If you aren't quite sure what airplane stall is, then you're in the right place. Today I'm going to tell you, in detail, all about it. In the most basic terms, a stall in an aircraft is when the wing stops producing lift. Lift is one of the key forces needed for a successful flight. No lift, no flight. It's that simple.
There are a few things that can cause an airplane to stall. But (normally) it's easy to recover. Today, I will talk you through the theory behind a stall and offer some practical advice for stall recovery.
What Is a Stall in a Plane?
There is something fundamental that you need to understand from the outset.
Stalling in an airplane has nothing to do with the engine. It's about how a wing works.
Wings are there for one reason alone -- to generate lift. Three things influence how wings generate lift, and they normally interact with each other during the course of a normal flight:
- The speed of the wing through the air
- The shape of the wing
- The angle that the wing is presented to the incoming air
The last factor on the above list has an official name. It's called the angle of attack. In normal flight, if you increase the angle of attack, you increase the amount of lift produced by the wing.
There are limits. If the angle of attack is increased too steeply, the wing eventually stops producing lift.
Do you know what this loss of lift is called?
An airplane stall.
The stall always occurs at a given angle of attack.
What Happens When a Wing Stalls?
To understand an airplane stall, let us look at a small amount of aerodynamic theory and how wings work.
Take a look at a wing in cross section. It will always have a curved upper surface. As the aircraft moves forward, the wing cuts through the air. The air flows over the top curved section of the wing and has to travel further and faster than the air going underneath the wing.
This creates low pressure on top of the wing, in something called the venturi effect.
This pressure differential between the upper and lower surface of the wing is called lift.
- If we increase the angle of attack by 'pulling up', we generate more lift.
- If the airplane goes faster, more lift is generated.
- If the curve is made more pronounced, more lift is generated.
Look at point #1 in particular.
There comes the point where the angle of the wing stops cutting through the air. Suppose it is presented at too steep an angle. In that case, the air stops flowing over the curved upper surface and will separate from the wing completely.
This is known as the critical angle.
This is not a good thing, as the wing is no longer doing its job in producing lift. When weight is greater than lift. What happens? The plane enters a high rate of descent. This is also known as a stall.
The good news is that this isn't normally a permanent situation. Still, in order to get the airplane flying again at a sufficient airspeed, you will need to learn how to recover.
Let's take a look at how to do this…
Airplane Stall Recovery
So, we have established that a stall is when a wing stops producing lift. Take a look at the numbered list I've just given above.
This should give you some essential clues as to how to recover from an airplane stall. I'll go through them now.
If you remember only one thing from this article, this next point should be it. Your response to the stall should be: -
Reduce the Angle of Attack
To stop a wing stalling, you need to reduce the angle of attack and move the wing away from the critical angle.
This means pushing the nose down to a point where the wing starts working again. It doesn't mean that you need to dive. In fact, many small GA aircraft can recover from a stall in just 100 to 200 ft. of altitude.
Increase the Speed
Remember what I said above? The more speed, the more lift produced by the wing. By increasing the aircraft speed, you make a stall far less likely.
This is achieved by applying moderate pressure on the yoke or stick to increase airspeed while simultaneously adding throttle to minimize height loss.
Change the Shape of the Wing
This isn't always applicable and depends on specific circumstances. Do you know why practically all airplanes use extendable flaps for take-off and landing?
It allows them to increase the size of the wing and generate the same amount of lift while flying slower.
Consider deploying the aircraft flaps, as this reduces the chances of a stall at slower speeds.
What does an airplane stall look and feel like? Read on, and I'll tell you.
What are the Symptoms of an Impending Stall?
Stalls tend not to be subtle, but it is well worth learning what a stall looks and feels like. Some aircraft have very pronounced stalls, but most newer models simply dip their noses to build up airspeed and fly themselves out of the stall.
Here's a quick guide so that you can easily recognize an airplane stall and take steps to recover:
- Low Airspeed – As speed reduces, the wings become less efficient. This reduction in lift may cause student pilots to try and pull the nose up to maintain altitude. This leads to an increase in the angle of attack.
- High Pitch Attitude – A high nose, or 'pitch attitude', means a high angle of attack. High angles of attack mean a stall is more likely as you approach the critical angle.
- Stall Warning Horn or Beeper – Most training aircraft are fitted with a stall-warning device mounted on a wing. This noisemaker is activated when the wing's angle of attack is too high. If this is activated, you are approaching a stall.
- Excessive Back Pressure Required on the Stick – As the wing becomes less effective, less lift is produced, making level flight harder. Remember one way I said you could increase the amount of lift? By increasing the angle of attack. Go too high with your angle of attack, and a stall is likely.
- Ineffectual Flight Controls – The faster the airplane flies, the greater the amount of air flows over the control surfaces. You can feel this in the cockpit. If the controls feel all mushy, it means there isn't much air flowing over them… Or the wing.
- Buffet – A sure-fire way to know that the aircraft is stalling is when you feel a judder or 'buffet'. This feeling is caused by the normally smooth airflow over the wing becoming turbulent as it starts to separate. If you feel a buffet, the very first thing you need to do is reduce the angle of attack by pushing the nose down.
Here's a tip: Your plane is designed to avoid the stall.
In fact, some aircraft are difficult to stall at all. You'll have to work hard and keep pulling back on the yoke or stick to keep it in a stall. If you let go of the control, the nose will dip, the angle of attack will reduce, and the airspeed will build up.
This is only true when the altitude required for recovery is less than your altitude off the ground. That's why you'll be learning to force a stall at altitude so you can learn how to quickly recover without fear of 'running out of sky'.
How Will I be Practicing Stalls?
You'll be practicing stalls with your instructor, typically at 2,000 ft. above ground level (AGL) or higher.
Why so high?
This will give you plenty of time to observe what a stall looks and feels like without the risk of descending into the ground. You can take your time to practice the stall recovery methodically before refining it to minimize the height loss.
You'll practice both power-on and power-off stalls.
Let's take a brief look at the difference: -
A power-on stall can occur during take-off or any flight phase where the engine is producing thrust. This stalling exercise is considered slightly easier as you will already have applied throttle before beginning the maneuver.
Why would a power-on stall occur?
This is normally the result of careless handling or inattention. Let's say you pulled up too quickly when climbing away from the runway after take-off or were being heavy-handed and applying a lot of backpressure on the stick or yoke to try and climb rapidly.
A power-off stall can occur when you're attempting to land. In fact, this is where the majority of stalls, and therefore accidents, occur.
During landing, the airspeed is already lower than in normal flight. Furthermore, the pilot may become distracted by other things, such as looking for the runway or other traffic.
Throw into the mix that by its very nature, to land, you will need to be close to the ground, and you can see how this makes the 'perfect storm' of conditions that can lead to incidents.
Remember, in flying, there are two things that you ideally want in abundance. Plenty of airspeed and plenty of altitude. During landing, you normally have neither, so it isn't the ideal place to stall.
Also, there is often a temptation to 'pull' the aircraft around to align with the runway, often at the cost of airspeed.
But here's the good news.
As a general rule, you'll never deliberately stall. You'll be learning to stall and recover for three reasons:
- To recognize the onset of a stall so you can prevent one from occurring
- To recover from a stall with a minimum loss of altitude if one does occur
- To demonstrate a stall during the practical test.
Never attempt a practice maneuver in which the lowest altitude you reach is less than 1,500 ft. AGL. It just doesn't give you enough room to recover before planting your plane.
What is Stall Speed in an Aircraft?
'Stall speed' is a little bit of a common misconception and something you need to be careful about.
In very basic terms, the stall speed is the minimum airspeed at which an aircraft must fly to make the wings produce lift. It is best to consider it as a general guide and use the signs I've mentioned above as the best indicator of when a stall is about to happen.
Why be careful when discussing "stall speed?"
Because there are a great many things that can influence it and change it, and these can be variable from day to day.
Here are some great examples of things that influence stall speed:
- Aircraft Weight – To maintain flight, the lift produced by the wings must exceed the aircraft's weight. If the weight increases, there is a requirement for more lift. To put it simply, the aircraft needs to fly faster as the stall speed is actually higher.
- Bank Angle – How do banked turns impact stalls? Significantly.
- You pull G's (a term given to the increased force of gravity) in a turn. Higher gravity means that momentarily, the aircraft weighs more. This is known as the load factor. An increased load means the critical angle is reached sooner. As a result, you'll need more lift to overcome the weight.
- Temperature – Warmer air makes the wings of your aircraft less effective. Again, you'll need to fly faster on a warm day when compared to a cold day to produce the same amount of lift.
In an ideal world, the only time you should ever really stall an aircraft is during your training. Stalling is when the aircraft wing stops producing lift, which we don't want for a successful flight. By practicing your stall recovery technique and identifying the onset of a stall, you'll be a better pilot and in a great position to fly safely.