P3D v1 Jet Pressure Ratio?

[lionheart]

Hey guys,

Working on the Learjet. One set of gauges are called 'Pressure Ratio' indicators. I hadn't heard of such a thing till now.

Trying to get them to function and its not working. Does anyone know anything about Pressure Ratio gauges?

The gauge has readings from 1 (not zero) to 3.0.

A couple of tries;

<Element>
   <Position X="150" Y="150" />
      <Image Name="ExhaustGas_Needle" PointsTo="North" ImageSizes="13,116">
         <Axis X="6" Y="116"/>
   </Image>
   <Rotate>
     <Value Minimum="0" Maximum="100">(A:TURB ENG PRESSURE RATIO,percent) 100 / </Value>
     <Nonlinearity>
 	<Item Value="0" X="46" Y="233"/>
       	<Item Value="50" X="141" Y="18"/>
       	<Item Value="100" X="251" Y="232"/>
     </Nonlinearity>
     <Delay DegreesPerSecond="45"/>
   </Rotate>
</Element>



<Element>
   <Position X="150" Y="150" />
      <Image Name="ExhaustGas_Needle" PointsTo="North" ImageSizes="13,116">
         <Axis X="6" Y="116"/>
   </Image>
   <Rotate>
     <Value Minimum="1" Maximum="3">(A:TURB ENG PRESSURE RATIO,percent) 100 / </Value>
     <Nonlinearity>
 	<Item Value="1" X="46" Y="233"/>
       	<Item Value="2" X="141" Y="18"/>
       	<Item Value="3" X="251" Y="232"/>
     </Nonlinearity>
     <Delay DegreesPerSecond="45"/>
   </Rotate>
</Element>

 

[lionheart]

I took out the '100 / ' portion at the back of the Value and that caused the gauge to now lock at 3.0 (full maximum). No movement.

Any idea's?

 

[WarpD]

It's the EPR value.

 

[lionheart]

I have tried a few more versions. Nothing is working.

Also, I wonder if this statement is also one of those where they stealthily hide a 1 and 2 in the string for engine number...?

For instance, is it...
(A:TURB ENG1 PRESSURE RATIO,percent) <-- engine number
(A:TURB ENG PRESSURE RATIO:1,percent) <-- engine number

And is this a percent reading? What kind of reading would a ratio be?

 

[lionheart]

Just found in a google that one uses 'ratio' as the measure in the statement.

I did enter that, but nothing is still occurring.

Sure the min-max shouldn't be 0-100.

 

[taguilo]

Bill,

The EPR value from FSX Avar is useless. You'll have to calculate your own's from a custom table.

Tom

 

[vololiberista]

In the airfile I had to adjust the EPR number so that the P7 values were correct.
When the engines are not running the pressure is equal throughout the casing hence (A:AMBIENT PRESSURE,inHg).
vololiberista

<!--P7 corrected Values -->
<Element>
<Select>
<Value>(A:Turb eng1 pressure ratio, ratio) abs (A:AMBIENT PRESSURE,inHg) * (>L:Eng_1_P7,number)</Value>
</Select>
</Element>

 

[Heretic]

Default EPR calculation behaviour is useless. Check this out, Bill:

http://www.fsdeveloper.com/forum/showthread.php?t=428293


You need to have at least one "EPR by N1" reference value from the real bird. A full blown EPR table would be much better though!

 

[lionheart]

Many thanks guys.

Massively appreciated.


Bill

 

[lionheart]

I never did get this working.

I consulted the gauge guru Dwight and he was able to get it working.

The key element is 'number'... Not ratio as the SDK states. sigh.....

<Element>
   <Position X="150" Y="150" />
      <Image Name="ExhaustGas_Needle.bmp" PointsTo="North" ImageSizes="13,116">
         <Axis X="6" Y="116"/>
   </Image>
   <Rotate>
     <Value Minimum="1" Maximum="3">(A:TURB ENG1 PRESSURE RATIO,number)</Value>
     <Nonlinearity>
 	<Item Value="1" X="48" Y="232"/>
       	<Item Value="2" X="142" Y="18"/>
       	<Item Value="3" X="251" Y="230"/>
     </Nonlinearity>
   </Rotate>
</Element>

 

[taguilo]

I never did get this working.

I consulted the gauge guru Dwight and he was able to get it working.

The key element is 'number'... Not ratio as the SDK states. sigh.....

It must be a bug in P3D then, because in FSX ratio and number work exactly the same.

Anyway, EPR for turbofans in FSX (and I guess P3D as well) is completely unaccurate BUT, as you are modeling a Lear 24 which uses old turbojet engines, I believe it might work as expected. Would be great to know how it performs in yours, according to the real values.

Tom

 

[lionheart]

Hey Tom,

If you would like to check it, let me know.

The 24B used the CJ610-6 engines. I do not have all of the values precise.

Today I adjusted RPM spoolup time to be more then 4 seconds as I had also heard that if you shoved the throttles to full, the turbines would sputter. (They had to be smoothly pushed in).

Anyways... Im just glad that this is working.

I hadn't thought of this as possibly being a P3D issue.

 

[Heretic]

Anyway, EPR for turbofans in FSX (and I guess P3D as well) is completely unaccurate BUT, as you are modeling a Lear 24 which uses old turbojet engines, I believe it might work as expected.

It doesn't even work on low bypass turbofans, so cahnces are low that it also works on turbojets.

 

[Roy Holmes]

FSX does not really have a clue what type of jet engine is modeled.
It does a pretty good job at modeling thrust for a single shaft turbojet if you make N1 the same as N2 (or, rather CN1 the same as CN2). However the other aspects, fuel consumption, engine pressures and temperatures are not well done.
Roy