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Visually inspect rod end connections for proper assembly, thread engagement, and stop nut security.
Re-adjust push pull tubes for maximum thread engagement and verify control system operation through full travel.
Inspect rear strut rod end connections for adequate thread engagement and condition of threads.
Add and tighten stop nuts during reassembly of rear strut lower end connections.
This document, Airworthiness Directive 128, issued on June 26, 2002, addresses critical safety concerns related to aileron push-pull tubes and rear lift struts with adjustable lower ends in various RANS aircraft models. It mandates inspections and adjustments to ensure the structural integrity and proper functioning of these components, aiming to prevent in-flight control issues.
Function Description: Aileron push-pull tubes are essential components of an aircraft's control system, responsible for transmitting pilot input from the cockpit to the ailerons on the wings. This transmission allows for the control of the aircraft's roll axis, enabling turns and maintaining level flight. The system typically involves a series of rods and bell cranks that convert linear push-pull movements into rotational motion of the ailerons. Proper connection and adjustment of these tubes are critical for responsive and reliable control.
Important Technical Specifications: The directive specifically highlights the importance of thread engagement for rod end connections. A minimum engagement of 10 full threads is required for all rod end connections in the control system. This specification is crucial for ensuring the strength and security of the connection, preventing disengagement under operational loads. The original assembly manual specifies a minimum of 6 full threads, but this directive increases the requirement to 10 threads due to a reported incident. Stop nuts, as per the assembly and parts manual, are also required to secure these connections. The stop nuts are 1/4" Plain Nut AN 345-416.
Usage Features: The push-pull tubes are used to connect the fuselage bell crank to the wing bell cranks (long aileron push-pull tubes) and the wing bell cranks to the ailerons (short aileron push-pull tubes). The S-7 models only utilize the short push-pull tubes. The proper adjustment of these tubes is critical for maintaining the correct rigging of the ailerons and bell cranks, which directly impacts the aircraft's flight characteristics and control responsiveness. The directive emphasizes the need to retain the position of bell cranks and ailerons according to the rigging instructions in the assembly manual during any adjustments.
Maintenance Features: The directive mandates a visual inspection of all rod end connections in the control system for proper assembly, specifically checking for at least 10 full threads of engagement and the presence and security of stop nuts. Additionally, technicians must feel the connection for any existence of play. If loose connections or insufficient thread engagement are found, the connections must be disconnected, and the threads visually inspected. Worn parts must be replaced with new ones.
A key maintenance step involves readjusting the long and short aileron push-pull tubes. The rod ends connected to the wing bell cranks must be turned all the way in and tightened against the push-pull tube end fitting. If it's not possible to turn the rod end all the way in while retaining the aileron and bell crank positions as per rigging instructions, stop nuts must be added to the rod ends, and the push-pull tubes turned in as far as possible to achieve a minimum of 10 full threads engaged.
After any work is completed, the control system must be checked for proper operation through its full range of travel. This includes visually inspecting each connection for free movement, binding, or interference, and checking for proper control surface deflection.
Function Description: Rear lift struts are structural components that provide support and rigidity to the aircraft's wings, transferring lift forces to the fuselage. The adjustable lower end of these struts allows for fine-tuning of the wing's angle of incidence and washout, which are critical for optimizing aerodynamic performance and ensuring stable flight characteristics. Proper adjustment is essential for maintaining the intended wing geometry and structural integrity.
Important Technical Specifications: Similar to the aileron push-pull tubes, the directive specifies a minimum thread engagement of 10 full threads for the connection of the rod end and adjuster end at the lower rear strut attach point. This ensures a secure and robust connection capable of withstanding the significant structural loads experienced during flight. The stop nuts required for these connections are 3/8" Plain Nut MS35650-3382.
Usage Features: The adjustable lower end of the rear lift struts allows for precise control over the wing's washout. Washout refers to the decrease in the wing's angle of incidence from the root to the tip, which helps prevent tip stalls and improves aileron effectiveness at low airspeeds. The ability to adjust this parameter is crucial for optimizing the aircraft's handling and safety across its flight envelope.
Maintenance Features: Maintenance for the rear lift struts involves inspecting the connection of the rod end and adjuster end at the lower rear strut attach for a minimum of 10 full threads of engagement. A visual inspection of the thread condition is also required, and any worn parts must be replaced.
During reassembly, a stop nut must be added and tightened. The directive refers to Figure 2, which illustrates the installation of the stop nut and the requirement to turn the rod end in a minimum of 10 turns. It's important to retain and check the wing washout as per the assembly manual during this process. The directive notes that Figure 2 shows a larger strut, and smaller strut fittings are of a square block design, implying that the general principle of adjustment and securing remains the same despite variations in fitting design.
The directive emphasizes the importance of these inspections and adjustments to prevent potential in-flight control issues, as demonstrated by the incident involving an S-12 model. Adherence to these mandatory procedures is crucial for ensuring the continued airworthiness and safety of the affected RANS aircraft.
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