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North American T6 Texan

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Re: North American T6 Texan

Postby xen_steda » Thu Mar 12, 2020 3:15 pm

Hi,

The T-6 Texan in the FGAddon Hangar has just been updated (3/12/20), including updates to the cockpit and FDM.

Concerning the FDM, When I entered a spin, some power came back on, even though throttle was all the way down to zero. This brought up more experiments and when at no throttle, the plane still can get power and increase RPMs for quite a while. I also noticed the just releasing the rudder back to a neutral position takes the plane out of the spin, which is not how it is supposed to be, opposite rudder to get out of a spin correct?

Could anyone take a look at this plane and see what might be going on "under the cowling"? I would really like to get this plane just right. Thanks.
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Re: North American T6 Texan

Postby D-ECHO » Thu Mar 12, 2020 3:21 pm

Nice work!

About the FDM:
*the aircraft is using YASim, which makes it impossible to correctly simulate stalls and spins (for the moment)
*The engine seems to be working correct as far as I can judge, what do you mean by "some power came back on", i.e. how did you measure the power? or was it just that the RPM increased?
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Re: North American T6 Texan

Postby xen_steda » Thu Mar 12, 2020 3:42 pm

D-ECHO wrote in Thu Mar 12, 2020 3:21 pm:how did you measure the power? or was it just that the RPM increased?


It's like the RPMs that increase. The propeller is a constant speed one, not sure if that has anything to do with it. It might just be the way the audio behaves for this plane that throws me off.
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Re: North American T6 Texan

Postby D-ECHO » Thu Mar 12, 2020 4:11 pm

As the spin is not correctly simulated, the aircraft gains speed during it, which I think logically leads to an increase in RPM, without an increase in engine power, so I think this is correct as is currently.
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Re: North American T6 Texan

Postby DFaber » Fri Mar 13, 2020 7:34 am

Just a quick note at a first glance at the FDM:
The Engine Setup is flawed. The R1340 has a reduction gear. The Prop doesn't turn at 2200 RPM. It should have a ratio of 0.666 (it is mentioned in the Wikipedia Article linked, though).

It stalls very hard, sometimes not at all, which is common to a quick and dirty FDM. Aileron control is too responsive. The Wing (and elevator) needs a re-write.

I'll write up some suggestions over the weekend.

Greetings
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Re: North American T6 Texan

Postby xen_steda » Fri Mar 13, 2020 10:26 am

DFaber wrote in Fri Mar 13, 2020 7:34 am:Just a quick note at a first glance at the FDM:
The Engine Setup is flawed. The R1340 has a reduction gear. The Prop doesn't turn at 2200 RPM. It should have a ratio of 0.666 (it is mentioned in the Wikipedia Article linked, though).


Hi there, and thanks for offering to take a look at this FDM. I have some good source material, better than the wiki, I think anyway. You are welcome to use them as you go over the numbers too:

EDIT: If anyone thinks they can put together a JSBSim FDM with any of these resources, please feel free to try! :mrgreen:

Full POH for the T-6/SNJ - Pages 16-19 (page numbers 6B-9 on the manual) has a "Principle Dimensions" Section with lots of good information, lots more other pages too.

Shorter Flight Manual for the T-6G Has less detailed information but worth looking through. This is the graphic that I got the 2200 RPM data from:
Image

Concerning the stall behavior, I had a really hard time playing with the figures of that, I have these (which can be found in the manuals. Perhaps this information will help:

Image

Image

And I did run the YASim geometry model through this script in Blender:

Blender YASim Import

This a pretty cool way to look at a visualization of the YASim data. The T6 looks pretty good I thought, but I am clearly not an expert. Thanks for looking to help!
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Re: North American T6 Texan

Postby DFaber » Sun Mar 15, 2020 3:00 pm

DFaber wrote in Fri Mar 13, 2020 7:34 am:J
I'll write up some suggestions over the weekend.


I'll correct myself: Since you don't seem to be interested in a Yasim FDM anymore, I'm not going to spend my spare time making one.

Good Luck
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Re: North American T6 Texan

Postby xen_steda » Sun Mar 15, 2020 3:07 pm

In fact I have been working on both versions and am still working on the YASim version with @dilbert who has experience flying this plane in real life. I always multi task, the JSBSim version is more of an experiment to be honest. Sorry about the possible frustration I caused you.
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Re: North American T6 Texan

Postby helijah » Wed Apr 08, 2020 6:39 pm

It's one of the last times I come on this site where it's possible to read everything but mostly nonsense and misinformation based on "I have read"... "I think"... "I was told that..." In short without interest.

For xen_steda the easiest way is not to come here and ask how to do certain things. Just look in my readme.txt files, my email address is present. A simple look and you can contact me directly. And contrary to the false information spread here I always answer and do what it takes to improve my 300 models.
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Re: North American T6 Texan

Postby stuart » Thu Apr 09, 2020 8:02 am

Hi Folks,

I've removed a couple of posts with an JSBSim vs. YASim argument, as they were detracting from the topic, which is the improvements that xen_steda wishes to make to the T-6 Texan.

Please can we concentrate on that here and accept that different people have different FDM preferences. Vive la difference.

@xen_steda - back on topic. You asked above about the sounds. Unfortunately those particular sounds cannot be used on the GPL aircraft such as the T-6, because the particular variant of the CC license is non-commercial only, which the GPL allows. I also suspect you might struggle to extract the sounds successfully. Have you had a look at the sounds in FlightGear itself? Also, I have wondered for some time if it would be possible to simulate an engine sounds from first principles - we know the RPM, number of cylinders etc. so perhaps it might be possible to create a simulation using that information?

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Re: North American T6 Texan

Postby helijah » Thu Apr 09, 2020 10:47 am

Indeed Stuart, but you have to admit that it is tiring when you spend a lot of time making models for FG. Fortunately a lot of real pilots write me and thank me.

I just updated the T6, some adjustments on the FDM and some cosmetic additions inside.

As far as the sound is concerned, I can't promise anything, but there is a T6 here in Chartres that regularly flies over our heads. Maybe, after the confinement, I could go see the pilot and ask him if it is possible to record his superb plane to have original and realistic sounds. I don't promise anything but I will do my best.
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Re: North American T6 Texan

Postby Alant » Thu Apr 09, 2020 2:43 pm

The standard T6 has a direct drive propeller, making the prop tips supersonic. This is the cause of the T6´s unmistakable rasping sound. I remember it well from my childhood, as T6 Harvards regularly came in and out of my local airfield (Southend) , which was less than 1Km away from our house.
One version, the R1340 , had a geared down prop, so it sounds more like a conventional aircraft.
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Re: North American T6 Texan

Postby helijah » Thu Apr 09, 2020 4:25 pm

Absolutely and this is the version with the R1340 that I modeled :) As well as the R1340 wing :)

Image
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Re: North American T6 Texan

Postby Michat » Fri Apr 10, 2020 12:13 am

stuart wrote in Thu Apr 09, 2020 8:02 am: Also, I have wondered for some time if it would be possible to simulate an engine sounds from first principles - we know the RPM, number of cylinders etc. so perhaps it might be possible to create a simulation using that information?

-Stuart


Just as yasim provides a solution for thousands of aircraft for which there is no airflow data, it does not seem like a bad idea to simulate the sounds of an engine from the first principles capable of providing an approximate solution for so many models for which we do not have records.

The other method I can think of involves samples. Since there is a GPL program capable of discriminating four voices and separating them obtaining the musical notes of each one in the timeline. Each note vibrates at certain frequencies. If we have engine sound registers even without great quality these can be recreated in the synthesis. If the motors really have rhythm when looping the loop.


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Re: North American T6 Texan

Postby stuart » Fri Apr 10, 2020 8:57 am

BTW, I had a look in the fgdata/Sounds directory, and noticed that we have a "wasp.wav" file, which I think is the sound from an R1340 Wasp radial engine, so would be appropriate here.

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