You would never think that water could cause these problems, but the fact of the matter is that it can and it will. Keeping your airplane warm and dry has some advantages. It keeps moisture out of the plane, and that can keep you out of some pretty hard to figure out problems. Lets take a look at your propeller, for example…
THE SET UP
You park your plane on the ramp, or even under an astroport in an area that has two attributes: humidity and cold. The night you park, your prop stops on a slight angle, and you leave it there, since you will be back tomorrow to go flying. It is a beautiful evening and dew forms as 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 vibrates 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!
When you parked with your prop near vertical, you created a way for water to get into your spinner — by running down the high blade. Most spinners have a good fit, and when conditions are right (dew or rain), water can freeze on the metal prop hub or spinner — one drop at a time — and form a frozen blob inside the spinner. That in itself is not a problem … it’s when you start the engine that the off-center weight of the ice blob turns the event into your own personal earthquake.
INSULT TO INJURY: In the three hours before the mechanic got to the plane (and after your extensive and graphic description of the nature of the problem) temperatures had risen, the ice melted away and with it, the problem! Now, you’re just another pilot who doesn’t know what the heck he’s talking about.
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 that pretty morning dew isn’t always so harmless. If you have an engine heater, keeping it plugged in when the temperature drops can 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!
Real World 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 a fouled plug or extra prime caused the problem, 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 to remove the aircraft’s 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.