The vast majority of GA pilots will no doubt have a firm understanding of the clean wing policy when it comes to winter operations.
The question we have to ask ourselves though, is do we realise that the same aerodynamic risk exists all year round?
Ice and snow contamination, depending on thickness and texture, will affect the efficiency of an aerofoil in different ways. The bottom line being that it affects it, so it is therefore important that before flight we remove anything that will impact aerodynamic efficiency.
Anything we or the environment do to our aerofoil will have the same effect as snow and ice, by disturbing what was otherwise a beautiful flow of air, from leading to trailing edge.
Some hazards are visible and easily identifiable on the walk around. A large number of bugs built up on the leading edge, for example. What is the difference between this and impact ice in terms of changing the shape of the leading edge?
Hangar rash and bird impact damage is always a subjective topic, as often a manufacturer will provide maintenance manual tolerances and allow an aircraft to remain in service. Whilst on a general performance level it may fall within acceptable limits, by definition the shape of the aerofoil has changed in that section.
I was once tasked to conduct a flight test on a business jet at a completion centre due to the fact that the aircraft had developed a very pronounced wing drop at the stall.
Sure enough, I found that the left wing dropped extremely violently and was outside of production flight test limits, whereas prior to the maintenance visit it had behaved impeccably. Obviously something had changed and it had to be aerodynamics.
Looking through the maintenance records, the clue was buried in the reams of paperwork. A wing anti-ice squawk had required the left leading edge to be removed and re installed as part of the troubleshooting and rectification.
When I ran my hand along the joint between the leading edge and wing skin, I immediately felt a “ridge” from excessive sealant. That ridge ran span-wise from wing root to wing tip, top and bottom. It was only measurable in millimetres protruding into the airflow, but the effect was devastating. Removed and resealed flush, the aircraft regained its composure with docile stalls.
We must never forget also that elevators and horizontal stabilizers are just as capable of stalling. So whilst it looks cool to run around in a Jeep caked in mud, allowing the tail feathers to look as if they have been in a fight with a Hershey bar can end in tears.
The most bizarre contamination of an aerofoil I ever experienced was after a day of operating in and out of ranch strips. The following morning when I went to get the 182 out, the stench from the hangar was overwhelming.
My nose eventually led me to what looked like and smelt like skunk meat, all over and stuck to the top wing!
No evidence of a prop strike or blood, no evidence of a bird of prey having used the wing as a picnic table.
To this day, whenever I do a walk around, I still look for aerofoil contamination, regardless of the season. Sometimes you just need a good sense of smell!