final high speed aerodynamics

Plain Flap

The simplest design. It is a hinged portion of the trailing edge that pivots downward, increasing the wing's curvature

Split Flap

Only the lower surface of the trailing edge hinges down. The upper surface stays flush with the wing. This creates a massive amount of drag with only a small increase in lift—great for steep descents

Slotted Flap

The most common type on modern planes. When it extends, it leaves a gap (slot) between the wing and the flap. High-pressure air from under the wing flows through this slot, re-energizing the boundary layer on top of the flap to prevent the air from "tripping" and stalling

Fowler Flap

Instead of just hinging down, this flap slides backward on tracks before pivoting. This increases the total surface area of the wing as well as the camber, providing the maximum lift possible

Trim Tab

The pilot adjusts this from the cockpit to "cancel out" control pressure

Balance Tab

Linked to the control rods so that it moves in the opposite direction of the main control surface. If you pull the elevator up, the tab goes down; the air hitting the tab helps push the elevator up, making it easier to move

Anti-Servo Tab

Usually found on "stabilators" (one-piece horizontal tails). It moves in the same direction as the control surface. This creates more resistance, giving the pilot better "feel" and preventing them from accidentally over-stressing the airframe with a sensitive tail

Servo Tab

Found on very large or older aircraft. The pilot’s controls move only the tab. The aerodynamic force on the tab then provides the muscle to move the giant main control surface

Spring Tab

A "helper" tab that only kicks in at high speeds. When the air becomes too thick and heavy for the pilot to move the controls easily, a spring mechanism engages the tab to assist

Leading Edge Flaps

Located at the front of the wing, these increase the wing's camber (curvature) to provide more lift at low speeds, typically during takeoff and landing

Spoilers

Panels on the upper surface of the wing that "spoil" lift and increase drag. They help the aircraft descend rapidly without gaining speed or assist in braking after landing

Subsonic Range

Any speed below Mach 0.75 (where airflow over the entire wing remains slower than sound)

Critical Mach Number

The lowest flight speed at which the airflow over any part of the aircraft first reaches the speed of sound

Oblique Shock Waves

Occur in supersonic flight when air is "compressed" as it hits a surface at an angle; the air slows down but remains supersonic

Expansion Fan

The opposite of a shock wave. It occurs when supersonic flow turns "away" from itself (like over a curved surface), causing the air to speed up and the pressure to drop

Speed of Sound at Sea Level

Approximately 661 knots or 761 mph

Axes of Flight

The aircraft rotates around three imaginary lines:

1. Longitudinal (Roll): Tip to tail.

2. Lateral (Pitch): Wingtip to wingtip.

3. Vertical (Yaw): Through the center of the fuselage

Static stability

The initial tendency to return to equilibrium

Dynamic stability

The response over time

Parasite Drag

Includes skin friction, form drag, and interference drag. It increases with speed

Induced Drag

A byproduct of lift. It decreases as speed increases

Pitot-Static Gauges

These rely on air pressure to function

Airspeed Indicator

Uses both Pitot (impact) and Static pressure

Altimeter

Uses only Static pressure to measure height based on the weight of the air

Vertical Speed Indicator (VSI)

Measures the rate of change in Static pressure

Atmospheric Pressure

The weight of the air above you. Standard pressure at sea level is 29.92 inches of Mercury (Hg) or 1013.2 millibars

Rotor Clutch

Allows the engine to start and warm up without the heavy rotor blades spinning immediately

Freewheeling Unit

A "one-way" clutch that automatically disengages the engine from the rotor if the engine fails. This is vital for autorotation, allowing the blades to keep spinning via airflow so the pilot can land safely

What are on the leading edge?

Slots, slats

What is on the trailing edge?

Flaps, tabs

Slats

are aerodynamic surfaces on the leading edge of the wing. When they extend, they move forward and down. They allow the aircraft to fly at a much higher Angle of Attack

Slots

are often confused with slats, but there is a key physical difference. Is fixed or automated gap between the leading edge and the rest of the wing.To prevent a stall by "ducting" high-pressure air from below the wing to the top of the wing

Winglets

are the vertical extensions found at the very tips of the wings. To reduce Induced Drag and improve fuel efficiency