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How to make an Aircraft....

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

Re: How to make an Aircraft....

Postby stuart » Wed Sep 09, 2015 3:09 pm

Hi chs90,

Just to add to what IH-COL has mentioned, there are a number of different aircraft repositories, some under different licenses. FGMEMBERS is one.

FGAddon is the aircraft repository supported by the core flightgear development team, and contains GPL-compatible aircraft.

-Stuart
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Re: How to make an Aircraft....

Postby legoboyvdlp » Wed Sep 09, 2015 3:37 pm

Hi stuart, just to tell you, FGMEMBERS is fully GPL compatiable, and also includes, in a clearly marked folder, called 'Aircraft-nonGPL', other aircraft.
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Re: How to make an Aircraft....

Postby IAHM-COL » Wed Sep 09, 2015 3:56 pm

yes.
As Stuart and Lego added; most aircraft in FG are fully GPL compatible, but other licenses could be hosted in FGMEMBERS-NONGPL (if these allow copying and redistribution), typically Creative Commons Family: See here:

https://github.com/FGMEMBERS-NONGPL

Also,

stuart wrote in Wed Sep 09, 2015 3:09 pm:
there are a number of different aircraft repositories ... FGMEMBERS is one.



This is inaccurate. FGMEMBERS is not a repository. FGMEMBERS is an organization in github that host and develops aircrafts for FG, every repository corresponding to one aircraft. The organization contains approximately 600 aircraft, some other 80 non GPL, and even several scenery packages.
If we gave everybody in the World free software today, but we failed to teach them about the four freedoms, five years from now, would they still have it? Probably not, because if they don’t recognise their freedoms, they’ll let their freedoms fall
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Re: How to make an Aircraft....

Postby bugman » Wed Sep 09, 2015 4:02 pm

I think Stuart was just clarifying the difference between FGMEMBERS and the official FlightGear FGAddon aircraft collection, as a distinction between the two was not originally made (actually FGAddon was not mentioned). It might be useful for chs90 to know that if he develops in a private repository, that none of his work and creations will be available from the official download pages and in the future will most definitely not be supported by the core FlightGear developers if he leaves. Such important missing information about the official hangar vs. one of the many private hangars is likely to influence his judgement.

Regards,

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Re: How to make an Aircraft....

Postby Gijs » Wed Sep 09, 2015 4:57 pm

legoboyvdlp wrote in Wed Sep 09, 2015 3:37 pm: just to tell you, FGMEMBERS is fully GPL compatiable

Are you sure?
787-8/FMC-DB/EGKK.xml wrote:Data copyright (c) 2011 European Aeronautical Group.
This data my not be used, recompiled, interpreted or
distributed for any purpose without the written consent
of Navigraph.
Airports: EHAM, EHLE, KSFO
Aircraft: 747-400
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Re: How to make an Aircraft....

Postby legoboyvdlp » Wed Sep 09, 2015 7:29 pm

That is in from omega....
They break copyright BIG TIME.
Merlion actually released a navigraph pack with procedures for all airports. Nice but....
Copyright violation.
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Re: How to make an Aircraft....

Postby IAHM-COL » Wed Sep 09, 2015 7:53 pm

bugman wrote in Wed Sep 09, 2015 4:02 pm:I think Stuart was just clarifying the difference between FGMEMBERS and the official FlightGear FGAddon aircraft collection, as a distinction between the two was not originally made (actually FGAddon was not mentioned).


Yes. You / Stuart others can mention to cchs90 about how to contribute and why to contribute to FGADDon. It is not my place to invite anyone to contribute there. I really can't even begin to explain how that's done, or have any authority to do that myself.
I can, on the contrary give him full push permit to any FGMEMBER repo on the flip of my keyboard, so it is possible for me to invite him to do so.
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Re: How to make an Aircraft....

Postby GeoffDraper » Thu Mar 31, 2016 6:00 am

I'm fairly new to FG. This is just my second forum post.

I want to use FG to investigate flying a glider on a fixed length towline: one end at the glider, other end fixed to the ground. In other words, as a kite. One way I'm thinking of doing it is to use a glider which already has a winch-launch capability. E.g. the DG-101G.

However I'd need to modify the winch functionality so that it can slow down and stop, and not auto-release. And maybe also move the towline attachment point further aft.

Does this sound feasible?

I think I can do this by modifying an existing aircraft definition, but not modifying FG itself. Is this correct?

I don't think this functionality would be of value to other users of FG, so I wouldn't want to add it to the "official" glider definition.

Thanks - Geoff
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Re: How to make an Aircraft....

Postby Richard » Thu Mar 31, 2016 8:48 am

All you need to modify is the JSBSim model, no C++ changes. Within JSBSim there are external forces that can be attached to the flight model at any point. These external forces need to be modelled - but again that's all in the JSBSim XML files.

You can modify your copy of the model files as you wish.

From a quick look either the ASW20 or the DG101G look suitable. I can't be certain but the aero model on the ASW20 could be better as it seems to come from UIUC data.

Step 1 is to fly these two gliders and find the one that handles most like a glider.
Step 2 is to modify the model definitions

JSBSim is well documented, but if you need help then ask as there are lots of us who understand its nuances.
Last edited by Johan G on Fri Apr 01, 2016 10:02 am, edited 1 time in total.
Reason: No need to quote the entire preceding post
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Re: How to make an Aircraft....

Postby GeoffDraper » Thu Mar 31, 2016 11:57 am

Hi Richard,

Thank you for your response. Very encouraging!

I'll try both of the gliders you mention.

I've had a look at the download of the DG-101G aircraft definition. It seems to consist of XML code to define the property tree, and NAS code to change tree values dynamically. Also key definitions - "w" etc.

Broadly, I think I'll need to :
- remove the auto-release code, just two lines.
- add a new letter ("z"?) to tell the winch to gradually decelerate and stop.
- maybe shift the tow-hook location aft as the winch decelerates.

I think you're saying I can do all this in my own copy of the aircraft definition, and then just add it (with a new name) to my installed aircraft folder, then fly it. Have I got that right?

Thanks - Geoff
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Re: How to make an Aircraft....

Postby sanhozay » Thu Mar 31, 2016 12:41 pm

GeoffDraper wrote in Thu Mar 31, 2016 11:57 am:- add a new letter ("z"?) to tell the winch to gradually decelerate and stop.

Note that "z" is already used to change max visibility. A lot of single letters are already used, but ALT or CTRL combinations are possible. If you open up the property tree and look at "/input/keyboard", you'll see which are mapped for that model, and you'll be able to work out what number to use for a given key mapping.

(You can overwrite existing mappings if you aren't worried about the underlying action).

I think you're saying I can do all this in my own copy of the aircraft definition, and then just add it (with a new name) to my installed aircraft folder, then fly it.

A lot of aircraft use file and folder paths internally that depend on being installed into a given folder, so renaming is not trivial.
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Re: How to make an Aircraft....

Postby Richard » Thu Mar 31, 2016 12:48 pm

GeoffDraper wrote in Thu Mar 31, 2016 11:57 am:I've had a look at the download of the DG-101G aircraft definition. It seems to consist of XML code to define the property tree, and NAS code to change tree values dynamically. Also key definitions - "w" etc.

Broadly, I think I'll need to :
- remove the auto-release code, just two lines.
- add a new letter ("z"?) to tell the winch to gradually decelerate and stop.
- maybe shift the tow-hook location aft as the winch decelerates.

I think you're saying I can do all this in my own copy of the aircraft definition, and then just add it (with a new name) to my installed aircraft folder, then fly it. Have I got that right?


See http://wiki.flightgear.org/Howto:Make_a ... _and_files for an overview of the usual conventions for files.

It's easier to just modify the files that are already there (after making a backup of course); as there are some complexities that might slow down progress when working with new or renamed files.

You shouldn't need to move the connection point; just calculate the appropriate force vectors in the aircraft X,Y,Z axes. Look for properties that are in fdm/jsbsim/external_reactions/ (use the / key to open the property browser)

If you want to see how this is done entirely using a JSBSim system look at the catapult or arrestor hook on the F-14. I'd probably change all of the winch calculations to be in a JSBSim system because then you can use a lookup table coupled with some maths to get the force vectors and magnitude correct for a winch.

Instead of rebinding the Z key maybe you could use the throttle position to control the winch speed. Before rebinding keys look in /input/keyboard to see which ones are available
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Re: How to make an Aircraft....

Postby GeoffDraper » Fri Apr 01, 2016 9:58 am

Hi sanhozay,

Thanks for your thoughts om my project. I can see I have a lot of learning in front of me...

Specifically, your ideas on key allocations, checking the property tree, and the inadvisability of renaming existing aircraft.

All new to me! And most helpful.

Best wishes - Geoff
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Re: How to make an Aircraft....

Postby GeoffDraper » Fri Apr 01, 2016 10:05 am

Hi again Richard,

Thanks again for your thoughts.

Sanhozay concurs with your idea of not renaming stuff. Got it!

I need to do some thinking / investigation re towline forces... Thanks for giving me an alternative approach.

And I love your idea of using the "throttle" to control the winch speed - neat.

I'm sure I'll have more questions as I progress...

- Geoff
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Re: How to make an Aircraft....

Postby ausdkunst » Sun Apr 03, 2016 11:36 am

Hi all,

I am developing a very small plane for my own collection and I have been running some problems. After taking off, the plane will start banking/turning to the right and it will keep spinning in circles until it crashes to the ground. What can I do to fix it?
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