Surface contamination and ice

Treat the leading edge as aerodynamic geometry

Frost, ice and damage change the flow before the pilot sees a large performance loss.

Roughness and separation

Leading-edge contamination can change transition, pressure recovery and separation. CLmax can decrease, drag can increase and the stall can occur at a lower α, sometimes with weaker warning.

The effect depends on shape and location; equal ice mass does not mean equal aerodynamic penalty. A thin rough layer at a sensitive location can matter more than a smooth-looking deposit elsewhere.

The complete aircraft changes

Ice can affect the tailplane, sensors, propeller and control surfaces as well as the main wing. Tailplane stall and wing stall can demand different aircraft-specific procedures, so a generic wing-stall response is not a universal icing checklist.

Use approved ice-protection limits, clean-aircraft requirements and current procedures. The clean-wing speed and warning schedule cannot automatically be trusted as unchanged in unapproved contamination.

Why a small deposit can change the warning sequence

Assume a clean wing reaches CLmax = 1.8 near its usual warning region. A contaminated shape might reach only 1.35 and separate at a smaller α. Even if the pilot holds the same speed and loading initially, the coefficient margin has fallen; the old clean relation between buffet, warning and the final lift peak may no longer apply.

The numerical change is a supplied example, not a reliable penalty for a given ice thickness. Ice horns, distributed roughness and local deposits modify different parts of the flow. An ice-protection system operating normally also does not imply that every unprotected surface is free from aerodynamic or system consequences.

In the laboratory, impose the 25% coefficient loss and compare the clean and reduced boundary at the same speed. Then identify why the model cannot answer whether a real aircraft is acceptable for departure. That decision involves clean-aircraft requirements, actual contamination assessment, holdover and inspection procedures where applicable, and the specific aircraft’s approved protection and operating limitations.

Recalculate the margin, then recognise the model limit

A numerical coefficient penalty can illustrate the direction of the risk, without predicting real icing aerodynamics.

Required and available coefficient

At unchanged weight and speed, required CL stays fixed while available CLmax can fall. The gap between the two is smaller even before a visible speed loss. Adding bank raises required CL again.

In the synthetic laboratory, a selected penalty reduces CLmax from a supplied clean value. This is an exercise input, not an empirical mapping from ice thickness to safety or a de-icing acceptance criterion.

Do not solve an unknown ice shape with a speed increment

A speed increase may reduce required CL, but it does not restore altered control balance, warning cues, tailplane margin or structural/system limitations. It is not a substitute for the approved icing procedure.

A meaningful decision needs aircraft-approved limitations and the actual environment. The teaching model only answers how the stated wing CLmax and load alter a calculated stall boundary.

Combine contamination and bank in one stated exercise

Suppose a clean 1 g stall speed is 80 kt. A supplied contamination effect reduces CLmax to 75% of clean, so the new 1 g boundary is 80/√0.75 = 92.38 kt. At load factor 1.5, the corresponding boundary is 92.38√1.5 = 113.14 kt. Separate square-root factors combine because both changes enter the lift requirement.

At 110 kt, this exercise no longer supports the stated 1.5 g condition, although the same speed would be comfortably above the clean 1 g value. Comparing only with that original 80 kt figure would miss both changes in the required/available coefficient balance.

Use the laboratory to hold speed fixed while introducing the imposed loss and then increasing load. Explain each loss of margin before adjusting speed. Finish by stating the operational limit of the result: it predicts only the consequence of the supplied wing coefficient, and cannot restore altered tailplane, sensor, propeller, warning or control characteristics through a generic speed increment.

Can you explain and apply the mechanism?

Four original questions. Work from the stated facts, then compare your reasoning with the explanation.