Peter's Flight Log

It was three weeks since my last flight due to bad weather. Although I still have to do a door-to-door circuits solo (meaning, I have to fly circuits for a full hour, starting from the hangar and returning to the hangar), ttoday we decided to break the circuits monotony with a brand new topic from the RPL curriculum: advanced stalls. 

My instructor for hours 32 and 33 was Davide (more about Hour 33 in the dedicated log post).

Let's start this log with a dive into stalls, and advanced stalls.

What is a stall?

What makes the magic of flight possible, is lift. An airplane flies because its wings create lift, an upward force that counters gravity. Lift happens when air flows over and under the wing, moving faster over the top surface due to its shape. This difference in speed creates lower pressure on top, lifting the airplane. Imagine blowing over a piece of paper held to your bottom lip; the paper lifts because the fast-moving air has lower pressure than the still air beneath it.

Lift is so important that there is a formula that describes it precisely:

The formula is:

Let's break it down:

• Cl: This is the coefficient of lift, which depends on the shape of the wing and the angle of attack. It's a number that represents how effective the wing is at generating lift. A higher coefficient means more lift.
• 1/2: This is a constant used in the formula to simplify the calculation.
• ρ (rho): This represents the density of the air. Air density decreases with altitude, which affects the amount of lift generated. The higher you go, the thinner the air, and the less lift the wings produce.
• V^2: This is the velocity of the aircraft squared. The speed at which you're flying greatly affects lift; the faster you go, the more air moves over the wings, and the more lift is generated. Doubling the speed quadruples the lift because of the squaring in the formula.
• S: This is the wing area, the size of the wings. Larger wings can generate more lift, all else being equal.

The lift formula highlights the interplay between speed, wing size, air density, and the wing's efficiency at generating lift. It's a fundamental concept for pilots and engineers, showing how changes in any of these variables affect the aircraft's ability to stay airborne. Understanding this helps pilots make informed decisions about speed, altitude, and aircraft configuration to maintain or adjust lift as needed during flight.

As per the formula, for a wing to generate lift, the air must flow smoothly over its surface. The angle between the wing and the oncoming air is called the "angle of attack." If this angle gets too steep, the smooth flow of air over the wing gets disrupted. The air can't "stick" to the surface; it separates, and the wing loses lift.

Imagine you're holding the string of a kite and running with it against the wind; it flies because the wind is flowing smoothly over its surfaces. If the kite tilts too much, the wind can no longer flow smoothly, and the kite will start to flutter and can eventually crash. That's similar to what happens in a stall.

In a stall, it doesn't mean the engine has stopped working. The engines can be at full power, but if the wings are not generating enough lift due to high angle of attack, the airplane will start to descend. Pilots are trained to recognize and recover from stalls, usually by reducing the angle of attack and sometimes increasing engine power, to get the air flowing smoothly over the wings again.

Understanding and preventing stalls are crucial parts of pilot training. It's about maintaining the right balance between speed, angle, and lift to keep the airplane safely in the air.

Common causes of stall

Stall is bad for flying. Ahem. 

So, knowing how to prevent it is important. So is knowing how to get out of a stall if you get in one. Here is a list of common causes of stall:

Understanding the common causes of stalls is key to preventing them. Here are some of the most common causes:

1. High Angle of Attack (AoA): This is the primary cause of stalls. The angle of attack is the angle between the oncoming air or relative wind and a reference line on the airplane’s wing. If the angle of attack increases beyond a certain point (critical angle of attack), the airflow over the wing separates, leading to a stall.

2. Slow Airspeed: While a stall can occur at any speed, it’s more likely to happen at lower speeds because pilots may increase the angle of attack to compensate for the loss of lift at slower speeds, inadvertently exceeding the critical angle of attack.

3. Abrupt Maneuvers: Sharp turns, aggressive pitch changes, or any sudden maneuver can increase the angle of attack rapidly, potentially inducing a stall if the pilot is not careful.

4. Poor Load Distribution: Incorrectly loaded aircraft can have altered flight characteristics, including changes in the center of gravity that might increase the likelihood of a stall under certain conditions.

5. Turbulence: Severe turbulence can disrupt the airflow over the wings, leading to temporary loss of lift. If the turbulence is strong enough or the aircraft is already near the critical angle of attack, this can induce a stall.

6. Icing: Ice formation on the wings alters their shape and disrupts the smooth flow of air, significantly reducing the wing’s ability to produce lift and increasing the risk of stalling at higher speeds and lower angles of attack than normal.

7. Inattention or Inexperience: A pilot’s failure to monitor airspeed, overreliance on autopilot without understanding its limitations, or misunderstanding the aircraft’s performance can lead to unintended stalls.

Stall exercises for the RPL

When I begun my training for the RPL, back in January 2023, I learned how to recognize a stall, and practiced inducing and recovering from a simple stall situation. That was Hour 5 of my training.

Simple stall exercise

On that session, we flew to the training area and climbed to around 4,000 ft to give us lots of altitude to make the exercises safe. The first "simple" stall exercises consisted causing a stall while flying straight and level, trying to hold altitude by gradually increasing back-pressure on the control column while reducing power to idle. As the airplane slows, it's pitch angle increases (angle of attack), until at some point lift is lost, and stall occurs. As stall approaches, the plane gives out a lot of warnings, which may include the stall warning horn, buffeting, a sudden loss of control effectiveness, and the nose dropping.

At the first sign of a stall, the pilot to push the control yoke forward to reduce the angle of attack below the critical angle. This is the primary action to recover from the stall. Simultaneously or immediately after reducing the angle of attack, the pilot must increase engine power to full or as appropriate to assist in the recovery. It is important for the pilot to use rudder inputs to keep the wings level or to level them if a wing has dropped during the stall, and to keep the ailerons neutral!

Neutral ailerons can be counter-intuitive when there is a wing drop, because the instinct to to turn the yoke to the opposite direction of the wing drop, something that can potentially put the airplane in a spiral dive (very dangerous).

Advanced stall exercises

Today, on Hour 32 of my training, I practiced several new situations were stalls can occur, that cover various scenarios of power, flap, attitude and roll settings.

Here's a series of advanced stall exercises that might be taught after a student has mastered basic stalls in straight and level flight:

1. Power-On Stalls (Departure Stalls):

   • These simulate a stall that might occur during takeoff or climb. The exercise starts with the aircraft in a clean configuration with a high power setting. The student gradually increases the pitch to mimic a steep climb until the aircraft stalls. This teaches how to recover from stalls with engine power available, emphasizing the need to lower the nose to reduce the angle of attack while managing power.

2. Turning Stalls:

   • This exercise involves inducing a stall while the aircraft is in a turn, simulating a stall that might occur during a banked maneuver, such as a steep turn or during an approach to landing when the aircraft is turning towards the runway. The key learning points include the proper coordination of ailerons and rudder to maintain balanced flight throughout the stall and recovery process, and the increased risk of entering a spin if the stall is not managed correctly.

3. Cross-Control Stalls:

   • Induced by applying opposite aileron and rudder (uncoordinated flight), leading to a stall. This type of stall is particularly dangerous because it can quickly lead to a spin. The exercise emphasizes the importance of coordinated flight and teaches the pilot how to recover from a stall that occurs in uncoordinated flight conditions.

4. Accelerated Stalls:

   • These stalls occur at higher-than-normal airspeeds due to an increased load factor, such as in steep turns. The exercise involves entering a steep turn and then increasing the back pressure on the control yoke or stick until the aircraft stalls. It demonstrates that stalls can occur at any airspeed, depending on the aircraft's angle of attack and load factor, not just at low speeds.

5. Stalls in Landing Configuration:

   • Simulating a stall that might occur on final approach or during the landing phase. The aircraft is configured for landing (gear down, flaps set for landing), and the student practices inducing and recovering from a stall. This teaches the importance of managing airspeed and pitch attitude during one of the most critical phases of flight.

6. Full or Partial Flap Stalls:

   • Practicing stalls with different flap settings to understand how flap deployment affects stall speed, the aircraft's handling characteristics during a stall, and the recovery procedure.

From the list, I practiced straight and level stalls, level and climbing turning stalls, , glide stalls, partial flap stalls, landing configuration stall. 

The HASELL checklist

The HASELL checklist is a pre-maneuver safety checklist used by pilots to ensure that the aircraft and its surroundings are safe for the execution of certain flight maneuvers, such as stalls, steep turns, or practice forced landings. The checklist helps to minimize risks during flight training or when performing these maneuvers. Each letter in "HASELL" stands for a critical check to be completed:

1. H - Height: Ensure sufficient altitude above the ground to safely complete the maneuver and recover, if necessary. This allows a buffer in case something goes wrong. A common rule of thumb is to ensure that the maneuver is completed no lower than 1,500 feet AGL (Above Ground Level), but this may vary depending on the maneuver and local regulations or recommendations.

2. A - Airframe: Prepare the aircraft for the maneuver. This involves setting flaps, landing gear, or other airframe configurations as required for the specific maneuver you're planning to execute. It’s about ensuring the aircraft is in the correct state to safely conduct the maneuver.

3. S - Security: Check that all loose objects in the cockpit are secured. Loose items can become hazardous projectiles during maneuvers involving changes in altitude or attitude. Ensure seat belts are fastened securely.

4. E - Engine: Verify that the engine instruments and parameters are within the normal operating range. Check fuel quantity, oil temperature, oil pressure, and other relevant engine parameters to ensure the engine is running smoothly and is capable of supporting the maneuver.

5. L - Location: Choose an appropriate location for the maneuver. This means away from populated areas, outside controlled airspace where special permissions are required, and ensuring the area is clear of other aircraft. Also, consider factors such as terrain and weather conditions.

6. L - Lookout: Perform a thorough visual scan of the area around the aircraft to check for other traffic. This is often done using clearing turns – one or more turns of at least 180 degrees in opposite directions – to ensure that there is no aircraft in the vicinity that could pose a collision risk during the maneuver.

The HASELL checklist is an essential part of safe flying practices, especially during training flights where various maneuvers are practiced regularly. It ensures that both the pilot and the aircraft are prepared for the maneuver, reducing the risk of incidents and enhancing overall flight safety.

Weather

The weather today was perfect!

Here's what BOM shows for the day:

For the 9am flight, ATIS reported this:

Information Alpha: RW 06, Wind VAR 3 kt, CAVOK, 17°C, QNH 1021

Pre-flight briefing

Before the flight, Davide gave me a 1-hour briefing that covered a bit of theory, conditions of stall, how to recognise a stall, and how to exit a stall. 

We also went through the details of exiting the circuit after takeoff, travelling to the training area, reaching exercises altitude (around 4,000 ft) and location (adjucent to the new western Sydney airport) and returning to the circuit for landing. I hadn't left the circuit since August 2023, so I was really looking forward to this.

The flight

Along the way, Davided pointed out the various landmarks I will need to be able to recognise everytime I fly to the training area.

The first demo was a 180° steep turn (60°). This turn generates 2G of force, which was much more intense that what I expected. I noticed some distortion of my vision which was getting worse with time. I'll be more prepared. Aside from a anti-G belt (which I don't have), I'll be able to use my abdominal and leg muscles to prevent blood from pooling in the lower extremities and away from the brain. Breathing can also help. Taking deep breaths before the maneuver and using short breaths during the turn to maintain oxygenation and counteract the effects of G-forces on the body.

That was fun, but the main "dish" of today's menu was up ahead. Davide continued with a HASELL check, and a demo of an idle power straight & level stall and recovery (00:39:33). After the demo, I did the exercise (00:42:17).

Before each set of excerises we'd do a HASELL check.

Next up was a 1500 RPM straight & level stall and recovery (00:44:44). In this excerises the right wing dropped, and I tried to use left ailerons to counteract it. This is exactly the wrong thing to do as it can cause a spiral and much worse stall, and it an excample of why pilots should follow their training and not their instinct. I did the exercise again and correctly.

I continued with a 1500 RPM level turn stall and recovery (00:53:27), a 1500 RPM climb turn stall and recovery (00:56:06), and a Glide stall and recovery (01:01:52).

Unfortunately we started running out of time, so Davide demonstrated an approach config (flap 2 stage) stall and recovery (01:03:21) which I will have to practice another time.

We then begun to fly back to Camden for full stop. We received ATIS (01:06:16), radio called inbound (01:08:37), and I completed the landing from late downwind (01:12:51). This was my first landing after three weeks break, and it was good!

Hour 32 instructor review

Here is Davide's review:

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