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Sukhoi 26M aerobatic

Questions and discussion about creating aircraft. Flight dynamics, 3d models, cockpits, systems, animation, textures.

Postby Flying toaster » Wed Dec 27, 2006 11:31 am

hvengel wrote:Tried this model today and found some problems. Installing the initial version from the first post at the top of this thread works but has overly sensitive brakes. I then followed the instructions in the 5th post to install the updated Su-26M.xml and Engines/Su-26M-prop files. At that point the aircraft will not taxi or move at all. Backing out those changes and only installing the updated propeller file works. Then adding the Su-26M.xml file causes the problem. So there appears to be something wrong with the updated Su-26M.xml file.

I am running FG 0.9.10. Does this model need a differenet version of FG (perhaps CVS)?


The Su-26 was made with the 0.9.10 release version (not the CVS one), and I tested it only on linux. Strange though that the aircraft will stay stuck. The main difference is that the gear has been relocated a few inches forward. How much throttle do you apply (the new propeller decreases greatly thrust at idle) ?

Once I can get to my PC I'll try a set everything up correctly

Thanks a lot for the feedback ;)

Enrique
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Postby hvengel » Sat Dec 30, 2006 12:15 am

I am running a Linux box. I tried applying full throttle and it will not taxi even at full power. It acts like the brakes are on or like the wheels are sunk into the ground. I don't think this problem is related to the gear being moved a few inches. I have been able to fly the older version with no problems other than it being a little tricky on landing because of the tendency to ground loop if you are not careful with the brakes.

One thing that I do a little different from most users is I start out with the plane on the taxi way rather than on the runway. Could this some how cause it to get stuck?

I start it at:

longitude -122.3590
latitude 37.6157
altitude 0
heading 120
airspeed 0

This will place you on the taxi way facing the opposite direction of a normal take off at KSFO. So you will need to taxi into take off position. I have to change the starting altitude for some planes since it appears that they are up in the air and will drop to the taxi way and crash if I set this to 10 feet which is the actual altitude of the taxi way at KSFO. This is the only aircraft I have tried that would not taxi from this starting position.
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Postby Flying toaster » Sat Jan 06, 2007 7:52 am

I have downloaded the version I put on my ISP server in order to see if I could replicate the behavior you describe ... And it just worked fine, even by relocating the aircraft using the coordinates you provide

That pretty much beats me since we seem to have the same set-up (linux box running 0.9.10).

The only hypothesis I can make at this point is that *maybe* you downloaded the updated 3D model (named very appropriately Su-26M.xml :( ) and put it in the root Su-26M directory (thus overwriting the FDM). But quite honestly I think that would rather crash the sim than achieving the behavior you are describing

To make sure that everybody installs it in the right order :
- first download the tarball and xvf it in the Aircraft directory of your flight gear install
- then the flight model to put it in the Aircraft/Su-26M directory
- Then the propeller model to put it in the Aircraft/Su-26M/Engines directory
- Then the 3D model config (Su-26.xml) to put it in the Aircraft/Su-26M/Models directory
- Then the 3D model config for the cockpit to put it in the Aircraft/Su-26M/Models directory
- Then the Set file and view files to be put in the Aircraft/Su-26M directory

And you should be all set ...

Hope it helps

Enrique
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Postby ajm » Wed Jan 17, 2007 3:09 pm

Hi Enrique, the Su-26 is looking better all the time... unfortunately though the latest JSBSim changes (now in FlightGear CVS) mean that the gear parameters might need adjusted.

It works perfectly here with FG CVS previous to the JSBSim merge but with later versions it bounces around violently on the runway (before the engine starts) until it crashes.

The good news is that with some tweaking I expect it will be even better than before - the Lightning suffered badly from gear jitter and since the JSBSim updates it doesn't any more.

Cheers,

AJ

PS, how much have you left to do before it goes into CVS? It looks very complete to me :-)
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Postby Flying toaster » Mon Jan 22, 2007 8:59 pm

Trying to compile the CVS version there with no luck :(
Apparently there is something broken with latest OSG

Still looking into it

I want to refine the FDM (moment coefficient), 2D panel, 3D external model and systems before declaring it fit for CVS...
You still can play with it but it is very much a development version not a release ;)
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Postby Flying toaster » Wed Jan 24, 2007 6:14 pm

Just compiled the latest CVS OSG and the latest CVS FG ... but it seems fairly broken on my linux rig.

Apparently FG seems to redefine somehow the APIENTRY macro used in OSG.
I hacked around this issue, but 3D render is completely weird (image looking like coded pay-TV) while 2D panels look just fine...

Anybody else experienced this ?

Enrique
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Postby ajm » Thu Jan 25, 2007 5:43 pm

Yes, apparently so; http://openscenegraph.net/pipermail/osg ... 73237.html

I just use Mathias' tarball; I'll probably move on to the next OSG release when that happens, rather than following yet another project.

Anyway, as you can read in that thread you could check out OSG CVS from a slightly older date and it should fix your problem for now.

Cheers,

AJ
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Postby Flying toaster » Fri Jan 26, 2007 6:34 am

Thanks a lot !

I compiled with the version of the 18th of January and it just runs fine, albeit with a few glitches but that is really normal for a CVS build.

One improvement that I really like is that the 2D panel instruments now get clipping which I sorely needed for this aircraft !

In order to fix a little the jitter issue, I reverted to the spring coefficients provided by Aeromatic (1830 for spring coeff, 366 for damping). Still some strong jitter when the aircraft is at rest, but somewhat less.

The "aircraft going stratospheric" issue is related to the adjustment of the spring coefficient of the ground contact for the wings tips. Since these are carbon fiber wings they will hardly flex when hitting the ground (more likely they will scrape hard, and break). I still have to sort this out.

The main problems I have with the OSG build is that some objects just won't load (OSG AC3D loader), some animations are broken (canopy, livery selection), and the transparent texture issue is even worse than it used to be in PLIB (the fuselage gets "erased" by the propeller).

This raises some questions regarding the aircraft being included in CVS.

As a user I would like to download the version of the aircraft that is compatible with the current release (especially if I downloaded the release in its binary form).

As a developer I would expect to download the most up to date model in order to take advantage of all the new features in the development branch. For this I would expect to go and download the latest CVS.

Sure enough the end user could upload the revision of the aircraft that was checked in at the time of the release, but I guess most end-users don't really want to learn the intricacies of version control...

Has this been looked into ?

Cheers

Enrique
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Postby tricky_trev » Tue Sep 11, 2007 7:47 pm

Hi Enrique!

Great model - it's really the type of plane I need!

Some questions:
1. Flies great, but perhaps the engine seems a little under-powered though? With the default, I can't do anything Jurgis Kairys does with his SU-31. www.jkairys.com

2. The model flies with a wierd aileron trim or torque from the engine. How can I trim the plane to fly dead straight?

3. Any chances for an SU-31?

Cheers! You've done well!!

Trev
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Postby Flying toaster » Wed Sep 12, 2007 6:01 am

Hi Trev

Regarding the engine, I still need to fix it. The prop/engine/drag combination is hard to fine tune, and I don't know on which parameter I should be playing.

Regarding the Yurgis Kayris routines, you have to consider that the Su-31 is somewhat lighter than the Su-26 (the fuselage was changed from a steel truss to a carbon fiber monocoque). Actually with the same engine, the Su-31 has a thrust to weight ratio of more than one in some conditions... This explains why it can almost sit indefinitely on its tail.

There is no aileron trim (nor pitch trim for that matter) in this aircraft. I read in an old article (1989) that the aircraft has the pecularity to have no central stick position. Wherever you put the stick it will stay there, and you actually have to bring it back to neutral position. This is something that you cannot duplicate in a computer joystick (unless you remove power from a force feedback stick).

So, since demonstration flights are short anyway ;) I thought I may leave it alone without trim (not nice for cross country flights though). If anybody comes up with an idea on how to implement something to mimic the real behaviour, I'll be more than happy to implement it.

The engine torque may be a little excessive, but I would still expect an aircraft weighing less than a ton with 400HP to be willing to spin around its propeller wildly (at least at low speed since at high speed this thing has tremendous aileron auhority). Not nice when you want to make a hammerhead or a clean loop.

Regarding the Su-31, I may give it some consideration but not before 1 year or so (other projects + RL catching up). I still need to release this as GPL, and right now I am in the finishing touches.
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Postby tricky_trev » Fri Sep 14, 2007 9:05 am

Thanks for your reply - it was very informative!

I'm actually using the SU26 as a "training simulator" for my new radio controlled SU-31 that is currently in contruction (it's a DELRO kit).

I'm using a gamepad which is set up just like the transmitter, and it is very dificult to make a clean loop as you said. And I fly a lot of F3A aerobatics so it's going to make some manouvres very dificult to handle on the simulator that normally would be fine in reality...

I've increased the HP to 2000 and played with the prop pitch a bit to give a better feeling in the air.

Now if I can trim the ailerons or torque so it flies straight, I'll be extremely happy. i'll let you know if I work something out.


By the way.... You say that the stick tends not to self centre. Could this be due to the "counterbalances" or whatever they are under the ailerons? What are these officially called, and what is their purpose?


Can't wait for the release! We'll have to have a party!!! :D

Greetings from Switzerland,
Trev.
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Postby moonman » Tue Oct 30, 2007 1:44 pm

Great model!! I'm really enjoying flying it and showing it off to friends as an example of what Flightgear is capable of!

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Re: Sukhoi 26M aerobatic

Postby julianjackson1 » Sun Jun 29, 2008 1:27 pm

Love the plane...it really shows off fg's capabilities in aerobatics
The propeller is just a big fan in front of the plane used to keep the pilot cool. When it stops, you can actually watch the pilot start sweating.
Callsign: AA-JVJ
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Re: Sukhoi 26M aerobatic

Postby lqiyun » Mon Mar 09, 2009 11:35 am

hi, erm, just curious, Is the plane out in CVS yet?

cheers,
qiyun
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Re: Sukhoi 26M aerobatic

Postby lqiyun » Tue Mar 10, 2009 2:56 pm

erm, i have a slight problem with the su26M (downloaded directly off the flightgear aircraft downloads site, using flightgear ver 1.9.1). It looks nice and everything but I can't get the engine to start up and there was no help file at all... Someone please help!!

Thanks,
qiyun
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