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Re: JSBSim Piper J-3 Cub

Postby Bomber » Tue Aug 08, 2017 8:34 pm

Ok cheers I have the most up to date then
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Tue Aug 08, 2017 11:53 pm

OK, general observations.

I wouldn't know which is more realistic.

"USA-35B" exhibits less tolerance for getting out of the flight envelope and thus my guess would be that might be more realistic.
"DU Y" is a bit more forgiving. Stall appears to be softer.

-1.2004/-1.2710
VS
-1.8/-1.9058

I broke the landing gear more than once with the "-1.8/-1.9058" numbers. It allows for a more aggressive stall or at least the ability to cause the same.
I would like to know where the -1.2004 comes from. I assume the -1.8 is taken from multiple current FG aircraft implementations?

Flaps generally speaking appeared to extend the envelope as you would expect, the pitch down made it more difficult to get close to a 3 point.

After more flying time I am not noticing the tightness of the aircraft near as much.

I took all these configurations to the water with floats, I am "ecstatic" with the way the hydro is working. It is really fun now to hit the small lakes around the globe.

Bush landings have improve drastically from the elevator range changes from earlier. I think that was a necessary and important modification.

I am not skilled in watching the indicators and assessing the differences so I really can't comment to that.

Over-all, the more I put this FDM through its paces, the more happy I become with it.

Regardless of which table we use USA-35B or DU Y, I think we should include them both in the FDM (with one commented out) so anyone can choose their preference.

I pushed a commented out USA-35B table and changed the ASI to display MPH VS KTS.
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Re: JSBSim Piper J-3 Cub

Postby Octal450 » Wed Aug 09, 2017 2:46 am

Is the Begin Preloading Mesh a MUST? It makes it take over 5 mins to load sometimes....... I removed that part in Nasal, and he works fine.... very annoying.

I pushed a commented out USA-35B table and changed the ASI to display MPH VS KTS.

That was my bad.... sry

The last autopilot update is now available stable V1.0.0m (pls sync git from svn)

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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Wed Aug 09, 2017 3:07 am

That was my bad.... sry

Josh, you shouldn't have admitted it, I really thought i had done that. But now that you mention it, I do remember when you did it :lol: . All in all though, it made it really easy to convert it to MPH because you already identified the tick-marks.

How about I add a GUI switch to give the user a choice to shut off the pre-load?

Personally I would rather wait at loading and not have any delay when switching views, liveries or a damage event occurs. But there is also a case for not having to wait on pre-load for a particular short flight where your not changing views, liveries or pushing the aircraft to a point of damage.

pls sync git from svn

Done!
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Re: JSBSim Piper J-3 Cub

Postby Octal450 » Wed Aug 09, 2017 3:14 am

@wlbragg
Well -- I helped and I hurt -- so I guess my score is still 0 :P

I don't see the point, as it doesn't save the settings. (See my AIRCRAFT CONFIG V1.4.4 system in A320, he saves the settings changed in the GUI dialog)

True.

Thx, doing some testing now,
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Wed Aug 09, 2017 4:00 am

I don't see the point, as it doesn't save the settings.

I'm not sure what your saying, this is persistent
If you check the box to pre-load resources, then from that point forward it will pre-load. Same if you uncheck it, it will no longer do the pre-load when you start up.
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Re: JSBSim Piper J-3 Cub

Postby Octal450 » Wed Aug 09, 2017 4:27 am

OK nice
but every time I start FGFS to J3Cub, I uncheck Allow damage. He reset on everytime I close FG. This is not the case with my system.

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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Wed Aug 09, 2017 4:45 am

every time I start FGFS to J3Cub, I uncheck Allow damage. He reset on everytime I close FG.

OK, probably a bug, I'll check it out.
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Wed Aug 09, 2017 5:00 am

Hm, it's working correctly on my system.

You probably already know this but you have to exit the sim with the "Exit" button to save the persistent settings?

If that's the case, and you are executing a proper exit, then there is something else going on. I know in the past I have had some very strange issues with a bad or corrupt aircraft-data cache file. I had to delete it and get a fresh one started before it straightened out certain issues. I think those types of issues tend to crop up more when your in heavy development by more than one person and maybe state data is being modified by one or more people. That is when I seemed to have the most trouble and it is usually something that is happening only on my end.
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Wed Aug 09, 2017 6:05 am

Bathtub landing and takeoff of the SuperCub. :D

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Re: JSBSim Piper J-3 Cub

Postby GinGin » Wed Aug 09, 2017 6:35 am

Nice, the freedom of landing and going everywhere :)
I like the sounds of water, quite realistic.
What do you use for recording and processing videos?
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Wed Aug 09, 2017 6:41 am

Same as above but a bit steeper approach.



I use OBS Studio to capture the window. No post processing, just upload to YouTube.
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Re: JSBSim Piper J-3 Cub

Postby dany93 » Wed Aug 09, 2017 10:43 am

wlbragg wrote in Tue Aug 08, 2017 11:53 pm:"USA-35B" exhibits less tolerance for getting out of the flight envelope and thus my guess would be that might be more realistic.

I agree, all the more that USA-35B are known as being the J3Cub wings.
I don't believe that the Du-Y lift curve (as it is) can be realistic. The stall angle and max CL are far from reachable, unless we accept the elevator tightness (-1.8 ).

Still I'm perplex when watching the attitude at high speed with USA-35B lift curve. Nose down, orientation/pitch-deg = -6.4 deg at 100 kt horizontal. Due to high CL for alpha around zero. Is it to get a low pitch-deg at the best-glide airspeed?

....with the "-1.8/-1.9058" numbers. It allows for a more aggressive stall or at least the ability to cause the same.

Both. The elevator is more brutal, making it more difficult to accurately control the pitch angle, and you reach the max-lift (CL-Max) angle, after which the lift starts to decrease. This is a true stall.

I would like to know where the -1.2004 comes from. I assume the -1.8 is taken from multiple current FG aircraft implementations?

Not really. That was my guess by trial and possibly error (shame :oops: ) or rather an estimated adjustment, although not blindly.
I see -1.12 (C172P), -1.16 (Seneca II), -1.8 (DR400), -2 (Tecnam P92 echo). I'm wondering if the C172P would not have the same problem (Cmalpha = -1.8 while it is at -0.65 for Cessna 182 in Megginson's table).

1- I changed the amplitude of elevator deflection angle (which was too weak at -8 deg Up) for -0.51 to +0.34 rd (-29.2 to +19.5 deg). Notice that these limits should be different for the J3Cub -34 to +29 deg) and the PA18 (-25 to +15 deg).
These values are based on the configuration books. J3Cub, PA18

2 - As it was not enough, I raised the initial -1.2 up to -1.8 in order to reach the USA 35B stall AoA and to be able to do a 3-point touchdown.
But this gives an elevator tightness. I still think that, if we admit the the stall angle should be reached and a 3-point touchdown can be done, this high elevator value is due to the high Cmalpha (pitch moment due to alpha, Cmalpha = -1.8 after Du Y at low speed, high alpha, to be compared with -0.61 to -0.65 from Megginson's tables for Cessna 182).
Otherwise, if we take Du-Y thesis values as granted (but what about its lift curve ?), I currently don't see what to do here.
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Re: JSBSim Piper J-3 Cub

Postby Bomber » Wed Aug 09, 2017 4:26 pm

What incidence are the wing root and tip at ?
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Re: JSBSim Piper J-3 Cub

Postby dany93 » Wed Aug 09, 2017 4:48 pm

In the FDM, I see
Code: Select all
<wing_incidence>  0.0349 </wing_incidence>

which makes 2deg.

Maybe some responses here? (I see 2 deg among others).
I also see
They should have 1 degree (3/8") of twist (washout)


But I was just looking for this.

I also find "Wing incidence (Root) 2 deg" in the J3C-65 Owner's manual.
Last edited by dany93 on Thu Aug 10, 2017 1:47 pm, edited 1 time in total.
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