Re: hello a question

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 have 
> full lenght of fuselaje=1220mm(48.03'') and full width
> fuselage=140mm(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´t 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 the 
centers of the two ends of the tube defined by the ax,ay,az & bx,by,bz 
params.  The ax & bx params define the length of the tube.  The ay/by params 
specify the 'yaw' of the tube, or whether the tube is angled to the left or 
right of the central axis of the aircraft and az/bz specifies the pitch of 
the tube - whether it's tilted up or down.

The width param specifies how wide the the fuselage is (the assumption is that 
the fuselage cross section is circular, or approximately so)

The taper and midpoint params are a little trickier to get your head around 
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 
seems to allow for, at most, a sort of B-29/Boeing-377 type fuselage, which 
compared to most aircraft is not tapered at all.  However, If the fuselage 
taper is related to the midpoint then we can get asymmetrical ellipsoid type 
egg shapes, which make more sense.  If the midpoint is placed forward of the 
midpoint of the longitude axis we'd get a tear-drop type shape, with the back 
of the fuselage trailing to a point, and if the midpoint is aft of the 
midpoint then we'd have a reversed tear-drop shape, with the 'thin' end 
leading.

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

For your aeromodel titan raptor 50 I'd disregard the boom entirely as it's so 
small that it would have little aerodynamic effect and therefore place the 
midpoint at about 0.9 i.e. nearly at the back of the fuselage.  I'd guess at 
a value of about 0.7-0.8 for the taper, favouring the lower end of that 
range.

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

LeeE


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