Slow flight below stall speed is a crucial skill for pilots to learn to gain effective control of an aircraft. So why is it so important and how is it done safely? Read on..
Introduction – Slow flight
During flight training exercises, pilots should become so familiar with the aircraft’s handling characteristics on the back of the drag curve that they can confidently control when, and if, an aircraft stalls. Most accidents occur during landing or takeoff when speed and altitude are low, so it would seem obvious that pilot training hasn’t equipped us properly for low slow flight. So why practice slow flight? Let’s dive in..
Why learn slow flight and stalling?
The objective of this exercise is to slow the aircraft in straight and level flight and gradually become accustomed to the attitude and feel of the aircraft. At some point, the aircraft will behave differently, and that point is when we’re on the back of the drag curve, and that’s exactly where we want to be! In this speed state, the aircraft behaves counter-intuitively compared to front of the drag curve flight, so the objective is to become so familiar with it that we KNOW how it feels and how to control an aircraft at those speeds instinctively. You can read more about the importance of flying Low and Slow in this article HERE1.
What happens in slow flight?
While flying in this speed range it should become clear that pitching up increases drag and rate of descent, and that a fair bit of power is required to prevent further loss of speed and lift. You should feel sink or climb, hear and feel engine power, and see attitude movement immediately on the biggest attitude indicator available – the picture out the front.
The aircraft should be trimmed to fly hands-off, and note that the rudder becomes more important for directional control at lower speeds. Once you get comfortable with each incrementally lower speed, and are capable of flying straight and level to maintain altitude smoothly and accurately, speed is further reduced until the aircraft is at minimum controllable speed.
Flight below stalling speed
Indicated airspeed is below stall, but the aircraft is still flyable because power is used to prevent loss of lift. One reason it doesn’t stall is because of the induced airflow over the wing roots from the propeller increasing lift in that area, and another is that a component of propeller thrust is now effectively reducing weight. If the aircraft is capable of a 1:1 power to weight ratio or better, it could climb in the vertical or hang off the prop. At this point, the pilot should fully appreciate the control forces necessary for airplane control and gain confidence in flight below stall speed.5
A fair bit of power will be required at flight on the stall buffet, which will require a fair bit of rudder to balance, and a strong arm to control the pitch attitude which may bounce around a bit. Pilots may find this uncomfortable if they haven’t experienced it before, so you may want to find an experienced aerobatic instructor to guide you through the exercise. I wouldn’t recommend practicing this by yourself initially either, unless you are very experienced and capable of handling stalls4 and spins without getting anxious.
What happens if a sudden burst of power is applied?
If a sudden burst of power is applied without balancing with rudder while flying at very slow speed, the aircraft can torque roll left2 and flick into a spin if ailerons are used instead of rudder to arrest the rotation. Note this is for most conventional engines, but if you have a contra rotating engine (such as a Chinese Nanchang, or many other Warbirds or British planes, it can be the opposite sense).
This is similar to the situation where a pilot gets low on the turn to final and overshoots the turn, so they fall into the trap of using rudder to assist the turn (whilst banked – now out of balance) and pitches up at the same time as boosting power to reduce rate of descent. Pilots can lose control if they haven’t learned how to fly along a constant flight path or how to control the aircraft at low speed, and ham-fisted ‘over-recovery’ actions themselves may cause loss of control!
Rolling and Spinning
Aircraft are made to fly hands-off (whilst trimmed), but they can’t be made totally idiot-proof without spoiling the whole challenge of flight. For an aircraft to spin, only one wing has to stall and that can only happen if the aircraft is unbalanced. By learning how to roll the aircraft properly and how to instinctively keep an aircraft in balance while rolling, pitching, and adjusting power, you’ll never inadvertently allow the aircraft to get into the configuration necessary for a spin to develop. This slow flight exercise is additional insurance that will prevent you from allowing the aircraft to stall, and it’s one of the things any instinctive pilot like Chuck Yeager or Bob Hoover would know that most of us probably don’t.
To apply the cautionary principle though, since spin recovery from low altitude is more challenging, this should be practiced at a safe altitude before trying it out at low level over the runway. The preceding is the whole foundation upon which your skill and consciousness will be developed, so it’s important that these elements are learned so well you become comfortable at any speed or aircraft configuration that’s realistically possible. Occasionally, instructors dream up “advanced manoeuvres” literally out of thin air, thinking they’re a potential lifesaver based on extremely unlikely scenarios.
However, unless that training is able to demonstrably improve both safety and efficiency in balance, over the longer term it will have a negative effect on both.
You can read more about Spin Avoidance and Stall Recovery HERE.3 as well as well as our comprehensive article on Stall recovery from our ex-fighter pilot Jorgo here
Conclusion – Slow flight
Having learned how to control an aircraft in the air and on the ground, the next phase is learning how to fly straight lines, instinctively allowing for drift; climb and descend at constant angles while speed, power, and flap are altered, and constructing a mental picture of a flight plan. This is the basis of navigation, but you’ve already learned most of that by this stage.
Hopefully this has helped you understand the importance of slow flight training and encouraged you to practice slow flight skills while being able to maintain altitude and control. Remember, if you need instruction, seek assistance from your flight instructor – they can show you slow flight maneuvering and maintaining controlled flight at slower speeds.
Check out a bit of further reading on slow flight and aircraft stall recovery here
- ‘Low And Slow’, D. Higdon, Aviation Safety Magazine. Published (updated): Oct 29, 2019. Accessed online at https://www.aviationsafetymagazine.com/features/low-and-slow/ on Oct 21, 2022.
- ‘Left-Turning Tendencies in Airplanes Explained’, Pilot Institute. Published: Dec 30, 2021. Accessed online at https://pilotinstitute.com/left-turning-tendencies-in-airplanes-explained/ on Oct 21, 2022.
- ‘Spin avoidance and stall recovery’, CASA.gov.au. Accessed online at https://www.casa.gov.au/licences-and-certificates/flight-instructors/spin-avoidance-and-stall-recovery on Oct 21, 2022.
- ‘Basic stalling’, Aviation.govt.nz. Updated: 2021. Accessed online at https://www.aviation.govt.nz/licensing-and-certification/pilots/flight-training/flight-instructor-guide/basic-stalling/ on Oct 21, 2022.
- ‘Factors affecting stall speed’, Experimental Aircraft Info. Accessed online at https://www.experimentalaircraft.info/flight-planning/aircraft-stall-speed-1.php on Oct 21, 2022.