position, which will cause a lot of vibration
in the rotor head. If the bolt is not tightened
enough, on the other hand, the blade will
move too much in lead and lag during
flight, again causing unwanted vibration.
A technique that I use is to tighten the
bolt just enough to keep the rotor blade
in position as the helicopter is tilted
The third movement allows the rotor
blades to flap or move in the vertical
position. This can be seen on full-scale
helicopters, where the rotor disc is not
flat but shaped more like a bowl, with the
tips of the rotor blades well above the
top of the main shaft. This coning angle
acts much the same as the dihedral in a
fixed-wing airplane to increase stability,
with the added benefit of also being a
shock absorber under turbulent flight
conditions. Many of our early helicopters
had this flapping movement built into
the rotor head. With the more aggressive
maneuvering that has taken over almost
every flying field, however, stability
has given way to improved aerobatic
performance. The result is that modern
aerobatic rotor heads have completely
eliminated this flapping effect.
The SwaShpla Te
The overall movement of the rotor head is
controlled by the swashplate, which has
an inner and outer ring. The outer ring is
stationary and is connected to the servos,
while the inner ring rotates with the rotor
head and is connected to the blade grips.
It’s important, therefore, for this inner ring
to maintain its relative position with the
rotor head while the helicopter is in flight.
This has traditionally been accomplished
by installing an adjustable follower on the
main shaft, which is also connected to the
inner ring of the swashplate. When using
a follower attached to the main shaft, the
timing of the rotor head can be adjusted
to suit the flying style of the pilot. As an
example, the follower is normally set up
so that the blade grips are 90 degrees
to the ball link on the inner swashplate.
By adjusting the follower away from this
90-degree position, however, the timing
of the rotor head can be changed so that
it reacts slightly sooner—or later—to
Many of our early
helicopters had this
built into the rotor
head. Modern aerobatic
rotor heads have
this flapping effect.
Flapping composite blade grips have given way to
the rigid, all-metal grip shown here. Thin spacers
must be used for a snug fit of the blade to the grip.
Part of the spacer is shown below the rotor blade.
To keep the inner portion of the swashplate in time with the head, the follower is built into the blade-grip
connection to the swashplate. Note the massive pushrod from the blade grip to the swashplate.
The swashplate converts vertical input from the servos to rotating cyclic- and collective-pitch control of the
rotor blades. Note the direct control from the servos, eliminating the need for bellcranks and extra pushrods.