FGTurbine EGT

[Octal450]

I'm submitting a ...

• bug report

Describe the issue
EGT is based on throttle. That is very wrong. It should be changed to N2 norm to be a bit more closer to proper.

What is the motivation / use case for changing the behavior?
While not exactly right, it at least makes the movement of the EGT gauges of aircraft that don't yet override the EGT with a correct calculation more realistic.

Fix

jsbsim/src/models/propulsion/FGTurbine.cpp

Line 221 in 9ea4925

EGT_degC = in.TAT_c + 363.1 + ThrottlePos * 357.1;

Change to
EGT_degC = in.TAT_c + 363.1 + N2norm * 357.1;

[seanmcleod70]

Does look like a very simple/basic model for EGT, and I would assume too responsive when based on ThrottlePos, and using N1norm or N2norm would be better.

don't yet override the EGT with a correct calculation

What does a correct calculation look like?

Came across this 4K video which shows N1, EGT. Fairly readable if you screen clip and sharpen a bit. TAT also somewhat readable. N2 is fairly difficult to read.

https://www.youtube.com/watch?v=ZelrHEDOU_M

Example:

[Octal450]

Every engine is different. No reason to fix the numbers in JSBSim.

I just want to fix the dynamics so it's not = throttle position. So planes (not mine) that don't override it have it look less silly.

Kind Regards,
Josh

[seanmcleod70]

No reason to fix the numbers in JSBSim.

Not planning to. But when someone mentions a correct calculation I'm interested in seeing the calculation and the data for it. Did you for example come across some table of N1/N2/TAT/EGT for some specific engine(s)? If so, can you share it?

Also to use it as a rough comparison to see how different it is to the current JSBSim model, and to a modified JSBSim model using N1 or N2 norms.

Similiar to how I came across a number of different ground effect models that had been published and compared them.

[seanmcleod70]

I took a brief look at your MD-11 GE engine EGT calc. Can you share the data that you used for coming up with this?

https://github.com/Octal450/MD-11/blob/d76a491aee04a4c3a29cb8a785c97e5d261a91f1/Systems/md-11-ge-engine-fadec.xml#L1272-L1303

		<fcs_function name="/systems/fadec/egt-cmd-1">
			<function>
				<sum>
					<property>propulsion/tat-c</property>
					<table>
						<independentVar lookup="row">/engines/engine[0]/n2</independentVar>
						<independentVar lookup="column">atmosphere/density-altitude</independentVar>
						<independentVar lookup="table">/controls/engines/engine[0]/cutoff</independentVar>
						<tableData breakPoint="0">
							         0    50000
							 10.0    0    0
							 35.0  430  330
							 50.0  425  325
							 62.9  320  205
							112.5  815  620
						</tableData>
						<tableData breakPoint="1">
							       0    50000
							 30.0  0    0
							 62.9  320  205
							112.5  815  620
						</tableData>
					</table>
				</sum>
			</function>
		</fcs_function>
		
		<lag_filter name="/systems/fadec/egt-actual-1">
			<input>/systems/fadec/egt-cmd-1</input>
			<c1>0.35</c1>
			<output>/engines/engine[0]/egt-actual</output>
		</lag_filter>

[Octal450]

@seanmcleod70 Sorry, I swore I replied to this. Please ping me if I forget.

The table is not written anywhere, I calibrated it by going through TONS of videos/pictures and noting EGT vs N2 vs TAT vs altitude.

Then I just fit into a simple model here.

Regardless, this issue isn't to fix the numbers, those are unimportant and change with EVERY engine type, it's just the actuation linked to throttle that I want corrected.

Kind Regards,
Josh

[seanmcleod70]

Yep, I wasn't looking to fix it to some specific numbers for some specific engine type, rather I was interested to see what real EGT data looks like, to do some comparisons etc.