Design Software

[Brad Mallard]

I am still in the design phase of my future plane. I would like to hear
opinions on design software, and even buy software that someone doesn't use
anymore.

Brad

[smjmitchell]

Hmmmm ...

You shouldn't need any software to design a light airplane except for
maybe an FEA program. However whether of not you need an FEA program
depends on the type of structure you are designing. For instance if
you are designing a tin airplane then there is little need for FEA
(unless you really know what you are doing you will just get trash out
because, for example, the FEA does not account for skin buckling). If
you are designing a composite airplane then a FEA package is strongly
recommended (but not essential) but it needs to laminated composite
element.

Generally you can calculate all the loads and do all the stressing
manually using relatively simple techniques and only moderately
advanced maths.

I get nervous when amateur designers start asking about software as
though it is an essential design tool. Usually this means that it is
being used as a black box to fill in a fundamental lack of engineering
knowledge with little understanding of what is actually going on
inside the code or any ability to interprete what the results are
telling them. That is dangerous. My suggestion is to invest your money
in a copy of Bruhn's "Analysis and Design of Flight Vehicle
Structures" and Stintons "Design of the Airplane" to name a couple of
good texts instead of software. Read them and understand what they are
saying and then decide if you still need software. If you can't
understand the texts then you are not sufficiently qualified to start
using design software ... period. In fact if you can't understand them
then you should seriously consider buying a set of plans for an
established design.

Yeah I know .... half of the group is going to rubbish what I have
just written but I have been around long enough to see how danagerous
non professional designers are with software that they don't
understand. (I earn a living designing and modifying all sorts of
airplanes - certified and homebuilt).

The safest way for a homebuilder to design an airplane is to produce
an evolutionary design that is based on an existing sound design and
do most of the design work by comparison to other aircraft designs.
The best design tool if you are using this approach is a cupboard full
of plans for a range of aircraft.





"Brad Mallard" > wrote in message
...
> I am still in the design phase of my future plane. I would like to hear
> opinions on design software, and even buy software that someone doesn't
use
> anymore.
>
> Brad
>
>



"Brad Mallard" > wrote in message >...
> I am still in the design phase of my future plane. I would like to hear
> opinions on design software, and even buy software that someone doesn't use
> anymore.
>
> Brad

[Stealth Pilot]

On 10 Nov 2004 03:49:57 -0800, (smjmitchell)
wrote:

>Hmmmm ...
>

>
>The safest way for a homebuilder to design an airplane is to produce
>an evolutionary design that is based on an existing sound design and
>do most of the design work by comparison to other aircraft designs.
>The best design tool if you are using this approach is a cupboard full
>of plans for a range of aircraft.
>

Stephen isnt it? ...from Sydney?

agree with all the rest of your jitters re software.

in glossing over the situation above I think you lost some important
considerations.

you have to understand how the design you choose to evolve from has
handled the stress considerations and how it handles normal use.
some ball park figures for the stress values are also good.
you also need to really understand what occurred when you see
something pretty dumb in the design. why did he do that?
not everything in a design is worthy of being copied.
sometimes the dumb stuff is copied verbatim from earlier designs.:-)

it also helps to know the design's crash history.

a cupboard full of plans is a good start but fill it out by talking to
users of the designs. their experience is a good tempering input which
helps to see what is important and what is useless.

Stealth Pilot

[Brad Mallard]

I appreciate the concern, but I am a Metallurgical & Materials Engineer that
has made a living as a design engineer for the last 10 years. I have had all
the hair pulling classes, and analyze loads for a living.

I am still in the design phase of my plane, and I have an original design
that I have taken parts from a dozen different planes I have seen and been
in before along with a few details of my own. I was wanting the software to
plug in my variables and throw it in a wind tunnel for analysis. I am very
familiar with Autocad, but it doesn't have a wind tunnel. I can change my
plane right now, but once I start ordering material, I will be set on my
path. So, right now I want to maximize efficiency with the aerodynamics.

That's what I want the software for at this time.

Brad


"smjmitchell" > wrote in message
om...
> Hmmmm ...
>
> You shouldn't need any software to design a light airplane except for
> maybe an FEA program. However whether of not you need an FEA program
> depends on the type of structure you are designing. For instance if
> you are designing a tin airplane then there is little need for FEA
> (unless you really know what you are doing you will just get trash out
> because, for example, the FEA does not account for skin buckling). If
> you are designing a composite airplane then a FEA package is strongly
> recommended (but not essential) but it needs to laminated composite
> element.
>
> Generally you can calculate all the loads and do all the stressing
> manually using relatively simple techniques and only moderately
> advanced maths.
>
> I get nervous when amateur designers start asking about software as
> though it is an essential design tool. Usually this means that it is
> being used as a black box to fill in a fundamental lack of engineering
> knowledge with little understanding of what is actually going on
> inside the code or any ability to interprete what the results are
> telling them. That is dangerous. My suggestion is to invest your money
> in a copy of Bruhn's "Analysis and Design of Flight Vehicle
> Structures" and Stintons "Design of the Airplane" to name a couple of
> good texts instead of software. Read them and understand what they are
> saying and then decide if you still need software. If you can't
> understand the texts then you are not sufficiently qualified to start
> using design software ... period. In fact if you can't understand them
> then you should seriously consider buying a set of plans for an
> established design.
>
> Yeah I know .... half of the group is going to rubbish what I have
> just written but I have been around long enough to see how danagerous
> non professional designers are with software that they don't
> understand. (I earn a living designing and modifying all sorts of
> airplanes - certified and homebuilt).
>
> The safest way for a homebuilder to design an airplane is to produce
> an evolutionary design that is based on an existing sound design and
> do most of the design work by comparison to other aircraft designs.
> The best design tool if you are using this approach is a cupboard full
> of plans for a range of aircraft.
>
>
>
>
>
> "Brad Mallard" > wrote in message
> ...
> > I am still in the design phase of my future plane. I would like to hear
> > opinions on design software, and even buy software that someone doesn't
> use
> > anymore.
> >
> > Brad
> >
> >
>
>
>
> "Brad Mallard" > wrote in message
>...
> > I am still in the design phase of my future plane. I would like to hear
> > opinions on design software, and even buy software that someone doesn't
use
> > anymore.
> >
> > Brad

[Jason Marshall]

Brad Mallard wrote:
> I appreciate the concern, but I am a Metallurgical & Materials Engineer that
> has made a living as a design engineer for the last 10 years. I have had all
> the hair pulling classes, and analyze loads for a living.
>
> I am still in the design phase of my plane, and I have an original design
> that I have taken parts from a dozen different planes I have seen and been
> in before along with a few details of my own. I was wanting the software to
> plug in my variables and throw it in a wind tunnel for analysis. I am very
> familiar with Autocad, but it doesn't have a wind tunnel. I can change my
> plane right now, but once I start ordering material, I will be set on my
> path. So, right now I want to maximize efficiency with the aerodynamics.
>
> That's what I want the software for at this time.
>
> Brad
>
>
> "smjmitchell" > wrote in message
> om...
>
>>Hmmmm ...
>>
>>You shouldn't need any software to design a light airplane except for
>>maybe an FEA program. However whether of not you need an FEA program
>>depends on the type of structure you are designing. For instance if
>>you are designing a tin airplane then there is little need for FEA
>>(unless you really know what you are doing you will just get trash out
>>because, for example, the FEA does not account for skin buckling). If
>>you are designing a composite airplane then a FEA package is strongly
>>recommended (but not essential) but it needs to laminated composite
>>element.
>>
>>Generally you can calculate all the loads and do all the stressing
>>manually using relatively simple techniques and only moderately
>>advanced maths.
>>
>>I get nervous when amateur designers start asking about software as
>>though it is an essential design tool. Usually this means that it is
>>being used as a black box to fill in a fundamental lack of engineering
>>knowledge with little understanding of what is actually going on
>>inside the code or any ability to interprete what the results are
>>telling them. That is dangerous. My suggestion is to invest your money
>>in a copy of Bruhn's "Analysis and Design of Flight Vehicle
>>Structures" and Stintons "Design of the Airplane" to name a couple of
>>good texts instead of software. Read them and understand what they are
>>saying and then decide if you still need software. If you can't
>>understand the texts then you are not sufficiently qualified to start
>>using design software ... period. In fact if you can't understand them
>>then you should seriously consider buying a set of plans for an
>>established design.
>>
>>Yeah I know .... half of the group is going to rubbish what I have
>>just written but I have been around long enough to see how danagerous
>>non professional designers are with software that they don't
>>understand. (I earn a living designing and modifying all sorts of
>>airplanes - certified and homebuilt).
>>
>>The safest way for a homebuilder to design an airplane is to produce
>>an evolutionary design that is based on an existing sound design and
>>do most of the design work by comparison to other aircraft designs.
>>The best design tool if you are using this approach is a cupboard full
>>of plans for a range of aircraft.
>>
>>
>>
>>
>>
>>"Brad Mallard" > wrote in message
...
>>
>>>I am still in the design phase of my future plane. I would like to hear
>>>opinions on design software, and even buy software that someone doesn't
>>
>>use
>>
>>>anymore.
>>>
>>>Brad
>>>
>>>
>>
>>
>>
>>"Brad Mallard" > wrote in message
>
> >...
>
>>>I am still in the design phase of my future plane. I would like to hear
>>>opinions on design software, and even buy software that someone doesn't
>
> use
>
>>>anymore.
>>>
>>>Brad
>
>
>
If that's what you want, search for X-Plane. I hear it has aerodynamic
modeling capability. As a bonus, you can virtually fly your new design
around.

Jason

[Dude]

"Wind tunnels, truck tests and large scale RC - or a test
pilot that you didn't like anyway - are still needed."

Oh boy, I hear a sound coming our way.

[smjmitchell]

Yes care must be exercised in using other designs for comparison as
well. I would take some of the more reputable designs. There are
certainly some very poor designs that are quite popular and so the
popularity of the design is not a measure of the goodness of the
engineering. However I think if a homebuilder exercises with care and
takes appropriate advice on some details then they stand a much better
chance of designing a successful homebuilt using this method than by
trying to do the analysis from first principles.

OK WRT aerodynamic software. I use the CMARC/PSW code from Aerologic
(Peter Garrison). This is a linear panel code and quite suitable for
what you need. Not cheap but probably the entry level aerodynamic
software if you want build a complete 3D model of the airplane. It is
not that easy to use and will realistically take you a year or part
time effort to learn properly and do the analysis on your airplane.
The support provided by Peter and Dave Pinella is excellant and I
would recommend this program. However I would also buy a copy of Katz
"Low Speed Aerodynamics" to accompany this program to help you
understand the theory and limitations of panel methods.

A simpler approach may be a Vortex lattice code. This is a cheaper
option but only allows a 2D planar model of the configuration. I use
the NASA VLM code. You may be able to find a source of this on the web
for download.

If it is aifoils you are interested in then use XFOIL. You can find
that free on the web. I use that and with care it is reliable for most
cases. ONce again though I would urge you to analyse a lot of airfoils
with known characteristics and learn the pitfalls of the code before
you use it to develop new sections.

Unfortunately there is no cheap FEA software that is any good. Entry
level is realistically in the range of $4000 USD. There are cheaper
codes though. It really depends on what you need to do and the sorts
of structure that you want to analysis. Give me more details and I can
advise further. I have used (and routinely use) a range of FEA codes.

WRT the X-Pilot program. I am not familar with it but it sounds more
like a flight simulation package. There are a number of such programs
around. Any flight simulation package that is worth anything will
require the input of a set of aerodynamic derivates for the aircraft.
This is not something that an amateur designer will be capable of
calculating with any accuracy. I think I can fairly safely say that
this is the domain of the professional - even professional engineers
stuggle with this. However if you want to try then get yourself a copy
of the USAF Stability and COntrol DATCOM and the relevant ESDU data
sheets as a starting point.

OK final comment. When using any software it is important to spend a
lot of time running it on problems with known results before you use
it to design something new. This helps you understand how to run it,
the pitfalls and helps teach how to interprete the output data. I
cannot emphasis this enough.

[Jay]

Buy a new old stock (5.66) version of X-Plane off E-bay for $5.

You will be asked to enter a parasitic drag number but the forces
beyond that will be calculated for you depending on the flight
surfaces you create and the air foils you pick or design.

Regards



"Brad Mallard" > wrote in message >...
> I am still in the design phase of my future plane. I would like to hear
> opinions on design software, and even buy software that someone doesn't use
> anymore.
>
> Brad

[Dave Hyde]

Jay wrote...

> the forces beyond that will be calculated for you...
**********

Change "calculated" to "estimated" and you'll be
close to correct. If you're doing a non-derivative
design and want some hope at all of being close
in your estimate you better understand the limitations
and assumptions that went into XPlane specifically
and blade element theory in general.

Dave 'carpe datum' Hyde

[smjmitchell]

I agree there is no way that you can accurately simulate the behaviour of an
airplane without the use of derivatives. All the "real" simulators work this
way. Even a model based on simple linear derivatives will have many
limitations associated with it.


"Dave Hyde" > wrote in message
...
> Jay wrote...
>
> > the forces beyond that will be calculated for you...
> **********
>
> Change "calculated" to "estimated" and you'll be
> close to correct. If you're doing a non-derivative
> design and want some hope at all of being close
> in your estimate you better understand the limitations
> and assumptions that went into XPlane specifically
> and blade element theory in general.
>
> Dave 'carpe datum' Hyde
>
>
>
>

[Dave Hyde]

smjmitchell wrote...

> I agree there is no way that you can accurately simulate the behaviour of
an
> airplane without the use of derivatives.

That's not my point. My point is that if you're going to trust
the results of _any_ design and analysis software you better
understand what it can do and how it does it. Particularly if
your design steps outside the bounds of what's 'typical' and thus
might violate some of the assumptions that went into the software.
Kinda what you said early on, I think.

> All the "real" simulators work this way.

Quite a few of very good sims use the base parameter in something
like a table lookup, and avoid stability derivatives for anything
but linear analysis.

Dave 'Bode' Hyde

[Dave Hyde]

I wrote:

> If you're doing a non-derivative
> design and want some hope at all of being close...

smjmitchell ...

> I agree there is no way that you can accurately
> simulate the behaviour of an airplane without
> the use of derivatives.

If your statement above was in respose to my
"non-derivative" statement, I wasn't referring
to stability derivatives, I was referring to a design
that's derived from a prior design, i.e. evolutionary.
Accurate simulation without the use of stability derivatives
is easy if you have estimated aero data. Dynamic derivatives
make it easier, but often times damping derivative estimates
are so inaccurate you might as well not use them anyway.

But having said all this, a simulation of a lightplane-envelope-type
airplane is not required before building one. Personally
I'd spend the time trying to get good aero estimates
or hard data (truck testing, R/C, etc) than in tweaking a
sim...and you need the hard data to do real tweaking anyway.

For home-design type stuff I use a CAD package(*) - designCAD right
now, but I've been know to use AutoCAD. Aero analysis is back-of-the
envelope. Structures so far is TLAR, but before I cut metal I
will have a professional FEA done by a non-advocate. I haven't
gotten to the engines yet :-)

The stuff I use at work is a little more detailed and somewhat
more accurate (and far more specialized), but the results are
usually pretty close to the home-done level stuff, which is
where we start anyway.

(*) and I barely scratch the surface of its capability.

Dave 'engineer, professional and amateur' Hyde

[smjmitchell]

> But having said all this, a simulation of a lightplane-envelope-type
> airplane is not required before building one. Personally
> I'd spend the time trying to get good aero estimates
> or hard data (truck testing, R/C, etc) than in tweaking a
> sim...and you need the hard data to do real tweaking anyway.

I agree ... there is no point in trying to simulate the flight
characteristics of a light airplane via a simulator. You gotta make a
choice. Do you want to be a scientist and analyse the thing to death or do
you want to build and fly it in a reasonable time. Most light aircraft are
evolutionary in design and that together with conventional design practises
(there are huge amounts of data out there in the public domain) eliminates
the need for all this advanced analysis. After all the vast majority of the
certified light planes currently flying were designed on drawing boards,
using simple analysis methods and emphirical data without CAD, panel codes
and FEA. Also all these advanced tools have NOT really resulted in any
significant advances in the state of light plane performance, safety,
styling, cost etc. You simply don't need all this stuff - well OK some of it
is nice to have - but lets be honest you can do the job without it and
really for a amateur designer it would be better to forget it. By the time
you learn the software, do the analysis, puzzle over the results, redesign
etc and then build the thing you will be an old man. Better just to dust off
the old drawing board and get on with the job using simple conservative
calculations and comparative design methods.


> Quite a few of very good sims use the base parameter in something
> like a table lookup, and avoid stability derivatives for anything
> but linear analysis

True but that is doing the same job as a derivative ... it is providing a
relationship between some state of the airplane (i.e. alpha, beta, control
deflections etc) and the forces acting on it (X,Y,Z,L,M,N). A derivative is
linearised where as the look up table approach can include the
nonlinearities.