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Resurrected NASA tail rotor technology from the Vietnam era bolsters Bell helicopters.
Resurrected NASA tail rotor technology from the Vietnam era bolsters Bell helicopters.

Given how critical the tail rotor is to basic helicopter flight, it is difficult to believe that ground-breaking NASA research on tail-rotor effectiveness (and the loss thereof) could languish in a filing cabinet at the Langley research center for nearly two decades. But it happened.