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Guest Ron Freimuth

Flight dynamics - drag couple of questions

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Hi,Anyone here who knows how to add drag when gear is down and flaps down?Is there also a way to add specific sounds for the drag of gear and flaps?regardsRoger

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I have found the drag scalar setting in aircraft.cfg but not the gear drag. It is so important then usually when holding i.e. 3000 ft before capturing the glide, just setting the gear down on a plane may give you a loss in vertical speed of about -500 at least.Roger

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Roger,In the flaps section of the cfg file there are scalors for pitch and drag. I believe that the drag for gear down is only in the air file. There were some posts about what lines to change, but it was several months ago (something about FSedit erasing the section?). Hopefully someone who knows the answer will post it.For sounds, look in the sound cfg file for any retractable. There are several different sounds available for both gear and flaps. John Woodward

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Greetings Roger,Not much of the flight dynamics can be accessed from the aircraft.cfg. Most of the data are in the air file. You need to obtain a good air file editor and then study the air file. Start by studying REC1101 in the default air files and progress from there.A good place to make your first steps on the long uphill road to air file editing is;http://perso.wanadoo.fr/hsors/FS_Soft/index.htmlEverything you will need is there or is aliased from there.>The sounds are aliased from the sound.cfg. Study several of the defaults. The parts relating to gear and flaps are self explanatory. Just choose a .wav file which you think is suitable, or create one, by manipulating the ones you already have, and then alias it.FSAviator

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Thanks both for your answer. I have in the while find the Flaps drag scalar in aircraft.cfg and using Aired.exe I have found the gear drag scalar. Anyhow, I made dramatic changes just to test and still do not notice any change in drag when lowering the gear. As regards the sounds, I havent find any specific command in any sound .cfg file for the noise made by the gear drag. There is a gearup and geardown motors noises, gear bump noise when touching but no genuine MSFS plane has the specific sound heard in the cockpit once the gear is down, just a bit more wind due to the excessive drag.Or do I miss something ??Thanks guys,Roger

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Check your *.air file and see if you have Section 1540. If so, it overides the Section 1101 entry. If you are using fs2002, the sections 1539 thru 1546 will cause problems if not tuned correctly. These sections are added by FS2002 and FS2004 FSEdit.It seems MS corrected the problems with these sections in FS2004.W. Sieffert

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Thank you W. Sieffert,I did use AAM.exe and found in REC 1540 that there was a gear drag value at 0. I set it at O.O5 and REC 1101 gear drag at 0,23. Now the plane behaves like a real one. When I am lowering the gear I get a speed decrease and a minus pitch. Now I would love to find a way to add more external wind noise at that moment ( when gear lowered). Any suggestions ????I am anyway still struggeling with some sounds problems specific to turboprop as the prop pitch sound and Throttle at idle. How can FS2004 be so messy about that. I understand why Olek Frolov did a new plane from scratch to bypass all those restrictionsRoger

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You may have to resort to a flaps gauge for the wind sound. Many designers seemed to use that technique in 2000/2002.Regarding prop pitch, find the PROPS sections in your sound.cfg file. Ensure you have a parameter for Flags=2 or Flags=4 for each of the Props sections.

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Milton,It's what I thought too about the the flaps and gear drag sounds and unfortunately I cant program gau files.As regards the props, I agree with the flag setting, but 99% of all prop aircraft either free or payware have nevertheless wrong sounds as regards the prop handling. The standard sound for the Beech 350 is giving to the plane designer the ridiculous example, i.e. at idle. Turboprop (with reverser) once at idle have a -3

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>Thank you W. Sieffert,>>I did use AAM.exe and found in REC 1540 that there was a gear>drag value at 0. I set it at O.O5 and REC 1101 gear drag at>0,23. Now the plane behaves like a real one. When I am>lowering the gear I get a speed decrease and a minus pitch. >..>Roger Most of the REC 1101 values are scaled by 2048. So, Cdg = 0.05 in REC 1540 corresponds to 2048 * 0.05 = 102 in REC 1101. AAM unscales most of the values it displays, so Cdg should also display very close to 0.05 in it. Unless aired.ini is used with AAM, then it should show the same value Aired does. FSEdit for FS9 appears to be improved some over the earlier versions. None set Cdg. If one finds an FSEdit AIR file satisfactory, he can set Cdg to about 0.02 for a start. I also found the new FSEdit set Cm_dt about 5X too high (but, only tried it on one AC). That can be set to more typical values, similar to the value in REC 1101 (no scaling involved). -0.5 to -2.0 pretty much covers the normal range.Ron

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Hi Ron,Thanks for your "light" in that field. Since I do look closer on the Air files of some planes I understand a bit more why they flight so badly.I noticed for instance that there is a value in REC 1511 ( Propeller reversing)"Idle Blade Angle". This value is by default set to 1 for turboprop aircrafts. That's simply wrong. I dont know every turboprops, but the major of them (ATR-DASH-SHORT-SAAB) have a blade angle coming back to -3

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>Hi Ron,>>I noticed for instance that there is a value in REC 1511 (>Propeller reversing)>"Idle Blade Angle". This value is by default set to 1 for>turboprop aircrafts. That's simply wrong. I dont know every>turboprops, but the major of them (ATR-DASH-SHORT-SAAB) have a>blade angle coming back to> -3

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>>However, that doesn't mean setting -1 deg or -3 deg in aircraft.cfg >>(AIR file entries are no longer used for these settings) generates >>the correct effect. One might have to modify the real angles a bit.Believe me, I changed that value in the air REC 1511 and not in aircraft.cfg file and it really works fine now. Cant explain. Roger

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>>>However, that doesn't mean setting -1 deg or -3 deg in>aircraft.cfg >>(AIR file entries are no longer used for these>settings) generates >>the correct effect. One might have to>modify the real angles a bit.>>Believe me, I changed that value in the air REC 1511 and not>in aircraft.cfg file and it really works fine now. Cant>explain. >Roger Good to know. At times AIR file entries are not imported correctly to aircraft.cfg. Or those in the AIR file don't work but those in the AIR file still do. I tend to set the same values in both files to be sure. Further, if one removes the value after the '=' in aircraft.cfg and reloads an AC in FS the AIR file value (if it exists) should be set in the aircraft.cfg line. Assuming things work as they should.Ron

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Douglas,Interesting comments.I only have time right now to say the MS prop thrust is supposed to be calculated by 'low speed formulas' at low speeds. Note the '80.0' ft/sec setting in the (prop) section. That is supposed to merge 'low speed theory' with the prop tables at 80 ft/sec (47 kts). Changing that '80.0' did have some effect to TO acceleration when tested in 2000. It might also affect reverse thrust performance, though should only when air speed is above the value set. Not for low speed backup. But, who knows?'Low Speed Theory' is needed to calculate static thrust since normal theory is based on J=V/ND, and V is zero or very low before air speed over the prop picks up. I think the theory calculates thrust per unit area of the prop's swept area and HP into the shaft. However, I found I could change static and low speed thrust by editing the Ce (Efficiency) prop table at J=0. So, things don't appear to work as claimed. Typical of things the Airheads get their fingers in.Note there is a 'min blade angle at idle' setting. That is important for 'simple' CS props. I found it should normally be set to the same mimimum blade angle used in normal flight. Otherwise, the prop might go to zero degrees at idle and RPM run too high. Of course, if the prop really drops below the minimum flight blade angle stop when on the ground then one sets something near that angle. There is also a question of what 'blade angle' means. It is similar to AoA for a wing. Note zero AoA produces a lot of lift with a cambered wing. A blade with its chord line at 0 degrees would still produce positive thrust.However, the 'low speed theory' may figure zero degrees gives zero thrust. I don't think blade camber is taken into account. But, MS might have added an arbitrary offset to the angle to 'make things simple'. 'Simple' doesn't mean realistic.One can see what prop thrust is with AFSD, etc. I set the reverse throttle setting to get appropriate reverse thrust in normal turbine engines. It depends on the turbine tables and I've found 50% is necessary to generate appropriate reverse thrust.I added 'Pitch' and 'Slip' to my XML Prop Test gauge to better see how a prop operates. 'Pitch' changes in a CS prop, I displayed it in feet rather than inches. A small AC FP prop runs maybe 66" pitch.From Pitch I calculated Slip. That may be 20 deg or more at high throttle, low speed but drops to near zero at cruise. When one pulls back the throttle Slip may go negative, which indicates the prop is absorbing power.However, 'Slip' is only correct if the prop tables are set with accurate values for each Beta. Conversly, if Slip is realistic, I'd figure at least some elements of the tables are accurate.The point here is 'slip' gives an intuitive number related to prop operation. It shows one the blade AoA. Meaning one should be able to use airfoil theory to see if prop performance is appropriate."Slip" might also give a better idea of reverse operation. Ron

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Ron,>Changing that '80.0' did have some effect to TO acceleration when tested in 2000. It might also affect reverse thrust performance, though should only when air speed is above the value set. Not for low speed backup. But, who knows?80, AFSD reported the prop thrust as -455 with the brakes set. Setting low_speed_theory_limit to 10 resulted in so much thrust in reverse that the tail struck the runway and bounced again and again with the thrust varying from -5000 to over -7000 between bounces. So I'd say it does affect reverse thrust, and that this is one more way to increase the reverse thrust effect for aircraft with propellers. Also, that the MS assertion in the SDK that it is the speed in ft/sec at which low-speed prop theory is blended into high-speed theory must be something less than accurate, (to put it kindly) since propeller thrust with the aircraft static and at idle RPM is increased by reducing this value. But see below for more testing with the C-172, both static and moving forward. >'Low Speed Theory' is needed to calculate static thrust since normal theory is based on J=V/ND, and V is zero or very low before air speed over the prop picks up. I think the theory calculates thrust per unit area of the prop's swept area and HP into the shaft.However, I found I could change static and low speed thrust by editing the Ce (Efficiency) prop table at J=0. So, things don't appear to work as claimed. Typical of things the Airheads get their fingers in.80, the time to 60 KIAS was 12 seconds. Changing it to 10 yielded an identical time to 60 KIAS of 12 seconds. I took screenshots of both takeoff runs from top-down view, and a comparison of those showed that the aircraft reached the same location on the runway both times. I found the same results testing in FS2002, but the MS C-172 in that version took 18 seconds to reach 60 KIAS.With low_speed_theory_limit at 80, AFSD reported thrust at idle RPM as 18, and 75 at 1000 RPM. Set to 10, idle thrust was 38, and at 1000 RPM it was 161. I've been using your excellent 'Comments on aircraft.cfg' as a reference, and the comment for the low_speed_theory entry states: "Lower may reduce TO distance - but 80.0 is good". I figured if 80 were good enough for you, then it was more than OK for me. But it looks to me like it doesn't affect the takeoff distance at all in FS2002 and FS9. As I mentioned previously, it does have a big effect on very low speed thrust and the breakaway power needed to start rolling. The FS9 C-172 would start rolling at 1250 RPM with low_speed_theory_limit at 80; with it set to 10 it would roll at 1000. The FS2002 C-172 would need 1400 RPM to roll at the default value of 80, and lowering low_speed_theory_limit to 10 reduced that to 1100 RPM. Exactly what you would expect when looking at the prop thrust in AFSD before and after editing.>Note there is a 'min blade angle at idle' setting. That is important for 'simple' CS props. I found it should normally be set to the same mimimum blade angle used in normal flight. Otherwise, the prop might go to zero degrees at idle and RPM run too high. Of course, if the prop really drops below the minimum flight blade angle stop when on the ground then one sets something near that angle.There is also a question of what 'blade angle' means. It is similar to AoA for a wing. Note zero AoA produces a lot of lift with a cambered wing. A blade with its chord line at 0 degrees would still produce positive thrust.

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Douglas, You have really been into 'props'. Good Comments! Have you visited the avhistory.org Air File - FD Forum? It's been up and down recently, due to moving to a different server. When one defines prop efficiency as Pout = V*Thrust divided by Pin = 2Pi*N*Torque you get zero when V is zero. The standard prop equations don't work well. While AC velocity, V is zero when braked, the air flowing past the prop is still moving. However, I think V relative to the AC is still the basis of Po/Pi. "Blade Angle" is typically measured at 75% of the distance to the tip. I came up with the simple formula to figure 'Pitch' (the forward distance a screw moves, per revolution, with no slip). Pitch is generally measured in inches, but I changed the display in my XML Prop AC Test gauge to feet. Knowing TAS in ft/sec, one can calculate relative 'Slip'. Note 'pitch' and 'slip' are based on Blade Angle, Beta. So, the prop tables have to be correct for each Beta column to get a realistic 'Slip'. Conversely, that helps verify the prop tables are approprite. As the FS2000 aircraft.cfg files became avalaible it was seen that the mysterious '80.0' in the AIR file prop record was shown in a comment as 'low speed theory limit'. One CFS guy tried different values and logged the TO roll for some CFS AC. There was an effect. However, my prop AC appeared to be OK with the default '80.0'. And, as you also mentioned, editing the prop tables still has and effect below 80 ft/sec. Besides the efficiency table, I've changed the Cp (Power) entries a bit. Lowering an entry means less load from the prop so it spins up faster with the same shaft torque. That way, I could adjust the run-up RPM to the specified TCDS value. Dr Lowry owns a C172 and used measurements from it for calculations in his 'Performance of Light Aircraft'. He gives a way to calculate prop tables from prop measurements and his combination of Blade Element and Momentum Theory. One has to find the 'Activity Factor', which amounts to how much of the prop disk is activated by blades. Wider, or more blades increases that factor. If one has a set of general prop curves he should find there is one value that gives the best overall prop accuracy. I think the C172 prop has a value at the low end of his curves. However, Lowry also has some more direct curves for the C172 FP prop and I started with them in setting the single row of entries needed for each prop table. Then, made fine adjustments to get RPM, TAS, Percent HP, and MP quite close to the C172 POH tables. Note the engine also has to have appropriate HP vs RPM and MP to get the powrplant-prop combination to work. Further, AC drags have to be appropriate. Too many things to adjust experimentally! But, I could set and verify drags somewhat independently of the powerplant, and set the engine curves from a combination of general knowledge and published data. That leaves mainly the prop curves to tweak for the final adjusments. CFS and FS2K set excessive prop efficiency, I decided they were 'raw' data, taken on a test stand with no AC fuselage interference. Lowry's text mentioned 'Slow Down Efficiency Factor' and 92% is a good value. So, I multiplied at least the high efficiency prop table entries by 0.92 to bring them down to the more realistic values a mounted prop gives. That is well known to be around 83% to 87% at cruise. While I might experiment with the J and Beta entries corresponding to climb to set them near 70%. I got Herve' to add Prop calculations to AFSD so I wouldn't have to calculate J for each TAS involved. That made it easier to adjust the prop tables. Douglas, you would probably like to look at my XML Prop Test gauge. While some of it has tricky strobes to reduce CPU overhead, the torque, power, etc. formulas aren't too hard to follow, And, XML parameters let me set appropriate scale factors directly. I found the Engine Power Parameter is only in kW, so has to be adjusted by 746 to get HP. The XML Parameters list also shows only kW available. While most of the things displayed in my XML test gauges are correct for any AC, some are specific to prop diameter, etc. So, I've had to enter those values for the specific AC I'm testing. But, the 'gauge' is so small I can set different variations in different GAUGESsubfolder names. If put in CAB files they would probably be under 10 kB. You could modify the XML gauge to display what you want to see. And, probably get ideas for other gauges that made use of the flight paremeters calculated. It would be easy to add "BMEP", since that's just based on total displacement and shaft torque. ------- I also want to improve the CHT some day. Bypass the FS "CHT" and generate a variable that changes with more than RPM. I'd also like to make CHT vary with Mixture. One could even display the rate CHT is changing, and if it got too high add 'damage' to some logged data that accumulated the effects of shock cooling. You can't save XML calculations in files (at least not FS2K2 XML) but a C gauge could. More realistic CHT readings would be a significant improvement to the more complex AC modeled in FS. I'd post a screenshot of my Test Gauge, but something is messed up in IE and I can't UL. However, my email address is listed here so you might email me if you like. I'll see what I could send you. Ron

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Douglas,Very good comments, Thanks. >>as you noted Mr. Frolov has done this brilliantly with his Dash 8-Q300,I know also a bit the real Dash8 for having spent more than 20 hours in the cockpit twice a week some years ago. ( I am private IFR rated Pilot) Here I heard the first time that the blade in the Dash8 -100 are at -3

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Ron,>Have you visited the avhistory.org Air File - FD Forum? It's been up and down recently, due to moving to a different server.

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"I agree. It would be a significant improvement in realism. Speaking of improvements, with FS9 CHT now varies with the cowl flap position. Also, some people have reported an increase in drag from open cowl flaps, but I haven

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Hi Ron,I would be interested in your prop xml gauge. You can sent it directly to roger.wielgus@noos.frBy the way do you think it would be possible to create an XML gauges able to play a particular sound file when the throttle is set in the beta range?Cheers,Roger

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>Hi Ron,>>I would be interested in your prop xml gauge. >By the way do you think it would be possible to create an XML>gauges able to play a particular sound file when the throttle>is set in the beta range?>Cheers,>Roger I just emailed you. I still need to do something so one doesn't get confused by 'Prop Test' from the AC dependent settings. At least I have some comments in the source. ;) There are recent threads on setting sound files from an XML gauge and I think the interface is in the AVSIM library. Ron

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Hi,Doug Dawson's "dsd-xml-sound.gau"Over 100 sounds possible!I'm very, very!!!! pleased with it.Jan"Procul Negotiis"

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