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Using multiple Aerotow hitches, YASIM?

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Using multiple Aerotow hitches, YASIM?

Postby StuartC » Mon Jan 22, 2018 3:58 pm

I am trying to utilise the aerotow system for use as a 4 point lifting harness, so far without luck as I can only get one hitch to be recognised.

I have defined the 4 points in the FDM and tried to define them in the set file using like <aerotow n="1"> etc defined in the <hitches> tags. Its not working.
Any ideas how this can be done?
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Re: Using multiple Aerotow hitches, YASIM?

Postby wlbragg » Mon Jan 22, 2018 5:47 pm

I am trying to utilise the aerotow system for use as a 4 point lifting harness

I never thought about using aerotow in that manner, as in applying it to a helicopter and lifting straight up, does that work? I really wish I had thought about that possibility a long time ago. That could be a game changer with some of my projects.

I looked at that code extensively at one time but couldn't say. It's probably not setup to loop through and recognize multiple connections. However, it might not be that hard to make it do that.
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Re: Using multiple Aerotow hitches, YASIM?

Postby StuartC » Mon Jan 22, 2018 6:21 pm

I can lift another chopper with it over Multiplayer as it is, but its a somewhat unsettling trip for the person being lifted as its lifting from a single point, there is nothing to maintain the attitude of the chopper/aircraft/vehicle being lifted and it tends to swing quite violently around the single central hook point.
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Re: Using multiple Aerotow hitches, YASIM?

Postby paju1986 » Mon Jan 22, 2018 7:10 pm

Are you using it for lifting stuff with the ch-47? that will be super cool :)

Regards!
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Re: Using multiple Aerotow hitches, YASIM?

Postby StuartC » Mon Jan 22, 2018 8:10 pm

Yes I am, or trying to.
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Re: Using multiple Aerotow hitches, YASIM?

Postby StuartC » Tue Jan 23, 2018 2:33 pm

Specifying 4 hitches in the FDM + the following code in the set file does produce 4 hitches in the property tree.

<hitches>
<aerotow>
<tow>
<length type="float">30</length>
<elastic-constant type="float">100</elastic-constant>
<weight-per-m-kg-m type="float">0.035</weight-per-m-kg-m>
<dist type="float">1</dist>
<connected-to-property-node type="bool"></connected-to-property-node>
<brake-force type="float">900000</brake-force>
<connected-to-ai-or-mp-callsign type ="string">*</connected-to-ai-or-mp-callsign>
<end-force-x type ="float">0</end-force-x>
<end-force-y type ="float">0</end-force-y>
<end-force-z type ="float">0</end-force-z>
</tow>
<speed-in-tow-direction type="float">0</speed-in-tow-direction>
<open type="bool">true</open>
<local-pos-x type="float">3.0</local-pos-x>
<local-pos-y type="float">1.0</local-pos-y>
<local-pos-z type="float">-1.0</local-pos-z>
<is-slave type="bool">false</is-slave>
<rope>
<rope-diameter-mm type="float">50</rope-diameter-mm>
</rope>
</aerotow>

<aerotow n="1">
<tow>
<length type="float">30</length>
<elastic-constant type="float">100</elastic-constant>
<weight-per-m-kg-m type="float">0.035</weight-per-m-kg-m>
<dist type="float">1</dist>
<connected-to-property-node type="bool"></connected-to-property-node>
<brake-force type="float">900000</brake-force>
<connected-to-ai-or-mp-callsign type ="string">*</connected-to-ai-or-mp-callsign>
<end-force-x type ="float">0</end-force-x>
<end-force-y type ="float">0</end-force-y>
<end-force-z type ="float">0</end-force-z>
</tow>
<speed-in-tow-direction type="float">0</speed-in-tow-direction>
<open type="bool">true</open>
<local-pos-x type="float">3.0</local-pos-x>
<local-pos-y type="float">-1.0</local-pos-y>
<local-pos-z type="float">-1.0</local-pos-z>
<is-slave type="bool">false</is-slave>
<rope>
<rope-diameter-mm type="float">50</rope-diameter-mm>
</rope>
</aerotow>

<aerotow n="2">
<tow>
<length type="float">30</length>
<elastic-constant type="float">100</elastic-constant>
<weight-per-m-kg-m type="float">0.035</weight-per-m-kg-m>
<dist type="float">1</dist>
<connected-to-property-node type="bool"></connected-to-property-node>
<brake-force type="float">900000</brake-force>
<connected-to-ai-or-mp-callsign type ="string">*</connected-to-ai-or-mp-callsign>
<end-force-x type ="float">0</end-force-x>
<end-force-y type ="float">0</end-force-y>
<end-force-z type ="float">0</end-force-z>
</tow>
<speed-in-tow-direction type="float">0</speed-in-tow-direction>
<open type="bool">true</open>
<local-pos-x type="float">-3.0</local-pos-x>
<local-pos-y type="float">1.0</local-pos-y>
<local-pos-z type="float">-1.0</local-pos-z>
<is-slave type="bool">false</is-slave>
<rope>
<rope-diameter-mm type="float">50</rope-diameter-mm>
</rope>
</aerotow>

<aerotow n="3">
<tow>
<length type="float">30</length>
<elastic-constant type="float">100</elastic-constant>
<weight-per-m-kg-m type="float">0.035</weight-per-m-kg-m>
<dist type="float">1</dist>
<connected-to-property-node type="bool"></connected-to-property-node>
<brake-force type="float">900000</brake-force>
<connected-to-ai-or-mp-callsign type ="string">*</connected-to-ai-or-mp-callsign>
<end-force-x type ="float">0</end-force-x>
<end-force-y type ="float">0</end-force-y>
<end-force-z type ="float">0</end-force-z>
</tow>
<speed-in-tow-direction type="float">0</speed-in-tow-direction>
<open type="bool">true</open>
<local-pos-x type="float">-3.0</local-pos-x>
<local-pos-y type="float">-1.0</local-pos-y>
<local-pos-z type="float">-1.0</local-pos-z>
<is-slave type="bool">false</is-slave>
<rope>
<rope-diameter-mm type="float">50</rope-diameter-mm>
</rope>
</aerotow>

</hitches>


The problem is you only get one rope and it only connects to the first hitch. So the problem is not the lack of hitches, its the lack of rope.
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Re: Using multiple Aerotow hitches, YASIM?

Postby Thorsten » Tue Jan 23, 2018 5:58 pm

I'd be surprised if that is implemented in a way you need it, because it's a pretty nasty problem in terms of how attitude of the towed object is enforced by the ropes as well as the towed objects' own airfoils (ropes being particularly nasty as a subset might go slack momentarily, lifting and re-establishing constraints later).

All in all, that's a tough problem even with the whole JSBSim toolkit available (I've soft of done the easier one with three hard connections, i.e. without the slackness issue).
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Re: Using multiple Aerotow hitches, YASIM?

Postby StuartC » Tue Jan 23, 2018 6:09 pm

I did reduce the stretch and increased the breaking tension for testing, but I cant experiment more until I manage to got ropes attached to all 4 points.
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Re: Using multiple Aerotow hitches, YASIM?

Postby Thorsten » Tue Jan 23, 2018 6:29 pm

That's what I'm trying to tell you - the code probably is not set up to allow that, because the math to make that work as you need is really hard (much harder than for a standard aerotow situation). There's not many people coding in the FG project who would be able to pull this off.

It would be quite a bit more than the effects YaSim usually takes into account.
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