# FS9 engine start, how to make them spool correctly!

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if you are trying to replicate the real aircraft...Find out the correct idle N1 & N2. Set the idle N1 in table 1502 CN1 vs CN2...set the N2 idle in table 1503 CN2 vs throttle.find out the N1 & N2 at standard day 16*C for engine start up.(You need to know the moment the pilot should introduce fuel.)Let's say you get 4% N1 and 22% N2 for start:Open table 1505: Corrected fuel flow vs. CN2find the farthest right line and verify your x= is at least 101 and you y= is more than x.then,at x=0 set the y= to 22.01. the y= at X=0 should NEVER BE LESS THAN N2 idle % at fuel on!!! That is where the MS team screwed up! Then make a guess and draw a gradual slope upwards from left to right starting at x=0 y=22.01 up to x=100 y=>100.The slope should start out flat with x= lower than y=. x should catch p to y near the middle and then y should catch up to x and pass x by the x=100 line.Last thing, set your N1 at N2 start speed to N1 start speed, in this example, 4% N1 at 22% N2.do a test start in the sim.Fine tune the slope to get the spool timing. If the aircraft starts without any jumpin in N1 or N2 but spools too quick, try adjust the fuel flow scalar in table 1501: spool up rate or in the aircraft CFG under fuel_flow_gain.In my aircraft I have video from the cockpit during start up so I was able to play the video and run the FS Start simultaneously. The engines spool within +/- 1 seconds and +/- 2 % N1 from fuel on to idle. No jump or spike...smooth as a baby's bottom.My spool up rate in table 1501 is set to 0.0015 My fuel_flow_gain in the aircraft CFG is set to 0.00075

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Hi,I really don't want to contradict you but,>if you are trying to replicate the real aircraft...>Which one? aircraft behave different on startup accoring to the type/brand/model of their engines, amongst other things.>>In my aircraft I have video from the cockpit during start up>so I was able to play the video and run the FS Start>simultaneously. The engines spool within +/- 1 seconds and>+/- 2 % N1 from fuel on to idle. No jump or spike...smooth as>a baby's bottom.>My spool up rate in table 1501 is set to 0.0015 >My fuel_flow_gain in the aircraft CFG is set to 0.00075>If your aircraft is a turbofan/turboprop, I think you're missing one critical point: engines need bleed air aid to start, and spool up time has a direct dependency on bleed pressure. FS doesn't simulate this, so in the end if you want to stick to the REAL procedure, you'll need to fake the gauge indicators for N1/N2/N3/EPR through a set of polinomials and other similar stuff. Setting the correct relationship between engine spools, fflow and spool rate as you stated is really important, but not complete IMHO. I know this very well, as I needed several months to develope a precise simulation of my RB211 engines (including all kinds of abnormal situations: hot starts, hung starts, compressor stalls, high altitude inflight starts, etc)Tom

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""So how is it an unstarted engine produces 20 PSI?""Because it is not realistic! Simply put.""That is a negative. The start N2 is set as I outlined above. about 19 PSI is calibrated to it. regardless of whether the engine starts at 30 N2 or 10 N2 it will have ~20 PSI of bleed air"" FS requires:16 PSI of fuel pressure18.8 PSI of bleed air115 pounds of fuel (set by thrust) and that is all regardless of N2 or fuel valve position.""Do I need to repeat that a real engine will be able to start with a variable range of bleed air supply,fuel flow and fuel pressure, depending on present conditions? Those fixed values enable FS to simulate startup in a generic set of engines; that is good for the sim but not real if you are modeling a specific engine, which is my case.""Most FDEs start at x=0 and y=0x is your fuel flow and y is your N2x needs to be zero at the point the engines will be started.In my A/c it is 25% N2 so my x=0 is y=25.01, or zero fuel flow at 25 N2. if you cut in the fuel early will continue to spool due to the starter but it will not start until reaching 25.If you start your FDE with x=0 and y=0 then at x=0.24 and y=24 your are injecting 24% of the total fuel flow into the engine at ignition. In reality you would hear a loud KABOOM followed by sirens...in FS it burns all that fuel in a huge spike.""Must I assume that you are putting fuel on immediately after opening the starter?? How bad :-( Fuel switch must be turn on ONLY when N2 spool rate has reached a certain number (usually marked with a magenta indicator on turbofans). Anyway, as long as N2 core rotates fuel pump is working, then if turn on fuel switch, fuel will enter and soak the combustion chamber at low RPM, also generating a dense white vapor trail from the engine's exaust, and most probably end in a hot start once the fuel ignites in combustion.I do not mean to offend you, but I think you should review the way a real engine works on startup and the parameters that are taken into account. Some of these are really difficult to understand in a whole.Tom

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you must have a language barrier because you appear to not comprehend anything i say.The fuel on from the beggining was a test to see at what point FS9 simulates the start.The variables I pointed out are constants. If you don't understand how that makes them important regardless of how unrealistic they are I can't help you.They can be manipulated however you want without complex coding and all using A vars.As far as how an engine works, there is a difference between needing to understand an engine and purposely breaking procedure in an effort to understand the sim.

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Sir,If you have ATP experience, then you must be familiar with CRM.Act that way and don't humiliate people.Jan"Beatus ille qui procul negotiis..."

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>The variables I pointed out are constants. Not to pick nits, but something is either a "variable" OR a "constant."It cannot ever be both simultaneously... ;)

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>you must have a language barrier because you appear to not>comprehend anything i say.>>The fuel on from the beggining was a test to see at what point>FS9 simulates the start.Maybe I can't comprehend you because you confuse your concepts too much. My fault anyway, and I apologize for that.>>The variables I pointed out are constants. If you don't>understand how that makes them important regardless of how>unrealistic they are I can't help you.But it was you who started the thread saying "if you are trying to replicate the real aircraft"... and was me who was trying to help you understand that those concepts pointed by you were important to the sim but not realistic in terms of actual engine behavior. That was all about, and in the end you state the same in the above paragraph, so yes, it becomes difficult to comprehend you, sorry again.>They can be manipulated however you want without complex>coding and all using A vars.Of course, and I suspect that lot of people in this forum know how to configure their engine tables to obtain what they want (I being one of them). Anyway, your findings do add another perspective; thank you for sharing that with us.>As far as how an engine works, there is a difference between>needing to understand an engine and purposely breaking>procedure in an effort to understand the sim.I don't see the point in doing an effort to understand how the sim works, without undrstanding the basic concepts of the real procedures just to help the sim behave as real as it gets.Tom

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Jan, I am not hear to humiliate. I am simply pointing out that his responses suggest he doesn't comrehend what I am saying.. My responses started with "Tom, you missed the point" and I still feel that way.If you guys think I am being negative, my apologies, but I am not at all. Bill,What I mean is the values the variables produce during engine starts are constants "at the point of ignition." That in itself is useful to know...to those who want to really know what FS is doing.Tom,We're all here to learn. All I am trying to say is every aircraft has a different system for start, and there are 10 million ways to design that, but if you want your engines to spool as the real aircraft...meaning once ignited, the spool at realistic rates of rotation with the ambient air and weather affecting it and smooth spool up...this is how. I am not trying to show anyone how to code the parameters outside of that, which is where you keep focusing. That's why I say you miss the point.I think where you get confused is when I say the variable outputs unrealistic values that can be used to get the engine to perform realistically. I just want the end product to perform realistically... which is what you want so we are on the same side.And trust me Tom you are a friend, not an enemy. You posted useful information in a civilized way for all to read, which is why I am here.

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>I don't see the point in doing an effort to understand how the>sim works, without undrstanding the basic concepts of the real>procedures just to help the sim behave as real as it gets.>Because if you understand 100% of the real thing and 0% of the sim you do more work than you need to and I don't have the time to work harder than I have to!It goes both ways. If you understand both you can do more.

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>Tom,>>We're all here to learn.Cannot agree more on this.>All I am trying to say is every>aircraft has a different system for start, and there are 10>million ways to design that, but if you want your engines to>spool as the real aircraft...meaning once ignited, the spool>at realistic rates of rotation with the ambient air and>weather affecting it and smooth spool up...this is how. Well, I have to disagree on this, not with the technical aspects of your sentences but with the mode you state them. I would prefer to read something like "this is a good way to improve startup" rather than "this is HOW a real aircrat starts". Because your method, no matter how great could be, is just one of many that other talented people use here; I for one don't use your approach and my engines start smooth as well, no matter how deep I fake the gauges in a further step. >I am not trying to show anyone how to code the parameters outside>of that, which is where you keep focusing. That's why I say>you miss the point.True, but as you were trying to show FS generic parameters as realistics when they are clearly not (some of them not even close), I tried to clarify that point. If that wasn't your intention, then probably you're right and I missed your point in the essentials. >>I think where you get confused is when I say the variable>outputs unrealistic values that can be used to get the engine>to perform realistically. I just want the end product to>perform realistically... which is what you want so we are on>the same side. Never thought that we were on different ones; maybe we have a different level of acceptation for some FS technical aspects.>And trust me Tom you are a friend, not an enemy. You posted>useful information in a civilized way for all to read, which>is why I am here.>Never could have post a line in this thread if I would consider you an enemy. I don't ever talk with enemies (don't know of having ones) but for sure can dialogue in a respectful manner with people that don't share some or all of my points of view. I see you are doing pretty much the same now, then let's keep our future exchanges this way :-)Tom

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>>It goes both ways. If you understand both you can do more.>I agree on this sentence for sure.Tom

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Would it be possible to post an example screenshot or two of the curve, and corresponding table of x/y values?I'm trying to plug this into the Dreamfleet 727, but I'm now stuck with hung starts (or whatever it's called when it just stops spooling up) at about 22-23% N2.... I'm also extremely confused with the x on the 1505 graph in pretty much all of the aircraft I checked being 0.6 or less... Including the Level-D 767 and PMDG737... I changed the scale to have the highest x=101 and scale the intermediate x values accordingly, and have had the failed starts ever since.....Any further advice, or clarification?Thanks. :)

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