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Sikorsky-Boeing SB>1 Defiant team overcomes transmission issue

30 April 2018
Artist's illustration of the Sikorsky-Boeing SB>1 Defiant concept for the US Army's Joint Multi-Role Technology Demonstrator (JMR-TD) progamme. Source: Lockheed Martin

The Sikorsky-Boeing team developing its SB>1 Defiant aircraft for the US Army’s Joint Multi-Role Technology Development (JMR-TD) effort has recently overcome an issue related to the aircraft’s complex transmission, according to a pair of team officials.

Boeing Director of Business Development for Cargo Helicopters and FVL Randy Rotte told reporters on 26 April at the AAAA conference that the team had to perform a complete “re-run” on a portion of the transmission system. Rotte said Defiant’s transmission issues were mostly related to the hardness of internal gears.

As the Defiant has two rotors that spin counter to each other, the Sikorsky-Boeing team is aiming to achieve new feats in helicopter engineering. Sikorsky Director of Business Development for FVL Richard Koucheravy said Defiant’s transmission must turn two rotor heads in opposite directions, while a traditional helicopter features a single rotor transmission with a single output shaft driving a single mast. Defiant’s transmission, he said, has two drive masts in opposite directions.

The Sikorsky-Boeing team has also tackled a transmission engineering challenge aimed at providing Defiant with additional power during hover compared with traditional helicopters. Koucheravy said a simple helicopter that has a single main rotor and tail rotor must also have an auxiliary drive or an additional drive shaft that goes back to the tail rotor. This tail rotor, he added, only carries about 15% of the aircraft’s total power, which makes it easier to drive an additional shaft back to the tail rotor because the aircraft only takes about 15% off the power.

On the other hand, Koucheravy said Defiant has to be able to take over 80% of the power and either put it into the main transmission or take about 80% of the power and push it back to the propeller.

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