The Art of the Helicopter John Watkinson - Karatunov.net

Other types of rotorcraft 367
the yaw control was fragile. The provision of a large fin area is a problem in coaxial
helicopters and synchropters as Figure 9.18 shows. There is a wedge of space in which
the fins can exist. The top of the wedge is defined by the rearmost flapping of the rotors
and the bottom of the wedge is defined by where the ground will be in a flared landing.
The difficulty is that the further back the fin area is, the more effective it is. However,
the further back the fin, the smaller it has to be. The only solution is to use a number of
parallel fins. The early Huskys had a habit of knocking the tops off their fins. This was
solved with a redesign, although expedience dictated making the top and bottom ends
of the fins from glass fibre that would disintegrate in any extreme manoeuvre without
causing any further damage.
Another difficulty with fins in helicopters is the wide range of directions the airflow
can come from. This makes it hard to maintain the optimum aspect ratio of the fin.
The Kaman Husky solved this problem very nicely by mounting the fins on a floating
elevator that would align itself with the airflow. Figure 9.19 shows that the fins were
then always correctly oriented.
The Husky had very low disc loading giving it excellent lifting ability and high altitude
performance. In 1961 a Husky reached almost 33 000 feet! The torque cancelling of
the synchropter meant that pilot workload was quite moderate and the lack of a tail
rotor meant it could land in difficult terrain. The Husky distinguished itself as a rescue
helicopter, particularly where crashed aircraft had caught fire. The Husky would hover
overhead, using the downwash to blow flames clear of the fire fighters and victims.
The Husky was superseded by conventional turbine helicopters that were faster, but
a number of surplus machines found their way into logging and aerial work where
speed was not of the essence. Their success in this niche led Kaman to produce the
Fig. 9.18 Finding enough fin area is difficult in a synchropter.
Fig. 9.19 The fins of the Husky are mounted on a floating tail plane so that they always align with airflow to
offer their best aspect ratio.