نظام المعيقات والمكابح الهوائية

Overview

The Spoiler and Speed Brake System uses hinged panels on the upper surface of each wing to rapidly increase aerodynamic drag and reduce lift on demand. The same panels serve multiple distinct functions: as speed brakes in the air (to increase descent rate or slow down quickly), as ground spoilers at touchdown (to dump lift and transfer weight to the wheels for effective braking), and as roll spoilers to augment aileron roll authority.

How It Works

When the speed brake lever is raised in flight, the flight control computers (or direct hydraulic routing) raise the spoiler panels symmetrically on both wings by 20–45°, depending on the aircraft and selected position. This dramatically increases profile drag and reduces the local lift coefficient. The net effect is a steep descent without excessive airspeed buildup. During roll manoeuvres, the FBW computers raise spoilers on the down-going wing asymmetrically, increasing roll rate beyond what the ailerons alone could achieve.

At touchdown, ground spoilers deploy automatically (armed before landing by the crew) when both main gear weight-on-wheels sensors register. Full deployment of all panels — sometimes 65–70° — kills virtually all remaining lift within seconds, preventing the aircraft from becoming airborne again and pressing the wheels firmly onto the runway for maximum brake effectiveness.

Key Components

• Spoiler Panels: Typically 5–7 panels per wing on large jets; numbered from inboard to outboard. Inboard panels are ground spoilers only; outer panels serve additional in-flight functions.
• Hydraulic Spoiler Actuators: Individual actuators for each panel driven by dedicated hydraulic circuits; some aircraft use electrohydraulic actuators for improved response.
• Speed Brake Lever: Cockpit lever with discrete detents (retracted, flight, full); also has an ARM position for auto-deployment at touchdown.
• Ground Spoiler Arming Logic: Monitors radio altimeter, throttle position, and weight-on-wheels; automatically deploys when all conditions are met at landing.
• Spoiler Mixer / FBW Integration: Computes the roll spoiler contribution needed to supplement ailerons based on roll rate demand.

Aircraft Applications

• Boeing 737-800: Six spoiler panels per wing; flight spoilers (panels 4–6) supplement ailerons in roll; all six deploy as ground spoilers at landing.
• Airbus A320: Five spoilers per wing; in Normal Law, FBW computes roll spoiler scheduling automatically; speed brake can be deployed by the Speed Brake Lever or automatically in certain autopilot descent modes.
• Boeing 777: Seven spoiler panels per wing; the wide wing benefits greatly from spoiler roll augmentation at low speeds. Ground spoiler deployment is coordinated with the autobrake system.
• Boeing 787: Composite spoiler panels with electrohydraulic actuators; active gust load alleviation uses spoilers to reduce wing bending moments in turbulence.

Advantages and Limitations

Spoilers give crews precise control of energy state during descent — particularly useful when ATC issues a late speed restriction or steep descent. Ground spoiler deployment at landing can reduce landing roll by 15–25% by optimising wheel brake effectiveness. The key limitations are aerodynamic noise (passenger-perceptible buffet) and the requirement to retract speed brakes before applying go-around power. Spoilers left extended during a go-around significantly impair climb performance; most aircraft have warning systems or automatic retraction tied to thrust lever advance.