How to From Three-Views To Plans
Running the numbeRs
Here is how I go about it; we’ll use my current project, a
Cessna 150, for some examples. The full-size Cessna
150 has a 33-foot 2-inch wingspan. Convert the span to
inches by multiplying the wingspan by 12. This gives you
a 398-inch span. To determine the scale of your model
airplane, divide the 398-inch span by the desired 80-inch
model span. You’ll come up with a figure of 4.975, which is
very close to a factor of 5, or 1/5 scale. This size gives us a
79.6-inch span for a 1/5-scale model, and using the 4.975
factor, the model is exactly 80 inches in span. If you want
a model with an 81-inch span (my ultimate choice for
scale size), the factor is 4.913. This turns out to be a goodsize model. Three-inch nose-gear wheels and 3 1/2-inch
main wheels are very close to scale. A 2 1/2-inch spinner
and 1/5-scale pilot bust also fit nicely.
From here, I enlarged my small three-view drawing to
a 15-inch wingspan. When we divide 81 by 15, we get a
multiplier factor of 5. 4 to draw my new plans.
Here’s where a good decimal scale is required. For the
math, simply set up your calculator with a 5. 4 constant
and multiply every dimension you take from the 15-inch-
span three-view drawing by 5. 4 and transfer it to the
full-size plan. All the dimensions are multiplied by your
multiplier except for the angles (these won’t change
regardless of scale or size).
When working with angles, a good number to know is
0.0175 inch. This is the 1-degree height, or rise, of a 1-inch
line. The Cessna root rib incidence is indicated as 1.5
degrees positive. So we take the chord length, which is
13. 5 inches, and multiply by 0.0175. This gives us 0.23625.
Multiply this by 1.5 degrees and we get 0.354 inch, or just
under 3/8 inch for the incidence. This is very handy when
you know an angle, like dihedral, and have to figure out the
dimension at the wingtip.
If your three-view drawing does not have a fuselage
centerline, add one to it. The prop shaft at the nose is
usually a good location. Measure down from the front of the
engine shaft to the bottom edge of the drawing. Assuming
that the fuselage was drawn parallel to the bottom edge,
use this dimension at the tail and draw the line accordingly.
The centerline is usually indicated on the fuselage cross-sections as well. Measure from the centerline to the top
and bottom of the cross-section outline, multiply these
dimensions by your multiplier factor of 5. 4, and transfer
the results to your model drawing to determine the size of
the full-size cross-section. The top view of the fuselage
is treated in the same way, measuring from the centerline
outboard to each side.
Drawing all the formers as viewed from the tail of the airplane is a
good way to check for any mistakes.
All of Nick’s airplane designs
use this basic fuselage crutch
to keep the formers in proper
alignment and position.
Here the fuselage is beginning to take shape. Any misalignments that arise at this stage are corrected
on the plans.
This shows the fuselage with the sheeting being installed.