---
title: "Aerofoils: controlling aircraft in flight"
subject: "Communication English"
chapter: 2
key: "semester_5/communication_english:aerofoils-control-aircraft-flight"
source: https://www.bctengineer.com/q/semester_5/communication_english/aerofoils-control-aircraft-flight
site: BCT Engineering
---

# Aerofoils: controlling aircraft in flight

Communication English · Chapter 2: Extensive Reading

- Asked in: 2079 Baishakh, 5 marks
- Video: [Aircraft Control Surfaces Explained | Ailerons, flaps, elevator, rudder and more](https://www.youtube.com/watch?v=XxrdhJanotw) — Joyplanes
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/communication_english/aerofoils-control-aircraft-flight
- Whole chapter: https://www.bctengineer.com/md/semester_5/communication_english/chapter-2

## Question

How do aerofoils function to control the aircraft in flight? (Aerofoils)

## Short answer

Aerofoils produce lift by curved upper surfaces causing faster airflow and lower pressure, with higher pressure beneath. Movable surfaces control flight: ailerons roll the aircraft, elevators change pitch, rudder controls yaw, flaps increase lift/drag, and trim tabs adjust balance.

## Answer

An aerofoil is a shaped surface, such as a wing, tailplane or propeller blade, designed to produce a useful force when air flows past it. Aerofoils both lift the aircraft and control its movement.

#### How an aerofoil produces lift
```text
        ___________
     _.-'           '-._     upper surface curved:
 -->(__________________)-->  air moves faster, lower pressure
                             lower surface flatter:
                             higher pressure --> LIFT
```
- The upper surface of the wing is curved and the lower surface is flatter. Air passing over the top travels faster, so its pressure is lower than the pressure beneath the wing.
- The pressure difference, along with the downward deflection of air by the inclined wing (angle of attack), creates **lift**.

#### Control of flight
Movable aerofoil surfaces change the forces on the aircraft:
1. **Ailerons** (on the wings) move in opposite directions. One wing gains lift and the other loses it, so the aircraft **rolls**, used in banking and turning.
2. **Elevators** (on the horizontal tailplane) move up or down to raise or lower the nose, controlling **pitch** (climb and descent).
3. **Rudder** (on the vertical fin) swings the nose left or right, controlling **yaw**.
4. **Flaps** (on the wing's rear edge) increase lift and drag at low speed, for take-off and landing.
5. **Trim tabs and spoilers** adjust balance and reduce lift or increase drag.

The pilot works these surfaces through controls, so that changing the airflow over each aerofoil gives control in the three axes.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How does an aerofoil produce lift?
   A. Air is slower above
   B. Pressure equal
   C. Curved upper surface makes faster air with lower pressure than below
   D. Engines push up
   Answer: C. Pressure difference and deflection create lift. (Key point: Lift)

2. What do ailerons control?
   A. Roll, by moving in opposite directions
   B. Pitch
   C. Yaw
   D. Speed only
   Answer: A. One wing gains lift and the other loses. (Key point: Ailerons)

3. Which pairing is correct?
   A. Elevators yaw; rudder pitch
   B. Elevators roll; rudder pitch
   C. Elevators control pitch; rudder controls yaw
   D. Both roll
   Answer: C. Elevators raise or lower the nose; rudder swings it left or right. (Key point: Elevators and rudder)

4. What do flaps do?
   A. Increase lift and drag at low speed for take-off and landing
   B. Reduce lift for cruise
   C. Control yaw
   D. Control roll
   Answer: A. They are on the wing's rear edge. (Key point: Flaps)

## Related in other subjects

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- [Monitoring vs controlling; EVA concept](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Amonitoring-vs-controlling-eva-concept) — Project Engineering, chapter 4
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