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Can a realistic turn & slip indicator be programmed?

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I never understood why MSFS has such a lausy implementation of the turn&slip indicator, particularly in what concerns slip.If you're flying, say, a twin, such as the default Beech58, and you fail an engine, you'll have to kick the ball, maybe using full rudder deflection, and add some rudder trim too. In MSFS while the ball initialy moves towards the correct side of the indicator, it soon returns to the center simply by levelling the wings (???). I presume there are variables,accessible to xml, that might be used to program a better slip indicator. Is this true? Has anyone designed such an instrument?Thx in advance!!!

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j.c.monteiro:>I never understood why MSFS has such a lausy implementation>of the turn&slip indicator, particularly in what concerns>slip.>>If you're flying, say, a twin, such as the default Beech58,>and you fail an engine, you'll have to kick the ball, maybe>using full rudder deflection, and add some rudder trim too. In>MSFS while the ball initialy moves towards the correct side of>the indicator, it soon returns to the center simply by>levelling the wings (???). >>I presume there are variables,accessible to xml, that might be>used to program a better slip indicator. Is this true? Has>anyone designed such an instrument? Hi Jose, I thought the 'ball' was better in FS2K2. Regardless, I've thought of adding some 'incidence_beta' to the 'ball' variable. Beta is sideslip angle, and does 'not return to zero'. On could use only the 'beta' parameter, but he would have to program a 'second order system' to emulate the ball's dynamics. Problem with the first idea is the new 'ball' would move directly with sideslip angle and more slowly with the 'ball' parameter. The end result might not be acceptable. Now I could low pass filter the 'beta' before adding the 'ball' to make them merge more or less correctly. I already use my Time Constant filter on beta and its rate "r" in a test gauge I've done. However, that is getting complicated. ;) Less so if elements are already working. Some day I might try to make a 'second order system' from my TC algorithm. Then I'll have it available for when I need it. I expect to let Herve' Sor's post my Jet Test gauge at his site soon. It has so many FS XML parameters and calculations in 'test base.xml' that I can't display all of them at once. I'm afraid it is difficult to understand some of the coding, RPN XML is really tricky and I had to normalize the "Time Constant" constants for different Strobe rates and the Tick18. I used various Physics concepts to calculate some things. Such as Fuel Tank Temperature. Ron

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Ron,You just need to get a Hewlett Packard calculator to practice your RPN!:(You should see how confused my flight instructor gets when I use mine! Of course he is an algebraic person and doesn't understand:LDALDXFunctionAnswerW. Sieffert

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>Ron,>>You just need to get a Hewlett Packard calculator to practice>your RPN!:(>W. Sieffert Heck, I got an HP-35 31 years ago at a discount when I worked for HP. I have a 15C now. My 5'th HP. It's 19 years old, but does more than I can remember anyway. I do use it at times to check my XML RPN. The two are quite similar. "STO 0" on my HP, "s0" in the xml file. I make a lot more errors in the files. Those long, clumsy variables don't help. At times I've had a "." when it should be a ",". Sometimes I display variables to see if they are working. Ron

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Ron, now you got me confused...but shouldn't the slip indicator (ball) show slip? Couldn't it simply read 'incidence Beta'?I think the Flight1 Cessna 410 I once bought for fs2002 had it working very nice. When an engine was failled, sometimes full opposite rudder wasn't sufficient to bring the ball to the center...

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>Ron, now you got me confused...>>but shouldn't the slip indicator (ball) show slip? Couldn't it>simply read 'incidence Beta'? The 'ball' variable includes dynamic effects. Due to the fluid in the glass tube, the mass of the ball, and the curvature of the tube. It is essentially a highly damped pendulum. "Incidence Beta" applies only to the AC. That may also tend to oscillate, but it doesn't include the dynamics of the 'ball'.>I think the Flight1 Cessna 410 I once bought for fs2002 had it>working very nice. When an engine was failled, sometimes full>opposite rudder wasn't sufficient to bring the ball to the>center... Maybe the 'ball' was enhanced. That requires a special slip indicator since one has to link it to any new 'ball' parameter. The FS2K Concorde has a true slip indicator. However, MS messed up, it barely moves. Eventually I'll try to program the Second Order 'Dashpot, Mass, Spring' dynamics in XML. Or, learn to do C gauges, which would make many things a lot easier. Ron

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I tried once to make a second order system to simulate a damped needle with a certain mass. The result was not really convincing. Due to the 1Hz "sampling" rate you end up with resonnce frequencies a godd deal below 9Hz. I had the feeling the needle was much too "heavy".BTW "numerical recipes" are good sources for code http://www.library.cornell.edu/nr/bookcpdf/c13-5.pdf .Arne Bartels

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>I tried once to make a second order system to simulate a>damped needle with a certain mass. The result was not really>convincing. Due to the 1Hz "sampling" rate you end up with>resonnce frequencies a godd deal below 9Hz. I had the feeling>the needle was much too "heavy". Can't you sample at TICK18? I do (for rates) in my XML test display 'gauge' and calculate several AC rates by taking successive differences between ticks, then filter with a 0.2 sec (typical) time constant. At 18/second I figure near 9 Hz components can be resolved. Much higher frequency than the 'ball'. No doubt some FS DLL includes a Second Order func call. All it would take is one. It could be used for the LG dynamics and any other place such a function was needed.>BTW "numerical recipes" are good sources for code>http://www.library.cornell.edu/nr/bookcpdf/c13-5.pdf .>Arne Bartels I've got the original Fortran + Pascal version and was just checking what it had to say about IIR/FIR filters. I think my simple "TC Filter" is of that kind, but I couldn't figure out much of the Numerical Recipies info on general filters. --- I broke my XML Test Gauge; for some strange reason two 'rates' stopped working (Displayed 0.000) when running in FS2K2, but worked in FS9. That is, until I edited a bit more and everthing quite. An extra ")" will mess up the XML. I looked for one but didn't see any. Also, many other things I've messed up in the paste. Some day I'll have to learn to do C gauges. I want functions, loops, etc. I want to get my XML 'Test Gauge' worked out well enough so I can have Herve' make it available at his site. It uses some ideas I found another XML gauge programmer worked out. In my 'gauge' most all the calculations are in 'Test Base.XML'. Which has no strings. The strings are in 'Jet Display.XML' and display only Text and numbers. I also strobe different calculation blocks, the Fuel Tank Temp needs to be calculated only every minute or so. With several hundred lines of XML parameter access and calculations it doesn't seem to have any effect on FPS. Unless I stretch the display window out a lot. Unfortunately, it's gotten rather complex and XML is hard to make sense of. I have some comments in the files, but hardly enough to explain the details. Ron

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For simple, and possibly dead wrong, engine-out scenarios, I move the engines on the Baron _waaaaaayyy_ out laterally, to generate enough yawing action on high power failures (such as during takeoff). Vmc speed is not handled at all in FS9 (rudder _always_ win). After an engine failure, you step on the ball as usual. However, you can still fly straight with the ball slightly deflected, while _not_ being in a slipped condition. A yaw-string is used for this (in real life). The mnemonic there goes "step _away_ from the string" :) I usually keep a clickable compass that changes into a yawstring for these purposes.Some interresting points are mentioned in this excellent article:http://www.av8n.com/how/htm/multi.html#sec-slip-string

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>For simple, and possibly dead wrong, engine-out scenarios, I>move the engines on the Baron _waaaaaayyy_ out laterally, to>generate enough yawing action on high power failures (such as>during takeoff). I changed the prop tables in the DF C310 so windmilling drag is about double what it would otherwise be. I suspect one added line of code in the MS sim1.dll would avoid having to do this but that doesn't help us. It has to do with how Po/Pi is calculated in the FS code. Prop Efficiency has to be negative to work right in the windmilling region as things stand now.> Vmc speed is not handled at all in FS9>(rudder _always_ win). After an engine failure, you step on>the ball as usual. However, you can still fly straight with>the ball slightly deflected, while _not_ being in a slipped>condition. I still ended up with too much control near Vmc. Howver, one had better feather the bad side soon if you don't want to hit the ground. >Some interresting points are mentioned in this excellent>article:>http://www.av8n.com/how/htm/multi.html#sec-slip-string I must have seen that site before, but spent another hour there. It also explained quite a bit on stalls. Futher, it gave me an idea of how to better ID the 'spin' related tables in some AIR files. BTW, I'm not even sure how the 'ball' should be in a slip. I remember now that I figured maybe it could be in the center if the AC is banked correctly in a slip. In contrast, sideslip angle, Beta is definitely high. Now the 'ball' measures acceleration in the lateral direction. VY is available in XML and I could differentiate it (as I did for TAS, VS, etc.) to get the lateral acceleration. That would be what the 'ball' sees; of course it adds its own dynamics. To see how 'sideslip' and 'lateral acceleration' vary I can take the ratio (or differerence) and display that. If the ratio is nearly constant then sideslip directly affects the ball. Otherwise, it's not so appropriate. Ron

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The yaw characterisics in FS seems to be a popular topic lately. Besides this topic, there are a couple of posts about it in the MSFS General discussion forum. There is one post from a person wants to know why the "turn coordinator ball is permanently glued to the bottom" in FS2002 (I have no idea what would be causing this, maybe auto-coordination is enabled), someone else writes that "The ball in my turn and bank indicator kind of goes nuts as I let the rudder center at the end of a turn and level the wings, and I'm guessing there's a better way to do it. Any advice on how to properly roll out of a turn from someone with real GA time?" (nobody has replied to this yet, and what works in a real airplane won't help much in Flight Simulator, especially where the default A/C are concerned), and finally sometime in the last three weeks I remember a post from a guy who wanted to know why the FS9 DC-3 banked to the right with full left rudder input.Has MS never heard the expression "step on the high wing"?Having just fixed this during my abortive attempt to create a silk purse out of the sows ear that is the FS9 DC-3's flight model, I should have replied to that topic that changing Cl_dr Roll Moment-Rudder from a positive number to a negative number would correct this bizarre behavior, but with my typing speed and aging brain synapses I often find that I only have time for reading the forums, and not for posting replies. On the subject of the behavior of the ball in FS, would gauge programming really solve the roll and yaw problems we have with Flight Simulator? Can a gauge correct the engine out behavior of the multi-engined A/C and still behave correctly during the rest of the flight envelope? Is it remotely possible that proper roll and yaw characteristics can exist side by side with the correct engine out behavior through the programming of the flight model code alone? Because I haven't had any success in accomplishing this. Most of this computer programming and gauge code is over my head (I can do some XML gauge programming though), and I tend to get a little befuddled and glassy eyed while reading it. I've found that I can program the roll and yaw characterisics in FS to an acceptable level of realism by increasing Rec 1101 Cn_beta Yaw Moment-Sideslip until the ball centers once a steady turn has been established and rudder and aileron inputs have been returned to neutral, then increasing rudder control authority with Cn_dr Yaw Moment-Rudder until full rudder deflection results in the 15 degrees of sideslip recommended by Ron in the AirEd ini, and then increasing Cn_da? Yaw Moment-Aileron? and Cn_p? Yaw Moment-Roll Rate until I have the adverse yaw where I want it. After these changes the A/C can be rolled into the turn with coordinated aileron and rudder, and once established in the turn at the desired bank angle the aileron and rudder can be returned to center and the aircraft will remain in a coordinated turn needing only some up elevator to maintain altitude.Problems with this method arise when increasing the adverse yaw effect (to model older A/C without differential or Frise type ailerons) causes the ball to remain towards the inside of the turn as the bank angle is established and the controls are returned to center, so another increase in Cn_beta Yaw Moment-Sideslip is necessary to center the ball. And with each increase to Cn_beta Yaw Moment-Sideslip, as the slipping effect of the adverse yaw is reduced, the rudder authority is also reduced, so Cn_dr Yaw Moment-Rudder needs to be increased, and so on and so forth until I find myself going around in circles, firmly established in the tail-chasing mode and with steadily increasing values for these airfile entries.The adverse yaw effect in FS is by itself undamped, and if no rudder is used - ailerons only - it causes a fast yawing moment to the inside of the turn as the ailerons return to neutral. I've been using the Cn_r Yaw Moment-Yaw Rate airfile entry to (once again!) increase the yaw damping and reduce this annoying tendency to more believable levels and prevent the nose from snapping to the inside of the turn when the yoke is centered.I have the yaw and roll behavior working working well in FS2002 with the DC-3 PH-DDZ by Jan Visser, Roy Chaffin, and Bill Rambow, and it works even better with the FS9 DC-3 (although there are terrible and for me insurmountable coefficient of lift problems with the FS9 DC-3 that I won't go into here), it is only when you fail an engine that the fly in the ointment becomes apparent. With all this yaw and roll damping going on, virtually no yaw into the dead engine results (even with the prop windmilling) and the A/C flys on with only a greatly reduced rate of climb to show that anything is amiss.I have experimented with moving the engine thrust locations outboard, but I found that a position about 800 feet from the reference datum is necessary to achieve the inflight effect that I am after, and moving them out that far made the engine sounds pretty faint (I should have anticipated that!), and ground handling was like a carnival fun ride, so I am going to try Ron's suggestion about windmilling drag and negative prop efficiency in the windmilling region for a possible partial solution to my problem (airfile propellor tables, my favorite form of entertainment:D).I'm just fooling around with the flight dynamics for fun, and have only so much time to devote to the pursuit of learning how to program it, but on a more serious note; it would be nice to practice engine failures in a twin in FS, although I no longer fly real world twins on a regular basis, having something at home to stay current on would be great. I'm probably asking too much from the simulator though, for instance, can the near snap roll that results from failure of the critical engine before or at Vmc be reproduced in FS?The failure of the critical engine on a twin and the resulting greater yaw moment (greater than if the right engine failed) is because of P-Factor (thrust centerline shifts to the right). I'm not sure how this is modeled in FS so 100% realism may not be possible. Maybe in one of those Elite PCATD simulators, but as I understand it that product is IFR only (although they claim that their hardware is now MSFS 2002 & 2004 compatible. I wonder if there is any advantage to using it for FS?) and I hate to spend that kind of money if FS could serve the need. I haven't looked into X-Plane yet either.It would be interesting to see how close to modeling a real aircraft engine failure scenario MSFS could get! This may be my next flight dynamics project. I have a Blue Arrow P-38J that I use in FS2002, maybe I'll go for a realistic "engine failure on takeoff" flight model for it. I always wanted to see if I am fast enough to handle the busier than a one-legged man in an ***-kicking contest emergency procedures for the P-38 when one engine quits on takeoff without falling victim to the infamous "graveyard torque roll". The trick would be accomplishing this without sacrificing the other flight characteristics.In real world flight, nobody is going to be stupid enough to try failing the left engine on takeoff (the past training and checkride practices of some regional airlines aside), just to see how their pilot ability measures up when the unthinkable occurs. Also, Vmc training at altitude in a normally aspirated twin results in a reduction in available engine power and the A/C's reaction is somewhat tamer than it would be in a takeoff at or near sea level. This is one thing that FS could offer us, a safe way to practice emergency procedures - if the flight model code will allow it.>BTW, I'm not even sure how the 'ball' should be in a slip. I remember now that I figured maybe it could be in the center if the AC is banked correctly in a slip. In contrast, sideslip angle, Beta is definitely high.

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Very interesting post Douglas!>may not be possible. Maybe in one of those Elite PCATDYes, I own ELITE v7.05, and I can confirm that ELITE does model the engine failure (crytical or right engine) very well on both the Baron and the Seneca (easier a LOT on the later...).X-Plane also does an excellent job in this area, particularly after v7. If you fail the right engine bellow Vmc there is no amount of rudder that will make you fly straight again...On both of these sims, if you fly uncoordinated (ruuder + aileron opposite) there is also no amount of aileron that will bring your "ball" back to the center.

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Thanks for the info on Elite and X-Plane.However, when I mentioned buying the Elite PCATD to my wife today, I got a lecture, then the evil eye in response to my carefully considered and entirely reasonable argument as to why this purchase was NECESSARY, and then the silent treatment ensued, so it looks like that idea is not gonna fly without a divorce. While I wait for her Sicilian blood to cool off, and for the weather report from the marital relations area to change from frosty cold with sleet and snow back to warm bright and sunny, I'm going to finally buy X-plane as that expense is pretty trivial when compared to the Elite setup which is (as I was informed in no uncertain terms by my beloved one), a MAJOR purchase.I see that there is an op-ed over at Flightsim that has much to say on the FS flight dynamics and the yaw/rudder issues along with some other problems.The fellow that wrote it makes some valid points, and he seems to know what he's talking about from a real aircraft standpoint (although his description of adverse yaw and using the rudder is more applicable to sailplanes with their long wingspans and high aspect ratios). It's worth a read, and be sure you don't miss the responses to it from the Microsoft cheerleaders in the Outer Marker forum, vastly entertaining!http://www.flightsim.com/cgi/kds?$=main/op-ed/ed316.htm

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How I understand you (regarding the ELITE purchase...). Imagine me with three of those at home (no, not all wives... two daughters...but they are one BIG HUGE wife against me...)Regarding ELITE, I was very lucky to win it (including the Genview databases covering Portugal & Spain) from a contest ran at their european site. I think your decision to buy X-Plane is a good one. I bought v6 last year, but didn't yet get superior authorization to order v7... ;-)X-Plane is (IMHO) evolving in the right track. I think Austin is again paying attention to what should bother hardcore flightsimmers in the very first place - flight model accuracy!You should download & test v7.1 RC3 !!! It works great for me!!!X-Plane is also the *** ONLY *** simulator capable of good helo replication, being it turboprop, prop, multi-engine, etc...

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I sen you a private message. You can also email me at any of the addresses bellow.

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I would just add that what the ball sees is total local acceleration. Consider it like coffee in a round-bottom cup held with the mouth parallel to the floor of the aircraft. When sitting still on the ground, the total acceleration is 1 g pointing straight down at the ground. But when flying, the total acceleration is usually near 1 g but varies a little. When doing a proper turn, the total acceleration should point down perpendicular to the floor of the aircraft and the ball should show that by staying in the center. In training we used to have to do "720's" or a steady turn twice around. During all that time the ball should stay centered. The coffe in a cup would stay centered in the cup even though the cup tilted with the aircraft. You would feel a force pushing you straight into the seat with no need to tilt your head. In fact, if you tilt your head in that maneuver, you get more messed up because the forces tell your body that the head should be straight but the eyeball says something is crooked.I looked in the parmeters that can be read by gauges hoping to finnd accel X, accel Y and accel Z. From that I could make a 'perfect' ball gauge. But all I found was TURN_COORDINATOR_BALL and who knows what drives that stupid thing.When I do a high-bank turn in a Learjet, there is no adverse yaw and the doggone ball should stay centered all the time. But you can see the yaw rate stay low even with a steady high bank until you kicj the rudder into the turn. Something in FS is terribly wrong. I don't think it is the gauge. I think it is the way the rudder works mathematically. It is screwed up.

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>I would just add that what the ball sees is total local>acceleration. ... Which is different from 'slip'>I looked in the parmeters that can be read by gauges hoping to>finnd accel X, accel Y and accel Z. From that I could make a>'perfect' ball gauge. But all I found was>TURN_COORDINATOR_BALL and who knows what drives that stupid>thing. But, there are Velocity X, Velocity Y, and Velocity Z parameters. I know they can be differentiated to give reasonable accelerations: ax, ay, az. Ron

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There is a better method. Just read and display the sideslip angle, beta. This is available in the parameter INCIDENCE BETA and it reads in degrees. I fashioned a quick and dirty little digital xml gauge that displays the angle to the nearest 10th of a degree. Then I used it to make adjustments in the Cessna Skylane RG I imported to FS9 from FS02.The rudder had the power to maintain a slip of 14.5 degrees left and about 13 degrees right (Directions refer to the yaw, not the slip.) There was no adverse yaw. I then went through the stability derivatives for roll and yaw. I came up with a combination that is more of a charicature of the real plane than a true representation. But it shows adverse yaw and requires that you step a little on the rudder pedal to counter it in order to make a smooth turn. It takes some practice to make nice turns but you can roll into a turn, hold the turn with zero sideslip and then roll out using a combination of aileron and rudder in each part of the maneuver. A very small amount of rudder is needed to hold the turn in a 30 degrre bank. I am currently playing with it. When I finish I will post it somewhere for downloading. It proves that we were all wrong in blaming FS for screwing up this rudder and ball business. We are also to blame - those of us who should know better. I never looked at the stability derivatives because I knew they could be a real can of worms. I hoped the planes would perform well enough that such fine tuning would not be needed. But that was a bad attitude. Now I am suspicious of everything in this sim - even the resolution of the rotation equations for a rigid body which is largely germain to this rudder-ball problem. Do they take into account properly the relative values for each of the moments of inertia in determining the roll-yaw coupling? The problem is that, if they do, we can screw it up by messing with some of these derivatives. Or, put another way, messing with these derivatives makes it possible to invent whole new laws of physics with no relation to reality what so ever. Of course, many people have been doing that for years by not using accurate moments of inertia.For that reason, we must tread lightly. I will be writing more about this with some examples.

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>There is a better method. Just read and display the sideslip>angle, beta. This is available in the parameter INCIDENCE BETA>and it reads in degrees. I fashioned a quick and dirty little>digital xml gauge that displays the angle to the nearest 10th>of a degree. Then I used it to make adjustments in the Cessna>Skylane RG I imported to FS9 from FS02. I display pitch, roll, yaw, alpha, and their deriviatives in my XML Jet Test gauge. I'm confused about Yaw; is it also Beta? that what I assumed. However, I'm not sure Beta = zero means the G vector is down (ball centered). It seems one can be in a slip, then bank the AC to center the ball. I have noted 'autorudder' only locks the ball and disabled the rudder. Beta is the same with it on or off. Another MS FAKE! >The rudder had the power to maintain a slip of 14.5 degrees>left and about 13 degrees right (Directions refer to the yaw,>not the slip.) There was no adverse yaw. I then went through>the stability derivatives for roll and yaw. I came up with a>combination that is more of a charicature of the real plane>than a true representation. But it shows adverse yaw and>requires that you step a little on the rudder pedal to counter>it in order to make a smooth turn. I use published SD's when possible. They appear to work well for SEL's. However, I generally adjust the Control Derivatives downward to keep control sensitivity from being too high. Real AC give FFB and that is a good cue for control moments. I set Cm_de so I can get about +3.5 G and -2.5 G. Cl_da to get a reasonable roll rate (at an appropriate TAS), and have taken to setting Cn_dr so I can get about +/- 15 deg beta. The C172SP 'fix' I did is popular, it has SD's hand adjusted to be near the real ones calculanted by Smetana. I wanted to do a quick fix and start from scratch, rather than copy what I already had in a C172N. The C172N is mostly set to Smetana's SD's. In fact, I have his DOS programs which calculate them -- however haven't had the ambition to put in all the details to reproduce his values. Besides reducing the Control Deriviatives we have found the Vertical Wing Offset affects Wing Leveling. Seems Cn_beta should include any wing offset effects but I found I had to reduce Cn_beta from the published value when the wing was set above the CG to avoid too much wing leveling. People have still complained that my smaller SEL's don't hold a bank as a real AC will. Howver, if I reduce Dihederal Effect they isn't stable enough to hold a good heading. Funny, since larger AC don't have this problem, even though the SD's may be similar.>It takes some practice to>make nice turns but you can roll into a turn, hold the turn>with zero sideslip and then roll out using a combination of>aileron and rudder in each part of the maneuver. A very small>amount of rudder is needed to hold the turn in a 30 degrre>bank. I am currently playing with it. When I finish I will>post it somewhere for downloading. It's been over 30 years since I flew a PA-28; howver roll-yaw dynamics in my SEL's seem nominal. Drag in a slip appears to be too low, but there is some. AFSD will report 'drag due to sideforces' when Herve' and I get this figured out better. >It proves that we were all wrong in blaming FS for screwing up>this rudder and ball business. We are also to blame - those of>us who should know better. I never looked at the stability>derivatives because I knew they could be a real can of worms. Most FS AC problems are due to poor parameters, not the basic flight model code. Beyond that, until one really gets into the details he may well be confused. I've concetrated on one thing at a time in my FD's and only more recently have gotten more into the Yaw-Roll Couplings. However, most of the effects are not too hard to understand if one thinks about them. I found 'Cn_p Yaw Moment - Roll Rate' was exactly what it says. When one is rolling into or out of a bank the ball moves to the side. It takes rudder to neutralize this. 'Cl_r Roll Moment - Yaw Rate' is impossible to eliminate (but ailerons compensate for it). I only recently realized this is due to the fact one wing is moving faster than the other when the AC is Yawing. Looking from the rear, a yaw to the left would create a CCW roll. When the roll rate is zero the ball should tend to return to center. There is a smaller 'Cl_dr Roll Moment - Rudder' which may require a limited amount of aileron in a turn. While 'Cn_da Yaw Moment - Aileron' (Adverse Yaw) is typically small and may even be zero. 'Cn_beta Yaw Moment - Sideslip' (Weathervane Stability) is what keeps an AC moving more or less 'straight'. Similar to how a weathervane aligns with the wind. Finally, 'Cl_beta Roll Moment - Sideslip' is the Dihederal Effect. One has to be careful with the signs of these parameters. FS convention is often reversed compared to some other conventions. Generally, its best to take a known good AIR file and be sure he sets the same signs it has. I think the MS AC at least get the signs right. ;) >I hoped the planes would perform well enough that such fine>tuning would not be needed. But that was a bad attitude. Now I>am suspicious of everything in this sim - even the resolution>of the rotation equations for a rigid body which is largely>germain to this rudder-ball problem. Do they take into account>properly the relative values for each of the moments of>inertia in determining the roll-yaw coupling? Everything can be tested. Perhaps some people here will be encouraged. The best tests are quantitiive. One might set related parameters to 0 to simply things (avoid other effects). I have confidence in the basic Roll dynamics. Cl_p, Cl_da, and Roll MoI appear to combine to generated appropriate roll dynamics. I have some formulas in Aired that give Helix Angle, Roll Rate, and Roll Time Constant. I tested a P-80A with heavy wing tanks at FL 350 and the Roll TC appeared to be consistent with the formula. Near one second. Something one doesn't even see with low Roll MoI and low altitudes. A quantitive test of Cl_da could consist of setting unbalanced wing tanks, calculating the extra_weight * distance and checking to see if aileron deflection was correct in "Cl_da * deflection (rad) * S*q*b = Unbalanced Roll Moment". One might check with the excess fuel set for the other wing also, since engine torque should have some effect. Just the same, roll rates are correct for specifice Roll Damping and TAS, so Cl_da (and its 2048 scale factor) are not in question. perhaps Cn_da, Yaw Moment - Ailerons (Adverse Yaw) would be worth checking. One need only check to see how much rudder it takes to neutralize a specific Cn_da (make it higher than normal). Both are normalized to S*q*b so that cancels out. If Cn_dr = |Cn_da| then a given aileron deflection should requre the same magnitude of rudder deflection to cancel the yaw. I don't think there are other effects to confuse such a test. Assuming sideslip is returned to zero. I expect Herve' will be adding Moments and Side Forces to AFSD. He will start on displaying TBL 473, Pitch Moment - alpha. More will be added as time and feasability allow. The idea being that if one can see how large certain components are then he has a better idea what is going on and if it reasonable. In the end, all forces and moments must sum to zero. That requires accelerations to be accounted for, but AFSD already does that to some degree as far as CD and CL go. ron

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Douglas, I was going to reply to your message, but think I covered a lot of points in the reply I just wrote to Tom.Ron

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> However, I'm not sure Beta = zero means the G vector is down>(ball centered). It seems one can be in a slip, then bank the>AC to center the ball. Beta=0 does not necessarily mean the ball will be centered. Because the ball measures specific acceleration, an aircraft could be in a bank with sideslip and accelerating laterally and still have a centered ball (at least momentarily). What is needed to drive the ball is aircraft acceleration in body axes plus gravitational acceleration transformed to body axes.> I have noted 'autorudder' only locks the ball and disabled>the rudder. Beta is the same with it on or off. Another MS>FAKE!Yikes! That's sad. Think of all the folks out there doing stall/spins turning final who think they're flying coordinated.

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HiI've tried to "fix" the default DC3 now using the techniques mentioned in this thread, but no success. Does anyone have an .air-file that takes care of these problems? Especially the wrong roll action. I've tried negative value on this, but nothing happens, it still rolls towards the wrong direction.I'm using Trev Morson's aircraft.cfg which fixes other (delay, power, etc) parts of the dynamics, but don't think this is relevant to rudder or engine out scenarios.

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>> However, I'm not sure Beta = zero means the G vector is down>>(ball centered). It seems one can be in a slip, then bank>the AC to center the ball. >>Beta=0 does not necessarily mean the ball will be centered.>Because the ball measures specific acceleration, an aircraft>could be in a bank with sideslip and accelerating laterally>and still have a centered ball (at least momentarily). What is>needed to drive the ball is aircraft acceleration in body axes>plus gravitational acceleration transformed to body axes. The 'ball' variable is at least partially correct, in fact it may be fixed in FS9. Otherwise, I can add a bit of 'sideslip' to the 'ball' variable to fake a better response. >> I have noted 'autorudder' only locks the ball and disabled>>Yikes! That's sad. Think of all the folks out there doing>stall/spins turning final who think they're flying>coordinated. However, the 'yaw_damper_gain' in aircraft.cfg does appear to let one set a more realistic yaw damper. A YD will help autocoordinate if it works correctly. I only could see two different conditions with that yaw_damper_gain in FS9. 0-0.20 and 0.20 to 1.0. I'm not sure what side the 0.20 belongs to. Regarless setting 0.20 appears to allow several degrees of sideslip angle with the YD on. Further, the YD does appear to move the rudder slightly to counter Yaw. As it should. Ron

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>Does anyone have an .air-file that takes care of these problems?:)If you want these files, then post a reply here or send me a Avsim P.M., or E-Mail me and I will zip them up and send them along to you.

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