What makes airplanes stall

From small single-engine rotary airplanes to massive twin- or four-engine commercial jets, stalling is a problem to which all airplanes are susceptible. During flight, an unexpected stall can pose a significant threat to the airplane and its passengers. But the good news is that most airplanes have safety systems in place to control and eliminate stalls.

A common misconception is that stalls are attributed to a mechanical problem in an airplane. In cars, trucks and other ground-based automobiles, an engine stall is, in fact, a mechanical problem.

Rather, airplanes experience stalls when the angle at which they enter the wind current is greater than the critical angle of attack. As a result, the airplane will drop, thereby reducing its altitude, until the angle of attack is correctly adjusted. With that said, the pitch of an airplane can also affect whether airspeed will cause a stall. An airplane gaining altitude at a high pitch may stall at a lower airspeed than an airplane flying horizontally at a flat pitch.

The student should also recognise the progressively increasing stick forces as the stall is approached. Reduced control effectiveness is usually followed by the stall-warning device. However, this is not a true symptom, as the device is mechanical and may not work. The type and operation of the stall-warning device fitted to the aeroplane should be described.

The last generally noted symptom is the buffet. This is caused by the turbulent airflow from the wings striking the empennage. This is because the airflow breaking off the high wing combined with the high nose attitude, results in most of the turbulent airflow missing the empennage.

At this point, as a result of the low airspeed, elevator effectiveness has been reduced to the point where no further increase in angle of attack can be achieved, even though the control column is held well or fully back. This results in the aeroplane sinking and the change in relative airflow causes the critical angle to be exceeded.

The aeroplane stalls, altitude decreases and generally the nose pitches down. It is important the student be able to correctly identify when the aeroplane has stalled. The recovery is broken down into two distinct parts: unstalling the aeroplane, and minimising the altitude loss.

To unstall the aeroplane , the angle of attack must be reduced. Since increasing the backpressure or pulling back increased the angle of attack, decrease the backpressure or check forward. In addition, no aileron should be used; ailerons must be held centralised, for reasons that will be discussed in the briefing Advanced stalling. However, the correct use of aileron must be stated right from the beginning in order to get the sequence right first time and every subsequent time.

You should be attempting to introduce stalling in its simplest and most basic form. Therefore, every effort should be made to avoid the wing-drop.

If the aeroplane has a known tendency to wing-drop in the basic configuration it may be necessary to explain this tendency and the result, as well as the reason for not using aileron in the recovery refer CFI. If an explanation is required, keep it as simple as possible at this level.

Your choice of terms — check forward, relax backpressure, ailerons neutral, no aileron, or ailerons central — should match your airborne patter. It should be made clear that reducing the angle of attack is all that is needed to unstall the aeroplane. The aeroplane will enter a descent, and the student can now regain straight and level from the descent PAT. The altitude loss will be about feet using this method, and will be the first recovery method the student practises.

For the least loss of altitude, the maximum amount of power is required hence carburettor heat COLD during the entry so smoothly but positively apply full power prevent yaw — keep straight and raise the nose smoothly to the horizon. There is no need to hold the nose down, as excessive altitude will be lost. Similarly increasing backpressure too rapidly, or jerking, may cause a secondary stall.

Nose-on-the-horizon may be used as the reference attitude. Of the attitudes the student is familiar with the level attitude is too low and the aeroplane will continue to sink, resulting in unnecessary altitude loss.

Alternatively, the climb attitude is too high, as the pitch-up created by full power combined with inertia may result in a secondary stall. A compromise attitude is required to arrest the sink and allow the aeroplane to accelerate to the nominated climb speed.

The simplest attitude to use is to put the top of the nose cowling just on the horizon. For some light aeroplanes this attitude is the same or similar to the climb attitude, but at least the student has not been encouraged to try to climb by simply pointing the aeroplane upwards. The aeroplane should be held in the nose-on-the-horizon attitude until the nominated climb speed is reached and then the climb attitude selected.

Common practice is to use the recommended or normal climb speed, for example 70 knots. However, you may nominate speed for best angle of climb or for best rate of climb refer CFI. Straight and level flight should be resumed at the starting altitude and the reference point or heading regained if necessary. All stalling exercises should finish with a recovery at the incipient stage, more commonly referred to as the onset. This is to emphasise that, under normal conditions of flight, the stall is avoided.

The second objective of this exercise is to recover at onset, which means at the stall warning or buffet. The stall itself is simply the stall and is sometimes referred to as fully developed, meaning that the stall has occurred.

A fully developed stall does not imply a wing-drop. The expected altitude loss from a recovery at onset depending on which symptom is first detected should be stated, for example, less than 50 feet.

With practice and improved situational awareness, this altitude loss can be reduced to zero — as the aeroplane is not permitted to stall see Figure 3. Encourage the student to take on more of the radio work, and to start their study for the radiotelephony exam. On the way out to the training area there is opportunity to practise climbing, straight and level and turning. When setting the aeroplane up and choosing a reference point choose one into or with the wind to reduce any problems the student might have with drift perception.

Start with a demonstration of the basic stall and recovery, rather than the recovery at onset. Although the student is being taught to avoid the stall, they still need to experience what it is they are trying to avoid. At this speed, an aircraft cannot climb without causing a stall. This speed is affected by several factors, including weight, altitude, and configuration, and different stall speeds are set based on this such as a minimum speed in landing configuration with fully extended flaps.

An uncorrected stall will cause the aircraft to fall. The first sign for a pilot is sluggish flight controls, which become much less responsive due to the changes in airflow, and possible buffeting. Pilots will train to recognize this, but this is more relevant in smaller aircraft that are flown manually.

An early stall is easily corrected by pushing the aircraft nose down to reduce the angle of attack. This is, of course, much more serious at low altitude when taking off or landing. If not corrected, the wing loses lift, and the aircraft will start to fall. A spin is another situation that can occur. This occurs when the aircraft has sufficient yaw at the point of stall. In this situation, one wing stalls before the other, and the difference in lift causes the aircraft to roll.

This is much harder for a pilot to recover from. Training is sometimes given on smaller aircraft as part of pilot training, but in general, the focus is on preventing a spin from ever happening. Commercial airliners are not designed or tested in this area.