Autopilot parameters

[LAdamson 240]

>I think you may be a bit optopmistic about how easy things are>to correct. I have been following the development of X-Plane>and Flight gear, and all I can say is at least the autopilot>works in FS9, if not perfectly. In X-Plane there are a lot of>autopilot issues (normally flakey), and in FlightGear, there>was none (as of the last release I looked at).>>I don't know if you followed the development of FS9, but the>team was not huge, and MS has never in the history of its>company realeased a polished, complete and bug free product>(nor on time). Not one. It is one of the reasons they are so>successful (even though on first glance it may seem to be>contrary to logic). >>They work on a philosophy of "good enough, now get it to>market". Their products are howerver always pretty and packed>with useless features which sells their product to the>uneducated, and for the most part, uncaring consumer public (I>don't mean that as an insult to my fellow humans, it is just>reality). It seems like MS follows the GM marketing philosophy>of the 30's: give them a cheaper car packed with more toys for>the same money as their competitor (GM soon outsold Ford, even>though in many respect their product was inferior).>>In the end though, FS9 is a game, not a Sim, and it makes no>claims to the contrary. It models many things far too>incorrectly to be considered a true simulator though it is>improving. (Even a brick will fly in MSFS).>>My opinion only, and I do understand your frustration (it did>take them a year to fix the huge, huge, huge memory leak that>should not have been present to start with).>>ShadWow, talk about opinions.... :D As being a Toyota pickup "truck" owner for 20 years, and witnessing the numerous problems of my son's Fords over the years, I ended up with one of those GM packed with "toys", Chevy Silverado Duramax's. Happily for me, it's been problem free for the 15 months I've owned it. If only my son could say the same! :) In fact, being as use to the Toyota product quality as I am, I'm pleasantly surprised just how well built & finished this GM vehicle is.Now that we've tackled the incorrectness of the Ford versus GM debate, I also disagree very strongly, with your claim regarding MSFS as only a game. "Games" as a rule don't come packed with real aviation data-bases, such as this one does. To the "un-educated, un-caring consumer.................there really would be no need.As to the philosphy of "good enough/get it to market", at least the "good enough" far surpasses the current "good enough" releases of X-Plane version 8, or perhaps FLYII (which as least has some valid reasons behind the problems).We are now so far off the topic of autopilots, that I can only add this. Always transmitted sentences of the Garmin GPSMAP 296 (NMEA 3.01) are GPRMC, GPGGA, GPGLL, GPWC, GPXTE, GPRMB, and switchables are GPGSA, GPGSV, GPWPL, GRPTE. As all of us aviation "experts" know, these NMEA sentences will need to be reduced for a minimum two second output required for the A/P interface. :( L.Adamson

[lonewulf 1]

Shad you are of course correct and I'm pretty well aware that FS2004 is a game rather than a Simulator. But OTOH I can say from my own flying experience that it is a really good game and in some respect very close to some kind of Simulator. It has every provison needed to come even a bit closer to "real" flying but the crucial thing is that some of these provisions are not accessible any more.Look, in that specific field where I was trying to gather some information - actually one autopilot and one autothrottle item - everything is working but it would only be a matter of changing some parameters to have it working as it should!! I think until FS2000 those parameters were accessible until somebody decided for any (unknown) reason that they shouldn't be accessible anymore.Think of buying a new car - a real fantastic one, the one you were dreaming of - but the manufacturer decided that it would only run in first gear! Although you know that there's a 5-speed gearbox the manufacturer just decided not to provide you with a gear lever. Wouldn't that leave you a bit frustrated although it looks great, runs smooth and the Airco is working flawlessly........?Of course I know that more than 90% of all issues of third party applications deal with visual effects, be it fantastic panels, well modeled A/C, photorealistic sceneries and MS did a great job on the wireframe to allow mutiple hot shot's to improve everything to the limit. But obviously nobody really cared about the A/C handling shortcomings although they could be improved quickly and easily. Obviously this is just lower priority at MS as only less that 10% really care for accurate A/C behaviour....So you see it's only this part which leaves me a bitter taste: I know it could be improved easily but nobody cares....How many of you did realize that on constant speed props the engine sound pitch still varies with the throttle lever (=power) position rather than with RPM ?!?! Had only one of the developer team ever been sitting in a C182 or similar he would know.......Oskar

[Guest iholrf]

>As being a Toyota pickup "truck" owner for 20 years, and>witnessing the numerous problems of my son's Fords over the>years, I ended up with one of those GM packed with "toys",>Chevy Silverado Duramax's. Happily for me, it's been problem>free for the 15 months I've owned it. If only my son could say>the same! :) In fact, being as use to the Toyota product>quality as I am, I'm pleasantly surprised just how well built>& finished this GM vehicle is.>>Now that we've tackled the incorrectness of the Ford versus GM>debate, I also disagree very strongly, with your claim>regarding MSFS as only a game. "Games" as a rule don't come>packed with real aviation data-bases, such as this one does.>To the "un-educated, un-caring consumer.................there>really would be no need.Actually, I was talking about GM's marketing philosophy in the 1930's... as stated in my post ;-) and which any automobile history buff will confirm as being completely correct.>As to the philosphy of "good enough/get it to market", at>least the "good enough" far surpasses the current "good>enough" releases of X-Plane version 8, or perhaps FLYII (which>as least has some valid reasons behind the problems).This is also well documented MS history. I was not passing jugement, simply stating reasons why things are not perfect and why things get broken. I may not be a 20000 hour airbus pilot, but I did spend many years of my life lately in game development and am somewhat familiar with the problems associated with getting a product to market.>>We are now so far off the topic of autopilots, that I can only>add this. Always transmitted sentences of the Garmin GPSMAP>296 (NMEA 3.01) are GPRMC, GPGGA, GPGLL, GPWC, GPXTE, GPRMB,>and switchables are GPGSA, GPGSV, GPWPL, GRPTE. As all of us>aviation "experts" know, these NMEA sentences will need to be>reduced for a minimum two second output required for the A/P>interface. :( Indeed we are.

[Guest iholrf]

I hear you, trust me, I do :).Shad

[Guest Ron Freimuth]

"autopilot">> Nor did they fix it in FS9. I have to wonder how much>>these MS guys really fly FS AC. They should have noted the>>problem before FS9 was released. A few people in the FS>Forum>>have noted the problem.>>>> Ron>>Youre exactly right. I think we have to deal with a main>problem here. As my background is purely flying (I'm a retired>airline captain) I am of course more concerned about oddities>in respect of dynamic behaviour of the flight model rather>than of scenery issues or shiny surfaces..:) >IMHO the FS developer team has a few shortcomings which are>not easy to define: Either they don't have competent>beta-testers or they simply ignore their inputs. Maybe also>the timelines are too dense for significant changes after>beta-testing. I figure the Flight Dynamics guys at MS are simply incompentent. Not necessarly those individual's faults. What can you expect when that part of the FS group is managed by people who I expect don't understand what skills those individuals need. Or, how to figure out if candidates know what they should. >There are a few real "stupid">errors/misbehaviours in FS9 (also in earlier versions) with>regard to the "real" flying world which - given the many>parameters involved in the flying model - could easily be>corrected. CFS2 had all the FD things working. Though the not generally used autopilot was messed up. Those FS guys generally damage as much as they fix in each new version. Flight Dynamics coding doesn't have to change like the grapics, ATC, etc does. So, why can't they get it right and leave it along? --- For one thing, it appears MS had the CFS1, then FS2K FD code done by an outside group. those MS guys don't seem to really understand a lot of stuff in the AIR file. They certainly don't bring out it's capabilities in their default AC. It's also my impression the FD group wasted a lot of time on things like 'FSEDIT'. Perhaps a good idea, but anyone who is familiar with FSEDIT knows it's worse than nothing. Even after some changes in FS9. If MS could hire an Oceanographer just to get the sea colors correct in FS2K, why can't they hire competent people to handle the FD? Probably because no one there really understands FD. If anyone does, he is probably stymied in getting things working correctly. How else can one explan stupid errors. Such as "Century of Flight" losing the 'prop on tail' effects. Especially bad considering that CoF has a lot of tail draggers.>So the simple question remains: Are they not aware>of the most simple issues of flying? Arey they just ignoring>any inputs to detected errors/misbehaviour? Or - most likely ->do they simply not know about some weak spots in FS?:-hmmm >Oskar I think MS got 'above it's head' in MSFS programming. People want more and more realistic simulation, and I don't think the group understands aircraft and aviation well enough to handle the task. Remember, MSFS' was originally done by Bruce Artick's group. Some people refer to the FS FD guys as 'Airheads'. It's not meant to be complementary. BTW, I've heard the MS FS guys 'hate me'. Wonder why. Ron

[n4gix 4,947]

>How many of you did realize that on constant speed props the>engine sound pitch still varies with the throttle lever>(=power) position rather than with RPM ?!?! Had only one of>the developer team ever been sitting in a C182 or similar he>would know.......I think what's more disturbing is that this is so in spite of the fact that many of the folks on the MSFS development team have their PPL and own aircraft!

[lonewulf 1]

> CFS2 had all the FD things working. Though the not generally>used autopilot was messed up.>> Those FS guys generally damage as much as they fix in each>new version. Flight Dynamics coding doesn't have to change>like the grapics, ATC, etc does. So, why can't they get it>right and leave it along? --->I fully agree. Why is nobody telling them? ;)> I think MS got 'above it's head' in MSFS programming. >People want more and more realistic simulation, and I don't>think the group understands aircraft and aviation well enough>to handle the task. Exactly my opinion too. But my guess is that it's even worse. It's that strange attitude that you can observe in many large companies (including MS..) which basically means "why should I improve it when I sell it anyway...."!!And when they set up a new version the literally EXPAND it's capabilities rather than IMPROVE it. > BTW, I've heard the MS FS guys 'hate me'. Wonder why.>> RonFit's exactly into what is said above, doesn't it? ;) Oskar

[Guest adameke777]

Ron> I think I got some comments from someone else on setting the>'derivative limit' to 45 to 90 degrees in that aircraft.cfg>file -- so it is active when one isn't close to the VOR>radial. Having the I & D boundaries set as per default MSFS aircraft.cfg will cause weird behavior as the I & D components become active (by common sense, you might expect an abrupt change in control). I set my I & D boundaries to 180, so all three components are active at all times.This, however, requires adjustments in coefficient values which have to be discovered by trial and error.> The real autopilot is in sim1.dll. The panel gauges only>control the inputs to it. FSUIPC 3.44 (and up) give access to autopilot variables.Adam

[Guest iholrf]

Hmmm, in one reply, you seem to take exception to my statements about why MS has problems with their product, but then on this post you seem to not only agree with them but have taken it to the point of some sort of personal frustraition. All I can say is:Its a game. Why in Zeus's name would you let any of this bother you? I have far more important things to invest my emotional reserves on.Besides, there are still parts of FS9 that quite frankly amaze me. Its a fine product with many things going for it. My complaints were directed more to those who, like me, want to make their own stuff, then release it to the public with "shiney surfaces and dynamic wing view" when they don't, have a decent panel, or perhaps ther is no VC or, on many AC even tankage is not right. There is one AC out there that is very popular with simmers. A large piston twin transport. It has a nice model, decent enough panel, and many textures, but the plane was about 1/10 th correct wieght, 1/3 the power, the wrong engine type, and had 200gals of fuel in two tanks and when the "gargo" area was loaded it fell on its tail. It took me about ten seconds to google for the correct values for this AC type (3500 hp per eng, not 1400, 2300 gallons of fuel, not 200, 79000 max take off, not 26000 etc.). So why did the person who released this to the unsuspecting public not bother to check these things him/herself?It is this type of thing that bugs me. Not the fact that a small, deadicated but imperfect team put out a not so perfect, yet still stunningly beautiful and thoroughly enjoyable game. Now, in all fareness, I do come from the Open Source world, where the motto is, fix it yourself or shut up. So, those things I can fix, I have; those things I can not, I am learning how to; the rest of the time, I am going to enjoy it. :)Shad

[Guest iholrf]

oops, this should have been a reply to Ron's reply to my ... err ... reply. :0Sorry Oskar, my bad.Shad

[Guest Ron Freimuth]

>Ron>>> I think I got some comments from someone else on setting>the 'derivative limit' to 45 to 90 degrees in that aircraft.cfg>>file -- so it is active when one isn't close to the VOR radial. Was that you, Adam?>Having the I & D boundaries set as per default MSFS>aircraft.cfg will cause weird behavior as the I & D components>become active (by common sense, you might expect an abrupt>change in control). Professionals typically use MathCad to model an autopilot system. With expensive AC simulation software linked to MatchCad. I suspect the old REC 1199 has parameters based on real autopilots. >I set my I & D boundaries to 180, so all>three components are active at all times.>Adam I think it makes sense to bring in the I FB only when close to the set point. Since one can live with slower dynamics, but get the advantage of zero long term error. One might bring in the D FB some distance before the SET point. That means one only gets the damping when it's more important: as the AC has to turn correctly toward the VOR/ILS without a lot of overshoot. "Less Stiff" control also is desirable when there is turbulence. I've worked with a lot of electronic FB systems, but never used adaptive gain control. JSBSIM (used in FG) allows one to set general control blocks for its AC. In fact, the last 'Back of the Envelope' Newsletter has some info on PID systems. I suspect the Gain Constants settable in FS9 aircraft.cfg are consistent. That is, they follow the standard. They 'appropriate' P, I, and D gains should only need to be adjusted a bit for a range of similar AC. I DL'ed the Jan 2005 "Flight Gear". I can see the autopilot gains need some adjustment. Many of jets are less stable in ALT hold than MSFS. ;) HOWEVER, that's just a matter of details, not a fundamental problem.>This, however, requires adjustments in coefficient values>which have to be discovered by trial and error. They can be set by analysis if one understands the system dynamics. Something I hope to do someday. Though, engineers usually make final tweaks in calculated settings. It seems to me a simple set of XML macros for P, I, and D would make it easy to configure more general control in XML gauges. Just stick the Macros in the right order in an XML 'autopilot' gauge. The VOR/ILS and GS lines in aircraft.cfg may work OK when set optimally, ALT hold doesn't have the adjustments I need. While SPD control is lousy and there is no real Yaw Damper. It appers the 'yaw_damper_gain' setting doesn't work correctly. Ron

[Guest _ak]

Very interesting notesRon, is there any formula that can convert IAS to CAS or vice versa on any altitude/speed?

[Guest Ron Freimuth]

>Very interesting notes>Ron, is there any formula that can convert IAS to CAS or vice>versa on any altitude/speed? Yes, but it's complicated. Involves compressability and other effects. Herve' Sors figured it out for AFSD. EAS is virtually CAS at lower speeds and is fairly easy to calculate from XML variables. One uses (Rho/2) * TAS(ft/s)^2 Rho is density relative to SL. So, it is equal to (density, slugs per square ft)/ 0.002376 While TAS is best calculated from Mach Number at 15 C multiplied by (sqrt Theta) (Theta is outside Temperature in K divided by 288.17 K, 273.17 + 15 C). CAS from TAS involves a big nest of Theta's, etc. Incidently, the FS variables are generally exact to five digits or more.Ron

[Guest Ron Freimuth]

>> CFS2 had all the FD things working. Though the not>generally>>used autopilot was messed up.>>>> Those FS guys generally damage as much as they fix in each>>new version. Flight Dynamics coding doesn't have to change>>like the grapics, ATC, etc does. So, why can't they get it>>right and leave it along? --->>>>I fully agree. Why is nobody telling them? ;) I had to ask beta team members to get a list of bugs I knew of to MS during the FS2K2 test. One or two got fixed.>> I think MS got 'above it's head' in MSFS programming. >>People want more and more realistic simulation, and I don't>>think the group understands aircraft and aviation well>enough to handle the task. >>Exactly my opinion too. But my guess is that it's even worse.>It's that strange attitude that you can observe in many large>companies (including MS..) which basically means "why should I>improve it when I sell it anyway...."!!>And when they set up a new version the literally EXPAND it's>capabilities rather than IMPROVE it. >Oskar There must be people at MSFS eagar to improve the simulator, get out good documentation with the help of outsiders, etc. But, I've heard such things have been vetoed by managment. It must be quite frustrating for a competent person to work in that group. They appear to have virtually no contact with the outside sim world. I think something is seriously wrong with the MSFS FD group. Perhaps other FS groups also. Incidently, I can see the need to get a product out that has some bugs. But, when the same bugs aren't fixed in the next edition, and things that worked before get broken I have to wonder about the climate in that operation. Ron

[Guest _ak]

>> Incidently, the FS variables are generally exact to five>digits or more.>InterestingI was researched perfomance charts for some regional jet. There was also CAS/Mach pairs for different altitudes and temperatures. I noticed that when IAS from FS matches CAS on chart, mach number little different, and vice versa. I tryed convert IAS from FS to mach by formulas from http://williams.best.vwh.net/avform.htmIAS from FS, and converted mach pairs was exactly matched pairs on chart.Difference between mach readed from FS variable and calculated mach about 0.015M when flying near 0.8M at FL370. Difference is not so big but noticeable.