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P3D v2 Setting Turbine Idle

Makes you wonder who really made Flight Simulator. Such a sophisticated platform.

I think I do not have the IQ level required to change the idle RPM of my bird, unfortunately. I have no degree's in space telemetry pattern configurations nor a background or degree in Quantum Physics, so this leaves me out. :S
 
I'm going well overboard here, but I don't know if you only want to adjust N1 and N2 or if you want to do the whole deal.


Table 1503:
X-axis: Throttle lever position. 0 = idle, 1.0 = full forward
Y-axis: The corresponding CN2 value. Lower curve: At sea level. Higher curve: At altitude as expressed by Inverted Atmospheric Pressure (e.g. 4.453 ~= 36000 ft)

Table 1504 is exactly the same but at high mach numbers!

Both of these tables set the boundaries of a three-dimensional field, from which MSFS will pick a CN2 value according to speed, altitude and throttle position.

When you've set 1503 and 1504, set up 1502. This links CN2 to CN1. X-axis: CN2; Y-axis: The corresponding CN1 value. Lower curve: Sea level. Upper curve: At altitude as expressed by IAP. In general, for a turbojet like the early Lerjets, CN2 is the same as CN1, while for two-spool turbofans, CN1 is lower than CN2 at low CN2 values and greater than CN2 at high CN2 values.

If you need to adjust turbine spool time, also set 1505. For a 727, I've set up a near-linear curve with x-axis values from 0 to 7. Y-axis values shut start at the max CN2 RPM that MSFS' jet starter can achieve (~20%) to make the engine start at all and end at the maximum possible CN2 for your jet. Fuel_fow_gain= in the aircraft.cfg can be used to tweak this if a further delayed or hastened engine response to throttle lever movement is desired.

Tables 1506 and 1507 basically determine how much thrust you will get at a specific CN1 setting, altitude and speed. 1506 sets the thrust itself while 1507 sets the engine drag due to speed.
Here's where it's getting a bit complicated. Keep in mind that actual thrust decreases with speed and altitude. The latter has already been determined in tables 1503 and 1504 in the CN2 field, because MSFS looks up CN2 (1503, 1504) before it looks up the corresponding CN1 value (1502) before it looks up the corresponding thrust (1506,1507).
Anyway, there are basically two philosophies on how to set these tables up.

1) 1506 and 1507:
You put the actual thrust (y-axis; as a fraction of static_thrust = in the aircraft.cfg) at a given CN1 (x-axis) and a given Mach (each curve) into table 1506.
Table 1507 is set up with the corresponding aerodynamical drag of the engine as expressed by a constant factor (y-axis) at a given CN1 value (x-axis). There are two curves for the lower and upper end of your speed envelope.

2) Only 1506:
You run your thrust numbers through a spreadsheet and adjust them for drag at every point before putting them into 1506. 1507 needs to be all zeros in that case. This is a bit more work-intensive, but at the same time a bit more accurate than the method above as 1507 supports less data points than 1506.

In any case, you will tell MSFS just exactly how much thrust the engine will deliver at a specific speed and altitude.

Important notes:
- MSFS uses CN1 and CN2 to do its thrust calculations, which is basically N1 and N2 adjusted for sea level. This is done for better comparing engine performance at altitude and sea level.
- There's still drag and lift to consider if you want to improve general aircraft performance, but these are entirely different animals.
- This will not solve any inaccurate EPR and EGT readings. You'll have to fake these in engine gauges after you've set up the engines.


And these are just the very basics to get decent performance. Not exactly rocket science, but it requires a bit of tinkering. And good resource materials. If you have an operating handbook of the Lear with engine tables, you're pretty well set up to do this. If not, you'll need to google. A lot. And look at in-flight cockpit photos or videos and decypher engine instrument readouts.


Further reading:
Roys document also describes MSFS' turbine engine handling pretty well:
http://www.fsdeveloper.com/forum/resources/fs-thrust-vs-altitude-calculations.43/

First hand history of my struggle:
http://www.fsdeveloper.com/forum/threads/too-much-drag-anemic-engines.428881/ (Lots of info, lots of desperation, lol.)

A general overview of how MSFS' flight dynamics work:
http://library.avsim.net/download.php?DLID=170811



I'm pretty sure that the experts like Roy or JX_ will come and add some more. Or slap me for tons of inaccuracies, lol.
 
Are you simply trying to overwhelm me and make me feel like I barely know anything! OH MY GOODNESS! ACK!!!!!!!!!!!

MACH NUMBERS? Is that like transdimensional shifted hyper light speed with respect to magnetic sphere field sciences?

I need a scaler, a 'set to 14,000 RPM' type of thing.

This could take weeks.

Nah, I'll keep it as it is. Thanks guys. Man, this is grim. I never knew adjusting turbine RPM idle points would be this sophisticated.
 
lionheart said:
Are you simply trying to overwhelm me and make me feel like I barely know anything! OH MY GOODNESS! ACK!!!!!!!!!!!

MACH NUMBERS? Is that like transdimensional shifted hyper light speed with respect to magnetic sphere field sciences?

I need a scaler, a 'set to 14,000 RPM' type of thing.

This could take weeks.

Nah, I'll keep it as it is. Thanks guys. Man, this is grim. I never knew adjusting turbine RPM idle points would be this sophisticated.
Click to expand...

I can hear eyebrow hair going gray over here.

It sounds more complicated than it actually is. Open an airfile with AAM and see what I mean.
 
if you just want to adjust idle you can do so in the first paragraph of Heretic's post...

"Table 1503:
X-axis: Throttle lever position. 0 = idle, 1.0 = full forward
Y-axis: The corresponding CN2 value. Lower curve: At sea level. Higher curve: At altitude as expressed by Inverted Atmospheric Pressure (e.g. 4.453 ~= 36000 ft)

Table 1504 is exactly the same but at high mach numbers!"
 
lionheart said:
Are you simply trying to overwhelm me and make me feel like I barely know anything! OH MY GOODNESS! ACK!!!!!!!!!!!

MACH NUMBERS? Is that like transdimensional shifted hyper light speed with respect to magnetic sphere field sciences?

I need a scaler, a 'set to 14,000 RPM' type of thing.

This could take weeks.

Nah, I'll keep it as it is. Thanks guys. Man, this is grim. I never knew adjusting turbine RPM idle points would be this sophisticated.
Click to expand...

Weeks? Lucky you! It took me months. The bog standard table 1505 is wrong and causes the engines to surge on start-up. Refer to the alien discussion mentioned above. I had to further adjust it to start ignition at 24% instead of the default 22%. EGT was faked in the air file so that I get the correct start-up temperatures and heat transfer rates. It's the only way. Also instead of EPR I have P7 which if you like is the back end of EPR. Then there's the slam test. That is to firewall the throttles and time them from idle to 96% N2. etc etc etc. After all that I had to build in the engine limitations i.e. max n1 etc. To give an example taking off at Heathrow everything is within limits and a 96% n2 seting for take-off 94% for climb. Taking off from Kuwait though is another matter. For one thing you don't want to be on the ground all that long during the day.The engines simply won't cool down after landing. Instead of 96% n2 for take-off you run at 102%. Now you are time limited before the engines pack up. If you get to 105-107% you have seconds!!!
One can see why many "developers" leave those tables well alone.
 
jx_ said:
if you just want to adjust idle you can do so in the first paragraph of Heretic's post...

"Table 1503:
X-axis: Throttle lever position. 0 = idle, 1.0 = full forward
Y-axis: The corresponding CN2 value. Lower curve: At sea level. Higher curve: At altitude as expressed by Inverted Atmospheric Pressure (e.g. 4.453 ~= 36000 ft)

Table 1504 is exactly the same but at high mach numbers!"
Click to expand...


I tried to follow this in AAM. I looked at table 1503 which, at first, seems like an ordinary X,Y graph which sounds like the terminology spoken here. So far so good. Then I clicked the modify button and the chart changed and became a bunch of upward sloping lines...I was lost.

Is there a better way to make this attempt? Another tool?

Background: I'm tinkering (well...trying to tinker) with the F1 Mustang which seems to idle around 45ish N1. From what I see in videos (sorry...my only source), when you cut throttle, it should drop down to 25ish N1. At them moment, I just want to see what the effect of that would be (with an eye toward making the airplane behave more similarly to the videos and airplane specs).

Gregg

EDIT: This is what I see before I click the Change Graph button...

6aAl3x9.png

This is what I see after I click Change Graph. I'm guessing that the segments above are all shifted together and put between two lines. The question is, what about this would cause an N1 idle near 45.
PRrTEYn.png
 
Last edited:
I found table 1502 this morning and also figured out you could edit the values below the graph without pressing 'change graph' (lord...am I a newb at this or what?) I did some 'corrections' based on various N2 positions and corresponding N1 positions from the videos and got the numbers much closer to them...at least at low mach. (The bright line below used to overlay the darker line.) Idle and low power settings are much more like the videos.

Gregg
hdzmr7H.png
 
I put my tables into Excel as I found it much easier to play around with the numbers and see the results.
It's also easier to see and iron out odd kinks in the graphs where one expects to see a smooth transition.
 
Since the CN1 to Shaft Torque has only 3 elements it's not easy to get good results. The turboprop shaft has almost no friction up to the idle position. And the idle position is a mix between 509 and 1508 tables. These 2 tables combined is what i used to get my first turboprop performance.
 
@DG
This thread is, I believe, about Turbine engine idle. As stated above, that is adjusted in 1503 for static and 1504 for dynamic (flight) conditions.
509 is the friction table for turboprop or piston engines, aka AIR_61S_ENGINE_FRICTION.
1508 is CN1 vs Percent Corrected max torque for turboprop engines, aka AIR_70_N1_TO_SHAFT_TORQUE.
Neither affect idle.

Roy
 
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