"could get a 99.9% flight model according to theory"could have, would have, should have.no PC simulator wil be 99.9% realistic. BTW: enough data is available to produce better than XPX flight behaviour. if its Cessna or Piper we don't care as long as it behaves at least somewhat like a generic General Aviation airplane. the nitty gritty can wait til XPX version 20.

Do your research. There already are add ons for x plane that are near 100% to rw aircraft. Just have to know where to look.The data you speak of has been used by at least a few developers to make these add ons. It's not very hard to find.

Do your research. There already are add ons for x plane that are near 100% to rw aircraft. Just have to know where to look.The data you speak of has been used by at least a few developers to make these add ons. It's not very hard to find.

Can you please recommend some X-Plane aircraft that are near 100% to rw aircraft. I have done my research and can't seem to find much, except for the CRJ of course. Are any of those well done aircraft freeware? I fly the x737 right now and it is a solid effort and my favourite X-Plane aircraft so far, but it falls short in a few areas including the flight model. I am reluctant to purchase anything else X-Plane related until the software gets more stable. I am really looking for a stable IFR trainer. So far I have not found a replacement for Rob Young's v88 aircraft for Fly! 2K. They are still the most realistic flight models i have ever flown on a computer. These aircraft are smooth, stable, have realistic inertia, are predictable and substantiated by real world pilots. I have never tried FSX, but i heard the Real Air aircraft are also very well done. Most X-Plane aircraft exhibit never ending phugoid oscillations in pitch which are very difficult to arrest, making the whole experience feel like a paper airplane in a video game. I think that even having 100% of all necessary manufacturer's data, plugging it into X-Plane will result in something that is not very close to real life. One has to understand the limitations of this software, it is not the same software in a $40 million Level D simulator. It is actually fairly basic at the core with calculations being done at very few places on the airplane. The best computer flight models are created with a lot of tweaking and feedback from real pilots. A rw pilot has to be committed to the effort and provide valuable feedback about how the airplane flies on the computer at every design iteration. The modeller has to understand the limitations of the software and know to how to work around it and make the necessary tweaks based on rw pilot feedback so that after many, many design iterations, the final plane will be close enough to the real thing. Rob Young took months to design these masterpieces for Fly! 2K and some of them have ghost vertical wings, ghost flying sufraces etc.. just so that by the end the rw pilot can say "this is close enough". I would much rather fly something that is highly tweaked with all these ghost creations as long as a real pilot has provided lots of feedback during the design of the flight model and has substantiated the model when it is done. This is just my opinion, i really think that understanding the limitations of the software and knowing how to work around it is key for flight model design.

You won't find freeware that has near 100% flight models for ANY sim. No one disputes that. Well, a few people do. But the sensible ones don't. Payware can be very close to 100% accurate.Systems are a different kettle of fish. X Plane uses physics (although some people call X Planes physics "hype"). Physics is physics. There is only one version of physics as WE know it. The problem is, about 98% of x plane aircraft authors know VERY little of what to add into their aircraft to have a complete flight model so x plane fills in the blanks. These blanks are rarely correct because there are literally thousands of variables involved in the aircraft of the world. That's why the dedicated developers (including freeware authors who spend a respectable amount of time making freeware) can make extremely accurate flight models. Because they research, and in many cases, purchase documentation on the aircraft just to get the right information. Inertia is, in my opinion, one of the most neglected factors in an x plane add on. So many developers don't know how to adjust it and decide to leave it. This includes the default aircraft. I could take an ultralight and adjust the inertia to make it fly like an An225. This is the flexibility x plane gives to developers. When the inertia is left at default values, it's almost never correct. Like I said, too many variables to accurately calculate it. The phugoid oscillations could be one of two things. Either the inertia, OR, flight models per frame. The flight models per frame can be adjusted in X Plane itself by the user. I think it's under Operations and Warnings. Setting it at 2 or 3 will eliminate oscillations. The other thing is, obviously, the inertia in the flight model. The comparison between a Level D simulator and a desktop simulator is easily misinterpreted. Most of the $40 million in a Level D simulator is the hardware, including the hydraulic jacks, instructor station, panel and computers that drive the systems, etc... So the SYSTEMS are far superior and far more accurate to any desktop simulator (although that's debatable with the PS1 747-400 simulator) but what can be accomplished with the flight model of a desktop simulator can be considered on par with a Level D simulator. Anything is possible with programming, even in flight models. Keep in mind, we are talking about FLIGHT MODELS ONLY (given what info can be obtained) when saying both platforms are on par with each other. Not systems simulation. I might correct you on the calculations being done in x plane. X Plane breaks down all the objects and airfoils and makes calculations on them as it's moving through the virtual world. This is not being done at very few places, but at all the places on the aircraft simultaneously. Obviously it can't calculate what several thousand rivets will do to the flight model, but then again, no simulator can do that. What it can do, is calculate what happens to a wing when an aileron or wing flap falls off. X Planes flight model actually takes that into account. Whether it's realistic or not is up for debate. I don't think anyone can debate it without real world proof, and I don't think very many people, if anyone, survived such an event. The point is, it's there and it happens based on physics.I cannot comment on how accurate an FSX or Fly2 flight model can be made, but I CAN comment on the x plane flight model. And just about anything can be done to make it accurate to the point that a rw pilot would be hard pressed to fault it. As for the add ons...People do freeware in their spare time. The one that comes closest is Mortens Archer. So you will basically get what you paid for...MOST of the time.These are completely unbiased choices...http://www.x-aviatio...&products_id=54http://www.x-aviatio...&products_id=29http://www.x-aviatio...&products_id=53http://store01.prost...e/Detail?no=185http://www.x-aviatio...&products_id=59And obviously the CRJ.There are others being worked on, but I won't post those unless you really want to know about them. The ones I posted have received the most positive feedback, and I have no problems recommending them for as close to a rw experience as you can get.

A few notes on the flight model. I just recently started to do some work with Planemaker.I chose an old 1st world war fighter, biplane, tail dragger. In retrospect I would have chosen something easier to start with as data is very difficult. Anyway the first thing I wanted to do, obviously, was get it up into the air before I started to fine tune and start the model in Blender.Straight off it flew ok very first time and landed ok. Speed was about 10mph down on the data I had. I thought that intial result was pretty damn good. A flyable landable aircraft from the box without any adjustments. Ok getting to my point now.Then I started in with the adjustments, wow!!! I fully understand now what is meant by lack of data. The prop work alone gave a big difference in speed, acceleration etc;. The airfoil of the elevator and tail fin makes quite a difference to performance, so much so it was absolutely essential to get this as close as possible.At the moment my plane is a bit too slippery in the air (inertia? as Goran mentioned in previous post, maybe).So my point was that it became increasingly obvious to me that working without the exact data makes things very difficult. I don't see too many issues with planemaker unlike many of the posters here. What I do see is a lack of knowledge of Planemaker (my case) and a lack of having the data you need.After my few months with planemaker I believe most flight model issues are due to(a) a lack of knowledge of Planemaker (my case, but I'm getting there)( :( a lack of dataMy observations anyway, hope post is not too long

Edited February 5, 201214 yr by jasonX

Glad to see someone actually seeing what planemaker is all about and how essential accurate data is and how accurate the flight model has to be modelled. Like I always said, any mistakes in how the aircraft flies in sim is down to the DEVELOPER. Not the platform. Good post, Jason. Good luck in Planemaker.

X Plane uses physics (although some people call X Planes physics "hype"). Physics is physics. There is only one version of physics as WE know it.

Ok this is something that needs to be understood by all non-enigneer users of X-Plane. I am an aerospace engineer and have taken courses in aircraft design, finite element analysis, computation fluid dynamics (CFD), aerodynamics and aircraft stability and control. I build finite element models during my day job and must mention that a large part of learning finite element analysis revolves around understanding its limitations. Solving for the forces on an aircraft in flight and truly simulating flight using CFD is a notoriously difficult problem. Let me give you an example: a small 3d portion of the wing takes me hours to solve on a super computer for a steady state, laminar flow condition. Keep in mind this uses thousands of elements in order to improve the accuracy of the analysis. You don't have to be an engineer to know the plane experiences conditions of turbulent airflow, which is difficult if not impossible to model. Every pre stall condition is a turbulent airflow condition, some airfoils aim for turbulent airflow in order to prevent early boundary layer separation, the 737 has vortex generators near the leading edge of the wing which introduce some turbulent airflow over the wing to improve stall performance (prevent boundary layer separation). It gets even more compilcated: dynamic, non-linear analysis for flutter and phugoid modes. A dynamic CFD analysis for a few seconds of a dynamic event on a small portion of the aircraft takes days to solve on a super computer. Even then the analysis has some error which needs to be accounted for. What do we do if we want to get a quick, conceptual, "back of napkin" calculation for a certain condition. We build a model using very few finite elements (kind of like the X-Plane model). This is a very coarse and rough approximation, but can be solved in seconds. In the case of the X-Plane model it can be solved every frame, quite a few times per second. This should give you an idea of how simple this model is, but what most people don't seem to get is the inherent error associated with such a basic model. There is no way dynamic events (phugoid, flutter, pretty much every non-steady state condition) can be simulated accurately using such a "coarse mesh" of minute elements. And flying a plane on a computer is all about dynamic performance. Industrical grade CFD still is not at the stage where it can simulate dynamic flight in real time, which is why we need wind tunnel tests (especially for turbulent airflow) and structural tests etc in order to certify an airplane. Maybe sometime in the future we could design and build a plane only by a computer without any structural or wind tunnel tests, but i can assure you it will not happen in our lifetime. This is the type of software limitation i was referring to in my earlier post. I am not slamming this software, it is very simple and limited CFD, but the approximation it can achieve is pretty quick and impressive. What virtual airplane designers need to understand is that getting all of the right numbers in this Plane Maker tool will still not result in a plane that behaves like the real thing, especially in dynamic stability. So what do you do in that situation? You get a real pilot on the team and adjust, tweak and fudge this model based on his feedback until it starts to behave like the real thing. Flight model design becomes more of an art than a science and Rob Young is one of the masters of this art. I have flown his models and am extremely impressed. I know they have ghost vertical wings to simulate slip and other tweaks like that, but i am happy with the end result because i understand the limitations of the software and a rw pilot has provided months of feedback and a stamp of approval. The rw pilot is key as they bridge the gap between the limited computer model and real life flight. So next time you think about X-Plane and "real physics" think about how basic and coarse this approximation is, but that doesn't mean it can't be tweaked to achieve a high degree of realism.

What do we do if we want to get a quick, conceptual, "back of napkin" calculation for a certain condition. We build a model using very few finite elements (kind of like the X-Plane model). This is a very coarse and rough approximation, but can be solved in seconds. In the case of the X-Plane model it can be solved every frame, quite a few times per second. This should give you an idea of how simple this model is, but what most people don't seem to get is the inherent error associated with such a basic model. There is no way dynamic events (phugoid, flutter, pretty much every non-steady state condition) can be simulated accurately using such a "coarse mesh" of minute elements. And flying a plane on a computer is all about dynamic performance.

That is absolutely not correct. Even a "simple" so-called table based flight model can accurately model dynamic modes (e.g. phugoid) _if_ the correct data are entered. You don't need CFD to accurately simulate phugoids etc.!In the case of X-Plane, the blade element theory based flight model should figure by itself the behaviour of the aircraft with a high degree of accuracy, at least in normal flight regimes.That's where _in my opinion_ lies the problem. That is, I think the seemingly low accuracy of X-Plane default models is not due to the fact that the flight model is too simplified, but instead to some internal flaws in its flight model.I say this because basic stability and control data, in normal flight regimes, can be predicted with a relatively high degree of accuracy using empirical methods and calculations (see e.g. Roskam texts on flight dynamics) that are less complex than the internal X-Plane flight model.So in the end I think the problem is not due to the fact that it's too simplified, but to internal flaws of the flight model engine itself. It's these internal flaws that require most designers to tweak significantly their models.Marco

That is absolutely not correct. Even a "simple" so-called table based flight model can accurately model dynamic modes (e.g. phugoid) _if_ the correct data are entered. You don't need CFD to accurately simulate phugoids etc.!In the case of X-Plane, the blade element theory based flight model should figure by itself the behaviour of the aircraft with a high degree of accuracy, at least in normal flight regimes.That's where _in my opinion_ lies the problem. That is, I think the seemingly low accuracy of X-Plane default models is not due to the fact that the flight model is too simplified, but instead to some internal flaws in its flight model.I say this because basic stability and control data, in normal flight regimes, can be predicted with a relatively high degree of accuracy using empirical methods and calculations (see e.g. Roskam texts on flight dynamics) that are less complex than the internal X-Plane flight model.So in the end I think the problem is not due to the fact that it's too simplified, but to internal flaws of the flight model engine itself. It's these internal flaws that require most designers to tweak significantly their models.

I think that 800XP's thoughts are right on the money. I've been thinking exactly the same for many years. And I'm looking at it, from pilot standpoint, and not that of an engineer. But what I do know, from years of airplane building, and constantly being around other aircraft, is that is doesn't take much in the way of appendages (vortex generators, root cuffs,etc) to dramatically make a difference in performance. Same can be said for small changes in vertical stab & rudder design, which significantly effects spin characteristics. I'm sure that Cessna would have loved X-Plane, if it could have saved them from loosing two LSA prototypes due to spins. Perhaps they just didn't consult X-Plane, but I doubt it would have made a difference. I'm not doubting that X-Plane can be made to realistically portray flight dynamics within reason, with "tweaks".....................but in all these years, I don't see it as being the all powerful flight dynamics engine, that some portray it as being.L.Adamson

"From 800XP"What do we do if we want to get a quick, conceptual, "back of napkin" calculation for a certain condition. We build a model using very few finite elements (kind of like the X-Plane model). This is a very coarse and rough approximation, but can be solved in seconds. In the case of the X-Plane model it can be solved every frame, quite a few times per second. This should give you an idea of how simple this model is, but what most people don't seem to get is the inherent error associated with such a basic model. There is no way dynamic events (phugoid, flutter, pretty much every non-steady state condition) can be simulated accurately using such a "coarse mesh" of minute elements. And flying a plane on a computer is all about dynamic performance.

That is absolutely not correct. Even a "simple" so-called table based flight model can accurately model dynamic modes (e.g. phugoid) _if_ the correct data are entered. You don't need CFD to accurately simulate phugoids etc.!

Look again, at to what he's saying. Do you actually believe that X-Plane can accurately predict phugoid and flutter, with any degree of accuracy? Could I use X-Plane to predict at what TAS... flutter would develop and destroy a new design? I certainly wouldn't want to depend on it! On the other hand, with "tweaking", these models CAN portray the symptoms of known events.

oh well it seemed like a good idea at the time lets throw it away then as it can't be done. Blow me the! negativity of some ppl. We'd still be living in caves with stone tools if we all had you guys outlook. Anyway what I know regardless of what you are saying is this. I can model a plane in planemaker and it flies straight off with a quite good degree of accuracy, and then of course we start to fine tune. Go on dispute it now! Tell me how wrong it all is!If I had you guys outlook on it, I'd probably take up cooking instead or something like that.

Look again, at to what he's saying. Do you actually believe that X-Plane can accurately predict phugoid and flutter, with any degree of accuracy? Could I use X-Plane to predict at what TAS... flutter would develop and destroy a new design? I certainly wouldn't want to depend on it! On the other hand, with "tweaking", these models CAN portray the symptoms of known events.

Regarding flutter, no it can't. X-Plane flight model does not account for aeroelasticity effects, so flutter effects, aileron reversal, etc. cannot currently be predicted at all and the only way to model them is a tweaking by the aircraft designer.Phugoid is a completely different story, it's entirely determined by the various aerodynamic and stability coefficients of the aircraft (plus the moments of inertia, which X-Plane underestimates but you can use custom values).As I said, my opinion is that with current CPUs, a real time (non CFD of course!) flight model could be made that would be capable of predicting with a very high degree of accuracy (say, 90% or so) the flight characteristics of a generic aircraft in normal flight regimes, and acceptable accuracy in stall/post stall regimes (leaving room for tweaking that part of the regime). Things like vortex generators can be easily accounted for, as MortenM and others have already explained in other posts.My opinion, again, is that the low accuracy (seemingly much less than 90% with regard to basic handling) of X-Plane flight model, when not "tweaked", is not due to it being too much simplified, but instead to some internal flaws than Austin is not aware of or does not acknowledge.Marco

Edited February 6, 201214 yr by Murmur

Worthless text

At least its better than FSX which is still buggy, extremely unstable and power waster after 7 years.

Regarding flutter, no it can't. X-Plane flight model does not account for aeroelasticity effects, so flutter effects, aileron reversal, etc. cannot currently be predicted at all and the only way to model them is a tweaking by the aircraft designer.

I would have to agree 100% here from an engineering standpoint. Especially as I was home ill yesterday on the sofa stuck watching a lengthy documentary on the Airbus A380 and was fascinated by the "flutter testing" described as the most dangerous segment of the flight test regime. They actually broke the plane at M.92 before continuing on to certify at .98M....scary stuff indeed.I equate the "flutter test" to building a bridge and then driving progressively heavier trucks over the span until it breaks to determine the load limit :(**edit**I would venture to say the only practical real world similar functional testing might be the "crush depth" assigned for submarines. Now while I have no knowledge of modern practice for live testing it was certainly not uncommon back during WWII for sub commnaders to routinely exceed the base "crush depth" during shakedown and part of evasive maneuvers.

Ok this is something that needs to be understood by all non-enigneer users of X-Plane. I am an aerospace engineer and have taken courses in aircraft design, finite element analysis, computation fluid dynamics (CFD), aerodynamics and aircraft stability and control. I build finite element models during my day job and must mention that a large part of learning finite element analysis revolves around understanding its limitations. Solving for the forces on an aircraft in flight and truly simulating flight using CFD is a notoriously difficult problem. Let me give you an example: a small 3d portion of the wing takes me hours to solve on a super computer for a steady state, laminar flow condition. Keep in mind this uses thousands of elements in order to improve the accuracy of the analysis. You don't have to be an engineer to know the plane experiences conditions of turbulent airflow, which is difficult if not impossible to model. Every pre stall condition is a turbulent airflow condition, some airfoils aim for turbulent airflow in order to prevent early boundary layer separation, the 737 has vortex generators near the leading edge of the wing which introduce some turbulent airflow over the wing to improve stall performance (prevent boundary layer separation). It gets even more compilcated: dynamic, non-linear analysis for flutter and phugoid modes. A dynamic CFD analysis for a few seconds of a dynamic event on a small portion of the aircraft takes days to solve on a super computer. Even then the analysis has some error which needs to be accounted for. What do we do if we want to get a quick, conceptual, "back of napkin" calculation for a certain condition. We build a model using very few finite elements (kind of like the X-Plane model). This is a very coarse and rough approximation, but can be solved in seconds. In the case of the X-Plane model it can be solved every frame, quite a few times per second. This should give you an idea of how simple this model is, but what most people don't seem to get is the inherent error associated with such a basic model. There is no way dynamic events (phugoid, flutter, pretty much every non-steady state condition) can be simulated accurately using such a "coarse mesh" of minute elements. And flying a plane on a computer is all about dynamic performance. Industrical grade CFD still is not at the stage where it can simulate dynamic flight in real time, which is why we need wind tunnel tests (especially for turbulent airflow) and structural tests etc in order to certify an airplane. Maybe sometime in the future we could design and build a plane only by a computer without any structural or wind tunnel tests, but i can assure you it will not happen in our lifetime. This is the type of software limitation i was referring to in my earlier post. I am not slamming this software, it is very simple and limited CFD, but the approximation it can achieve is pretty quick and impressive. What virtual airplane designers need to understand is that getting all of the right numbers in this Plane Maker tool will still not result in a plane that behaves like the real thing, especially in dynamic stability. So what do you do in that situation? You get a real pilot on the team and adjust, tweak and fudge this model based on his feedback until it starts to behave like the real thing. Flight model design becomes more of an art than a science and Rob Young is one of the masters of this art. I have flown his models and am extremely impressed. I know they have ghost vertical wings to simulate slip and other tweaks like that, but i am happy with the end result because i understand the limitations of the software and a rw pilot has provided months of feedback and a stamp of approval. The rw pilot is key as they bridge the gap between the limited computer model and real life flight. So next time you think about X-Plane and "real physics" think about how basic and coarse this approximation is, but that doesn't mean it can't be tweaked to achieve a high degree of realism.

I am 100% in agreement with you and thanks for sharing your professional inputsI actualy enjoyed tuning dynamics back in the days for FS2000 with an MSFS user who is himself a retired flight engineer like yourself and he kind of told me the same thing regarding the topic...And I remember achieving with this gentleman fairly convincing flight dynamics using the straight forward tables of MSFS models...Actualy this topic always remind me of a famous quote by the late british actor Laurence Oliver who said once "no matter what acting technique you use, what's important is to convince the audience..."And I feel the same about the PC simulated flight dynamics, no matter how the code behind is fancy , the importance is the felt behavior on screen by the end-user...And sometimes, in PC simulators dynamics, and I can speak about MSFS, I learned that one needs to "cheat" with values beyond the acurate data of the real world equivalent, in order to achieve convincing results on screen... And to me this is ok...All in all, we must not be obsessed with the code behind or the data being pluged as is... The result counts and i saw MSFS models deliver a good show when it comes to convincing behaviorAnd I suppose the word "Accurate" should be removed from the PC simulators dictionary :)Cheers

Edited February 6, 201214 yr by Claviateur