747 FSX - Power setting surging in cruise w/autothrottle

[Guest angelsonefive]

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.

[Sartanius 399]

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

[downscc 1,327]

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.

[Sartanius 399]

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

[Guest Betabry]

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

[falcon999 24]

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. :(

[downscc 1,327]

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."

[Guest Betabry]

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

[plowry 0]

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 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.

[Daniel choen 23]

same problem here, is there any solution?Daniel.