Cannot properly increase propeller pitch and engine throttle

[S&J]

How did I get you to adjust the GPH ?

[TheEagle]

How did I get you to adjust the GPH ?

I don't get the point ? What exactly do you want me to do ?

[S&J]

Ok go to each alt and first adjust the VE untill the fuel flow is 24. Then adjust the BSFC untill the power is 310.

Record these two values at each height.

Do this up to the critical alt.
you must also have changed this value in your engine file

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<ratedaltitude1>16000</ratedaltitude1> <!-- 17000  -->

It's another error in jsbsim, and this value will give you a critical alt of 17kft

Remember adjust the mixture to 11.3 AFR as you go along

Also as you've not set your Ram effect to zero you must adjust the wind to zero.

[TheEagle]

VE and BSFC

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Altitude      VE        BSFC

0             0.7037    0.3939
1000          0.698     0.394
5000          0.67      0.394
10000         0.637     0.3938
15000         0.6069    0.394
17000         0.5962    0.3938


I think the differences of BSFC are ignorable - they are the result of me not further changing VE if fuel-flow is 24.02 or BSFC if power-hp is 310.01
Now, what are we doing with the VE values ? Calculate the mean value and put that into the engine file ? Or create an interpolation table ?

[S&J]

Well done

You're correct BSFC doesn't change it remains constant.

VE as you've demonstrated does change up to the critical alt and then reverses.

The answer is you're going to create a table in an XML system file of ambient pressure vs VE

[TheEagle]

Like that ?

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   <function name="volumetric-efficiency">
       <table>
           <independentVar lookup="column">atmosphere/density-altitude</independentVar>
           <tableData>
               0              1000     5000  10000   15000     17000
               0.7037    0.698    0.67    0.637    0.6069    0.5962
           </tableData>
       </table>
   </function>
 

[S&J]

I've never seen a horizontal table before, so I was curious to see if it works, it doesn't

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            <table>
               <independentVar>atmosphere/density-altitude</independentVar>
               <tableData>
                  0      0.7037
                  1000   0.698
                  5000   0.67
                  10000   0.637
                  15000   0.6069
                  17000   0.5962
               </tableData>
            </table>

[benih]

This table structures are really useful, i use them alot.
Just as a side note to another pitfall: the reference values need to always be getting bigger, otherwise it won’t work (also true for two dimensional tables!)

So this table would be wrong:

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<tableData>
5   1
4   2
3   3
</tableData>

[TheEagle]

Actually I got the following for my horizontal table:

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In file /home/user/fgfs-addons/Aircraft/c210-family/Engines/Continental_TSIO-520-P.xml: line 30
Malformed function name with number: 0 and property name: volumetric-efficiency but no "#" sign for substitution.
Segmentation fault (core dumped)


Will try the vertical one.

[TheEagle]

Yep, vertical one worked. What's next to do ?

[S&J]

So you now have a turbo charged piston engine that works correctly in 'static' conditions.

But what about when it's in motion ?

You have a ram effect of 0.1 but I'm wondering if you know this to be correct or just using an existing value ?

The Cesna 172 uses a ram effect of 1

Personally, during my testing of the Merlin I'm more prone to believe the ram effect to be nearer 3 to deliver known results. I'd therefore suggest this as a valid starting point, which we might come back to once we've put a proper prop on.

But for now what you need to do is create another column for your table based on the qbar value at 204kts at 17kft.

Using the orientation property set this to zero degs and the wind in your weather to 204kts, and the pressure and temp to that at 17000ft.

Record the VE value needed to keep the MP and fuel constant. Do this for higher alts untill you establish the critical alt at speed. ( This being the point at which the MP drops)

We can then build a 3d table to modify the VE to take into account the changes in qbar and ram effect.

[S&J]

Just realised you'll need to remove all the lift and drag calcs for you to be able to increase the wind speed.

[TheEagle]

What do you mean with

Using the orientation property set this to zero degs

Which orientation property ?

[S&J]

orientation/heading-deg

[TheEagle]

Ah, you mean to align the aircraft with the wind ?