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AJ-2 Construction Revisited

Old 05-05-2012, 12:09 PM
  #1  
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Default AJ-2 Construction Revisited

This thread will cover building a Kevin Matney's AJ-2 QM kit. The model flies great and is available at competitive pricing.

This is my second time for building this model.

The kit consists of:

1) Fiberglass fuselage
2) Wing cores
3) Tail cores
4) Landing gear
5) Plans

Here is a link to the site:

http://www.matneymodels.com/qm.html
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Old 05-05-2012, 12:17 PM
  #2  
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Default RE: AJ-2 Construction Revisited

Begin by making wing skins from 1/16" thick balsa sheets.

Use lightweight balsa for the bottom skins. The top skins should be made from medium weight balsa wood.

There is no need to glue the skins together. Just tape them together at this point.
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Old 05-05-2012, 12:20 PM
  #3  
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Default RE: AJ-2 Construction Revisited

The tail skins are made similarly.

The skins should be about 17" wide as the tail is glued together as one piece.
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Old 05-05-2012, 07:14 PM
  #4  
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Default RE: AJ-2 Construction Revisited

This wing is sheeted in one process.

The first step is to make a one piece wing skin. This is done by joining sections together with masking tape. The tape between the top and bottom cores makes a hinge.

Next is the addition of carbon fiber on the bottom skin. I tack it in place with 3M77.

Tack pieces of 5" wide fiberglass cloth at the joint between the top and bottom trailing edges. For the time being it will be a hinge between the top and bottom sheets.

A layer of 3/4 ounce fiberglass cloth is placed over the sheeting. The fiberglass cloth makes it easier to get just the right amount of finishing epoxy on the skins. It also adds some strength.
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Old 05-05-2012, 07:18 PM
  #5  
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Default RE: AJ-2 Construction Revisited

The wing cores and shucks are joined with 3M77 adhesive and masking tape.

Waxed paper is also tacked in place on the shucks to prevent the wing from sticking to the shucks.
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Old 05-05-2012, 07:22 PM
  #6  
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Default RE: AJ-2 Construction Revisited

Mix about 1 ounce of finishing epoxy per wing half. About 0.1 ounce of 91% rubbing alcohol was added to thin out the epoxy. This was spread over the wing sheeting with a plastic squeegee.

The other wing half is done the same way.
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Old 05-05-2012, 07:26 PM
  #7  
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Default RE: AJ-2 Construction Revisited

Cut the slot for the vertical sheer of carbon fiber. This acts like a spar and adds significant strength to the wing. Don't leave it out.

Mix about 0.4 ounce of finishing epoxy and spread it into place using an epoxy brush. Add the carbon fiber making sure there is a good glue joint.
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Old 05-05-2012, 07:34 PM
  #8  
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Default RE: AJ-2 Construction Revisited

The wing cores were slid between the wing sheeting. This was then placed between the shucks.

Verify the parts are straight by reviewing the markings on the sides of the cores. Kevin added marks so you can tell the wing is straight.

Temporarily pin the parts together and then tape parts together with masking tape. The pins should be removed prior to adding the parts to the vacuum bag. You don't need holes.
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Old 05-05-2012, 07:39 PM
  #9  
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Default RE: AJ-2 Construction Revisited

The bag is made from 4 mil thick plastic tarp and is sealed with latex caulking. A piece of rope goes around the perimeter of the wing and allows a channel for the vacuum to flow.

About 6" of Hg vacuum is applied and parts are allowed to dry overnight.
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Old 05-06-2012, 12:30 PM
  #10  
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Default RE: AJ-2 Construction Revisited

Trim off the outside of bag to remove parts. That way you don't have to mess with the caulking.

The leading and trailing edges are trimmed flush to the shucks.

Remove the tape and lightly sand the edges.
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Old 05-06-2012, 12:34 PM
  #11  
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Default RE: AJ-2 Construction Revisited

I glued the leading edge on with 6-minute epoxy. Draw a line down the center of the leading edge and then shape as desired.

The trailing edge was shaped with a sanding block. Sand down to a sharp trailing edge. The fiberglass cloth makes a nice thin edge.

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Old 05-13-2012, 02:42 PM
  #12  
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Default RE: AJ-2 Construction Revisited

The tail surface is a skinned foam core.

The balsa sheets should be about 1/4" wider than the shucks.

A piece of 0.021" thick carbon fiber is used at the joint.

Finishing epoxy is squeegeed on the balsa sheeting.

Lay the cores on the sheeting. Mix some micro-balloons and finishing epoxy. Apply the mix on the edges and carbon fiber.

Lay the top sheeting on and tape the sheets together.
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Old 05-13-2012, 03:12 PM
  #13  
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Default RE: AJ-2 Construction Revisited

The tail surface was placed between layers of peel ply (nylon fabric) and placed in the vacuum bag.

I'm building two AJ-2 models at this time.
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Old 05-13-2012, 04:03 PM
  #14  
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Default RE: AJ-2 Construction Revisited

After a couple hours the tail surfaces were removed from the vacuum bag and peel ply.

Here is what one looks like after cleaning it up a little. It weighs about 1.25 ounces.

I'm going to allow it to dry further before shaping.
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Old 05-18-2012, 08:04 PM
  #15  
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Default RE: AJ-2 Construction Revisited

While you guys were dreaming of your next race a new wing was being born.

This one is similar to the earlier post except it uses carbon tow for reinforcement on the bottom.

Good luck MOKAN!
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Old 05-19-2012, 11:36 AM
  #16  
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Default RE: AJ-2 Construction Revisited

This morning the leading edge (1/4" x 3/8 balsa) was glued and shaped (with knife and sanding block).

The trailing edge was shaped with a sanding block.

What's better than one AJ-2? Two of course! [8D]
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Old 05-20-2012, 01:01 PM
  #17  
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Default RE: AJ-2 Construction Revisited

I installed the firewall (3/8" thick aircraft plywood) and engine.

The pictures show the sequence of events.

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Old 05-20-2012, 01:08 PM
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Default RE: AJ-2 Construction Revisited

More firewall installation pictures:

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Old 05-20-2012, 01:13 PM
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Default RE: AJ-2 Construction Revisited

More firewall installation pictures:

Vaseline is spread on the backside of the motor mount prior to epoxying it to the firewall.
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Old 05-20-2012, 01:18 PM
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Default RE: AJ-2 Construction Revisited

The front beams of of the motor mount are attached with epoxy and fiberglass cloth.

The last picture shows the engine installed on the motor mount.
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Old 05-21-2012, 07:19 PM
  #21  
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Default RE: AJ-2 Construction Revisited

I installed the firewall and engine in the second AJ-2 tonight.

The second time was much easier and quicker.
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Old 05-25-2012, 07:24 AM
  #22  
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Default RE: AJ-2 Construction Revisited

Loving this build, keep it coming.

Thank You
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Old 05-25-2012, 08:13 AM
  #23  
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Default RE: AJ-2 Construction Revisited

It's good to see some interest! [8D]

In the USA most buy composite models.

I've found that if you are a good Q500 builder you can build a QM40.

I will continue this weekend.
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Old 05-25-2012, 05:32 PM
  #24  
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Default RE: AJ-2 Construction Revisited

A 1/4" thick piece of plywood is being installed in the following pictures.

Note: I am mounting the gear further back than shown on the drawings. This is to reduce bouncing on landing.
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Old 05-26-2012, 01:04 PM
  #25  
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Default RE: AJ-2 Construction Revisited

The following pictures shows the installation of 3/4" diameter dowel and 1/8" thick plywood on the wing:
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