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Now and Then RC Plane Maintenance
Simple checks now can prevent a crash “then”
Text, photos and video by Tom Hintz
Posted – 6-25-2015
All RC airplanes need checking over now and then. Those powered with gasoline engines are subjected to far more vibration so we need to check those aircraft even more frequently. New planes must be checked early in their life as the parts settle in and wood compresses which can dramatically loosen fasteners. Just how frequent these checks should be depends on your flying frequency. Of course you can wait for the plane to let you know maintenance has been put off too long by shedding a part that is crucial to staying in the air.
Clean Up and Covering
I start by giving the whole plane a good cleaning because when I leave the flying field I am way too tired and/or hot to do it then. I use Simple Green and paper towels to clean my planes up and then after all of the maintenance is done, I go over the covering again with Monokote Cleaner and Polish because it seems to brighten up the colors and give the plane a shine that Simple Green alone doesn’t do.
This is also a great time to find and repair loose and damaged covering. No matter what you do, the summer sun will loosen covering in places. We also are going to develop “hangar rash” from transporting the plane or landing it “close” to the runway. However it happened now is a good time to fix those dings before the covering peels off even more. One point is that I have found it better to clean the covering thoroughly before going after it with a heat gun or iron as that can “set” the dirt in some coverings.
The process of cleaning your plane is also a good time to check for broken or loose hinges. Make sure you check all of the hinges and not just the ones at the ends that you can see move easier. When the glue on hinges starts to fail it is never all at once. However, when enough of the glue eventually fails all of the hinges can pull out at the same time shedding a control surface that you really did need.
Over the years I have found that using medium or thin CA glue (depending on the gap surrounding the glue on the hinge) works great at repairing a loose hinge. Usually the actual gap between the hinge itself and the epoxy that originally held it in is very small and irregular. Running some CA in there can do a great job of securing the hinge once again and you are ready to fly quickly. Going out in the woods to find the lost aileron that caused your plane to commit suicide in the field is way more work.
Wings and Mounts
Depending on the plane design you might have removable wings and we need to check a couple things there as well. We have to make sure that whatever type of fastener used is secure and blind nuts are tight. Most wings have alignment pins on one or both ends and they frequently come loose after a bunch of use. Some of these pins include a spring clip (hairpin) to further secure the wing so we need to be sure these devices are tight and aligned properly.
Remember the bolts holding removable horizontal stabilizers on. Many of us never do remove the horizontal stabilizers which just gives the fasteners more time to back out. I check these often and use removable thread locker on them whenever they are taken out.
Inside the fuse there are doublers and other reinforcements that contribute to the wing integrity. I look these over for cracks or separations. It is very easy to fix a little crack now rather than a big split later. Stuff like this is not going to get better on its own.
I go over all of my servos to make sure that they are still tight in the air frame, the arm is still tight on the servo output shaft and that linkages remain secure. If you have been flying with a bunch of trim dialed in this would be a good time to adjust the control surfaces so you can neutral out the trim settings.
Pull-pull cables “settle in” over time so they frequently need to be adjusted a little to snug them up so the rudder performs correctly. It is easy to let loose pull-pull cable go unnoticed because you just get used to how the rudder works with slop in the cables.
Wiring for the servos usually makes up the biggest mess in the fuselage so this might also be a good time to make sure none of the wires have come loose and are waving around waiting to be grabbed by the pull-pull or throttle arm and jerked out of the receiver. A couple little tie wraps will help secure everything in neater bundles and keep wires out of harm’s way.
Another key stress point on most RC planes is where the landing gear connects to the airplane. There can be a bunch of vibration when those little wheels are spinning hard during takeoff and landing so we need to check everything from the bolts that hold the gear to the plane to the wheel collars that keep the wheels from falling off. A failure at any of those points can mean severe damage when you try to do the next landing without some of the landing gear where it is supposed to be.
On many planes you can see the reinforcement where the main gear bolts to the fuselage. This is a good time to make sure that the internal nuts and bolts are tight and that there are no cracks in the structure surrounding the gear mounts. Fixing cracks now is way easier than trying to glue a sea of small pieces back together when the gear torques out.
Make it a point to look over all of the internal fuel lines and connections. Look for drips of fuel or “wet spots” inside the fuselage. I use small tie wraps on virtually all of the fuel line connections and I check all of them to be sure all remains intact. Tanks with the expanding rubber plug must also be checked for seepage and that the screw that expands the plug is tight. This is also a good time to check fuel filters to be sure they have not become contaminated.
Under the Cowl
The area hidden beneath the cowl needs special attention because heat cycles are added to the influence of vibration. Fasteners on the motor itself as well as motor mounts, mufflers and other bolt-on pieces frequently loosen up. Regardless of the actual number of flights, all of my new planes go to the shop and have the cowl pulled after the first day of flying so I can check everything for security.
Even prop bolts need special attention because the wood (and other materials) tends to compress under the pressure of the prop bolts and washers. As the wood compresses, even slightly, the tension on the bolts is reduced and they become looser than when we installed them. Using thread lock is advised but during initial uses the prop itself can compress so without turning at all, the bolts holding it on are looser.
Wood definitely compresses but it doesn’t compress indefinitely. I find that after checking prop bolts four or five times, they tend to loosen slower or not at all. However, that does not mean I stop checking them. Forcing myself to pull the cowl occasionally means I automatically re set the prop bolts, insuring the integrity of the prop.
With the cowl off we can also get a good look at the firewall itself. Another important area is the motor box that most gas planes (and others) have. Hanging a motor on either type of mounting system insures vibrations that will work on glue joints over time. Finding and fixing cracks and separations now will always be far easier and cheaper than replacing a crashed air frame.
All of this maintenance should be common sense but far too many of us are lulled into inaction because the plane keeps flying and performing well. The problem is that they can perform great right up to where they fall apart and impact something unforgiving, like the ground. There are no warning lights or other indicators to sound the alarm that something is coming loose. We need to look to find them.
The good news is that this kind of maintenance can often be completed in less time than it takes to recharge the on-board batteries. It is not a long and involved procedure. Like anything else, if we do it a few times we get faster at it. It is easier to get myself to do this kind of checkup because in the past I have found something that was easily repairable but would have killed the plane if overlooked. I suspect many of us can be inspired by the prospect of saving a plane and the pile of money it represents.
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