Keeping your airplane warm and dry has some advantages; let’s take a look at your propeller, for example. You would never think that water could cause problems with your propeller, but the fact of the matter is that it can and will.
THE SET UP
You park your plane on the ramp, or even under an astroport in an area that has two attributes: rain and cold. The night you park, your prop stops on a slight angle, and you leave it there. Over the evening, the rain falls and the temperature drops. By the time you arrive in the morning, the temperatures are barely above freezing, and you are ready to fly.
As you start the engine and advance the power to low idle, the engine begins to vibrate as if it lost a prop blade! Trying to adjust the power higher or lower does not help the situation. You shut down the engine and call the mechanic. Three hours later when the shop opens, he checks out your plane and the problem is gone!
WHAT HAPPENED?
When you parked with your prop on a slight angle, you set up a way for water to get into your prop spinner — by running down the high blade. Most spinners have a good fit, and when the temperature drops and it rains, the water can freeze and form a frozen blob inside the prop spinner. When you start the engine, the ice blob throws your prop spinner out of balance, which you feel as excessive vibration. As the temperature rose over the three hours before the mechanic got to the plane, the ice melted away, and with it, the problem!
THE DEFENSE
Don’t park with your prop on an angle that could allow water to enter the spinner when it is cold outside. Remember, it rains when you least expect it and a bit of dew on the prop can become a pool in the spinner. If you have an engine heater, keeping it plugged in when the temperature drops can be enough to keep the prop hub warm enough to prevent ice. Finally, if your engine vibrates badly when started, shut it down and check it out. Running with high vibrations can do anything from ripping the spinner off the plane to wrecking the crankshaft nose seal!
Case Study
Prop spinner ice is hard to detect, because it hides inside the spinner. One owner of a Piper Arrow found this to be the case. The plane had recently returned from an annual inspection and was running well. Following a preflight on a cold morning, the pilot started the plane, and noted a spray of water from the prop spinner. As the engine settled down at 1000 rpm, he also found it hard to not notice that the engine, which had previously idled smoothly and quietly, was trying to shake him out of the cockpit.
He promptly shut the engine down and, thinking the problem was caused by a fouled plug or extra prime, went to see his A&P for repairs. The A&P inquired as to anything out of the ordinary on the start, and when provided with the information on the water spray, he handed the owner a screwdriver and told him he had ice in his spinner.
Several minutes and removed screws later, our intrepid pilot got the spinner off the plane. Sure enough, inside the spinner was a large, flat block of ice, shaped like a tongue, stuck to one side of the spinner. The pilot removed the ice, reattached the spinner to the backplate, and started the plane up again without incident.
It’s that time of year. Be careful.
