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P3D v4 FS Thrust vs Altitude calculations Version 2 doubt + table 1524

Draken

Draken

Messages
118
Hello,
I'm trying to learn....

1) Somewhere (page 3) in "FS Thrust vs Altitude calculations Version 2" it is stated ".....One can, for example, do a FS flight test at full throttle at close to sea level, 10K, 20K, 30K, 40K altitude and record stabilized Mach and net thrust,...".
How can I read net thrust in a flight test?

2) To avoid to re-invent the wheel, what it is stated in "FS Thrust vs Altitude calculations Version 2" (tables relation and calculations) has been already converted in a spreadsheet to facilitate the calculus?

3) What is table 1524? What are the I/Os and related formulas?

Thanks a lot!

Sergio
 
You need to create a test gauge that outputs all the parameters you are interested in recording. I usually get to the test conditions (altitude etc) then pause the sim and write down the numbers.
FS (and P3D) does not have a gross thrust variable but does have one for net thrust. The document explains how you can find out what ram drag amounts to and hence get gross thrust.

I created this document a long time ago and do not have a dedicated spreadsheet for it. You will find the equations etc much more understandable if you create your own spreadsheet.

1524 is a table of afterburner thrust factors vs Mach. If the factor is 1.5 at Mach 0, then your thrust including afterburner is 1.5 times static dry thrust.
Roy
 
Hi Roy,
have you a test gauge suitable for to pass me?
Not because I'm lazy, but if possible I would like to not open a new challenge to prepare it.
Thanks in advance!

Sergio
 
Last edited:
Sergio,
Try these,
Window02=Debug
[Window02]
Background_color=1,1,1
size_mm=250,300
window_size_ratio=1.0
visible=0
zorder=10
window_size=0.25,0.30
position=8
ident=10010
gauge01=F-35B_Flight_Test_Debug,0,0,250,300

Roy
 

Attachments

Roy, I'll do ASAP.
In the meantime THANKS!

The attached picture is from air wrench of the graph of available vs required thrust.
I would like to act on the yellow highlighted portion.
THRUST AVAILABLE VS REQUIRED.png




Sergio
 
Last edited:
Roy,
I "installed" your gauge and I can see the pop-up window, however it is all black.
I put the xml and its bmp in P3D Gauge folder, but I see just a black rectangle in the pop-up window.
What I did wrong?
Thanks!

Sergio
 
There are lots of things you can do wrong and usually only one correct way. I would need much more detail to help solve the non-appearance.
Roy
 
Please let me know what detail and I'll provide it.
I'll be able to work on it the next Tuesday afternoon.
I'll give details on how I modified the original panel.cfg
Was the placement of the two files correct?
Thanks.

Sergio
 
Last edited:
Roy,
in the meantime, a doubt.
In your script:
gauge01=F-35B_Flight_Test_Debug,0,0,250,300
is the numbering

gauge01

valid even if in the original panel.cfg there are already 89 gauges references?
Thanks.

Sergio
 
Last edited:
Roy.
Thanks for the input.
By the way I was already looking at trying to figure out a way to fix.

Sergio
 
Last edited:
Roy,
from my understanding of the SDK help your script should be as follows:

Window03=Debug


[Window03]
file=flight_test_debug.bmp
Background_color=1,1,1
size_mm=250,300
window_size_ratio=1.0
visible=0
zorder=10
window_size=0.25,0.30
position=8
ident=10010
gauge00=..\gauges\name_of_the_aircraft.gauges!F-35B_Flight_Test_Debug,0,0,250,300

Plus, the XML file in aircraft gauges directory and BMP file in aircraft panel directory.

However it still doesn't work.

I attach what I see. Just the bmp.

I'm out of ideas.

Sergio
 

Attachments

  • test gauge.png
    test gauge.png
    24.2 KB · Views: 177
Last edited:
Roy,
pardon me!

I tried also:

Window03=Debug


[Window03]
file=flight_test_debug.bmp
Background_color=1,1,1
size_mm=250,300
window_size_ratio=1.0
visible=0
zorder=10
window_size=0.25,0.30
position=8
ident=10010
file=flight_test_debug.bmp
Background_color=1,1,1
size_mm=250,300
window_size_ratio=1.0
visible=0
zorder=10
window_size=0.25,0.30
position=8
ident=10010
gauge00=Flight_Test_Debug!F-35B_Flight_Test_Debug, 0,0,250,300

Plus, the XML file in a folder, named Flight_Test_Debug, within aircraft panel folder and BMP file in aircraft panel directory.

Again, I see just the pop-up window.

Could you kindly check the xml?
I ask you so, because with the same panel.cfg editing I was able to launch a SDK xml gauge example (pressure gauge), so the panenlc.g syntax should be correct.

Thanks a lot!

Sergio
 
Last edited:
You are nearly there.
unzip the background and the code into the same folder. In mine I have them both in a folder called Test_gauges.
The background is drawn because it is called up in the gauge as the image. You do not need any other reference to Flight_Test_Debug.bmp.
<Gauge Name="F-35B_Flight_Test_Panel" Version="1.0">
<Image Name="Flight_Test_Debug.bmp" Bright="Yes"/>

Here are the relevant parts from my panel.cfg

//F-35B MODSIM Panel configuration file dated 23 October 2021

[Window Titles]
Window00=Weapons Configurator
Window01=vACMI client
Window02=Debug
Window03=Varwatcher
Window04=PLG2LN3
Window05=Traffic

VIEW_FORWARD_DIR=-1.000, 0.000, 0.000


[Window02]
Background_color=1,1,1
size_mm=250,300
window_size_ratio=1.0
visible=0
zorder=10
window_size=0.25,0.30
position=8
//window_pos=0.7,0.7
ident=10010
gauge01=Test_gauges!F-35B_Flight_Test_Debug,0,0,250,300

Within each Window your gauge numbering is unique so you can have more than one gauge01 so long as they are contained in different windows.


Roy
 
Roy

I understood that P3D works at standard ISA conditions.
No matter of seasons and time.

I'm going to record model thrust at several ambient temperatures and altitudes, making a table.
Thrust will be recorded either MILITARY and FULL A/B condition.
Doing that, I'll use the official flight envelope path to check if the model speeds are coherent with the official values

I'll use then NASA JET ENGINE to record thrust values at the temperatures and altitudes even if, I have not all the inputs to feed NASA JET ENGINE.

BTW, what inputs are you able to pass to
NASA JET ENGINE?
Or, better rephrasing, what inputs are to mandatory be passed to Jetson for our scope (in your paper you mention air intake).

One point is that the engine I'm looking at has the compressor and turbine revolving at the same rotational speed.
So, in my understanding of the definition s, N1= N2.

In the meantime I'll read your paper over and over again to clarify what you explained.
I need to draw a flow chart to help me visualize the links among tables, putting together the formulas in the cells.
At the end I would like to create a spreadsheet which will link the tables.

Sergio
 
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Roy,
since reading your paper I got myself lost, hoping to clarify myself, I read in one of your dated back posts: "The Mudpond website has an excellent paper entitled “How the jet engine tables work” and I would suggest having that paper available while reading this article."
Since the link http://www.mudpond.org/jet_flow_chart.pdf is dead, I would ask you a copy if it is still in your hands. Thanks!

Sergio
 
The Mudpond chart showed how the tables interact, but not why and to what extent. Similarly there was not a single stock airplane in FSX or P3D that had each table interact correctly so while it is hard to believe, not one stock jet in those sims had accurate performance. To keep things simple I only covered a jet which had the turbine physically connected to the compressor. In that type of engine, if max RPM was some value of 100% the engine should hold 100% across its envelope. That is easy to achieve with the tables, just use what is in the paper with, preferably, lots of altitude table elements. Doing that the engine should hold close to 100% at all altitudes. You will notice that MSFS has similar tables but they tend to have a sea level and max altitude table element only. That would work if the atmosphere was uniform, which it is not. Another reason why MSFS is inaccurate thrustwise across its envelope.
I did consider having twin spool engines, where N1 and N2 are different, in the paper, but considered that it would most likely give less accuracy. Typically, a single stage engine requires a low idle RPM because you need low thrust for idle, landing and taxying. In a twin spool engine N1 can be set low to meet the low thrust requirement while N2 can run faster. In fact N2 is basically there to generate torque to drive N1. N1 pulls in the air that exits as thrust.
If an engine has gone through an update or performance improvement, it is probably going to operate at a higher RPM than its original version so it's manuals might stipulate 103.4% for some engine parameter compared to 100% for the original. This complicates the sim engine table calculations, but the math is the same, just different values than a single stage turbine.
I had a look for the Mudpond flow chart no luck.
Roy
 
Roy,
1) the issue is on my side, not on your paper
2) until next September I won't have access to the airfile, neither to Excel. So my current activity is harder because no verifications of what I'm reading of your explanations can be done
3) I do want to thank you again for your support and patience.

Having said this.
Fortunately I have all the aircraft manuals to get info of performances.

The engine I'm looking at is a turbojet 17 compressor stages, 3 turbine stages and afterburner.
Compressor and turbine run on the same shaft (N1=N2).
Military thrust 11870 pounds
Full AB thrust 17500
Max rated speed 7460 RPM
Max engine speed 105.5%
Idle 70%
During military and afterburning ops RPM may be not 100% but will vary with Compressor Inlet Temperature.
CIT is perfectly managed by the original aircraft simulator.

For the scope of what discussed in your paper:
a) any observation , thought from your side about this engine characteristics to drive me?
B) to JETSIM what information should I pass to, apart air intake area?


Now, with premise 2) here above, since your paper is so interesting and challenging that I can't wait, I'll put down some notes of my doubts for each table mentioned in your paper and I'll post them.

I hope you'll be willing to clarify them.

Won't you?

Later, on September, I'll go through the entire process you clearly mentioned.

Sergio
 
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