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VC10 project under way - any interest?

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Re: VC10 project under way - any interest?

Postby Octal450 » Tue Jan 12, 2021 5:32 am

hi Alan,
That's great but not what I meant, I'm talking about the FCS. Its using generic style JSBsim (at least in the git file i glanced thru). You should model each surface and each actuator!

Kind Regards,
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Re: VC10 project under way - any interest?

Postby Alant » Tue Jan 12, 2021 10:04 am

Josh
Is this what you mean? This is how I have implemented the rudder inputs in my TSR2,

Code: Select all
      <channel name="Yaw">

         <pure_gain name="Rudder trim limit">
            <input>fcs/yaw-trim-cmd-norm</input>
            <gain> 6.0</gain>  <!-- 1=6deg, British convention, left is positive -->
            <output>fcs/rudder-trim-limit</output>
         </pure_gain>

         <pure_gain name="rudder cmd deg">
            <input>fcs/rudder-cmd-norm</input>
            <gain> 12.5</gain>  <!-- 1=12.5deg, British convention, left is positive  -->
            <output>fcs/rudder-cmd-deg</output>
         </pure_gain>

         <summer name="rudder sum">
            <input>fcs/rudder-cmd-deg</input>
            <input>fcs/rudder-trim-limit</input>
            <input>fcs/afcs-rudder-cmd-deg</input>
            <input>/systems/flight_test/rudder_input</input>
            <output>fcs/rudder-sum</output>
         </summer>

         <pure_gain name="rudder norm">
            <input>fcs/rudder-sum</input>
            <gain>0.08 </gain><!-- 1=12.5deg -->
            <output>fcs/rudder-pos-norm</output>
         </pure_gain>

         <pure_gain name="rudder rad">
            <input>fcs/rudder-sum</input>
            <gain>0.01745329251994329576923690768489</gain>
            <output>fcs/rudder-pos-rad</output>
         </pure_gain>

      </channel>


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Re: VC10 project under way - any interest?

Postby Alant » Tue Jan 12, 2021 10:35 am

There is more to it than that of course. The servos require hydraulic and electrrical servises to operate. The VC10 rudder is split into 3 section. The upper section is reserved for the yaw damper.
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Re: VC10 project under way - any interest?

Postby Gijs » Tue Jan 12, 2021 10:53 am

Alant wrote in Tue Jan 12, 2021 10:04 am:
Code: Select all
         <pure_gain name="rudder rad">
            <input>fcs/rudder-sum</input>
            <gain>0.01745329251994329576923690768489</gain>
            <output>fcs/rudder-pos-rad</output>
         </pure_gain>

Note that you can use <toradians> for this, so you don't need to write down the conversion factor ;-)
Code: Select all
<fcs_function name="fcs/rudder-pos-rad">
   <function>
      <toradians><p>fcs/rudder-sum</p></toradians>
   </function>
</fcs_function>
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Re: VC10 project under way - any interest?

Postby Octal450 » Tue Jan 12, 2021 2:14 pm

HI Alan,
Sort-of, you can see my example here: https://github.com/Octal450/MD-11/blob/ ... 11-fcs.xml

Each surface has his own actuator and gain set-up, the actuator simulate the hydraulic. That way each surface is independent. When hydraulics fail and some surfaces are loss, the control authority responds realistically by default. My convention is negative = upwards for ail/elev and negative = left for rudder.

Kind Regards,
Josh
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Re: VC10 project under way - any interest?

Postby Alant » Tue Jan 12, 2021 4:17 pm

Josh
Thanks for the example. It is very comprehensive, and easy to follow.
At the moment the main effort is getting the machine flying., so I am keeping things simple for now.
We still have Flightgear´s 707 style hydraulics, electrics etc, so will not go into the detail at this stage, and will keep with just single aileron, rudder, elevator etc. channels until the aircraft systems are in place. I will put a basic controls interface (along the lines of the TSR2 one) into JSBSim.
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Re: VC10 project under way - any interest?

Postby Octal450 » Tue Jan 12, 2021 8:31 pm

HI Alan,
If you insist, but I always found it easier to get that done first, so I don't have to make changes to my aero later. :) But to each his own.

Be informed that the 707 hydraulics didn't do anything to the aileron/elevator/rudder. So you'll have to add that yourself.

Kind Regards,
Josh
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Re: VC10 project under way - any interest?

Postby zakalawe » Fri Jan 22, 2021 10:57 pm

Checking in - what state is the FDM expected to be in for manual flight? Is it sensible to try and fly it, or better to wait a while?
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Re: VC10 project under way - any interest?

Postby Alant » Sat Jan 23, 2021 12:06 am

Not as good as I hoped for.
The pitch trim is a long way from what I expected. The drag is too low. The handling does seem reasonable.
I have started using VSPAero( which I have used in the past) to see if I can get some more believable numbers.
First results should come in a few days. I will keep you posted.
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Re: VC10 project under way - any interest?

Postby zakalawe » Sat Jan 23, 2021 4:20 pm

I noticed the drag as well, but the thing that really got me was lack of aileron authority, which seemed to get worse at higher speeds: I'd attempt a moderate turn, which over-develops (eg to 60 degree bank, when I was aiming for 30 degree) , despite first centering and then reversing the controls input. This might just be my inexperience at handling the aircraft : maybe I'm exceeding the control authority.
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Re: VC10 project under way - any interest?

Postby Alant » Sat Jan 23, 2021 7:05 pm

Yes, I saw similar things. Yuk . I think what you were seeing was a spiral mode instability which built up to a level that the aileron could not control. Also the spoilers are not yet simulated. They add about 50% to the aileron roll power.

The present Datcom version (not pushed to git yet) also has a mildly divergent dutch roll. As with most swept wing airliners the VC10 has a full time yaw damper, which is not yet simulated. Without the yaw damper the pilot needs to be practiced in controlling dutch rolls with the rudder pedals. This is OK for a test pilot but not for the average airline piilot. The passengers would probably complain and/or be airsick also.

I spent most of my time last week making reset-in-air work without the engines cutting out. That done
I can now launch at any flight condition.

This bought up the pitch trim startup problem that I mentioned in the previous post as there is insufficient pitch trim authority at speeds over 250 kt, and the JSBSim trim algorithm gives up .

As Datcom does not allow me to simulate the effect of the 4 rear mounted engines in their nacelles this may be a contributary factor. These engines will act like a second horizontal tailplane, adding to the pitch stability.

The basic VSPAero VC10 setup is now complete, so I will soon have an alternate set of aero data to compare against. VSPAero also allows me to add the engine nacelles and the bullet fairing at the top of the T tail, but for now I will be comparing against my Datcom model.

Thanks for the comments. I will make a post when I make the next FDM update.

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Re: VC10 project under way - any interest?

Postby Octal450 » Sun Jan 24, 2021 4:44 am

Nice updates Alan, keep em coming! Will give her a try soon.

As Datcom does not allow me to simulate the effect of the 4 rear mounted engines in their nacelles this may be a contributary factor
What about, one wider engine? May not be perfect but could be ok for approximating.

Kind Regards,
Josh
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Re: VC10 project under way - any interest?

Postby S&J » Sun Jan 24, 2021 12:45 pm

mach of 5 to 100, are you sure ?

Code: Select all
      <function name="aero/moment/ground_effect">
         <description>Pitch Moment_due_ground_effect</description>
         <product>
            <property>aero/qbar-psf</property>
            <property>metrics/Sw-sqft</property>
            <property>metrics/cbarw-ft</property>
            <table name="aero/coefficient/CM_ground_effect">
               <independentVar lookup="row">aero/alpha-deg</independentVar>
               <independentVar lookup="column">velocities/mach</independentVar>
               <tableData>
                  5.0   10.0   20.0   30.0   40.0   50.0   100
                  -10   -0.0186   -0.0129   -0.0052   -0.0022   -0.0011   -0.0006   0.0000
                  -6   -0.0109   -0.0075   -0.0030   -0.0013   -0.0007   -0.0004   0.0000
                  -4   -0.0031   -0.0021   -0.0009   -0.0004   -0.0002   -0.0001   0.0000
                  -2   0.0029   0.0021   0.0009   0.0004   0.0002   0.0001   0.0000
                  0   0.0070   0.0051   0.0024   0.0010   0.0006   0.0003   0.0000
                  2   0.0097   0.0072   0.0035   0.0016   0.0008   0.0005   0.0000
                  4   0.0113   0.0083   0.0042   0.0019   0.0010   0.0005   0.0000
                  6   0.0120   0.0088   0.0046   0.0020   0.0010   0.0005   0.0000
                  8   0.0113   0.0084   0.0046   0.0020   0.0009   0.0005   0.0000
                  10   0.0089   0.0067   0.0037   0.0016   0.0006   0.0002   0.0000
                  12   0.0061   0.0046   0.0025   0.0010   0.0003   0.0001   0.0000
                  14   0.0034   0.0027   0.0015   0.0006   0.0002   0.0000   0.0000
                  16   0.0008   0.0009   0.0006   0.0002   0.0000   -0.0001   0.0000
               </tableData>
            </table>
         </product>
      </function>
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Re: VC10 project under way - any interest?

Postby S&J » Sun Jan 24, 2021 12:51 pm

I'd also be taking fuel from tanks 0, 1, 5 & 6 and you're not doing which will move your CoG in the Y axis.
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Re: VC10 project under way - any interest?

Postby Alant » Sun Jan 24, 2021 2:44 pm

Thanks. It should read height above ground. I blame Mr Cut and his accomplice Mr Paste.
I corrected this schoolboy error some time ago on my local workspace, but things are still not corect, so I did not push the changes to github.
I am setting the C of G to a representative one before any tests. I am using this chart as a check. Image
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