Aug04 Victorian Soaring Association Inc Harness Inspection /Repairs/Maintenance Edwin Grech-Cumbo Victorian Soaring Association Inc

Aug04 Victorian Soaring Association Inc Harness Inspection 1 Their are two main functions of a harness. The everyday function is to restrain the pilot in the sailplane under normal flight loads resulting from both manoeuvring and gusts. The "once in a lifetime" function is to restrain the pilot in the event of an accident. Because no one can predict when an accident will occur harnesses must always be in top condition. AN 85 Strongly RECOMMENDS that the harness webbing be replaced after 10 years of Service!!!!!!!

Mike Note  AN85 worth a read has a lot of information on the seatbelts and on cushoning, not all cushons are created equal. Victorian Soaring Association Inc

Harness Inspection 2  The maximum loads which the harness system is expected to absorb according to JAR 22 is 9 g forwards and 4.5 g upwards - more if aerobatic. This means that a human body weighing 110 kg loads the webbing, seats and attachment points to the equivalent of 990 kg. All components of the harness and the harness attachment points must withstand this load.

Mike Extra  Recent studies have suggested that this loading is within the capacity of most people to survive and so future requirements may dictate that harnesses should be strong enough to withstand loads up to 25 g. To ensure this level of strength the inspection procedures on harnesses will need to be adhered to very closely. Victorian Soaring Association Inc

Harness Construction 3  As a woven material, harness webbing has threads: u threads running along the material >> warp direction u threads running across the material >> weft direction  The warp threads provide the strength of the material and the weft threads hold the material together.

Victorian Soaring Association Inc Harness Construction  When webbing is loaded the load tends to concentrate towards the edge of the material as shown in the following overhead. This is why frayed edges on the webbing are so detrimental to the strength of the webbing and webbing with frayed edges must be replaced quickly. 5

Victorian Soaring Association Inc Harness Construction 6 Warp Weft Load distribution in webbing

Victorian Soaring Association Inc Harness Performance 7  There are many factors affecting how well people are restrained in a glider. These include the way the harness is installed in the glider, the type of cushions used, the condition of the webbing, the manufacturing standards of the straps (including the stitching quality etc) and the condition of the fittings.

Victorian Soaring Association Inc Harness Installation The way a harness is installed in a sailplane is the single most important factor in determining the effectiveness of the harness. 8

Victorian Soaring Association Inc Harness Installation This force diagram shows that the shoulder strap loads causes in a high resultant compression load (R) in the spine 9

Victorian Soaring Association Inc Harness Installation Maximum shoulder strap angle = 25° 650 to 675 mm Shoulder Strap Load R Correctly installed harnesses are much more efficient at restraining the body. The shoulder strap loads are smaller for a given deceleration and a lower percentage of those loads is compression in the spine. 10

Mike Note  The cushions used with the harness also have a large influence on harness performance. Seats with excessively soft cushions are compressed under acceleration. As the foam is compressed the webbing comes loose and the body "submarines" under the belt. When the acceleration stops, the foam then rebounds resulting in possible injury to the abdomen and spine.  To reduce the likelihood and effects of submarining, energy absorbing, non re- bounding foams should be used. See AN85 for more details. Victorian Soaring Association Inc

Harness Care  At each Form 2 inspection wash the harness webbing with mild soap and warm water to remove dirt and accumulated sweat. 11

Victorian Soaring Association Inc GFA Harness Requirements Seat harnesses, in addition to complying with requirements of CASA Order , are required to be fitted with an approved type quick release box of a type unaffected by acceleration forces and with lap strap adjusters operated by an upward pull action. In addition, harness webbing must show high resistance to degradation under exposure to ultra violet rays. 12

Mike Note  Civil Aviation Order (CAO ) was issued in August 1975 and looks like it has been revoked. Use of these specifications are no longer required as CASA now approves such equipment under regulation CASR of the Civil Aviation Safety Regulations Victorian Soaring Association Inc

Harness Repairs  Any repairs to an occupant harness must be carried out to the original manufacturer’s repair scheme or an approved webbing & stitching scheme.  Metal fittings must only be replaced with genuine replacement parts. 13

Victorian Soaring Association Inc Harness Inspection Practical Inspection Demonstrate correct inspection of harnesses during a Daily Inspection of a glider. No sign of deterioration, Triple Fold, Plenty of meat, Release test, 14

Victorian Soaring Association Inc Harness Inspection Deterioration from exposure to sunlight is probably the main reason for harnesses becoming unserviceable in Australia. AN 85 very strongly recommends that they are replaced every 10 years if there is not a manufactures specification otherwise, it needs to be assesed each year though as club gliders actually need to be replaced more often than this 15