FOUR AND FIVE POINT GLIDER SEAT HARNESS STATIC AND DYNAMIC TESTS

Abstract

Previous studies on aircraft seat harness have primarily dealt with an upright pilot seating position, and with a flat seat pan. The present paper deals with the semi-recumbent seating position found in modem gliders, with a steeply raked thigh contact area as the front part of the seat pan.

The conclusion was reached in Germany that the 5th strap of a glider seat harness passing between the legs of a male pilot would cause injury in the crotch region in the event of an accident. Dipl.Ing. Martin Sperber of TuV Rheinland, Cologne, Germany, carried out an experimental study, following which he designed a glider seat pan and 4 point harness anchorage points that were stated to be as effective as a 5 point harness.

A German glider manufacturer, DG Flugzeugbau, has ceased fitting 5 point harness in their gliders, and has also ceased fitting a hard point for retro-fitting a 5th strap. This was on the grounds of the presumed risk of legal liability for injury caused by a fifth strap. This decision caused concern in the United Kingdom, leading to the undertaking of the present study.

The study was carried out using both 4 point and 5 point glider seat hamess approaches. The tests were carried out with the harness tight and with the harness slack. Three test conditions were studied: 1) The angle of the lap strap relative to the vertical axis was noted when pilot dummies of three different sizes were placed in the seat. It was concluded that for very small and very large pilots, it would be a benefit if the lap strap anchorage points were moved forward. The forward angle of the lap strap may provide an explanation for the development of slackin the lap strap under certain conditions. 2) The effect of negative-g force was simulated by inverting the test rig and pilot dummy. The separation of the buttocks of the dummy from the horizontal portion of the seat pan was measured by a probe, and also by overlaying hansparencies from a video film. A 5 point harness was more effective at reducing this separation than a 4 point harness. The separation was most marked with a slack 4 point harness - this could lead to the pilot loosing control of the glider. A test flight in a DG 300 was carried out. 3) The effect of a vertical impact in the longitudinal axis of the glider fuselage (the X axis) was simulated on a decelerator test track, with an impact velocity of 9-10 metres/sec. and at L5-L69. High speed video was used to record the effect of the impact from a side view and from a front view. Motion analysis was carried out on the film, and a transparency overlay study was carried out. The loads in the hamess straps and in the crotch area were measured. With a 5 point harness, both tight and slack, the lap straps and the QRF remained in the conect position over the pelvic bones, with no risk of injury to the internal abdominal organs. With a 4 point harness, on impact, the lap straps moved upwards to a position under the lower rib margin, with the QRF in the epigastrium ("the pit of the stomach"). Serious injury to the internal abdominal organs could result.

The 5th strap, in the accident situation, caused a high injurious load in the crotch. It is recommended that the 5th strap be re-designed so as to avoid injury to the crotch region.

It is concluded that a 5 point harness should be fitted to gliders, with a re-design of the 5th strap being carried out.