Secrets of the NH90

Crash test results of the world’s first composite fuselage helicopter are shrouded in mystery.

Pre-production crash tests of the innovative military NH90 helicopter have taken place at Eurocopter’s Ottobrunn facility in Germany.

But despite being acclaimed as a success by the manufacturer, full details of the all-composite fuselage’s ability to survive a crash have been cloaked in secrecy and classified suitable for release to customers only.

Even this process has left at least one client unaware that the tests had even occurred.

The Norwegian government confirmed to The Engineer this week that it was unaware the test had taken place.

‘We have not been made aware of any problems and we have not heard about the test or seen any results,’ said Kaare Helland-Olsen, a spokesman for the Norwegian ministry of defence, which signed up to buy 24 machines in 2001.

He said the Norwegian government would now expect to be made aware of any significant developments that might have an impact on the helicopter’s capabilities. ‘We would now expect to see the test results,’ he added.

Though modern helicopters use some composite panelling to reduce the machine’s weight, the NH90 has opted for an all-composite fuselage.

When exposed to stress and impact composites behave differently from metals, depending on type and method of manufacture.

However, the level of vibration in helicopters caused by rotor blades and other constantly moving parts, and the result of this stress on a full composite structure is notoriously difficult to predict at the modelling stage and only becomes fully apparent during flight tests.

‘These problems from vibration can be unfavourable, but adding reinforcement in the affected areas can help,’ said Denis Howe, Professor Emeritus in aerospace vehicle design at Cranfield College of Aeronautics.

‘Safety requirements are also changing all the time and it may be the case that this caused the need for the tests.’

In a statement the manufacturer NH Industries said the crash test was witnessed by representatives from some customer countries. High-speed film was then analysed to measure the integrity of the fuselage structure, the energy absorption of the lower floor, load absorption mechanisms, fuel system seals and troop seating.

The company said the results indicated that with the exception of a few unnamed areas deemed ‘non-critical’, the design proved its ability to withstand a crash.

The NH90 is designed to replace the UH-1 series, the Puma family, Lynxes, and Sea Kings.

NH Industries, a consortium formed by Eurocopter, Agusta-Westland and Stork Aerospace, has orders for over 400 aircraft from countries, including Germany, Italy and Finland, with first deliveries scheduled for 2004.

Confirming that it planned to continue with its order, a spokesman for the Netherlands ministry of defence said: ‘We have seen the test results. Although there are still some technical problems, we believe these will be corrected and we are still confident that the helicopter will be delivered as planned.’

The UK opted out of ordering the NH90, instead choosing Augusta-Westland’s Merlin which had an earlier delivery date. But it was delivered well over budget and more than five years late.

While the UK has no immediate plans to buy the NH90, the MoD said it was keeping its options open over the design.

On the web