Here’s a look at the tiling and scaling functions in Adobe Acrobat Pro.
On the table, the new numbers match
standard wood thicknesses of 3/32 and
3/16 respectively. Perfect—that makes this
1.5x jump a simple conversion.
So what happens if we want to scale
the little 109 to some oddball size like
1. 79? Let’s do the math:
1/16 x 1. 79 = .063 x 1. 79 = . 113 and 1/8
x 1. 79 = . 125 x 1. 79 = .224
When we check our table, we see that
the wood that we need isn’t found on the
chart of standard wood thicknesses. Are
we doomed? Not really. We have a couple
of options to keep us in the game.
The first is to pick the closest things
on the list and keep going. The most
common problem to result from the
wood sizes being off is that any notches
in the design will be either too tight or
too loose. Tight notches can be opened
up with a file. Loose notches might be
filled with shim stock.
Alternatively, we could adjust the size
of the wood itself. This is most practical
when making strip wood for stringers
or the parts for a built-up tail. By using
a stripping tool, we can cut the strips to
any size we need. If necessary, we can use
a sanding bar to sand oversize stock down
to a custom size.
So even in the case where we convert
the plans by a strange ratio, it will still
be buildable, although it might take
slightly more work to get the parts to
How Far Can We Go?
As a rough guideline, the size of most
plans can be doubled or cut in half and
still made to work. The limiting factor
is whether the structure will still be
effective at the new size.
I’ll illustrate my point by driving this
to an extreme. Let’s consider scaling the
Stahl Free Flight (FF) Wildcat up to a
1/4-scale monster. We’ll do a little more
math to figure out the scaling factor:
• Stahl Wildcat wingspan = 19 inches
• 1/4-scale wingspan = 38 feet (the ful
l-scale wingspan) / 4 = 9. 5 feet.
• Convert 1/4 wingspan to inches = 9. 5
feet 12 = 114 inches.
• Scale factor = 114 inches / 19 inches
The fuselage of the original Stahl
design uses eight 1/16-inch formers spaced
roughly 2 inches apart. These formers
are tied together by six 1/16-inch square
stringers that appear to be reasonably
close together in the model.
After multiplying these values by 6.0,
our upscaled Wildcat will be built with
chunky 3/8-inch thick formers spaced
more than a foot apart. A better plan
would be to use a greater number of
As for the stringers, the upscaled
version now has bulky 3/8-inch square
stringers that are spaced inches apart. The
structure that worked well as a tiny FF
model now looks like a loosely associated
collection of lumber.
Another complication comes when
fitting motors and other hardware.
Builders who choose to make large-scale
changes on a set of plans need to consider
whether the framework is designed to
handle the loads it will see as a larger or
smaller model. Modifications to motor
mounts, battery trays, etc., could also be
These concerns aren’t meant to rule
out radical adjustments to existing plans.
They are simply offered to show that
builders who successfully take on these
projects do more than print a bigger piece
of paper and buy thicker wood.
Winding It Up
I began this conversation by talking
about how the number of plans available
to builders is nearly limitless. Now that
we can change the scale at will, our
options are truly infinite. It’s a great
time to be a builder
AMA Plans Service
(800) 435-9262, ext. 507
27 Model Aviation JULY 2017 www.ModelAviation.com sponsored by HOW-TO issue