Coefficient lift and Angle of Attack chart

Basic Stall Symptoms

Most aircraft accidents occur during the take-off and landing phase of the flight. Collisions with obstacles during climb out, runway overruns on landing occur every now and then. On this part of the site we will take a look at the various factors contributing to the performance of the aircraft in this part of the flight. Hopefully we help the pilot ensuring safe operation during these critical phases of the flight as the rules require that of the pilot in command.

Recognizing an approaching stall is part of pilot training as during landing appraoch the aircraft is flown close to the stalling speed for the configuration the piot has set. During training the pilot is learned to handle and act upon an stall of the aircraft.

Stall symptoms

These symptoms describe the low speed non accelerated stall. Its possible to induce stall at higher speeds as in level turns and fast pitch up accelerations where some symptoms will not show at all.

Reduced airspeed

If airspeed reduces and the pilot wants to remains at the same altitude, the aircraft will stall eventually if the airspeed keeps reducing.

Control effectiveness

As the aircraft slows down there is less airflow over the ailerons, rudder and elevator thus the amount of deflection needed is greater to control the aircraft. An indication of approaching slow speed stall.

Pre-stall buffet

Angle of Attack compared to Relative Wind

When the AOA of the wing increases the separation point moves forward and the streamlined airflow wil become turbulent and separates from the wing. This turbulent wake then meets the aft fuselage and tail section of the aircraft. This will be felt by the occupants of the aircraft as a rumble or buffet. Not all aircraft have a pronounced buffet, this depends on the size and location of elevator.

Wing design is such that the wings stalls from the root toward the wingtips so that the ailerons remain effective as long as possible. For this to happen the angle of incidence of the wing is larger at the root and smaller at the wing tips. Some aircraft have a stall fence on top of the wing, others employ a discontinuous leading edge (Kodiak from Quest Aircraft) creating a vortex over the wing at high angles of attack. Both devices prevent the stall from progressing to the ailerons so that they remain effective.

Nose attitude

During a straight and level stall the nose high attitude is a good indication of an approaching stall, but remember that using flaps lowers the nose and an aircraft can be made to stall in any nose attitude. A stall occurs when angle of attack of the incoming airflow and chord line becomes too large, this has nothing to do with nose attitude and is called a high speed or accelerated stall.

Stall warning

In some aircraft a stall warning device is fitted in the form of a horn or light. This device is set to indicate a stall warning around 5 kts above actual stall speed.