Dangers during take-off: ground effect and stall speed
One of the greatest dangers arises when an aircraft takes off with insufficient speed. Especially with wet or contaminated wings, the induced drag increases while the lift decreases at the same time. This can cause the aircraft to remain in the ground effect - a narrow layer of air above the surface that temporarily provides additional lift.
Without sufficient speed or climbing power, the aircraft remains just above the ground and touches down again after a few metres, often requiring an emergency landing. Light aircraft, gliders and self-launching motorised gliders are particularly at risk here.
How rain, ice and dirt change aerodynamics
Dirty or icy wings increase the drag considerably and shift the stall speed to a higher value. This means
- The take-off roll distance is longer because the aircraft needs more speed to generate sufficient lift.
- When the rotation speed is reached, the aircraft may not be airworthy.
- During flight, the risk of a stall increases because the wings cannot deliver the planned performance.
Even thin layers of water or ice can trigger these effects. The following therefore applies: Dry and clean wings are essential for safe flight.
Prevention: clean wings - always and everywhere
General aviation can learn a lot from the safety standards of commercial aviation. There are clear rules for commercial aircraft: No aircraft may take off if snow, frost, ice or water cover the wings or other critical components. The same caution should be standard in general aviation.
Practical tips for avoiding contamination:
- Park the aircraft in a hangar:
The safest way to avoid contamination is to park the aircraft in a protected area. - Check thoroughly before starting:
Before every take-off, check the wings and all aerodynamic surfaces for signs of moisture, dirt or ice. - Clean the sash:
If the aircraft is parked outside, make sure that the wings are completely dry or free of ice and frost before take-off. - Do not start in the rain:
Gliders and self-launching motorised gliders in particular should not take off in the rain. Wait until the wings have dried. - Use suitable equipment:
Wear protective tarpaulins or covers when the aircraft is left outside for long periods.
Avoid accidents: Safety through preparation
The STSB report HB-2033 and other sources such as AOPA and Boldmethod urgently warn of the dangers of contaminated wings. Accidents caused by iced wings or water films are often avoidable if pilots observe the basic safety rules.
Examples from practice:
- Frozen wings: Even a thin film of frost can impair the aerodynamics of the wing to such an extent that the aircraft goes into a spin during take-off rotation.
- Water film in the rain: Rainwater can disrupt the surface flow on the wing and drastically reduce the climb performance.
Conclusion: Safety First, Every Flight
Whether in general aviation or commercial aviation, clean wings are not an option, but a necessity. Contamination from rain, dirt or ice fundamentally changes the flight characteristics and significantly increases the risk of accidents.
Pilots should always be aware that thorough preparations - from inspecting the wings to analysing the weather - are an essential part of any safe flight. Because: "Safety first" applies to every flight and at all times.
Source references:
StaySafe