Zothecula writes: Certainly one of the more intriguing things on display at this year's Paris Air Show, the Sherpa by Belgian startup Sagita aims to make the helicopter simpler, more efficient, more reliable and more affordable. The helicopter's rotors are directly driven by turbines which are themselves powered by hot air and fumes from the helicopter's power plant. Sagita claims that this makes the the aircraft approximately 85 percent efficient while doing away with the need for a tail rotor.
We warn the reader in advance that the proof presented here depends on a
clever but highly unmotivated trick.
-- Howard Anton, "Elementary Linear Algebra"