Spoilers, Speed Brakes and Air Brakes

Spoilers and speed brakes are aerodynamic devices that reduce lift (spoiler) or increase drag (speed brake) — both without fundamentally altering the wing.

Terms and difference

Spoiler

Aerodynamic flaps on the upper surface that, when extended, disrupt the flow (to "spoil" it).
Reduces lift via flow separation.
Increases drag.
Use: roll control (some aircraft), ground spoiler for landing.

Speed brake / air brake

Special brake flap mainly producing drag without reducing lift significantly.
Use: rapid descent without speed gain.

Dive brake

Specific form on dive bombers or aerobatic aircraft.

Applications

1. Roll control via spoilers

Some aircraft (gliders, some airliners, F-16) use spoilers for roll:

Extend one wing spoiler → lift drops there → aircraft rolls that side.
Advantage: no adverse yaw (see lesson "Adverse Yaw").
Example: gliders often combine spoilers with flaps.

2. Ground spoiler (landing)

Extend after touchdown:

Reduce lift → more tyre pressure on runway → better braking.
Drag increases → deceleration.
Significantly shortens landing distance.
Examples: all airliners, many modern high-performance GA aircraft.

3. In-flight spoiler

In flight for rapid descent without speed gain:

Glider: extensively used for altitude control on approach.
Airliners: for rapid descent (emergency, ATC instruction).
Examples: A320 has 4 spoiler panels per wing.

4. Approach maintenance

Steep approach with stuck flaps can be supported by spoilers/speed brake.

Construction

Glider spoiler

Very wide and vertically extended (typically 1–1.5 m).
Aerodynamically very effective.
Operated by lever ("airbrake lever"), often continuously variable.

Airliner spoiler

Several narrow flaps along the wing.
Roll spoiler: only on one side.
Ground spoiler: all together after touchdown.

Speed brake — typical construction

F-16, F-18: speed brake at tail.
A320: combined spoiler/speed-brake function.
A380: tail cone speed brake.

When NOT to use?

Spoiler on final

Extending before touchdown risky in gliders — lift reduced → sink rate rises → hard touchdown.
After touchdown safe.

Near stall

Spoiler disrupts flow → stall risk elevated.
Observe POH limits.

On take-off

Ground spoiler NOT before lift-off (would delay take-off).
Use flaps not spoilers for T/O.

Comparison with flaps

Aspect	Flaps	Spoilers
Location	trailing edge	upper surface
Lift effect	increases	reduces
Drag effect	increases	increases
Stall speed	drops	rises
Use	T/O, landing	landing brake, roll, glider sink
Effect on α_stall	usually lower	usually lower

Glider specifics

Gliders depend heavily on spoilers:

Altitude control on approach.
Emergency descent (steep approach).
Short touchdown for short fields.

Some gliders have tail brake (tail-mounted air brake) in addition.

Practical PPL relevance

Standard trainers (C172, PA-28, DA-40, DR400): no spoilers.
When spoilers present: follow POH procedure (glider training, some high-performance GA).
Awareness for observing airliners important: spoilers visible after touchdown.