This first theory session covers the aerodynamics of slow flight and stalling, how and why a stall happens, and how to recognise an impending stall.
Part 2 covers recovery techniques, factors affecting stall speed, instrument indications, and the HASELL check. Together these prepare the student for what they will experience in the air.
Most people have stalled cars either at traffic lights or on a steep hill.
The key points are that the engine doesn't have enough power to continue producing the force required to move forwards.
- We're used to stalling in a car - when the car doesn't have enough power to continue climbing a hill (until we change gears or apply more power).
- Set 38% throttle for best stall.
- How is a stall different for an aeroplane?
- This is where our analogy breaks down: it's quite different.
- First, in a car, it's about not having enough force available to keep moving you forward (whether at the lights or on a hill), whereas in an aeroplane it's about not having enough force to hold you up in the air.
- Second, in an aeroplane it's not necessarily related to power - you can stall a plane both when you're going slow or fast.
Part 1 builds the foundation: what a stall actually is aerodynamically, why it matters, how control effectiveness degrades before the stall, and the symptoms that warn us it's coming. Part 2 covers recovery and the factors that change stall speed.
Click Direct-To to advance to Stall Aerodynamics.
- Briefly review that the Lift force is just one of the four forces, balancing the weight.
- The lift is split into the vertical component of lift and the horizontal component of lift when banking.
Use a physical aeroplane model to show, or have the student show, what happens as we increase back pressure or decrease back pressure.
As the elevator changes, the angle of attack of the wing, the main lifting surface is changed.
Note the spirals of air, with some air going backwards - we'll see more of this later.
- When this angle between the surrounding airflow and the wing passes a critical angle (around 16 degrees), the air breaks away from the wing as we'll see soon.
- It's a good thing that aeroplanes are designed to pitch forward when they stall - it doesn't have to be that way, but it's designed in to help in a stall
Lead in: But what does that look like outside of a wind tunnel? Is it something we can see? With some help of wool, yes!
One of the best *real* visualisations I've found for what's actually happening in a stall is achieved by taping pieces of cotten or wool to the wing of an aircraft.
The key misconception to address is that "stalling = going too slow."
While slow speed is the most common trigger, the stall is always caused by exceeding the critical angle of attack.
This is fundamental — return to it throughout the lesson.
The pitch-down tendency is a useful natural self-recovery tendency in most light aircraft — the nose drops, AoA reduces, airflow reattaches, and lift returns. The danger is when we instinctively pull back to "stop the nose dropping."
Click Direct-To to advance to Stall Avoidance.
You might notice that pulling back on the controls and slow flight are risks that we're exposed to both during take-off and landing.
There are videos on the internet showing stalls on take-off due to these two factors, such as:
- https://www.youtube.com/shorts/4Px1f3ukBpo
but I removed the slide with that from the deck since it's quite confronting for the first stalls lesson. Feedback was maybe introduce those for advanced stalling. Leaving the link here in the presenter notes in case.
The only real problem in this video and many others like it, is that it happens so close to the ground. It's easy to recover from if you have sufficient height, but low to the ground you don't have that option. That's why the **H**eight, for sufficient height, is the first item is our **HASELL** check.
In what stage of a flight might you find yourself pulling back on the controls, slowing the aeroplane down and possibly turning steeply?
The turning stall and base-to-final stall (with a low, slow, uncoordinated turn) is a leading cause of fatal general aviation accidents. Plant the seed now — we will explore this more in Lesson 16 (Advanced Stalling).
This connects to the secondary effects covered in Lesson 1 — rudder-alone use causes roll; aileron-alone causes slip. Combining them incorrectly near the stall is dangerous.
Keep this brief — induced drag is covered in the aerodynamics theory. The key takeaway is: at slow speed, you need more power to stay level, not less.
The power required as you slow down isn't shown so dramatically here, but it can still be seen:
At the minimum power required, around V_x, as we slow down further, *more* power is required.
Click Direct-To to advance to Recognising the Stall.
We will practise recognising the imminent stall in the air and recovering the moment the warning sounds, before the full stall develops. This is the preferred recovery technique.
To see buffetting, use full power and 15 or 16 AoA
17 and 17.5 show lift dropping to nothing, but 18 collapses the simulation at full power.
Relate this to the hand-out-the-window analogy: at slow speed, very little force on the hand. The student will feel this in the air today.
The stall warning vane works by detecting the angle at which air is flowing into the leading edge. As AoA increases, the stagnation point moves down toward the lower leading edge, causing the vane to deflect and trigger the warning. Some aircraft use a heated pitot-type sensor instead.
Emphasise: in a fully developed stall, the instinct to pull back makes things worse. The control column must move forward to reduce AoA. This is counter-intuitive for new students and must be reinforced.