Weight on wheels proximity switches

What is a Weight on wheels proximity switch?

Weight on Wheels Proximity Switches are sensors primarily used in the aerospace industry to detect whether an aircraft is on the ground (wheels bearing weight) or in flight (no weight on the wheels). These devices play a crucial role in the safety and operation of aircraft, providing critical information to the aircraft’s electronic system.

How does it work?

Weight on Wheels (WoW) proximity switches operate by detecting the presence or absence of weight on an aircraft’s landing gear. Here’s an overview of their functioning:

1. Sensing Mechanism: The switch uses proximity sensors (often based on magnetic, inductive, or capacitive technology) to detect the relative position of the landing gear components. This indicates whether the wheels are supporting the aircraft’s weight or not.
2. On-Ground Detection: When the aircraft is on the ground, the landing gear compresses under the aircraft’s weight, triggering the sensor to send a signal indicating the “weight on wheels” status.
3. In-Flight Detection: During flight, the landing gear extends, and the sensor detects the absence of compression. This triggers a signal to indicate the aircraft is airborne.
4. Integration with Systems: The data from the WoW switch is integrated into the aircraft’s electronic systems, enabling critical operations such as:
   • Activating or deactivating ground-based systems (e.g., braking systems, spoilers).
   • Preventing in-flight deployment of ground functions.
   • Providing input to avionics for automation and safety protocols.

This simple yet effective mechanism ensures safe and efficient operation by supplying real-time status of the aircraft’s ground or flight condition.

How to Detect Aircraft Weight on Wheels

One way to detect whether an aircraft is on the ground or in the air is to use a sensor on the wheels to provide information about their position and weightbearing status. Another option is to compute the position of the aircraft landing gear from other state data. Some systems use a combination of these two approaches. The proximity sensors used to detect weight on the wheels can be active, with integrated electronics, or passive with external electronics.

What are the advantages of Weight on Wheels (WoW) proximity switches for detecting an aircraft’s weight?

Weight on Wheels (WoW) Proximity Switches offer several specific advantages for detecting an aircraft’s weight and determining whether it is on the ground or in flight. Here are the key benefits of these devices:

• High Precision: WoW switches provide accurate detection of the aircraft’s weight status, ensuring reliable differentiation between ground and flight conditions.
• Enhanced Safety: By supplying critical data to systems like braking, landing gear operation, and avionics, they help prevent operational errors and contribute to overall aircraft safety.
• Durability and Robustness: Designed to withstand extreme conditions, including temperature fluctuations, vibrations, and shocks, these switches are highly durable and suitable for demanding aerospace environments.
• Low Maintenance: With no mechanical parts subject to wear, WoW proximity switches require minimal maintenance, reducing operational downtime and costs.
• Integration with Systems: These switches seamlessly integrate with the aircraft’s electronic systems, enabling automation and ensuring that ground and flight-based functions operate correctly.
• Lightweight and Compact Design: Their compact and lightweight construction minimizes additional weight on the aircraft while maintaining high performance.
• Resilience in Harsh Conditions: WoW switches maintain functionality in adverse weather, high altitudes, and other challenging conditions, ensuring uninterrupted operation.

This simple yet effective mechanism ensures safe and efficient operation by supplying real-time status of the aircraft’s ground or flight condition.

Effects of Bad WoW Proximity Switches

Faulty weight-on-wheels proximity switches can send an intermittent electrical signal to the landing gear mechanism. This leads to intermittent hydraulic pressure in the landing gear hydraulics, which can cause uncommanded landing gear extension. When the landing gear deploys or retracts at the wrong time, the result can be a gear-up or belly landing. It can cause serious damage to the aircraft and even put people on board at risk of injury.

The Risks of Uncommanded Landing Gear Deployment

During the early 2000s, two T-45 military jet trainer aircraft experienced uncommanded landing gear extension when the aircraft were traveling at high speed and in high conditions. The Navy had to limit these aircraft to flying only at low speeds until they were able to find the problem with the landing gear control system and resolved it.

Uncommanded landing gear deployment in flight poses a significant risk to the safety of aircraft and their occupants. Such incidents can lead to a substantial increase in aerodynamic drag, causing a loss of speed and excessive fuel consumption. Additionally, at high speeds, landing gear is not designed to withstand aerodynamic forces, which can result in severe mechanical failures or structural damage.

The aircraft’s balance and stability may also be compromised, making piloting more challenging, especially during critical maneuvers. Furthermore, interference with other systems, such as flaps or pressurization systems, increases operational risks. Finally, these events cause significant stress for the crew and can provoke dangerous reactions from passengers. To prevent such situations, it is essential to have reliable systems like Weight on Wheels sensors, which ensure the safe and precise management of the landing gear.

Here are the main dangers associated with this situation:

• Increased aerodynamic drag
• Structural damage
• Imbalance and loss of control
• Pressurization issues
• Collision or observation-related risks
• Impact on operational performance
• Human risk

Promixity Switches are Safety Critical Components

Air/ground sensing prevents various systems from operating inappropriately on the ground or in flight. It also ensures systems are enabled or disabled as befits the aircraft’s situation.

Proximity switches and sensors should be considered a safety critical part of aircraft landing gear control systems. They provide reliable information on the status of the landing gear. They can help to ensure that aircraft landing gear remains stowed while the aircraft is in the air and deploys only when it is needed for landing.

Crouzet, a specialist in critical components

Crouzet offers a range of critical components specially designed for the aerospace industry, combining reliability, safety, and compliance with the sector’s stringent standards. Among its flagship solutions are robust proximity sensors and switches, essential for managing landing gear, flaps, and cargo doors, as well as electromechanical and linear actuators used to control flaps and hatches.

Its DC and brushless micromotors ensure optimal performance for applications such as fuel pumps and air conditioning systems. Crouzet also provides solid-state relays and electromechanical contactors that withstand vibrations and extreme temperatures, along with safety devices like emergency controls and monitoring systems.

The “Weight on Wheels” sensors are particularly critical for determining whether an aircraft is on the ground or in flight, ensuring the safe management of systems. With its expertise and ability to deliver customized solutions, Crouzet is a trusted partner in meeting the rigorous demands of the aerospace industry.