I should looked more into the mechanics of reaction wheels before answering. The acid test for helicopter design is, in my opinion, do the military incorporate the ideas? If they don't, then there is probably a drawback to prevent further research.ĮDIT The other answers regarding acceleration of the reaction wheel pretty much explain the line above, it's not just a drawback, it's impossible to implement. To counter the weight of the machine, and the torque of the main rotor of the helicopter, the reaction wheel, as I'm sure you know, would either have to be very heavy, or have a serious angular velocity, to achieve sufficient angular momentum and perform a useful stability restoring role. There is an alternative to reaction wheels, that is thrusters at the rear which allow the machine to get closer to trees, powerlines and general operate as safely as possible in confined space.Īlso, many models of helicopters use ducted rear rotors, such as that shown below. This is really an engineering question, imo, but I like applied physics. So either that angular momentum is the spinning of the helicopter's body (which is what we're trying to avoid) or that of the reaction wheel, whose angular momentum must be steadily increasing under the action of the angular impulse to the system. Therefore, the helicopter system's angular momentum must increase steadily (unless there's a countering torque from the tailfan). The air imparts a steady angular impulse to the helicopter. You can also think of this from a conservation of angular momentum, without thinking about the origin of the torques. Clearly this is impossible from an engineering standpoint. Therefore, to counter that torque, the reaction wheel would have to accelerated uniformly and indefinitely. Now the torque imparted on the helicopter by the air through the main rotor is steady - or at least its of roughly constant direction. However, you don't get a torque from spinning a reaction wheel at constant angular velocity but by changing and accelerating that angular velocity. That would indeed impart an opposite torque for short lengths of time. You propose instead to impart an opposite torque through a reaction wheel. You're talking about a device (in helicopters the tail fan imparting horizontal thrust) that counteracts the torque imparted on the main rotor (and therefore on the helicopter) by the surrounding air as the main rotor is dragged through the air.
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