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DHC-6 Twin Otter development

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Re: DHC-6 Twin Otter development

Postby wlbragg » Sat Nov 18, 2017 8:11 pm

@Jonathan, I installed the DHC-6 through the aircraft center in the qtlauncher a few days ago. I show three variants (wheel, float and ski). It doesn't say YASim or JSBSim. It is not giving me any prompt to update. Do you know what I should be seeing, a YASim and JSBSim variant, each with the three undercarriage choices or is it now only suppose to show the JSBSIm version?

Edit:
I noticed you it was committed 5 hours ago, maybe it takes awhile to show up in the launcher?
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Re: DHC-6 Twin Otter development

Postby dg-505 » Sat Nov 18, 2017 10:28 pm

Hi Anders, you're correct ;)
Actually the problem with the beta range and thrust reverse was the reason why I stopped working on this update for more than half a year.
Someday I will give it another try....


Hi Wayne
AFAIK if you use the official aircraft hanger in the launcher, it recieves it's data from http://mirrors.ibiblio.org/flightgear/ftp/Aircraft/.
I don't know how often this gets updated, but I expect it to be there in a few days.
However, the update is already in the SVN repository at sourceforge.
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Re: DHC-6 Twin Otter development

Postby tonghuix » Sun Nov 19, 2017 9:13 am

why the dhc-6 in JSBsim always stall alarmed, and falling stall at less than 80kt with or without flap same result, with flap (9 deg) the stall speed could extended to 85kt.
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Re: DHC-6 Twin Otter development

Postby dg-505 » Sun Nov 19, 2017 11:25 am

Well, as I said before, the aerodynamics are taken from a public source (see here).

In terms of aerodynamics i hasn't been modified, so if you have any ideas how to make the flight behaviour more realistic (and how to translate it to JSBSim code), I'm open to every idea ;)
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Re: DHC-6 Twin Otter development

Postby mifi » Sun Nov 19, 2017 11:33 am

I have a new observation, but first I want to thank you for your efforts on making this aircraft better.

I tried several times to get the JSB version of the aircraft off the ground with a 80 degree crosswind of 16 knots. I couldn't. As soon as I opened the throttle and the aircraft gained a little speed, it would turn into the wind beyond correction. I tried the steering wheel and the rudder and asymmetric thrust, but the turn into the wind was uncontrollable. So I reverted to the version with the old FDM and that flew as expected in the same conditions.

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Re: DHC-6 Twin Otter development

Postby dg-505 » Mon Nov 20, 2017 5:49 pm

The reason for this is most likely that the FDM is almost not tweaked.

To all Twin Otter pilots and JSBSim geniuses: Please help to improve the flight dynamics by making reviews, or (even better) tweak the FDM configuration files! I'll also try my very best...

Thanks
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Re: DHC-6 Twin Otter development

Postby mifi » Tue Nov 21, 2017 8:10 am

dg-505 wrote in Mon Nov 20, 2017 5:49 pm:The reason for this is most likely that the FDM is almost not tweaked.


It probably is, yes. That's why I reported it. I do not have the knowledge to help with the FDM, but I can help testing.

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Re: DHC-6 Twin Otter development

Postby erik » Tue Nov 21, 2017 10:34 am

Setting minpitch in HARTZELL-T10282H.xml to 0 (zero) should fix the thrust reverse.

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Re: DHC-6 Twin Otter development

Postby dg-505 » Tue Nov 21, 2017 6:16 pm

Okay, but this could lead to a problem:
When the propeller is in constant speed range, the Constant Speed Unit sets the propeller pitch between 11° and 87°. 87° pitch is also Feather.
With power levers at idle, prop pitch is always 11°.
When activating reverse thrust, prop pitch changes from 11° to 0° (that's called Idle Null).
And reverse range is betwenn 0° and minus 15°. There the prop pitch is controlled directly via the power lever while the fuel flow to the engine gets limited so that the propeller doesn't exceed 2000 RPM.

Any idea how to translate this to JSBSim (or Nasal code)?
(I tried something like this in Nasal/thrust-reverse.nas and Systems/Engine.xml, but nothing worked...)


The above described is a bit simplified. Here's a graphic that describes the Constant Speed Range and the Beta Range:
Image
Image
Pictures by Pierre V. Dehaye, http://www.cram.com/flashcards/twin-otter-dhc6-300-1980260

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Re: DHC-6 Twin Otter development

Postby AndersG » Tue Nov 21, 2017 6:52 pm

dg-505 wrote in Tue Nov 21, 2017 6:16 pm:Any idea how to translate this to JSBSim (or Nasal code)?
(I tried something like this in Nasal/thrust-reverse.nas and Systems/Engine.xml, but nothing worked...)


You can set the propeller blade angle directly using the JSBSim properties propulsion/engine[n]/blade-angle.
See for example the ZLT-NT (Systems/engine-control-jsbsim.xml).

However, off the top of my head I don't know how it would interact with the built-in JSBSim constant-speed mechanism - ZLT-NT doesn't have any (AFAIK). At worst you'd need to make your own constant-speed controller that you can switch off when moving into the beta-range. I guess a single PID would do and would probably not be too difficult to tune.
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Re: DHC-6 Twin Otter development

Postby erik » Wed Nov 22, 2017 7:41 am

Turns out I was wrong: minpitch could be set to 11
It looks like the extra500 in FGAddon has a working thrust reverse implemented which sets /controls/engines/engine[0]/reverser to true to make reverse active.

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Re: DHC-6 Twin Otter development

Postby scarymovie » Sat Nov 25, 2017 4:42 am

Hi,

I realized that the landing lights and taxi light do not work/visible. Am I doing anything wrong?

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Re: DHC-6 Twin Otter development

Postby dg-505 » Sat Nov 25, 2017 12:34 pm

Thanks for the report.

I'll check that out at the next opportunity.
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Re: DHC-6 Twin Otter development

Postby bschack » Tue Dec 05, 2017 5:15 am

First of all, many thanks for a great airplane. I'm looking forward to the JSBSim model.

I have 2 quick suggestions to improve the avionics side of the Twin Otter:

  1. Marker beacons - These make flying ILS approaches much easier, because they give audio (and visual) indications of your progress along the glideslope.
  2. Audio control panel - When listening to ATIS or the morse ident of a navaid, it's nice to be able to just cut off the audio with a button. Right now I have to turn the volume down to zero, which takes more time and effort.

I did a quick look through the standard instruments, and I think the KMA20 panel will perform both functions. However, I've never developed an aircraft, so I offer no guarantees on how well it will integrate with the Twin Otter, nor on its completeness/functionality.

Thanks,
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Re: DHC-6 Twin Otter development

Postby dg-505 » Tue Dec 05, 2017 5:21 am

Hello Brian,

thank you for your ideas.

I also had the idea to integrate an audio panel to this aircraft, but didn't find time yet.

Currently I can't continue because due to an error FlightGeae doesn't start, but I keep that in mind.

Cheers
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