Flight Dynamics

[ErichB 3,642]

I was going to post this as a response to a current thread but I thought I'd start it as a completely new thread as it is a pretty fundemental subject for a flight simulator.

 

We have a diverse crowd of people on these boards with varying degrees of programming/coding knowledgel and flying technical knowledge and sometimes a combination of both.  Then you have those know little about either and are often the loudest vessels.  I often see terms being thrown about which have been latched onto as buzzwords, but I often wonder whether people fully understand what they are talking about when they use these terms. One which often comes up is 'flight dynamics'. 

 

I've been flightsimming for 16 years and previously held a PPL myself until the cost could no longer be justified. But I do occasionally still fly and have a reasonable understanding of how an aircraft 'should' behave - as do most others on these forums. (fora?).  I would absolutely agree that default aircraft are shocking when it comes to flying them.   I had read in another thread that 'Microsoft Flight' had an 'improved' the flight dynamics engine. As I understand it,  the code base which LM bought from MS was stock FSX code with the 'old' FD engine.   I would have thought, that flight dynamics is a pretty fundemental aspect of any simulation application - particularly for a company like LM who market the platform to commercial users. So, my first question is, why would LM replace the weather engine, and a number of other 'engines' and not replace or 'improve' the FD engine?  Secondly, what is it about the flight dynamics engine which is flawed?  As I understsand it, each aircraft has its own particular FD model.  So if we look at Majestic's Q400 or PMDG's family, or A2A's 172, or Real Air's Duke, we would argue that the 'flight dynamics' are pretty accurate, because the developers made it so. That says to me that the methodology of creating 'the flight model' is unique and specific to each aircraft.

 

I'm assuming that the other approach to creating flight dynamics in a simulator is to create a core simulation FD engine to accurately determine how any aircraft with a defined geometry and defined power/engine parameters will react in its flight environment with all other variables taken into account (so called 'blade element theory'?? )  Isn't this what XP is supposed to do... and if that is the case, why do the default aircraft in airplane also fly so unconvincingly?    

 

That's what loses me and then I think to myself, does anyone really understand what they are talking about when they talk about 'flight dynamics' within the simulator.

 

Can someone explain the alleged 'flaws' in the flight dynamics and why their is an argument to change/upgrade the engine and, if this being the case, why this is not currently on P3D's list of 'to do' items?

[Alpha Floor 237]

First of all, I'm not an expert on programming so I might well be one of your vessels

 

As I understand it, there's really no "flight dynamics" simulation on Microsoft Flight Simulator. I understand that each "simulation object" has it's own "behavioral tables" assigned to them. That is, at this given attitude, configuration and speed, with this given atmosphere, the airplane must behave like "this", a predefined value.

 

While X-Plane does compute flight dynamics in real time based on the interaction of geometry and atmosphere by breaking the airplane into "pieces" and applying the equations of motion to each one of those pieces, the accuracy of the model depends on a lot of things: The number of "pieces" you break the plane down, the order of the numerical integration method, the order of the simplified equations of motion etc... 

 

In essence, if you let the real aircraft fly under a series of conditions and record all of the results, then write them down as tables and import them to a simulator, the simulator will behave just like the real thing. Whereas if you let the simulator compute what's happening in real time figuring out the aerodynamics, you don't necessarily have to get any better results, although you might get them if the "table-based" simulator hasn't good values to begin with.

 

I think that having the dynamics of an aircraft "tabulated" for all possible scenarios would be optimal because the CPU wouldn't be stressed computing in real time, and because the "model" would be based on real experimental values, not on theoretical results of simplified equations. But then you have to define, to what degree do you "tabulate" the real thing's behavior, or even whether that information is available for flightsim developers (which I doubt)...

 

So I honestly don't know what's best for a desktop flight simulator.

[davenicoll 104]

Does each aircraft add on developer not do their own flight dynamics so LM do not have an input. I would also say it is very rare for a simmer to just stick with the default.

[WarpD 824]

Alpha Floor is incorrect and quite literally spewing Laminar Research propaganda regarding how flight dynamics are done in FS.

 

I have a really, really expensive book on flight dynamics and it's really a very interesting read (if you love absurdly complex math!). Most interesting part about it... all of the formula and methods used in FS are discussed throughout the book. Blade element theory is discussed in part of one chapter, about propellers. It is shown to be no more accurate in calculating a propeller's performance than traditional methods.

 

In short... propaganda is just that... and is rarely fact. Let's leave it out of discussions.

[Alpha Floor 237]

 

 

Alpha Floor is incorrect and quite literally spewing Laminar Research propaganda regarding how flight dynamics are done in FS.

 

Yeah well, I said I'd prefer a good table of known values rather than real time computations based on a simplified model. I'm not defending either MFS or Laminar...

 

What's your book by the way? PM if don't want to go offtopic!

[ErichB 3,642]

Yeah well, I said I'd prefer a good table of known values rather than real time computations based on a simplified model. I'm not defending either MFS or Laminar...

 

What's your book by the way? PM if don't want to go offtopic!

 

I'd prefer that we didn't slide down this muddy path and rather just focus on why there is a view that the fligth dynamics engine in P3D would benefit from a replacement or 'improvement'?

 

For what it's worth Ed, I didn't think his answer was biased in favour of any sim.  That is NOT what i want to get from this thread.

[WarpD 824]

http://www.amazon.com/Aerodynamics-Aeronautics-Flight-Mechanics-McCormick/dp/0471575062

 

The point of my post is that claims of superiority or inferiority in either direction are honestly not factual. Like pretty much anything else... garbage in, garbage out.

 

The basic flight model is accurate in how it provides the ability to create a fairly accurate flight dynamics envelope for a given aircraft.

[jcomm 5,929]

It all depends, IMO, on the use you want to give to your simulator, and one can actually use different simulators for different purposes...

 

FSX / ESP and P3D can use external FDMs. As far as I understand, the Majestic Q-400 is the only example of an aircraft for FSX that uses an external FDM, namely JSBsim, also used in Outerra and Flight Gear ( and other projects... )

 

I can only give you my own experience.

 

For GA and IFR flight simulation I use ELITE Premium v8.6. ELITE also has a line of products that uses P3D's visuals and  FDM, or P3D just for the visuals.  ELITE is what most FSX and other sims users would easily call an "on-rails" simulation, but it is actually a great GA flight simulator for the full range of GA aircraft included in it's fleet. In any sim, good and bad examples of aircraft models (regarding flight dynamics) can be found, but what makes ELITE and other specific sims so special is the detail, the amount of specific data used to tailor their flight / engine / instruments / systems modeling, and believe me, being "table-based" doesn't put it anywhere behind X-Plane when it comes to compare the way a given model behaves on both sims, at least among those I was able to use in X-Plane 10... the same applying to FSX...

 

For soaring, I prefer to get in RW gliders and fly whenever I can, but when it's not possible to go to the field, Condor has always been a good choice. There simply is no glider for FSX or X-plane that can get any way near the sophistication of the glider models, again specific and "handcrafted" in two plane packs ( the only two available for that sim, plus the default ones ). They are the closest you can get to flying a glider for real!

 

Presently ( well, since a couple of months ) I completely lost any interest in either FSX / P3D or X-Plane. Instead I had to resist my natural opposition to use combat flight simulators and have moved to DCS, which I already had and started using because of the P-51d, and IL2 Battle of Stalingrad, as well as my most recent acquisition - Rise of Flight! Believe me, after flying an aircraft in any of these, using any other civil sim looks sooooooo old-fashioned ...

 

I never understood why we couldn't have in the civil flight simulators such good flight dynamics :-(  It took me years to accept the change, but now I am 90% of my simmer time in IL2, DCS or RoF, and the remaining 10% in Condor.

 

The release of Aerowinx PSX, again a specific, highly detailed simulation of a b744, might change the statistics :-) and it will allow it's users to make use of either X-plane or FSX for the visuals only ;-)

 

A sound flight dynamics base, a feature that is common to DCS, IL2 and RoF, and also Condor, is what makes the success of those simulators. Then, lot's of specific data, based on test flights of the real aircraft being modeled, systems, engines, is what makes this simulators so special. Add to it all of the AI required for Combat Flight simulation, and you have the recipe for success. In the civil side I was striving to have good graphics and credible flight dynamics, and most of the time couldn't even have my AI ON, for risk of turning the sim into a slide show.... 

 

It's true that some aircraft designed for FSX will be very realistic, but some simple aspects of, say, a reciprocating engine, like the simple / basic relation between mixture and Fuel Flow, or the correct modeling of a CS prop, will also be far from reality if the core FDM / System simulation is used. We can find similar problems in X-Plane, and of course in DCS, IL2, RoF, I guess, but overall their quality is far superior in terms of detail, and sensation of really being there !

[Gregg_Seipp 568]

All I can say is that it's astonishing how well it can work.  Bernt Stolle's and RealAir's FDEs in FSX are really well done...the spin and handling characteristics of the RealAir birds...the feel of being 'up there' and moving through the air of Bernt Stolle's.  His 337 model is a work of art. 

[ErichB 3,642]

All I can say is that it's astonishing how well it can work.  Bernt Stolle's and RealAir's FDEs in FSX are really well done...the spin and handling characteristics of the RealAir birds...the feel of being 'up there' and moving through the air of Bernt Stolle's.  His 337 model is a work of art. 

 

Great, so what I'm getting from all of the opinion above is that there is nothing really flawed at all about the flight dynamics methodology used in P3D IF the FD developer understands his art (and maths) for the specific aircraft he is building the FD model for.  As you have rightly said Gregg, the Real Air and A2A models are capable of realistic spins, which to me,  is a good acid test for my question.

 

I am therfore still amiss as to why some naysayers instist that the flight dynamics engine needs improvement - as all the tools capable of making a good job out ot it seemingly already exist.

[Gregg_Seipp 568]

 

 

As you have rightly said Gregg, the Real Air and A2A models are capable of realistic spins, which to me, is a good acid test for my question.

 

Well, I'll definitely say that the RealAir C172 spins are astonishingly real. 

[jcomm 5,929]

Here's an example of what I think is a sound basis for flight dynamics :

 

http://www.youtube.com/watch?v=o3tJlFsGRSE#t=63

 

Nothing like this in either FSX, P3D or XP....

 

But for pure IFR you can perfectly use even Luiz Monteiro's Online or standalone simulators! They're great! Or FSX, but the focus on the instruments and the way you access them, is far from being tailored for IFR training...

 

For VFR FSX can be great, I think... specially if you have good scenery. X-Plane 10 is also a good choice with it's OSM-based scenery.

[ErichB 3,642]

Here's an example of what I think is a sound basis for flight dynamics :

 

http://www.youtube.com/watch?v=o3tJlFsGRSE#t=63

 

Nothing like this in either FSX, P3D or XP....

 

But for pure IFR you can perfectly use even Luiz Monteiro's Online or standalone simulators! They're great! Or FSX, but the focus on the instruments and the way you access them, is far from being tailored for IFR training...

 

For VFR FSX can be great, I think... specially if you have good scenery. X-Plane 10 is also a good choice with it's OSM-based scenery.

 

Interesting! 

 

It's not that i'm looking for a seperate flight dynamics simulation.  I want to have my cake and eat it.  I have P3D with all that is good and wonderful about it and that's what i intend to stick with, so my question still remains....

 

Is it broken...or not.

[jcomm 5,929]

Interesting! 

 

It's not that i'm looking for a seperate flight dynamics simulation.  I want to have my cake and eat it.  I have P3D and that's what i intend to stick with, so my question still remains....

 

Is it broken...or not.

 

I would prefer it to any of the civil alternatives right now, ELITE excluded, but that's other stuff.

 

I think P3Dv2.2 is great! I really liked it. The Flight Dynamics are those of FSX, but heck! That's good provided you use the best addons and limit your flight envelope to what you should be doing when flying VFR, IFR, Line, etc... Aerobatics / stunt flying are another story... even soaring... leaves a lot to be desired...

 

With A2A, RealAir, Bernt, Majestic, PMDG, etc... you can't go wrong ...

[ErichB 3,642]

I would prefer it to any of the civil alternatives right now, ELITE excluded, but that's other stuff.

 

It's good, and I think P3Dv2.2 is great! I really liked it.

 

With A2A, RealAir, Bernt, Majestic, PMDG, etc... you can't go wrong ...

 

It's not that I need convincing.  :rolleyes:  I'm pretty converted and have been happy with A2A, RA, Majestic PMDG for a long while.  

 

What I am trying to do is establish whether the flight dynamics engine/system/module inherent in FSX/P3D is broken or needs to be replaced.  Again, I'm only raising this because there are some people on the forum who have indicated that LM need to improve it.    My question is still 'how' and 'by doing what to it'?,

 

But I'm increasingly of the belief that they haven't a blithering clue what they are actually talking about and am led to conclude that the flight dynamics is only as good or as bad as the individual publisher/developer of each aircraft chooses to make it.