Aviation safety investigations & reports

Ligeti Stratos, 1 km SE Penfield VIC, 22 September 1987

Investigation number:
198701462
Status: Completed
Investigation completed

Summary

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This aircraft was intended to be the production version of the "Stratos" aircraft. The prototype version had successfully flown some 340 hours. The production model incorporated significant changes made by the designer/pilot. These changes included the removal of the dihedral from the main wing and the use of full span elevators on the canard wing and full span ailerons on the main wing. The engine mounting was lowered such that the ducted propeller was totally below the main wing and the lower part of the propeller duct was extended well forward to form a "channel or strake". The main purpose of the "channel wing" was an attempt by the designer to lower the stall speed of the aircraft to 30 knots and to reduce both landing and takeoff speeds and distances. As far as the investigation could determine, the effect of these modifications had not been checked by wind tunnel or other methods prior to this flight. On the day of the accident the pilot and his assistants had worked at the factory preparing the aircraft for testing. The preparation included a determination of the centre of gravity, although no record was kept of these calculations. Following these preparations the aircraft was loaded onto a trailer and taken to Penfield. The weather conditions at the time were fine, with light winds. The pilot subsequently carried out a series of taxying tests, to establish the optimum position for the control column. He then conducted a take-off, and operated in the local area for about 17 minutes. Witnesses reported that the aircraft then carried out a very slow pass over the aerodrome at a height of between 400 and 500 feet above ground level. About one minute later it was seen to turn back towards the strip. However, shortly after the turn was completed, control of the aircraft was evidently lost. It is uncertain whether the aircraft suddenly pitched nose up or nose down, but all witnesses agreed that it then fell vertically while the nose swung in a pendulous motion. The aircraft struck the ground in an inverted attitude with little or no horizontal speed. An inspection of the aircraft found that all airframe components were essentially intact and there was no indication of any airframe or control failure prior to ground impact. The engine was test run and strip inspected and no fault could be found. No aerodynamic testing was carried out on the airframe to determine the likely effect on performance of the various modifications made to this aircraft. However, given that the prototype appeared to suffer no adverse flying characteristics, it is possible that the modifications incorporated in the new aircraft had an adverse effect on the stall characteristics. Analysis of the modifications indicates that the most significant effect on the stall characteristics would have resulted from use of full span elevators on the canard wing. The use of full span elevators results in a relatively uniform loading of the canard as the elevator is deflected approaching the stall. The result is that the canard would be developing more lift, compared to the same wing without full span elevators, before the wing stalled and the stall would be sharper. Because the main wing is still producing lift at this stage the nose down pitch following the stall of the canard would be aggravated. It is considered likely that the accident sequence was initiated by a full canard stall followed by a rapid nose down pitch. Also, the altitude at which the flight was conducted would not have allowed the pilot time to make the necessary corrective control imputs following the stall before the aircraft impacted the ground.

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General details
Date: 22 September 1987   Investigation status: Completed  
Time: 1750    
Location: 1 km SE Penfield    
State: Victoria   Occurrence type: Loss of control  
Release date: 17 June 1988   Occurrence category: Accident  
Report status: Final   Highest injury level: Fatal  

Aircraft details

Aircraft details
Aircraft manufacturer Ligeti Aero-Nautical Pty Ltd  
Aircraft model Ligeti Stratos  
Aircraft registration Not registered  
Serial number N/A  
Type of operation Sports Aviation  
Damage to aircraft Destroyed  
Departure point Penfield VIC  
Departure time 1730  
Destination Penfield VIC  
Last update 09 May 2016