You’ve probably noticed in your house that there are a few doors that seem to stick in the summertime. By the time winter rolls around the door doesn’t seem to stick anymore. The reason this happens is that cold air in the winter can’t hold as much moisture and this causes wood to dry out and shrink. Wood props are equally affected by this problem and it’s important that you torque your prop bolts in November or December to ensure that the bolts haven’t loosened up.

When the previous owner delivered my plane, he flew it in over the mountains from Salmon Arm. It was mid-December a few years back. Overtop of Lake Louise he noticed something go flying past the canopy but didn’t think much about it until he got home. By then I’d already noticed that one of the air baffles had broken off and had been sucked forward into the prop. What he saw was the baffle and pieces of the prop going past the canopy. The prop bolts had loosened slightly with the cold weather, enough for the prop to get a bit of movement even with 6 drive bushings firmly embedded in the back. The prop was actually causing the spinner to walk causing elongated holes and creating cracks and deformations in the spinner. The vibrations caused by the loosened prop was what caused the baffles to break. The back of the prop had actually begun to char slightly from the heat generated by the movement of the prop.

When I removed the prop, the bolts didn’t feel loose and I still needed a ratchet to remove them, but they were less than the 200 pounds of torque required by the manufacturer. If you have a wood prop and haven’t checked it yet this year, then it might be a good time to double check the bolts with a good torque wrench before your next flight.