CHT & EGT per cylinder

Help creating logic scripts for Air Manager Instruments

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Keith Baxter
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Re: CHT & EGT per cylinder

#31 Post by Keith Baxter » Mon Nov 16, 2020 5:42 pm

Ralph wrote:
Mon Nov 16, 2020 5:31 pm
As far as I know the cap is the number of FPS. This exactly the reason why you want to keep your subscribes small.
Hi,

So what I am deducting from this is that if I have a fast GPU card I will get more data read fires than a slower GPU card. How would one consider this in a filter?

This might be for another thread. But another interesting topic for discussion on handling dataref subscribes and at what level a filter is to be applied, be it time,value or data size. An argument for a filter at subscribe level also exists in big buses.

Keith
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Re: CHT & EGT per cylinder

#32 Post by Ralph » Mon Nov 16, 2020 8:57 pm

That's indeed correct. To filter you send the incoming data to your function each timer tick. Since this is all no issue in general, especially because more data makes for a more fluent gauge animation, and it can be solved with a timer, I don't see why you would want an API function for this. But indeed something for a whole different discussion :)

JackZero
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Re: CHT & EGT per cylinder

#33 Post by JackZero » Fri Mar 19, 2021 10:59 pm

Hi Keith,
in my current rework of the EDM 700 I use two options: If you have a plane with REP expansion, there are dedicated datarefs for all cylinders, so these will be used. Otherwise I have written a dedicated routine that emulates different CHT and EGT for the different cylinders and stores them so that the instrument code itself doesn't need to distinguish those two cases and could easily be adjusted to newer/different Sim versions that have dedicated values as well. On startup, two random numbers between 0.95 and 1 are generated for each cylinder, which will be multiplied for calculation. One is a fixed offset for that cylinder, the other one is a variable offset that will change in time... this value is changed via a timer by +/- 0.001 every 10s. So there is no fixed hottest cylinder, and the hottest cylinder may (on rare occasions) even change in one flight... a maximum variance of 10 % (although rare) might be a bit high, but again, this would be a delta of 120°F at normal engine temps, which isn't completely improbable. But the values might use more tweaking.
One problem persists though and that is that all cylinders will obviously peak at the same moment, but solving that would probably be a non-trivial task.

Code: Select all

local egt_variable = {1,1,1,1,1,1}
local cht_variable = {1,1,1,1,1,1}
local egt_fixed    = {1,1,1,1,1,1}
local cht_fixed    = {1,1,1,1,1,1}

function update_offsets()
    -- increase or decrease by max +/- 0.001
    for i = 1, CYL_COUNT do
        egt_variable[i] = var_cap(egt_variable[i] + 0.002 * (math.random() - 0.5),  0.95, 1); 
        cht_variable[i] = var_cap(cht_variable[i] + 0.002 * (math.random() - 0.5),  0.95, 1); 
    end
end

if not USE_REP then
    math.randomseed(os.time())
    
    for i = 1, CYL_COUNT do
        egt_variable[i] = 0.95 + 0.05 * math.random();
        cht_variable[i] = 0.95 + 0.05 * math.random();
        egt_fixed[i] = 0.95 + 0.05 * math.random();
        cht_fixed[i] = 0.95 + 0.05 * math.random();
    end
    
    -- update egt/cht offsets evey 10 seconds:
    timer_start(0,10000, update_offsets)
end
Regards
Florian

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Keith Baxter
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Re: CHT & EGT per cylinder

#34 Post by Keith Baxter » Sat Mar 20, 2021 10:38 am

Thank you Florian,

I will give it a try on the PA46 Air Frame and revert.


Keith
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Re: CHT & EGT per cylinder

#35 Post by JackZ » Sat Mar 20, 2021 2:12 pm

Well I guess that EGT Peak and CHT temp rise is a bit more deterministic than that, essentially due to the physical location of each cylinders relative to the entrance of the cowling.

Both Continental and Lycoming engines are flat four or six cylinders engines, ie they have 2 or 3 cylinders on each side lined up behind each other in two opposite rows.
The actual numbering logic of the cylinders differ between Lyco an Continental, but the principle is the same.

The two cylinders that are closer to the entrance of the cowling obviously receive the most airflow, while the two farthest ones receive the same air but already heated by the previous cylinders.
The farthest two cylinders are usually the hotter ones, sometimes the middle ones, because air circulation is less optimal, but rarely the first two cylinders. If the first two are hotter this is an indication of a mechanical problem.

My 10 cents
Jacques
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Re: CHT & EGT per cylinder

#36 Post by Keith Baxter » Sat Mar 20, 2021 2:53 pm

JackZ wrote:
Sat Mar 20, 2021 2:12 pm
Well I guess that EGT Peak and CHT temp rise is a bit more deterministic than that, essentially due to the physical location of each cylinders relative to the entrance of the cowling.

Both Continental and Lycoming engines are flat four or six cylinders engines, ie they have 2 or 3 cylinders on each side lined up behind each other in two opposite rows.
The actual numbering logic of the cylinders differ between Lyco an Continental, but the principle is the same.

The two cylinders that are closer to the entrance of the cowling obviously receive the most airflow, while the two farthest ones receive the same air but already heated by the previous cylinders.
The farthest two cylinders are usually the hotter ones, sometimes the middle ones, because air circulation is less optimal, but rarely the first two cylinders. If the first two are hotter this is an indication of a mechanical problem.

My 10 cents
Jacques
Jacques,

100's My cousin. That is what I know. It is open to interpretation and what the simmer might want. A boring instrument that is static or a lively one that likes to give indication changes.

To be used to change fuel flow? I think we are a long way from getting engine wear within the sim, let alone per cylinder.

To me, a a more realistic interpretation would come from a variety of datarefs. Just not had the time to try anything just yet.

Fuel flow and injector (injectors the norm these days) wear needs to be considered. Often a overheating cylinder can be due to a low fuel mix or advanced ignition timing.

Unfortunately these things are not available within the sim so one has to look at alternatives to get the best compromise.

Keith
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Re: CHT & EGT per cylinder

#37 Post by Keith Baxter » Sat Mar 20, 2021 3:42 pm

Uncle Jacques ;)

The argument about the foremost cylinder being the coolest is not the case on the VW motor. In the late 1970's I was a VW apprentice and always cylinder 3 valves burned. Cylinder 3 is the foremost cylinder on the old bug.

The issues as I can remember were partly due to timing and damaged air flow ducting for cab heaters.
vw_cylinder.jpg

Also what part do separators play?

Keith
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JackZ
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Re: CHT & EGT per cylinder

#38 Post by JackZ » Sat Mar 20, 2021 4:15 pm

@Keith Baxter Are talking about the VWmotors that have been converted in aviation?
I am not familiar with those engines

Here I’m talking about aviation engines which are under an open cowling at the front just behind the propeller. Air is forced through this cowling and is evacuated at the bottom rear of the cowling, sometimes with the help of cowl flaps to increase the airflow speed.
My YouTube Chanel on the A320 (Real SOPs by an Airline Pilot IRL):
https://www.youtube.com/playlist?list=P ... 0Q6SBASRqJ

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Re: CHT & EGT per cylinder

#39 Post by Keith Baxter » Sat Mar 20, 2021 4:21 pm

Hi,

Rather than a random version

I think a model based on..

wind direction
wind speed
altitude
airspeed
elevation temp
engine config
engine hours
separator
timing
fuel mix


Keith
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Re: CHT & EGT per cylinder

#40 Post by Keith Baxter » Sat Mar 20, 2021 4:22 pm

JackZ wrote:
Sat Mar 20, 2021 4:15 pm
@Keith Baxter Are talking about the VWmotors that have been converted in aviation?
I am not familiar with those engines

Here I’m talking about aviation engines which are under an open cowling at the front just behind the propeller. Air is forced through this cowling and is evacuated at the bottom rear of the cowling, sometimes with the help of cowl flaps to increase the airflow speed.
Just the principle Jacques.

Keith
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