Pull String Control System

A Pull String control system works very well.  Make sure you install the pull string BEFORE you cover the plane.  MUCH EASIER!!!

They are easier to adjust and don’t strip your servo as easily as the traditional push piano wire system does. In this write up I will explain how to install a String Pull system in your plane.  This is more commonly used on the elevator and rudder.  You just need some aluminum tubing and string.  The string can be purchased from any fabric store.  Be sure to get strong polyester string.  Pull on it hard to ensure it will not break easily. 

In the picture below you will see how the string looks after its installed, keep in mind you will need to build custom control horns as in my other write up.

In the next picture below you will notice that the string route through the servo horn and back to the other side of the control horn. 

Don’t get intimidated by this as once you do it the next time is a breeze and you will learn to love the system.  You can use small washers in place of these fancy custom plates that are mounted under the servo screw to hold the string in place.  To adjust all you need to do is loosen the screw and adjust.  Simple!! 

Now, here is the tricky part.  You are probably saying to yourself there are not enough strings to loop around each elevator horn, right?  Well let me explain.  The elevator servo will have two string ends coming from it.  You will need to tie a “Y” off of each string end.  One “Y” will route through to the top of the elevator and the other “Y” will route to the bottom.  Make sense? 

Here is another picture

Notice how the string has to hook to both sides of the horn.  This is because it is a Pull system not a Push system.  This is one side of the elevator.  You will need to do this to both sides.

To secure the string all you need to do is wrap around horn and then use a small drop of CA to secure the string.  Then tie a knot.  The CA allows you to pull the string tight and hold it in place while you tie the knot.  If you don’t CA before tying the knot you will be fighting to keep the string tight. Allow enough loop to be able to remove the string off horn if you ever need to.  I usually tie my knots about ½ to 1 inch from horn.

This will take patience and practice.  Use aluminum tubing to route the string through the fuse.  Be sure to debur the tubing so rough spots don’t cut the string. 

Installing cable system for ailerons

In a previous write up I showed you how to cut out and build your ailerons.  There are several ways to set up your ailerons and “power” them.  One of the more common ways is to use piano wire where each wing will have its own dedicated servo.  This way works great but requires more work and doesn't seem to work as well. 

 In this write up we will be using a Push Cable made by Sullivan.  This size is .032 w/Gold-N-Clevis 36”

*Please realize that if you choose this method you will not have flap-working ailerons.

This method works very well and the ailerons move very smooth and are easy to adjust.  I highly recommend this method. 

After ailerons are cut out and built you will need to decide on the placement of the cable.  Make sure you are not making sharp bends in the cable as you need the cable to flow smoothly in the cable tubing.  See picture below on my placement. 

You will need to decide on the servo placement so it doesn't interfere with the other components in the fuselage.  The cable should be placed straight through the ribs.  Using a little drill bit you can drill these holes through the ribs by rolling the drill bit with your fingers.  Once the cable is in place use medium CA (NOT thin) to glue the cable in place.  You will have to cut the tubing to allow the E-Z connect that mounts to servo wheel.

Mount a small balsa plate that the end of the wire can mount to.  Trim off excess tubing as shown below.  Be sure not to glue the cable to the tubing.  Use small amount of CA.  Use Caution!!

The last step is to mount the control arm to the aileron.  Then I use DuBro E-Z connector and mount the connector in the arm.  Then the wire routes through the E-Z connector for easy adjustment.

Cutting ailerons on a wing

When building a plane from scratch you first need to decide if you want ailerons on your plane.  Some planes do better without ailerons where on other planes they are a must. 

For this write-up I will be demonstrating how to install wings in a fully built wing.  Yes, I said fully built wing.  It’s important to fully build your wing right up to the point before covering it. 

In this picture we are installing ailerons in a scratch built Sig Kadet Senior.  These plans were shrunk to a 38” wingspan.  

   

The first step is to measure and mark where you want the ailerons to be.  In this case, since this is a simple trainer, we want smaller and longer ailerons.  If it were an aerobatic plane we may consider larger surface area ailerons for more throw.  Notice how I have marked the ribs where the ailerons are to be cut.  I will not get into how big and whereabouts to cut your ailerons as this will be your choice and discretion.  Just be sure to mark both wings the same so they match perfectly.

Next step is to cut out the aileron.  Using a blade shown in the pics, make a straight cut up and down.  Be careful and be sure to pay attention where you are cutting these as you would hate to mess up a freshly built wing.  I mean come on, it took you at least a month of building. 

Now it’s onto putting the wing back together.  Using a thin strip of balsa that is the same height as the inside ribs, cap off the inside so that the inside is secure.  Depending on how even you cut your ailerons you may need to sand these down a little to get the straight.  Also, be sure to cut them back to compensate for the thickness of the balsa cap that will be applied to the ribs and also the aileron or the ailerons will stick out and this would be ghetto.  We don’t ghetto build around here.

After you have capped both insides of the wing its time to cap the ailerons. You will be cutting these at a 45 degree angle.  If you cut them straight they will not be able to pivot.  Once you have cut them and sanded them even cap them with a strip of balsa.  See picture below.  Do this to both sides. 

Now its time to hinge them.  You can buy different size and kinds of hinges.  For our application we will be using Du-Brohinges.  They seem to work really well as they are very light and have small holes to bite onto the CA. 

Install small plates on the wing where you want the ailerons to attach.  I have found two to three hinges will hold it just fine.  Be sure to mount the plates a little below the top of the rib as you will be capping this later and want to leave enough room for two plates and the aileron in between.  Go ahead and glue the wood caps in place but DO NOT glue the hinges in place.  You will install hinges after you cover.  Just be sure that they slide in and out with little force.

In the next article we will look at how to control the ailerons.

Building a custom Cowl

In this write up I will show you how to make your own custom cowl.  This cowl will be stronger than the cowls you will find in typical ARF and kits. 

You will need an empty 2 liter bottle and a chunk of wood.

First, your plane/fuselage will need to be pretty much complete.  In this write up I will be using an old bed post as this will be the correct size. 

 Next you will need to draw some dimensions on the shape of cowl you will need.  Be prepared to have a few chunks of wood as you may mess up your first couple of tries.  Using a sander will help with this job.  Begin shaping the cowl how you wish. 

Using the motor begin to really pay close attention on where the motor will sit under the cowl.  Be sure to leave enough room for the cowl to overlap the front of the plane.  You will need this to mount the cowl to the plane.

Notice the cowl and motor placement in the pictures.  Also, note how I am using a bolt to hold the cowl while working on it.  This helps tremendously.

After the mold is exactly how you want it now it’s time to shrink the pop bottle around it and make the cowl.  Be sure that the cowl has been hand sanded to get out any small bumps.  They will show through the cowl. 

Put a light coat of flour over the mold before placing bottle top on.  This will help removing the bottle later.

Cut the top off the bottle and place over mold.  I use a bench vise as this holds it very will while I shrink it.

Using a heat gun, shrink the bottle so it is completely shrunk around the mold.  An extra set of hands may help here.  Be sure to use gloves and face mask as the bottle may let off harmful fumes.

*I had to do this twice and use another bottle as I messed up.  That’s why the next picture has a green bottle.

After the shrinking is over, use a Dremel tool to cut it out how you wish. 

Now it’s time to Paint and install!!  Save the mold for when you crash and need to build another!

Upgraded Landing Gear Replacement

1-First step, decide on placement for landing gear on the airplane.  Take in mind the CG when deciding this.  Cut a very thin piece of ply and glue on top of balsa to reinforce the wood from breaking.

2-Drill a small hole as the picture shows.  This hole should be just big enough so the wire and be pushed through.

 3-After deciding on the gauge of wire that would be suite the weight of the airplane bend one piece as shown in the picture below.  You will need to bend the tip of the wire and drill an additional hold for the wire to hold in place.

4-Repeat the process from the other side of the fuse.  Be sure that the wire overlaps the other wire so they are snug together.  Small clamps can be used to hold the wires in place. 

5-Take some very small bare wire and wrap the joints.  Wrap approx 5-10 times.  Be sure the wire is tight and the landing gear wire stays snug against the side of the fuse

6-Use flux/solder to solder the joints of wrap wire.  Then clip the excess wrap wire.

  

7-Use thread and needle to sew the side landing gear wire to the fuse.  3-4 wraps is all you need.  This holds the landing gear wire in place.

8-Last step.  Bend the landing gear to fit your wheels.  Use aluminum tubing through the hub of the wheel to help eliminate the wheel from riding up the landing gear wire.  Use locking collar to hold wheel to landing gear.