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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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