Nose Cone Help

[Jacoolo]

ok, I`ll keep waiting

just throw two cents more to make me more clear to understand

by section of VSS I understand the profile created in VSS feature. In first VSS You created parabola arc with equ length as I suppose, right?

However the last VSS contains the profile which is eliptical quadrant arc, right?

In the end it looks to me that it is/can be so, because the cross-section of first VSS in trimmed area is right eliptical quadrant arc(and that is the reason why the last VSS fits so nicely to the first one)

I am only far away from understanding why cross section of first VSS seems to be eliptical quadrant arc?(I assume it is somehow connected with the profile of first VSS)

 

[jeff4136]

Jacek,


Concerning the matching of the trimmed nose surface and the fuselage
section curves; looking back on page 5 of this discussion and,
particularly, at ...
http://www.math.umn.edu/~rogness/quadrics/ellparab.shtml
... the nose surface is an elliptical paraboloid. It has the
characteristic of being elliptical when sectioned.
(With, I believe, some constraints on section plane orientation(?).
If the trim plane is not rotated about an axis normal to a plane
containing either the sweep trajectory or section the surface trim
curve may not be elliptical. I think I've tried it in the past and
found that to be true but ...?)


Regarding the fuselage VSS sketcher relation:
_ I chose to vary Rho to transition into and out of a more
rectangular shape (flatter top, bottom, sides) because that
(going by Chris' pics) seemed to be the intent.
_ The cosine function assures that the change in Rho begins and
ends tangent to a zero degree curve (horizontal if change is
plotted as Y to X = t) which is appropriate for the constant
rho of the sectioned nose.
(The way I offset and inverted the function is probably sloppy.
Equations are not my forte and I'm not eloquent with them.
But it seemed ok for a quick and simple VSS demonstration.)


> how about the situation where the section of
> first VSS is gonna be different than parabola


A situation where the elliptical paraboloid (or an ellipsoid?) won't
serve as a suitable foundation? Good question, interesting for a few
reasons. My first thought (though I surely don't know) is that we'd
have to look hard to find that situation in a general aviation nose
cone. For more general cases I've wondered about and asked (general
audiences, I've a few ideas of individuals I might bother with the
question but haven't) a few times. I suspect there are other known or
predictable, to the 'high schoolers of shape definition' in some
disciplines, relationships like that among combinations of primitives,
conics or more complex shapes (while most of us will be very hard
pressed to describe a cone and orient a plane to get a conic curve
with specific attributes).

Edited by: jeff4136

 

[Jacoolo]

thx for explanation jeff

however I just reminded asking about it by myself in following post

[url]http://www.mcadcentral.com/proe/forum/forum_posts.asp?TID=37 731&PN=0&TPN=2[/url]

where I suppose if not the first - the very good example of the use of eliptical arcs considering surfaces transition was introduced!



still there is a little mess in my head while trying to figure it all out - but if I can afford Your attention for a little summarise for me, would it be that:

* no matter of type of profile(parabola, eliptical) for VSS, it ends up with a surface which cross section is always eliptical quadrant right?

sorry for asking more then twice to catch the clue if it looks like so

 

[jeff4136]

Jacek,


> sorry for asking more then twice


Not a problem.


> no matter of type of profile (parabola, eliptical) for VSS,
> it ends up with a surface which cross section is always
> eliptical quadrant right?


If I understand that; no.
My objection is to "no matter of type of profile (parabola, eliptical)".


The resultant shape created by the sweep (or whatever function might be
used) must be (must satisfy the mathematical definition for any point
tested) an elliptical paraboloid or an ellipsoid. Certain combinations*
of trajectories, sections, section control and section plane orientation
will do that.


* The elliptical paraboloid is a constant normal direction, constant section.
An ellipsoid is constant normal direction, variable section.

 

[Jacoolo]

I`ve just thought I catched the thing

well, gotta rethink all once again

thx jeff

 

[jeff4136]

I usually find it a little easier if I've got something to look at, play with ...


2009-01-06_161735_ellipsoid--wf2.prt.zip

 

[rklatte]

I've been watching this post since it started and I just
wanted to say thanks to everyone who helped clarify some
of these surfacing issues, especially you Jeff!

I just wish some of my work right now lent itself to
surface modeling

 

[Guest]

I
rarely do this technique. However, you are correct, you can actually raise the
tip of the nose a bit even when you don't smile. It lasts about 2 months in
many cases and I think it is unpredictable and a waste. It can also spread to
the upper lip and drop the lip a tiny bit and also can affect the nostrils by
slightly splaying them at times as well. hope that is clear.

best
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nose right scam