Cyclic/collective pitch mixing

Lore & Background

Older model helicopters use three independent servos to manipulate the swashplate. The elevator servo tilts the swashplate forward and aft (longitudinal cyclic), varying the aircraft's pitch. The aileron servo tilts the swashplate left and right (lateral cyclic), varying the aircraft's roll. The collective pitch servo raises and lowers the entire swashplate, varying the collective pitch of all rotor blades. An intermediate mechanical mixing system transfers control inputs from the servos to the swashplate, hence the name mechanical CCPM (mCCPM). This requires an elaborate system of control rods and levers, often containing many ball bearings.

To reduce mechanical complexity, newer model helicopters use a software system (usually running on the transmitter) to mix the control inputs of three interdependent servos controlling the swashplate. The three servo linkages are arranged around the swashplate at 120° intervals (with a variation using 140° + 140° + 80° intervals). In addition to lower mechanical complexity, the interdependent servos share the workload.

An evolution of electronic mixing is the advent of flight controllers, otherwise known as 'flybarless systems'. Flybarless systems provide two key benefits: by removing the mechanical flybar from the rotorhead, there is less mass and lower aerodynamic drag resulting in improved efficiency. The accelerometers in the flybarless system also provide electronic stabilisation, allowing for finer levels of tuning and greater flight characteristics.

Reader's Guide

CCPM represents a significant shift in radio-controlled helicopter design by enabling multiple servos to collaboratively control the swashplate across all axes. This approach reduces the mechanical complexity inherent in older systems that relied on a single actuator per axis and an elaborate network of control rods and levers. The transition from mechanical mixing (mCCPM) to electronic mixing, typically implemented in the transmitter, simplified the airframe and improved reliability. The subsequent development of flybarless systems further advanced the concept by eliminating the mechanical flybar, reducing mass and aerodynamic drag while introducing electronic stabilisation through accelerometers. This allowed for finer tuning and enhanced flight characteristics. CCPM's legacy is its role in streamlining helicopter control, making models more efficient and precise, and paving the way for modern flybarless flight controllers.

Did You Know?

• CCPM reduces mechanical complexity and increases precision of swashplate control.
• Older model helicopters use three independent servos for elevator, aileron, and collective pitch.
• Electronic mixing uses three servo linkages arranged at 120° intervals (or 140° + 140° + 80°).