----- Original Message -----
Sent: Tuesday, February 09, 2010 10:38
PM
Subject: [FlyRotary] Re: CAD
program
Monty,
Did a little web surfing today. Lot of information out
there on Alibre, plusses and minuses. Hard to determine whats what since
everything is subject to opinion and prior experience. I've noodled around a
bit with ProE. Designed a few assemblies for UAV related work and did a one
week course on Wildfire about 5 years ago. But havent used it recently and
would probably need to relearn a lot. Considerably less experience with
Solidworks, but what I did find in playing with it is that it is a lot more
user friendly than ProE. I'm more or less used to the sketch concept so not
clear to me what the short coming is with it (never had experience with
anything else).
Can you elaborate a little more on what you mean about
Alibre not doing conic sections? From what I saw today I thought the biggest
hang up with it is that it cant handle surfaces.
Seems like pricing has changed numerous times for
Alibre. Currently there are three levels priced at $97, $499, and $999. There
is still a demo available but not clear from the website what you get to demo,
how long the demo period is, or what happens at the end of it.
The picture is less clear for Rhino, at least to me.
Nothing I find on the web, either from the Rhino site or others, really helps
explain for the rookie how it works, how it differs from the typical
parametric modeler, and what the negatives are compared to a parametric. I
gather it is really good with surfaces, and good for quickly developing good
conceptual models. Not clear if you can actually get engineering drawings out
of it that you can actually build something with. I'd like to know a lot more
about it.
One downside to Rhino compared with getting into
Alibre is initial cost. $1000 unless you can get the student discount ( I may
have to consider going back to school at age 53 just to get the discount). The
demo version of Rhino is presumably full featured (not entirely clear from the
website) but is only good for 25 saves and then it dies.
Just to clarify what it is I want to do. I've been
wanting a motorglider for years. Van started on a design for his RV-11 10
years ago. I think it’s a great concept. Moderate performance
but considerably better than the very compromised Xenos design from
Sonex. The RV-11 became stalled due to his perception that there was no
market. Last update was about a year ago and he said he was working on it
again. But he no longer replies to email questions about it and has made
it clear that he doubts he would ever market a kit.
My current glider has the same wings he planned
for the RV-11. I'm pretty sure I can build an RVish sheetmetal fuselage and
tail surfaces similar to what he had in mind. And I assume it can be done
relatively inexpensively. I'm thinking pretty seriously about it. You've got
my attention if Rhino can actually help with all the sheetmetal
stuff.
Mike
Sent: Tuesday, February 09, 2010 9:07 AM
Subject: [FlyRotary] Re: CAD program
You can probably get by with the hobby version of
Alibre. I think it is around $250. I can't remember what all the restrictions
are.
I think you can make Alibre work if all you do is
flat wrap developable surfaces. If you are going to do sheet metal it will
probably get you where you want to go.
Alibre's big handicap is that it will not do
conic sections. Conics are THE foundation of all aircraft and boat
lofting. Everything is also sketch based. I don't really like sketches. I
blame Pro E for everybody going to sketches. Even the once great Unigraphics
has succumbed to the dark side. A pox upon the geek who
invented sketching! Constraint based sketching is really good for
mechanical parts and mechanisms. Or something where you have a family of parts
that may need changing. It is too limiting for free form parts. I will at
least give Alibre credit for not requiring all sketches to be fully
constrained. That can drive you crazy. Of course not having them fully
constrained means you occasionally have one blow up. You'll see what I mean.
Get the demo version and play around with it.
I think you can do the same with Rhino. Try before you buy.
I think you can get the student version of Rhino
for $200. That is a fantastic deal. Even $900 is not bad. Trust me, it will
save you that much in headaches if you are designing an airplane. Especially
if it is sheet metal. You can unwrap all your surfaces and plot out flat
patterns. Or better yet send a .dxf file to the waterjet guy to cut your skins
out with the holes all pre punched just like one of van's airplanes. You can
have somebody with a CNC router make up all your form blocks for the ribs and
bulkheads too. If your cad file is perfect, the parts will be. They will
go together just like a quick build kit. How much is that worth to you? After
that you can make as many as you want, over and over and over. I look at it
and say you can't afford not to have a cad program.
Classroom vs tutorials is a personal thing. I've
always been good at the tutorials. But I've been doing cad for so long
that I can pick up just about any program and be doing work in an hour. If you
don't have the basics a class is a good Idea. You aren't going to get conic
lofting skills from a basic tech school though. You could go to one of the
seminars that Rhino puts on from time to time after you have the basics
down. In the end the only real way to learn is by doing. In the
beginning there is going to be a lot of pounding your head against the
monitor. That's just the way it is. When you get to the point you know it is
the software's fault not yours, you will have arrived. Some folks have a
natural ability for this and others don't. You will know within a couple weeks
which camp you are in, especially if you take a class. You may hate
working in cad, some people do. You may also find it addictive. Just
a warning.
I could show you most of what you need to know in
an afternoon if you had the basics down.
You could use the Bruce King method for a one
off. Google BK flyer. He uses cad to lay out the bulkheads, but then
makes poster board patterns for the skins. You just have to decide which way
you prefer to work.
One word of advice in Rhino.....Planar.
Monty
----- Original Message -----
Sent: Monday, February 08, 2010 9:15
PM
Subject: [FlyRotary] Re: CAD
program
Thanks Monty. Alibre was the tool I was thinking of.
Never seen Rhino but I will take a look. Building an airplane is sort of an
excuse to learn the tool. I suspect that I could design/build what I want
without it. But it might help me visualize the end result before I go to far
down the wrong path. Clearly I'm not going to invest huge $ in a cad package
to build a one off.
Mike
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