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zachlog

NGX Taxi Performance

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After pushback/start engines, at idle N1 is appoximately 22%, the A/C does not move. At about 24% N1, the A/C wants to REALLY move so it does not seem to behave like a heavy A/C. All Realism sliders are at 100% per the Introduction manual. Is there anything else that can be done to have the acceleration during taxi be more like a heavy A/C ? The question is regarding acceleration and taxi speed at ~24% N1 NOT about braking (works fine). Thanks,Zach

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I find the taxi performance to be spot on. What the NGX models, and other FSX aircraft fail to take into account, is the effect of inertia. Once you reach the threshold where the amount of power (N1) is sufficient to the move a heavy aircraft, inertia increases subsequent acceleration and makes it difficult to stop the aircraft simply by reducing N1 back to the threshold.

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737NGThrust UseThrust use during ground operation demands sound judgment and technique. Evenat relatively low thrust the air blast effects from the large, high bypass engines canbe destructive and cause injury. Airplane response to thrust lever movement isslow, particularly at high gross weights. Engine noise level in the flight deck is lowand not indicative of thrust output. Idle thrust is adequate for taxiing under mostconditions. A maximum of 40% N1 should be adequate to initiate taxi in mostsituations. Allow time for airplane response before increasing thrust further. Break away thrust is about 35% N1.

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The NG ops manual mentions using rev idle when taxing during slippery conditions like ice. In the G-5/550 it's normal procedure to use rev idle during taxi. The plane will speed up quickly with idle thrust and the carbon brakes get a little grabby once warmed up. We use 1 eng in rev idle to maintain taxi speed and 2 eng in rev idle to slow prior to turns.

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737NGThrust UseThrust use during ground operation demands sound judgment and technique. Evenat relatively low thrust the air blast effects from the large, high bypass engines canbe destructive and cause injury. Airplane response to thrust lever movement isslow, particularly at high gross weights. Engine noise level in the flight deck is lowand not indicative of thrust output. Idle thrust is adequate for taxiing under mostconditions. A maximum of 40% N1 should be adequate to initiate taxi in mostsituations. Allow time for airplane response before increasing thrust further. Break away thrust is about 35% N1.
Some manual might have what you quoted above, but I agree with the OP.The NGX will start taxiing at 23% N1. I have to find a sweet spot around 23.5-23.8% to maintain taxi speed without losing/gaining any.At 24% N1 and higher the NGX wants to accelerate well past 20 knots. I don't load my aircraft terribly heavy but it's not terribly light either.I think this issue is what the OP was talking about, and quoting what the plane *should* do doesn't change the fact it *doesn't* do it.

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I never watched my N1 while taxiing, but i can control taxi speed pretty easily without brakes or reverse thrust. I can even hold it steady by modulating the throttle.

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Some manual might have what you quoted above, but I agree with the OP.The NGX will start taxiing at 23% N1. I have to find a sweet spot around 23.5-23.8% to maintain taxi speed without losing/gaining any.At 24% N1 and higher the NGX wants to accelerate well past 20 knots. I don't load my aircraft terribly heavy but it's not terribly light either.I think this issue is what the OP was talking about, and quoting what the plane *should* do doesn't change the fact it *doesn't* do it.
I believe quoting the manual on this is very good because that is where you will get the description of how Boeing says the real a/c will act.I also find the taxi behavior of the NGX to be very realistic.If you push the throttles up, you will not get an immediate response, but you will have to hold it and find that place where the NGX will begin to move, then lower the throttles to a spot that will keep the proper taxi speed consistently.It took me a while to get used to it, but now I'm very comfortable with the way the NGX taxies and I agree that it is "spot on".

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Don't think I have ever been able to taxi below 30% N1, think once when I was REALLY light, but then I still had to hold at least 28-29%.

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Some manual might have what you quoted above, but I agree with the OP.The NGX will start taxiing at 23% N1. I have to find a sweet spot around 23.5-23.8% to maintain taxi speed without losing/gaining any.At 24% N1 and higher the NGX wants to accelerate well past 20 knots. I don't load my aircraft terribly heavy but it's not terribly light either.I think this issue is what the OP was talking about, and quoting what the plane *should* do doesn't change the fact it *doesn't* do it.
ummm, I wasn't dis-agreeing with the OP. I just gave him the rw BBJ info from the manual for a comparison to further hi light the issue. People here are quick to give theory on the way the real aircraft behaves so I posted the fact. My post wasn't intended to change the fact that it doesn't do it nor detract from the issue.

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I Have seen some jets taxi with one reverser out to keep from having to ride the brakes.
Such action could destroy the engine by hot gas reingestion, minimum airspeed usually 60 Kt for reverse thrust operation.

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I never watched my N1 while taxiing, but i can control taxi speed pretty easily without brakes or reverse thrust. I can even hold it steady by modulating the throttle.
It takes more than 30% to get the aircraft to start moving, but once it is moving you drop below 25% and can keep a good taxi speed. Very small movements of the thrust levers make a difference.

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It takes more than 30% to get the aircraft to start moving, but once it is moving you drop below 25% and can keep a good taxi speed. Very small movements of the thrust levers make a difference.
Not sure if you are referring to the real A/C or the PMDG NGX. My observations are quite different than yours. Per my original post, it starts moving and continues to accelerate quickly at ~24% N1.....and this is the problem. 30% N1 is take off roll numbers (only 10% below where TO/GA is activated). Again, the issue is not slowing it down (the brakes work fine). Zach

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Not sure if you are referring to the real A/C or the PMDG NGX. My observations are quite different than yours. Per my original post, it starts moving and continues to accelerate quickly at ~24% N1.....and this is the problem. 30% N1 is take off roll numbers (only 10% below where TO/GA is activated). Again, the issue is not slowing it down (the brakes work fine). Zach
That's not really true. I have seen airport instructions that say to keep taxi N1 below 40%, so 30% must be used for taxi also.Using 30% to break to a roll, then pulling back is not unreasonable.

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Such action could destroy the engine by hot gas reingestion, minimum airspeed usually 60 Kt for reverse thrust operation.
In the Gulfstreams(G-5 or better) it's normal during taxi as long as you stay at reverse idle.As far as the NG, this is from the ops manual. During taxi, the momentary use of idle reverse thrust may be needed on slipperysurfaces for airplane control. The use of reverse thrust above reverse idle is notrecommended due to the possibility of foreign object damage and engine surge.Idle reverse thrust may be necessary on slippery surfaces to control speed whiletaxiing. Consider having the airplane towed rather than relying on extended use ofreverse thrust for airplane control.

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It is amazing how many people are giving out their theoretical knowledge when nobody is asking them to.The OP is right and there is something to be adjusted within FSX. The NGX (at average weight) taxies with throttles approx@24%. 1/10th percent less on my throttles and the airplane starts decelerating and stops very quickly (and in my opinion unrealistic). A few notches forward and the acceleration is too much and brakes have to be used. I have very good (and calibrated throttles) and still find it difficult to control the taxi speed. Yes, there is a sweet spot but its margins are extremely narrow IMHO. Something is not right and has to be looked into.

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It is amazing how many people are giving out their theoretical knowledge when nobody is asking them to.The OP is right and there is something to be adjusted within FSX. The NGX (at average weight) taxies with throttles approx@24%. 1/10th percent less on my throttles and the airplane starts decelerating and stops very quickly (and in my opinion unrealistic). A few notches forward and the acceleration is too much and brakes have to be used. I have very good (and calibrated throttles) and still find it difficult to control the taxi speed. Yes, there is a sweet spot but its margins are extremely narrow IMHO. Something is not right and has to be looked into.
I think there's something wrong with your setup, because for me and others everything works well. I don't have the problems you describe. I usually push the throttles to 30-35% until the plane starts moving, then i drop them a bit and let the plane accelerate to 10-20kts, depending on how straight the taxiway is. When i need to stop i just put the throttles to idle and the plane slowly coasts to a stop. It feels very realistic and smooth.

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I think there's something wrong with your setup, because for me and others everything works well. I don't have the problems you describe. I usually push the throttles to 30-35% until the plane starts moving, then i drop them a bit and let the plane accelerate to 10-20kts, depending on how straight the taxiway is. When i need to stop i just put the throttles to idle and the plane slowly coasts to a stop. It feels very realistic and smooth.
What kind op set up are you referring on.I have no idea how the real plane behave, but I notice the same behavior in the PMDG. At 1/3 full (with fuel) the plane starts moving at 24%. If I load it full then it starts moving at 28%. (well that difference feels realistic :-) ).If I use F3 or the throttle to 30% the plane is moving immediately very very fast and I have to heavily brake to get the steering possible.So what should I change in my setup? Regards. Eric

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What kind op set up are you referring on.I have no idea how the real plane behave, but I notice the same behavior in the PMDG. At 1/3 full (with fuel) the plane starts moving at 24%. If I load it full then it starts moving at 28%. (well that difference feels realistic :-) ).If I use F3 or the throttle to 30% the plane is moving immediately very very fast and I have to heavily brake to get the steering possible.So what should I change in my setup? Regards. Eric
Well... I don't know what your setup is, nor am i that familiar with the NGX's inner workings. If you're using FSUIPC, you might want to try setting up your controls via FSX, rather that FSUIPC. It causes all sorts of unpredictable problems.

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I think there's something wrong with your setup, because for me and others everything works well. I don't have the problems you describe. I usually push the throttles to 30-35% until the plane starts moving, then i drop them a bit and let the plane accelerate to 10-20kts, depending on how straight the taxiway is. When i need to stop i just put the throttles to idle and the plane slowly coasts to a stop. It feels very realistic and smooth.
Cristi, I think Martin above is the only person who understood my original question and is staying on point. You say there may be something wrong with the setup. OK, where do I look for remediation ? If 24% N1 makes the A/C behave as if it's made out of paper instead of an A/C with a ZFW of ~100,000 lbs., what tweek do I go after ? Please keep in mind that the performance/realism sliders are 100% to the right per the Introduction. Thanks for any suggestions you may be able to provide since your observations/experience is what I was expecting to see. Zach

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Cristi, I think Martin above is the only person who understood my original question and is staying on point. You say there may be something wrong with the setup. OK, where do I look for remediation ? If 24% N1 makes the A/C behave as if it's made out of paper instead of an A/C with a ZFW of ~100,000 lbs., what tweek do I go after ? Please keep in mind that the performance/realism sliders are 100% to the right per the Introduction. Thanks for any suggestions you may be able to provide since your observations/experience is what I was expecting to see. Zach
All i was providing were my observations with the plane. I do not get the same problems you are getting, and apparently, neither does the lawyer+pilot guy who doesn't sign his posts with his full name, as per the forum rules. Anyways, back to the point: I find the plane behaving just as the real thing should (mind you, i've never flown a 737, or anything larger than a 2 seater). At about 30-40% load, the airplane unsticks at about 35% and is accelerating smoothly. Just after it starts to move, i just pull the throttle back a bit, and everything's well. At idle, the plane slows down to an eventual stop. I don't need to ride the brakes and I don't need to use reverse thrust. In fact, most of the time I can taxi to the runway without touching the brakes, holding a max of 20kts on the straights, and 10kts in the turns.Since others don't complain about this, it must be something on your end, but as to what that is, I couldn't tell you. Submit a ticket to PMDG. If they can't figure it out, no one can. P.S.: I do not have any kind of friction model modifications on my sim (i don't even know if such a thing exits). I also have my sliders to 100%

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Zach and Martin, i have the same problem. What i've realised is full weight or empty it take the same trust to move the a/c. If it is indeed a setup issue, when u guys figure it out let me know. spranger

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Zach and Martin, i have the same problem. What i've realised is full weight or empty it take the same trust to move the a/c. If it is indeed a setup issue, when u guys figure it out let me know. spranger
Honestly, my gut tells me this is not a setup issue. The key here is the 24% N1. At idle (~22%) the A/C is stationary (no brakes), at 24%, reached very carefully and with the lightest possible touch of the throttle, we are off to the races. I had a similar issue with the 400X with lower GWs, it taxied very well with higher ones. I have not tried variable GWs with the NGX yet but the problem seems to be more acute with the NGX. I will let you know if I find anything but in general, this seems to be a problem somewhere between FSX and the NGX model. Zach

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Thanks Zach. to move from 22-24 is literally millimeters for my trottle. Im a RW dash 8 pilot, flew 737 in the sim. if u figure anything out let me know. and vice versa Spranger

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