C121-31 – Robinson Helicopter Push-Pull Tube Assembly
Available now on the Airparts.aero Marketplace.
Overview
The Robinson Helicopter C121-31 is a genuine OEM, flight-critical main rotor pitch control tube assembly, engineered specifically for the R44 series helicopter. This push-pull tube is a primary structural linkage in the flight control system, responsible for transmitting precise cyclic and collective inputs from the swashplate to the main rotor pitch horns. This action directly controls the pitch angle of the main rotor blades, and therefore the attitude and lift of the aircraft. Manufactured from high-strength aluminum alloy and subject to strict life limits, the C121-31 is an essential component for ensuring the safety and positive control of the helicopter.
Key Features
- Primary Flight Control Linkage: As a main rotor pitch control tube, it is a direct link in the primary flight control system. Its structural integrity and precise length are essential for accurate and repeatable control response.
- High-Strength Aluminum Construction: Fabricated from a high-strength, aerospace-grade aluminum alloy tube. This provides the necessary rigidity and compressive strength to transmit control inputs without buckling, while remaining lightweight to minimize mass in the dynamic rotor system.
- Precision End Fittings: Features precisely machined end fittings designed to accept spherical rod end bearings (heim joints). This allows for the slight misalignment required as the swashplate and rotor hub articulate through their full range of motion.
- Life-Limited Component: This is a mandatory-replacement, life-limited component. It must be retired from service upon reaching its specified flight hour or calendar life limit, whichever occurs first, to prevent failure from metal fatigue.
- Genuine Robinson OEM Part: As a genuine factory part from the Robinson Helicopter Company, it guarantees perfect fitment, certified material strength, and conformance to the rigorous quality control and safety standards of the original aircraft Type Certificate.
Technical Specifications
- Part Number: C121-31
- Component Type: Main Rotor Pitch Control Push-Pull Tube
- Material: High-Strength Aluminum Alloy
- Application: Transmits control inputs from the swashplate to the main rotor pitch horn.
- Life Limit: 2200 Flight Hours or 12 Years from date of manufacture, whichever comes first (must be verified against the current R44 Maintenance Manual).
- Certification: FAA Production Approval
Aircraft Compatibility
The C121-31 is the specified main rotor pitch control tube for the Robinson R44 series of helicopters. It is imperative to consult the current R44 Illustrated Parts Catalog (IPC) for final verification.
- Primary Helicopter Models:
- Robinson R44 Raven I
- Robinson R44 Raven II
- Robinson R44 Clipper I & II
Applications
The C121-31 has a singular, flight-critical application:
- Main Rotor Control: Directly controls the pitch of the main rotor blades in response to pilot inputs. It is responsible for both collective (lift) and cyclic (directional) control.
- Mandatory Overhaul/Replacement Item: Must be replaced upon reaching its 2200-hour / 12-year life limit during the aircraft's major overhaul, or immediately if any damage such as dents, corrosion, or bending is found.
Why Choose C121-31?
In a helicopter, the main rotor pitch control tubes are among the most critical components for safety of flight. A failure of this linkage would result in a complete loss of control of the aircraft. Using a genuine Robinson C121-31 OEM part is the only way to ensure the component has the correct material properties, manufacturing quality, and a known, fully traceable service life. The risk of using a non-certified part or continuing to operate a time-expired component in this application is unacceptable. For the safety of the aircraft and its occupants, strict adherence to the OEM part and its life limit is mandatory.
Order Your C121-31 Pitch Control Tube Now
Ensure the safety and airworthiness of your aircraft with a new, genuine Robinson Helicopter flight control component. Visit Airparts.aero to order your C121-31 main rotor pitch control tubes today.
The C121-31 push-pull tube is a critical element in the R44's simple yet effective rotor control system. As the pilot moves the cyclic or collective controls, these inputs are transferred via a series of tubes and bellcranks to the swashplate. The swashplate then moves up, down, or tilts. The C121-31 connects the rotating portion of the swashplate to the pitch horn on the rotor grip. As the swashplate moves, it pushes or pulls on the C121-31 tube, which pivots the blade grip and changes the rotor blade's angle of attack. Because this tube is constantly in motion and under load from aerodynamic and centrifugal forces, it is susceptible to metal fatigue over time, which is why Robinson mandates a strict 2200-hour/12-year life limit.
Note: This is a life-limited, flight-critical component. Installation must be performed by a certified A&P or AME mechanic with experience on Robinson helicopters, in strict accordance with the current Robinson R44 Maintenance Manual. All maintenance actions, including installation and retirement of the old part, must be meticulously documented in the aircraft's permanent records.
