Definition
A high-lift wing flap design that, when extended, opens two narrow gaps (slots) between the main wing and the flap segments. Air from beneath the wing flows up through these slots over the upper surface of the flap, energizing the airflow and delaying separation. This allows greater flap deflection without stalling the airflow, producing more lift and more drag than a plain, split, or single-slotted flap of equivalent size.
Plain English
A flap that splits into two pieces with two small openings between them when lowered. Air rushes through those openings and stays attached to the flap, letting the wing produce much more lift at low speeds without the airflow breaking up.
Context Anchor
Seen in discussions of flap types, aircraft design, and landing or takeoff performance.
Derivation
"Slot" comes from a Middle English word meaning a narrow opening. The name describes exactly what you see: two narrow gaps that open up when the flap deploys. Knowing this helps the term feel less abstract — the slots are real, visible openings that channel air.
Why Pilots Care
They produce markedly higher lift at low airspeeds, shortening required runway lengths for takeoff and landing.
Intuition Check
Do not read “double-slotted” as simply “two flaps.” Here it means the extended flap system creates two narrow airflow gaps that help the flaps work at higher angles.
Example Sentence 1
On final approach, the pilot selected full flaps, and the double-slotted flaps deployed to give the steep, slow descent the short runway required.
Example Sentence 2
With double-slotted flaps fully extended the aircraft could maintain level flight at a lower approach speed.