Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.")

Aero-News has called upon the expertise of Thomas P. Turner, master CFI and all-around-good-guy, to bring our readers -- and us -- daily tips to improve our skills as aviators. Some of them, you may have heard before... but for each of us, there will also be something we might never have considered before, or something that didn't "stick" the way it should have the first time we memorized it for the practical test.

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Aero-Tips 09.06.06

It's not too early in the season to review the formation of frost.

Frost forms on cold nights when the skies are clear, generally when winds are light. When surface temperatures reach the freezing point and enough moisture is present to condense in the cold air, frost will almost certainly crystallize.

Note: Cloudy skies and/or winds greater than a few miles per hour will usually prevent frost formation. Exception: in fog, which may form in as much as moderate winds, heavy frost may collect as saturated air blows onto cold aircraft surfaces.

Frost forms most quickly on metal and smooth or glassy surfaces-exactly the materials most wings are made of. You'll see frost on wings, tails and windscreens long before it forms on the surrounding ground-smooth metal or fiberglass surfaces will cool faster than the ground, so they may be below freezing when other surfaces' temperatures are still above the freezing point. Frost forms in crystals (very important for aviators-more in a moment), so once the first crystals form the frost will spread quickly across the rest of the chilled surface.

Why it's important

Frost may be pretty to look at, but it can have a significantly detrimental effect on flying. The crystalline structure of frost creates turbulence in the airflow nearest the wing -- the boundary layer -- and will degrade lift development, accelerating the stall. Worse yet, the loss of lift is unpredictable, and may not be symmetric from one wing to the other.

Because there is no way to predict the aerodynamics of a frost-contaminated airfoil the only safe approach to flight is to remove the frost completely from all flying surfaces before attempting to take off. The best method is to move the airplane into a heated hangar, allowing the frost to melt off. In most cases it will melt rapidly. If the aircraft is parked where it will be exposed to sunlight, often the frost will melt off quickly as soon as the sun hits it-be patient; when it begins to melt it will melt rapidly. A less desirable third method is to spray ice-melting liquids on the wings. Be very careful to keep these chemicals away from windows and other acrylics; double-check manufacturers' directions and spray-can warning labels before using any chemicals on composite surfaces. In all cases, once frost is removed start up and fly as quickly as is safe, so melted frost does not re-freeze into clear ice on wing surfaces, or in control hinges or other critical areas.

Aero-tip of the day: Watch for frost as the season progresses, and remove frost completely before attempting to fly.

FMI: Aero-Tips