Anti-Skid & Auto-Brakes - Aircraft Brakes - Airframes & Aircraft Systems #23

Summary

This lesson delves into the intricacies of brake modulating and automatic braking systems in modern airliners, highlighting their significance for safe and efficient landings. The script explains how anti-skid systems prevent wheel lock, ensuring optimal braking, and details the components of electronic anti-skid systems, including sensors, control units, and servo valves. It also covers the auto brake system's capabilities, such as providing maximum braking during rejected takeoffs and adjusting deceleration rates, emphasizing the system's swift response and precise braking application.

Takeaways

• 🛫 **Brake Modulation Systems**: Modern airliners are equipped with brake modulating systems, commonly known as anti-skid systems, which are crucial for optimal braking during landing, especially on short runways and in adverse weather conditions.
• 🔒 **Skid Prevention**: The primary function of these systems is to prevent wheel skidding by ensuring there is only a small degree of slip between the wheel and the ground, which is essential for effective braking.
• 📉 **Deceleration Control**: Brake modulating systems control the deceleration of individual wheels, using a selected datum figure for wheel deceleration that exceeds the maximum possible rate of the aircraft.
• 🔧 **Mechanical vs. Electronic Systems**: While mechanical systems have been used since the 1950s, most modern aircraft utilize electronic or electrical systems for more precise control.
• 🚫 **Touchdown Protection**: Anti-skid systems include touchdown protection to prevent brake application before the aircraft has touched down, ensuring safety and proper braking only after landing.
• 🔄 **Adaptive Pressure Bias Modulation**: Electronic anti-skid units adapt brake pressure to prevent immediate return to skid conditions, maintaining optimal braking efficiency.
• 🔒 **Locked Wheel Protection**: In case of wheel lock due to wet or icy conditions, the system releases brake pressure to the affected wheel until it spins up again, then reapplies pressure.
• 🔍 **Break Torque Sensor**: Sensors detect excessive torque during braking to prevent damage to the landing gear, especially with carbon brakes, by reducing brake pressure when needed.
• ✈️ **Automatic Braking Systems**: Modern aircraft feature automatic braking systems that can be selected for landing rollout or rejected takeoff, providing quick reactions and precise braking force for the required deceleration.
• 🔄 **Selectable Deceleration Rates**: Pilots can select different landing deceleration rates using controls like rotary switches or push buttons, with specific settings for maximum braking during rejected takeoffs.

Q & A

What is the primary purpose of a brake modulating system in aircraft?

The primary purpose of a brake modulating system, also known as an anti-skid system, is to prevent skidding by ensuring there is only a small degree of slip between the wheel and the ground during braking.

Why is optimum braking crucial for modern aircraft?

Optimum braking is crucial for modern aircraft due to their high landing speeds, low drag, and high weight, especially when operating from and into short runways in bad weather conditions.

How do mechanical and electrical brake modulating systems differ?

Mechanical systems have been in use since the early 1950s, while most modern aircraft use electrical or electronic systems, which offer more advanced control and reliability.

What is the role of the anti-skid unit in an electronic anti-skid system?

The anti-skid unit in an electronic anti-skid system measures wheel speed, computes wheel speed information, and modulates brake pressure to prevent skidding and optimize braking.

What are the three main functions provided by the anti-skid unit?

The three main functions provided by the anti-skid unit are touchdown protection, skid prevention, and locked wheel protection.

How does the touchdown protection feature work in an anti-skid system?

Touchdown protection prevents the brakes from being applied before the aircraft touches down by monitoring wheel speed and air-ground logic. Brakes can only be applied once the aircraft is on the ground and the wheels have spun up.

What is the purpose of the adaptive pressure bias modulation circuit in electronic anti-skid units?

The adaptive pressure bias modulation circuit ensures that after a skid, the brake pressure applied to the wheel is lower than the pressure that caused the skid, preventing an immediate return to skid conditions.

How does the locked wheel protection system respond to a wheel lock during braking?

If a wheel locks due to a wet patch or ice, the anti-skid controller releases the brake pressure to that wheel completely until it spins up again, then reapplies the pressure.

What is the function of a break torque sensor in an aircraft's braking system?

A break torque sensor detects excessive torque during braking to prevent damage to the landing gear strut or strut mountings, especially with carbon brakes.

How does the auto brake system differ from the anti-skid system in its operation?

The auto brake system automatically applies the brakes after touchdown and decelerates the aircraft at a predetermined rate, whereas the anti-skid system modulates brake pressure to prevent skidding and optimize braking.

What happens if the anti-skid system is unserviceable during auto brake operation?

If the anti-skid system is unserviceable, the auto brake system is disabled to prevent potential safety issues during braking.