< December, 2014 >
|Composite LE Forming
by Mike Sotomayor
During the construction of our new Staudacher we came across a method of pre-forming the leading edge of the wing that I would like to share with you.
In most cases we will need to buy the Carbon Fiber, the epoxy,and the pumps used to dispense the epoxy Resin and Hardener.
I have found CST Composites (cstsales.com) to be VERY helpful in the purchase and use of the products we will need and they sell.
We laid out the wing ribs over the plans and determined the span would need to be 52 inches.
A sheet of 4foot by 8 foot by 2 inches thick Styrofoam was purchased from the local Home Depot and was cut into three 10-inch wide lengths.
We then cut these down to our 52 inch length and, using3M77, glued the three lengths together to make a 6 inch thick by 10in. High by 52in. Long foam block.
I recommend that the contact cement spray be left off the top 4in. Of the foam. This will allow the Hot wiring of the foam to go much more smoothly. Now mark a centerline on each end of the foam block and set the block aside.
The next step is to make a pattern of the root rib leading edge and the wing tip leading edge. Add a centerline at this point for a reference and make the effort to keep the form as smooth as possible.
Next we need to cement some aluminum foil to the edge of the wingrootLE and the wingtipLE form that the hot wire will be following. This is necessary to prevent the wire from burning into the wood pattern.
With the L.E. patterns formed we are ready to affix them to the foam block.
We used two 3-inch nails, one on each side of the pattern and it worked well.
With the foam block secured at the bottom to prevent unwanted movement and the patterns secured to the foam block we are ready to hot-wire the foam.
This part of the foam cut is very important so take your time and be patient.
And be sure to have a helper!
When you get the foam cut, set it aside and remove the patterns as you have some more work to do!You will need to trim the patterns you just used by the thickness of the wing skins you plan on using.
We used 1/8th in. sheeting on the wings and so the patterns were trimmed back 1/8th of an inch all the way around the pattern and the aluminum foil was re-applied to the pattern edges.
For the next step we needed to prepare some balsa sheets of 1/16th inch thickness to fit the foam form.
We used two layers of the 1/16th sheets to make the skin equal 1/8th in.
We also pre-formed the 1/16th sheets by spraying them with a mixture of water and amonia and then setting them into the form and allowing them to dry.
Lay a sheet of wax paper into the foam block and lay the first wing skin into the foam block.
Thoroughly mix your epoxy according to the manufacturers instructions and brush it onto the sheeting.
Lay the CF or Fiberglass clothe on top of the skin and recoat with the epoxy.
When you are sure the glass or carbon fibber is well coated, set the second skin on top of the assembly and then lay another sheet of the wax paper over the wingskin.
Now set the molded foam piece you cut out into the foam block.
Set some weights on the piece in such a way that they push the foam piece you cut into the foam block.
Give the assembly overnight to cure.
Now go grab a nice tall cold one! You have earned it!
I know that this method seems long, but you will find that it is longer in the telling than the doing and the results are well worth the time. Good luck and let me know how you fare!
Created on 01/01/2008 06:54 AM by odettman
Updated on 01/01/2008 06:56 AM by odettman
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