft is the minimum rate that should always be commanded in order to comply with atc. And thus the autopilot should always command this even when it's pitching up or down to adjust speed. I too have noticed a levelling off on times.
In the U.S. for turbojets it's 1000 fpm. This is because around the world really, ATC uses what's called the "vacated altitude rule" that once an aircraft has reported or is observed out of an altitude, another aircraft below or above may be assigned that altitude. That falls apart if aircraft were allowed to level off anywhere (say, 100 feet above their previous altitude, like this autopilot sometimes does). That's why you're not allowed to level off in your climb, unless you get explicit permission (or it's something obscure like a cruise clearance or a block altitude).PMDG needs to fix the VNAV code to limit it to a minimum climb of 1000fpm (if aerodynamically able, of course), and in a non-crossing restriction descent (where you are in fact allowed to level off) there also needs to be a minimum descent rate of 1000fpm.Plus of course the original point of this thread, the change in climb/descent rate needs to be clamped to a maximum g force, whatever the real autopilot limits it to (1.1? 1.2?). Pulling 2g+ climbs like I've seen with this just isn't realistic.Just some constructive ideas for SP2 I hope!

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There is no needing to reproduce it, it happens quite frequently also to me for example and I share your thought it is not real even if I am not a real pilot.I would add, I had few times a 6000 fpm under normal circumstances but just for few seconds.I ended up stating that that flight was a part of the Shuttle training program, no problem therefore.-

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Are you totally sure about the 1000fpm rule? That's quite a rate to comply with for all stages of flight...in all jet aircraft.in the uk it's 500fpm

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Are you totally sure about the 1000fpm rule? That's quite a rate to comply with for all stages of flight...in all jet aircraft.in the uk it's 500fpm
Hmmm, no I'm not sure. That's just what I was trained (rw controller in US) but I looked into it: In our "airman's information manual" at http://www.faa.gov/air_traffic/publications/atpubs/aim/Chap4/aim0404.html section 4-4-10(d) it does say to advise ATC if unable to keep 500 fpm in the climb. That's not legally binding, but pilots here do tend to follow that. So it seems to be 500 fpm here too.I guess from an ATC perspective we just never expect or see 738's go below 1000fpm until they're just about to their cruising altitude. And I've never seen them level off like this sim does when assigned a faster speed, ever. And I've never seen any B738 go above 2,500 fpm in normal climb. The fastest climb rate I ever saw in a commercial jet was 4,000 fpm in an empty B747-400 in 1997. It was on a repositioning flight and I guess the pilots just wanted to try it out. I've never seen a B738 do anything like that above 10,000 feet, though, ever. And yet climb rates like that seem pretty common with this current version. When I'm online, I always click off the VNAV after 10,000 and dial in a more realistic V/S rate so the online controllers can expect something more real-world.

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Flew from KRAP to KMSP today and had VNAV armed on takeoff. When I reached 1500 AGL (I had 10 degrees nose-up climbing at 2900 FPM) I engaged the Autopilot (CMD A) and the aircraft immediately pitched up another 10 degrees and ascended at 4600 FPM for about 10 seconds then settled back to around 3200 FPM. This happens on just about every flight unless I fly it up to 10000 by hand. I don't have a problem with steep descents - only climb. I am using ASE with registered FSUIPC and SP1.

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It works with REX weather Dave.FSUIPC works perfectly for me in combination with REX weather.I haven't disabled turbulence in FSX.I never get the 2000-3000 fpm issue you do. However, despite having turbulence suppression on in FSUIPC... I still get some turbulence.Have you looked at the thread on the forum, regarding FSUIPC and ASE settings? It's obviously a lot more complex with ASE than REX weather.I do have ASE but not installed, i think I'll stick to REX weather then if ASE is so naughty.Nope, not for me with REX and FSUIPC.I have wind smoothing at something like 8 seconds per knot as I recall, and turbulence, variance and gusts suppressed.
I have pretty much the same settings and oriented myself along one long thread in this forum talking about ASE/FSUIPC weather settings.It works pretty well, but I do get these oscillating decents/climbs which the OP talks about. Even when there's no wind indicated.I suspect it has to do with the speed bug shifting around at certain speeds, adapting to pressure, temperature or whatever conditions that get injected by ASE, and the NGX autopilot reacts violently towards these changes, chasing the speed bug by altering pitch.I'd definitely like to see a resolution for this issue.

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