The Art of the Helicopter John Watkinson - Karatunov.net

Fig. 7.49 In the Lockheed AMCS, the gyro is caused to precess by springs as before, but the gyro motion
controls actuators that drive the swashplate. This prevents control forces disturbing the gyro.
the same level of training as his full-size counterpart. Beginners often fit extra weights to
the flybar to reduce the following rate even further. The flybar also allows the use of inexpensive
and lightweight wooden blades whose following rate alone would be too fast.
The Bell system was difficult to replicate in miniature because of the hydraulic
dampers, and the pure Hiller system was found to produce a very low following rate
in models. As a result a hybrid system combining both and aptly called the Bell-Hiller
system evolved. This uses the cyclic mixing of the Bell bar, as well as the Hiller paddles
and control rotor feathering. There are thus three rods coming from the swashplate: one
to each of the flybar mixer arms, and one to feather the control rotor. This arrangement
gives a good balance between stability and response, although the number of
links involved makes it look like a dog’s dinner. The falling cost of the piezo-electric
gyroscope and its minute size mean that the flybar can now be eliminated in the model
helicopter.
7.27 Autopilots and AFCS
Autopilots vary in complexity, but the general goal is that the pilot is relieved of the
need to maintain some parameter of the flight. In a helicopter it is possible to begin
with stabilization of the roll axis only, and then add extra features. Automatic control
of the tail rotor allows balanced turns and flight at minimum drag. Control of the pitch
axis allows the airspeed to be held, and altitude can be held with collective control.
Some systems can achieve a stable hover in a fixed location without pilot intervention.
Control 313