Mathematics for Today's Modeler

Modeling these days seems to be getting more
technical, even though the techniques used to build
the models offered here are exactly the same as
they were over 50 years ago when the true art of
modeling was in full swing. For that reason, many
are confused about how to figure out the "why's
and where-for's" involved.

   So what I'll do is list a few of the simple equations
I use all the time to set up my models and to
estimate the kind of performance the model will
deliver. All you have to do to make them work on
your specific model is plug in the numbers. So, grab
your calculator and let's get started:

1- Watts:        watts = volts X amps

2- Power Loading:     
watts divided by flying weight
(in lb.) = watts per lb. To convert the flying weight of your
model in ounces to pounds, simply divide the weight (in ounces)
by 16

3- Wing Area: wing span (in inches) X wing chord (in
inches) =
wing area (in sq. in.) divided by 144 = wing
(in sq. ft.)

4- Wing Loading:       
flying weight (in oz.) divided by
wing area (in sq. ft.) = wing loading (in oz. / sq. ft.)  

5- Stall Speed:    
wing loading divided by 4 X 3.47 =
stall speed        
This is just a rule of thumb, but it will get you
in the ball park as to knowing how fast your model will land:  

6- Propeller Pitch Speed: rpm X pitch (in inches)
divided by
1056 = flying speed  (in MPH)    This will
give you a ball park idea of how fast your model will fly at full
throttle with a given prop and battery combination.

7- Scale:   full scale wing span (in inches) divided by
the model's wing span (in inches) = scale

The basic formulas listed here should be helpful in
getting you heading in the right direction. The speed
related items are just a rule of thumb, but being
precise really isn't necessary since we can't know
the exact speeds we're flying anyway.

And finally, to properly set up a model's power
system for best all around performance for a
Light-Weight Park-Flyer type scale model, a good
rule of thumb for powering your model is that the
calculated top speed using formula #6 should be
roughly 4 times the stall speed obtained using
formula #5.