Re: [Flightgear-flightmodel] hello a question

[leee <le...@sp...>]

On Thursday 30 August 2007 23:08, lina maria perez perez wrote:
> My name is lina and I am new in this thing but I'm trying to learn, now I=
'm
> trying to make the model of an helicopter that I need for my project, but
> there are some things that I don't understand, this is
>
> fuselage: This defines a tubelike structure.  It will be given an even
>           mass and aerodynamic force distribution by the solver.  You
>           can have as many as you like, in any orientation you please.
>           ax,ay,az: One end of the tube (typically the front)
>           bx,by,bz: The other ("back") end.
>           width:    The width of the tube, in meters.
>           taper:    The approximate radius at the "tips" of the fuselage
>                     expressed as a fraction (0-1) of the width value.
>           midpoint: The location of the widest part of the fuselage,
>                     expressed as a fraction of the distance between A and
> B. I don't know how to define my fuselage, I know that the helicopter hav=
e=20
> full lenght of fuselaje=3D1220mm(48.03'') and full width
> fuselage=3D140mm(5.51'') (The helicopter is an aeromodel titan raptor 50)=
 but
> don't know how to relate it, the part that I have most confuse is in
> ax,ay,az: One end of the tube (typically the front),  bx,by,bz: The other
> ("back") end. I don=C2=B4t know how to made this part. and all, haw I say=
 I'm
> new in this but I hope that you can help me.
>
> Thanks a lot.
>
> LINA.

Hi Lina,

regarding fuselage elements in YASim, think of a tube, or ellipsoid, with t=
he=20
centers of the two ends of the tube defined by the ax,ay,az & bx,by,bz=20
params.  The ax & bx params define the length of the tube.  The ay/by param=
s=20
specify the 'yaw' of the tube, or whether the tube is angled to the left or=
=20
right of the central axis of the aircraft and az/bz specifies the pitch of=
=20
the tube - whether it's tilted up or down.

The width param specifies how wide the the fuselage is (the assumption is t=
hat=20
the fuselage cross section is circular, or approximately so)

The taper and midpoint params are a little trickier to get your head around=
=20
and less obvious to understand - at least I find it so:)

I don't see how these two params can be separated as taper on it's own only=
=20
seems to allow for, at most, a sort of B-29/Boeing-377 type fuselage, which=
=20
compared to most aircraft is not tapered at all.  However, If the fuselage=
=20
taper is related to the midpoint then we can get asymmetrical ellipsoid typ=
e=20
egg shapes, which make more sense.  If the midpoint is placed forward of th=
e=20
midpoint of the longitude axis we'd get a tear-drop type shape, with the ba=
ck=20
of the fuselage trailing to a point, and if the midpoint is aft of the=20
midpoint then we'd have a reversed tear-drop shape, with the 'thin' end=20
leading.

If this is so, and I'm not sure I've got it right;) , the radius then=20
specifies the curvature of the ellipsoid.  Referring to the taper element f=
or=20
wings, I would say that a taper of 0.0 would produce a cone (or pair of=20
cones) with the base of the cone(s) at the midpoint, and a taper of 1.0 wou=
ld=20
give a perfect egg-shaped ellipsoid.

=46or your aeromodel titan raptor 50 I'd disregard the boom entirely as it'=
s so=20
small that it would have little aerodynamic effect and therefore place the=
=20
midpoint at about 0.9 i.e. nearly at the back of the fuselage.  I'd guess a=
t=20
a value of about 0.7-0.8 for the taper, favouring the lower end of that=20
range.

Perhaps AndyR might see this thread and clarify - it's something I've never=
=20
been that sure about but working on the basis I've outlined seems to have=20
worked for the fixed wing aircraft I did.

LeeE