You are mistaken.

First of all the equations governing fluid flow, the Navier Stokes equations, have no known solution. Modern mathematics does not have a method for determining the solution unless certain simplifying assumptions are made. The only way to get an approximate solution is to use a numeric solver, and these are very computationally expensive. I guarantee that Cliffs of Dover is not running numerical solutions to the fully viscous Navier Stokes equations.

There are certain assumptions that are "good enough" for the consumer flight sim market, and these are in use in all flight sims.

You can keep using the term "6DOF FM" which I assume means that the aircraft are free to move in all six degrees of freedom. That is not the same as a flight model that corresponds 1:1 with reality.

Yep, the same for target visibility: there are still unknown variables in the equation.

IMO the road to take is still the "table based" as Tag says, both for the mandatory approximations and CPU usage.

Think about real time weather: I hope they really didn't take this road because it's madness. I think the good way is to have external CPU greedy applications who provide simplified tables, and then use these tables ingame.

I don't know very well the methods XPlane use to calculate FMs: IIRC the plane developer needs to use some external applications were the data are processed to result in the final plane package.

Have anyone tested their WW2 planes?

Interesting.. So your saying that that all the PC flight sims since the mid 1990s who claim to have implemented a 6DOF FM were lying to us?

Emmmmm.. don't take this personal, but we will have to agree to disagree on that, sorry

Interesting, but fluid flow equations and navier stokes equations are not used in a 6DOF FM

Hence me stating 6DOF and not fluid flow or navier stokes

Not only is 6DOF good enough for PC game flight simulation, but it is good enough for most if not all military flight simulations.

On that note, don't confuse flight simulation with aircraft design technics (which you appear to be doing)

Where fluid flow and navier stokes equations are used a lot in aircraft design, and yes the last time I check the full up fluid flow FMs were too CPU intensive to be run in real time.

Granted there have been a few PC flight sims that claimed to be using fluid flow (real-time computational fluid dynamics (CFDs)) for their FM, as was the case back in 1995 with Flight Unlimited. But the equations had to be stripped down (dumb down) to run in real time on a PC such that all the benefits of a fluid flow FM were lost

You assume correctly

I got news for you, no simulation is 1:1 with reality

it's very good comments Ace.

Just remember tht "compressibility" related interferences with "normal" flows regime start to occurs well bellow the 0.5 Mach regime and non potential flows are to be preeminent once AoA increase.

With WWII planes you are both dealing in most of the flight regime with both this problem and simplified equation are hardly accurate. Just hve a look of the drag coeff in a high subsonic flight regime ;)

For GA simulation like in Flight Unlimited or even RoF (the early Flight models where really good until stupid EGO plane where introduced), simplified equation related to design coeff are accurate enough for builiding a good sim. Cleverness of the FMder will do teh trick once the plane depart from the range of parameters where simplified equation are not good enough.

IN WWII flight sim, things are more complicated with most of the flight regime in combat being at the edge where simplified eq simply does not do anymore the trick. It's then IMHO a matter of assessment of what will have a predominant effect and what won't. There of course it's all debatable and really sensitive to the accuracy and honesty of the historical materials submitted for building the flight models :(.

Modern studies could be done in some arrowing section of the FM to assess a specific behavior. That's what I wld hve done perso like building a generic high speed/highG model with, let's say a 23015 wing section AR of 5 straight trezoidal wing etc... etc..

But I am sure those guys there in the Moscow suburb had more in mind and done alrdy plenty :rolleyes:

Tht's what plsd me with CoD is both the honesty and the willingness do things good

No, that's not what I'm saying at all. Re-read what I wrote.

So you agree it's an approximation to reality then, as I said earlier?

The ideal simulation will follow principles of aircraft design and accurately reproduce reality.

No kidding, this is the point I was trying to make from the beginning.

Ok lets re-read it..

Hmmm.. Sorry but even after the re-read it appears you are under the impression that no PC flight sim has ever implemented a 6DOF FM, which is just not true.

Granted you did not come out and say they are lying, you just implied it.

As for mistaken..

In light of the fact that many PC flight sims have implemented a 6DOF FM, it appears that you are the one that is mistaken, not I

First thing to note I never said a 6DOF is reality, hence the name 'simulation'

What worries me about what you said is that you seem to think a CFD FM is equal to reality, which is just not the case.

I have this saying, no sim ever was, is, or will be perfect (read equal to reality)

Kind of sums it all up don't it?

Depends on your definition of ideal..

I think it is safe to say that most people here would agree that a simulation that takes 3 hours to simulate 3 minutes of flight time is NOT ideal..

Your mileage may vary?

So you agree a CFD FM like a 6DOF FM is an approximation to reality then, as I said earlier?

S!

It is true..

All simulations have limits.. Thankfully most of the errors due to the limits are smaller than what most humans can precive.

The good news is the 6DOF FM code has been around for years.. 30+ easy! I have a copy of an old F16 FM writen in FORTRAN from the late 70s early 80s. The math of it all has not changed much, just the code that it is implimented in and the PC it runs on. What use to take a super computer can no be done on a low end PC

Agreed!

Oh, there is abundance of proof that the 109 for instance is too slow. Please look up again the corresponding threads.

I guess that there has been similar data posted for other planes as well.

EDIT: On the how to do a sim: I have a couple of years experience in the aerospace business as an engineer and I work for a research institute in this field. One field of our research are hypersonic planes. As any hypersonic plane has to accelerate through the subsonic velocity range (and deccelerate later for landing) we put some effort in studying subsonic aerodynamics. From all experience we have collected I can say one thing: there is not ONE single simplified method that can predict accurately the aerodynamic forces in the subsonic region (but some adequate approximations) for low and medium subsonic speeds. When the speed approaches transsonic speeds it basically gets guesswork.

Only halfway trustworthy aerodynamic results by calculation would be to do the fully viscous NS-equations (provided they can be solved correctly) but this is not at all practicable for a flight sim as the calculation for one flight point only (Ma, altitude, angle of attack, sideslip angle) would take a lot of time and we would need an enormous number of flight points in order to create a sufficiently large data base. And again, as a researcher who respects himself, I would request to verify some calculated points by wind tunnel tests ...

And we yet have not even talked about the damping coefficients which are even more difficult to assess by wind tunnel tests let alone determine by calculations ...

Abundance.. Really? Well if there is an 'abundance' of 'proof' than it should be a simple task for you to 'pick one' and provide the link to it for review.. Right?

I have a beter idea..

As noted, I have 'looked' and have yet to see 'one' that would quality as 'proof'

But maybe I missed the one your refering to?

So since you seem to think there is an 'abundance' of 'proof', please pick the best one and provide the link to it for review, that way we are both on the same sheet of music

I like to avoid guess work

Agreed 100%

As I allready noted, no sim is perfect!

And no sim ever was, is, or will be equal to reality!

Hence the name 'simulation' in place of 'reality' ;)

I knew that you would ask other ppl to do the search work for you.

Instead I now ask you to provide a proof that there is no data. I have not enough time to do this work for you. Remember: you brought up this whole: leave-it-as-it-is-because-there-is-no-proof thing. And please spare me anything like: "So you don't have proof". I know this argumentation strategy too well and it just bores me. You just look up the threads by yourself or proove that there is no data available. Otherwise I would just take you as of the same kind as all the others that you blame for making unfounded assertions.

Furthermore I come to believe that even if I or anybody else provided proof you would just call it to be no proof. You're a man on a mission. So any effort would be wasted on you imho.