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FS2004 EGT Question

Discussion in 'Gauges' started by vololiberista, 17 Feb 2017.

  1. vololiberista

    vololiberista

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    When starting the RR Conway in real life the EGT starts to climb between 11-13%n2 but the fuel is not admitted into the engine until 24%n2. In the sim model EGT doesn't move until fuel is entered so I presume it is linked to fuel flow. Is that the case? If so is there any way I can get the EGT to start rising as described before fuel is entered? Many thanks.
     
  2. Heretic

    Heretic Resource contributor

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    Add an offset that increases from 11% N2, reaches its peak at 24% N2 and then decreases again?
     
  3. vololiberista

    vololiberista

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    Do you mean a second variable in the gauge?

    This the current code and as you can see it is already quite complex. As it also incorporates ambient cooling.
    Code:
    Gauge Name="TGT 1" Version="1.0">
       <Image Name="EGT_back.bmp" Luminous="1"/>
       <Element>
          <Position X="448" Y="452"/>
          <Image Name="Needle_EGT.bmp" PointsTo="North" Luminous="1">
             <Axis X="145" Y="365"/>
          </Image>
          <Rotate>
             <Value Minimum="0" Maximum="800">(A:General eng1 exhaust gas temperature, celsius) (L:LastEGT1,enum) &gt; if{ (A:ENG1 EXHAUST GAS TEMPERATURE, celsius) (L:temp adj1,number) - (L:E1_hotstart, number) - }
    els{ (L:LastEGT1,enum) } </Value>
           
             <Nonlinearity>
                <Item Value="0" X="111" Y="622"/>
                <Item Value="50" X="90" Y="570"/>
                <Item Value="200" X="98" Y="290"/>
                <Item Value="400" X="402" Y="87"/>
                <Item Value="600" X="754" Y="257"/>
                <Item Value="800" X="774" Y="629"/>
             </Nonlinearity>
    <Delay DegreesPerSecond="60"/>
          </Rotate>
       </Element>
    
    <Element>
          <Select>
             <Value Minimum="0" Maximum="800">(A:General eng1 exhaust gas temperature, celsius) (L:LastEGT1,enum) &gt; if{ (A:ENG1 EXHAUST GAS TEMPERATURE, celsius) (L:temp adj1,number) - (L:E1_hotstart, number) - (>L:EGT1_read_out,number) }
    els{ (L:LastEGT1,enum) (>L:EGT1_read_out,number) } </Value>
          </Select>
       </Element>
    
    
       <Mouse>
    <Tooltip>Engine1 EGT: %((L:EGT1_read_out,number))%!03d!&#176;%c %</Tooltip>
       </Mouse>
    </Gauge>
     
    Last edited: 17 Feb 2017
  4. Heretic

    Heretic Resource contributor

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    Yup. Or a custom, independent EGT system in the first place.
     
  5. Roy Holmes

    Roy Holmes Resource contributor

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    Volo,
    Remember that all the various engine temps and EPR are generated for display separately and after the sim calculates engine performance.
    So A: anything to do with engine temp,garbage is just that and you need to do as Grumpy suggested.
    But, how can EGT rise if no combustion is taking place, no fuel flow till later?
    Roy
     
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  6. WarpD

    WarpD

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    Massive flame throwing ignitors??? :D
     
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  7. vololiberista

    vololiberista

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    Hi Roy,
    egt.jpg
    In this image you can see the needle is pointing to below 50 celsius. And two painted green lines that must be in-line. This is the at-rest engine off position and in real life the engines cannot/should not be restarted until this position is achieved. The first position on the scale is 50 celsius. What happens in real life is that as the air is compressed during the start-up it gets hot just like a bicycle pump. But that doesn't register on the gauge until after 11%n2. To precisely what temperature I don't know as yet. But I would say more than 50 if not 100. So what I want to model is the needle moving off mark after 11%n2 and then the actual EGT to continue as seen in my code above once the engine has started. All this to be in a smooth operation as it were. (L:LastEGT1,enum) is the ambient cooling variable after shut down.

    So I am trying to think of how I can add a variable to what I already have to start the needle in motion and then the existing code take over once that initial temperature has been passed. Ideas welcome. :idea:
     
    Last edited: 18 Feb 2017
  8. taguilo

    taguilo Resource contributor

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    Have you checked that personally in a real VC10 cockpit? Do you have any document about this behavior?
    EGT rise is the primary indication for light up, which obviously needs fuel injection. It sounds very weird to me that EGT would rise 50-100 ºC without fuel being burnt, just because of "hot compressed air".

    Tom
     
  9. vololiberista

    vololiberista

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    I have it on good authority from a Flight Engineer who was in the RAF and worked on the engines for 8 years. And he currently maintains ZD241 at Bruntingthorpe in ground running order. I have asked him by how much the temperature rises and am awaiting his reply. I was surprised myself when he mentioned it. But seeing as it was/is his job one has to believe. My suspicion is that the needle comes off its park and up to no more than 50c.
    Here is the aircraft in question ZD241.

    and this one
    from 2:20. You need to turn your sound up to maximum. :)
     
  10. chris

    chris

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    I've just had a look at some old datalogs I have from a CF6-6 cranking at 2350rpm before ignition.
    Ambient temperature 93.5'F
    T3 temperature 122.6'F.
    (T3 is the temperature exiting the compressor section.)
     
  11. vololiberista

    vololiberista

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    What seems to be happening in real life is that the starter switch is thrown and at 11%n2 the HP cock is partially opened and around 22-24%n2 the HP cock is set to "run" ie. fully open. From what I can tell the EGT rises to about 300c from 11%n2, stays at 300c for some seconds and then from 22-24%n2 rises more rapidly to its max before falling back. So I need to introduce a fake variable to count up to 300 and stay there until the real EGT catches up and passes it. I have tried starting from 11%n2 but the sim rolls back and won't ignite the engine.
     
  12. WarpD

    WarpD

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    At 300 C, that's over 570 F... I don't think the laws of physics would allow for simple compression to achieve that temperature in the engine. There would have to be fuel burning. Also, EGT is measured at the rear of the engine and thus would be where the exhausted air is decompressing which would actually cause a drop in temperature, not a rise.
     
  13. Heretic

    Heretic Resource contributor

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    Maybe the burner cans need to be preheated or cleared of residual fuel before actual startup? :D
     
  14. vololiberista

    vololiberista

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    It seems that the burners light-up much earlier ie. at 11%n2. There are three settings to the HP cock. Closed, Start and Run. So I think that's the key.
     
  15. taguilo

    taguilo Resource contributor

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    Now it makes sense. At 11% a first line of fuel is added when the HP cock is partially open. Then a second line of fuel is enabled when the HP cock is full open, at 22-24%.

    Tom
     
  16. vololiberista

    vololiberista

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    It didn't realy make sense to me either. I found a video with the EGT gauge for engine 4 showing. Not the best resolution but it seemed clear as to what was happening.
     
  17. vololiberista

    vololiberista

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    I have done an overlay code to start the needle moving at around 12%n2. The main code kicks off at 22%n2 and catches up. It then moves the needle further to max EGT. The problem is that there is too long a delay. The overlay code takes the needle to 300c and then it waits until the main code catches up. That wait is too long. Yes, I can slow down the overlay code but then the needle movement is too slow. Is it possible to speed up the main code at least until it gets to EGT300c?
    Code:
    <Element>
    <Select>
    <Value>
    (A:General eng1 starter, bool) 1 == (A:Eng1 N2 RPM, percent) 12.3 &gt; and
    if{ (L:E1_light_up, number) 1 &lt; if{ 1 (>L:E1_light_up, number) }
    1 300 (L:E1_light_up, number) rng if{ (L:E1_light_up, number) 1.000065 * ++ (>L:E1_light_up, number) } }</Value>
    </Select>
    </Element>
    This is the code that starts the needle off.

    And this is the main code
    Code:
    <Value Minimum="0" Maximum="800">(A:General eng1 exhaust gas temperature, celsius) (L:LastEGT1,enum) &gt;
    if{ (L:E1_light_up, number) (A:ENG1 EXHAUST GAS TEMPERATURE, celsius) (L:temp adj1,number) - (L:E1_hotstart, number) - (L:E1_light_up, number) &gt;
    if{ (A:ENG1 EXHAUST GAS TEMPERATURE, celsius) (L:temp adj1,number) - (L:E1_hotstart, number) - } }
    els{ (L:LastEGT1,enum) } </Value>
    The main code basically hinges on (A:ENG1 EXHAUST GAS TEMPERATURE, celsius).
     
  18. vololiberista

    vololiberista

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    Everything could be solved if ignition could be made to work below 22%n2 :(
     
  19. taguilo

    taguilo Resource contributor

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    And why is that you can't add fuel at 11 % and customize the entire code from there?

    Tom
     
  20. vololiberista

    vololiberista

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    I can kick off the starter etc., at 11% but the EGT behaves strangely going up and down. And it too doesn't start to rise at the same time. So I presume I am missing something. I've tried fiddling with this and that but to no avail.
    Code:
    <Value Minimum="0" Maximum="800">(A:General eng3 exhaust gas temperature, celsius) (L:LastEGT3,enum) &gt; if{ (A:ENG3 EXHAUST GAS TEMPERATURE, celsius) (L:temp adj3,number) - (L:E3_hotstart, number) - }
    els{ (L:LastEGT3,enum) } </Value>
    (L:LastEGT3,enum) is the ambient cooling down parameter. The rest besides (A:ENG3 EXHAUST GAS TEMPERATURE, celsius) are other adjustments related to cooling air etc.

    Starter code. The n2 start value is (L:ign,number)
    Code:
    <Value>(G:Var1) if{ (A:Circuit general panel on, bool) (A:Eng3 N2 RPM, percent) (L:ign,number) &lt; &amp;&amp; if{ 0 (&gt;K:TOGGLE_STARTER3) 0 (&gt;K:THROTTLE3_SET) } els{ (G:Var1) -- (&gt;G:Var1) 0 (&gt;K:MIXTURE3_INCR) } } (G:Var1) 0 != (A:General eng3 starter, bool) ||</Value>
    Whatever I do the n2 needle gets to 11%, stops and returns to zero.
     
    Last edited: 20 Feb 2017

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