Saturday, October 26, 2013

It's Time To Look Out For Icing....

                                                    The weather has turned cold, it was 29 degrees this morning in Charlotte. That means it is time to consider the effects of icing on your airplane. The main considerations I will get into involve how ice accumulations on the airfoils affect flight. I just reviewed an excellent article published by AOPA*. Well worth reading, as I only touch on many things discussed therein.

I would like to reference three articles I have written on the subject of icing:
                Ice Beware It’s  Everywhere-2/1/09
                Ice Will Get You Unless You Do It Right-2/15/09
                You May Not Be Able To Prevent Significant Icing From Forming On Your Plane

Quick review. So you arrive at the airport and find that there is just a little fuzz type of ice on the wings, no thicker than a piece of “coarse sandpaper”*. No problem, right? Wrong according to most authors, who claim that even this thin accumulation of ice may decrease lift and increase drag. The referenced article offers this: frost and thin ice accumulations may decrease lift by as much as 30% and increase drag by 40%. So pay attention to your planes lifting surfaces.

Now if you arrive at the field and your plane has a thick crust of ice and or snow all over, you better go for a cup of coffee and prepare yourself for a tough job ahead. You have to get the white stuff off!  Why can’t you just scrape a bit off and fly away. Because, basically the presence of the snow, ice and whatever, has changed the shape of the airfoils of the `wings and stabilizer. This decreases the lifting ability of the flight surfaces to provide lift. Importantly the stall speed increases as does the drag. So pay attention to your planes lifting surfaces.

I am not going into what flight conditions pose the most problems for icing. Check the listed reference for a good discussion of those factors. They also discuss carburetor and induction inlet icing.

I will relate one of my experiences with arriving at the airport ready for a quick departure, only to find my Cessna 340 covered with a layer of clear ice. My wife was with me, and we had to spend almost an hour whacking and banging on the ice. After I decided that enough was gone from the main lifting surfaces, I decided to give it a try. The plane was lightly loaded, the air temp about 34 degrees. The plan: keep the plane on the runway longer than usual, thereby taking off with some excess airspeed. If the plane responded normally, continue the take-off, if not chop the throttles and land. All was ok, the take-off felt normal with good control responses, so off I went.   

In flight icing in my experience, never caused me any real problems. I always was alert for a decrease in airspeed due to drag, or an apparent mushiness of the controls. The biggest fear was to get into a stall due to the negative effects of the ice on airspeed and lift. Make sure that the stall warn deice was on and carb heat on when flying that type of engine in icing conditions.

So study up on the negative effects of icing and plan ahead. The big trick is to AVOID getting  into ice and always leave yourself an out.

*Aircraft Icing-Weather Advisor AOPA  SA11-11/02
NTSB Safety Alert- Aircraft Ground Icing