# RE: [Flightgear-devel] Problem with ballistic sub-model

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Arnt Karlsen wrote:```
```
> Sent: Friday, September 17, 2004 10:03 AM
> To: FlightGear developers discussions
> Subject: Re: [Flightgear-devel] Problem with ballistic sub-model
>
>
> On Fri, 17 Sep 2004 07:56:42 +0100, Vivian wrote in message
> <[EMAIL PROTECTED]>:
>
> > Ampere K. Hardraade wrote
> >
> > > Sent: Thursday, September 16, 2004 7:12 PM
> > > To: FlightGear developers discussions
> > > Subject: Re: [Flightgear-devel] Problem with ballistic sub-model
> > >
> > > On September 16, 2004 01:08 pm, Vivian Meazza wrote:
> > > >
> > > > There are some other basic shortcomings as well: the submodel
> > > > doesn't inherit the parent accelerations, or the velocities and
> > > > accelerations due to roll, pitch and yaw. Only release
> droptanks
> > > > when flying straight and level
>
> ..uh, in the real world, this is possible if not permissible,
> with fun
> consequenses like one or more hard points releases jammed for
> at least a while etc.
>
> > >
> > > They shouldn't inherit accelerations.
> >
> > Quite right - they shouldn't. I was getting over
> enthusiastic there,
> > and forgetting my Newtonian physics.
>
> ..don't worry, there is also Murphy law physics.  ;-)
>

Right, back to Newton :-). I think I've solved the problem. Mixing
elevation up = positive with  speed down = positive  nearly made my brain
blow a fuse

I had to reverse a number of signs to get it right. I took the opportunity
to add roll to the submodel so that droptanks will come off with the right
orientation. I not yet added either the parent rotational speed to the
submodel, or yaw, so if you release droptanks with significant roll rate or
yaw angle on the aircraft the submodel will not be quite right. Straight and
level, or nearly so, is fine.

I've asked Erik to upload the modified files to CVS. It looks OK on the
Hunter, but perhaps Lee could give the revised submodel a good test.

Regards

Vivian

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