CAD Tool For Design Tiny Aircraft

On Tue, 2 Oct 2007 13:14:34 -0700, "Jerry Steiger" wrote in :

"Le Chaud Lapin" wrote in message
oups.com...
1. One dimension of fuel tank depends on required fuel capacity.
2. Fuel capacity depends on mass of certain parts.
3. Mass of parts depend on geometry and density of material of those
parts and load requirements, etc..
4. Load requirements depend on configuration of other structures.

And it would seem that there is a right way and a wrong way, and
again, finding the right way is more art than science. "Reaching" too
deep into model to extract parameters to be used elsewhere might be a
bad idea. Deliberate indirection and hierarchy would be important.
There would also be opportunity for circular references.

This is going to be very tricky. There HAVE to be circular references in
your optimization. When you change the weight of the fuel tank, you have to
reevaluate the size and weight of all of your other components to account
for the new load. But now you have changed the weight of the rest of the
components, so the fuel tank needs to change again. If you are lucky, the
solution converges and you end up with a design that works. If you start
from the wrong spot, it might never converge.

The good news is that you seem to have the type of mind set that would allow
you to work through this type of problem. The bad news is that it is an
extremely complex problem that requires a lot of deep knowledge in many
areas of design.

Speaking only from practical experience with RC models (~14 years total),
the envelope for small aircraft is extremely forgiving for ordinary
flight regimes. Most RC aircraft can double or triple their fuel load
without noticeably affecting flight performance.

Look at the college competitions for evidence. A few years back,
a weight-lifting competition was won at around 19 pounds of payload
for an aircraft powered by a plain-bearing 0.40 ci engine. Engines
like that are usually used to fly ~5 pound trainers with a wingspan
between 40" to 48" or so.

Drat. The American Institute of Aeronautics and Astronautics
website is down right now ... Here's a report on the 2006
competition:

http://mae.eng.uci.edu/aiaa/DBF2006.pdf

If you're trying to fly an RC aircraft across the Atlantic with
a gross weight of 5 kg (11 pounds), then you DO need to consider
a multitude of tradeoffs such as you describe:

http://www.progressiveengineer.com/profiles/maynardHill.htm

An engineer friend of mine likes to say, "One observation is worth
ten thousand expert opinions." Regardless of what the design
software predicts, the product needs to be tested in flight to
see whether the theories work. (I'm assuming that the initial
post in this thread was about a flying model.)

Something funny happens as you go down in scale. It has something
to do with Reynolds Numbers and the volumetrics of small aircraft
(volume decreases far more quickly than area). This means that
the power-to-weight ratio favors the model aircraft and that,
as a general rule, the ratio of the strength of materials to
G-forces increases. A 1/4 scale model (using 1/4 of the linear
dimensions) has 1/16 the area of the prototype and just
1/64th of the volume.

One way to get in the ballpark when designing a new model is
to select dimensions from aircraft that are already known as
good flying designs. The airfoils that work well for full scale
do not work well on small aircraft (as a general rule--Clark Y
airfoils probably scale OK; fighters and bombers from WW II on
generally do not scale well).

So a lot depends on the kind of aircraft the other poster
wants to build, whether it is supposed to fly, and what kind
of performance is to be optimized.

Marty
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Personally, I prefer a pure geometry based modeler. Simple
dimensional changes affecting many components may take longer, but
it's far easier to make large sweeping changes if necessary, or switch
to an alternate design approach. Most of my work nowadays is large
machine design (though my degree is in aero engineering), for which I
use KeyCreator (formerly Cadkey). Same price range as SWX, though,
which I don't define as "cheap".

-Dana

This seems like it would be a helpful link.

http://www.darcorp.com/

Jon Banquer
San Diego, CA
http://worldcadaccess.typepad.com/bl...mment-76366100

On Oct 4, 10:05 am, jon_banquer wrote:
Personally, I prefer a pure geometry based modeler. Simple
dimensional changes affecting many components may take longer, but
it's far easier to make large sweeping changes if necessary, or switch
to an alternate design approach. Most of my work nowadays is large
machine design (though my degree is in aero engineering), for which I
use KeyCreator (formerly Cadkey). Same price range as SWX, though,
which I don't define as "cheap".

-Dana

This seems like it would be a helpful link.

http://www.darcorp.com/

Just want to summarize that SolidWorks seems to be what I was looking
for. Alibre's CEO makes a compelling argument about tactics of
salespeople to derail reason (in this case, he's talking about
SolidWorks), so I might at least give that a look. But I spoke to
sales engineer yesterday and SolidWorks is surely what I was looking
for.

Thanks for all the links Jon & All. I've been looking at them.

So much to learn, so little time.

-Le Chaud Lapin-

On Thu, 04 Oct 2007 08:05:05 -0700, jon_banquer wrote:

This seems like it would be a helpful link.

http://www.darcorp.com/

WHY would you "think" that?
Other than it's about something else you have no clues about.
--
Cliff

On Thu, 04 Oct 2007 08:05:05 -0700, jon_banquer
wrote:

This seems like it would be a helpful link.

Oh, I forgot: Keycreator: http://kubotekusa.com/

Jon Banquer! Small world, eh? I wondered what you were doing on
rec.aviation until I realized this is crossposted to
comp.cad.solidworks. Been quite awhile since we got into ****ing
matches on the Cadkey webforum... I gave history based parametric
modelers a good try, I really did (UG, SWX, and Inventor) but I got
tired of having the inability to model something the way I wanted
based on the constraints of an earlier design version... and want back
to a pure geometry modeler (KeyCreator). It certainly has some warts,
too many IMHO, and I think Greg Marr still gets annoyed when I bitch
too much, but warts and all it's still the best tool I've found for
the kind of work *I* do... YMMV.

-Dana
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Does fuzzy logic tickle?

Jon Banquer! Small world, eh? I wondered what you were doing on
rec.aviation until I realized this is crossposted to
comp.cad.solidworks. Been quite awhile since we got into ****ing
matches on the Cadkey webforum... I gave history based parametric
modelers a good try, I really did (UG, SWX, and Inventor) but I got
tired of having the inability to model something the way I wanted
based on the constraints of an earlier design version... and want back
to a pure geometry modeler (KeyCreator). It certainly has some warts,
too many IMHO, and I think Greg Marr still gets annoyed when I bitch
too much, but warts and all it's still the best tool I've found for
the kind of work *I* do... YMMV.

Hi Dana,

One day more users many come to realize that you really need both
approaches in one system. I believe UGNX 5 has made major progress in
this area and probably is the leading system for using both
approaches. KeyCreator should be adding parametrics and SolidWorks
should be adding more tools for working directly on non-native
geometry.

Jon Banquer
San Diego, CA
http://worldcadaccess.typepad.com/bl...mment-76366100

On Sun, 30 Sep 2007 19:40:11 -0700, jon_banquer wrote:

On Sep 30, 7:27 pm, Le Chaud Lapin wrote:
On Sep 27, 6:16 pm, Dana M. Hague





d(dash)m(dash)hague(at)comcast(dot)net wrote:
A fully 3D program is, IMHO, a must for any kind of design, anything
else is silly. A parametric modeler, however (like SWX and many
others) can be very cumbersome to use... and I've used a lot of them
over the years. Yes, if the design constraints are set up correctly
from the start, minor changes can be ridiculously easy... but if not,
or if you don't have a clear idea of where you're going from the
start, you can find yourself boxed into a corner and have to start
from scratch.

Personally, I prefer a pure geometry based modeler. Simple
dimensional changes affecting many components may take longer, but
it's far easier to make large sweeping changes if necessary, or switch
to an alternate design approach. Most of my work nowadays is large
machine design (though my degree is in aero engineering), for which I
use KeyCreator (formerly Cadkey). Same price range as SWX, though,
which I don't define as "cheap".

I read all the responses and looked around the 'Net, and it seems that
SolidWorks, if not what I'm looking for, is create by people who had
the mindset I was looking for.

But now I am confused. I thought parametric modeling was good.

I program computers from time to time, and being able to change the
structure of a component and have everything that depends upon it
change accordingly is simply invaluable, so I cannot see why this
would be bad. That's precisely the behavior I want.

For example, in my miniature aircraft I envision, there is only one
fuel tank, and it's cylindrical, but its radius and length are a
function of several other parameters.

I am guessing that, like in programming, there is an art to
structuring the interdependencies so as to minimize likelihood of
running into dead-end that you mention.

Finally, I was really surprised to learn that parametric modeling was
not fundamental in all CAD programs. I cannot imagine what it would
be like to try to optimize a design without it. What do people do
without parametric modeling? Tweak every single component manually
during optimization phase?

[I am going to give Alibre a look also.]

-Le Chaud Lapin-- Hide quoted text -

- Show quoted text -


Suggest you find your way ASAP to www.kubotekusa.com and view their
video on direct dimension editing to see what can be done without
parametrics.


Such as their dimensions being their displayed Parametrics?
Pretty good for aircraft & airfoil shapes, is it? Or driven features?


Jon Banquer
San Diego, CA
http://worldcadaccess.typepad.com/bl...mment-76366100

[
The real problem right now is that the major CAM systems need video done to
cover their massive gap in documentation. I'm speaking of MasterCAM and
Gibbscam.

If you would like to read my interview and what I had to say about this problem
you can read it here.

http://blog.novedge.com/2007/07/an-interview-wi.html
] - clueless

From that novedge.com link:
[
Franco Folini

UPDATE -- July 8, 2007 -- I had to close this blog post to further comments and
to remove the personal attacks between Jon and some other newsgroups readers.
Before the interview, I made an agreement with Jon about the style of the
interview and the way to handle it. Jon didn’t respect our agreement, posting
comments under fake names. Jon’s authentic and fake comments are all posted from
the same IP address, 72.199.251.224. I can now see that my trust in Jon was
misplaced.
]

From that worldcadaccess.typepad.com link:

[
QUOTEThe real problem right now is that the major CAM systems need video
done to cover their massive gap in documentation. I'm speaking of MasterCAM and
Gibbscam.

What version of Mastercam are you talking about ?

The current version has a HUGE help file with MANY MANY videos available via
links inside the help file.

Posted by: Mattapotamus | Jul 21, 2007 at 13:27
]

Snicker

Tell us again about your aerospace shops ..... P&W & etc. .... or if you've
ever actually even seen GibbsCAM or MasterCAM ....
Clearly you've never actually used either. Nor any other similar system.
--
Cliff

On Thu, 27 Sep 2007 17:33:00 -0700, jon_banquer wrote:

Users should have the option to use "a pure geometry based approach"
or a parametric approach in one package.

And you get the history-based & parametrics back exactly how?
Using a fake-history generator?

Unfortunately at this point
they don't have this option. There is no reason KeyCreator shouldn't
add parametrics. Using parmetrics is often faster when creating parts
from scratch.

How many bricks is enough to build a wall?

Why Kubotek refuses to do this for KeyCreator is beyond
me.

Because you are clueless.
HTH
--
Cliff

On Sun, 07 Oct 2007 09:02:36 -0700, jon_banquer wrote:

Jon Banquer! Small world, eh? I wondered what you were doing on
rec.aviation until I realized this is crossposted to
comp.cad.solidworks. Been quite awhile since we got into ****ing
matches on the Cadkey webforum... I gave history based parametric
modelers a good try, I really did (UG, SWX, and Inventor) but I got
tired of having the inability to model something the way I wanted
based on the constraints of an earlier design version... and want back
to a pure geometry modeler (KeyCreator). It certainly has some warts,
too many IMHO, and I think Greg Marr still gets annoyed when I bitch
too much, but warts and all it's still the best tool I've found for
the kind of work *I* do... YMMV.

Hi Dana,

One day more users many come to realize that you really need both
approaches in one system. I believe UGNX 5 has made major progress in
this area and probably is the leading system for using both
approaches.

Still utterly clueless, eh?
Another system you've never used & know nothing much about: UG.

KeyCreator should be adding parametrics and SolidWorks
should be adding more tools for working directly on non-native
geometry.

Snicker

Jon Banquer
San Diego, CA
http://worldcadaccess.typepad.com/bl...mment-76366100

Snicker
--
Cliff