Nose Gear - Landing Gear - Airframes & Aircraft Systems #16

Summary

This lesson delves into the intricacies of aircraft's nose landing gear, focusing on its structural design, the steering system, and the challenge of nose wheel shimmy. It explains the importance of the nose gear's ability to self-center and castor, ensuring safe ground maneuverability and preventing damage during retraction. The discussion also covers various steering mechanisms, from simple linkages to hydraulic systems, and strategies to mitigate shimmy, including hydraulic dampening and the use of double nose wheels.

Takeaways

• 🔧 The nose landing gear is typically lighter than the main gear due to carrying less weight and being subject to direct compression loads.
• 🛠️ The nose gear must be able to withstand shearing loads from towing operations and is designed to meet several requirements including steering and self-centering capabilities.
• 🔄 The nose wheel steering system allows the aircraft to be maneuvered on the ground, with hydraulically powered systems being more accurate and fuel-efficient.
• 🔧 The nose gear is designed to self-center before gear retraction to prevent damage to the aircraft structure.
• 🚫 The term 'shimmy' refers to an unstable oscillation in the nose undercarriage, which can be dangerous and is minimized through good maintenance and specific design features.
• 🔄 Castering is the ability of the nose wheel to turn in response to differential braking, thrust, or aerodynamic forces and return to its central position when forces are removed.
• 🔧 The steering system of the nose gear includes components like talk links, steering actuators, and control valves to facilitate ground maneuvering.
• 🔧 Safety features like the bypass valve allow the nose wheel to caster in case of hydraulic failure, ensuring the aircraft can still be maneuvered.
• 🔧 To reduce tire scrubbing, some aircraft have steerable body gear that operates in the opposite direction to the nose gear during turns.
• 🔧 Methods to counter shimmy include hydraulic damping, shimmy dampers, double nose wheels, and maintaining correct tire pressures.

Q & A

What is the primary function of the nose landing gear in an aircraft?

The primary function of the nose landing gear is to support the aircraft during takeoff, landing, and while taxiing. It is usually a lighter structure than the main gear because it carries less weight and is typically subject only to direct compression loads.

Why is the nose gear design complicated?

The nose gear design is complicated by several requirements: it needs to have a steering system or the ability to caster, it must be able to self-center before gear retraction, and it also needs to have a method of countering shimmy.

What is the purpose of the drag brace assembly and side struts in the nose gear?

The drag brace assembly provides fore and aft support, while the side struts provide lateral support to the nose gear, ensuring stability during various aircraft movements.

What is castering and why is it important for aircraft without a nose wheel steering system?

Castering is the ability of the nosewheel to turn to either side in response to differential braking, thrust, or aerodynamic forces, and to return to its central position when the forces are removed. It is important for aircraft without a nose wheel steering system to enable maneuvering on the ground.

Why is automatic self-centering of the nosewheel essential prior to landing gear retraction?

Automatic self-centering of the nosewheel is essential to ensure that the nose gear is in a central position with the wheels pointing in a fore and aft direction before retraction. This is necessary because the restricted space available for stowage will not be sufficient if the nose gear is not centered, which could cause severe damage to the aircraft structure.

How is steering control achieved in hydraulically powered nosewheel steering systems?

In hydraulically powered nosewheel steering systems, steering is controlled by a cockpit steering wheel or tiller, a control valve, steering cylinders to hold the nose gear, and a mechanical feedback device to hold the nose wheel at the selected angle.

What is the role of restrictors in the hydraulic nose wheel steering system?

The restrictors in the hydraulic nose wheel steering system provide dampening for the steering operation and help to prevent nose wheel shimmy, which is an unstable oscillation or vibration that can be induced into the nose undercarriage.

What is shimmy, and how can it be minimized in aircraft?

Shimmy is an unstable, rapid, sinuous idle oscillation or vibration that can be induced into the nose undercarriage. It can be minimized by good maintenance, fitting restrictors in the hydraulic nose wheel steering system, and by fitting a shimmy damper or using twin nose wheels or twin contact wheels.

Why is it recommended to use the largest turning circle possible when maneuvering large aircraft on the ground?

Using the largest turning circle possible helps to improve the turning circle, reduce tire scrubbing, and minimize the risk of damage to the tires and aircraft structure, especially for body gear which are near the center of the turn.

How does the safety bypass valve in the nosewheel steering system function during a hydraulic failure?

The safety bypass valve allows the nosewheel to caster if there is a hydraulic failure. If the hydraulic system fails, a spring pushes open the valve, allowing fluid to flow freely between the actuators, thus enabling the nose wheel to caster.