Excel For Calcs?

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HeliDev

Well-Known Member
Joined
Jul 7, 2003
Messages
108
Im in a heavy math part of my design right now, and Im finding doing all the calc by hand very time consuming. What Im after is a method of just being able input the data and change teh variables as required.
Ive had amthcad recomended to me, hawever this is far beyond my price range at $3000AUD per copy.
Any one set up excel for this type of thing?
Any help appreciated.
 

Ivan

Active Member
Joined
Dec 8, 2003
Messages
38
Location
Manitoba, Canada
Hi Spaced,

I'm in the same boat, i.e. I can't afford software that would be really useful. I use Excel for all my computer number crunching because it's free, I already have it, and it's so quick to set up.

Of course, it has its limitations. You can't just take an expression in formula form and evaluate it over a range without making a big table of values. It can't perform any manipulation of equations (like integration or differentiation). Fortunately, most of those limitations have a simple work around--do the higher level math by hand, and then feed the resulting expressions into your Excel cell. Not a big issue, as I generally like to work through everything at least once by hand before trusting a computer with iterative calculations anyway.

My biggest (and so far unsolved) problem with Excel is with double-checking my work. It is a huge undertaking to proofread anything, as the formulae refer only to the cell number, not its contents nor its variable label. So, to verify an equation, I have to scroll back and forth to figure out what variables are being referenced, while writing it all down on paper to keep track. I then check my paper representation of the cell formula against my notes to ensure that the cell is doing what I want it to do. It's a terrible method of error-trapping, and only gets more annoying as your spreadsheets get bigger.

I've started writing a bit of Visual Basic code in an effort to replace some of my Excel work. It's pretty, and much easier to debug the math, but now I have a bunch code to debug! And the whole point of this has been to design a plane to build, not a giant coding exercise.

So, long story short--Excel ain't perfect, but it's good enough for me.:D

Regards
 

orion

R.I.P.
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
AAAAAH, reminds me of the good ol' days. When I sterted in this business the only tools I used was a design methodology that I developed and of course the basic hand tools, the most advanced of which was a hand calculator. I did have my computer (the old original Mac) which unfortunately, without really functional software, was about as useful as the door-stop, which it later served as anyway.

Even once I had the steps outlined and formulated, so I could not only do point designs but some level of refinement also, it generally took on the order of one to two weeks for a single iteration, and at least several days for a bit of secondary optimization.

I did finally bite the proverbial bullet and got MathCAD, and then spent about two or three months programming in the procedures. I never liked Excel, mainly for the reasons described above. Over the years I wrote four seperate programs, as well as about three versions of each as the complexity evolved. As of late last year though, I finally sat down long enough to combine all into one, all encompassing code. It now covers about fifty or sixty pages of tiny font equations so debugging or modifications are sort of a pain, but it works the way I like, so I'm not complaining.

I also used a bit of curve matching software so as to be able to put in plotted data, so the program now runs with only the basic variable inputs(about a dozen or two)), and calculates virtually everything else by itself.

MathCAD is great but if all you're working on is just one airplane of your own design, I think you're right, it is a tad expensive.

There are however several Excel programs publically available that are capable of doing at least the basic number crunching. I found that they do have limited applicability but for most homebuilt stuff, they seem to at least get you in the ballpark. I don't have the links at this computer but I'm sure someone else on this board may have the source sites that you can go to.
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,217
Location
Saline Michigan
I have spreadsheets for weight and balance (predicting and tracking progress); trim (wing and tail sizing, control authority, etc, and linked to w&b sheet); aero loadings of the wing/tail/control surface/fuselage (wing and tail sizing); composite structure analysis through failure criteria check by lamina (iterations for spars and skins); and some others...

Excel works great. If you are really up to designing the aero and structural stuff, you can write these easily. No, I am not porting them to anyone, but talk to me nice and I can run checks of your calcs for you.

Knock yourself out man!

Billski
 

Largeprime

Well-Known Member
Joined
Feb 18, 2004
Messages
60
I have done a lot of work in excel. From complex probablistic financial projections to engineering work.
Not a great soluition to run a buisness on, but fine for a one of.

If you can do it by hand, then you can in excel.
If you are not comfortable doing it I will help.
PM me
 
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