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Guest WhiteRock

C of G question

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Great simulation, both airplane and panel.. Best panel ever.. I'm having a problem with C of G.. No changes to the load [pax or fuel], set stab at 4.75 to 5.0 for take off.. Airplane has a tendancy to over rotate, as I feed in nose down trim.. During climb with auto pilot engaged [CWS and heading select], requires large input to lower nose, and very quick to raise nose.. Using PDCS power settings for all phases of flight.. At cruise, stab is at lesas than 2 units, and there are occasional flickers of stab out of trim light.. Have tried modifing load to find a mor forward c of g, but no luck.. Any advice ??..

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What you're describing sounds like an excessively aft CG indeed...do you have the original weight and balance numbers in the aircraft.cfg? Are you using the aircraft.cfg appropriate for the model in use (the Terry Gaff and FFX modesl use different config files)? Are you using an external loader?The cruise trim sounds like its in the ball park, and an occasional flickers of the stab trim light is also normal.RegardsBob ScottATP IMEL Gulfstream II-III-IV-V L-300Santiago de Chile

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I am using the aircraft config that was part of the zip files [v1.2 thru v1.23] I have not changed any data.. Yes this is aircraft.cfg for Terry Gaff (there is fuel in right tip with a comment "DO NOT REMOVE").. I am not using an external loader.. Just flew again, and stab trim in cruise was actually <1.. In my expierience, I don't remember stab trim ever getting that far forward..

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I modified weights in aircraft config to try and get a more forward c of g:---------------------------------station_load.0 = 165, 43.5, -1.36, 5.5, Captainstation_load.1 = 165, 43.5, 1.361, 5.5, First Officerstation_load.2 = 165, 36, -3, 4, Flight Attendantstation_load.3 = 165, 36, -1.44, 4, Flight Attendantstation_load.4 = 825, 30, 0, 4, 1A to 1F //6 seats per row 660 = 4 of 6 occupied per row x 165station_load.5 = 770, 27, 0, 4, 2A to 2Fstation_load.6 = 660, 24, 0, 4, 3A to 3Fstation_load.7 = 660, 21, 0, 4, 4A to 4Fstation_load.8 = 660, 18, 0, 4, 5A to 5Fstation_load.9 = 660, 15, 0, 4, 6A to 6Fstation_load.10 = 660, 12, 0, 4, 7A to 7Fstation_load.11 = 660, 9, 0, 4, 8A to 8Fstation_load.12 = 660, 6, 0, 4, 9A to 9Fstation_load.13 = 660, 2, 0, 4, 10A to 10Fstation_load.14 = 660, -1, 0, 4, 11A to 11Fstation_load.15 = 660, -4, 0, 4, 12A to 12Fstation_load.16 = 660, -7, 0, 4, 13A to 13Fstation_load.17 = 495, -10, 0, 4, 14A to 14Fstation_load.18 = 330, -13, 0, 4, 15A to 15Fstation_load.19 = 330, -16, 0, 4, 16A to 16Fstation_load.20 = 330, -19, 0, 4, 17A to 17Fstation_load.21 = 330, -22, 0, 4, 18A to 18Fstation_load.22 = 330, -25, 0, 4, 19A to 19Fstation_load.23 = 330, -28, 0, 4, 20A to 20Fstation_load.24 = 165, -33, -3, 4, Flight Attendantstation_load.25 = 165, -33, -1.44, 4, Flight Attendantstation_load.26 = 2100, 27, 0, -0.98, Cargo Hold 1FWDstation_load.27 = 3300, 18, 0, -0.98, Cargo Hold 2FWDstation_load.28 = 1700, -7, 0, -0.98, Cargo Hold 1AFTstation_load.29 = 1500, -16, 0, -0.98, Cargo Hold 2AFT---------------------------------------------This seems to have made attitude control more appropriate, but still very responsive to any nose up input [using CWS].. I took a screen image climbing through FL240, and had stab trim in view (see att.)

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Attachment did not work, I'll try again.. I was over max allowable.. I trimmed it down..

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Any ideas ??.. Is this problem unique to just me ??.. Am I missing an updated .air file ??.. Can I offer any more data ??..

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I found the TAT/CG gauge, and interestingly, the stab trim was set automatically appropriate to data presented on this gauge (%MAC and stab trim units for takeoff).. Did not use any manual trim during initial climbout.. Aircraft settled nicely into climb with flap extended (V2+ bug ~165kts).. As soon as I began to retract flap (on schedule), the aircraft required an increasing forward pressure [nose down] on elevator.. I applied this with manual pressure, and did not use manual trim.. Transitioning above FL100, I engaged the autopilot (aileron and elevator) to engage CWS, and stab trim went to ~1.5 units.. Even in spot view, it is apparent that stab is almost at full nose down authority.. Is it possible that this problem is in the .air file ??.. All other parmeters are nominal.. Should I address this to "TheTinMouseProject@gmail.com" ??.. This last evaluation was done with the LAN Chile cargo aircraft with cargo load found in this forum..

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The takeoff trim is designed (in r/w) to trim the jet to approximately V2 + 10. As you accelerate in the climb, more nose-down trim is needed.The number of units reflected on the gauge may not correspond well to r/w settings at high airspeeds, but there was a problem earlier with pitch oversensitivity and instability related to trim rate and resolution. With CG in normal limits I flight tested the model to ensure that the fwd trim limits (as reported internally in FS, not by the gauge itself) are not actually reached until approximately Vmo. Could be that the gauge needs recalibration, or some more FDE work in the future, but I'm busy with a couple other projects right now.RegardsBob ScottATP IMEL Gulfstream II-III-IV-VSantiago de Chile

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I thank you for this information.. I have also continued to fly the aircraft, experimenting with different load configuations, and have found that if you modify the aircraft.cfg to create a more forward CG [22-24 %MAC with centre tank empty and 15000lbs in wing tanks] that the flight characteristics for trim are actually very good through all flight regiemes.. The default load out put CG @ 28+ with a full centrer tank and as you burn off fuel, CG moves further aft, to the point where there is no more nose down trim [stab] available, and all you have left is elevator input; this is where everything really falls apart as far as CWS.. I do not have any knowledge in working with SDK's or FDE's, but I would agree with you that there is something out of wack [for lack of a better term].. Can one get tutorial info on working with these applications, and would TinMouse allow me to tinker with their fine work ??..Glenn Reed

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I need correct myself from last post.. When I said "all flight regimes", I was inaccurate.. It was while flying at <220kts with flaps set at 1 or greater.. Basically flying a circuit pattern.. Given this, I cleaned up and accererated to ~240kts [auto pilot engaged] and was able to watch stab trim run forward out of green and stab out of trim illuminated.. any input via CWS created exaggerated results in vertical speed to the point where to regain control, I disengaged auto pilot and hand flew aircraft.. As soon as I did this, stab trim came back into the green band appropriate with CG noted in the gauge..Glenn

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hmm it looks like mines problem while trying to get control after takeoff with trims. Whatever I've done, I couldn't get correct settings or flight conditions on elevators and trims. Trims goes directly nose down position after t/o.I've a question, whic fuel tank using first in 737-200?.I'm using only wings tanks for short flights.(except 1000lbs on center)maybe I've to try change balance settings because after takeoff aicraft wants to nose up even trim in nose down position!

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The default load out in the aircraft config [cfg] file is very tail heavy, even with a fuel centre tank.. You can modify this in the payload/fuel under aircraft while in the sim, or you can modify the aircraft.cfg file outside of the sim.. This is a nice way to do this, as you only have to make the changes once.. I modified the config file with the following:------------------------------station_load.0 = 110, 43.5, -1.36, 5.5, Captainstation_load.1 = 165, 43.5, 1.361, 5.5, First Officerstation_load.2 = 165, 36, -3, 4, Flight Attendantstation_load.3 = 165, 36, -1.44, 4, Flight Attendantstation_load.4 = 990, 30, 0, 4, 1A to 1F //6 seats per row 660 = 4 of 6 occupied per row x 165station_load.5 = 990, 27, 0, 4, 2A to 2Fstation_load.6 = 990, 24, 0, 4, 3A to 3Fstation_load.7 = 990, 21, 0, 4, 4A to 4Fstation_load.8 = 990, 18, 0, 4, 5A to 5Fstation_load.9 = 990, 15, 0, 4, 6A to 6Fstation_load.10 = 990, 12, 0, 4, 7A to 7Fstation_load.11 = 990, 9, 0, 4, 8A to 8Fstation_load.12 = 990, 6, 0, 4, 9A to 9Fstation_load.13 = 990, 2, 0, 4, 10A to 10Fstation_load.14 = 990, -1, 0, 4, 11A to 11Fstation_load.15 = 660, -4, 0, 4, 12A to 12Fstation_load.16 = 990, -7, 0, 4, 13A to 13Fstation_load.17 = 660, -10, 0, 4, 14A to 14Fstation_load.18 = 990, -13, 0, 4, 15A to 15Fstation_load.19 = 660, -16, 0, 4, 16A to 16Fstation_load.20 = 990, -19, 0, 4, 17A to 17Fstation_load.21 = 660, -22, 0, 4, 18A to 18Fstation_load.22 = 990, -25, 0, 4, 19A to 19Fstation_load.23 = 990, -28, 0, 4, 20A to 20Fstation_load.24 = 165, -33, -3, 4, Flight Attendantstation_load.25 = 165, -33, -1.44, 4, Flight Attendantstation_load.26 = 2145, 27, 0, -0.98, Cargo Hold 1FWD //Maximum 2146 lbsstation_load.27 = 3320, 18, 0, -0.98, Cargo Hold 2FWD //Maximum 3340 lbsstation_load.28 = 2320, -7, 0, -0.98, Cargo Hold 1AFT //Maximum 4040 lbsstation_load.29 = 495, -16, 0, -0.98, Cargo Hold 2AFT //Maximum 3459---------------------------------I use this [load out] and an empty centre tank with 7500lbs in each wing tank.. Set your stab trim to ~4.5-4.75 units and aircraft will fly nicely during takeoff and initial climb.. There is still a problem with trim once you clean up and speed up.. This is caused either in the flight dynamics or in data calculated for the autopilot trim.. Fix for this will have to come from TinMouse..

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I applied those settings into tinmouse aircraft.cfg (after got backup :) ) and made a test flights with 1000lbs in center, 3500lbs ineach wing tanks. stab trim has been set as 4.75.When I set fuels, look it up on C/G point in loading diagrams. Actually C/G center looks gone back a little than previous loading set.Now, take off was better than before but as you said that not perfect although it was much more controllable. While takeoff phase now I could set trim in GREEN section and could get A/P engage in two touch and go attempt.according me, maybe C/G can be get backward a little. what should be C/G value actually? so what is our target to find out correct loading balance values on this airplane.thanks for helpsp.s I applied into TMII original model's aircraft.cfg, not in FFX/kittyhawk, but if necessary, I can try in them.

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Confirmed my settings [aircraft.cfg] for load out same as posted.. Payload is reported as 27,695lbs.. 78% [7462lbs] in each wing and zero in the centre (this was normal ops for short range flight)..Panel gauge reports CG at 21.0%MAC which should be ~5.25 units nose up according to supplied documentation..In my tests, I flew aircraft at less than 220kts with flaps 1 and aircraft flew perfectly and I was able to fly a coupled or manual ILS.. As soon as I cleaned up [flap 0] and accelerated [~240kts] stab trim [with aito pilot engaged] moved forward to ~1.5 units ['Stab out trim' illuminated] and CWS became very sensitive, to the point where aircraft was unflyable with CWS.. As soon as I slowed down and extended flaps 1 all returned to normal..In my experience, normal CG for B737 was in the 18-24%MAC [4-5 units nose up].. I am trying to get some actual manual w/b sheets so I can do a real calculation..I only loaded TMII..

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