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Chris Willis

Ground Friction On 2004

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Anyone know If excessive taxi thrust has been addressed? Thanks From Jim

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I found that this problem disappeared when I upgraded my PC.The excessive thrust was a simptom of a delay caused between the frame rate slowing everything down and me putting extra thrust to compensate for this visual slowing. I now have a 2400xp processor and 8X AGP 128MB geforce4 video card and my taxing is as smooth as silk. Hopefully it will be the same with FS2004!

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>I found that this problem disappeared when I upgraded my PC.>The excessive thrust was a simptom of a delay caused between>the frame rate slowing everything down and me putting extra>thrust to compensate for this visual slowing.I am glad it works for you however I tested it many times any required high-thrust needed to mainatin rolling has nothing to do with frame rates or some other delays. Even the 767PIC design team knew about the bug. For example on this very aircraft any thrust below (if I recall) 30% and aircraft will eventually stop (and if it stopped it is not because your frame rates are too low ;-) ). There is no way to keep aircraft moving with an idle (or very close to) thrust. The issue is the rolling friction and someone here provided some evidence the problem might have got fixed in FS2004 though at this point it is not 100%.Michael J.http://www.reality-xp.com/community/nr/rsc/rxp-higher.jpg

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Glad you caught that regarding fps/taxi friction Michael--when I read the post, I kept thinking "How's that again?"I'll try to set up a test between the two sims tonight.... I'll measure the length of time it takes an aircraft at idle thrust to fsll from a known speed to another known speed, given the same aircraft, loadouts, winds, etc.... I wish I could say ground friction modelling has changed, but I honestly don't think it's changed much, if it has. I know at takeoff at KMFR, which I'm using as my FS2004 default airport, it seems to take full thrust to get the takeoff roll going. But slowing the aircraft "seems" different--for the better...

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John,When making 'experiment' make it as simple as possible...And I think the simplest thing to do is not to measure any times.Just measure amount of N1 thrust to keep a jet moving on the runway - say at 10-15 kts. Keep decreasing the thrust until the aircraft starts slowing down and will eventually stop. Note the minimum thrust needed. End of test.Michael J.

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"Just measure amount of N1 thrust to keep a jet moving on the runway - say at 10-15 kts. Keep decreasing the thrust until the aircraft starts slowing down and will eventually stop. Note the minimum thrust needed. End of test."Will do.... Probably about five hours from now before I can give it a try, however.

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Interestingly enough, PSS aircraft do not generally suffer from this problem. I think their FDE designer changed the thrust curve so that idle thrust on the ground is usually sufficient to keep the A/C rolling. So apparently there are ways to get around it if an FDE designer knows how to "rig" the .AIR file.

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>there are>ways to get around it if an FDE designer knows how to "rig">the .AIR file. yes, but this creates other side-effects. I don't think anybody managed to circumvent the problem without paying some price.Michael J.

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My test results were interesting...I used a flight model of the Ariane 737 I had modified heavily. Had 70 pax in the loadout, plus full fuel.Had to get N1 to approx 50-55 to get moving, and to maintain a taxi speed of 20kts, N1 was 39. Same results, both sims. Yet the movement seems different in FS2004--a bit smoother acceleration, and a more gradual loss of speed when thrust is cut. But my opinion is highly subjective. The significant point is, given the same flight model, the numbers are exactly the same. Leave it to a commercial pilot to say whether these numbers are realistic. I suspect the flight model has as much to do with the issue as the modelling of ground friction....-John

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also the Project Airbus A320 rolls nicely with idle thrust.Walter

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1) Nope, fs2004 stays the same in terms of ground friction. I think this has to do with the simple fact that, starting in fs5, MSFS no longer had two models, one for ground handling, and the other wich was enabled as soon as the aircraft got airborne. Because of this missing feature, models that are accurately designed (like the Siai Machetti), tend to slip sideways along the rw during takeoff due to the torque and slipstream effect. If you set up winds, even the airliners slip sideways if they have their FMs correctly parametrized - why? because there being no special treatment of ground physics they weathervane just like if they were airborne...2) MSFS tried to overcome this problem by increasing ground friction, having as a side effect that a LOT of thrust is required to get most aircraft to taxi speed and to mantain it...3) Yes, the Jet engine model can be tweaked (at least it could in fs2002, by editing Table 1506 of the ".air" file. If we do it correctly (just as I did for PICA320... ;-) ) it'll not affect flight regime because you have mach on the Y axis, and you can modify thrust up to a mach value corresponding to, say, 80 KIAS, thus having no effect as soon as you get airborne with most airliners.4) As you can test, in fs2004, the LearJet is very well designed (it has the most complete 1506 table I ever saw on any MSFS air file!!!). It taxies perfectly at ground iddle under a wide range of GWs.Maybe fs10 will bring us back the two physics models (used in fs4). After all we are now getting moving clouds (wich was a feature in fs5, lost begining with fs95) and the ATC finally allows for initial and cruise alt, with the possibility of requiring alternative FLs, just like ATP allowed 10 years ago!!!

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>1) Nope, fs2004 stays the same in terms of ground friction. I>think this has to do with the simple fact that, starting in>fs5, MSFS no longer had two models, one for ground handling,>and the other wich was enabled as soon as the aircraft got>airborne.I think you finally correctly identified the problem. That would explain everything.It is a big omission crying to be fixed.In FLY! there was a seperate ground and air simulation.Thanks.Michael J.http://www.reality-xp.com/community/nr/rsc/rxp-higher.jpg

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Hi j.c.monteiro, "After all we are now getting moving clouds" "After all we are now getting moving clouds (wich was a feature in fs5, lost begining with fs95) "We never lost moving clouds, they have ALWAYS moving in fs98, fs2000 and fs2002 I hope you saw them in those version. If you don't know how the clouds move, they move with the wind. There is no new thing in fs2004 about the moving clouds, the only difference, is now the cirrus move, but in all others version, all cumulus, thunderstorm clouds was moving.ThanksChris Willis[link:fsw.simflight.com/FSWMenuFsSim.html]Clouds And Addons For MsFs

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