Maintaining your Fleet

by Len Buffinton

Just like the car in your garage, your sailplanes and tow-plane will need some maintenance on a regular basis to keep them flying trouble free.

It’s a real good Idea to look over your ship in the comfort of your shop. Why wait until something breaks to fix it. Most sailplane related issues are pretty standard from plane to plane. The maintenance of our tow planes should also be very similar to each other airframe wise, its the motor system which will vary the most.

We’ll start with the sailplane.

This probably comes as no surprise to you. The single most repaired part of a sailplane is the landing gear. That one little wheel is constantly taking a beating. The retract unit is always under significant pressure. The aluminum pieces that make up the unit, live in a dusty, dirty, grass filled environment. These elements get to every part eventually.

Maintaining the retract unit is pretty simple and can range from tightening screws to completely removing the unit and disassembling it.

These screws will constantly work themselves loose and make the whole unit sloppy. Tightening the screws will not only hold in the axle and wheel assembly; it keeps the whole unit rigid. If you’re having problems with the wheel getting stuck half way up, first check these axle screws. Another major issue with these screws not being tight is ware and tear on the whole unit. If the wheel is loose, you loose the rigidity of the whole assembly, therefore allowing it to twist and bend at will. The sliding lock will start to snag, the pivot arm will bind, and all these nice smooth metal parts will begin to wear.

Remember:

Any metal-to-metal connections should have loctite applies to them.  Use blue loctite if you want to be able to take it apart again in the future. Use RED if you want a permanent connection. Red loctite requires heat to separate.

Hint : always shake the loctite container before each use

Lubricating the retract

Believe it or not, it’s not a good Idea to lubricate the retract unit. The reason why is because the oil/grease will attract all the dust, dirt and grass that gets kicked up as you roll across the ground.  So, how do you keep everything moving freely? The best way to so this is to use a dry type of lubricant. I’ve use graphite spray and wax with very good success. When applying the  lubricant, be certain to get all of the sliding parts. It takes very little friction to make these units stick, and quickly become a nightmare.

Servo linkage

Although it’s not always thought of, the servos need to be looked at when performing your regular maintenance. It takes a strong servo to move the retract unit in the first place, so any time there is any type of binding, the servo still tries to move something. Check the linkage for bending. It’s a good practice to avoid using threaded rod for this linkage. Threaded rod is much weaker that a solid wire, and under strain, will bend.

The control are which the servo connect to will also need care. This arm will slide sometimes on the shaft it is connected to. If you remove the arm, you can file a flat spot where he set screw seats.

Gear doors

Depending on how the gear doors are mounted be sure the hinges are still in good condition. It’s pretty typical for the plastic hinges to break.

If you use rubber bands to close the doors, they should be changed out at least every six months.

The Wheel

Even though you are a great pilot, you make smooth landing and never fly on asphalt, you need to check out the wheel. Evert time the sailplane makes a sharp turn (ground loop) on the roll-out; you put a tremendous amount of strain on the side of the tire. The tire will peal off the rim or at least start to tear. Replace the wheel as soon as you see any issues.

Lastly, check out the bolts holding the whole unit in plane. Those bolts loosen over the season; again, loctite will help keep everything in place, but check this often, as even loctite is no match for Mr Murphy’s Law.

Flying Wires and Fittings

If your plane has flying wires, you need to pay attention to the attach fittings. Turn buckles should be safety wired so they can not unscrew. Cables and wires will stretch out, check them often and especially after a maiden flight. If you have a rough landing, be suspect of your cable fittings. Do not fly a plane until all the fittings are secure and tight.

TOW PLANE MAINTENANCE

The tug takes a tremendous amount of abuse over the season. If you’re smart, you will look over the tug every time BEFORE heading out to an event.

With a tow plane, what can go wrong, will go wrong. And it always seems to be when there is a long line waiting for a tow.

The **%*$*#@% Landing Gear

Fortunately, I’m blessed with some very good tow pilots; they respect my equipment and treat the tow planes with care. That respect is one of the reasons we have few issues with the tugs, but we still have some. Others have not been so lucky.  The main nemesis of the tow planes will be the gear. On the Pilatus Porter we fly, the landing gear system is a scale looking, shock-absorbing strut.  This gear, although it looks great, is the weak point of the plane. Even with the softest of landings, the gear is working away, trying to hold 31pounds off the ground. The fields are smooth, but still make the plane shake. You need to pay attention to the gear. Look it over. Grab it and try to twist it, turn the plane over and check the mounting bolts. The tires will also want to peal off if you turn to sharp. That’s a lot of inertia when the plane rolls through a tight turn.

Exhaust system

The second issue will be the exhaust system on gas-powered planes. If using a flex exhaust, be careful of the coupler. I have had at least 3 units come apart at the seams. You will notice a barking sound as it begins to give out.

Servo Arms

The next area of concern is the servo arms. Before flying your tug, make sure the arms have not vibrated loose. This is VERY common,  so use a little blue Loctite to ensure you don’t end up with a rude surprise.

Control linkages

When getting an ARF, be careful of he hardware. I elected to use the clevises from an ARF because they were all set up already, with nice threaded rod connectors, boy was that a mistake. By about the 50^th flight, which was only the second day, the little pin that goes through the control horn came apart. Thinking this was a fluke, I replaced it with one I had on hand from another ARF, same thing again a short time later. Needless to say, they were all taken off and replaced with Dubro hardware. The other benefit to replacing the hardware was if I needed something at the field, it was more likely someone would have a Dubro or GP clevis than a metric one. That’s something to consider.

The tail wheel

Having traveled to quite a few aerotow events, I can say most tugs in the USA are tail-wheel airplanes. However, attending an aerotow in Switzerland last summer, most of the towplanes were nose wheel (trike gear) planes. Perhaps it’s due to having a paved surface to fly off. On a grass runway, a nose wheel plane will take a beating, leading to down time for that tug.

Whichever you fly, be certain the “steerable wheel” is in very good working condition. On a tail dragger, the tail wheel always needs to be check and adjusted. The wheel back there takes abuse, not from the flying, but from the handling of the plane by the ground crew, not to mention getting it in and out of the car/truck/trailer. Check the steering cables or springs. You need good control of the tail wheel with a tug; you will be taxiing in close so the line handler can get the tow line.

Other misc items

Loose motor mounts

Loose Prop/spinner

Battery maintenance

Muffler bolts

Fuel tank and fittings

All these items should be looked over carefully too, however, after 2 full years of towing and thousands of tows, the main issues with the tugs we the first 5 items listed.

Lastly, make sure you have a good fueling system. If you have an electric gas/fuel pump, be certain to charge it. Also, have a back up hand crank pump too. I’ve had to pull out that hand pump more than once last season.

With a little care and forethought, you can have a trouble free season, but you MUST maintain your fleet. Don’t wait until something breaks to fix it, and don’t wait until the day before the event to get the planes into the shop. You just may end up rushing the repair or simply run out if time.