Q-40 Racing Discuss AMA 422 and any other variants of Quarter 40 racing

Stinger Build Thread

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Old 02-12-2009, 08:03 PM
  #1  
sahartman21
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Default Stinger Build Thread

I received my "Stinger" short kit from Don Stegall today.

The kit contained:

1) A fiberglass fuselage
2) Foam cores (both white and pink cores)
3) Plans

Don indicated that landing gear will be sent out later.
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Old 02-12-2009, 08:11 PM
  #2  
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Default RE: Stinger Build Thread

I'm planning to build the model as a Thunder Tiger Pro 40 powered racer, also called Q-40 Sport or 425 class racing.

The kit builds into a model that looks like a real aircraft. It will fly around 130 mph and can be built for about the same cost as a 424 class racer.

The following pages will show the construction of this model and promote the Q-40 Sport class of racing.

Below is a photo of the plans.
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Old 02-16-2009, 05:09 PM
  #3  
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Default RE: Stinger Build Thread

Below is a picture of some of the motor mounts available for the different engines.

The mount on the right is produced by Jett and is available to fit a Thunder Tiger Pro 40.

The mount on the left is one of Jett's new mount/needle valve combinations.

The other mount is a fiberglass type and is suitable for the Thunder Tiger Pro 40.

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Old 02-16-2009, 05:18 PM
  #4  
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Default RE: Stinger Build Thread

use the metal mounts, and use the ply nose ring to tie the mount in firmly, cheap power gain and better needle setting s
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Old 02-16-2009, 05:29 PM
  #5  
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Default RE: Stinger Build Thread

I'm planning on using the Jett mounts for the Thunder Tiger Pro 40.

Using this mount allows you to later go to a 422 class engine and corresponding Jett mount.

As you said, attach the front of the mounts for a much firmer and better running engine.
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Old 03-01-2009, 09:29 AM
  #6  
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Default RE: Stinger Build Thread

I decided to work on the fuselage first on this model.

Begin by washing the fuselage with soap and water to remove any residual mold release wax.
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Old 03-01-2009, 09:31 AM
  #7  
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Default RE: Stinger Build Thread

Dry it off and then use a file to remove any large pieces of extra resin.
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Old 03-01-2009, 09:35 AM
  #8  
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Default RE: Stinger Build Thread

There were a few low areas that needed to be filled.

I mixed some polyester filler and then applied some to the areas.
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Old 03-01-2009, 09:39 AM
  #9  
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Default RE: Stinger Build Thread

Here is an example of what is done.

Apply some filler to the low area.

Continue to apply to other areas as applicable.

The polyester filler dries in about 15 minutes.

In a couple minutes sand the areas with sandpaper as needed.
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Old 03-01-2009, 09:43 AM
  #10  
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Default RE: Stinger Build Thread

The following is what it looks like after about 1/2 an hour of touch up.
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Old 03-01-2009, 09:58 AM
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Default RE: Stinger Build Thread

The wing was vacuum bagged last night.

Several have never sheeted a wing so the next few frames will show more detail than normally given.

Begin by sizing the skins approximately 1/4" wider on the front, back, and width of wing shuck.

The skins on the Stinger are 1/16" thick balsa. Light weight balsa is strong enough for the Thunder Tiger Pro 40 powered racer. You can also use medium if you prefer.

The balsa was cut to size and held together with masking tape. There is no need to glue the sheets together as the wing sheeting epoxy will glue the entire assembly in later steps.
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Old 04-04-2009, 12:07 PM
  #12  
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Default RE: Stinger Build Thread

Spray some 3M77 on the shucks and attach the waxed paper.

The paper keeps the glue from sticking to the shucks in later steps.
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Old 04-04-2009, 12:12 PM
  #13  
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Default RE: Stinger Build Thread

A 1/2" x 18" piece of carbon fiber becomes a spar on the top of the wing.

Begin by identifying the location of the spar. Use a wide razor saw to cut a slot deep enough that the carbon fiber will slide in.

Widen the slot using a piece of 60 grit sand paper. This allows the glue to flow in at a later time.
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Old 04-04-2009, 12:20 PM
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Default RE: Stinger Build Thread

You can skin the wing in one piece or in two pieces. The method shown below provides detail on how to do it in one piece.

Begin by laying out the individual sheets as needed. Tape them together on the back side with masking tape.

Tack the carbon fiber pieces to the balsa sheeting using 3M77.

Cut a piece of 3/4 ounce fiber glass cloth large enough to cover the entire skin. Tack the cloth on using 3M77.

Cut a piece of 2 ounce glass approximately 5" wide and tack in place where the top and bottom skins join. This later becomes part of the ailerons.
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Old 04-04-2009, 12:37 PM
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Default RE: Stinger Build Thread

I use disposable vacuum bags made from 4 mil plastic and inexpensive caulking. Commercial versions also work fine. I just got started this way because plastic tarps and caulking are available locally.

Lay out a piece of plastic about 18" wider than the shucks and about twice the length.

Lay a piece of rope on the side of the shucks. Lay the vacuum tube in place and tape both the rope and vacuum tube down so they don't slide around.

Apply 2 beads of caulking around the outside of the shucks. Apply some extra caulking over the vacuum tube so that parts seal.
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Old 04-04-2009, 12:51 PM
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Default RE: Stinger Build Thread

Over the years people have used a variety of adhesives to attach the wing skins. I've used most of them and can definitely state that I prefer using epoxy to attach the cores. The method shown below results in a lightweight and strong wing.

I prefer Matney's Models "Skin It" epoxy and the following frames show its use.

Use a scale ($15 version from Harbor Freight works great) to weigh out 2 containers with epoxy. Each should have 1 ounce of resin and 0.25 ounce of hardener. A container of epoxy is used per wing half.

Begin by applying glue to the center carbon fiber strip. Use some glue from each container.

Drizzle the remaining glue from a cup on one wing half. Drizzle out the other cup the same way.

Use a plastic squeegee to spread out the epoxy. If you run out of glue just continue to spread out the existing glue using the squeegee.

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Old 04-04-2009, 01:08 PM
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Default RE: Stinger Build Thread

Once the epoxy is applied to the skins it is time to wrap the skins around the cores.

I laid the cores between the skin. Part of the skin wraps from the trailing edge over the top of the core.

Slide that assembly between the top and bottom shucks. Do your best to align the cores in the same relative position as they were cut.

I temporarily pinned the assembly together with tee pins. Wrap some masking tape around the assembly to hold parts together. Once taped together remove the pins that initially lined up all the parts.
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Old 04-04-2009, 01:31 PM
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Default RE: Stinger Build Thread

Lay the assembly in the vacuum bag. Place a long piece of paper towel on top of the shucks.

The extra length of plastic was laid over the top of the skins. There is a layer of caulking between the 2 pieces of tarp. You have to smash the bead of caulking to form the seal. Go around the outside and particularly check any folds that exist in the plastic tarp.

Apply some weight to the top of the shucks as needed until they lay flat on the surface.

Turn on the vacuum pump and gradually pull the air from the bag. When the bag is almost flat turn off the pump and readjust parts as needed to lay flat. Turn the pump back on and allow it to pull down to 6" of Hg vacuum. Mine shuts off when it gets to this level. Other types are adjusted to only reach that level of vacuum.
Once everything seals up you leave it alone until the epoxy dries. Allow to dry approximately 24 hours before removing from the bag.
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Old 04-04-2009, 02:52 PM
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Default RE: Stinger Build Thread

Trim the tips and double check the alignment of the cores in the shucks.

After aligned apply Tee Pins as needed to hold parts in alignment.

Remove the tape and trim the skins flush with the leading and trailing edge.

Sand the leading edge as a piece of balsa will later be glued there.
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Old 04-04-2009, 02:55 PM
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Default RE: Stinger Build Thread

The wing weighed about 8 ounces at this point. The leading edge will add about an ounce and the wing tips have not been added.
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Old 04-04-2009, 07:41 PM
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Default RE: Stinger Build Thread

Attach the 1/4" thick leading edge with epoxy. Hold the leading edge in place with masking tape until the glue dries.
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Old 04-07-2009, 08:46 PM
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Default RE: Stinger Build Thread

The Stinger and my Proud Bird have balsa wing tips.

The following is how you add some strength so they don't break so easily. Wood for both the Stinger and Proud Bird are prepared here:

Begin by cutting pieces of 3/8" light balsa.

Between the balsa sheets there will be a piece of 4 ounce glass cloth.

Squeegee some epoxy on the balsa and the glass cloth. Then lay the parts together.

The parts were put in a homemade vacuum bag and the air was removed (6" of Hg).

The result will be a balsa-fiberglass-balsa laminate that will be much stronger than a single layer of balsa.
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Old 04-07-2009, 08:53 PM
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I'm watching this thread with great interest...learning a lot! Thanks [8D]
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Old 04-07-2009, 09:07 PM
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Default RE: Stinger Build Thread

Believe it or not vacuum bagging is much easier than it looks.

I've only been doing this for about a year.

This is the only way to sheet a wing.
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Old 04-08-2009, 03:22 PM
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Default RE: Stinger Build Thread

Scott- so what you end up with is a 3/4" thick slab of balsa with a fiberglass stiffener in the middle, that you can glue on to the end of the wing, then shape? The glass (and epoxy) add stiffness with minimum weight gain I assume. Keep on posting, learning from every one! Randy
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