Loss of control Wasp Air Buggy II, 20 km north-east of Kingston, South Australia, on 3 December 1989

Circumstances:

The pilot had purchased the aircraft some time prior to the accident and did not fly it until he had completed a full training course on gyroplanes of some 7-8 hours. Since completing the training, the pilot had flown about ten hours on type, mainly on windmill inspections on the property. The witnesses to the accident reported that the pilot had taken off on a windmill inspection and they had seen him return about 15 minutes later. As they watched from about one kilometre away, they saw the pilot approach the landing area at about 400 feet above ground level and commence a turn. The aircraft was then seen to nose over and continue in a dive until it struck the ground and exploded on impact. The South Australia Rotor Club was co-opted to assist with the investigation and through their assistance it was learned that this type of gyroplane was fitted with a large pilot cabin that extended some two feet in front of the rudder pedals. Other pilots have reported that this fitment induced severe pitch down in flight and/or severe yawing due to the imbalance of the air loads on the cabin compared to the correctional force available from the moments of an unmodified empennage. In effect, the anti-yaw moment from the rudder and fin is insufficient and the aircraft is without an effective horizontal stabiliser for effective anti-pitch control. A reduction of power at the onset of any perceived instability would be instinctive and would also reduce a pilot's ability to control the yaw due to the reduced propeller wash over the rudder and fin. The conclusions drawn from the investigation were that the pilot experienced a pitch down and/or yaw in flight that resulted in the imposition of negative g forces. These forces caused the retreating main rotor blades to dip and strike the fin and rudder. At the same time, the propeller would have disintegrated on contact with the rotor blades as they dipped into its arc. The blade strikes were such as to stop the main rotor and put the aircraft beyond the control of the pilot.

Significant Factors:

The following factors were considered relevant to the development of the accident:

1. Faulty design. The aircraft was unstable when fitted with a large forward cabin.

2. An uncommanded DEPARTURE from controlled flight caused the main rotor blades to strike the propeller and empennage.

3. The rotor blades were stopped in flight rendering the aircraft uncontrollable.

Recommendations:

1. That the Civil Aviation Authority, in conjunction with the Australian Sports Rotorcraft Association (ASRA), advise all gyroplane operators of the design instability of the Wasp Air Buggy II when fitted with a large cabin.

2. That the CAA, in conjunction with the ASRA, devise and/or approve a suitable modification to the empennage of gyroplanes in conjunction with the fitment of large cabins.

3. That the short period oscillation of gyroplanes operated in Australia be examined. i.e. fit or replace the horizontal tailplane. A number of accidents in Australia can be attributed to DEPARTURE from controlled flight as a result of excessive pitching, (porpoising).