Principles of Flight: 6 Latest ATPL Questions Explained

Principles of Flight becomes much easier once you stop treating drag, lift coefficient, wake turbulence and stall behaviour as separate topics. Many exam questions are testing the same aerodynamic relationships from different angles.

In this walkthrough, we break down six recent ATPL Principles of Flight questions from Subsonic Aerodynamics, with clear explanations of the logic behind each answer. You’ll revise induced and parasite drag, wake turbulence, CLMAX, aerofoil geometry and the aerodynamic effects of wing icing.

Prefer to watch instead? You can follow the full walkthrough on our YouTube channel, where we explain each question step by step.

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6 Latest POF Questions Covered in This Blog

• AIR-277182: Induced Drag — Factors Affecting Drag at Constant IAS

• AIR-252781: Wake Turbulence — Understanding Formation and Behaviour

• AIR-251712: CL vs Angle of Attack — Identifying CLMAX on an Aerofoil Graph

• AIR-252758: Aerofoil Comparison — Ordering Aerofoils by Increasing Lift Coefficient

• AIR-251982: Parasite Drag — Effect of Doubling True Airspeed

• AIR-277744: Wing Icing — Premature Boundary Layer Separation and Stall Warning

Smart ATPL Prep: How to Build Exam-Day Confidence. Build a calmer revision routine and avoid rushing into the wrong answer during the exam.

Question 1: Factors Affecting Induced Drag at Constant IAS

Question ID AIR-277182:  Induced drag at constant IAS is affected by:

1. Aeroplane weight

2. Angle between wing chord and fuselage centre line

3. Engine thrust

4. Aeroplane wing location

Correct Answer: Aeroplane weight

Explanation

There are two main types of aerodynamic drag to keep separate in Principles of Flight: parasite drag and induced drag.

Induced drag is directly linked to the production of lift. A wing creates lift by establishing a pressure difference between its upper and lower surfaces. Near the wing tips, this pressure difference produces vortices and downwash, which tilt the lift vector slightly rearwards. That rearward component is induced drag.

The key relationship is simple:

More weight → more lift required → more induced drag.

At a constant IAS, a heavier aeroplane still needs to support a greater weight. To maintain level flight, it must therefore generate more lift, which requires a higher lift coefficient and usually a higher angle of attack.

The result is greater induced drag. This is also why induced drag is greatest at low speeds, when the aircraft must operate at a higher angle of attack to generate enough lift.

Exam Tip

When the question says constant IAS, ask: “What would make the aircraft need more lift?”

Also remember the basic speed relationship:

Induced drag ∝ 1 / V²

So as speed increases, induced drag decreases.

Principles of Flight: 7 Latest ATPL Questions Explained.  Continue your POF revision with another set of recently reported exam questions covering critical Mach effects, wing planform design, asymmetric flight, longitudinal stability and high-altitude performance.

Question 2: Wake Turbulence

Question ID AIR-252781: Which of the following sentences is correct regarding wake turbulence?

1. Heavy aircraft produce stronger wake turbulence than lighter ones.

2. Wake turbulence is stronger behind a light aircraft than a heavier aircraft.

3. Aircraft mass does NOT influence wake turbulence.

4. As an aircraft's angle of attack increases to a high angle, the wake turbulence becomes weaker.

Correct Answer: Heavy aircraft produce stronger wake turbulence than lighter ones.

Explanation

Wake turbulence is closely related to the induced drag we discussed in the previous question.  As the wing generates lift, air flows around the wing tips from the high-pressure region beneath the wing towards the lower-pressure region above it. This creates wingtip vortices that trail behind the aircraft.

The more lift the aircraft must produce, the stronger these vortices become. A heavier aircraft requires more lift to remain airborne, so it creates stronger wingtip vortices and therefore more severe wake turbulence than a lighter aircraft under comparable conditions.

The same logic explains why the final option is incorrect. A higher angle of attack generally means a higher lift coefficient and stronger circulation around the wing. After formation, the vortices normally descend behind the aircraft, commonly at roughly 500–1,000 ft per minute during their initial development.

Exam Tip

Link wake turbulence back to lift:

More lift → stronger vortices → stronger wake turbulence.

A useful real-world memory aid is: Heavy + Clean + Slow = strongest wake

“Slow” matters because more lift coefficient is required, while a clean wing concentrates the lift distribution without high-lift devices altering the wake pattern.

Question 3: Identifying CLMAX on an Aerofoil Graph

Question ID AIR-251712: Consider the “CL vs angle of attack” graph of a non-symmetrical aerofoil, with the X axis representing angle of attack and the Y axis representing CL. The angle of attack at which the aerofoil achieves CLMAX can be found on the graph…

• at the point where it crosses the X axis.

• at its highest X value.

• at the point where it crosses the Y axis.

• at its highest Y value.

Correct Answer: At its highest Y value.

Explanation

This question becomes straightforward once you pay attention to what each axis represents.

The X axis shows angle of attack, while the Y axis shows the coefficient of lift, CL. As angle of attack increases, CL increases until the aerofoil reaches its maximum lift coefficient: CLMAX.

Because CL is plotted vertically, CLMAX must be found at the highest point on the Y axis. The corresponding angle of attack is the critical angle of attack. This is the point at which the aerofoil produces its maximum coefficient of lift.

If the angle of attack increases beyond this point, airflow separation becomes more extensive and CL begins to decrease. The wing has entered the stall region.

Exam Tip

Do not overthink the graph. If: Y axis = CL,  then: CLMAX = highest Y value.

And remember the aerodynamic relationship:

Critical AoA → CLMAX → beyond this point CL falls.

Principles of Flight: 6 Latest ATPL Questions Explained. Revisit another recent POF walkthrough covering manoeuvring load diagrams, spoiler effects, centre of gravity, swept-wing stalls and important aircraft speed limitations.

Question 4: Ordering Aerofoils by Increasing Lift Coefficient

Question ID AIR-252758: Refer to the image. What is the sequence that represents the ordering of the aerofoils by increasing CL?

Correct Answer: 3, 4, 1, 2

Explanation

This question tests whether you understand what influences the coefficient of lift (CL).

For ATPL purposes, three useful factors to look for are angle of attack, camber and aerofoil thickness.

In the figure:

• Aerofoils 1 and 2 have the same basic section, but aerofoil 2 is at the higher angle of attack.

• Aerofoils 3 and 4 are also identical to each other, with aerofoil 4 at the higher angle of attack.

• Aerofoils 1 and 2 have greater camber and thickness than aerofoils 3 and 4.

Start with aerofoil 3. It combines the smaller camber/thickness with the lower angle of attack, so it produces the lowest CL.

Aerofoil 4 has the same section as 3 but a higher angle of attack, so its CL increases.

Aerofoil 1 has the more favourable aerofoil shape, with greater camber and thickness, giving it a higher CL than 3 and 4.

Finally, aerofoil 2 combines that greater camber and thickness with the higher angle of attack, so it produces the greatest CL.

The correct increasing order is therefore: 3 → 4 → 1 → 2

Exam Tip

When comparing aerofoils, work through the image systematically rather than trying to judge everything at once:

1. Compare angle of attack

2. Compare camber

3. Compare thickness

For this question:

• low AoA + less camber/thickness = lowest CL

• high AoA + more camber/thickness = highest CL

Question 5: Parasite Drag — Effect of Doubling True Airspeed

Question ID AIR-251982: What happens to parasite drag if the true airspeed of an aircraft is multiplied by two, and all other parameters are kept constant? The parasite drag…

1. is unaffected by speed.

2. will be multiplied by four.

3. will be divided by two.

4. will be multiplied by two.

Correct Answer: Will be multiplied by four.

Explanation

Parasite drag includes drag that is not directly associated with producing lift, such as skin-friction drag, form drag and interference drag.

The parasite drag equation can be written as:

Parasite Drag = ½ × ρ × S × V² × CD₀

The important part of the equation for this question is V².

If True Airspeed is doubled: 2² = 4, so, assuming all other parameters remain constant, parasite drag becomes four times greater.

This is one of the fundamental differences between parasite and induced drag. Parasite drag increases rapidly with speed, while induced drag decreases as speed increases. Together, the two create the familiar total-drag curve, with minimum total drag occurring around VMD.

Exam Tip

A very quick memory trick:

• Parasite drag → V²

• Induced drag → 1 / V²

So: Double speed → parasite drag ×4 while induced drag moves in the opposite direction.

Pilot Maths: 10 Formulae Worth Memorising. Go deeper into useful pilot formulae for descent, climb, navigation, weather and ATPL revision.

Question 6: Wing Icing

Question ID AIR-277744: Flying in areas of unanticipated icing, ice accumulation on the wings may result in the stall warning system failing to trigger. This is due to the aeroplane stalling at a lower _____ because of premature boundary layer separation.

1. angle of attack

2. attitude

3. Indicated Airspeed (IAS)

4. True Airspeed (TAS)

Correct Answer: Angle of attack

Explanation

Ice contamination changes the aerodynamic shape and surface roughness of the wing. Even a relatively small accumulation can disturb the boundary layer, increase skin-friction drag and cause the airflow to separate from the upper surface earlier than it would on a clean wing.

As a result, the contaminated aerofoil reaches its maximum lift coefficient and stalls at a lower angle of attack.

This creates an additional danger: the stall warning system is designed around the normal aerodynamic characteristics of the clean aircraft. If icing causes the wing to stall earlier, the normal warning margin can be reduced or even lost. The aircraft may therefore reach the actual stall before the pilot receives the stall warning expected under clean-wing conditions.

Icing can also increase aircraft weight and therefore stall speed, but that is not what this particular question is asking. The key clue is premature boundary layer separation, which points directly to a reduced critical angle of attack.

Exam Tip

Focus on the wording:

Premature boundary layer separation → stall happens earlier → lower critical AoA.

Do not be distracted by IAS or TAS. For this question, the examiner is testing the aerodynamic stall condition, not the speed indication.

Stalls Explained: The Basics of Lift Loss in Flight. Want to go deeper into Questions 3 and 6? Review the relationship between angle of attack, maximum lift coefficient, airflow separation and the aerodynamic conditions that cause an aircraft to stall.

Keep Practising

Subsonic Aerodynamics becomes much easier when you start seeing the links between lift, drag, angle of attack, CL and airflow separation rather than memorising each rule separately.

Practise more questions from the relevant Principles of Flight chapters in the Airhead ATPL Question Bank to see how the same aerodynamic principles appear under different exam wording.