TRADITIONAL helicopters have a vertical tail rotor to stop the main rotor
from spinning the craft endlessly round and round. But running that second rotor
wastes around 8 per cent of the chopper鈥檚 fuel, says Vladimir Savov, an expert
in aerodynamics at the Bulgarian Air Force Academy in Sofia. So to save that
fuel, Savov has invented the 鈥渞otopter鈥�, a helicopter that flaps its rotors.
Helicopters can already fly without tail rotors鈥攗sing counter-rotating
main rotors or elaborate fans on the tail boom鈥攂ut Savov has taken a
different tack that he says will be far cheaper. To fight the tendency of a
helicopter to turn in the opposite direction to its spinning rotor system, Savov
has removed the engine that spins the main rotors. Instead, flapping the rotors
up and down makes them spin of their own accord.
Savov鈥檚 design involves an engine driving a crank
(see Diagram) that creates
an up-and-down reciprocating motion that in turn drives two separate rotor arms.
By flapping the rotors up and down, and carefully choosing the angle each
rotor鈥檚 aerofoil presents to the air during its cycle, the rotors begins to
rotate on their own.
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鈥淭here is no rotating moment transmitted to the rotopter rotor blades, so
there is no torque reaction鈥攁nd so no need for a tail rotor,鈥� Savov said
in a telephone interview from his home in Pleven. 鈥淭he efficiency of the system
could be comparable to that of a standard helicopter,鈥� he claims.
The downside of the idea is the distinctly odd鈥攁nd slightly
alarming鈥攙ibrating motion of the rotors, which would probably make for a
very uncomfortable ride in a full-sized machine (see video at
www.geocities.com/CapeCanaveral/Runway/ 7551).
鈥淭his could be a big problem鈥擨 just don鈥檛 know yet,鈥� says Savov, who
plans to undertake vibration isolation tests.
A spokesman for Westland Helicopters in Yeovil, Somerset, says: 鈥淪avov鈥檚
video shows it works, but it will take a lot more modelling to prove it can
actually move forwards and remain stable.鈥�