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Guest Ron Freimuth

Serious FDE bug in FS2004?

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Guest Tom Goodrick

I stumbled onto a CG issue when I imported my Beech Duke (my FD, aircraft designed by Chuck Dome). The payload I had was just two of me (230 lbs) in the cockpit and nothing else. This is a forward CG condition. My CG gauge shows it as -8.89% but, since I use zero as the Refernce Datum, this is really 16.11%MAC. The problem observed was that trim required was nose up almost off the scale in FS9 but was in the normal range in FS02. I put an elevator trim gauge (ie- pitch trim) on the panel and noted 11.0 degrees required to fly level at a slow speed. But by changing the htail_incidence from 1.0 to 3.0, the trim became 5.5 degrees, which is much more reasonable.I looked for the CG thread you mentioned but could not find it.A complete discussion of my CG testing with photos can be found athttp://www.billvons.com/cgi-bin/yabb/YaBB....;num=1060530241

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Guest Ron Freimuth

>My investigation of the new bugs in the FS2004 flight model>appears to be reaching a conclusion. Unfortunately I have a>potentially new and serious bug to report. This new bug>appears to be a direct consequence of the failure to process>the REC1101-50 variable ..........>>As has been pointed out in various posts MSFS calculates>induced drag from AoA rather than CL. This is not a material>problem if AoA is positive or rendered positive. In REC404 of>the air file it has always been possible to declare CL=0 at a>negative AoA. REC1101-50 was then set equal to that negative>AoA and modified the induced drag equation thus; Sometimes 1101:50 was positive. One might want Cdi Min to occure at a small CL. However, I have never been able to get CD to fit AC data unless I set 1101:50 to the point where total CL (TBL 404, Incidence and Twist) was at or close to (0.2 deg) the point Body AoA generated CL=0.>Induced drag = AoA value from REC404 minus negative value in>REC1101-50 multiplied by (everything else)>>In FS2004 the position appears to be as follows;>>The flight model has no such modifier. If the current AoA is>negative and the current CL is positive it calculates the>induced drag as negative since the 1101-50 correcting variable>has been removed. I suspect 1101:50 is internally set to the point CL=0.0. For FS9.0, that would be at the point TBL 404 goes through zero. Normally a negative number (~ -3.0 deg). Now FSEdit generated a new Lift table and the equivalent of most of REC 1101. I noted it did set the equivalent of 1101:50 correctly for the CL vs AoA curve plus any externally set Incidence and Twist. Rather than being in degrees (deg16) it was in radians, float8.>The FS2004 flight model has no 1101-50 modifier and so it>presumably calculates the induced drag using minus one degree>yielding a negative induced drag. With current tools it is>difficult to tell if it truncates the impossible negative>result to zero. Cdi = IDK*(m*AoA')^2. Where AoA' is based on body AoA, the point CL is zero. 1101:50 was used to adjust for Incidence, Twist, and TBL 404 before FS9. That is equivalent to IDK*CL^2 when the lift slope is linear. Since CL=m*AoA', CL^2 = (m*AoA')^2. 'm' is the lift slope in TBL 404. Howver, CL vs AoAw is curved, and saturates. So, there is some quesiton of how 'm' is calculated from TBL 404. For 'normal' TBL 404 shapes, 'm' has been verified to be very close to the average slope between CL=0 and CL=max. >If you test in FS2004 at an IAS which forces AoA negative, but>CL positive in REC404 what do you all see?>>My tests appear to confirm zero or negative induced drag when>it should be positive and potentially very positive in an>aircraft of large mean incidence flying at significant AoA <>mean incidence. I doubt that occures. However, I spent some time testing two AC 'fixed' for FS9. I flew the C208 and some other AC inverted at quite a high altitude (17,000 ft for the C208). I set full power and noted the final IAS when in normal flight (I could use ALT hold in that case), and inverted. I didn't have enough trim to hold the AC inverted, so I had to use the JS also. As far as I could see, IAS settled down at 125 IAS when inverted. The same as when not inverted. Induced drag should be significant at 125 kts, it is probably near Cdo around 96 kts IAS. If Cdi were much different from what it should be, IAS would be quite different. Especially if it went negative. I have flown many AC inverted in FS9 and haven't noted anything that seemed different as far as drag goes. >Where FS2002 would correctly calculate substantial induced>drag at 5dAOA the bug in the FS2004 flight model apparently>causes it to see the AoA as minus one degree causing it to>calculate instead either a small negative drag (a thrust) or>maybe truncates it to zero. Herve' Sors emailed me and said he will soon have a new AFSD that works with FS2K4 and FS2K2. He didn't find any big problems, he does know about the Incidence and Twist and will simply not use them if FS9 is detected. Of course, I will carefully check AFSD readings for consistency. In case either it or FS9 has a bug(s). >There appears to be a requirement that a negative AoA must not>be associated with a positive CL in FS2004 unless the flight>model is patched by Microsoft. In FS9, body AoA is identical to wing AoA. Almost all AC have some positive CL at a negative AoA. CL only reaches zero at a negative (sometimes 0.0) AoA. I have not seen changes in drag/speed when FD files were correctly modified for FS9 and I doubt I will in the future. This includes my Concorde, which sets CL=0 in TBL 404 and certainly represents one end of the spectrum. >'Janes' normally declares root and tip incidence if they>differ. Taking the example of a BE36 Bonanza the root>incidence is 4 degrees and the tip incidence is 1 degree.>>The average incidence is (4+1)/2 = 2.5 degrees >>By default you will settle for using average incidence as an>approximation of mean incidence. By simply shifting TBL 404 to the right by 2.5 degrees from the wing alone, one will incorporate that 'average incidence'. BTW, TBL 404 (and the new equivalent) were the ONLY tables in the AIR file that related to Wing AoA. All the others were based on Body AoA. One reason I've set many of my more recent AC so Incidence + Twist/2 = 0.0. No need to shift all the non-linearity tables which are based on Body AoA.In reality the average>incidence and the mean incidence are only the same if the wing>twists smoothly from the mid span (middle of fuselage) to the>tip. Therefore if you seek greater accuracy you should consult>a three view drawing and note whether the wing has a centre>section. Previous to FS9, one shouldn't have set the wing incidence to the physical value anyway. Same for tail incidence. The real AC has to increase 'root incidence' because of downwash. Even air ahead of the wing is moving down before it gets to the airfoil. There is no place in the AIR file for downwash to be set, thus it must be accounted for by setting Body AoA to the equivalent, rather than physical value. While the H. Stab will appear to generate a down force even if it is at incidence zero. That's becaues downwash behind the wing pushes it down a bit. 'epsilon' is on the order of -0.5 to -1.0 degrees. Givng a real AC with zero tail incidence an effective negative incidence. Which is desired. However, the H. Stab could also be inverted relative to the wing camber. I don't know if this is done, but an airfoil with small camber turned upside down would have a similar effect to a negative tail incidence. BTW, it's confusing how to define neg or positive for the tail. In this case, I mean the tail incidence (or effective incidned) that pushes the tail down (unless the elevator is pulled up).>OTHER BUGS.>>Taking into account the information in this post I conclude>that failure to process REC1101-50 accounts for all of the>difference in observed dynamic performance between FS2002 and>FS2004. I was cautious, and stated I'd have to do more testing. I've done more and am quite sure this change is not a problem. Other than that ordinary users shouldn't be expected to edit TBL 404. A table MS does not even admit to. ;) I checked a few of the prototype AIR files in AIRCRAFTprototypes. Those I looked at did have new TBL404's. Set for nominal CL at AoA=0. I'd suggest people simply rip TBL 404 out of one of these new AIR files and replace TBL 404 in an AIR file based on one of the FS AC. Aired will cut and paste. In fact, you don't need to remove the old TBL, just set Aired to 'unsorted' and ADD the new table AHEAD of the old one. Further, if TBL 404 has been modified, you will have both the old and new one to look at in the same AIR file if any further changes are required. Note 'nominal CL' doesn't mean 'correct for a different AC'. However, pitch should probably come out reasonable, since AC with high wing loadings also fly faster. So, AoA is generally about the same at cruise. >I have addressed all the other bugs that have been reported in>the FS2004 FDE code within the thread 'Resolving CG issues in>FS2004'. The only other FS2004 flight model bug which I can>find after extensive testing, and which cannot be patched by >using means explained in the two threads, is the 'distributed>load MOI bug' , (see post 4 of the CG thread ). You missed the loss of 'prop effect on rudder'. FS2K2 lost the effect on the H. Stab. Guess MS wanted to finish their damage. ;( Also, the SPD Hold is still messed up. And, it appears the new [autopilot] lines don't all work.>A number of posts in this thread report that FS2004 is also>not processing this or that, or incorrectly evaluates>something. I have read those reports carefully and I believe>that every one relates to changes which took place with the>transition from FS2000 to FS2002. I am as certain as I can be>that the only new bugs in FS2004 relate to the three key>variables which Microsoft have admitted removing.>-->FSAviator. I was amused by all the new things reported in aircraft.cfg. Things that were introduced in FS2K2 or even earlier. -RAF

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Guest IanK

>> Cdi = IDK*(m*AoA')^2. Where AoA' is based on body AoA, the>point CL is zero. 1101:50 was used to adjust for Incidence,>Twist, and TBL 404 before FS9.>> That is equivalent to IDK*CL^2 when the lift slope is>linear. >> Since CL=m*AoA', CL^2 = (m*AoA')^2. 'm' is the lift slope>in TBL 404. Howver, CL vs AoAw is curved, and saturates. So,>there is some quesiton of how 'm' is calculated from TBL 404. >For 'normal' TBL 404 shapes, 'm' has been verified to be very>close to the average slope between CL=0 and CL=max. >In reality the average>>incidence and the mean incidence are only the same if the>wing>>twists smoothly from the mid span (middle of fuselage) to>the>>tip. Therefore if you seek greater accuracy you should>consult>>a three view drawing and note whether the wing has a centre>>section.>> Previous to FS9, one shouldn't have set the wing incidence>to the physical value anyway. Same for tail incidence. The>real AC has to increase 'root incidence' because of downwash. >Even air ahead of the wing is moving down before it gets to>the airfoil. There is no place in the AIR file for downwash>to be set, thus it must be accounted for by setting Body AoA>to the equivalent, rather than physical value.Actually the IDK determines the down wash angle as this is the physical mechanism that generates vortex lift induced drag.This rotates an otherwise vertical lift vector aft but the value of the mean downwash angle over the chord (say half that existing at the TE) [McCormick's book explains this well]. So ©Di = ©L*sin(mean_downwash_angle). Since the DW increases with lift this can be compared with CDi = CL^2*IDK therefore IDK = sin(DW)/CL. As IDK is a constant then CL is proportional to sin(DW) then CDi is proportional to sin^2(DW) and to CL^2 as expected from simple lifting line theory.Sorry just nitpicking.These formula may not be exactly correct as I am doing this from memory and I will have to look it up again.> I was cautious, and stated I'd have to do more testing. >I've done more and am quite sure this change is not a problem.> Other than that ordinary users shouldn't be expected to edit>TBL 404. A table MS does not even admit to. ;) They do as "Mike Schroeter, a leading member of the Microsoft FS9 development team" says to edit the lift table from a quote I say on the Frugalsworld board."The correct thing to do, which is what I changed,is to go into the table with alpha for the whole airplane, because we don't really care what the wing does by itself. We are simulating the whole airplane, which is what the table represents. So this is actually a correction."Now we know!However this still means we still can't model real a/c as they usually don't have parabolic drag curves near min drag never mind approaching stall.> -RAFIan

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I always figured to model the whole aircraft not just the wing. Julian

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Guest Ron Freimuth

>>Even air ahead of the wing is moving down before it gets to>>the airfoil. There is no place in the AIR file for downwash>>to be set, thus it must be accounted for by setting Body AoA>>to the equivalent, rather than physical value.>>Actually the IDK determines the down wash angle as this is the>physical mechanism that generates vortex lift induced drag.>This rotates an otherwise vertical lift vector aft but the>value of the mean downwash angle over the chord (say half that>existing at the TE) [McCormick's book explains this well]. So>©Di = ©L*sin(mean_downwash_angle). Since the DW increases>with lift this can be compared with CDi = CL^2*IDK therefore>IDK = sin(DW)/CL. As IDK is a constant then CL is proportional>to sin(DW) then CDi is proportional to sin^2(DW) and to CL^2>as expected from simple lifting line theory. All I know is downwash angle and its effects aren't easy to account for. One reason modeling the Voyager was easier: I didn't have to account for wing downwash on the horiz stabilizer.>>> I was cautious, and stated I'd have to do more testing. >>I've done more and am quite sure this change is not a problem.>> Other than that ordinary users shouldn't be expected to >edit>>TBL 404. A table MS does not even admit to. ;)>> They do as "Mike Schroeter, a leading member of the Microsoft>FS9 development team" says to edit the lift table from a quote>I say on the Frugalsworld board.>>"The correct thing to do, which is what I changed,>is to go into the table with alpha for the whole airplane,>because we don't really care what the wing does by itself. We>are simulating the whole airplane, which is what the table>represents. So this is actually a correction.">>Now we know!>>However this still means we still can't model real a/c as they>usually don't have parabolic drag curves near min drag never>mind approaching stall.>Ian Ian, I think you are confusing Section Polars with the complete AC. Ron

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Guest FlyboyMichael

What do you guys think about the following statement:The following is from Mike Schroeter, a leading member of the Microsoft FS9 development team. He has indicated that it can be released to the public. However, the source of where I got this information is private, as it concerns the FS9 beta, and we are under NDA concerning this. All the beta testers are aware of it, and can confirm that this exists and is word for word as I have copied it here."The changes to the parameters in question were intentionally made. Thereason is essentially that they simply represents offsets from alpha whenentering the lift table. In most aircraft, the incidence and twist anglesare relatively small, and generally even offset each other. Thus, the neteffect is usually small. The correct thing to do, which is what I changed,is to go into the table with alpha for the whole airplane, because we don'treally care what the wing does by itself. We are simulating the wholeairplane, which is what the table represents. So this is actually acorrection.In reality, this shouldn't "disable" any aircraft because of the nature ofthese anglesas I mentioned above. While it is understandable that there may be minordifferences with FS2002 performance, most users haven't noted any majorproblems because of the reasons I mentioned above. So where are thecomplaints coming from. First, I've seen flight models where the incidenceangle is used to tune the cruise pitch angle of the aircraft in flight.This is an incorrect method that would result in masking an incorrect lifttable with a bogus incidence angle value. The lift table should be tuned,which in fact people are already discovering. I believe this is why duringthebeta this issue didn't become the major problem that it is being made out tobe in the NGs now. It did come up in the Aircraft NG awhile back, but wasquickly understood. The other thing that is going on is that people arechanging this value, and when they see it doesn't affect the runtime, theyassume something is broken. In the FS2002 SDK, we explained that manyvalues are there for use in the Fsedit aero generation. These values arestill inputs into the aero generation. This is being updated in the (soonto be completed) FS9 aircraft sdk.So there is no conspiracy going on to dumb things down for the Xbox or toprevent terrorist training (this has certainly been an interesting thread onAvsim!). I know change in the FM can often be a source of angst, fear, andin this case panic, but we are still focused on more realism and morecapabilities in the long run. Hope this helps.Mike

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"The correct thing to do, which is what I changed,is to go into the table with alpha for the whole airplane, because we don't really care what the wing does by itself. We are simulating the whole airplane, which is what the table represents. So this is actually a correction."In particular I pick up on "because we don't really care what the wing does by itself". This to me sounds silly. The wing and the "whole aircraft" are often doing different things. An independant action on the wing will affect the way the "whole aircraft" behaves. This occurs during practically any activity with the possible exception of straight and level flight. Andrewp.s. I'm a pilot, not an engineer. ;)

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My aeronautical engineer/sim developer contact, Mike Dornheim, concurs with the "whole aircraft" approach, and as I indicated in an earlier post, guessed that this was what MS was after by eliminating/consolidating the variables in question prior to MS issuing its statement. This would strongly support, in my mind at any rate, the recent news from MS.The aircraft works as a collection of interacting systems and it is the behavior of the entire aircraft as a unit that we are concerned with here. It's a flight simulator, meant to simulate flight in aircraft already designed and developed, rather than a wing design simulator that considers only the wing as a single component. To be even more brief, the flight simulator is intended to simulate the experience of flying and airplane, not designing one from the ground up, and MS is using more or less proven techniques to build its simulators. There are "bugs" but they are not detrimental to the overall simulation experience (how many sim pilots REALLY worry about cowl flap drag, for example?). If I can develop a good-flying, convincing aircraft that is representative in most particulars of the "real thing" then I have done my job.I agree with the changes MS have made and think this will play out as a plus in the end.

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Guest Ron Freimuth

>The following is from Mike Schroeter, a leading member of the>Microsoft FS9 development team. He has indicated that it can>be released to the public. However, the source of where I got>this information is private, as it concerns the FS9 beta, and>we are under NDA concerning this. All the beta testers are>aware of it, and can confirm that this exists and is word for>word as I have copied it here. I heard there is now a change in the NDA. That beta testers can not release info they learned in the beta test(s). Thus, Beta Testers now have an UNFAIR ADVANTAGE. To the degree they discovered things during the beta test that they can't "let out" even if they wanted to. In fact, they could start on upgrading their AC (which would include many commercial products) before those excluded from the FS9 beta test could. And, also use NDA info to their advantage. I'd hardly think they wouldn't take advantage of such details. I believe it is ILLEGAL under the "1896 Sherman AntiTrust Act" (as worked out in Case Law) for a developer to give advantages to specific companies/individuals (say in a Beta test) at the expense of those it excludes. All external companies, etc. in the same class must be given the same access to 'private information'. If they want to charge $10 million, OK. But, anyone willing to pay the $10 million has to be given access. >"The changes to the parameters in question were intentionally>made. The reason is essentially that they simply represents offsets >from alpha when entering the lift table. In most aircraft, the >incidence and twist angles are relatively small, and generally even > offset each other.>Thus, the net effect is usually small. The correct thing to do, >which is what I changed, is to go into the table with alpha>for the whole airplane, because we don't really care what the >wing does by itself. We are simulating the whole airplane, >which is what the table represents. So this is actually a>correction. "is to go into the table with alpha". Fortunately, we know that is TBL 404. Certainly MS never explained it. Nor, does his statement explain 'how to fix that table, or even 'how to get at it'. In addition, he ignores the fact that 1101:50 is no longer effective. While FS9 should effectively set it to the "appropriate value" if TBL 404 is correctly modified, this does not result in the same Cdi parabola the original AIR file may have been set for. I'm talking about the times 1101:50 was purposely set to make Cdi_min occur at a small CL. Which is what virtually all NACA airfoils show. Laminar Flow airfoils tend to have a drag bucket which occurs at a high enough CL so a pilot can sometimes find it during cruise and gain several kts for the same power setting. While one couldn't make the drag parabola into a bucket in FS, the minimum of Cdi could be shifted to more closely approximate such an airfoil. But, not in FS9. >complaints coming from. First, I've seen flight models where>the incidence angle is used to tune the cruise pitch angle of the >aircraft in flight.>This is an incorrect method that would result in masking an>incorrect lift table with a bogus incidence angle value. The lift >tableshould be tuned, In fact, real AC have the root wing incidence set to adjust AC pitch. However, I will agree that TBL 404 should apply to the complete AC, not just the wing. That is, include the effect of incidence and twist in the AoA offset. As mentioned above, 1101:50 was also 'disabled'. Thus, one can't necessarily UG an AIR file to give the same results in FS9 as in FS2K2 by adjusting TBL404.> in the beta this issue didn't become the major problem that>it is being made out to be in the NGs now. It did come up in the >Aircraft NG awhile back, but was quickly understood... Since beta testers couldn't talk about this change (until the last week, when at least some were given permission), those 'not in the know' ended up spending a lot of time finding out the HARD WAY after FS9 was released. What other secret information do beta testers have that the rest of us don't? How long will the rest of us have to fool around to discover other changes? Including the much larger number in the rest of FS9?-RAF

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Guest IanK

>quote>>I saw on the Frugalsworld board.>>>>"The correct thing to do, which is what I changed,>>is to go into the table with alpha for the whole airplane,>>because we don't really care what the wing does by itself.>We>>are simulating the whole airplane, which is what the table>>represents. So this is actually a correction.">>>>Now we know!>>>>However this still means we still can't model real a/c as>they>>usually don't have parabolic drag curves near min drag never>>mind approaching stall.>>Ian>> Ian, I think you are confusing Section Polars with the>complete AC. >> Ron>Nope. Most books assume the parabolic drag (polar) law is used for flight performance predictions (of a whole aircraft). This will work over small ranges of CL say

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A recent poster has reposted the quote from Mike Schroeter as though it were new information. The original is in this thread at post 58 and has been much discussed in this thread since. This is old ground. We have been debating the simplest means by which the variously affected FS2002 FDE may be updated to equal accuracy in FS2004. Having taken into account all of the information provided by all of the contibutors I believe we have almost reached a final conclusion.SUMMARY - new build FDE for FS2004:The deletion of the pitch variables by Microsoft does not prevent new build aircraft for FS2004 having the same accuracy as new build aircraft for FS2002. CASE 1.Displayed pitch must be controlled by shifting the real world CL/AoA curve by the negative complement of mean incidence, within TBL 404.SUMMARY - FS2002 conversion to FS2004.The deletion of the pitch variables by Microsoft degrades the displayed pitch and performance envelope of most aircraft when they are imported into FS2004.CASE 2.Aircraft prepared for use in FS2002 with TBL 404 matching REC1101:50 and also using the method which is now mandatory in FS2004 and described above as CASE (1) do not need to be fixed.CASE 3.Aircraft prepared for use in FS2002 with TBL 404 matching REC1101:50, but which did not comply with CASE (1) above need the described shift of TBL404 to correct the displayed pitch. CASE 4.Aircraft prepared for use in FS2002 with a discrepancy between the content of TBL 404 and REC1101:50 need corrections to both the displayed pitch and the induced drag for use in FS2004. TBL404 could be used to provide either correction, but not both at once.Case 4A - TWO PART FIX TECHNIQUE.The MDL author rotates the MDL nose down by the mean incidence of the real aircraft and the FDE author uses TBL404 to correct the induced drag error. For these aircraft the induced drag correction is not equal to the mean incidence shift and must be empirically determined or calculated from the FS2002 FDE TBL404 and REC1101:50 content mismatch. The FDE author must alter the nosewheel oleo compression code to correct the MDL rotation on the ground. This technique saves time and guarantees identical performance in FS2004 after conversion.Case 4B - NEW BUILD TECHNIQUE.Alternatively to avoid the need for MDL rotation much of the aerodynamic content of the FDE may be rewritten from scratch using the CASE 1 method. It will be theoretically possible, but difficult and time consuming, to match performance in FS2002 to performance in FS2004, whilst also ensuring display at the correct pitch. I believe this thread has now reached its natural conclusion unless someone describes additional cases or can contribute a simpler technique for fixing all those FS2002 aircraft (probably the majority) described in case (4). Having read all the posts carefully I conclude that the Summary and Cases 1 to 4 above are 'disputed' in only one respect, all other 'disputes' having been resolved. The point still in 'dispute' is at the very core of this thread because it is the key to controlling pitch display correctly in FS2004.I can illustrate the key 'disputed' issue using a snippet from a recent post by Ron Freimuth.Ron said;As the summary above discloses I believe that to the contrary to understand how to produce FDE for FS2004 or how to convert FS2002 FDE for use in FS2004 it is necessary to understand that it is not 'normally' anything in FS2004. In FS2004 the value of AoA at CL=0 has to be coded equal to the real world value adjusted by the negative complement of mean incidence for the aircraft in question, unless the MDL author rotates the aircraft by that value instead. Now that Microsoft have removed the pitch variables these are now the only two means to set the correct displayed pitch. Hence the need to estimate mean incidence with great care whoever is setting the pitch in FS2004. I can use a recent post from Curious George to illustrate this well. He said;< in the case of the Whitley mentioned earlier, when Table 404 is adjusted downward by 6.5 degrees (that is, where zero lift occurs at -6.5 degrees AoA), the AoA and pitch are identical in cruise, both coming in at -2.9 degrees at a cruise speed of 145 mph IAS. >This implies that previously in Fs2002 CL=0 was at zero AoA in FS2002 which may be correct for the Whitley. The variable deletions by Microsoft discussed in this thread make pitch and AoA falsely equal so that the Whitley displays at the correct -2.9 degrees nose down pitch in the cruise. To achieve this the CL=0 v AoA cross must be at exactly minus 6.5 degrees because the Whitley has a mean incidence of 6.5 degrees. (I am taking that value on trust from Curious George, but anyway this illustrates very well why there is no 'normal' value for CL=0 v AoA in FS2004)If CL=0 had been associated with AoA = -3 in TBL 404 the Whitley would display 3.5 degrees more nose up than in real life. It would cruise with + 0.1 degrees of pitch instead of the real world -2.9.This is why mean incidence must be carefully researched and then used to modify the real world AoA for CL=0, and every other CL, by shifting TBL 404 as described.. FS2004 simply has nowhere else to get the pitch data.If we can all agree that to display the correct pitch attitude FS2004 depends on the FDE author shifting the real world CL v AoA curve by the negative complement of mean incidence then we are all in agreement about all the cases unless someone eventually provides a simpler fix for case (4).This may, or may not, revolve solely around differences concerning treatment of downwash issues. Some FDE authors may wish to add the rider;... and then shift TBL 404 again to take account of downwash issues.to each case.Ron - is that the only difference between my summary above and your position on how CL=0 v AoA must be calculated for use in FS2004, or do you still believe that the value of CL=0 v AoA may be 'normalised' in FS2004? Now I will try to reply to all other loose ends since my last post. Ron said;Thank you. I define the autothrottle bugs as gauge bugs. As you say they were present in FS2002.Some may be for use only by FSEdit when it appears. Some were last time, as you know. I do not yet regard that as a bug. We will know only when we see FSEdit Mk2. Mike Schroeter's comments in post 58 of this thread may be a warning to that effect.Curious George - I do not understand why you are still unable to rotate and recompile an MDL for which you have the source code. I have tested that it works. The rotation will show in the FS2004 aircraft selection screen when you succeed. See case 3 at the top of this post for why a single shift of TBL 404 may work for the Whitley, but does not work for most.Finally a 'bug' is the failure of a program to process its own declared variables to obtain a mathematically correct result. The MSFS flight model has many omissions which are on some wish lists, but omitting capabilities which some would like to see included is not a bug. Sometimes it is better that Microsoft omit something and allow us to do it well, than attempt to add something which is then limited to low accuracy. Quality third party FDE already have appropriate simulation of cowl flap drag if the real aircraft is thus handicapped.Addendum:Everyone interested in this thread also needs to understand the thread started by Tom Goodrick concerning the 'Poor Standard Atmosphere' in FS2004. For the time being discrepancies of drag can only be judged by reference to displayed IAS. Pending conclusion of the ISA thread I suggest that all tests for drag discrepancy be made with REC1101:0Ah (IAS weighting factor) set to minus 32767 (zero pitot position error IAS = CAS) in the FS2002 air file and with no ASI modifier in the FS2004 aircraft.cfg. --FSAviator

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I concur with the above, both philosophically and scientifically (inasmuch as real science is applicable here.;-) )If FSAviator has successfully rotated a visual model to adjust the cruise pitch, then my experiment may be in error, as I did not rotate the model myself, it was adjusted by the original author and I had no way of confirming exactly what was done. I took this on faith but did not verify it. So my posts on this can be considered imcomplete. Also, the mean AoI for the Whitley is conjecture on my part, but is likely very close to reality as this aircraft was well-known for its high AoI and odd, nose-down cruise attitude. At any rate, any ballpark number would have sufficed for testing purposes, and as FSAviator pointed out in his post, the results of the table shift for AoA were quite satisfactory, exactly mirroring the "old" method as used in FS2002/CFS2.Otherwise, I believe the issues have been settled to my satisfaction.If I come up with additional results from testing I will post here.

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Curious George, you said,"The aircraft works as a collection of interacting systems and it is the behavior of the entire aircraft as a unit that we are concerned with here. It's a flight simulator, meant to simulate flight in aircraft already designed and developed, rather than a wing design simulator that considers only the wing as a single component. To be even more brief, the flight simulator is intended to simulate the experience of flying and airplane, not designing one from the ground up"I'd like to tackle you on this and I ask others to also advise because I don't know if the 2002 flight model covers what I'm asking.I disagree with the "entire aircraft" idea, as I see individual surfaces needing to be separated out then brought together to give a true representation of what happens to the "entire aircraft". If I can, by example:An aircraft is turning at a particular rate of turn in a heavy wind. The lift from the wing on the inside of the turn is reduced, whereas the lift on the wing on the outside of the turn is increased. Add to this, the action of each aileron changes the differential lift between the two wings. Add to this, the moving direction of the wind, relative to each wing, significantly alters the effect on each wing. Further add, the angle of sweep (forgotten what it's called) on each wing, relative to AoA. Given conditions, the wind could actually produce a situation of more lift on the inside wing than the outside wing. Can a "whole aircraft" approach calculate an attitude for this?I don't know how complex this all gets, and I don't know how FS2002 accounts for these, but to take a "whole aircraft" approach, to my unskilled mind surely could not account for such differentials, in this or any other manouver.As a layman, speaking to you learned folk, please be gentle with me. ;)Andrew

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