Re: [Jsbsim-devel] Fwd: Re: Patch to allow compression of the struts.

[Richard H. <rj...@za...>]

On 06/10/2017 07:01, David Culp wrote:
> functionality in FlightGear.  The first attempt to add this to JSBSim
> (IIRC about 12 years ago?) was rejected because it was far too external
> ...
> I think a better solution would be to move all the carrier ops business
> out of both YaSim and JSBSim and put it in FlightGear's FDM interface.

As you might be aware I implemented a simulation of the AN/SPN-46 
Precision Approach Landing System (PALS) and matching ARA-63 receiver to 
provide a workable ACLS (one that allows channel selection and thus two 
or more systems in close proximity in a fleet). It uses inter object 
communications via my Nasal Emesary implementation. This approach 
abstracts the objects from knowing anything about each other and works 
well.

I plan to use a similar inter object communication (either Nasal or via 
a Nasal extension) to provide the ability for an aircraft to be attached 
to the launchbar and to handle all of the associated logic required up 
until the point of launch. The launch (and hold back) would need to be 
within the FDM loop to run at the right frame rate.

However I suspect that the only place that the catapult interface is 
going to work correctly is again within the landing gear. I have 
previously tried to use an external force attached at the right 
place[1], together with a matching hold back and the result is that the 
aircraft tends to move as the forces aren't in the right place and it 
only takes small disturbances to cause a twitch that feeds back through 
the gear and results in a small movement. The only solution I can see 
for this is to allow any contact point to receive an external force and 
also to be locked to a specific point in space.

So this brings us back around to the bigger question about where stuff 
belongs. I don't believe that a reliable implementation of launch or 
holdback can be provided externally to the landing gear as it is 
currently coded. The trouble is that I'm not quite sure how to achieve 
this without adding something that might be considered 'core unrelated 
code' into the landing gear - and that is what needs to be discussed as 
I'm not prepared to invest my time into this without clear guidance from 
the JSBSim core developers on the details of how to approach this.

-----------------------

[1] the only way I can keep the aircraft locked in position is to have 
the external force acting through the same point as the mean engine 
location.