World Wide Helicopters

By convention used worldwide, helicopters are categorized by weight. Specifically, "light", "medium lift", and "heavy lift" helicopters. Light helicopters are those generally considered below 12,000 pounds [5,000 kg] maximum gross weight. "Medium lift" are generally considered those from about 14,000 pounds to 45,000 lbs [6,000 kg to 20,000 kg]. There is some disagreement in terminology regarding the use of "heavy lift." Some within the industry refer to helicopters above 50,000 pounds as "heavy lift" while others reserve this term for the very largest helicopters, those above 80,000 pounds. Within Army aviation, the largest helicopter is the 54,000 pound [20,000 kg] CH-47D Chinook, most often referred to as a medium lift helicopter.

Helicopters are flying machines which can fly in any direction or hove over a point on the ground without moving. Helicopters usually have a single main rotor mounted on top of a body or fuselage of the helicopter to generate a lift force to hold the helicopter in the air, and a tail rotor or other yaw control system to maintain directional control of the helicopter. Several different yaw control systems have been developed (such as blown tail booms and shrouded fans), but traditional tail rotor systems with exposed tail rotor blades are still the most popular.

With all of their rotating rotor blades, gears, and mechanical linkages helicopters are typically more complicated and expensive than other types of aircraft such as fixed-wing airplanes. Helicopters are also generally more difficult to fly than airplanes, and model helicopters are particularly difficult to control. As a result, pilot of model helicopters frequently crash and damage their models. Helicopters can be very expensive to repair, so relatively few modelers have the patience, skill, and budget to master them. Components that reduce the complexity and cost of helicopters make helicopters more available to the general public, easier to maintain and repair, and generally more competitive with other types of aircraft.

There are many different types of helicopters which are currently in use, including single rotor helicopters, dual rotor helicopters, transverse rotor helicopters, and several other related helicopter-type rotor-based flying aircraft. However, among the different types of helicopters currently being used, it has been found that those with dual rotors are among the most versatile, due to their increased lifting capacity from the increased air flow resulting from the two rotors being used on the aircraft.

Primarily, there are three common configurations of dual rotor helicopters which utilize the contra-rotating effect to benefit the rotor craft, the first being a twin rotor design which includes two rotors mounted on the aircraft, one mounted behind the other, the second being intermeshing rotors which are mounted close to each other with the rotor blades intermeshing over the top of the aircraft, and finally a coaxial rotor design which includes two rotors mounted one above the other on the same rotational axis. It has further been found that the coaxial rotor system is generally more cost-effective, as the size of the helicopter does not have to be expanded to accommodate the position of the two rotors as they are positioned one atop another. A further benefit of the coaxial rotor design is that, in forward flight, the lift provided by the advancing ends of each rotor compensates for the retreating half of the other, eliminating one of the key effects of dissymmetry of lift, namely retreating blade stall.

Unfortunately, however, coaxial rotors have several disadvantages which must be addressed in order to permit the coaxial rotor system to function properly. For example, there is an increased mechanical complexity of the rotor system due to the required linkages and swash plates for a dual coaxial rotor system. Furthermore, because each rotor system needs to be turned in an opposite direction, the central rotor shaft or mast itself is far more complex, and provisions for making pitch changes to the upper rotor system must pass through the lower rotor system.

The most significant and potentially deadly problem encountered with coaxial rotor systems, however, is that during extreme aerobatic maneuvers of the helicopter, such as those encountered during combat or the like, the upper rotor system may accidentally contact the lower rotor system during operation thereof, which results in the contacting blades disintegrating due to the high rate of speed at which the upper and lower rotor systems are rotating, and this disintegration of the rotor blades results in rapid disintegration of the remaining elements of the rotor system due to the unbalanced nature of the upper and lower rotor systems, and the entire rotor structure quickly becomes unstable and self-destructs. This, of course, results in the helicopter falling from the sky and further results in the almost certain death of the pilot and crew of the helicopter. There is therefore a need for a system or device which will generally prevent accidental intermeshing of the upper and lower rotor systems.

Tail rotor systems on helicopters are extremely important because the control the direction of flight. Tail rotors are also more likely to be damaged than other parts of a helicopter because they are often operated near obstruction such as trees or the ground, and are lightly constructed to prevent a tail-heavy condition of the helicopter which would adversely affect the helicopter in flight. Impact of the tail rotor blades on an obstruction can cause the helicopter to loose control and crash. Tail rotor failure and tail blade strikes, on obstructions are one of the most common types of helicopter accidents which lead to personal injures of the pilot and bystanders and loss of the helicopter. What is needed is a tail rotor system that is simple, inexpensive and less susceptible to damage.