Forum focuses on safety initiatives

 - December 1, 2008, 6:50 AM

Crashworthiness Study

Cockpit airbags and X-shaped harnesses could reduce the severity of injuries in crashes with high horizontal deceleration components by as much as 22 percent. Pilots and forward-facing passengers, meanwhile, can be protected from predominantly vertical impacts by energy-absorbing seats, but only if the absorbers are optimized for the weight of the occupant.

These findings emerged from research carried out under the European Union’s U4.8 million, 45-month Helicopter Occupant Safety-Technical Applications (Helisafe-TA) research program, which concluded late last year. Outlining the work and the findings, Marius Lützenburger of the German Aerospace Center (DLR) said the research included three full-scale drop tests of Bell UH-1Ds at the Italian Aerospace Research Center test facility near Naples, 15 sled tests in Germany and Spain of generic helicopter mock-ups and extensive simulation studies.

The Hueys used for the drop tests were fitted with three Martin Baker safety seats and dummies representing the pilot and forward- and side-facing passengers; metal parts replaced the engines and gearboxes. The structure, seats and dummies were instrumented with 128 data acquisition channels to measure the accelerations on the structure, seats and dummies, the loads on the dummies and the displacement of the seats. DLR used the results from the drop tests to refine and verify its structural model of the UH-1D using the DRI-Krash modeling software.

The sled tests were carried out using FAA Hybrid III dummies, most representing the 50th-percentile male (166 pounds in weight and with a sitting height of 35.7 inches) but some representing the 95th percentile (223.2 pounds, 36.8 inches), and Euro-SID dummies for the side-facing passenger. Occupant safety was assessed against the IRSIX injury severity index, which includes femur forces, pelvis acceleration, chest deflection, neck extension, head injury criteria and lumbar spine loads, weighted according to whether the impact was mainly horizontal or mainly vertical.

Where the loads are mainly vertical, the IRSIX is dominated by the lumbar spine load criterion, which means that in most cases the overall value is optimized by minimizing those loads and, in turn, depends mainly on the characteristics of the seat energy absorbers.

The crash test measurements were used to support simulations using various absorber characteristics. The results revealed that absorbers optimized for the 50th-percentile dummy resulted in unacceptably high spine loads when used for the 95th-percentile dummy, but the loads on the 50th-percentile dummy were within acceptable limits when using a seat optimized for the 95th percentile. So the best solution would be a system in which the force level of the absorbers is optimized for the 50th percentile and additional absorbers could be activated for heavier occupants. But where occupants of varying weight and size are using non-adaptive seats, it is best to use absorbers optimized for the heaviest.

Looking at crashes that included a high horizontal deceleration component, Autoflug of Germany and the UK’s Coventry University analyzed various restraint systems. A cockpit airbag and X-harness system enabled the pilot IRSIX to be reduced by 22 percent. Improvements of 13 to 20 percent were achieved for forward-facing passengers. But no improvement could be effected for side-facing passengers, as the choice of harness could not reduce the severity of contact with the bulkhead.

Curved Approach Could Increase Capacity

Henk Haverdings, a research scientist at the Netherlands National Aerospace Laboratory (NLR), used its helicopter pilot station (HPS) fixed-base simulator and Narsim/ TWR air traffic control tower simulator to evaluate the potential use of a simultaneous non-interfering (SNI) approach to Amsterdam Schiphol Airport.

In addition to an increase in capacity, SNI procedures offer the possibility of reduced noise footprint, better obstacle clearance and better separation between fixed- and rotary-wing traffic. Segmented procedures using glideslopes of up to 10 degrees and curved final segments had been developed in the earlier Optimal research program.

The NLR simulation compared the standard three-degree, 130-knot ILS approach to Runway 27 with a 7.5-degree curved approach using a curved final segment and a final approach speed of 60 knots. It evaluated three different methods of displaying the guidance cues and the workload on pilot and controller by day and night and in calm and moderate winds.

The simulation revealed specific deficiencies in the procedure design. Completing the curve at a higher altitude than the 500 feet tested would reduce the pilot’s workload, for example, while a high convergence angle with fixed-wing traffic using Runway 27 complicated the controller’s task. But the pilots assessed the workload as only mildly demanding, and while the controller’s workload was higher than for the standard ILS approach, unfamiliarity was a factor along with the converging traffic. But even with the flawed procedure used the simulation demonstrated that SNI procedures could certainly increase capacity, and optimizing the approach would increase it further. o䀀