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Building The U. Maine Trainer

- Adding The Tail Surfaces -

(last update: 16 Sep 2012)


Once the fuselage reinforcing glass has cured, the following may be added to the fuselage:

Using some conformal weights, and some wood blocking, stabilize the fuselage on the bench. This should be done in a way that makes the step where the horizontal stabilizer will be mounted, level.

There is a block at each tip of the horizontal stabilizer. They are there to help keep everything square once the epoxy is applied, and the assembly is left to cure.

Test fit of the horizontal stabilizer.

A generous amount of left over wax paper is used simply because it helped make the height correct. A single sheet would have served well enough if catching errant epoxy was the only concern.

Use a centerline to mount the horizontal stabilizer.

Use a center line on the horizontal stabilizer to line it up on the fuselage mounting step.

Align it aft as well.

Line it up aft (at the rear) as well.

Mix up some 5 minute epoxy, and apply it to the step. Then place the horizontal stabilizer on the step. Place a sheet of wax paper on top, followed by a conformal weight.

Horizontal stabilizer in place, while epoxy cures.

If you can reach underneath, use some cardboard or Popsicle sticks to scrape away any dripping epoxy from the joint. If you don't do this now, there will be more sanding later.

Another angle of the stabilizer in place, while epoxy cures.

Above is another angle on the same layup.

An elevator will need to be attached to the horizontal stabilizer.

Cutting the elevator from stock

Here again some eye balling has been done. The elevator spans the full width of the horizontal stabilizer, and is about 4.5 cm in width. It is cut from the same material (6mm / 0.25 inch, blue insulation foam) as the horizontal, and vertical stabilizer. Exact dimensions are not necessary. Just make sure it is wide enough to be effective. If you only make it 1cm wide, as opposed to 4.5cm, it will be hard to control the pitch. If you make it much wider than 4.5 cm, the pitch will be quite sensitive at the controls.

Cutting the rudder from stock.

While we are at it, we will cut the rudder from the stock foam as well. The dimensions are roughly as follows:

Rudder dimensions.

Work your dimensions as you see fit. We chose ours on the fly. Make sure the bottom does not drag on top of the horizontal stabilizer.

On the elevator there are a couple cut backs, since the tips often get dinged up anyway.

Elevator cut backs.

The next thing to do is get the vertical stabilize in place.

It helps to have the centerline of the fuselage marked. Note that no torque offset is used on the vertical stabilizer. It is simply aligned with the centerline of the fuselage.

Fuselage centerline at the vertical stabilizer

Be sure to have some tape available for the next step. The tape will be useful when gluing the vertical stabilizer in place.

Coat the bottom edge of the vertical stabilizer with some 5 minute epoxy, and align it with the fuselage centerline.

Aligning the vertical stabilizer.

Check the vertical alignment with some type of square. In the photo a carpenter's triangle was used.

Checking the vertical stabilizer alignment.

The bottom edge of the vertical stabilizer can wander, so double check that it hasn't gone too far. This may require a few iterations of checking with the square, and tweaking the tape.

Checking the vertical stabilizer bottom edge wander.

The epoxy cures pretty quick, so there isn't a whole lot of time to get it all lined up.

While the vertical stabilizer epoxy cures, the elevator and rudder can be prepped for attachment. Both these control surfaces will be fastened to their respective stabilizers using hinges. There are many types of hinges. The hinges used in this case are available through model supply houses. There are a number of vendors, and manufacturers for these hinges. Take your pick. If you want you can even use duct tape as a hinge. I like using traditional mechanical hinges.

Before any of that happens, the hinge edge needs to be beveled, so that there will be enough clearance for the elevator and rudder to move without binding.

Beveling the horizontal stabilizer hinge edge.

In the photo above the hinge edge of the elevator is beveled using a sanding block.

Here's what it looks like when your done beveling:

A view of the horizontal stabilizer bevel down the edge.

It takes only a few strokes on each side.

The same thing needs to be done on the rudder's vertical stabilizer edge.

With the bevel done on the horizontal stabilizer, the hinges can be placed. In the photo below four hinges are used. There needs to be enough hinges to carry the load, and prevent bowing of the surface under load. Four hinges seem to do the trick in this case. In the upper left of the photo you can see that only two hinges were used on the rudder.

Hinge placement on the horizontal and vertical stabilizers.

With the hinges located on the elevator and rudder, these locations need to be transfered to their respective stabilizers.

Hinge locations transfered to the horizontal and vertical stabilizers.

How did we make room for the hinge flaps in "solid" foam? Here's how:

Using a center scribe on the horizontal stabilizer.

... using a center scribe...

Making space for hinges on the horizontal stabilizer.

... and doing some old fashioned cutting with an Xacto knife.

Use the hinges to check for spacing. If you have already glued your hinges into the rudder and elevator, just use some spares.

Hinge fit check.

It is often a good idea to make a center "hole" in the hinge flange cutout so as to allow for glue/epoxy to flow, and make a better bond.

Alowing for hinge epoxy flow.

In the above photo a piece of control rod is used to make the epoxy relief hole. Note that the foam is being pinched as the rod is applied. This helps control the size of the hole, and reduces the chance of breaking the foam. The depth of the hole need not be deeper than the length of the hinge flange.

Up to this point nothing has been glued. It has all been dry fit. Now that everything seems to be free to move, and there is no binding, it is time to apply the epoxy, and make things more or less permanent.

The first thing to do is epoxy the hinges to the horizontal stabilizer, and the vertical stabilizer.

Applying epoxy to horizontal stabilizer hinge slots.

Be careful with the epoxy. It is easy to apply too little or too much. Too little and the hinge will not be fully anchored to the slot. Too much, and the pivot point of the hinge will get overrun with with epoxy, and cease to be a pivot.

Allow the stabilizer hinge epoxy to cure.

Let the hinge epoxy cure such that gravity will pull any excess epoxy away from the hinge pivots.

Once the hinges have cured, one last test fit of the elevator, and rudder can be made.

One last test fit.

In the photo above, notice that the elevator clearance cutout has been drawn on the rudder with a black marker. This was done now rather than when the rudder was cutout of the foam stock. No particular reason for this delay in applying the cutout. However, be sure to make the cut in the rudder before you epoxy it to the vertical stabilizer hinges. It is much easier to make the cut on the bench now, rather than have to do so on the plane.

Be sure to make your epoxy relief holes in the hinge slots of the rudder, and elevator.

You will probably have to mix up another batch of 5 minute epoxy, to glue the rudder, and elevator onto their respective hinges.

Fill the rudder hinge slots, then slip the vertical stabilizer hinge flanges into the epoxy filled rudder slots.

Fitting the rudder onto the vertical stabilizer hinge flanges.

Then do the same for the elevator hinge slots, and fit it as well.

Fitting the elevator onto the horizontal stabilizer hinge flanges.

If you have done things correctly, the slots should be well whetted with epoxy but not so much so that epoxy flows down onto the hinge pivots.

Hang the fuselage so that if the epoxy does run out of the hinge slots it does not flow onto the hinges.

Letting the hinge flanges cure.