MAKE Terry Kilby, Getting Started

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2/Airframes
What Is an Airframe?
The airframe is the main body of the aircraft. All other compo-
nents—propellers, batteries, computer, etc.—are mounted to
the airframe. Airframes can vary greatly in size and complexity.
Some of the airframes we built when we first got interested in
flying were very simple designs sketched on the back of a nap-
kin, and cut from pressboard with a jigsaw. Today, we use
computer-aided design (CAD) software to design our frames
before cutting them out with a computerized numerical control
(CNC) machine. We will touch on many of the popular design
types in this chapter, but first let’s take a quick look at how
these actually fly.
Thrust Vectoring
One common trait you will see with all of these airframes is that
they use both clockwise and counterclockwise propellers. This
is the foundation that allows multirotors to move in all direc-
tions. Every other motor spins in a different direction from the
one directly next to it, allowing each motor to be balanced by its
opposite motor. As a result, nearly all UAVs feature an even
numbers of propellers (with one exception that we will discuss
in the next section). On a quadcopter, for example, the NW and
SE motors might spin clockwise while the NE and SW motors
spin counter-clockwise (speaking in terms of compass bear-
ings). By configuring the aircraft this way, all we have to do to
move the quadcopter in any direction, including yaw, is change
the speed of a certain combination of motors. For example, to
yaw the aircraft in a clockwise direction, we would increase the
speed of the NW and SE motors. The “push” of one motor and
the “pull” of the other will turn the aircraft in the direction we
want.
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