Frost

[I fLy pLaNeS]

When I think of frost I think of it affecting the upper surface of the wing. Is frost below the wing and also on the top of the fuselage a danger?

 

[Dr Pokenhiemer]

Frost GENERALLY affects the leading edges and the front 1/3 of the leading edges and control surfaces. When it forms, it's like little jagged peaks and creates parasite drag. This is the reason you cannot takeoff without "polishing" the frost smooth. All the frost does not need to be removed, just smoothed. The fuselage is not a a leading edge nor a control surface, however, depending on the size of the plane and the magnitude of the frost, you will have a little extra weight, but I've never heard of that being a factor.

 

[RipCurl]

Say I get all the frost off the wings with some glycol, but the whole fuselage is still frosty as can be. Would the extra drag be something to worry about?

 

[Dr Pokenhiemer]

Never was a problem for me. I flew cargo in a C210 during a couple of winters. Never deiced the fuselage. Even had to deice the Lear once and they just got the wings and tail to clear the freezing rain. The rest of the frost will sublimate off within a few minutes. Watch it on your windshield. Make sure to clear you view, but watch the rest of the frost disappear shortly after takeoff. MAKE SURE you students understand that they cannot take off with frost on the wings or control surfaces though as I explained earlier.

 

[groundpointsix]

Didn't the FAA come out with something last winter saying "polished frost" was no longer an acceptable method of operating and that the airplane had to be completely free of frost?

 

[Dr Pokenhiemer]

Section 91.527: Operating in icing conditions.

(a) No pilot may take off an airplane that has—
(1) frost, snow, or ice adhering to any propeller, windshield, or powerplant installation or to an airspeed, altimeter, rate of climb, or flight attitude instrument system;
(2) Snow or ice adhering to the wings or stabilizing or control surfaces; or
(3) Any frost adhering to the wings or stabilizing or control surfaces, unless that frost has been polished to make it smooth.

 

[avbug]

Frost can make an increadible difference in the amount of lift available. In a light aircraft, it may make the difference between being able to climb out of ground effect, or not. It may double or more, your takeoff distance. It may increase your stall speed considerably.

Frost on your fuselage may or may not be very detrimental to your performance, but many aircraft derive lift from the fuselage, too. Frost can act as a starting point for more ice, as well as aerodynamic penalties associated with the roughness.

Think clean airplane. Forget the notion that frost sublmiates. It may, or it may not, but it's a foolish thing to plan on. A little like assuming that engine roughness will go away. Any ice, even frost, can be very dangerous.

Stick to the clean airplane concept. It's always a good policy.

 

[I fLy pLaNeS]

Thanks for the info

 

[JohnE]

Section 91.527: Operating in icing conditions.

(a) No pilot may take off an airplane that has—
(1) frost, snow, or ice adhering to any propeller, windshield, or powerplant installation or to an airspeed, altimeter, rate of climb, or flight attitude instrument system;
(2) Snow or ice adhering to the wings or stabilizing or control surfaces; or
(3) Any frost adhering to the wings or stabilizing or control surfaces, unless that frost has been polished to make it smooth.

How does one "polish" frost?

 

[Dr Pokenhiemer]

Rub it with your hands or a cloth to make it smooth--just knocks the jagged tops off to reduce drag.