Charles' Cozy Mark IV Project

Serial # 1394

Website last updated on: March 8, 2016

Page updated on: August 19, 2009
December 7, 2009

Chapter 11 - Building the Elevators


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Step   1 - Cutting foam cores and bonding to the torque tubes
Step   2 - Installation of the bottom skin
Step   3 - Installation of the top skin
Step   4 - Installing the NC-6 inserts and the NC-3 hinges in the canard
Step   5 - Checking elevator travel and installing tip fairings
Step   6 - Installing the pitch trim belcrank and the elevator mass balance weights

Chapter Overview

In this chapter, I will manufacture and mount the elevators on the canard. The elevators are the primary pitch control surfaces. They are a simple, hinged, slotted flap attached to the canard. They move up or down together as the control stick is moved fore and aft.

The elevators are cut out of styrofoam using a hot wire cutter. Then they are bonded to an aluminum tube and fiberglassed. Hinge brackets will be installed as well as balance weights. Finally, the elevators will be attached to the canard.

The critical requirements in this chapter are:

  • The elevator contour must be exact to insure pitch stability
  • The elevator weight must be as light as possible and balanced to avoid flutter

Step 1 - Cutting foam cores and bonding to the torque tubes

Jeff and I hot wired the elevator cores in one evening. I believe I had the wire too hot as the thin leading edge that goes around the aluminum tube curled a little bit.

Jeff and I discovered it was best to cut from the trailing edge to the leading edge. This is opposite from the numbers on the templates. By the time the hot wire got to the leading edge, it had cooled down enough, on the second core, that the leading edge did not curl.

The cut out for the aluminum tube was a little bit small. I used some 3M super 77 spray adhesive to hold a couple of sheets of #60 grit sandpaper to a broom handle. Two passes of this through the holes was enough for the aluminum tube to fit.

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Sand paper glued to a broom stick used to sand the inside of the holes on each of the elevators. Two passes was enough to allow the aluminum tube to fit.

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Aluminum tube installed on the elevator cores. They were micro'd in place and weighted down while curing.

 
Step 2 - Installation of the bottom skin

Installing the bottom skin was really easy. Once it cured, it looked great.

I did have two hiccups when fiberglassing the top of the elevators.  First, I rounded the foam on the trailing edge a little too much.  This meant I had to have more micro than I think is normal.  Unfortunately, the placing of the micro was at the end of the layup and I was tired, even though it was only a two hour layup.  I didn't do a very good job.

The next day when I checked the contour with the template, the trailing edge didn't match up very well.  I then added more micro and really worked it well till it was just about perfect.  The result looks really good. However, there was one spot that needed a bit more micro, so when I added the end pieces, I put a little more micro in that one spot.  It looks perfect now.

The second problem I had was using too much bondo.  I was tired of using just a little bit of bondo, as the plans are always saying.  I used sparing amounts of bondo on the canard it completely collapsed just before I was going to fiberglass it.  The pipe along the trailing edge even popped off!  I didn't want to take that chance with the elevators.  So I used a big glob, about a half-inch in diameter in three places on the bottom of each elevator.  This spread out to a circle about 1.5 inches in diameter when I push the elevators onto the bench.  Boy, it held really well!

When it was time to remove the elevators from the bench, I carefully used a chisel to get under the elevator to lift it off the table.  I heard some omnimous sounds of cracking foam as I forced the elevator off the table.  I was as careful as I could be, but damaged it anyway.  Upon inspection, the damage was a 2 to 3 inch area around each bondo blob that was soft when pushed with a finger.  This was caused when the fiberglass was torn away from the foam. 

Yesterday, I went to Walgreens and they gave me a 5 ml syringe, without a needle, which they give to parents with small children.  I drilled two holes at each bondo blob at the edges of the softness.  I injected some epoxy and watch it fill the entire area beneath the bondo blob and come squirting out the second hole.  It was really cool to see it actually work! After curing, these spots are now hard as rocks.  I think the problem is solved at the expense of a bit of extra weight on each elevator.


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Bottom of elevators. If you look closely, you can see where the Bondo was that held them to the bench.

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Close-up of the two holes I drilled in the bottom of the elevators and then injected one with epoxy until epoxy came out of the other hole.

 
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Close-up of the two holes I drilled in the bottom of the elevators and then injected one with epoxy until epoxy came out of the other hole.

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Close-up of the two holes I drilled in the bottom of the elevators and then injected one with epoxy until epoxy came out of the other hole.

 
Step 3 - Installation of the top skin

Fiberglassing the top of the elevators was easy. No problems were encountered.

Step 4 - Installing the NC-6 inserts and the NC-3 hinges in the canard

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Both CZNC-12A elevator torque tube offsets are installed on the spool piece.

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Pine boards used to allow the CZNC-12A elevator torque tube offsets to over hang the edge of the bench while the elevators are being attached.

 
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Installing the hinges.

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Installing the hinges.

 

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Installing the hinges.

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Installing the hinges.

 

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Installing the hinges.

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Installing the hinges.

 

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Installing the hinges.

 
Step 5 - Checking elevator travel and installing tip fairings

In this step, the amount of up and down elevator travel is verified as being within the acceptable range. Also, the tip farings are made from a block of foam.

I was quite pleased with the elevator travel I had. It meets the specifications of +30° and -15°.

I was a bit aprehensive about making the tip fairings. The right side of my brain does not get much practice and I was worried I would not be able to get a pleasing curve. Fortunately, it turned out to be pretty easy, however, on the right side I sanded a little too much. This was easily fixed by piling on micro and sanding it down to shape.

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The block from which the canard tip will be made is micro'd to the canard.

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Canard tip micro'd to the canard.

 

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Left canard tip showing the markings for the shape.

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Right canard tip showing the the top surface after shaping.

 

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Shaping the front of the canard tip.

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Shaping the front of the canard tip.

 

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Shaping the front of the canard tip.

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Shaping the front of the canard tip.

 

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Shaping the top of the left canard tip.

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More shaping of the tip.

 

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Outboard end of the canard tip showing the hole for the elevator hinge.

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Outboard end of the canard tip showing the hole for the elevator hinge.

 

 

 

 

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Originally, I was planning on using some tubing to go over the elevator hinge, however, the walls of the tubing were too thick. Notice how the top of the hole for the elevator hinge is missing. There is not much clearance between the elevator hinge and the top of the tip after shaping. I then changed to using a McDonald's soda straw. This straw was left over from the tubing used for the brake lines on the landing gear.

 

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Shaping of the bottom of the canard tip.

 

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These strips of plywood are used to keep the elevator in trail when attaching the tips.

 

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Overall view of the canard.

 

 

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This is the gap between the canard and the top of the table. As you can see, the canard is not perfectly flat.

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This is the gap between the canard and the top of the table. As you can see, the canard is not perfectly flat.

 

 

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I was a little over zealous in shaping the bottom of the tip. To correct the problem, I piled on a bunch of micro and then sanded it down.

 

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This is the tip after sanding the micro down.

 

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This is the exit hole for the elevator hinge pin. The black lines are just alignment lines.

 

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Various views of the hinge pin after it has been shaped. Note the hole in the end of the pin used to remove the pin once it has been inserted all the way.

 

 
Step 6 - Installing the pitch trim belcrank and the elevator mass balance weights

This step went very easily. The mass balance weights were installed and they balanced as expected.

Installing the pitch trim belcrank was also very simple. No problems were encountered.

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Installing the pitch trim belcrank.

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Installing the pitch trim belcrank

 

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Installed mass balance weights.

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Installed mass balance weights.

 

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Checking the balance of the elevators. They balance nose down for both.

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Checking the balance of the elevators.

 

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Checking the balance of the elevators.

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This is the cut out in the canard for the elevator mass balance weights.

 

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Another view of the cutout for the mass balance weights in the canard.

 

On to chapter 12!