On Samstag, 31. Januar 2004 12:46, Christian Mayer wrote:
> Jon Berndt schrieb:
> > I just discovered that our property "metrics/eyepoint-x-ft" shows that it
> > is expected to be in units of feet. However, it is specified in inches in
> > our config file (in structural frame), and the property is bound to the
> > GetXYZep() function, which reports the eyepoint in the same way it is
> > specified: units of inches, in structural frame. I suppose this ought to
> > be changed.
>
> If we'd use SI units everywhere we wouldn't have that prolem...
> (and if NASA would have consitently used SI they wouldn't have lost one
> Mars probe...)
I am also used to the SI system.
But all I have seen up to now in the area of physical aircraft models is given
in units of feet and such. So I think the FDM should be able to work using
this values.
What I can think of is an extension to the property tree, either private to
JSBSim or better in Flightgear in general.
I would like to be able to tie a value with a given unit into the property
tree. Then there should automaticaly appear a set of values in the property
tree which represent this value in different units.
There are many possible scenarios how this can happen. The most compatible one
will be to tie a value with unit into the property tree without the unit
extension in the name. Then there are automatically the usual unit values in
the tree. For example the angle of attack will be tied to the variable
'alpha' with an angular unit originaly given in rad, but that alpha will not
appear as 'alpha' in the tree, but instead two variables appear. One
'alpha-rad' and one 'alpha-deg'. The same can of course be done for unit
conversion from and to the SI system.
The other possibility, which is not that backward compatible, will be that
each value is represented by a whole directory. Inside this directory there
are then only unit names. For example the angle of attack will then be
accessible through alpha/deg or alpha/rad.
This will also simplify building aerodynamic coeficient lookup talbes which
are sometimes given in, say 'lift per degree elevator deflection' or, for an
other aircraft type in 'lift per rad elevator deflection'.
I know, this is simple scaling, but I think that simple things should be left
to a computer ...
:)
If someone has spare time to work on such a automatic unit system ...
Also, I have not looked into the property tree implementation if this could be
done easily.
Greetings
Mathias
--
Mathias Fröhlich, email: [EMAIL PROTECTED]
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