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PilotSchool Knowledge Base

Understanding Stall Speeds and Influencing Factors

Effect of Variables on Level Flight Stall IAS

Weight

Frost and Ice

  • Effect: Increase
  • Explanation: Contamination of wing surfaces with ice or frost disrupts airflow, reducing lift and increasing stall IAS. This can be up to 15 knots higher with significant contamination.
    In-Flight Icing: Aerodynamics of Icing - NASA

Altitude

Manoeuvres

Power

  • Effect: Decrease
  • Explanation: Increased engine power adds thrust and can sustain lift at lower airspeeds, thus decreasing the stall IAS. When power is reduced, the stall IAS may increase.
    Aerodynamics for Naval Aviators - H.H. Hurt Jr.

Wind Shear Vertical Gusts

  • Effect: Increase
  • Explanation: Vertical gusts can cause a rapid change in load factor, potentially bringing the aircraft to its critical angle of attack more quickly and increasing stall IAS.
    Aviation Weather - Smith, J.

Flap

Why an Aeroplane May Stall at Different Speeds

An airplane stalls at different speeds primarily due to varying factors such as weight, load factors, environmental conditions, and configurations. Weight affects the stall IAS because a heavier aircraft needs more lift, hence a higher airspeed near the stall. Manoeuvring increases the stall speed because of increased load factors, causing the aircraft to approach its critical angle of attack more quickly. Power changes, altitude, and flap settings also significantly impact the stall speed by altering the balance of lift and flow dynamics over the wings. These variations explain why the stalling IAS isn’t a fixed number, but a variable dependent on several conditions and configurations.
Factors that Affect Stall Speed - Bar-or Aviation

Effect of Using Ailerons When Approaching and During the Stall

Using ailerons near or during a stall can exacerbate the condition. Ailerons increase the local angle of attack on a wing’s outer portion. In a stall scenario, this can cause the wing to exceed its critical angle of attack quicker, worsening the stall, especially if ailerons are deflected downwards on the stalling wing. Therefore, aileron inputs should be minimized in stalls, and rudder should be used to maintain coordination and stabilize the aircraft.
Why You Shouldn’t Use Ailerons In A Stall - Boldmethod

Manoeuvres Leading to Stalls at Different Stalling Angles

Accelerated Stalls

Accelerated stalls occur when the aircraft undergoes high-load maneuvers like steep turns or abrupt pull-ups, causing it to reach its critical AoA at higher speeds and different attitudes compared to level flight. In these situations, the aircraft may stall at higher airspeeds (above the normal stall speed) due to increased G-forces.

Turns

In banking turns, the increase in G-forces necessitates a higher angle of attack to maintain lift, thereby raising the stall speed. This can cause the aircraft to stall at different angles depending on the bank angle and load factor during a turn. These stalls require pilots to be vigilant about changes in stall characteristics when maneuvering.

Understanding these factors is critical for pilots to manage their aircraft effectively through various flight conditions and avoid unintended stalls through appropriate technique and anticipation of altered stall characteristics.
Aerodynamics for Naval Aviators - H.H. Hurt Jr.