Randy;

 

You can get some ideas and information from my website http://members.cox.net/alg3/airplane.htm; take the link to ‘Custom cowl’.  I have also attached photos of my main cooling scoop mold, and the resulting scoop.  I used urethane foam that you can by at Home Depot, or elsewhere, in 4’ x 8’ ft sheets, 2” thick and laminate together and shape. (I think it is called ‘sheathing’, used as insulation or buffer when pouring foundations).  I hard-coated by painting on a slurry of epoxy and micro-balloon, and then apply mold release.

 

The number of plys of glass depends on the weight of the cloth and the size and shape of the object.  I think my scoop was mostly a sandwich of bi-directional (BID) 8.5 oz. cloth (a Rutan cloth, PN# RA7725 from Aircraft Spruce) on both side of a layer of 18 oz Tri-Ax cloth.  I think the tri-ax is equivalent to the knitted e-glass that Spruce sells.  This combination is equivalent in strength to about 5 plys of BID.  Usually start with the minimum number of plys you think you might need, then when the part is off the mold you can decide if it needs more strength; add more layers of glass as needed.

 

Plan your cloth sections for your mold, wet out your plys of cloth on 2 or 4 mil plastic (drop-cloth), then put another layer of plastic over and squeegee out the excess epoxy. I usually used the plastic Bondo applicators you can get at your auto parts store as squeegees.  Trim the pieces to the size/shape you want, peel off the plastic on one side, lay the cloth onto the mold, then take off the remaining plastic, and stipple into place a remove any bubbles and wrinkles with chip brush (1 – 2” cheapo paint brush).  Overlap an inch or so where cloth sections meet.

 

Any time you are putting more plys over areas that are cured, sand the surface with a 50 – 60 grit paper to get good adhesion.

 

Don’t be concerned if you have to make 1 or 2 cuts to get your part off the mold – you can always glass them together again with a couple of plays on each side. 

 

Wetting out the glass plys basically consists of pouring a fine stream of epoxy back and forth over the cloth; then spread evenly with your chip brush.  I find the brushes work better if you trim the bristles about 3/8” shorter.

 

Fiberglass is wonderful stuff. You can make just about any shape you want.

 

Good luck,

 

Al G.

 

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of randy echtinaw
Sent: Sunday, August 31, 2008 6:38 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Composite instruction

 

I am eventually going to have to build a custom composite radiator/oil 

cooler pod ala P-51 and possibly a cowling if I cannot get aluminum to 

work around my RX-8 engine. I am looking for some good reference books 

on how to do this especially concerning making male molds - release 

agents - cloth to use - number of layers required - etc.??

My plane is wood/tube/fabric - thought I might as well use a little 

fiberglass too :))

My biggest concern is making them as light as possible but still 

having the needed strength and stiffness.

Thanks

 

--

Homepage:  http://www.flyrotary.com/

Archive and UnSub:   http://mail.lancaironline.net:81/lists/flyrotary/List.html