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Author Topic: JSBsim Ground handling  (Read 3446 times)

bomber

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JSBsim Ground handling
« on: June 10, 2015, 06:04:27 pm »

Can I ask while I'm in the land of the nod tonight, could someone have a look at the JSBsim planes within Outerra and see if they have the ability to steer... not using the rudder so be carefull it's not simply because you're at speed but steering using the wheels and ground contact...

I'm having an issue with the Cessna.....


Simon
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

Uriah

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Re: JSBsim Ground handling
« Reply #1 on: June 10, 2015, 10:41:05 pm »

A simple way to test this would be to edit FCS so there was no rudder control. I always assumed the FDM accounted for nose wheel steering, but that was an assumption and I could very well be wrong.

Code: [Select]
  <contact type="BOGEY" name="NOSE">
   <location unit="IN">
     <x>  -165.65 </x>
     <y>   9.00 </y>
     <z> 0.0 </z>
   </location>
   <static_friction>  0.80 </static_friction>
   <dynamic_friction> 0.50 </dynamic_friction>
   <rolling_friction> 0.02 </rolling_friction>
   <spring_coeff unit="LBS/FT">      12224.52 </spring_coeff>
   <damping_coeff unit="LBS/FT/SEC"> 5374.20 </damping_coeff>
   <max_steer unit="DEG"> 15.00 </max_steer>
   <brake_group>NONE</brake_group>
   <retractable>1</retractable>
  </contact>

I am too darn busy to look into it, but when I have some time I will if you are still having problems.

Regards,
Uriah
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bomber

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Re: JSBsim Ground handling
« Reply #2 on: June 11, 2015, 04:20:19 am »

No worries I'll check it out tonight after walking the dog.
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

bongodriver

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Re: JSBsim Ground handling
« Reply #3 on: June 11, 2015, 04:33:29 am »

I'm pretty sure they do use wheel steering, most of them still steer at such a low speed it could not possibly be rudder.
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Levi

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Re: JSBsim Ground handling
« Reply #4 on: June 11, 2015, 09:49:58 am »

Simon, the main problem with the steering on the Cessna is located within the Autopilot System.
The output for "ap/roll-command-selector-steering" is "fcs/steer-cmd-norm" which is forcing the property "fcs/steer-cmd-norm" to be set to 0, therefore it overrides any user input.

Now in "</ground_reactions>" you have -2 degrees as "max_steer". Negative is for taildragger aircraft, and positive is for tricycle aircraft.

With 30-40 degrees it should be fine I guess. However, you could use a </scheduled_gain> in </flight_control> as I did with the F-117, so at low speeds you can have more steering angle than at high speeds.

With this, you will have great maneuverability when taxing at low speeds, and high precision when taking off at higher speeds.
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