Winter maintenance

Model Airplane News, Feb 2000 by Bell, Rick

By the time you read this, we Northeasterners will be in the midst of winter and experiencing the dreaded downtime that accompanies it. I use this downtime, however, to ensure that my hells remain safe and trouble free by making certain that everything is shipshape and ready to go when flying season returns. Because they have more moving parts and vibration sources (just like full-scale helicopters), our model helis need more maintenance and attention to detail than do fixed-wing models. So clean off your workbench, grab a cup of coffee and let's get started.

PREVENTIVE MAINTENANCE

Before you store yourheli for the winter, remove all the fuel from the tank, and charge the batteries. To keep batteries in top condition, cycle them once a month during the off season. I use a logbook to track my batteries' performance, and I recommend that you do this, too.

I start by giving the heli a thorough cleaning. Remove the canopy and main rotor blades, then clean every nook and cranny using a rag, a small screwdriver and some household cleaner. Remove all the oil, grease and dirt build-up. To thoroughly clean them and inspect the bearings, some areas of the heli will have to be disassembled. If you put in a lot of time on your machine, all the bearings should be removed and checked for smoothness then regreased as necessary. A rough bearing will cause vibration and will eventually fail.

After the heli is nice and clean, I check all the pushrods and ball links for wear. Remove the ball links and clean them, then check them for smoothness; they should not be too tight or sloppy. If the bearing has a lot of slop, replace it. One linkage that needs special attention is the throttle pushrod. Because it's attached directly to the engine, it's subject to extreme vibration; it really takes a beating. I usually replace the link and the ball on the carburetor arm. Once all the

links have been cleaned and inspected, reattach the pushrods, but not to the servos. Move the linkage by hand and check for binding or excess slop. Now is the time to make any necessary repairs.

When you've finished, check the servo arms for cracks. Replace any defective arms but be sure to replace them with arms of the same size.

If your pushrods have Z-bends, now is a good time to upgrade them by adding ball links. Over time, Z-bends wear out the holes in the servo arms, and this reduces control precision.

SERVO AND RADIO CHECK

Check the mounting screws, and tighten any that are loose. Grab the servo output arm and check for wear or slop in the servo spines. Check the servo lead wires, and look for any that might be frayed or chafed from rubbing against the frame. Replace any defective servos. While in the radio area, check the gyro wiring and connectors for wear. If you use a mechanical gyro, remove its outer case and make certain the springs are tight.

All newer helis use composite servo trays; check them for cracks. If your heli has wooden servo trays, check all the glue joints and reglue any that are suspect.

FRAME, BOOM AND TAIL ROTOR

Loose bolts are another Source of vibration. Check all the nuts and bolts that hold the frames together, and tighten any that are loose. Also look for cracks, especially around the engine and landing-gear mounts. These areas are subject to high stress and vibration.

After I've checked the frames, I remove the tail boom and inspect the drive system. If the heli uses a belt to drive the tail rotor, check it for wear. If the heli uses a wire drive, remove the wire and clean out any old grease and then relubricate it before replacing it. For torquetube drive systems, check the support bearings for smoothness, and make sure that the drive ends are secure.

It is very important to check the tail rotor and gearbox. Remove and disassemble it check the bearings and relubricate the gears. The setscrews holding the tail-rotor hub to the shaft should be checked for security and retightened if necessary. Check all the links for slop or binding. I also disassemble the tail-rotor blades' grips, and I check the thrust bearings for wear then relubricate them before I put them back together. The tail-rotor blades and tail fins should also be inspected for cracks or other damage. Replace any defective parts.

MAIN ROTOR HEAD

Because the main rotor head is the most important part of any helicopter, I completely disassemble it for inspection. I start with the bearings and check them for smoothness, especially the thrust bearings; they take quite a load. I clean them, and I use a magnifying glass to inspect the grooves in the races. I check for dents or pockets that prevent the bearing from turning smoothly. If any are less than perfect, I replace them.

Once I'm satisfied with the bearings, I check the feathering shaft for straightness and wear and the blade grips for signs of stress.

I check the blade-retaining bolts by placing them in a drill and spinning them to see whether they are bent; if they are, I replace them. I also check the flybar and its paddles and all the pushrods and associated links.