Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Steep Turns — Theory Part 1:

Load Factor and the Aerodynamics of Steep Turns

CASA Recreational Pilot License (Aeroplane) — CASA Sample Syllabus Lesson 18, Theory Part 1

All text and presenter notes in this briefing are licensed under Creative Commons BY-SA 4.0. More info

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Turning in a car

Back in our lesson 04 turning, we used the analogy of turning in a car. Although you've probably never turned quite like this in a car, imagine:

  • What do you feel as you go around the corner?
  • In which direction does your body want to continue?
  • Why don't we turn planes like this?

A body in motion continues in a straight line at a constant speed, unless acted on by an external force — Isaac Newton's first law

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Turning in a car — continued

We then looked at an example of car turning that shares more similarities with turning in an aeroplane.

  • How do the forces felt in this corner differ from the previous one?
  • In what ways is this turn similar to the turns we do in an aeroplane? How is it different?
Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Turning in a car — continued

This week, our car analogy is more like this:

That "pressure", or feeling of being "heavier" is the load factor. A load factor of 1 is exactly what we feel on a flat road or flying straight and level. A load factor of 2 feels as if gravity has doubled and we're twice as heavy.

  • In a car, what effect do you expect the load factor to have on the car?
  • What about in an aeroplane? What effect do you expect the load factor to have on an aeroplane turning like this?
Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Turning in a car — continued

This week, our car analogy is more like this:

That "pressure", or feeling of being "heavier" is the load factor. A load factor of 1 is exactly what we feel on a flat road or flying straight and level. A load factor of 2 feels as if gravity has doubled and we're twice as heavy.

  • In a car, what effect do you expect the load factor to have on the car?
  • What about in an aeroplane? What effect do you expect the load factor to have on an aeroplane turning like this?

The steeper and tighter we turn, the harder the wing has to work — and today we'll find out exactly how much harder.

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Why do we even practise steep turns?

How can steep turns help us? Imagine flying up a narrow valley under cloud only to find a dead end requiring you to turn around. That's where knowing how you can get the smallest radius turn is going to be incredibly helpful. So:

  • Traffic and terrain avoidance — turning hard, deliberately, when you need to
  • Aircraft handling — a steep turn is an excellent test of coordination and attitude flying
  • Understanding the limits — feeling load factor, the higher stall speed, and how a turn can go wrong (the spiral dive) at a safe height, so it never surprises you low down
Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Theory Lesson Overview — Part 1

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Learning Objectives — Part 1

By the end of this session, our aim is to be able to:

  • Describe the aerodynamic forces acting on an aeroplane in a level turn
  • Explain how bank angle determines load factor ('g')
  • Explain why the stall speed increases as load factor increases, and calculate it for a given bank angle
  • Outline the attitude and instrument picture we expect in a steep turn
Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Waypoint 1 — Revision: Turning

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Recall: what makes an aeroplane turn?

  • What actually turns the aeroplane? What is the name of the force that causes the turn?
Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Recall: what makes an aeroplane turn?

  • What actually turns the aeroplane? What is the name of the force that causes the turn?

When we bank, the lift force tilts with the wings. It now has:

  • a vertical component — holding us up against weight
  • a horizontal component — pulling us around the turn. It is this centripetal force that turns the aeroplane in an arc.

It is the horizontal component of lift that turns the aeroplane. Rudder only keeps the turn balanced.

Next: can you recall the sequence or mnemonic that we use for turning?

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Recall: entering and holding a turn

From Lesson 4, the sequence to enter a medium turn — Lookout, then BBB:

  • Lookout — clear the airspace in the direction of turn
  • Bank — aileron into the turn, with coordinated rudder
  • Balance — keep the ball centred
  • Back-pressure — hold the nose up as lift tilts away from vertical

Then hold the turn with the same BBB — Bank with aileron, Balance with rudder, Back-pressure with elevator.

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Waypoint 2 — Forces in a Turn

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

A head-on diagram of an aeroplane banked in a level turn. The total lift force is drawn perpendicular to the wings, tilted with the bank. It is split into a vertical component of lift equal to and opposing weight, and a horizontal component of lift pointing into the turn labelled as the turning (centripetal) force. Weight is drawn straight down.

The forces in a level turn

In a level turn, the vertical component of lift must still balance weight — otherwise we climb or descend.

  • Vertical component of lift = Weight (to stay level)
  • Horizontal component of lift = the turning force

So as we bank more steeply, the lift has to be tilted further — yet its vertical part must still equal weight.

To keep the vertical component equal to weight at a steeper bank, the total lift must increase.

Let's try it out!

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Watch the lift tilt as we bank

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

What "load factor" means

Load factor is the ratio of the lift the wings produce to the weight of the aeroplane:

  • In straight and level flight, lift = weight, so load factor = 1 g
  • In a level turn (or a turn where we're not accelerating vertically), lift must exceed weight, so load factor is greater than 1 g
  • Load factor is what we feel as apparent weight — the push into the seat

Load factor depends only on the bank angle for a level turn — not on the aircraft's weight or speed.

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Waypoint 3 — Load Factor and Stall Speed

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Load factor grows quickly with bank

A line graph. Horizontal axis labelled Angle of Bank in degrees from 0 to 90. Vertical axis labelled Load Factor in g from 1 to 6. A curve starts at 1 g at 0 degrees, rises gently to about 1.4 g at 45 degrees and 2 g at 60 degrees, then sweeps upward steeply toward infinity as it approaches 90 degrees. Dashed marker lines at 30, 45, 60 and 75 degrees.

Notice how the load factor accelerates past 60° — a level turn beyond 60° very quickly demands loads the airframe (and pilot) may not tolerate.

Bank angle Load factor
0° 1.0 g
30° 1.15 g
45° 1.41 g
60° 2.00 g
75° 3.86 g

A 60° level turn = 2 g: the wings carry twice the aircraft's weight.

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Why does the stall speed increase with the bank angle?

Bold Method has a great article Why does stall speed increase with bank angle which is worth reading in your own time, but in outline:

The wing always stalls at its critical angle of attack — always the same angle of attack regardless of speed. But in a level turn:

  • The wing must produce more lift to provide an equal an opposite force for the increased load factor - effectively an increase in weight.
  • More lift at a given speed needs a higher angle of attack
  • So the wing reaches the critical angle at a higher speed than in level flight

It turns out that the stall speed increases with the square root of the load factor:

The stall doesn't wait for you to be "slow" — a steep turn can stall the wing at a speed that feels perfectly safe in level flight.

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

A line graph. Horizontal axis labelled Angle of Bank in degrees from 0 to 90. Vertical axis labelled Stall speed multiplier, as a multiple of the level stall speed, starting at 1. A curve starts at times 1.0 at 0 degrees, rises gently to about times 1.19 at 45 degrees and times 1.41 at 60 degrees, then climbs steeply as it approaches 90 degrees. Marked points at 30, 45, 60 and 75 degrees.

Stall speed in a steep turn

Applying :

Bank angle Load factor Stall speed multiplier E.g. 50kts
0° 1.0 g × 1.00 50 kts
30° 1.15 g × 1.07 54 kts
45° 1.41 g × 1.19 60 kts
60° 2.00 g × 1.41 71 kts

In a level turn with 60° of bank, the stall speed is 41% higher than in level flight.

If your clean stall speed is 50 kt, at 60° of bank the wing stalls at about 50 × 1.41 = 71 kts.

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

The dangers of unbalanced flight close to the stall speed

Like any flight close to the stall speed, steep turns must be balanced — keep that ball centred:

  • In a skid (too much rudder into the turn), the inner wing slows and can reach the critical angle first — it stalls and drops into the turn
  • With the higher stall speed of a steep turn, an unbalanced stall can flick into a wing drop or spin entry very quickly
  • The recovery from a stall/spin needs height — which is why we do all of this at altitude

Balanced flight is not just tidy flying — near the stall it is what keeps a wing drop from becoming a spin.

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Effects on the aircraft's systems

Higher bank and 'g' can affect more than the wing:

  • Fuel — prolonged unbalanced flight or steep manoeuvring can uncover a fuel pickup; watch fuel state and selected tank
  • Pitot / static — unusual attitudes can briefly disturb the airflow into the pitot, giving a misleading airspeed
  • Flap — flap is used in the minimum-radius turn as it allows the plane to fly slower with a lower stall speed, just be sure never to exceed the flap limiting speed () for your aeroplane (Q: the load would increase by the load factor on the flaps as well, so should be reduced, I'd think?)

Know your aircraft's limits before you fly them. Check the flight manual / POH for 'g' limits, flap speeds and any manoeuvre restrictions.

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

'g' limits — symmetrical and rolling

The airframe has certified load-factor limits — the flight envelope:

A V-g diagram, or flight envelope, showing load factor on the vertical axis against indicated airspeed in mph on the horizontal axis. A curved red line on the left is the accelerated-stall boundary, rising from the origin. Horizontal boundaries mark the positive and negative structural limit load factors. Maximum structural cruise speed and never-exceed speed are marked on the right. The enclosed area is divided into a green normal operating range and a yellow caution range, with orange structural-damage and red structural-failure zones beyond the limits.

  • Symmetrical limit — the maximum 'g' pulling straight (both wings loaded equally)
  • Rolling limit — a lower limit that applies while rolling (ailerons deflected), because one wing is loaded more than the other. Usually or 66% of the symmetrical limit. For example, a P28A with 3.8g symmetrical limit will have a rolling limit of 2.5g
  • Abrupt or combined pitch-and-roll inputs at speed can exceed these limits

Smooth, progressive control inputs keep us inside the envelope. Snatching at the controls at speed is how airframes get overstressed.

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Waypoint 4 — Attitude Flying and Instruments

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Attitude flying in a steep turn

A steep turn is flown by attitude first, instruments second:

  • Set the bank against the natural horizon; set the nose on the horizon for level flight
  • Hold the picture — small, smooth corrections
  • If the nose is too low, the fix has an order: reduce bank first, then raise the nose, then re-establish the bank

Using elevator alone to raise a dropped nose in a steep turn just tightens the turn and loads the wing further. Reduce bank first.

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

The instrument picture

Cross-check the instruments to confirm what the attitude is telling you:

Instrument In a steep level turn
Attitude indicator High bank angle; nose on the horizon
Altimeter Steady — the test of a good level turn
VSI Near zero if level; a climb or descent shows the nose is off
Airspeed Steady — held with power against the extra drag
Balance ball Centred — balanced throughout

Attitude sets the turn; the instruments confirm it. Don't fly the instruments — check them.

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Waypoint 5 — Recap

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Summary — Part 1

What we covered:

Topic Key point
Forces in a turn What actually turns the aeroplane?
Load factor What is load factor, and what sets it in a level turn?
Stall speed What happens to the stall speed as we bank more?
Unbalanced flight Why is balance so important near the stall?
Attitude & instruments If the nose drops in a steep turn, what do we do first?
Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Summary — Part 1

What we covered:

Topic Key point
Forces in a turn The horizontal component of lift turns the aeroplane; rudder only balances it
Load factor Lift ÷ weight; in a level turn it is set by bank angle alone (60° = 2 g)
Stall speed Rises with √(load factor) — 41% higher at 60° of bank
Unbalanced flight A skidding stall drops the inner wing and can enter a spin — keep it balanced
Attitude & instruments Fly the attitude; if the nose drops, reduce bank first, then raise the nose
Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Objectives Check — Part 1

Can you:

  • Describe the forces in a level turn, and say which one turns the aeroplane?
  • Explain what load factor is, and what sets it in a level turn?
  • Calculate the stall speed at 60° of bank, given a 50 kt clean stall speed?
  • Explain why a skidding steep turn is dangerous near the stall?
  • State the correct first action if the nose drops in a steep turn?
Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Arrival

Steep Turns — Theory Part 1: Load Factor and the Aerodynamics of Steep Turns

Questions?

Any questions before we move on to Part 2?

Part 2 covers: the steep level and descending turns, maximum-rate and minimum-radius turns, recovering from a spiral dive, and sideslipping.

This first theory session builds the "why" behind steep turns: the aerodynamic forces acting in a turn, how bank angle drives load factor ('g'), and how load factor raises the stall speed. We finish with the attitude and instrument picture the student will see. Part 2 puts this to work: the steep level and descending turns, maximum-rate and minimum-radius turns, spiral-dive recovery, and sideslipping. This lesson revises the medium turn from Lesson 4 (Turning). Have the student's turning knowledge fresh — this brief assumes it.

Most of us have experience being pressed sideways when turning in a car (playing corners). What stops a plane from being able to turn like this is, effectively, that it doesn't have tyres gripping the ground - instead it's slipping through the air.

It's similar in that we're banking around the corner, and so a force perpindicular to our vehicle is now helping the turn. It's different in that with the car, that "Lift/Turning" force is being provided by the *ground*. In an aeroplane, it needs to be provided by the lift of the wings. Interestingly, railroad tracks and car roads do actually do this to some degree, just nowhere near as obviously.

Just as the ground (and car suspension) has to provide the extra centripetal force to turn the car in addition to holding the car level, in an aeroplane it is the *wing* that provides this extra centripital force force in addition to holding the aeroplane level, for a level turn. To do so, the wing requires a *higher angle of attack* for the same speed to stay level (just as it would in straight and level flight with extra weight). This therefore increases the stall speed, just like extra weight would.

The key seed to plant: the extra weight you feel is not just a sensation — the wing genuinely has to produce more lift, and that has real consequences for how fast the aircraft will stall.

CASA underpinning knowledge: operational circumstances where steep turns are required [A5 4(a)]; hazards when performing performance manoeuvres [A3 4(g)]. Frame the lesson positively: we go up high and explore the edges of normal flight on purpose, so that the sensations and the recovery actions are familiar rather than alarming if they ever happen for real.

About 26 minutes for Part 1, leaving headroom in the 0.8 hr theory window shared with Part 2. Part 1 is the theory — why load factor and stall speed change in a turn. Part 2 is the practical manoeuvres that apply it.

These map to CASA lesson-18 underpinning knowledge A5 4(b): the relationship between angle of attack and stall; effects of weight, 'g' force and angle of attack; higher stall speeds when the aeroplane is turning; and symmetrical and rolling 'g' force limitations.

Click Direct-To to arrive at Revision: Turning.

Ask first, reveal on the next slide. Let the student commit to an answer. A common misconception is that the rudder turns the aeroplane. It doesn't — the rudder balances the turn.

Revision from Lesson 4 (Turning). Use a physical model before the interactive on the next slide. The horizontal component of lift is the centripetal force. The rudder's job is to balance the turn (counter the aileron drag on entry and keep the balance ball centred), not to yaw the aircraft around.

This is straight revision but it is the backbone of everything today. If the student is shaky on the entry sequence or on what each control does during the turn, firm it up now before we steepen the bank. Emphasise lookout: about 85% of a visual turn should be spent looking out. Students frequently sacrifice lookout for accuracy.

Click Direct-To to arrive at Forces in a Turn.

PHAK Ch 5 (Aerodynamics of Flight) — Forces in Turns. This is the canonical head-on force diagram. This is the heart of the whole lesson. Walk it slowly with the interactive on the next slide. The steeper the bank, the more the total lift vector must grow so that its shrinking vertical component still holds weight.

Interactive demo (four-forces with banking). Suggested script: - Start level, head-on view. Note lift (L) balances weight (W). - Bank to 30 and note that Lift decreases at first (as the aeroplane accelerates downwards) before being restored to match weight as it settles in the descent. - Increase the attitude to 5, power to 70 to restore straight and level. - Gradually bank to 45 degrees. Point out the aeroplane starts to sink — the vertical component of lift again temporarily reduces before settling into a descent. - To restore level flight, add power to 100% and raise attitude to about 10 degrees - Gradually bank to 60 degrees and let it settle - harder to maintain level flight. - Have the student predict, before you reveal it: at 60 degrees of bank, how much bigger is the total lift than weight? (Answer: twice — 2 g. Next waypoint.)

CASA A5 4(b): effects of weight, 'g' force and angle of attack. The surprising-but-important point: for a *level* turn, the load factor is fixed by the bank angle alone. A 60-degree level turn is 2 g whether it is a Cessna 152 or a jet, heavy or light, fast or slow.

Click Direct-To to arrive at Load Factor and Stall Speed.

PHAK Ch 5 (Aerodynamics of Flight) — load factor in turns. Mathematically, load factor = 1 / cos(bank angle); the graph is our own Desmos plot (linked on the slide). Emphasise the shape of the curve: it is not linear. Between 0 and 45 degrees it is gentle; past 60 it runs away. This is why 60 degrees is the practical limit for a sustained level steep turn in a training aeroplane. The graph was created at [Desmos graph](https://www.desmos.com/calculator/hhrwghazxf)._

CASA A5 4(b): relationship between angle of attack and stall; higher stall speeds when the aeroplane is turning. Tie this straight back to Lesson 5 (Stalling): the stall is always about angle of attack, never simply airspeed. The steep turn is the clearest everyday example of stalling at a "normal" speed. If the student is keen to understand why it is the square-root of the load factor, this can be worked out using the lift formula: consider which parts of the lift formula can change (density is constant, as is surface area, as is the lift co-efficient at the max AoA). If the lift force changes by a factor of n, then re-arranging and solving for V shows that V equals the old V multiplied by the square-root of n.

This is the same table the student met in Lesson 5 (Stalling) — repeat it deliberately; it is the single most important number in this lesson. Worked example to say aloud: at 60 degrees of bank with a 50 kt clean stall speed, the aircraft stalls at about 70 kt. If you rolled into a hard 60-degree turn at 75 kt you would have only a 5 kt margin — and pulling harder to tighten the turn would close it entirely. This is exactly the base-to-final accident scenario, and why we practise steep turns and their stall high up. The graph plots stall speed multiplier = 1 / sqrt(cos(bank angle)) — the square root of the load factor. It is our own Desmos plot, created at https://www.desmos.com/calculator/fu2pfd1szr

CASA A5 4(g) and A5 4(b): dangers of unbalanced flight. HF/NTS: undesired aeroplane state — prevention, identifying, controlling [NTS2 4(e)]. Connect to Lesson 5's coordinated-flight slide and the skid-into-the-turn hazard. This is the mechanism behind the classic base-to-final stall/spin. We are practising the ingredients (steep bank, back pressure, higher stall speed) deliberately and safely so they are understood.

CASA A5 4(b): effects on fuel, pitot and flap systems. A5 4(c): contents of the flight manual and pilot operating handbook. This is a reader instruction, not a placeholder — the student should look up their own aircraft's manoeuvring limit load factors (symmetrical and rolling), flap limit speed, and any placarded restrictions before the flight.

CASA A5 4(b): symmetrical and rolling 'g' force limitations. This directly supports the spiral-dive recovery in Part 2, where a smooth (not snatched) pull is essential. Keep this at RPL depth: the message is that the rolling 'g' limit is lower than the symmetrical one, and that smooth inputs — especially when fast, as in a spiral-dive recovery — keep us safe. Source: FAA PHAK Fig 5-55. Note the axis is indicated airspeed in mph and the limit values (Va, Vne, +/- limits) are for the PHAK's sample aircraft — point students at their own POH for the actual numbers.

Click Direct-To to arrive at Attitude Flying and Instruments.

FIM background: in steep turns, using the elevator to control height also tightens the turn; the correct order is to reduce bank, raise the nose, then re-establish bank. This is a very common student fault and a direct precursor to the spiral dive we cover in Part 2. About 85% of the turn is still lookout — do not let the student bury their head chasing the numbers.

CASA HF/NTS: use of checklists and standard operating procedures [NTS2 4(h)]; situational awareness through a disciplined lookout-then-instrument scan. In Part 2's steep descending turn the instrument cross-check becomes more important, because the steep nose-down attitude makes the visual gliding attitude hard to judge.

Click Direct-To to arrive at the recap.

This blank-key table is the progressive-reveal recall element — have the student answer each cell before showing the filled version on the next slide. It is the answer key for this recall slide. TODO: consider swapping this default recall table for a lesson-specific creative recap — e.g. hand the student a physical model and have them "fly" a 60-degree level turn while narrating the forces and the control inputs, or have them sketch the head-on force diagram from memory and label the two lift components. A creative activity here is more memorable than the table.