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lonewulf

odd behaving of PSS fly-by-wire

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Hi all. Did someone (besides me) notice that elevator trim is working when flying manually? :-hmmm I was really kind of shocked when I noticed that. And it does on all types, be it A320 or A330. THIS IS COMPLETELY WRONG!! There are no trim buttons on any sidestick! There is always autotrim as long as you are in normal law.Besides that: is there any fix/update planned for the very poor behaviour of all Airbuses when flying manually in FS2004? I remember that in FS2002 it was much smoother. In FS2004 it is almost impossible to manually follow flight director commands. In FPV it's ok.Oskar

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Guest Phoenix_7

fly-by-wire is not possible in FShave you tried the alternate FDE files provided by Bob Scott, see the message pinned at the top of the forumJohn PSS SUPPORTsupport@phoenix-simulation.co.ukhttp://www.avsim.com/pss/phoenix.jpg

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Guest jmf

Hi John,Nothing is impossible ;)I did a quick experiment with a gauge I created and managed to come up with a reasonable fly-by-wire system. I believe that with more work it is possible to implement a realistic fly-by-wire systems for the airbus or any other plane.The idea was to use a series of PID controlers to control bankrate and g-load. Aft and forward stick selections allow selection of a g-load. Neutral position results in 1G. This means that if the stick is left neutral the plane will maintain current attitude, ie, either maintains height or current rate of climb/descent. Left and right stick selections will result in a given bankrate. If neutral then bankrate is zero and current bank is kept and that includes any bank between -30 and +30 degrees (that includes leveled wings). If bank is outside these limits then upon release of the stick bank is returned to within these limits.With this very crude system the general hand flying feel is much improved. The only aspect that doesn't work perfectly is the g-load controller which has some trouble in keeping the plane at the same height when stick is neutral and climbrate is zero. But this can be improved. Also I am not entirely sure of the logics of the airbus fbw when the plane is turning. Does it keep the height or does the pilot need to select a g-load factor to stop it going down?This has been originaly tested on a default FS plane and does not work with the PSS since there will be conflicts between the controlers and the PSS systems. However there seems to be potential!!A proper FBW system would be a revolution in FS!!Cheersjmf

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Well, I'm not sure what we are talking about now..:-) I'm simply complaining about the bad handling characteristics in manual flying. Interestingly flying with FPV results in almost perfect fly-by-wire behaviour. With FD however - especially after T/O - it's almost impossible to keep a more or less constant pitch attitude as autotrim is not or only veeeery slowly working. The only remedy is actually put in some trim (which really hurts me....)Unfortunately I don't have FS2002 anymore on my machine but I'm almost 100% sure that it was much better there. Maybe some of the flight guidance characteristics have changed within the two FS generations so it would need some redesign of the flight model by PSS.BTW it sounds a bit strange to me that PSS people simply answer that fly-by-wire would not be possible in FS!! I'm afraid they don't even know that it actually is kind of implemented. It would just need some improvement.Oskar

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Guest jmf

LonewulfIt is very simple actually. Fly-by-wire is simply not implemented in the A330/340 series and probably all the PSS airbus products. There is only a few of the flight envelope protections but that is about it. If I am not mistaken, this is acknowledged somewhere in the A340 documentation.I didn't say it was easy to implement such system, but it is not impossible!If you do a google search on FBW system you will find out lots of information about this topic.What I tried to describe was a possible implementation of a simple FBW system for the PSS airbus series. This would allow more realistic hand flying characteristics. In very simplistic terms, in FBW aircraft, the stick does not control the flight controls directly. The stick allows the pilot to control bankrate (ie rate of change of bank angle) and g-load (ie g-force accelaration). In other words, the pilot selects how fast he wants to bank the plane and how fast he wants to go up or down. When he wants to stop turning and/or stop going up/down, the stick is left neutral. In order to achieve this, several computers transform the stick inputs into the required flight surfaces deflections that result in the required performance (ie change in bank and change in g-force). And I say again, I wish one day PSS consider implementing such system.Cheersjmf

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ok ok :) Thank you for your extended explanations about FBW. In fact I'm a retired Airbus Captain with some 6000+ hours on A320/330 ;-) When I first purchased the A320 I was quite impressed on how the "pure flying" part was implemented i.e. autotrim, stable bank when releasing the stick (roll rate zero..). I am still convinced that it was performing better on FS8 than on FS9 I only wish I could verify that. I was of course not so impressed when I noticed about the missing envelope protection although some of the features like "alpha floor protection" was showing up including "thrust lock".IMHO it is not so important how you model the FBW concept. If you can do it based on the true issues as you properly described for g-load in pitch axis and roll rate in roll axis that's even better. It can't be that hard to implement at least the pitch limits, AOA limits, bank limits of 33/66 degrees etc. All these factors ARE PRESENT in the flight dynamics model of FS. I consider this as a very weak point when it comes to advertising the PSS Airbuses.Flight Guidance, FMGC usage are nicely implemented so why not do some homework to REALLY make the Airbuses a bit more than they are now. It's this attitude towards the customer which is quite embarrassing. It's kind of an "we made it and it's perfect. Take it or leave it" attitude that should be corrected. There's soo much to be improved. So why not do it?Oskar

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Guest godinhoc

Humm Interesting the gauge, that you are implementing.Are you thinking put it available ???Kepp in touch about your progress.Regards Carlos GodinhoTAPVirtualLong Range Fleet

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Guest vrandar

Whatever the limitations with the A320/A330/A340 family, PSS have made it clear for a long time that they will not be issuing patches or updates, however often we ask or however much we want them. There is much that could be improved and I'm sure they could do it (as could a number of us if they would sell the code). But it is probably not commercially viable for them to do so as they would have to charge us again - and possibly more than we paid first time round - for these updates and that would be unwelcome in the FS community, would probably not generate a profit but would generate a negative backlash.

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Guest Phoenix_7

the reason is quite simplewe are a small company and do not have the resources available to go back and update a 3 year old productJohn PSS SUPPORTsupport@phoenix-simulation.co.ukhttp://www.avsim.com/pss/phoenix.jpg

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Guest jmf

Hi lonewulf,duh ..... ;)There was actually a small chance that my assumption was right (ie, you didn't know what fbw was). In any case I tried my best to clarify both issues. I have to admit that I don't know all the details of the fbw real implementation.However from the little I managed to learn I could come up with a reasonable system for FS that did the trick.I am not an expert on the air files but I thought that it just models the flight dynamics and it does not implement the various controllers such as the autopilots etc. But I maybe wrong on this one.What basically I tried to do was to overide the stick inputs, ie, prevent them controlling the flying surfaces directly but read those inputs to derive the demanded performance in terms of bank and g-load. I then generate the required movements on the flying surfaces to achieve the required performance. That was implemented with a series of simple PID controllers. The greatest problem is to derive realiable methods to measure bankrate and g-load signals required for the controllers. These are noisy and there is limited computing power to clean them up. Also you want response time to be reasonable.Of couse that this does not work with the PSS buses because of a conflict with their own gauges. I understand that it is not comercially viable to support products forever but it is always possible (and advisable) to accomodate some requests to keep costumers happy. Perhaps some sort of cooperation could lead to a solution to this fbw "saga". There must be a way to override what PSS does to the flight surfaces when the AP is off.Cheersjmf

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Guest jmf

Hi Carlos,I kept quiet so far as I didn't get far. It was just a proof of concept but not very usefull at present. Actually this happened some time ago and I have to acknowledge some help given by our "own" guru Jose Oliveira.I have very little time (=none) at present (present = past few years :( ) and had to abandon the project for the time being. However without some more information from PSS there is little I can do to push the idea forward anyway.1 abra

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