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Impressions on FSX Flight and Powerplant models

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This link to the Airfile Decode Forum" at Avhistory.org has some comments on FSX relative to flight and powerplant models. Also, on the Beta SDK:In general, people are not impressed.RAF

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Apart from yourself, "people" in that FSX discussion are Administrator, DVA2728, Ian, Carl, Bear-AvHistory, and jcomm. I make that 7 in total.

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Meaning what? That these "people" aren't qualified to make those observations? By my account, those few people have contributed more to understanding the core FS flight dynamics than everyone else in the community combined.--Jon

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Well, with all due respect to those seven individuals... I don't think that FSX is as 'bad' as they're implying.I understand they didn't get changes they wanted incorporated, but I think that statement applies to a lot of people and not just the topic of flight dynamics.This post comes across to me as an attempt to say that we shouldn't support FSX. If my impression is wrong, then what is the actual point?

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>Well, with all due respect to those seven individuals... I>don't think that FSX is as 'bad' as they're implying.>>I understand they didn't get changes they wanted incorporated,>but I think that statement applies to a lot of people and not>just the topic of flight dynamics.Well I agree there are many things in addition to FDs that could/should have been improved, but when you've had 4 years to do something better and made virtually no attempt to improve the underlying quality/fidelity of the FDs, I think it deserves at least a little 'informed' whining.>This post comes across to me as an attempt to say that we>shouldn't support FSX. If my impression is wrong, then what>is the actual point?Naw, of course we support it. If we didn't what would be the point in whining about it. What I don't understand is why criticism has to be looked at dismissively as though "only 7 people are complaining about it, so who cares". These are the people (Avhistory alumni) who originally decoded the .air file, brought us tools like AirED, AFSD, AirWrnech, etc. and documented in detail the aircraft.cfg. If you don't want to listen to what they say, that's fine, but it would be ignorant to dismiss it.I look at those comments as an attempt to confirm what hasn't changed, and that's at least as important as understanding what has. If their frustration is coming through, then blame them for that, not for providing useful information.I guess I really don't have anything more to say about this. I just have a great deal of respect for what many of these people have contributed to the community, and despite whatever motives you may think they have, the end result is a better understanding of what we have to work with.--Jon

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"In general, people are not impressed."That right there is a dismissal of FSX. Plain and simple.The flight dynamics in FS are good, better than given credit. In fact... it's AvHistory.org that has repeatedly stated that as a consensus.So... the question is... why the turn-around? Now, because ACES didn't incorporate changes they desired, the flight dynamics and powerplant models are total crap?Sorry... while I can agree that the .air file could use enhancements... I don't believe that FSX is suddenly the horrible sim that they're portraying it as.

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>Sorry... while I can agree that the .air file could use>enhancements... I don't believe that FSX is suddenly the>horrible sim that they're portraying it as.I never see they're portraying the FSX as a horrible sim.they just make the point that ACES make eye candy changes more important than flight model...the FM is mature enough to grow and improve, but is far away from being good.Looks like ACES followed the heading of an ARCADE GAME in a SIMULATOR. IMO

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>"In general, people are not impressed.">That right there is a dismissal of FSX. Plain and simple.How about this alternative; people are not impressed with the fact that there have been no changes which improve flight dynamics, and that is disappointing to the people who DO CARE about such things. YOU may not find that a problem, other people do. Your equating "people are not impressed" with "dismissal of FSX" is simply spin and has no measurable value.>The flight dynamics in FS are good, better than given credit. >In fact... it's AvHistory.org that has repeatedly stated that>as a consensus.Of course they've acknowledged they work - AVhistory does mostly WWII-era aircraft. They certainly work well for low-speed A/C, but this simulation has evolved beyond the C172. Without proper high resolution tables, compressibility is out the window in simulating high performance aircraft. "Good" only gets you so far. If you'd read the posts you'd see the most of the complaints were based on high-performance failings.>So... the question is... why the turn-around? Now, because>ACES didn't incorporate changes they desired, the flight>dynamics and powerplant models are total crap?Not that I'm that interested, but for fun please quote me the individual who said "total crap" (I'll even settle for "garbage", "trash", or "POS"). WHERE are you getting this from? With regard to "why the turnaround", see above. What seems to be becoming clear here is that you're not really interested in "why the turnaround", you're interested in blowing what's been said way way out of proportion because you seem to think there's more value in pointing out other people's frustration than rationalizing your own points.>Sorry... while I can agree that the .air file could use>enhancements... I don't believe that FSX is suddenly the>horrible sim that they're portraying it as.Again, and this is so trivial as to be funny, where was the "horrible sim" analogy even IMPLIED!I'm sure we both have better things to do, and for the record it's been fun, but this is getting stupid, so I quit. You may have the last word sir, but I employ you to do more listening and less embellishing.--Jon

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Ok... here's the last word:Since FSX is still a step forward for FS itself, what does this thread offer in the forward direction?Simple as that.

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Meaning that they are only 7 of the 33,000+ members of this forum and hardly qualify as "people".

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"Without proper high resolution tables, compressibility is out the window in simulating high performance aircraft."Can you point me to published sources of the data needed to complete such tables for, say, a 747?

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>"Without proper high resolution tables, compressibility is>out the window in simulating high performance aircraft.">>Can you point me to published sources of the data needed to>complete such tables for, say, a 747? Dr. Roskam has published values for Cdo as a function of Mach in different editions of his Engineering Texts. I used Roskam's values to approximate Cdo and Cdo(M)[TBL430] for a 727 FM I did. I couldn't find the exact values, but remember Cdo ~ 174 Drag Counts at Mach 0.80, and increases by a dozen counts in something like 0.02 Mach. Ian Kerr provided me with the for Cdo values for the 727 as listed in one of Roskam's text's. Dr. McCormick also has graphs of for some aerodynamic coefficents in his 1995 'Aeronautics and Astronautics' Text. Boeing publishes data in various 'Flight Performance Engineering Manuals' for specific jet transports. The manuals are difficult and expensive to obtain. More generic information is published in the Boeing 'Jet Transport Flight Performance Enginneering Manual'. Which I have a copy of. I found various Mach dependent parameters for the 747 in a variety of sources. Eventually, I was able to DL a .pdf file based on a 1969 NASA document that contained values for the 747-100 and other aircraft. Ian Kerr has a large library relative to aircraft performance where he is employed. Including 'Datcom' approaches for calculating drag, etc. In virtually all cases, transonic variations in Stability and Control Derivatives requre much greater resolution than the 0.20 M available in FS AIR files provides. FS98 and later AIR files include one high resolution table that uses IEEE float8 variables for "Lift Slope vs Mach". TBL 401 actually modififies Oswald Efficiency by a factor of [TBL 401(M)]^2. So, it is possible to set adequate resolution for 'Induced Drag Coefficient vs Mach'. Regardless, that doesn't allow one to adjust "Zero Lift Drag" as a function of M nearly close enough. One can also reverse engineer drag parameters from published FM tables. RAF

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I'm a bit confused as to how the change to zero lift drag would come into play in flight. Do we normally operate these aircraft at the airspeeds where that variance would be seen as preventing accurate simulation?Also, is the value of significant enough a change to truly prevent accurate flight dynamics without it, or is it just a personal pet peeve of yours that it's not supported?Bottom line... does the end user actually see a completely different aircraft with the good doctor's values or is it something so trival that it's insignificant?

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>This link to the Airfile Decode Forum" at Avhistory.org has>some comments on FSX relative to flight and powerplant models.> Also, on the Beta SDK:>>>>In general, people are not impressed.>>RAFGreat video.He talks like the main character of the "Sick Sad World" tv-show. :DMarco

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>Great video.>He talks like the main character of the "Sick Sad World">tv-show. :DSorry guys! Wrong forum, lol.Marco

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I just want to reinforce Jon's comment regarding the contributors to the Avhistory.org forum.Have you ever tried to create an FDE from the ground up - rather than crudely "adjust" the default 737?These people can and do. They probably understand more about the FS simulation and real world flight/engine dynamics than the rest of us put together. As Jon said, they even created the tools we use.The authenticity of the flight experience surely depends very largely on the accuracy of aircraft behaviour - unless, of course, we all want a totally stable point-and-shoot arcade game.So it really is to be regretted if FSX has not enabled more subtle and realistic adjustment than FS9 and predecessors.Let's hope this is not the case.CheersChris

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>I'm a bit confused as to how the change to zero lift drag>would come into play in flight. Do we normally operate these>aircraft at the airspeeds where that variance would be seen as>preventing accurate simulation? Prop aircraft models generally don't require Compressibility (Mach) effects in the model. Though, Compressibility does have some effect for high performance aircraft flying at high altitudes. Jet aircraft almost always enter the transonic range; that's why most jets have swept wings to delay the Critical Mach Number (MCr), where flow first becomes supersonic and shock waves form.>Also, is the value of significant enough a change to truly>prevent accurate flight dynamics without it, or is it just a>personal pet peeve of yours that it's not supported? I've found one can model typical jet transports fairly closely with the coarse, default Mach tables. Which have an implicit Mach scale going from Mach 0.0 to Mach 3.2. In increments of 0.2 Mach. TBL 401 is also critical, fortunately that can be set with high resolution in the transonic region; it uses floating point datums that can be set as needed. At lower flight levels and/or flight weights, Cdp predominates. Total drag coefficient, CD, equals Cdp + Cdi. Cdi is typically 35% of Cdp. Cdp = Cdo + Cdm, and Cdm may only be 2% of Cdo at Typical Cruise Mach. However, to model an aircraft such as the 747 at the highest normal cruise, M 0.865, one has to compromise the Cdm table, which can only be set at M 0.6, 0.8, 1.0, etc. Fuel consumption varies almost directly with Drag. If one wants accurate PPH over the normal range of cruise Mach's problems often arise. The coarse Mach tables are mainly a problem with supersonic jets, such as fighters. Ability to penetrate the 'sound barrier' realistically, and accurate cruise fuel flow require higher resolution tables than provided in MSFS/CFS. While more than just Cdm affects drag, real graphs of this component typically show Cdp (Cdo+Cdm) starting to increase rapidly at Mach 0.975, peaking around 1.00, then often dropping as the hypersonic realm is entered. In FS/CFS, one can only set straight line variations at M 0.8, 1.0, 1.2, etc. Which gives way too much increase at M 0.9, but possibly not enough at M 1.0. >Bottom line... does the end user actually see a completely>different aircraft with the good doctor's values or is it>something so trival that it's insignificant? In the end, it's just a matter of whether 'Arcade Game' performance modeling is good enough, or if something better is desirable. MSFS graphics have continued to increase in resolution, I often have a hard time telling if an image is of a real aircraft, or an FS screen shot. Unfortunately, fine structure detail in the AIR file tables has generally not increased since FS98 (though, a few new tables have been added since FS98). According to the Avhistory.org thread, high resolution Mach tables were implemented in the pre-beta CFS4 (which never got to beta testing). But, the enhancements implemented in CFS4 were discarded in the later development of FSX. RAF

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Sounds to me like the vast majority of FS users would never see a difference.Given that, and considering MSFS is a commercial product designed to target a broad audience of customers... I don't see the lack of supersonic aircraft modelling as being a critical failure.Not that I'm against improved flight dynamics, I'm just not agreeing that FSX is to be poo-poo'ed.It's like I said before... some people didn't get what they consider to be the only important changes. That does not make FSX bad.

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Hi,No one here said that FSX was bad. They said that the FDE was no improvement over FS9. And I guess if that is one of the important things to them, then this is disappointing. I have no problem with someone saying that, as long as the background is clear (which it was). I am also disappointed that the FDE's have not been improved, or at least brought back up to FS2002 levels.However, while the FDE equations might not have changed, several people have commented that the flight experience in FSX is better, due possibly to better interpretation of the same FDE's.--Tom GibsonCal Classic Propliner Page: http://www.calclassic.comFreeflight Design Shop: http://www.freeflightdesign.comDrop by! ___x_x_(")_x_x___

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>Hi,>>No one here said that FSX was bad. They said that the FDE was>.........>However, while the FDE equations might not have changed,>several people have commented that the flight experience in>FSX is better, due possibly to better interpretation of the>same FDE's.>>-->Tom Gibson I have mentioned that I suspect the FM iteration rate has been increased, or improved. Based on user reports, and the fact that the Ultra Light is set with lower MoI's and weights than would be stable in FS9 and earlier. I have also mentioned the new SDK (in the FSX Beta) still has the same old explanations for lines in aircraft.cfg. Some are amateurish, others vague. Some are simply wrong. Moments of Inertia are given in "slugs per foot squared" in some places. Simply wrong, the correct English dimensions are "slug - foot^2". They still have 'Time Constant' bass ackwards. The line with 'Prop Coefficient of Friction' is incorrectly named. A year ago someone determined that it actually relates to Prop Coefficient of Power (Cp) (at high Beta). Such matters do little to inspire confidence. RAF

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"Moments of Inertia are given in "slugs per foot squared" in some places. Simply wrong, the correct English dimensions are "slug - foot^2". "In England, and all other counties that have adopted SI, the units of moment of inertia are kilogram metre squared.

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>"Moments of Inertia are given in "slugs per foot squared" in>some places. Simply wrong, the correct English dimensions are>"slug - foot^2". ">>>In England, and all other counties that have adopted SI, the>units of moment of inertia are kilogram metre squared. True, kg-m^2 in SI. g-cm^2 in CGS. However, much, probably most, of the aerodynamics engineering literature still uses English units. Including, I think, NASA documents. English engineering units are fine, as long as they are correctly applied. While European "Metric" measurements in common aviation usage as at least as ######ized as the English usage goes. For example, aircraft weights are given in kilograms, which is not a weight, but a mass. RAF

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