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Guest David Ketchum

747 FSX - Power setting surging in cruise w/autothrottle

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Hi,With the latest update to the FSX 747, I'm noticing that with autothrottle engaged that engine power setting constantly surges up and down during cruise. I had orginally attributed this to FSX's goofy interal real-world weather logic (or lack thereof), but then tried it in calm/clear conditions. The problem does not seem to be related to wind. Also, I disconnected my USB throttle quadrant to make sure it was not the source of the problem and it still happens without it being attached.Specifically, the autothrottle does not seem to be able to find a power setting that results in constant mach number at alitude, and seems to spend the entire cruise portion of the flight searching for a power setting it can never find. Up and down, etc, never staying the same.I do get a stable Mach number cruise, it's just that the autothrottle has to yo-yo up and down constantly to maintain it. Has anyone else noticed this on their installation?I have the latest 2.10 update installed and I have also run the Flight1 registry repair toolThanks!-David Ketchum

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David,I notice you replied to my post from a while back about this. I was hoping the service pack would fix the issue but it doesn't seem to have.It seems like the autothrottle logic is slightly flawed -- when the plane is going too slow the throttle increases to speed it up, but it doesn't pull back until the speed has already reached the target speed. But because it takes a few seconds for the thrust to drop in response, the plane keeps accelerating to a few knots over target speed, which means that the throttle then has to pull back to slow down again, and so the cycle continues.The LevelD 767 (the only other payware airliner I have to compare this with) doesn't seem to have this problem; it finds a stable thrust setting pretty quickly after reaching cruise.Colin

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Hi Colin,I concur 100 percent with your observations, and as I mentioned in the other post experience the exact same thing. You are not alone. :)I wonder if anyone else will chime in with the same problem? This would help identify a problem with the software itself and make it more visible to PMDG hopefully.I will make a video of this phenomenon and post on Youtube later today to illustrate what's happening in hopes that perhaps PMDG can take a look at it. -David

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i too have noticed this but what with the other problems regarding heading select i am experiencing i have not mentioned it for fear of overloeding the forum with issueskav

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i may add that i see the exact symptoms you have deicribed here but also there is a slight porpoising effect too as the surging has an affect on vert speedthe surging is not always present but the other day the autopilot was not capable of correcting it i had to disconnect and hand fly the aircraft to correct the bouncing by thinking ahead insted of the deleyed auto throt reaction you have described. only then did it smooth outkav

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Just to add my two penny {cents} worth. I have seen exactly the same problem since I installed the FSX update.John Rooum

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Im getting a similar problem, with the throttle constantly twitching up and down during flight.

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Add me to the list for the surging; it's not extreme, but noticeable.However, last night I did experience a strange behavior while cruising at fl325 in a loaded F. Suddenly engine 3 indicated an overspeed warning (not sure of the exact title, thrust on all four reduced, and the FMC popped up stating a max FL of 155....? After reducing alt and babying #3 back in line I was able to climb back to 325 and continue. However, the FMC continued to complain about max of 155.Note- this was with failures disabled in fsx.

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Add me to the list for the surging; it's not extreme, but noticeable. However, last night I did experience a strange behavior while cruising at fl325 in a loaded F. Suddenly engine 3 indicated an overspeed warning (not sure of the exact title, thrust on all four reduced, and the FMC popped up stating a max FL of 155....? After reducing alt and babying #3 back in line I was able to climb back to 325 and continue. However, the FMC continued to complain about max of 155. Note- this was with failures disabled in fsx.
I have the same problem as wellGuthrie Zuehlke

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Hi, On the max alt warning, just press VNAV twice. And I also experience the surges in thrust @ cruise. Andrew Christe

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Still happens...is there a fix besides buying FSUIPC @$60 when I do not need it otherwise?It must be stressed that this problem does not happen, ever, with my LDS 763.IMHO that is a dangerous situation in need of immediate attention.Because, obviously, which product am I more liable to fly?Not trying to be snarky but just because this product has been out a while does it mean support for it is abandoned?Thanks.

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I have this problem as well. It's really the only troubling issue I have with the PMDG 744. This behavior only occurs when VNAV Mode is enabled, both during cruise and descents. Oddly it doesn't happen during the climb phase. I recently got back into flight simming and am using the PMDG 744X in FSX SP2 on a Dell XPS 720 H2C running Windows 7 x64 RTM. If this one issue with the Queen could be resolved it would make this combination nearly unbeatable. Suggestions welcome...Doug

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Doug, this old thread actually hints at several different symptoms.Is your indicated airspeed changing rapidly? Does it happen with no weather selected (clear all weather)?Or, are the throttles constantly moving back and forth? This is just an animation, doesn't affect flying.

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Doug, this old thread actually hints at several different symptoms.Is your indicated airspeed changing rapidly? Does it happen with no weather selected (clear all weather)?Or, are the throttles constantly moving back and forth? This is just an animation, doesn't affect flying.
I get that hunted feeling too, with the thrust levers flapping back and forth. I agree with Dan, that it's probably purely cosmetic, but it does look a bit disconcerting. I confirm that the IAS is not (for me anyway) hunting - just the thrust levers; Oh yes - and the yoke too, though less frantically.

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Doug, this old thread actually hints at several different symptoms.Is your indicated airspeed changing rapidly? Does it happen with no weather selected (clear all weather)?Or, are the throttles constantly moving back and forth? This is just an animation, doesn't affect flying.
Hi Dan... thanks for responding. I fly with the default FSX "clear" weather since my experience with third party weather apps has been a bit disappointing. This "porpoising" occurs at all cruising altitudes and is manifested by oscillating IAS (+/- 10 knots or so), altitude fluctuations (+/- 100 feet or so), with the throttles and yoke behaving as would be expected for the situation. This only occurs with VNAV enabled. VS and FL CH modes are quite solid. The Queen just can't seem to hold a steady altitude or follow a constant descent path in VNAV. This has always been the case with this aircraft since I've owned it. This does not happen with other third party aircraft in my stable.Thoughts?Doug

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It is not normal. She should be realistically solid in VNAV, as solid as without VNAV flying on MCP control for SPD and ALT. Maybe a screen shot would help.

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It is not normal. She should be realistically solid in VNAV, as solid as without VNAV flying on MCP control for SPD and ALT. Maybe a screen shot would help.
Dan - the numbers I used in my post above were from memory and turned out to be quite exagerated. It's interesting how far off I was in my judgement from what the numbers actually are. I did not have time to prepare the screenshots for posting so I'll post them tomorrow. In the meantime I will provide corrected numbers from a brief flight this evening. IAS only fluntuates 0.5 knots, and this is a constant cycle. Altitude varies +/- 20 feet, and this is a constant as well in unison with IAS. The "porpoising" is steady and continuous with the throttles and yolk joining in. This can't possibly be correct behavior since it is clear the Queen is hunting for the sweet spot and just can't settle down. Again, this also occurs during descent in VNAV. Screenshots tomorrow...Doug

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I too am having this issue in FSX. With clear skies(no weather) at cruise the aircraft bounces +/- 20ft from assigned altitude. I'm actually afraid to try it with weather! For me this is happening while in VNAV or SPD/ALT modes. I'm not buying the "the autopilot is just that sensitive" excuse because if that's the case then it's modeled incorrectly. I sincerely doubt that the real autopilot has this flaw. Has anyone managed to resolve this?I'm kind of disappointed in this version of the 747. When it came to FS9 I swore by PMDG but since moving to FSX I've had nothing but trouble. I'm kind of disappointed I spent all this money to upgrade everything.Bryan Smith

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I too am having this issue in FSX. With clear skies(no weather) at cruise the aircraft bounces +/- 20ft from assigned altitude. I'm actually afraid to try it with weather! For me this is happening while in VNAV or SPD/ALT modes. I'm not buying the "the autopilot is just that sensitive" excuse because if that's the case then it's modeled incorrectly. I sincerely doubt that the real autopilot has this flaw. Has anyone managed to resolve this?I'm kind of disappointed in this version of the 747. When it came to FS9 I swore by PMDG but since moving to FSX I've had nothing but trouble. I'm kind of disappointed I spent all this money to upgrade everything.Bryan Smith
I have not seen the porpoising that is being described, but I do experience some movement in all aspects of flight across all of the add-on aircraft I have. The models are simulating movement in an air mass so the aircraft's attitude should not be constant. In my R/W experience aircraft are never at a constant altitude or heading on autopilot. There is always some movement. +/- 20ft and .5 knots is a very small margin of change. :(

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Bryan, does this also happen with clear weather (no weather) is selected?By the way, +/- 20ft , if done slowly, is actually a good lock on altitude especially at higher flight levels. Real airplanes do it, but you are right in that simulators seem to act like they are on steel rails and everyone expects "precision."

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I guess we'll just have to agree to disagree then... all I know is I shouldn't be getting seasick from watching the horizon (out the windows, not the PFD) when there is no wind. when I say bounce I mean bounce. a full oscilation from bottom to top to bottom again takes about 8 seconds. Makes me feel like I'm crab fishing with the guys from deadliest catch lol.Yes this is with the clear skies weather selected. that is 0 wind at all altitudes and a constant barometric pressure of 29.92 at every weather station. 0 clouds. absolutely nothing but a huge planet sized mass of dead still air.... Sorry if I sound frustrated I just remember that the FS9 version didn't do this. I guess I'll just have to invest in some Dramamine if I ever want to fly this bird in FSX again. Does the MD11 do this as well? I was contemplating buying it but if it bounces around too I guess I'll just have to stick with my 767. That or go back to FS9 :( Bryan

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Does the MD11 do this as well? I was contemplating buying it but if it bounces around too I guess I'll just have to stick with my 767. That or go back to FS9 :mellow: BryanFrom my experience with the Md-11 over many months there is no bounce but the N1 reading goes through periods during cruise when it fluctuates (75 - 85%). Graphically the throttles move back and forth and the fuel flow is correspondingly up and down. It realy would be nice to get it fixed. Peter.

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