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How to start a rocket engine

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How to start a rocket engine

Postby tea » Wed Aug 30, 2017 6:13 am

I'm working on my simple rocket model (simulating spaceX falcon9), using jsbsim FDM.

I read jsbsim manual and the wiki page about FGRocket, set up the propulsion configuration in the jsbsim config file ( define simple engine file on Aeromatic, thruster file, define fuel and oxidizer tank), but I have no idea how to start the engine in FG.

I tried configure the -set.xml following the thread viewtopic.php?f=66&t=29482# but it was piston engine and didn't work for me. Check the Vostok and SpaceShuttle project but fail to recognize what I need.
I tried to change the internal property setting (set controls/engines/engine/throttle to 1, add sufficient fuel in the tank, engines/engine/running true, controls/engines/engine/mixture=1, etc.)
Now jsbsim/propulsion/engine/fuel-flow-rate-pps=91.5, but thrust-lb always 0, and the model stay still. Is there a normal starting sequence for rocket engine, or is it possible that some number was wrong to prevent it from starting.

my code for reference
Code: Select all
  <propulsion>
    <engine file="Main_engine">
      <location unit="M">
            <x> 41.76 </x>
            <y> 0.0 </y>
            <z> 0.0 </z>
      </location>     
         <orient unit="DEG">
            <pitch> 0.0 </pitch>
            <roll>  0.0 </roll>
            <yaw>   0.0 </yaw>
         </orient>
         <feed>0</feed>
         <feed>1</feed>
     
         <thruster file="Main_nozzle">
            <location unit="M">
               <x> 41.76 </x>
               <y> 0.0 </y>
               <z> 0.0 </z>
            </location>
            <orient unit="DEG">
               <pitch> 0.0 </pitch>
               <roll>  0.0 </roll>
               <yaw>   0.0 </yaw>
            </orient>
         </thruster>
    </engine>
 
        <tank type="OXIDIZER" number="0">
         <location unit="M">
            <x> 12.0 </x>
            <y> 0.0 </y>
            <z> 0.0 </z>
         </location>
      <radius unit="M"> 1.8 </radius>
         <capacity unit="KG"> 274000.0 </capacity>
         <contents unit="KG"> 10.0 </contents>
      </tank>

      <tank type="FUEL" number="1">
         <location unit="M">
            <x> 28.0 </x>
            <y> 0.0 </y>
            <z> 0.0 </z>
         </location>
      <radius unit="M"> 1.8 </radius>
         <capacity unit="KG"> 137000.0 </capacity>
         <contents unit="KG"> 10.0 </contents>
      </tank>
         
  </propulsion>


engine file
Code: Select all
<?xml version="1.0"?>
<!--
  File:     Main_engine.xml
  Author:   Aero-Matic v 0.83

<rocket_engine name="Main_engine">
  <isp>            282.00 </isp>
  <shr>              1.23 </shr>
  <max_pc>       86556.00 </max_pc>
  <variance>         0.10 </variance>
  <prop_eff>         0.67 </prop_eff>
  <maxthrottle>      1.00 </maxthrottle>
  <minthrottle>      0.00 </minthrottle>
  <slfuelflowmax>   91.50 </slfuelflowmax>
  <sloxiflowmax>   105.20 </sloxiflowmax>
</rocket_engine>


Any clue or reminder will be greatly appreciated. :)
tea
 
Posts: 4
Joined: Wed Aug 23, 2017 7:03 am

Re: How to start a rocket engine

Postby Thorsten » Wed Aug 30, 2017 8:22 am

Now jsbsim/propulsion/engine/fuel-flow-rate-pps=91.5, but thrust-lb always 0, and the model stay still.


Obvious question - what about the oxidizer flow rate? Is the oxidizer tank not recognized by any chance?

Check the Vostok and SpaceShuttle project but fail to recognize what I need.


They're fairly obscure in that there's plenty of systems interfaced with the engine... I'm not sure we have a 'simple' rocket engine somewhere - maybe the X-15 would be a better example, it's a fairly old FDM with no frills.
Thorsten
 
Posts: 11057
Joined: Mon Nov 02, 2009 8:33 am

Re: How to start a rocket engine

Postby tea » Thu Aug 31, 2017 3:27 am

Thanks for your reply! And I forgot to mension, oxi-flow-rate-pps was 105.2

maybe the X-15 would be a better example, it's a fairly old FDM with no frills.


quickly downloaded and start the engine successfully just by setting the throttle to 1... and by logging the propulsion data I discovered sth different between them:

For my model, the Total Vacuum Impulse increases as I increase the throttle, but others ( Total Impulse, engine X Force.... ) are all 0
For X-15, both Total Vacuum Impulse Total Impulse, and X Force increase.

Do you know the possible reason for this ?
Thanks ahead
tea
 
Posts: 4
Joined: Wed Aug 23, 2017 7:03 am

Re: How to start a rocket engine

Postby Thorsten » Thu Aug 31, 2017 5:02 am

Then it'd seem you have a number (or unit definition...) wrong in the chamber pressure - the engine doesn't get the exhaust out against the atmosphere pressure and as result the vacuum thrust is there, but there's nothing at sea level.
Thorsten
 
Posts: 11057
Joined: Mon Nov 02, 2009 8:33 am


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