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Flight Dynamics - Realisim ?

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I am not a pilot. However, it seems strange to me that when I turn a Cessna 172 (yoke) and abruptly reverse that turn there is no inertia. The aircraft immediately begins to respond by changing wing positions (wing up/down). The reaction is almost identical to that in slew mode if you turn the yoke left and right. The only difference seems to be that in slew mode the action is faster.The atmosphere is elastic and the aircraft has mass, therefore I would expect some overshoot when I stop a turn with the yoke. An overshoot that declines in some mathmatically modeled manner. Rather I see an instant stop to the turn with the aircraft moving in the turned-to direction. This seems very unreal and cartoonish. I seem to recall with my periodic explorations of X-Plane that turns initiated by the yoke could be halted with reverse yoke but there was a component of inertia. You often hear about how smooth the X-plane flight model is and perhaps this is one of the areas that contributes to that perception.Please, this is not an X-Plane vs. FS message.Dick Boley KLBE

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You got it Dick. You may not be a pilot but your sense of real-world physics is pretty good (btw, I am a pysicist by profession). You are absolutely right - the default FS aircraft lack inertia (on top of other shortcomings) therefore I don't touch them with a 10-foot pole.Therefore I suggest you stick with add-on aircraft only. Some of them are really, really good. Michael J.http://www.reality-xp.com/community/nr/rsc/rxp-higher.jpg

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You may not be a pilot... but you should be. You're observations are correct. To simulate inertia, you can (and I say this lightly) increase the null zones and decrease the sensitivity of the stick n rudders. If you have equipment with software that can curve the axes', give that a try. I have and it helped a little. The draw back is you'll get a heavier feel and not one, which is closer to real life. It's a lame substitute that seems to work some what, though more for larger aircraft than light. Frankly I don't understand why the stick routines can't be closer to the real thing and illuminate the linear feel we find in flight sims. The reason may be due to processor power. I honestly don't know why.I know that all the computations required to model one wing of an actual aircraft can bring a 3 gig machine to it's knees. In there may lie the answer.

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Hmmm . . . When I do a dutch roll in a 172 the plane responds quite nicely IMO. It may take a little more time in RL compared to MSFS but it's close enough to be fun. Unless you have the real planes available to fly and test next to the simulation's planes they will still fill your days/nights with flying enjoyment.

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It all depends on where you derive pleasure - either from the flight model realism, the visuals, or both.My ideal is to have an accurate flight model with realistic visuals. The holy grail for flight simulation is to have a 100% accurate rendition of the real world in terms of how it looks and how its physics work, but that will *NEVER* happen, because no matter how powerful any computer ever becomes, it will need infinite power to exactly simulate the real world, which is mathematically impossible.However, flight simulation is coming ever closer to simulating a realistic flight environment, and I'm enjoying the ride!James

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I would expect a plane to come out of a turn virtually immediately if you neutralize the control the surfaces. The planes inertia will cause it to go in a straight line unless forces are applied that cause it to do otherwise. To demonstrate that FS9 aircraft do have inertia maintain level flight and deflect the rudder fairly hard. The planes nose will point quickly in the direction of deflection but the plane will sideslip in the direction it was going due to inertia. The problem is that the "feel" of inertia isn't convayed to the pilot. One factor of good flight modeling is that "feel" of inertia.Or at least thats how it seems to meDavid

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It's easy to nitpick the flight dynamics to death if you want. Personally I would start elsewhere than enertia. But my feeling is that computer-based flight models are always going to be impressionistic, compromising certain characteristics in order to emphasize others. So it goes.

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That may be true but over time degree of compromise has come down while realism has increased. The Real Air Decathalon is probably the best example of this. David

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>going to be impressionistic, compromising certain>characteristics in order to emphasize others.Word "compromise" suggests that someone spent weeks fine tuning their aircraft dynamics. That simply doesn't apply to Microsoft's shoddy work "in the box". Others designers work is the biggest testimony of that.Michael J.

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>>And why even bother - there are excellent aircraft to begin with.Amen to that. Bill

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>You got it Dick. You may not be a pilot but your sense of>real-world physics is pretty good (btw, I am a pysicist by>profession). >>You are absolutely right - the default FS aircraft lack>inertia (on top of other shortcomings) therefore I don't touch>them with a 10-foot pole............>Michael J. FS AC have plenty of 'inertia'. What is wrong is Roll Damping: Cl_p is usually set way too high so the Roll Damping Factor is then too high. Roll Helix angle is adjusted by making Cl_da high and consistent with Cl_p. The end result is the Roll Time Constant is so low it's often virtually non-existent. So, many AC start and stop in rolls almost instantaneously. MS Jets, and most amature FD's are especially bad, with Cm_q and Cl_p often 10X a realistic value. Many desktop pilots comment on 'what a stable platform this AC is for IFR work'. ;) The fact MS Airheads can't even get basic Stability Derivatives right in most of their AC shows how INCOMPETENT they are. Many are supposed to be degreed aero engineers. But, details in their flight models show they just can't cut it. Further, the relatively good C182 in FS98 was damaged as MSFS versions progressed. Some CFS/FS AIR files are set more realistically, it would appear there is no consistency in who does the FD work. Generally the settings in MS aircraft.cfg files are right. That includes MoI's. But can hardly make up for bad settings in the AIR files. People who have run into the MS Airheads comment on 'how friendly and helpful' they are. What is more important:A. FriendlyB. CompententRon

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There isn't a huge amount of roll inertia in a 172. Most of the Skyhawk's mass is within the width of the cabin; the only major weight beyond the cabin doors is the fuel tanks. While a real 172 doesn't respond like a sport plane, the feedback of its controls are rather immediate (at maneuvering speed) and are part of what makes the craft an good trainer.If you want to transition into a model with a high amount of roll inertia, try any of the Cessna twin's. Back in the day, I got a job flying a 310 for a company. Being young and anxious to build twin time I might have been a bit "optimistic" with my representation and experience. Prior to my first passenger flight I figured I had a least better check myself out (!!!) in the a/c, so on a cloudy Sunday PM, I pulled the 310 out of the hanger, had the fuel tanks topped and proceeded to take to the skies. I had about 200 hours of twin time, most all of it instructing in PA-44's and BE-76's. The 310 was a big airplane in comparison, but it was very stable and had a (relative) ton of power. After practicing stalls, steep turns, and Vmc practice, I returned to the pattern, intending to land and put her away. The 50 gal of fuel in each tip (300lbs per side) made for a very stable flight, but turned into a nightmare of an approach. I couldn't help but over control. It took a good deal of aileron to initiate a roll that once started wouldn't stop. The technique of opposite aileron to arrest the roll sounds simple enough but I might as well have been landing on Mars that afternoon. After my fifth or sixth go-around I began to seriously wonder if I would be able to get it down on the 200' x 5000' strip! Finally something clicked and I greased it on, my shirt soaking wet. The line boy had witnessed the half hour of botched attempts with varying degrees of roll oscillations and asked what was up. I think I told him that I was practicing go-arounds. This could probably be written up as a "Never Again" story... My next flight was with passengers and went without a hitch... except for the forgotten nosewheel chalk on the return trip, but that's another story.

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Thanks Dennis. My "anxiety" arose when "flying" the new Decathalon. Its roll and opposite aileron stopping of the roll was quite abrupt. Noticing this I tried the RealAir 172 and the stock 172. They also seemed to be able to stop rolls abruptly. Now I was not sure so I loaded the 747 and it too seemed to stop a roll abruptly with opposite arileron but with a small amount of inertia. So I tossed out the question. Agree that given that most of the mass is within the fusalage the FS2004 simulation is probably quite close. I notice that verticle movements do have some "overun" when you change the elevator direction which further supports the involved mass. Need to play with some load placements to see how that effects the aircraft. THANKS.As to the requirement for more modest expectations. I am glad that Rob Young, and other talented craftmen, did not accept the out-of-the-box functions. I really cannot submit to the "this is only a $50 product". Rather my expectations are built upon the total revenue which is unkown, but undoubtedly in the several millions. From the millions grossed from this product Microsoft must be meeting their overheads and reaping some sort of profit or the project would not have made it this far. I would be very interested to know what portion of that revenue is due to repeat customers who purchase FSxxxx because of the addons (read substantial improvements)!Dick Boley KLBEPS: From watching the TV program it seems that the Wright Flyer had plenty of intertia such that it was very difficult to control. According to the commentary the lack of a rudder/stabilizer caused the beast to slip and slide all over the place. My favorite is the Bill Lyons Pietenpol. It is a real handful..

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Echo that. The defaults merely give a glimpse of what is possible.For inertia, try the MAAM-Sim B25 - flies like a big bird with a bombload, or the FSD International Porter - the difference in repsonse at the slow speeds of which the aircraft is capable is very marked. Freeware, Trev Morson has done a great job modelling the DC-3 more realistically.Allcott

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>Word "compromise" suggests that someone spent weeks fine>tuning their aircraft dynamics. That simply doesn't apply to>Microsoft's shoddy work "in the box". Others designers work is>the biggest testimony of that.>>Michael J.>Michael,Assuming the default a/c are easier to handle than their addon counterparts, is it possible that MS does indeed deliberately make their defaults this shoddy way to make the product more 'user friendly' to the mass market?After all, is'nt bottom line for them not realism which satisfies the relatively few(thousand) of us who care but a product that is as profitable as possible?I'm not siding with or against them - its just a thought that popped when I read your posts:)regards,Mark

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I'm not really sure that this is a pure inertia problem because in many ways, MSFS has that well in hand. Where I seem to notice this the most is during landings in small aircraft like the RealAir SF 260 or the new Decathlon. As you make small changes in pitch and roll on short final the resulting movement just isn't fluid. It's as if the movement rate goes from zero to full speed and then back to zero again with no visible ramping up or down at the ends. Aircraft just don't move like this no matter how light they are and in anycase you can see it in a heavy jet too. I frame lock at 30 and everything is smooth so it's not an FPS problem. This is something that's bothered me for a long time so I'm glad to see that other folks are picking up on it.TonyDigital-Flight

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I wonder how much of this is a function of the control sensitivity rather than the aircraft model. It may also be a function of limited feedback to the "pilot"; when in a real airplane there are many sensory inputs contributing to the sensation of roll than simply what is viewed on a 17" screen. I find that it is easy to over-control roll in the sim. The minor corrections that happen almost subconsciously in the real world are harder to detect in the sim and result in larger than intended corrections.The other thing absent in the sim the the modeling of turbulent wind gusts on approach. The sim tends to over-exagerate airspeed swings and understates the effect on roll that a gusty crosswind can have on light aircraft. It is not uncommon in the RW to have near full control deflections in adverse approach conditions. The real pilot can go from neutral aileron to near full left or right and back to neutral in a repeately in fractions of a second, something that I have not seen duplicated in MSFS.The bigger gripe that I have is the modeling of pitch trim. In the real world, you use trim to hold the control in position, not to allow the control to return to neutral (unless you're in a 'bus, but then you don't have to trim either!).

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Wow- this is one of the best threads I have read in a long time! Thanks for the story above Dennis sounds like it was a hair-raiser! Y'all have it together upstairs here and it shows, makes for good reading and intellectual response. I am too very interested in seeing how others observe this FS

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I don't think it's the control hardware simply because I don't see this happening in X Plane while using the exact same input hardware.I also don't think it's a perception problem because it doesn't look right in outside views as well. Not everyone has flown a small plane but most of us have watched them land. The movement I'm seeing looks very wrong no matter how I view it. I think that wahtever the cause is, it's happing in the flight modeling.On trim, in a real aircarft trim tunes out control forces. In other words, if you're holding 2 lbs. of back pressure on the yoke to maintain a certain rate of climb you can adjust the pitch trim to bring that force to zero at that stick postion. Unlike a joystick, the zero force postion of a stick or yoke in a real aircraft is always changing depending on trim setting and airspeed. Functionally though, trim is used the same way in both the sim and in real life. In this case to maintain a pitch attitude for rate of climb without having to constantly hold back pressure on the control. TonyDigital-Flight

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David:>>I would expect a plane to come out of a turn virtually immediately if you neutralize the control the surfaces. The planes inertia will cause it to go in a straight line unless forces are applied that cause it to do otherwise.Sorry, David, not at all.In a real world aircraft, if you neutralize the controls in a gentle turn, the plane will gradually straighten up. If you neutralize the controls in a standard turn, the plane will remain in the same turn and go round and round in circles - you will have to apply opposite control to straighten up. And in a severe turn, the turn angle will actually continue to steepen if you neutralize the controls.While intertia does keep an object moving in a stright line, the inertia of an aircraft is a tiny fraction of the lift and drag forces. >>To demonstrate that FS9 aircraft do have inertia maintain level flight and deflect the rudder fairly hard. The planes nose will point quickly in the direction of deflection but the plane will sideslip in the direction it was going due to inertia.That's nothing to do with inertia, it's an airflow issue. That is why aircraft are turned not with the rudder, but with the ailerons. The sole function of the rudder in a turn is to counter the adverse yaw caused by the imbalanced drag the ailerons produce.Incidentally, if you like flying a Cessna 172, download the RealAir one from the library here - it's a VERY good flight model. (And doesn't have the horrible taxiing characteristics of the default plane.) Be warned though... the FS Cessna 172 is a lot more forgiving than the RealAir one - slow speed boo-boos in that will put you into the ground. (Which brings up one of my favourite MSFS bugs - If you crash a plane within the airport boundary, the ATC controller will say "Contact ground when able" :-) Umm, I already "contacted the ground!" Richard

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>I wonder how much of this is a function of the control>sensitivity rather than the aircraft model. It may also be a>function of limited feedback to the "pilot"; when in a real>airplane there are many sensory inputs contributing to the>sensation of roll than simply what is viewed on a 17" screen. >I find that it is easy to over-control roll in the sim. The>minor corrections that happen almost subconsciously in the>real world are harder to detect in the sim and result in>larger than intended corrections.>>The other thing absent in the sim the the modeling of>turbulent wind gusts on approach. The sim tends to>over-exagerate airspeed swings and understates the effect on>roll that a gusty crosswind can have on light aircraft. It is>not uncommon in the RW to have near full control deflections>in adverse approach conditions. The real pilot can go from>neutral aileron to near full left or right and back to neutral>in a repeately in fractions of a second, something that I have>not seen duplicated in MSFS.I took on board the advice that was given by a respected expert on sim matters a long time ago - it might even have been for FS2002, but the advice is just as valid for FS9. Always calibrate the controller in VC, and watch the virtual equivalent. The problem is that the short `throw` of most joytsicks makes things seem over-sensitive, leading to massive over-compensations. The solution was the opposite of what you might expect - make the sensitivity HIGHER, then use tiny controller movements. Just as in a real aircraft there is almost never a need to use full control deflections in normal flight so it is with the sim. If you increase the sensitivity you get more movement of the virtual surfaces early on in the movement of the controller. Manage the controller and you manage the aircraft. In those situations where full deflection is needed, then you notice the extra stick or yoke movement immediately and register it as `much greater` than `normal` which is a similar feeling to real flight.I hope that's clear - I just re-read it and I'm not sure I'm making myself understood!Allcott

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>>The bigger gripe that I have is the modeling of pitch trim. >In the real world, you use trim to hold the control in>position, not to allow the control to return to neutral>(unless you're in a 'bus, but then you don't have to trim>either!).This is very well stated!! I only use a MS Joystick and it returns to the neutral position when you let go of it -- so this is not how a real a/c controls work. I don't really worry about threads like this -- I believe that the Sim is only meant to be used for either a visual simulation of flight ( as in a game) -- or as an intellectual simulation. In this latter case, you are using much the same intellectual energy that you do when actually flying - so it is valuable in that sense as a training tool -- but anybody who seeks so called "realism" is delucing themselves!Barry

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Bazza:>>This is very well stated!! I only use a MS Joystick and it returns to the neutral position when you let go of it -- so this is not how a real a/c controls work. The feel is pretty good with a decent yoke though. In the sim, as you dial in up pitch, you gradually release the amount of force on the yoke. The fact that the yoke is returning to the neutral position really doesn't feel that different - to me anyway - from releasing up pressure on the yoke in the RW, even though there the yoke doesn't go back toward the panel as you do so. Unless you're a really heavy handed driver, the physical deflections in most of the situations that you'd be dialing out with trim aren't that large anyway.Richard

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I don't think it's hardware per-se either, but I my guess (and it's only a guess) is that the control acceleration algorithm is as much of a factor as is the inertia model.You're correct in the function of trim, however take the extreme example of slow-flight: at 55 KIAS in a 172 the yoke is nearly in your lap and will stay there (assuming level flight). This is because that is the amount of control deflection required to offset the nose-down CG moment at that specific airspeed. In FS, the yoke would be centered. This isn't a huge "playability" issue, but it does bug me.

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