making a big impactIN FOCUS: Chinook 'crash' tackles safety unknowns
The machine in question - an old
Rather, the agency hopes its destruction of a retired Chinook will point the way to a new set of design guidelines and computer modelling techniques. These will ensure a next generation of more- or even fully-composite helicopters can at least match their metallic predecessors for impact survivability.
As lead test engineer
Designs in carbonfibre may thus require new thinking about shape, and need to evaluate construction options such as metal-carbon sandwich materials, or weaving other fibres into carbon fabrics.
Data from this test series should also help
When, for example, will it be adequate to test a small section of an airframe with a relatively small impact, and when will it be necessary to test large sections to destruction? In composite engineering, says Annett, such questions remain unknowns, as it is not possible to merely extrapolate from existing models. The behaviour of composites, he stresses, is "not similar" to metallics.
The other partners in the testing - the
Military standards for rotorcraft crash design have already advanced far beyond those for civil aircraft, owing the to improved standards for seats, landing gear energy absorption and fuselage structure demanded for the Boeing AH-64 Apache and Sikorsky UH-60 Black Hawk programmes.
In its Langley test - which Annett describes as an attempt to recreate a "severe but survivable" impact, by hoisting the Chinook fuselage about 9m up on cables and swinging it into the ground like a pendulum -
Inside, the fuselage was loaded with 13 instrumented crash-test dummies and two uninstrumented mannequins. Seven more high-speed cameras captured the action, as did 11 head-mounted video cameras of a type widely used by mountain bikers and other extreme sports enthusiasts - "cheap and rugged", says Annett.
New seat designs were also tested. Some of the dummies rode on normal Chinook cloth jump seats with a lap belt, but others - including the "pilot" and "co-pilot", but also some of the "passengers" - had Apache-style "stroking" seats, which deform on impact to absorb energy.
Early indications are that the dummies in energy absorbing seats fared much better than their counterparts on ordinary seats, which Annett says is, of course, obvious and hardly surprising. But what makes this test special is the vast amount of data gathered, particularly from the high-speed cameras. In addition to all that image data, inside and outside the fuselage, each dummy was wired up to output between 10 and 30 data channels. All of the data - over 15s - was synchronised to less than a tenth of a millisecond.
And, in what Annett describes as a real coup for the test engineers, they actually recorded almost all of the data they set out to get. Very little - maybe 5-10% - was lost to the mayhem of the crash. The result is "hundreds of thousands of data points" that will take months to analyse. Meanwhile, Annett and his
Nobody wants to be on a helicopter that crashes, of course, but after the success of this particular example of destruction testing, with any luck the experience will make future real-life accidents at least a bit more survivable.
A distinctive black-spotted colour scheme offered a reference for structural performance analysis
David Learmount dives into the issues surrounding aerospace safety, and offers his succinct views: flightglobal.com/learmount
The dummies used in the experiment were wired with sensors, including head-mounted cameras
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