Comments on aircraft.cfg

[Guest Ron Freimuth]

>Last night I used AFSD for the first time to monitor flight >of the aircraft I am designing. I am beginning to see the >value of this application because it displays the Center of >Gravity as computed in real time. Using the Empty Weight >Position (which I assume is a _static_ center of gravity >excluding variable weights such as fuel and pilot and >baggage) and adding in the current remaining fuel, pilot >weight and other defined station loads. This has turned out to be another long reply. I hope it isn't too confusing. AFSD and test gauges display an FS2K+ Token Variable that is the current CG relative the the MAC (Chord of virtual rectangular wing). The only panel that used this was the FS2K2 Concorde, but knowing the variable is very useful for an AC. Real AC often have balance limits defined relative to the MAC. 25% is taken to be the Center of Lift in most cases. Since most real wings are close to 1/4 the distance back from the leading edge. The range for transport aircraft is typically 15% to 35% MAC. Though sometimes it might be different. In part, due to how the location of the MAC is defined. Light AC are more confusing. Usually the Balance is given as an acceptable range for a 'Moment Arm'. Private Pilots are required to pass an FAA written test that includes problems of Weight and Balance. Most of us soon forget how to do it after the test. ;) >Maybe I am wrong on this, but it finally occurred to me that >the aircraft CoG needs to be in a certain place in relation >to the center of lift for the aircraft to fly safely and >optimally. The airframe, etc. has to be designed so the CoG >is where it needs to be, not the other way around. It really >does not matter if the aircraft itself is well balanced as >much as the CoG in relation to the wing. Absolutely Correct! An AC may not be stable if empty. But, with a pilot it should be appropriately balanced. The old J-3 Cub has two seats, one ahead of the other. If only the pilot is in the AC he normally sits in the rear seat to get appropriate balance.>I think that I saw this when playing with balsa gliders as a >kid. We used to tape a penny to the nose to get them to fly >with more stability. I assume this put the CoG fore of the >center of lift, making the wing more stable. Aft CoG makes a >wing unstable. Of course, once the airspeed feel off the >glider would nose down more readily to the floor with the >penny than without. The more the CG is set forward, the more stable the AC is in Pitch. However, one doesn't want it so stable it is hard to rotate for TO, etc. An aft CG makes the AC more responsive in Pitch, but when one gets too far back it won't even be stable without constant control by the pilot. Actually, it's the "Neutral Point" that determins the static pitch stability. This point is normally behind the 25% MAC location. Perhaps at 50% MAC. I've acciently set payloads incorrectly and had AC that were balanced too far aft. Such AC are not pleasant to fly. Whether simulated or real. In all cases it is assumed one can Trim the pitch so no control force is needed. But, that doesn't mean the AC is stable.>You could probably get the glider to balance perfectly with >your finger supporting the stick fuselage, but I doubt that >would be the right CoG for flight. You would want to balance >it on your finger at the CoL point of the wing for flight. And, it is common to use two fingers, one at each end of the wing, to get the balance about 1/4 of the way back from the wing's LE. That's a start, small adjustments will change the final flight dynamics.>AFSD allows you to see where the CoG is in relation to the >CoL when setup correctly. WRT the above example, although >the wing is more stable the more fore the CoG, you reach a >limit where there is too much nose down. So there have to be >fore and aft GoG limits and you can watch the CoG in AFSD >while adding and removing fuel and station loads to be sure >CoG is within limits. The only problem is some FS AC are stable even though the CG is way off. It's due to other things. For example, FSEdit sets a new CoL offset for the Wing that may be "-2.5" (ft). That may be to adjust for setting the wing_apex in aircraft.cfg, rather than LE of the MAC. And, may apply more to swept wings. Regardless, it is confusing and another reason to not let FSEdit do things behinds one's back. Setting AC as I suggested in my 'Comments on aircraft.cfg' appears to give appropriate balance and AFSD, etc. gives appropriate % MAC values. This is also the way REAL AIRCRAFT are defined. By the virtual wing, rather than a tricky wing with sweep, taper (ratio of tip to root chord), etc. >Also, I can see where if the aircraft design needs the CoG >to be a bit forward for stability, that trim can compensate >for this to keep cruise level. In fact, it is common to set the Horiz Stabilizer so it pushes the tail down in normal flight. Note that means the CG will then have to be forward where it would otherwise be. I've read that the down force on the tail is typically 5% of the load the wing supports and keep this in mind when setting 'horiz_tail_incidence'. AFSD shows this Horiz Stab Force as a Coefficient of Lift (CL). AFSD also shows the Wing CL. Which is typically 0.35 in cruise. 5% of 0.35 = 0.017 and I typically see values around -0.025 in my AC. Note the sign is negative, since the lift is downward. This down force on the tail adds to the load on the wing. Typically 5%. Now I've seen pretty stable FS AC with no tail incidence. That is only one part of what determings 'Static Pitch Stability'. Which relates to how well and AC stays at constant climb, descent, or cruise pitch. Normally, changing the incidence of the H. Tail will also change the trim. However, I've noted most MS FS2K2 AIR files have set the pitching moment due to H. Stab incidence to zero. Leaving the H. Stab 'Lift'. It's the 'Lift' that affects the pitch stablility, and this 'trick' eliminates the need to change the internal 'trim' offset. This can be confusing, since most AIR files are set so changing the horiz_tail_incidence will change the pitch trim. There is a paramter in REC 1101 of the AIR file which mentions "(trim)", and that can be adjusted so the panel trim is near zero in cruise. However, setting the horiz_tail_incidence to 0.00 often still results in stable AC, so one might only get into this if he is willing to experiment and understand the details. Conversly, FSEdited AC require a lot of trim. Due to an error in the way the new parameters are set. ;( In such cases, one might be able to change the horiz_tail_incidence to move the panel trim closer to the center. I think imported AC get the horiz_tail_indcence set from the value in the AIR file. Which is where it is set in pre-FS2K2 AC.>Right now, my Empty Weight CoG is behind the CoL slightly. I >placed this by trail and error adjusting until the aircraft >did not try to tip back vertically. I can tell it is still a >little unstable and now I know why, with the aft CoG. I found that the FAA specs sometimes give no 'empty weight' CG. It's the loaded CG that counts, and I'd assume that one pilot would be enough to move the CG within the acceptable limits. However, when there is an 'empty weight' CG spec, one can adjust "empty_weight_CG_position=x,0,0" in aircraft.cfg to get it to the official % MAC (or, the equivalent balance arm moment). Just comment out any station loads (you need station_load.0 set to 0.0 lbs or it will be added and set to 0.000 0.000, 0.000, 0.000) and set zero fuel in the tanks. Ifreference_datum_position=0.00, 0.00, 0.00empty_weight_CG_position=0.00, 0.00, 0.00Then the[WEIGHT_AND_BALANCE]empty_weight =110000 Will be set exactly at the reference_datum_position. In this case, offset in x, y, and z by 0.00 ft from the FS Reference. Which is at 1/4 MAC, etc. One can also change that 'empty weight' location to change the loaded balance of the AC. Since it essentially moves the empty weight setting by x, y, z ft (long, lateral, vertical). In fact, with the FS datum at the vertical offset of the wing (which can be above the vertical CG in a high wing AC) one might set the empty weight to 0.0, 0.0, -2.0 to move the CG down. Which may improve or cure runway jittering. >However, I have discovered through AFSD that TRIM is active >in the simulation all the time, even when I do not want it >for this aircraft that has no trim and was defaulting to -14 >incredible! Now my CoG is all wrong because of this. Pitch Trim comes up at bad negative values when an AC is loaded in FS2K2. Annoying. It needs to be set to a positive (up) value for TO, but should be near 0 degrees in cruise. One way to kill the pitch trim would be to set elevator_trim_effectiveness=0.0 However, your AC will have to be balanced correctly so it is reasonably trimmed in flight. 15% to 35% MAC may be acceptable; the most desirable value can be determined by experiment. Which means some pitch trim is needed, even though it can't be changed. Changing horiz_tail_incidence +/- 2 deg may trim it, but the appropriate way is to change "Pitch Moment Coefficient at AoA=0 (trim)" in REC 1101 of the AIR file. Typically it comes out in the range of "+/- 100". If an AIR file sets aileron trim and one doesn't want it for a simple AC he can set: aileron_trim_effectiveness=0.0>I see a setting in AirEd for Elevator Trim TRUE/FALSE. Will >this get rid of trim on my aircraft? It may. Though REC 320 seems to be replaced by lines in aircraft.cfg now.>I have one more question. I am confused about where the >Visual Model Center and Reference Datum should be. The VMC >is at 0,0,0 in the GMAX scene. However, I can move the >visual model anywhere in relation to this point. Where >should it be? Should I drag the visual model around so that >the Empty Weight CoG is at 0,0,0? The .mdl should probably be set to 0, 0, 0. Then one knows where it is in the AC flight model. 1/4 MAC behind the LE. For swept wings this point isn't obvious in the spot view, but I eyeball it. Or, the CoV could be placed at the actual CG of the AC. Which would be below the wing in a high wing AC, a bit above for a low wing. Remember that wings with dihederal have the CoL above the root. For big jets it appears to be near the vertical center of the fuselage, especially after the wings have flexed up in flight. This isn't all that critical, but it does affect wing leveling. The FS2K Concorde is a good example to study. It places the CoL 63 ft behind the CoV. Note there is a Center of Lift Record in the AIR file that sets the CoL at -63.0. While aircraft.cfg has the references set for the official factory reference. The idea is to have the AC rotate about the correct point in the spot view. And, have the pilot's eye at the correct point so the runway falls away appropriately in rotation. I check the spot view while I move the JS. > Should the Reference Datum >be located at the Empty Weight CoG position? I think you >mentioned that the 0,0,0 is usually the center of gravity >location (Empty Weight or in flight?). The Reference_datum is often set to 0, 0, 0. Everything is referenced from it. However, I think it might be good to set it something like 0.0, 0.0, -2.0 for a high wing Cessna. Below the CoL and CV, but balanced along the fuselage And, set empty_weight_cg_position = 0.0, 0.0, 0.0. Perhaps directly in line with the prop shaft. Then, the prop thrust will be directly ahead of the CG and the passenger station loads can be at 0.0 vertically. >>The MS docs talk about setting Reference Datum to the >published Reference Datum of the aircraft being modeled so >that published locations for loading can be used. To me this >implies that Reference Datum is at the same location as >Empty Weight CoG. No, that means it might be at +6.0, 0.0, -2.0 for something like a C172. Often the offical Reference Datum is at the prop spinner tip. In this case, one would set the empty_weight_cg_position=-6.0, 0.0, 0.0. Note the FS Cessna 182's have that CG set slightly behind the CoL of the wing. Apparently where the Real AC's CG is when empty.>* Wing Apex: line perpendicular to where the extreme leading >edges join at the centerline (in rectangular or swept wing). >* Leading Edge: for purposes of our calculation either >rectangular wing or the extreme leading edge at apex for >swept wing The Wing Apex is meant by MS to be the LE apex of a swept wing, or the LE of a rectangular wing. Note I always assume a rectangular wing and set the 'wing_apex' to the LE of such a wing. MAC/4 ahead of the CoL (often 0.0, 0.0, 0.0. Thus, my setting for this wing apex is not at the visual apex. >* Apex is placed 1/4 MAC ahead of Reference Datum >* Reference Datum is placed 1/4 MAX behind leading edge >* These are two ways of stating the same location and >distance >* In this case, Reference Datum corresponds to standard >Center of Lift? Yes.>* Where is Empty Weight Center of Gravity located and where >should I expect In Flight Center of Gravity to be located? Relative to the reference_datum, at or near the FS Reference. Often 0.0, 0.0, 0.0. But -X, 0, 0 if the reference_datum is at +X, 0, 0. >I assume that if Reference Datum is Center of Lift then you >do not want CoG aft of it because the wing will be unstable. I like to see 25% MAC CG on a test gauge when an AC is fully loaded. Or, at a typical flight condition. However, this can vary some if one sets realistic station loads. 22% to 28% MAC doesn't seem to make much differene in pitch stability as long as the AC can be trimmed for the current CG. Since you don't want to have a pitch trim, you need to have the AC interally trimmed so the CG can be adjusted so balance is near 25% MAC. See my comment near the top about the parameter in REC 1101 of the AIR file that can adjust pitch trim. >And you do not want fuel and etc. to push it too far fore of >CoG although still stable. You want to have "dynamic" CoG >fall in a range between CoL and some point forward where >trim can still keep the aircraft from nose down excessively. I've noted fuel tanks are often a bit behind the CoL. As they drain the weight decreases, but so does the down force behind the wing. The end effect is little change in trim is needed to account for fuel use. I expect this is by design. In big jets, the center tank is somewhat forward of the CoL, and the wing tanks are behind it. I've set them so the CG is at 25% MAC when full, though the real AC may be a bit different. Also, the wing tanks should be set about 1/3 of the distance to a wing tip if they fill most of each wing. Note the wing is usually tapered and most of the fuel is inboard from the center of each wing. Wing tip tanks should be placed where they really are. Half the wing span from the fuselage center for each one.>I think I am getting closer, but still have a lot to sort >out. You've probably already answered many of these >questions, but they still have not clicked with me. >Steve I have gone though all this confusing stuff many times and often set something wrong. I see the % MAC is way off. So, I comment out the station loads, set zero fuel in the tanks and see if the CG is now right. Then, look thought my settings to see which is wrong. I found I'd set one of two station loads at the wrong location yesterday, after I fixed that CG came out at 25%. While I don't think much of MS AIR files, they seem to get the stuff in aircraft.cfg right. At least consistent for the correct wing location, etc. Look at different MS AC to see the variations (thought, the CoL offset in an AIR file may be offset for the aircraft.cfg settings to work. i.e. Concorde). Those who do the G-Max model can set many things, such as the LG, the same as in G-Max. Though some adjustments on 'compression', etc. may be needed to make an AC stable on the runway and the articulation may not end up completly consistent with what works well for the dynamics. Ron

[Guest]

Ron, You haven't been able to see any benefit from the wing dihedral setting in the cfg? With my current projects: B-1B, F-14D, F-16C, and F/A-18C". I can see a change once I change this variable for testing purposes. I use the setting as per the specs for the aircraft. Great info that you have provided. take careJulian

[Guest]

Ron,thanks for you all your help. The aircraft is now flying with greatly improved stability and controllability. Before last nights changes the aircraft would take off, nose up, begin oscillating in pitch, increasing in amplitude until it stalled. I suppose you would call this negative static longitudinal stability. Does not make for a very enjoyable flight!The first move I made was to throw out the original Ref Dat Long. The original location was leftover from the Cessna inspired SingleProp aircraft configuration I based my aircraft on. It was 3.6ft long and zero lateral, zero vertical. I did not really know what I was doing, so although I suspected it might be easier to set this to zero, so instead I dragged my visual model over to match this location measured from the visual model center (GMAX scene center).However, by last night is was clear the calculations were just getting too messy and that this offset was creating more confusion than anything else it might be good for. Trying to find 1/4 MAC back from a ref datum that was 3.6 feet forward of visual center is just much for this inexperienced designer. So I set all three components of the reference datum to zero.Then I moved the visual model so the wing model leading edge matched the new measured leading edge matching the revised reference datum. Of course, I will have to recalculate the positions of all my lights and so forth.To start with a new flight model, I calculated 1/4 MAC according to your instructions and placed the apex 1/4 MAC ahead of the new reference datum of zero. I then cleared out my old empty weight and set all three empty weight components to zero. This places the empty weight center of gravity at the same position as the reference datum longitudinal position and the center of lift there also.Once this was complete, the aircraft was able to takeoff without stalling too badly if I worked the controls and remain steady in flight with quite a bit of nose down elevator.What I discovered, as I said before, through AFSD, was that the default elevator trim was set to 19.5 degrees on aircraft initialization. Now wonder I was experiencing trouble on takeoff and confused about the center of gravity!So I set out to turn trim off or set it to neutral. I put a trim gauge on the panel, but moving it from 19.50 to 0 every time was becoming tiresome. So I went looking in aircraft.cfg for the trim setting. I found elevator_trim_limit= 0.500I discovered through experimenting that this value is not exactly what you might expect. It is both the _upper_ and _lower_ limit for the trim input. So 10 degrees limit is 10 nose up and 10 nose down. I set it to zero in a bid to get rid of trim altogether or keep it locked at neutral, but the aircraft seemed to respond badly to that setting. So I chose 0.5 half a degree as close enough to zero. It worked! No more trim problems.(for anyone reading, why I do not want trim is that my aircraft is like a Tiger Moth or other early aircraft that did not have trim)Level flight seemed much more stable and flew hands off for a half hour once stabilized.With this and the new reference and empty weight, center of gravity is reported as 1.3 by AFSD with 50 lbs of fuel in two equidistant wing tanks a foot behind reference datum and a FAA standard pilot weight of 170lbs temporarily set to 0,0,0 position from reference datum. I will probably have to move the pilot location a bit to match the seat position later.The flight performance was still not what anyone would call home about.I decided to look at the Cessna 172 to see how it might differ from my aircraft configuration.The Reference Datum is 3.6,0,0The Wing Apex is -2.4 Long, 0 VertThe Empty Weight is -3, 0, 0I did not expect the Center of Gravity (which I believe is what Empty Weight location represents), to be equal with the wing height. It would seem to me this would make the aircraft top heavy.However, if you look at the high wing as suspending the weight of the aircraft like a pendulum from a string, it may not appear so strange.Looking at the H Tail, which is very influential on longitudinal stability (pitching), I see that the Cessna 172H Tail Apex Vertical is zero.To me, this places the Apex Vertical at the same height as the Ref datum and the main wing.H Tail Apex Vertical = Wing Apex Vertical = 0It is clear from the visual model that the C172's main wing is higher than the horizontal stabilizer wing. Odd. But apparently the zero location works in flight.If you look at the SDK the H Tail Apex Vertical is shown located at the middle of the H Tail (vertical stab on the example).The aircraft seemed to handle a little better. I tried setting the H Tail further behind the aircraft for more leverage, maybe more stability, but no improvement. So I went back to the original distance.Next, I decided on a hunch to look into the wing incidence. The aircraft is controllable, but still seems to exhibit too much pitch instability and pitch up on takeoff. The incidence was one of the few figures I had on the original aircraft, 3 degrees.So I got the Tiger Moth out and did a full throttle takeoff, yes there is a little nose up tendency, but it will climb hands off with any pitch oscillations self-damped.I tried setting incidence to zero. The takeoff began to look more like the Tiger Moth. Very good!The aircraft still exhibited the same pitch instability. While digging through the air file I discovered what I think is the real culprit behind all these problems. The H Tail incidence had been naively set to 3, from the original Cessna configuration. I set it to -2.0 according to your annotations on the aircraft.cfg file and the aircraft is much more pitch stable on takeoff and climb to cruise. In fact flight characteristics are nearly where I expected they should be, not perfect on takeoff and I have not tried landing, but I think it is where I want it for now.So anyway, I jumped the gun with my previous message. You were right to suspect something else was wrong.StevePS: The landing seems less stable than it was. Tends to sink too quickly on final. This aircraft always seems difficult to line up with the runway (at least using the keyboard---my yoke is disconnected).

[Avcomware 1]

Hi, Ron and everyone. While I consider myself somewhat knowledgeable in the world of Aviation, sufficient to instruct to the CFI level, I am constantly, pleasantly surprised, of the amount of in depth understanding and knowledge that some of you poses. I tried to achieve a

[Guest Ron Freimuth]

>Ron, >>You haven't been able to see any benefit from the wing >dihedral setting in the cfg? Actually, I don't think I tried changing it. Since there is a parameter in REC 1101 in the AIR file for Dihedral Effect.>With my current projects: B-1B, F-14D, F-16C, and F/A-18C". >I can see a change once I change this variable for testing >purposes. I use the setting as per the specs for the >aircraft. >>Julian I'll try changing it some time. Are you sure you didn't use FSEdit to set the new AIR file records from 'Sweep', 'Dihederal', etc? Ron

[Guest Ron Freimuth]

>Ron, >thanks for you all your help. The aircraft is now flying >with greatly improved stability and controllability. Good. So my approch really works. ;)>The first move I made was to throw out the original Ref Dat >Long. .........>However, by last night is was clear the calculations were >just getting too messy and that this offset was creating >more confusion than anything else it might be good for. >Trying to find 1/4 MAC back from a ref datum that was 3.6 >feet forward of visual center is just much for this >inexperienced designer. So I set all three components of the >reference datum to zero. Yes, I usually start with 0, 0, 0. When everthing is balanced well I eventually set the reference_datum to some positive number to set the real location. Then, subtract that offset from all the longitudinal entries for LG, lights, Wing, etc. It's also a lot easier to calculate moments for the passengers, fuel tanks, etc. with the reference at zero. >Then I moved the visual model so the wing model leading edge >matched the new measured leading edge matching the revised >reference datum. Of course, I will have to recalculate the >positions of all my lights and so forth. >To start with a new flight model, I calculated 1/4 MAC >according to your instructions and placed the apex 1/4 MAC >ahead of the new reference datum of zero. I then cleared out >my old empty weight and set all three empty weight >components to zero. This places the empty weight center of >gravity at the same position as the reference datum >longitudinal position and the center of lift there also. Which is appropriate. Unless the empty weight is elsewhere. In which case the station loads, fuel tanks, etc. would likely be unbalanced enought to bring the AC within the CG limits with just the pilot aboard. Regardless, the empty_weight CG should be near the CoL, only if one wants to model an AC exactly is there much reason to set it otherwise. One does want the CG to be within specs with different payload and fuel loadings, but that can be checked by watching the CG reading with only the front seats loaded, or only the pilot in front and heavy passengers and baggage aft. Or, move the empty_CG so CG is at or near 25% with a full payload and fuel.>Once this was complete, the aircraft was able to takeoff >without stalling too badly if I worked the controls and >>What I discovered, as I said before, through AFSD, was that >the default elevator trim was set to 19.5 degrees on >aircraft initialization. Now wonder I was experiencing >trouble on takeoff and confused about the center of gravity! That's the normal MS setting for SEL's. I set it to the TCDS, which may be 15.0 degrees. Or, 10 to 13 degrees for Horiz Stab Trim. As you noted, there is only one limit, so I have to set +10 degrees even if the H. Stab range is 0 to 10 degrees. >So I set out to turn trim off or set it to neutral. I put a >trim gauge on the panel, but moving it from 19.50 to 0 every >time was becoming tiresome. If you save a situation with pitch trim correct for TO, it will be set that way when loaded. Same for flaps, rudder trim, etc. But, if you reload just the AC, it goes to some negative number. Very annoying during flight tests, where I change a parameter, save aircraft.cfg or the AIR file, then reload the aC in flight. For jets I generally have to Pause the sim before reloading, then adjust the trim to it's previous flight setting before unpausing the sim. FS2K didn't have this defect.> So I went looking in >aircraft.cfg for the trim setting. I found >>elevator_trim_limit= 0.500 >>I discovered through experimenting that this value is not >exactly what you might expect. It is both the _upper_ and >_lower_ limit for the trim input. Right.>... So I chose 0.5 half a degree as close enough to zero. It worked! >No more trim problems. >>(for anyone reading, why I do not want trim is that my >aircraft is like a Tiger Moth or other early aircraft that >did not have trim) OK when payload doesn't change and fuel tanks are near CG. >Level flight seemed much more stable and flew hands off for >a half hour once stabilized. That's how most real AC fly. Though, they may turn slowly.>With this and the new reference and empty weight, center of >gravity is reported as 1.3 by AFSD with 50 lbs of fuel in >two equidistant wing tanks a foot behind reference datum and >a FAA standard pilot weight of 170lbs temporarily set to >0,0,0 position from reference datum. I will probably have to >move the pilot location a bit to match the seat position >later. Sometimes I add 20 lbs of baggage at a location which balances and AC. Note the EYEPOINT will be at the same location as the pilot's seat, but perhaps 2 ft higher. >The flight performance was still not what anyone would call >home about. >>I decided to look at the Cessna 172 to see how it might >differ from my aircraft configuration. >The Reference Datum is 3.6,0,0 >The Wing Apex is -2.4 Long, 0 Vert >The Empty Weight is -3, 0, 0 With it's rectangular wing, the LE would be at the 'Apex' setting. The 172 chord is about 4.8 ft. 4.8/4 = 1.2 ft. So, the 25% MAC (CoL) would be at 3.6 - 2.4 - 1.2 = -3.6 ft. That came out right!>I did not expect the Center of Gravity (which I believe is >what Empty Weight location represents), to be equal with the >wing height. It would seem to me this would make the >aircraft top heavy. I just realised that yesterday. The aircraft.cfg file puts the vertical CG at the level of the wing. I'd suggest trying: "3.6, 0.0, -2.0" for the reference_datum. Then, the prop will be below the wing and so will the vertical CG's of the passegers, etc. However, the vertical CG isn't that critical. The main effect appears to be that when it is below the wing, the AC tends to level it's wings more. While for a SEL low wing AC setting the vertical CG say, 1 ft high makes the wings level less. I then adjust the 'Dihederal Effect' parameter in REC 1101 of the AIR file to get reasonable wing leveling. Which generally means 'not too much'. However, I've also suspected AC that jitter on the runway, especially when braked, have the vertical CG too high. This is a problem with many smaller AC. While one can adjust the LG 'static compression' values and 'damping factor' and sometimes improve this jitter, it would be nice if setting an appropriate vertical CG took care of this problem. That would be at about the middle of the fuselage in many AC, but making it lower would be acceptable if it fixed the jitters. I forgot if moving the vertical CG down fixed any of my AC, but the DF C177 didn't have jitters, so I may not have tried to move the CG. Actually, the Visual Center was set near the vertical CG (not on the wing vertically), soI would set the 'Wing_Apex_Vertical' setting to +2.0 ft. The prop shaft was not exactly on the vertical CG.[GeneralEngineData]engine_type=0Engine.0=-1.75, 0.00, 0.70 Note I set it 0.70 ft above the reference datum, which was at the vertical CG. Based on a C177 drawing. This means increasing power will also tend to pitch the AC down slightly. It will speed up a bit relative to idle power IAS. Typical of many real AC. As an option, one could set this line instead://Engine.0=-1.75, -0.40, 0.70 //Set Prop sliders to 1/2 or more In this case the prop shaft is set 0.40 ft to the left of AC lateral center. With prop sliders set to include prop effect, increasing the throttle changes rudder trim much less than if the offset were not present. One needs about 1.2 deg of right rudder trim, but hardly has to change it at all, wheter in a climb or cruising. The Real C177 may set the engine mounting so the shaft is a couple of degrees CCW of the AC body. Setting a lateral offset is similar. But, if the prop sliders (mainly the "P-Factor") are set at zero the offset causes the AC to yaw to the right with increased throttle. 50% to 100% works fine. >However, if you look at the high wing as suspending the >weight of the aircraft like a pendulum from a string, it may >not appear so strange. That's called the 'pendulum effect'. It is not the correct explanation for the change in wing leveling realative to wing location, but it is easy to remember. I haven't tried to understand the 'correct explanation'.>Looking at the H Tail, which is very influential on >longitudinal stability (pitching), I see that the Cessna 172 >H Tail Apex Vertical is zero. >To me, this places the Apex Vertical at the same height as >the Ref datum and the main wing. >>H Tail Apex Vertical = Wing Apex Vertical = 0 If it had an effect without FSEdit, the appropriate height would be at about the vertical center of the fin. Half way from the bottom to the top. Or, a bit lower, since most fins are wider on the bottom than the top.>It is clear from the visual model that the C172's main wing >is higher than the horizontal stabilizer wing. Odd. But >apparently the zero location works in flight. FSEdit should should set the new parameters in the AIR file in a way to account for the high tail. But, messes up so much it isn't of much use. The FS C182's were set with many realistic parmeters at least as far back as FS98 (probably based orignally on Bruce Artick's verson) and the complete AC, including the location of the tail is more or less accounted for. The FS2K2 C172SP was much worse. >If you look at the SDK the H Tail Apex Vertical is shown >located at the middle of the H Tail (vertical stab on the >example). >>The aircraft seemed to handle a little better. I tried >setting the H Tail further behind the aircraft for more >leverage, maybe more stability, but no improvement. So I >went back to the original distance. Placebo effect!>Next, I decided on a hunch to look into the wing incidence. >The aircraft is controllable, but still seems to exhibit too >much pitch instability and pitch up on takeoff. The >incidence was one of the few figures I had on the original >aircraft, 3 degrees. >>So I got the Tiger Moth out and did a full throttle takeoff, >yes there is a little nose up tendency, but it will climb >hands off with any pitch oscillations self-damped. >>I tried setting incidence to zero. The takeoff began to look >more like the Tiger Moth. Very good! I said before: don't set Wing Incidence to the full physical value. ;) Though, TBL 404 can be shifted to have the same effect as changing incidence. But, changing incidence is easier. "cruise_lift_scalar=1.0" could also be dropped to perhaps 0.8 to have a similar effect to reducing incidence.Don't assume that increasing "pitch_stability=1.0" to a higher value will give more desirable pitch stability. An overdamped AC takes forever to trim. Also, the MoI's should be at least approximately correct. At least for a start.>The aircraft still exhibited the same pitch instability. >While digging through the air file I discovered what I think >is the real culprit behind all these problems. The H Tail >incidence had been naively set to 3, from the original >Cessna configuration. I set it to -2.0 according to your >annotations on the aircraft.cfg file and the aircraft is >much more pitch stable on takeoff and climb to cruise. Oh oh. Looking at my commented aircraft.cfg I see I had used -2.0 deg for horiz_tail_incidence. But, I'd reversed the signs of two REC 1101 parameters in the AIR file. Normally, that is 0.0 to +3.0 degrees. It depends on the AIR file. Regardless, the idea is to set the sign of that parameter to push the tail down. If changing it to -2.0 degrees helped pitch stability, then that sounds reasonable to me. I don't completly understand the advantage of a down force on the tail. I think in part it means the CG then has to be more forward to balance at a given trim. >In fact flight characteristics are nearly where I expected they >should be, not perfect on takeoff and I have not tried >landing, but I think it is where I want it for now. >So anyway, I jumped the gun with my previous message. You >were right to suspect something else was wrong. >Steve There are a large number of things which interact. However, if one starts with a good, similar AIR file, then getting the CG, LG, etc. in the correct places goes a long way to having a good flight model. >PS: The landing seems less stable than it was. Tends to sink >too quickly on final. This aircraft always seems difficult >to line up with the runway (at least using the keyboard---my >yoke is disconnected). If it is too stable in pitch with a forward CG, it would seem it might also be too stable in Yaw. Making it harder to turn rapidly. I just thought of this. However, you might try reducing "roll_stability" (which also requires reducing "aileron_effectivness" or going the opposite way. Also, try adjusting "yaw_stablity". The problem is that unless the basics are roughtly correct, changing one or two parameters to improve one characteristic may make others worse. I always set CG so it is near 25% MAC since that is normally optimum.Ron

[Guest Ron Freimuth]

My original message had this line:htail_incidence=-2.0 <<0.0 to -3.0 may improve pitch stability For most MS FS2K2 AIR files, that would behtail_incidence=2.0 <<0.0 to 3.0 may improve pitch stability The sign depends on the signs of two H. Stab parameters in REC 1101 of the AIR file. The idea is to set the incidence of the H. Stab so it pushes the tail (or CG with MS AIR files) down a bit. Requiring nose down trim to compensate. Often, AC seem stable in static pitch with this angle set to zero. I think I got into this more in my Dash 8 message.Ron

[Guest]

To Avcomware,Some comments on your previous messages:< Hi, Ron.Thanks again for your information and dedication. While other factors are important in the Feel of a simulation, for Real, Serious, and Knowledgeable Pilots the FLIGHT DYNAMICS has to be and IS the most important factor in a simulation. It

[Guest]

I hear very litle discussion of how much fidelity to real counterparts the aircraft have in flight. It appears that if it has a pretty model and flies reasonably well that is enough. I'd like to know that if I succesfully fly the simulated version I would have a reasonable chance of flying the real aircraft. It would be nice if these differences were collected somewhere.Steve

[Guest]

> I'll try changing it some time. Are you sure you didn't >use FSEdit to set the new AIR file records from 'Sweep', >'Dihederal', etc? >> Ron Ron, I refused to use FSEdit given my experiences in the past. :)You have a good one. Julian

[Guest Ron Freimuth]

"4. They enable a nose down attitude for a better view of the landing area."Now Microsoft did a fine job on numbers 1, 2, and 3. If you don't trust your senses you can even use the Flight Analysis feature of FS2002 to confirm that number 2 (steeper glide angle) is working in a realistic fashion, but when it comes to number 4 something either went terribly wrong or is operating precisely according to design.I have come to believe this may be intentional, as with all Microsoft virtual aircraft it seems you are in the approximate touchdown attitude at around 600' AGL. This does away with the need to break the glide and flare for a soft landing, (or indeed to learn how to land at all) you simply manage to coax the tail low monstrosity over the runway threshold and drive it onto the concrete at about a 700 FPM rate of descent, but don't worry, there won't be any airframe or landing gear damage to pay for, and your spine will be none the worse for wear after your "arrival" at the scene of the crash. ..." ----------------------- I think a lot of the problem is the view over the panel. If set up correctly, an FS AC should give the same pitch as the real one does under the same conditoins. I always set the "V" indicator so I know where the horizon is. However, the view_forward_direction also has to be set correctly in panel.cfg to put it on the horizon. Further, MS shifts the view angle down about 2 degrees at lower altitudes. So, the 'V' will be below the horizon when pitch is zero when landing. Assuming the pitch is appropirate in cruise, it should be correct at other weights and IAS values. Though, the slope of TBL 403 "CL vs Wing AoA" should be approximately right so lift tracks AoA correctly. For non swept wings, the slope is often near 6.28 * (AR/[1+AR]). Perhaps 5.5 for an AR of 7.2 to 1. That means CL increases by '5.5' for each radian change in AoA. One tenth radian is 5.73 degrees. so CL should increase by 0.55 for that change. A higher lift slope would mean AoA decreases less as CL is increased for the current IAS and weight. Flaps reduce pitch. Though the Lift Slope stays the same in FS AC. If "Lift - Flaps" is too low (REC 1101) then the nose will be too high at lower speeds. "Lift - Flaps" is per radian of flaps deflection. 57.3 degrees. Flaps typically only deflect to 40 degrees. So, the increase in CL with 40 degress of flaps would be "Lift-Flaps" * 40/57.3. About 70% of the value set for "Lift - Flaps". This value may be 0.30 to 0.60 for a small AC with simple flaps. 0.30*0.70 = 0.21. Full flaps increase stall AoA from perhaps 1.5 to 1.7. Not all that much. Nor would this drop the nose a lot at low speeds. For jets with sophisticated Flaps, "Lift - Flaps" may be quite a bit larger than 1.0. Note the "Pitching Moment - Flaps" (REC 1101) does NOT change the pitch at a given weight and IAS. It only affects how much trim has to be changed (if any) when flaps are deployed. This value may be "-0.07" for high wing AC, "0.04" for a low wing AC. Of course, appropriate CG, pitch moment variation (REC 478), Elevator moment (and elevator lift), etc. affect the dynamics and they may change with changes in AoA. Ron

[Guest]

Hi Ron, I have always been a keen observer of aircraft. From a very young age I enjoyed watching airplanes takeoff and land, and growing up in an aviation oriented family I had plenty of opportunities to observe them, and to this day it remains one of my favorite pastimes. My first experience with flight simulator was with FS2000 a little over a year and a half ago. My initial enthusiasm for this product was tempered somewhat when I realised that something was far wrong with the landing characteristics of the computer aircraft, and landing is of course the most important part of flight, and one that I have been and always will be fascinated with. The first hint that something was not quite "as real as it gets" came when I found that I could not see the runway on final approach after nailing the approach speed for whatever aircraft I happened to be using. Learning how to raise my seat by using the keyboard command and much later by editing the panel CFG helped in that I could now have the runway in sight on final at the proper airspeed, but my joy at overcoming this obstacle soon turned to disappointment when I realised that flaring the aircraft to reduce the rate of descent on touchdown left the aircraft's nose much too high in the air. This was quite noticeable from the cockpit view by both outside visual reference and instrument indications, and when I learned to use the spot plane and instant replay features I was astonished at the extreme nose up angles the aircraft assumed. I could not land the jetliners by the book (the aircraft handbook that Microsoft provided) without risking a tailstrike on each landing. And this was after tracking the ILS localiser and glideslope, reducing power at the recommended height, and initiating a 3 degree flare before touchdown. I wasn't looking for a perfectly soft touchdown, I know from talking with airline pilots and riding jumpseat that the rate of descent of a large airliner at touchdown can vary from 100-250 FPM and that a firm arrival in the touchdown zone is preferable to a long float ending in a grease job halfway down the runway, especially when braking conditions are reported as poor. So rather than hold the aircraft off the runway by increasing the pitch attitude and trying for a soft landing I stuck with the recommended 3 degree flare and firm touchdown. Even so, the tailstrikes still occurred. It seemed to me that the computer aircraft (even with flaps extended) suffered from a lack of lift at lower airspeeds, making an excessive nose up pitch attitude necessary to attain a higher angle of attack and generate sufficient lift to reduce the descent rate to an acceptable level before touchdown. There were other issues with the flight dynamics of course, but most of them were easily solved, or improved to acceptable levels. And when I became aware of the possibilities for editing the flight dynamics by using FsEdit and FDE from Abacus, I jumped in with both feet and began working on them! My earliest efforts to alter the pitch attitude in the landing configuration concentrated on the flaps lift scalar and the wing angle of incidence, and while matters improved somewhat for the largest aircraft I remained without a remedy for the medium and small types. After changing over to FS2002 and finding that the problem still persisted in this newest release from Microsoft, I became more determined than ever to cure this odd behavior and found that any time spent on FS2002 was usually engaged in trying to reverse engineer the flight dynamics programming. I am not a computer science graduate, nor am I an aeronautical or aerodynamics engineer, but I do have a working knowledge of some aeronautical matters gained during my years as an instrument rated private pilot as well as a degree in Applied Aviation Maintenance Technology but even so the lack of computer knowledge made for slow going (and still does!). I recently found that some uneducated editing of TBLDB 401 would improve things considerably, but wondered if another, better way (considering that for the most part I don't know what I'm doing) to address the problem might exist. That sums up my efforts to date.To illustrate what I'm talking about, I have attached 4 screenshots to this message, which I will descibe as follows:Unaltered Default AIR & CFG Files Beechcraft KingAir 350Image 1. On final approach to Chicago/Midway - Airspeed 109.8 KIAS (Vref for 15000 lbs) Altitude about 500' AGL, rate of descent 500 FPM, pitch attitude +2.32 (as recorded by AFSD).Image 2. Touchdown at Chicago/Midway, (after floating and floating due to the lack of drag) note the extreme nose high attitude, and this with a descent rate at touchdown in excess of 100 FPM ! Beechcraft KingAir 350 AIR & CFG Files Altered by changing TBLDB 401 & increasing wing angle of incidence to +3 (no other changes made)Image 3. On final approach once again to Chicago/Midway Airspeed 109.1 KIAS (Vref for 15000 lbs) Altitude about 500' AGL, rate of descent 500 FPM, pitch attitude -3.85 (as recorded by AFSD).Image 4. Touchdown at Chicago/Midway, normal landing attitude, VSI read "0" at main landing gear contact, happy virtual pilot on board.The first flight model (default Microsoft) required shifting the view_forward down to maintain visual contact with the runway on final.The second flight model (TBLDB 401 & Wing AOI increase) required no forward view shifting. The forward view remained normal throughout every phase of flight.These results may be duplicated by editing the default KingAir AIR & CFG files with wordpad and AirEd. The wing_incidence in the CFG was changed from 1 to 3. In the AIR file TBLDB 401, the y values .2, .4, .6, and .8 were increased to 1.7, 1.6369, 1.6018, and 1.5687. Note that these changes lack any of the many refinements necessary to create a decent flight model, and have been performed on previously unaltered Microsoft files for the experimental purpose of changing only the pitch attitude in the landing configuration. As I mentioned above, I have been in the habit of airplane spotting since childhood, and I have NEVER seen a real airplane make a normal approach for landing with the pitch attitude exhibited in Image 1. The only exception that comes to mind would be the largest and heaviest transport category aircraft, and please note that a 737 does not fit into this category nor does it assume a large nose up pitch attitude on final or at touchdown.I hope this clarifies my position on this subject and that you agree that something must be somewhat awry with the way these aircraft "fly".However, if you find yourself not in agreement with any of the above, or if you feel that nothing satisfactory can be done to correct the problem due to limitations in the Microsoft software then the matter need go no further and I shall refrain from mentioning it again.As someone once said, when there are no solutions, there are no problems!Happy Landings!!

[Guest Ron Freimuth]

>Hi Ron, > I have always been a keen observer of aircraft. From a very >young age I enjoyed watching airplanes takeoff and land, and >growing up in an aviation oriented family I had plenty of >opportunities to observe them, and to this day it remains >one of my favorite pastimes. A lot of people would run outside when a small AC passed over my home town. Some years later I actually got in a Club C172 and had my PPL four months later.>first hint that something was not quite "as real as it gets" >came when I found that I could not see the runway on final >approach after nailing the approach speed for whatever >aircraft I happened to be using. Yes, virtually all panels obscure the view compared to a real AC. I've thought a 'portrait' monitor, with the heigth 4/3 the width would help. But, only Apple supports that aspect ratio. With more heigth, the size of the panel would be smaller, but it could be placed lower down, where it belongs. If one has the panel on a second monitor then he can't see it without glancing away from the view. The best place would be just under the monitor that shows the View. > Learning how to raise my >seat by using the keyboard command and much later by editing >the panel CFG helped in that I could now have the runway in >sight on final at the proper airspeed, I found I can land the Concorde much better with the 'UP' view. Which really just sets the winshield frame around the view. However, I also need to see some intruments. Same goes for other jets.>overcoming this obstacle soon turned to disappointment when >I realised that flaring the aircraft to reduce the rate of >descent on touchdown left the aircraft's nose much too high >in the air. This was quite noticeable from the cockpit view >by both outside visual reference and instrument indications, >and when I learned to use the spot plane and instant replay >features I was astonished at the extreme nose up angles the >aircraft assumed. I could not land the jetliners by the book >(the aircraft handbook that Microsoft provided) without >risking a tailstrike on each landing. Jet transports are generally alowed to settle on the runway at near zero pitch. Not higher than 6 deg for the 737. Real Pitch, not the changing 'V' indictor. Which also applies to the horizon. While I tend to land jets too nose high, I can't say I have seen unreasonable approach pitch, at least not with my AC. ;) But I set them up with a lot of correct parameters and tables, and get pitch vs Flaps, IAS, etc. near the official values for jets. For example, the 727 should be at -1 deg pitch with full flaps at 130 IAS on the -3 deg GS (at a certain landing weight). But, near 8 deg pitch at 220 kts when in level flight. Full 40 degree flaps are not normally used, and the pitch during approach varies from 1 to 8 degrees, depending on the point in the approach. I've never seen tables for approach and landing pitch for small AC, and go by experience and reports from pilots familar with the AC. In the past, many FS AC had way too low Induced Drag. Which is predominent at landing speeds. This was compensted by high LG and Flaps drag. FS2K2 sets the Induced Drag from the Wing dimensions, and the only way to modify it is with the Oswald Efficiency Factor in aircraft.cfg. 0.7 to 0.85 is about right;, and that should make Induced Drag about right. The cfg file that comes with FDEdit may even have the parameter that affects Induced drag in pre-FS2K2 AC incorrectly identified. One reason so many older AC are far from correct. LG drag is always lower than 'Drag - Zero Lift'. That is, in real AC. That leaves 'Drag - Flaps' applicable for landings, and '160 to 220' appears to be appropriate. Ground effect reduces Induced drag when the wing is close to the ground. However, I can't even see GE unless I increase TBL 400 a bit at the low end. It may be that the wing is not at the correct vertical location, too high and GE would be too low. That was mentioned in this thread for the C172SP and I think I should fix it in my modified version (thought, it may be everthing but the wing and LG contact points that are off). Then, the default GE table might be OK; they numbers in it do agree with the theoretical values I've found elsewhere.> And this was after >tracking the ILS localiser and glideslope, reducing power at >the recommended height, and initiating a 3 degree flare >before touchdown. I wasn't looking for a perfectly soft >touchdown, I know from talking with airline pilots and >riding jumpseat that the rate of descent of a large airliner >at touchdown can vary from 100-250 FPM and that a firm >arrival in the touchdown zone is preferable to a long float >ending in a grease job halfway down the runway, I'm happy with -400 fpm. FS AC typically 'crash' only when VS is near -1000 fpm or faster.>when braking conditions are reported as poor. So rather than >hold the aircraft off the runway by increasing the pitch >attitude and trying for a soft landing I stuck with the >recommended 3 degree flare and firm touchdown. Even so, the >tailstrikes still occurred. But the tail can't strike if pitch is only 3 degrees! Now the 727 will strike the tail on TO rotation a bit over 8 deg pitch, so can't raise the nose too much untill the AC has ascended a bit.> It seemed to me that the >computer aircraft (even with flaps extended) suffered from a >lack of lift at lower airspeeds, making an excessive nose up >pitch attitude necessary to attain a higher angle of attack .. Or, you are too slow for the weight. Normally the Airspeed indicator reads close to the one in the real AC. Which means near 10 kts low at high angles of attach for SEL's. But, closer to true IAS for jets. And for the the King Air. AFSD shows 'Q', Dynamic pressure in lb per sq ft. I'll check right now how much lift one gets during landing with no flaps. I see TBL 404 shows CL= 0.025 at AoAw=0 deg. Wing Area, S = 310 ft^2. Wing Incidence is 1 deg, but the twist of -1.5 degrees nearly cancels out. So, TBL 404 is close to AoAbody, which shows in AFSD. Now Weight = Lift = Q * S * CL. You mentioned 15,000 lb. I'll not consider flaps. But, calculate AoAb (pitch in level flight) at 100 kts IAS. I think Q would be 31 (another calc gives 29)(Q can be checked in AFSD). So, Lift = 15,000 lb = 31.0 * 310 * CL. CL= 1.56. Now TBL 404 peaks at CL = 1.44. So, you couldn't fly at 100 IAS and 15,000 lb without some extra lift from flaps. TBL 320 gives flaps deflection = 0.70 radian, and REG 1101 shows 'Lift - Flaps' = 0.67. At 0.7 radian deflection Flaps add 0.7 * 0.67 = 0.47 to CL. So, with full flaps, maximum CL is 1.44 + 0.47 = 1.91. Which is not that much above the 1.56 calculated as required at 100 kts. AFSD shows these parameters, and I assume close to what I just calculated. In fact, AFSD just goes backwards, and calculates the diplayed CL from the weight and other parameters. Looks like stall would be near 16 degrees AoA. So, at 100 kts, full flaps, 15,000 lbs, AoA would be about 16 * 1.56/1.91 = 13 degrees. This might decrease by 1 deg due to GE, but is way too high for landing! Assuming I didn't make any errors, this explains why your pitch is so high, especially at 78 kts. I see "full_flaps_stall_speed=76.8" in aircraft.cfg. I don't know if that's realistic for the King Air, the number doesn't change the actual stall speed unless FSEdit is used. I often watch AoA during landing, and don't know Vref or what the correct approach speed is. So, I never found the MS King Air to require too much pitch during landing. MS generally gets the Wing Area correct, and that's the main thing that affects this. AFSD will show your current weight, I assume it really was at rated gross. >and generate sufficient lift to reduce the descent rate to >an acceptable level before touchdown. TBL 404 shows CL ~ 0.03 at AoAw=0. While many other AC are around CL = 0.20. That mainly changes pitch in cruise, anytime the AoA isn't way up. I assume the King Air is about right in cruise.>There were other >issues with the flight dynamics of course, but most of them >were easily solved, or improved to acceptable levels. Steve Small improved the King Air. He used to be qualified in them, so I'd expect his hack was about right in pitch. I see his AIR file is 'protected' so I can't compare it with the MS one right now, but I suspect the parameters above are about the same as in the MS AIR file I'm looking at.And >when I became aware of the possibilities for editing the >flight dynamics by using FsEdit and FDE from Abacus, I >jumped in with both feet and began working on them! >...............>medium and small types. After changing over to FS2002 and >finding that the problem still persisted in this newest >release from Microsoft, Unfortunately, many MS FS2K2 AC are quite bad. I heard they said 'we are still working on the flight models' months before the FS2K2 release. Looks like they 'didn't have time' to improve them from the earlier versions. They didn't give the beta testers any time to critique the 'final beta' flight model code either. Perhaps they didn't want to get feedback about the lousy autopilot and more than one bug. ;(>graduate, nor am I an aeronautical or aerodynamics engineer, >but I do have a working knowledge of some aeronautical >matters gained during my years as an instrument rated >private pilot as well as a degree in Applied Aviation >Maintenance Technology.... When I lived in CA I knew a guy who got a degree in that at San Jose State. Then, they put him on the staff to teach Maintenance Technology.>To illustrate what I'm talking about, I have attached 4 >screenshots to this message, which I will descibe as >follows: >Unaltered Default AIR & CFG Files Beechcraft KingAir 350 I'll try flying the King Air again and check the landing speeds and pitch.>As I mentioned above, I have been in the habit of airplane >spotting since childhood, and I have NEVER seen a real >airplane make a normal approach for landing with the pitch >attitude exhibited in Image 1. ....... Bet you know how they should look better than I.>However, if you find yourself not in agreement with any of >the above, or if you feel that nothing satisfactory can be >done to correct the problem due to limitations in the >Microsoft software then the matter need go no further and I >shall refrain from mentioning it again. Leave me a private AVSIM message and I'll send you some of my AC for your critique. Just the landing View is a big problem in FS, and even better panels only improve on this some. Ron

[Guest Ron Freimuth]

I flew the King Air (SS's hack) at 14,000 lb gross. It was close to what I calculated. I had to approach at 110 kts with full flaps, using AFSD's autoland. The nose was up over 10 degrees at 90+ kts. .... Checking Steve Small's AIR file (perhaps not his final version), I see he reduced Flaps Lift to 41% of the MS AIR file. Lift Coefficient with full flaps would be 0.29 lower than the MS AIR file with full flaps. Increasing full flaps stall IAS by 8.4%. About 7 kts. Regardless, the MS King Air would still be very nose high at 85 kts and near stalling. The Wing Area, Flaps Lift, and airfoil CL vs AoA always come out compatable with the stall speeds, etc. All you need to do is understand Lift = CL*S*q. Where 'S' is wing area, and q is dynamic pressure. AFSD shows this, but it can be calculated from IAS. CL changes with AoA, TBL 404 shows the maximum. Add Lift_Flaps*(Flaps_deflection/57.3) for the increase in CL with flaps. I assume S is really 305 ft^2 for this AC. Another factor I didn't consider is Elevator Lift. When the elevator is pulled back it pushes the tail down. This increases the load on the wing. AFSD showed 'Lift - Elevator' going below -0.1 when I pulled the JS back to slow down. That -0.10 directly subtracts from Wing CL. Also, there is "Lift - H. Stab". That only has a value if the horiz tail has an angle of incidence. It was neglible in the King Air I just flew. But, is typically -5% of CLwing. I haven't checked the airfoil for the King Air's wing, but CLmax in TBL 404 is 1.44. Which seems appropriate. For a C172 CLmax is about 1.52. For many jet transports, 1.2 to 1.3 (except for crazy MS jets).Ron

[Avcomware 1]

Hi. I had a few days where my total dedication, undivided attention and involvement was required, and I am glad to see that this discussion continues. Very informative and helpful discussion. It reminds me of the Advanced R&D meetings where we had very opinionated and results oriented, problem solving, brain storming sessions, with double and triple PHDs individuals that can approach Pilots when it comes to debating and discussing related issues. I tried a number of things that Ron and Donna mentioned, but I never allowed myself to deviate too much from what I knew to be realistic values. Sometimes knowing something can interfere with the experimentation process. Maybe this is a sign that I am taking this whole thing a little too far for now. A lot of good information. I am at different stages, most elements are at rote or understood, some applied. The problem I have is that I cannot correlate all the available information. This is compounded by the fact that some elements need to be adjusted based on experience and empirical engineering rather than real data. I am glad that I was able to find a place where some of you have the knowledge and dedication to pursue this hobby. I ended up wit about 3 .air, .cfg file combinations that I can do some of the things that I need. The problem is that I have to interrupt the flight, load another aircraft, rename / copy the combo files and reload the aircraft that I use every time I want to take advantage of the modifications. I was hoping that there maybe a way to simplify this process, maybe a background task? I will continue to see if I can find something that satisfies most of the requirements, but I keep going back to Ron