Melchior FRANZ

> Sent: 04 August 2004 14:49
> To: [EMAIL PROTECTED]
> Subject: [Flightgear-devel] Re: yasim + bo105 + vrp + @#%$#@ == argh!
> 
> 
> * Jim Wilson -- Wednesday 04 August 2004 15:28:
> > Melchior FRANZ said:
> > The only difference is JSBSim has the extra feature of 
> specifying the 
> > VRP which is an offset from where 0,0,0 ends up being 
> specified.  It 
> > saved changing all the entries for existing flight model 
> configs that 
> > had 0,0,0 at the firewall, etc.
> 
> Yes, I know. For the bo105 it's the nose, though. Not 
> exactly, actually (see below).
> 
> 
> 
> > It sounds like you pretty much understand what is going on, 
>  but just 
> > keep in mind this FDM side is only about where the lon/lat/alt gets 
> > reported in FlightGear.
> 
> Thanks, and, yes, I know.  :-)
> 
> 
> 
> > BTW I noticed that the bo105 fuselage in CVS is not 
> anchored exactly 
> > to 0,0,0 but it is offset (I think it is 0.17 forward and 
> 0.51 down).  
> > This should probably be fixed.
> 
> I will fix it later. It has to do with the fact that Maik 
> "fdm-modeled" a Bo105, while I "3d-modeled" a Bo105CBS (which 
> is 10 inches longer).
> 
> 
> 
> > Keep in mind that exactly straight down isn't possible, and 
> remember 
> > the camera is moving too.  So yeah that "illusion" can work 
> from any 
> > direction, even with what appears to be a good fixed reference.
> 
> OK, but this wouldn't have such a dramatic effect.
> 
> 
>  
> > The solver places the bo105 CG as follows on my copy:
> >   -2.491, -0.000, 1.091
> 
> Sounds good.
> 
> 
>  
> > I'm not really sure how the aircraft should turn and what relation 
> > rotation would have to CG.  Note that your FDM thinks the 
> nose is 1.5 
> > meters (add the offset I mentioned above) below the CG.
> 
> I would expect it to turn pretty much around the main rotor 
> axis/CG, or maybe slightly forward on ground (because of a 
> possible forward pitch and the skid friction). But never 
> would I expect a rotation around the nose, which seems 
> physically impossible to me.
> 
> 
> 
> > If there is a bug in YASim this would be the first I've seen of it.
> 
> Not necessarily. Maybe the tail rotor doesn't apply the force 
> correctly. It could be a pure helicopter/rotor problem.
> 
> 
> 
> > Is it possible that you never had the model positioned with 
> the target 
> > offset correct all at the same time?
> 
> That's what I'm talking about. The 3d model was always placed 
> wrongly (not by me, by the way. :-)  The 3d model was placed 
> with the main rotor axis aligned with what YASim thinks is 
> the nose. That's why I thing the bug was masked.
> 
> 
> 
> > Did you put the target offset in the right place, in the right file?
> 
> I think so, yes. (Well, I hope so, at least. :-)
> 

Well, I don't know. I've just flown it using a recent CVS download. It
looked really good to me. The point of yaw seemed to be just about at the
rotor hub.

Hmm ...

Regards,

Vivian




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