sahartman21

Recently I have started flying the faster Q-500 classes.

The following shows the basics for building a wing strong enough for the 426 or 428 classes.

The steps can be completed in a couple hours.

I begin by making a set of 10.5" wide wing skins. You can also purchase wide wing skins from National Balsa Wood Company.

1) I weigh each sheet and pick out 3 light sheets for the bottom skin. Three medium weight sheets are picked out for the top skin. The top skin needs to be stronger as it is in compression in a turn.

2) The sheets are trimmed and taped together. These are then trimmed to 10.5" wide.

3) The top and bottom are joined with masking tape, leaving around 1/8" gap between the joints to allow for folding.

sahartman21

I prefer to sheet wings in one piece.

Join the shucks together with 3M77. Masking tape is also used to strengthen the joint.

Lightly spray the shucks and apply a piece of waxed paper.

sahartman21

The cores are joined together with 3M77 to make a 48" span section.

sahartman21

The wing can be bagged using commercial vacuum bags or homemade as shown here.

1) A 4 mil thick piece of plastic tarp works fine. The picture shows a 3' wide by 50' long package.

2) Cut a piece about 10" longer than the wing span.

3) You also need some cheap latex caulking, caulk gun, and some twine.

sahartman21

Kevin Matney's Kits show and I use a 0.021" x 1/2" x 36" piece of carbon fiber laminate as the top spar.

1) Use a razor saw to cut a slot for the spar.

2) Mix about 0.4 ounces of finishing epoxy (Skin It or your favorite)

3) Dab the epoxy into the groove using a disposable brush.

4) Push the spar in the groove and adjust for proper fit.

http://www.cstsales.com/carbon_Laminates_36.html

sahartman21

I tear a 3/4" wide piece of 0.007" thick carbon laminate for use on the bottom sheeting.

The carbon should be placed approximately at the thickest section of the wing. For this wing it was approximately 7" from the trailing edge.

It was tacked in place with 3M77 adhesive.

The following site shows some 48" long pieces:


http://www.cstsales.com/carbon_laminates_48.html

sahartman21

Cut two pieces of 2 ounce fiberglass cloth. Each should be approximately 5" wide by 24" long.

Tack the pieces in place with 3M77 adhesive.

Cut a piece of 3/4 ounce cloth to cover the skins. Lay this in place.

sahartman21

Mix approximately 1 ounce of finishing epoxy (Skin It or equal) for each side.

I add about a cap full of 91% alcohol to the mix to thin it out.

Immediately drizzle the epoxy on a wing half and squeegee as required to cover the side.

Do the other side the same way.

sahartman21

The cores are placed between the shucks and then parts are temporarily pinned in place.

Masking tape is wrapped around the shucks and the pins are removed (don't want to make a hole in the bag).

sahartman21

The parts are laid on top of the 4 mil thick tarp.

The twine is routed around the outside of the shucks. The vacuum tube is taped in place beside the twine.

A piece of paper towel is placed on top.

Latex caulking is applied on the outside of the shucks and seals the bag.

sahartman21

The bag is closed and parts are sealed with caulking. I just step on this to insure the caulking spreads out.

Place a couple small weights (quart paint cans work fine) on the shucks to hold them flush with the floor.

Turn on the vacuum pump and gradually remove the air from the bag. Spend a couple minutes to insure there are no leaks. Look particularly around the tarp folds.

My vacuum pump is set to keep about 6" of Hg vacuum. It runs when you first plug it in and shuts off at around 6" of Hg vacuum.

It typically takes around 8 to 24 hours for the finishing resin to cure. In the winter time I place an electric blanket over the shucks to insure the epoxy is warm enough to cure.

Kevin Matney

My Feedback: (1)

Great Job you did good!!!!!

BarryReade

My Feedback: (1)

How many inches of Mercury vacuum do you pull?  I heard that anything over 10" will over compress the foam?

sahartman21

I set my vacuum pump to pull around 6" of Hg vacuum. It should run when you first plug it in and shut off around 6" of Hg vacuum. Mine starts running again when the vacuum gets around 3" of Hg vacuum.

The EZ-VAC system runs all the time and pulls around the same vacuum. I know someone that uses the EZ-VAC system. He swears by it.

http://www.acp-composites.com/acp-vbs.htm

BarryReade

My Feedback: (1)

I went back an reread the article again and who did you get your pump from? 

Bill Vargas

My Feedback: (5)

When I built my wings I would add some C/F 56K Tow to the LE during the lay up thus eliminating the need for gluing on a balsa stick LE and sanding that to shape,,, and a 1" strip of 1/32 ply at the TE over a 5 - 6" strip of 1/2oz cloth cut on the 45 to enable you to sand down the LE for a nice razor sharp TE.

I used to get all my CNC cut one peice foam cores at www.flyingfoam.com and ask for Bob,,, He might still have the wing file but not sure cause its been a while


BV

sahartman21

My vacuum pump was homemade and was based upon a refrigerator compressor. See my comments to the following thread:

http://www.rcuniverse.com/forum/m_10735021/tm.htm

I've used a 1/2" wide piece of 1/32" thick ply to reinforce the trailing edge. You are correct in that that method works fine also.

The layers of fiberglass cloth at the trailing edge serve the same function. This method results in two layers of 2 ounce fiberglass cloth plus two layers of 3/4 ounce fiberglass cloth between the layers of balsa wood. This will also sand down to a thin durable trailing edge.

Both methods work fine. Do what you are comfortable with.

BarryReade

My Feedback: (1)

Is there any reason for not leaving the balsa sheeting off and just using CF cloth to cover the core except for cost.

sahartman21

I don't have any experience with a full carbon fiber wing.

Bill Vargas

My Feedback: (5)

I have seen that method done before with blue foam cores. Don t use regular white foam or the surface will look like a golf ball. The hard part will be the tips. It requires a lot of epoxy and the wing will be heavy. Ailerons were attached using silicon and brass tubing simular to the torque rod methods that are used today in most composite wings. The high point of the wing plus the thickness of materials used will have to be factored in to meet the rules for the wing.

BV

BarryReade

My Feedback: (1)

I looked at a wing yesterday that a fellow had built for a heavy lift contest that was made with the CF cloth. It looked great but had a (singular) dimple in the left wing panel. He covered it top and bottom with one continuous piece of cloth. he used waxed mylaron top of the CF cloth and when he took it out of the shucks and peeled the mylar off he trimmed the trailing edge and sanded the excess squeezed out ontheleading edge. His ailerons just used the CF cloth that covered the wing for the hinges. looked great

sahartman21

Barry,

For vacuum bagging with pink or blue foam most people use a higher vacuum setting.

This should be considered before purchasing a pump.

twitte1

Scott,

Where do you locate the top spar? I know that traditionally it would be on the CG, but with racing the CG may move forward or back. What do you use as a guideline?

Trey

sahartman21

I try to locate the carbon fiber and the top spar in the thickest section of the airfoil.

That said, some of the newer airfoils have the thickest section farther back than the CG. I still try to locate it near the thickest section. You may have to compromise to avoid putting the carbon right in the middle of the aileron servo.

sahartman21

Here is the wing after the leading edge and trailing edge are finished.

The sheeted cores weighs a very respectable 9.55 ounces.

The photos show the trailing edge shapes to a sharp edge.