What Is A Level D Simulator?

[lefthanddownabit]

FFT Applications

What are the views on the FFT product currently being promoted and now unbelievably approved by French DGAC, Indian and NZ authorities for just about everything a LD FFS does despite not complying with a raft of requirements of JAR-STD-1A or international equivalents for even a Level B sim, let alone LD?

The French DGAC is a JAA/EASA member and can't act unilaterally in the way suggested.

The FFT is an FTD/FNPT type trainer, so it meets JAA and FAA requirements for such devices. The idea of these type of devices is to allow the FFS to be used more efficiently, it's pointless to tie an FFS up for procedure training where motion and visual is not required.

It's not a new type of device, it's a new product range for the manufacturer. Their previous FTDs having been more basic.

The manufacturer claims up to 50% of initial and conversion training can be done out of the FFS, which means the FFS is still required for at least 50% of it. A lot of such training is carried out on fixed base trainers now, including in the UK.

They also say it could be used for recurrent training if regulations are changed. That might be a step too far, and I'm not sure the industry would accept that, despite the claims of the experts they cite. It would require a major change to established practice. It is true that sometimes an FFS motion trips, the crew don't notice and continue to "feel" motion cues. However when you lose motion you also lose vibration and buffet, and these can't be "interpreted" from flight displays and situations as they claim.

[ZFT]

The French DGAC is a JAA/EASA member and can't act unilaterally in the way suggested.

I beg to differ - they have.

Additionally MCA plan to perform ALL their recurrent as do Deccan on FFTs.

( I don't disagree with any of your other comments)

[lefthanddownabit]

Lookup table "problems"

Hi AirRabbit,

You should take a look at the link provided by XPMorten to see someone else's "take" on the limitations of "look-up" tables.

I did, it's bit of a rant by X-Plane's designer. Not exactly an independent view.

However, and, please feel free to correct me if I am in error, once generated and applied they certainly do modify the outcomes of those EOM – and, though I may not have done it very well, that IS the reference I was making

You will always have to calculate aero coefficients in any aero model, good or bad. It is how they are modelled which makes the difference. Without modelling coefficients how would you construct an aero model? Even X-Plane must use them.

For example, a major US airline had an older version of the A300-600 / A310 simulator (and now I don’t remember which cockpit was actually replicated) in which a pitch-up and bank angle combination beyond a certain point would simply “hang” the simulator at that pitch/bank attitude with no control input from the pilots

If this were really true I'd be amazed the airline's FAA POI allowed them to continue to use the sim without correcting the problem, which I have never seen the like of in thirty years in flight simulation.

In fact, what you are refering to is a training scenario for unusual attitudes, not a defect due to problems in a look up table. The sim is driven to the preset unusual attitude selected by the instructor. While going to the attitude pilot inputs are ignored. The pilot controls are then unfrozen and they are expected to recover using the methods they have been trained in. Apparently the simulator in question needed some rudder during recovery, which may have lead the F/O to use rudder primarily.

Whether or not unusual attitude training is completely valid in an FFS is arguable, but if properly constructed it can be useful.

There is no mention in the NTSB report of the simulator itself being suspected as a cause, only the airline's training program which emphasised rudder use at high AOA.

I have personally “flown” this particular simulator and it DID what I describe here.

I'm sure you have, but was there someone on the IOS who maybe decided to throw you an unusual attitude to deal with?

Finally, I'm still puzzled by this statement of yours:

Several decades ago the simulation industry went to the aerodynamic model; and quite frankly, I think that is why X-plane has a pretty nice product.

[john_tullamarine]

'Flying' the big jets on MSFS will always be the closest I'll ever get to doing actually doing it. So try not to laugh at us nerdy PC 'pilots' too much. Perhaps many are like me and will never get the chance to really do it.

If one twists the comment around a little and encompasses the general thrust of the thread, the following observations might be made ..

(a) various levels of simulation all have various levels of "value"

(b) "value" needs to be measured against the technical needs of the user and the desired training (or even entertainment) outcomes sought from the simulation in a cost/benefit style of assessment

(c) at the lower capability end (at a miniscule fraction of the cost of units at the other end of the scale) one finds some procedural value in the maintenance of basic scan patterns and rate and, for instance, I/F letdown procedural skills maintenance

(d) progressively moving up the scale of fidelity (and cost) one finds adequately realistic systems procedural trainers

(e) moving into the higher fidelity (and cost) region one gets progressively closer to the aircraft and can utilise the commercial benefits of ZFT capabilities. (I'm not sure that my Pawnee and Callair endorsements years ago count as ZFT exercises but one could stretch a point, I guess ...)

Do we ever actually get to the "aircraft" in the simulator ? Of course not, although, with enough resources and investment thrown at the model, the approach may have sufficient fidelity to achieve near all reasonable training outcomes

Do we really need to model the aircraft with total fidelity ? Likewise, of course not .. only to the level appropriate and necessary for the training outcomes required. Anything more is into toys for the boys .. even if we all like to get to play with the bigger and shinier gadget in town.

Does that mean that low end simulations are inferior to high end ? Depends on one's point of view .. if the assessment is training outcomes driven it is really a matter of horses for courses .. the optimum through training program will have a range of simulations of different technical validity levels to achieve a desirable mix of cost/benefit.

I could never see the value of "misusing" a FFS on FB for initial ground school basic systems training if a cheap and simple training mockup or CBT package were available to address the same requirement .. a few thousand dollars invested to free up a $20M asset for "serious" training always made good sense to my way of thinking .. and the serious airline driven by the dollar is far more interested in generating the income from selling any excess time

So those who might laugh at nerdy PC pilots miss the point, I suggest .. it all comes back to horses for courses .. whether for Industry training or just entertainment.

[XPMorten]

You will always have to calculate aero coefficients in any aero model, good or bad. It is how they are modelled which makes the difference. Without modelling coefficients how would you construct an aero model? Even X-Plane must use them.

In X-Plane, we design airfoils - like you do in real.
The flight model uses this as a base for it's calculations.

http://www.xplanefreeware.net/morten/DIV/AM.png

Cm, Cd and Cm at different AoA's, Re# etc.
You can use/create real ones (NACA or whatever) or invent your own.
The model will perform accordingly.
There is offcourse 1000's of other variables we enter as well.
Body's are offcourse modelled also.

So, you could say that unlike MSFS, XP has an athmosphere. ANYTHING you put in it will get affected by forces.
This is what makes XP a fantastic "hands-on" simulator. If your main
purpose is flying on AP and pushing buttons, flightmodel is of less
importance. System modeling is, which MSFS is good at.

Cheers,

M

[lefthanddownabit]

So those who might laugh at nerdy PC pilots miss the point, I suggest .. it all comes back to horses for courses.

Exactly right. If you fly an aircraft that has a high fidelity add-on available for use in MSFS (747-400, 737NG, 767-300, ATR72, MD-80 to name a few) it would make a lot of sense to use it as a tool for personal study. One ATR operator I know of was considering using the MSFS ATR as part of their training programme, it's systems simulation being so good.

New pilots now being trained are from the video games generation. They may well have been/still are nerdy PC pilots too.

[Mad (Flt) Scientist]

In X-Plane, we design airfoils - like you do in real.
The flight model uses this as a base for it's calculations.

Cm, Cd and Cm at different AoA's, Re# etc.
You can use/create real ones (NACA or whatever) or invent your own.
The model will perform accordingly.
There is offcourse 1000's of other variables we enter as well.
Body's are offcourse modelled also.

So, you could say that unlike MSFS, XP has an athmosphere. ANYTHING you put in it will get affected by forces.

I'm sure that MSFS has an atmospheric model too; that's not a feature that you need to have calculated coefficients for. Our FFS sim models have an atmosphere, and we use lookup tables. It couldn't be otherwise.

And whether the aerodynamic data are in lookup tables is somewhat secondary - the key is what is the BASIS of the aerodynamic data. One could run the CFD-like routines in Xplane to generate lookup tables, and obtain the same degree of fidelity with either the lookup implementation or the "calculation" implementation.

For a "real" simulator we have no choice than to use lookups, because our models are ultimately based upon flight-matched data, not CFD or impirical predictions - we start with the latter, implemented in a tabular format for reasons of code execution and efficiency, then gradually the data are refined in the light of measured flight test responses.

To be frank, I'd be more trusting of sparse, but flight test derived, data, than I would be of wholly predicted data; there are too many times when the "predictions" guys say "but we didn't predict that" for me to be comfortable without some validation.

[AirRabbit]

Hey there lefthanddownabit

For example, a major US airline had an older version of the A300-600 / A310 simulator (and now I don’t remember which cockpit was actually replicated) in which a pitch-up and bank angle combination beyond a certain point would simply “hang” the simulator at that pitch/bank attitude with no control input from the pilots.

If this were really true I'd be amazed the airline's FAA POI allowed them to continue to use the sim without correcting the problem, which I have never seen the like of in thirty years in flight simulation.

Your level of amazement does not surpass my own. However, now you can legitimately say you’ve seen something for the first time in “30 years in flight simulation.” FAA POIs aren’t necessarily responsible for evaluating every aspect of a particular simulator’s programming. And, besides, if someone were sitting in the observer’s seat of a simulator and watch someone “fly” it as I described, and the pilots used the techniques I’ve described, my impression would be that the observer would probably think the exercise had considerable merit. In fact, if YOU were the pilot in that simulator, unless you actually let go of the controls at the appropriate time (to recognize the simulated airplane didn’t react as you would have expected) I think it quite likely that you, also, may have thought the exercise had at least some merit.

In fact, what you are refering to is a training scenario for unusual attitudes, not a defect due to problems in a look up table. The sim is driven to the preset unusual attitude selected by the instructor. While going to the attitude pilot inputs are ignored. The pilot controls are then unfrozen and they are expected to recover using the methods they have been trained in. Apparently the simulator in question needed some rudder during recovery, which may have lead the F/O to use rudder primarily.

Actually, in fact, I am referring to a training simulator that was used for training the recovery from unusual attitudes. Two things about that:
First, we are describing two separate simulator scenarios. There is, or rather I believe it now should be described as “was,” a series of upset recoveries that, as explained to me, contained an external disturbance (e.g., wake turbulence, atmospheric, etc.) being introduced, causing the simulated airplane to respond accordingly. The flight control inputs from the pilot stations were “ramped down” (but not frozen) according to a pre-programmed rate and then “ramped back in” when the aircraft reached a predetermined minimum value of pitch, bank, and/or yaw. I know, for a fact, that this “control issue” (the ramping down and up) was not widely known outside of the airline simulation and/or training departments – and probably not known very widely within those same departments. And there are several training organizations (including airlines) who use that same “technique,” for the same purpose – and, if I’m reading you correctly – one that you do not agree with. If I’m right in my assumption, I am fully, 100%, in agreement with you. I believe that is irresponsible training – leading to a gross misunderstanding of aircraft response to pilot input. I am hoping that these other organizations will recognize the problems this causes and remove that idiocy from their programs – if it still exists.
Second, the simulator to which I am referring was not programmed the way I described above. In this particular machine, the pilot could fly it into the pitch/bank area that ran the computer into an “unknown” zone – and it simply “maintained” what it had until something else happened. Once flying the simulator to that position – you could get out and go to lunch – to return an hour later and find the simulator still in the pitch/bank attitude – waiting for something to happen. What that was, required one of the pilots to use some of the flight controls that were not in an “unknown zone” – like the rudder. Using a small amount of down-wing rudder to move the nose of the simulated airplane more to the horizon, apparently moved the computer back into an area where it found viable information and the simulated airplane regained its responsiveness to pilot input. For quite a while there was an on-going argument about the viability of using rudder input to “help” the airplane recover from a nose high attitude. The pros and cons varied all over the place – but the basic premise was that pilots should not be taught to NOT use flight control inputs, particularly when they were small and coordinated. Unfortunately, the part about not repeating that input and not repeatedly reversing those inputs was not discussed – at this airline, nor any other training organization or airline – to my direct knowledge until after the frightful accident in New York.

Whether or not unusual attitude training is completely valid in an FFS is arguable, but if properly constructed it can be useful.

Generally, I agree with you here. Although, I believe the use of a simulator for training upset recoveries is useful only as long as we stay away from the procedures to be used. As we’ve said here, outside of the flight test validated envelope the performance of the simulator cannot be trusted to be anything like the performance and handling of the airplane in the same situations. However, for someone who has never been in such an attitude (whatever that attitude may be) the ability to see and recognize the relationship of the altimeter, airspeed, ADI, etc. movements in comparison to the “outside view” can be tremendously valuable. Things like, What is the shortest distance to roll to get to the horizon? What is “g-loading?” How many “g’s” can you expect to generate with rather modest movements of the controls (via reference to control force) when in such situations? And so on. Where I think we get into trouble is when we try to “teach” a pilot what to do to recover his/her airplane from such situations.

There is no mention in the NTSB report of the simulator itself being suspected as a cause, only the airline's training program which emphasised rudder use at high AOA.

First, the reference I made was not referring to the American 587 accident out of New York.
Second, the incident I AM referring to was looked into by the NTSB and there were questions about the simulator’s programming. There also were questions from the NTSB when they were investigating the AA587 accident.
Third, I don’t think that anyone could say that the training program you reference “emphasized rudder use at high AOA.” Actually, I think all the statements contained in the AA587 report reflect a training program that called for coordinated use, or minimum use, of the rudder. And, as I recall, statements were obtained from instructors and students having completed that particular course of training.

I have personally “flown” this particular simulator and it DID what I describe here.

I'm sure you have, but was there someone on the IOS who maybe decided to throw you an unusual attitude to deal with?

No, actually, there was not. I could give you the names of the persons who were with me on that simulator flight, but I’d wind up, if not actually disclosing my identity, surely limiting the area of consideration – and, with my apologies, I am not ready to do that.

Finally, I'm still puzzled by this statement of yours:

Several decades ago the simulation industry went to the aerodynamic model; and quite frankly, I think that is why X-plane has a pretty nice product.

What I meant was that a reasonably inexpensive program could be had that used a completely developed aero-program, including the medium through which the “airplane” traveled; the air – and those interested in how aircraft shape affected the aerodynamics could plug those shape changes into the program and see the results. I fully recognize that the Austin Meyer link provided a biased point of view – but that hardly makes what he says less truthful.

[AirRabbit]

Hey john tullamarine:
I generally agree with your hierarchy of simulation “value,” and I go back to my on-going campaign to convince simulator and training device manufacturers, pilots and pilot organizations, as well as regulatory authorities of essentially these same points. Value to the pilot without compromising what it is that the pilot is likely to learn and take into the airplane for application.

What I object to is those who claim to be “pilots” making statements like “If you find you’re too high in the flare, all you have to do is pop some more flaps and push the nose over slightly. You just have to be careful to not land on the nose.” Please note, this is not a “made up” line – but a quote from another forum.

I guess I am acutely aware that we have pilots of all experience levels – including those legitimately desiring to become a pilot one day – and some who like the idea of being able to talk intelligently with “real” pilots when their experience is limited to or is largely on something like MSFS. I worry that if one of the lesser experienced pilots, say just past solo, were to read and believe the statement I quoted above, were to find himself or herself in that situation – too high in the flare – and decided to just “pop” some more flaps and push the nose over – we could see one less participant on the forum – and we’d never know why. Perhaps that is a bit overly sensitive, but I guess that’s a burden I have to live with.

[XPMorten]

To be frank, I'd be more trusting of sparse, but flight test derived, data, than I would be of wholly predicted data; there are too many times when the "predictions" guys say "but we didn't predict that" for me to be comfortable without some validation.

The aircraft modeling in XP is offcourse not only made by
entering known acf data into the sim and hope the flight model does the rest.
In fact, a big portion of the variables are unknown and impossible
to find out in many cases.

So, we use reverse engineering. This is based on real FDR data, manuals
and the good help of professionals like all of you on this site
We calculate and calibrate many key variables so we HIT the
real numbers while we still are WITHIN the laws of aerodynamics and the flight model of XP.

Don't worry, no "predictions" guys around here, we usually hit
the numbers we wan't to hit

btw, well said John_T

M

[lefthanddownabit]

XPMorten said:

In X-Plane, we design airfoils - like you do in real.
The flight model uses this as a base for it's calculations.

That's not strictly true. You enter the 2D aerodynamic data (lift, drag, pitching moment) for an aerofoil. X-Plane can't take the aerofoil shape and calculate it's properties from that. Essentially you have a set of data curves for each aerofoil element. Somewhere in X-Plane there will be a lookup table to calculate each coefficient versus AOA for that aerofoil element. So ultimately X-Plane is lookup table based for aerofoils at least.

AirRabbit said:

I fully recognize that the Austin Meyer link provided a biased point of view – but that hardly makes what he says less truthful.

I'm sure he believes it is true. It is really only his opinion, however. He uses too much rhetoric for me, like a politician.

As for the confusion over what incident you were talking about, I hope you can understand why I thought you meant AA587. If you can point me at the NTSB report for the incident you refer to I'd be interested to read it.

The POI does not evaluate the simulator, but has the power to withdraw approval, in this case based on a serious defect not being corrected. Also after an FAA evaluation, the POI still has to authorise the simulator's use for training, so can affect the outcome. The recurrent FAA inspection visits should also pick up on such a defect if it was written up, as it should have been, or if they encounter it themselves. In my experience, the FAA can, and often do, use their power to force operators to update or correct their simulators. However if no one reported it then you can't blame the simulator for not fixing itself.

It's possible an error in the data curves caused the sim to enter a false trim state at this pitch and roll condition which needed some sideslip to exit. However this kind of thing is fixable easily enough.

[AirRabbit]

Hi lefthanddownabit

As for the confusion over what incident you were talking about, I hope you can understand why I thought you meant AA587. If you can point me at the NTSB report for the incident you refer to I'd be interested to read it.

Of course I can understand your reasoning – I was trying not to be overly specific as I generally don’t like airing other people’s laundry (dirty or otherwise) if I have a choice. The accident report (what there is of it) to which I was referring is at the following link:
http://www.ntsb.gov/ntsb/brief.asp?e...08X07893&key=1
However, it didn’t get the write up to match anywhere near the level of communications, interviews, on-site simulator looks, etc., that took place during the investigation. Sometimes I get very disappointed with the way some of the activities of the Board are carried out. I hasten to add that generally they are a very fine group of folks performing a superior service for the aviation industry – its just that there are times when politics rears it’s ugly head – and one never knows from what direction it comes.

The POI does not evaluate the simulator, but has the power to withdraw approval, in this case based on a serious defect not being corrected. Also after an FAA evaluation, the POI still has to authorise the simulator's use for training, so can affect the outcome. The recurrent FAA inspection visits should also pick up on such a defect if it was written up, as it should have been, or if they encounter it themselves. In my experience, the FAA can, and often do, use their power to force operators to update or correct their simulators. However if no one reported it then you can't blame the simulator for not fixing itself.

I agree with your statement completely. However, when one does not know that the simulator is programmed incorrectly in some way, sometimes it is extremely difficult to determine that improper programming without flying the precise profile at issue. Most FAA recurrent evaluations call for about 2½ hours of subjective flying and about 1½ hours of objective testing. And normally, things like an evaluation of a particular simulator’s ability to adequately train recovery from unusual attitudes, will be accomplished only if the airplane and simulator manufacturer agree with the programming involved.

However, to the point at issue, as I said earlier if the FAA POI had sat in the simulator and observed one of the profiles that used this particular scenario, it is my opinion that he (or she?) would have thought the exercise had considerable merit. And, importantly, if a pilot were actually flying the simulator (aside from the ridiculous ramping away of control and then ramping back in that control effectiveness later on – I still believe that is negative training!), particularly if he (or she) was flying it the way the briefing told them to fly, that pilot would probably NOT have noticed the tendency of the simulator to achieve the “magic” pitch-bank limit and stay there. This is because the pilot would have applied the down-wing rudder, on cue, to bring the nose down toward the horizon (and the computer back into a known area) and he (or she) would likely never have been aware of what had just happened.

I do not know if this particular circumstance was ever “written up” in the simulator log. Had it been, I’m quite sure the FAA Simulator evaluators would have checked – and, to my knowledge, the FAA never conducted such an evaluation. So, I guess we all can take that for what it’s worth.

[lefthanddownabit]

Hi AirRabbit,

Thanks for the link. Since the flight controls on the A300-600 are irreversible, after AP disconnect any control oscillations would have to come from the flight crew surely? Alternatively, maybe it didn't fully disconnect, so continued to fight the crew's recovery actions.

You are correct about the limited time for recurrent FAA evals. So the onus is on the sim operator to encourage crews to write things up and so get them fixed, rather than just say "the sim always does that" and ignore it. Maintenance engineers cannot fix things they are unaware of.

On the other hand you will always get the pilot or instructor that has a bee in his bonnet about something or other and continually writes something up which is not a defect.

[AirRabbit]

Hi lefthanddownabit

Of course, if there is anything I’ve learned in the years I’ve spent in this industry, it is that “eye witnesses” are not generally the most reliable of witnesses. However, having said that, some of the passengers on board the flight indicated that the bank angle achieved got much more than what was alleged by the flight crew or acknowledged in the “official” report. And, some of the persons with whom the flight crew allegedly spoke immediately after landing, originally indicated that the story the crew gave at first was somewhat different than the one they gave later to the investigators. Again, surely speculative; but interesting nonetheless. And, lest someone believe I’m out to “get” the crew … I am not! I just want the training exposure experienced to focus on the skills learned and reinforced to be the same skills that are necessary and proper to use when in flight.

Actually, I had not considered your theory of potentially incomplete A/P disconnect; an interesting point I do admit. But, I do know what simulator was used for the most recent training of this crew; and I do know what was taught regarding the use of the rudder in that simulator (and now I know why) – and some of the stories told about the initial discussions immediately after the incident/accident match suspiciously closely to what would likely have happened had the crew followed the techniques used in the simulator.

[lefthanddownabit]

Hi AirRabbit

Presumably the angles mentioned in the report are from the FDR. To most people in the cabin 50 degrees bank will feel more like 90. Even the flight crew might initially overestimate the max bank angle they reached.

You're in a much better position to judge what really went on than me of course. I just enjoy technical debate.

I would certainly expect this aero model to be valid for all AOA's up to stick shake, but if you have significant sideslip as well, even at 7 degrees alpha, no commercial aircraft aero model is going to stand up very well. The 737 aero model had to be revised for just that reason after the rudder hardover incidents.

[XPMorten]

Somewhere in X-Plane there will be a lookup table to calculate each coefficient versus AOA for that aerofoil element. So ultimately X-Plane is lookup table based for aerofoils at least.

The airfoil designer decides the Coeffs vs AoA for each airfoil
section, not the sim.

Anyway, you are missing the point. Lets take an example;
Lets say you go for a 1 hour complete flight. Thats 3600 secs.
Lets say your simulation rate is atleast 30 frames/sec.

In other words, if you use a lookup table and want to hit book values
at all times, you will need 100.000 sets of data since WEIGHT changes constantly, also in cruise.
If you do the EXACT same flight, only with a small change in
Takeoff weight, you will need another 100.000 sets.

Now imagine if you do cross control maneuvres, stalls, engine cuts etc etc. you will need dusins of tables for each frame.

I can assure you that a 40kb .air file in MSFS is not capable handling this. A $15 million Boeing sim yes, maybe.. .

Cheers,

M

[lefthanddownabit]

Lookup tables, how they really work!

XPMorten said:

In other words, if you use a lookup table and want to hit book values
at all times, you will need 100.000 sets of data since WEIGHT changes constantly, also in cruise.
If you do the EXACT same flight, only with a small change in
Takeoff weight, you will need another 100.000 sets.

You have completely misunderstood how lookup tables work. There are no tables of performance versus weight, or anything else. What you have is this:

For each aero coefficient, there will be a lookup (or function) table. This is analogous to the data you enter for the aerofoil in X-Plane. On an FFS this might be two or three dimensional (say a function of AOA, Mach and Sideslip). In MSFS they are all one dimensional, e.g. CL v AOA. Some may actually be linear equations for simplicity. So MSFS will compute the lift coefficient for the current AOA. Other lift effects are added (due to flap, gear, spoilers, etc) then CL is converted to Lift by multiplying by (0.5*rho*V^2*S), yes MSFS knows about this too! The same applies to all the other coefficients in other axes (I doubt MSFS considers sideforce, but it will have CD, CM, Cl and CN.

These forces and moments are integrated in the EOM (which is, I concede, simplified compared to X-Plane, and the only real difference between the two sims). The effect of changing weight (and anything else) will be automatically considered by this model, in exactly the same way as X-Plane.

There are some global tuning factors in the aircraft.cfg file, which also sets values like stall speed, Mmo, etc. Note, the aircraft.cfg file does not set aerodynamic stall speed, the value is just to trigger the stall warning message. Tuning factors make the designers job easier, but don't detract from the validity of the model.

An FFS has CL, for example, broken down into many contributing functions, whereas MSFS will probably only have the basic lift curve slope, but that is just like X-Plane too.

Even X-Plane only considers one dimensional functions for its aerofoils (CL, CD and CM versus AOA). You can have two functions (one for high Reynolds No, one for low) with linear interpolation in between but that is still quite crude, especially for high speed aircraft.

Reading the X-Plane forums I came across references to MSFS using a "behavioural" model, which ties in with your thoughts on how lookup tables work. It is an entirely false description of how the MSFS aero model works.

[XPMorten]

You are right, I was way to optimistic about how MSFS works

Even X-Plane only considers one dimensional functions for its aerofoils (CL, CD and CM versus AOA). You can have two functions (one for high Reynolds No, one for low) with linear interpolation in between but that is still quite crude, especially for high speed aircraft.

True, but you are forgetting that we in X-Plane CAN build a wing out
of up to 12 wing sections with 4 airfoils on each. Each section
can consist of 10 stations - 120 total - with different incidence on all
of them. We also have airfoils on Stabs, props and pylons.
It also models downwash on the tail in e.g a slip which is sort
of 3D.

XP is not perfect, but it's improving every day.

Cheers,

M

[lefthanddownabit]

True, but you are forgetting that we in X-Plane CAN build a wing out
of up to 12 wing sections with 4 airfoils on each. Each section
can consist of 10 stations - 120 total - with different incidence on all
of them. We also have airfoils on Stabs, props and pylons.

I wasn't forgetting that, and I recognise that makes for a powerful engineering based sim design tool. But as I say, you won't find that sort of model breakdown even on a Level D FFS, which generally use "whole aircraft" data. That doesn't make the FFS less accurate, but it's only as good as the manufacturer's data that goes into it.

I'm not pro MSFS, or anti X-Plane, there's room for both, depending on what you want out of the simulator.

One question for you, purely out of interest: how does X-Plane represent the aerodynamics non-aerofoils like the fuselage, for example?

[XPMorten]

how does X-Plane represent the aerodynamics non-aerofoils like the fuselage, for example?

A couple of years ago we discovered a huge error on the fuselage/body lift model.
Actually we managed to get a WINGLESS B777 to stay in the air at
an AoA of about 15 deg about FL100! After numerous atempts to
get Austin to change the model we ran out of arguments.

Then, finally, we accidentally got in contact with the CHIEF DIRECTOR of Aerodynamics
at NASA Dreyden (!). Austin finally backed down and the modell was changed A rocket body has pretty much the same issues as a fuselage.

Don't know all the details, but we know it's based on length and frontal area. Possibly also the 3D shape to some extent, at least for
supersonic flight. Lift, drag and downwash is calculated. Parasite drag is entered by the designer since this will vary from design to design.

Cheers,

M