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michal

if microsoft is wrong about taxi way/runway friction ......

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then does that mean that takeoff and landing rolling distance is wrong too? For example it requires an unreal high thurst setting and longer runway to takeoff and something like that? In fs I have to use 30-40 perent n1 thrust to taxi while in RL a little over idle thrust will do, but I think it doesn't take 2-3 times runway length to takeoff.

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Such a good question----Pity your post seemed to be missed, it's a good one. I've flown often out of Sky Harbor and SFO. In FS2002, takeoff point in the jets is within meters of that in "real life".... I've never been at the controls of a real jet, but I fly often as a passenger. To get rolling, it seems that quite a bit of thrust needs to be applied, just going by the sound of the engine. In MSFS I find once I'm rolling in say, a 737, I can back off on the thrust to keep it going at a set speed. It's nowhere near 30-40pct....I notice when taxiing, that RL pilots seem to go out of their way to let the aircraft keep rolling, even if it's at a 1mph pace. I suspect in the heavy jets there's a good reason for this--namely that once their mass stops moving, it takes a bit of energy to get it going again.-John

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>then does that mean that takeoff and landing rolling distance>is wrong too? Nope, I don't think so. Yes, the thrust required for taxiing is unrealistic but it does not necessarily translate into wrong takeoff/landing distances. Why ? Because ground friction becomes negligible compared to aerodynamic drag forces when you move faster than say 50 mph. So your takeoff length (accuracy) will be primarily dictated by how well aircraft's drag is modeled, not the ground friction. Michael J.http://hifi.avsim.net/activesky/images/wxrebeta.jpg

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Interesting question. Never thought of it myself.

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No. While the static friction is very high, the kinetic friction is within realistic range, so once you're moving it's all good.

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>No. While the static friction is very high, the kinetic>friction is within realistic range, so once you're moving it's>all good.well, this is what I originally thought too. But I guess their kinetic friction is also screwed up - it just takes too much power to keep aircraft rolling. Jet aircraft should be able to keep moving on flat ground with idle power - shear impossibility in FS2002 (if I recall in 767PIC you need at least 20% N1 to stay in motion). I am not even sure their model distinction between static and kinetic friction - I will check it tonight.Michael J.http://hifi.avsim.net/activesky/images/wxrebeta.jpg

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There may also be a difference between friction coefficients (both static and dynamic) for taxiways and runways.If there is, that could account for the correct behaviour on runways yet incorrect on taxiways.

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>There may also be a difference between friction coefficients>(both static and dynamic) for taxiways and runways.Well, I don't think there is a "correct" taxiing behaviour anywhere. And on the subject of distinction between taxiways and runways - there really should be no (measurable) difference at all. Rolling friction on a flat "hard" surface is really primarily a function of forces in the aircraft wheels, axles, brakes, bearings, tires, etc - at least this is where the main contribution comes from. And whether you are on a dry lake bed in Edwards, CA or on a runway at Cape Canaveral has a secondary effect - provided the surface can be classified as "hard". In other words a 747 pilot would hardly notice any difference while taxing on ceramic tiles versus a concrete. Is Microsoft doing anything about it in the upcoming FS9 ?? *:-*Michael J.http://hifi.avsim.net/activesky/images/wxrebeta.jpg

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I modestly suggested that a serious ground friction "code" to be part of the next FS. It was among the ideas/suggestions posts. And I hope it was concidered. I think friction and slipery factor should be included not necessarly physically speaking but as a performance/handling factor. If its a rainy or snow weather in FS I think the density of precipitatoin should influence the friction and slipery factor on the runwayCheers

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>If its a rainy or snow weather in FS I think the>density of precipitatoin should influence the friction and>slipery factor on the runway>That would be wonderful but does anyone think Microsoft is up to this level of realism ? I have my doubts. Let them fix just the rolling friction and perhaps properly handle differences between static and dynamic friction (so you need more power to get moving than if you were already moving) and they win my admiration just for that. Slippery stuff could wait for .. FS11 ?Michael J.http://hifi.avsim.net/activesky/images/wxrebeta.jpg

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Since you're raising this interesting question of friction and contaminated rws, I should point out that there is only one PC sim I know about that has consistently modelled such effects: AS2 (www.nomissoft.com).Simon Hradecky took his calculations to the point of different degreess of icy rws, and the effects it has even during taxi!!!Yet, MSFS, and CFS do account for diferent degrees of friction depending on rw type. I don't know how it is internaly represented though...

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>Yet, MSFS, and CFS do account for diferent degrees of friction>depending on rw type. That's the reason why probably they can't get it right. Like I said there should be no measurable diff for different hard surfaces as far as rolling friction is concerned. Unless they want to do brakes and/or slipping simulation which clearly they are not doing. Sounds like they need to hire a physics consultant ...Michael J.

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