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JSBSim Piper J-3 Cub

Postby wlbragg » Fri Dec 18, 2015 8:18 am

I would really like to start converting the Piper J-3 Cub we have in fgaddon to include a JSBSim FDM version. Then I want to add several of the c172p features to it, floats, skies, bush kit, effects, etc. I need a pro to help with the FDM and I will do the rest.
I was wondering/hoping we could use the c172p FDM (including two engine option, if indeed that is a RL practice to upgrade the engine) and just change what was needed to fit the Cub's profile. If that is possible it would save a ton of work and leave it in a state where the rest of the build would be relatively simple.

Any takers?

Repository https://sourceforge.net/p/flightgear/fgaddon/HEAD/tree/trunk/Aircraft/J3Cub/
Last edited by wlbragg on Tue Apr 12, 2016 1:22 am, edited 3 times in total.
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Re: JSBSim Piper J-3 Cub

Postby Thorsten » Fri Dec 18, 2015 10:57 am

See if you can find aero and windtunnel data, also as much performance data as you possibly can. If you manage, it's straightforward to implement the windtunnel data for an FDM. it requires a bit more to tune what you don't know to the performance data, but it's not rocket science.

If you don't have data, don't do JSBSim, the result will be worse than YaSim.
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Re: JSBSim Piper J-3 Cub

Postby erik » Fri Dec 18, 2015 12:05 pm

It depends, AeromatiC++ uses the same principles as YASim does. The only drawback is that it does not account for fuselage effects like drag and side force. I've actually though about adding the option to read YASim configuration in AeromatiC++ because of this.

I've put all the proper J3 Cub data in AeromatiC++ and came very close to some wind-tunnel data I found.
I'll put this config online somewhere today.

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Re: JSBSim Piper J-3 Cub

Postby Thorsten » Fri Dec 18, 2015 12:40 pm

I'll trust your superior expertise with that one, Erik.

(Still - it'd be good to get as much aero data as possible to get most from JSBSim...)
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Re: JSBSim Piper J-3 Cub

Postby erik » Fri Dec 18, 2015 12:45 pm

True, Aeromatic2 is a nice start for a configuration.
AeromatiC++ creates a decent aircraft approximation.
But nothing beats wind-tunnel data.

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Re: JSBSim Piper J-3 Cub

Postby erik » Fri Dec 18, 2015 1:06 pm

Here's the J3 Cub FDM for JSBSim (it does not include anything else):
http://www.adalin.com/ehtw.info/J3Cub-jsbsim.zip

As stated, it was created using AeromatiC++ but it was improved using actual wind-tunnel data.

It probably still needs refinements for (gear) locations and the like.
Treat this as a decent start: It does not include any other fancy effects like floats.

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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Fri Dec 18, 2015 4:56 pm

That's great, thank you, it's a good starting point.
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Sat Dec 19, 2015 8:22 pm

OK, we have a flyable start to this project (see first post). The gear is still mucked up but with a little luck and trickery you can get this in the air to feel the FDM.

For now I just added the FDM to my Bush version of the Cub.
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Re: JSBSim Piper J-3 Cub

Postby gsagostinho » Sat Dec 19, 2015 11:58 pm

If you need any help with something I am capable of, let me know ;)
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Re: JSBSim Piper J-3 Cub

Postby erik » Mon Dec 21, 2015 3:08 pm

Here's a nice update for the FDM:
http://adalin.com/ehtw.info/j3cub-jsbsim.diff

    Updated maximum deflection angles for rudder, elevator and aileron
    Changed a number of coefficients to account for Reynolds number
    Updated Lift en Drag due to alpha
    Make tail wheel steerable
    Removed Mach effects
    Add stall behaviour

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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Tue Dec 22, 2015 5:48 am

gsagostinho wrote in Sat Dec 19, 2015 11:58 pm:If you need any help with something I am capable of, let me know ;)

Thank gsagostinho!

I decided to change the repo to a SourceForge project and start over using the original Cub from fgaddon (no bushkit yet). I still plan on making this aircraft similar in features as the c172p. Anyone interested in helping is more than welcome.

Eric's new patch has been applied.
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Re: JSBSim Piper J-3 Cub

Postby erik » Tue Dec 22, 2015 12:11 pm

The next version feels very good to me by taking into account
    Reynolds Number
    Thrust effect on Lift, Roll and Pitching moment
    Trust effects on Rudder and Elevator effectiveness
    Stall behaviour

It would be great if someone with real life experience in the Cub could take it for a spin when it is available.

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Re: JSBSim Piper J-3 Cub

Postby erik » Tue Dec 22, 2015 5:52 pm

This update is now pushed to the repository in the first message.

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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Tue Dec 22, 2015 8:02 pm

Thanks Eric, really nice, after the holidays I hope to produce some major activity on this project. :D
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Wed Dec 30, 2015 5:59 am

Eric, when you get a chance try the contact point changes and the commented out spring and damping coeff. The coeff are similar to the c172p. I was trying to get some stability but don't really know if it was more or less stable.
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