Conference vmszoo::rc

  Hi 
  
  The scratch aids from Frank are pretty good. I received a hardcopy
  and an .exe file, a program who calculates model parameters.
  
  My opinion about scratch aids like this: A well base to ensure,
  that the design will not be completely wrong. But dont take the
  output as absolute, exact parameters. As example take in the
  hardcopy the table wich recommends engine sizes for given
  wing-areas. Of course, dates like this are depending on:
  
  	- Engine power (4 or 2 stroke, layout etc)
  	- Propellor
  	- models weight
  	- wingload
  	- expected performance
  	  and so on
  
  Re.-1
  
  Tom, I agree with you, it is interesting to see whats going on
  and who is active.
  
  Franz :-)

Tom, I wrote that program.  The source code was in Pascal.  When I
deleted my files out in California for the move here, I nuked the
program too, so I would be forced to write a new one from scratch; I
wanted to include some other features and was afraid that I would
get lazy, if you know what I mean.  

The program is based on several formulas.  One source I used was a
text on free flight rubber models by Wm. McCombs.  This gave some
simple methods for calculating CG and for getting proportions.  The
main source for proportions was the series of articles by Chuck
Cunningham in RCM.  These proportions are basically the same as in
the mailer that Frank sent out (Frank--I got it today); and these
are the time-honored proportions used by most designers.  The thing
I don't like about them is that they dictate the tail arm, defined
in my program as the distance from the leading edge of the wing to
the leading edge of the tail; but effectively the same distance as
defined in the mailer as between the trailing edges of those two
surfaces.  This dictate is what allows them to specify that the
tail, for instance is 20-22 percent of the wing area, and so forth.
If you tried to go out of these proportions, you would throw off the
CG.

In my program, I paid lip service to those proportions by using them
to determine the flyability, but I calculated the CG from scratch
using the formulas given by Ron Van Putte in Model Aviation a couple
of years ago.  These were in an article on Canard design.  The
formulas are tricky, but are duck soup for the computer.  Thus, you
can fudge the tail area as you wish, and the program will not get
mad at you.

Other information came from some diverse sources.  The determination
of engine size was from a terrible book on model design; so bad I
don't remember the name... and the calculation of stall speed vs CL
was taken from Andy Lennon's article in MAN a couple of years ago.
It is just a tranposition of the basic CL formula.  I thought it
would be nice so you could take the CL profile and go out to find a
wing with a similar curve.   

A nearly identical program, using nearly identical formulas, but
written in BASIC appeared in MA last year.  I said Humbug.  Anyway,
I wrote it more as an exercise in Pascal than anything else, since I
prefer to do my designing with the calculator.  The program merely
checks my button pushing.  Sorry about the way it rips out its data;
it takes a fast control S to get it all.  Now I know how to do file
operations, and next version will write it out nice and tidy to a file.

        I have a collection of Fortran-IV programs that I wrote for model
        rocket use on my home system available on the net. To the best of
        my knowledge, all should be in standard enough Fortran to run with
        any Fortran complier. If not, please let me know. All can be found
        in CRVAX1::DISK$RGK:[PDT.ROCKETS]. Feel free to use any of them,
        but remember that I own the code, so don't try and sell them! A
        few of them might be of interest to model airplane builders: 
        
        BALSA.FOR - generates a balsa density chart - useful for selecting
        the right type of balsa fro the right application. I take a copy
        of this and a small scale with any time I go shopping for balsa. 
        
        CHARGE.FOR - to design nicad and lead acid battery chargers. 
        
        NEUTRA.FOR - computes the stability of a plane. I use it for
        designing model rocket powered gliders, but it should work for
        everything from hand launched gliders thru sailplanes. The default
        stability factor of -.2 is good for my models and HLGs, but may be
        a bit big for RC models. You might try something like -.1 or so. 
        
        Most of my Fortran programs use a screen I/O package that can be
        found in QUERY.FOR and LOG.FOR. 

        CANARD.BAS - this program was lifted out of a Model Avaition a
        couple years back, and does similar to NEUTRA, but for canard
        designs. Note that NEUTRA will handle canards fine, if you give it
        a negative moment arm! 
        
        If anyone has typed up any of the other programs that have
        appeared in MA (or elsewhere) over the years, I'd like copies.
        I'll make any contributions available in this same directory. 

I forgot to add that my design program is available on 
CLOSUS::[TAVARES]MODEL.EXE.  The program that I mentioned in my last
note, that does essentially the same thing as mine, would probably
be better to use, however, because its in BASIC and its code is
readily available.

Those who wish a copy of the page with the Van Putte equations can
send me a request at PYONS::TAVARES.  Please include your correct
mailstop.  This offer is good for as long as I'm on the system.

The equations are used both for canard design (the page comes from
the same article that Bob's canard design program comes from), and
with a simple change, for conventional model design.   My program
covers only the conventional case.

Oops! Correct file specificatin is:

CLOSUS::WRKD6$:[TAVARES]MODEL.EXE

They buy me a book and send me to school and that's what they 
get...

    I'm new to design- anyone wish to comment?
    

The Reynolds number is really a measure of the efficiency of a lifting section.
As I recall it relates to the wing cord, aspect ratio, air speed, and to make
things interesting they through in the size of a molecule of air. 

It is said to be a really efficient wing the number must exceed 1,000,000. Few
models with with the exception of pylon racers can actually reach this number,
I believe a 1:1 scale 747 is around 12,000,000. 

John.

        Reynolds Number: The product of the velocity, V, a characteristic
        length, l, and the density of a fluid, p, divided by the
        viscosity, u, and called R or Re. 

		R = V l p / u = V l / v

        where v is the kinetic viscosity and equal to u / p. 

        So much for the textbook definition. What IS a Reynolds Number? It
        is a non-dimensional ratio for comparing similar aerodynamic
        conditions. Similar shaped wings will behave the same at the same
        Reynolds Number. It really has nothing to do with the "efficiency"
        of a wing. The length in question is the wing chord. 

        For example, say you wanted to wind tunnel test wing sections for
        a B52. Your wind tunnel isn't big enough to hold a WHOLE B52 wing.
        So you build a model of the wing, in 1/10 scale. You can't scale
        the air itself down as well, so you have to adjust one or more of
        the other parameters in the equation so that the Renolds number
        remains unchanged. You can either increase the velocity by a
        factor of 10, or decrease the kinetic viscosity by the same factor
        of 10. 

        The Reynolds Number also gives some indication of the type of flow
        over an airfoil. At under 10K, flow is usually laminar. Between
        10K and 100K it transitions, and above 100K it is usually
        turbulent. Note also that Reynolds Number is not exclusive to air;
        the relation holds for any fluid; be it air, water, oil, or
        chicken soup. The number quoted in .-1 sounds about right for big
        jets; supertamkers have Renolds Numbers on the order of several
        Sagans. 

        That's billions and billions to non-Cosmos watchers!