The Hawk Fuselage Lay Up Process
 Admiring a professionally made sailplane fiberglass fuselage is a common occurrence for many of us RC sailplaners.  We do it at contests and at our own flying field.  For example, the Artimus, NYX, Eraser, etc. all have beautiful workmanship.  So the idea of making a fiberglass fuselage with our own hands is naturally a daunting one.  The Houston Hawk project addresses this anxiety head on because we will be laying up our own personal fuselage.  This document, in addition to actually making your own personal fuselage, will help ease the anxiety.  With instruction from professional fuselage maker Don Cleveland and just paying attention to a few details along the way, your fuselage will be strong and beautiful.

Safety

     There are a few safety issues in making this fuselage.    

  • Eye Protection:  It’s best to use eyewear to protect from cloth fibers and epoxy splatters.  Bring your own glasses/safety glasses to Don’s house and wear them as you work.
  • Gloves:  Its possible to develop sensitivity to uncured epoxy.  Don provides latex gloves for us to use.  If you already have sensitivity, you might consider vinyl gloves or have someone else make the fuselage for you.

  • Ventilation:  Don keeps the garage door open during the process.  If you already have a respitory problem, maybe a fan would help.  Epoxy fumes are not strong, but they do exist.  There is no polyester smell to this epoxy. 
            
  • Touch:  When removing the cured fuselage from the mold, be very careful.  Cured epoxy and cloth can be like needles.  Avoid running your hand down the fuselage until the cleanup, sanding and smoothing has been done on the seams, canopy and fin.

The Mold

 The quality of the mold is of utmost importance for a straight flying sailplane.  The mold for the Condor is in two pieces, a right side and a left side.  There is also a separate mold for the canopy. Fortunately, the mold we are using is already made and is extremely well done.  It is the Condor mold that was used in the late 90’s for the Condor kit that was distributed by Sleggher’s. 

 

 I have one of the Condor kits at home and the fuselage is great.  It’s total unpainted weight, including canopy, is 8.4 oz.  The fuselage I made on October 4th weighs 9.4 oz including the white Krylon paint.  So our fuselages are in the ballpark.

Preparing the Mold

 This is the first important detail.  In order to keep the epoxy from sticking to and ruining the mold, it has to be 1) cleaned thoroughly with alcohol, 2) waxed with Carnauba car wax, 3) apply PVA mold release, and if desired 4) sprayed with 4-6 light coats of Krylon paint.  This process takes 2 or three days elapsed time.  Fortunately for me, Don prepared the mold.  He has a vested interest in preserving it.

Cutting the Cloth

All of the cloth should be cut to size prior to mixing any epoxy.  There are six layers of cloth used in this fuselage resulting in a very strong structure.  The cloth has to be cut to size for both sides of the mold.  Here is the sequence of cloth application:

  1. 1.5 oz fiberglass used the entire length,
  2. 6 oz fiberglass used from nose to the middle of the wing,
  3. 6 oz fiberglass used in the wing area,
  4. 6 oz fiberglass around wing saddle area
  5. strip of Kevlar used from the wing TE to just past the fin LE
  6. 6 oz fiberglass used the entire length

 

There are two layers of fiberglass used on the canopy, 1.5 oz and 6 oz.  Again, having a professional show you where to put the cloth is a detail that results in a strong, good-looking fuselage.

Mixing the Epoxy

Don has a preferred brand of epoxy (MGS).  It is clear and has a pot life of one hour.  You will be mixing about three batches during the lay-up process.  For consistent pot life, epoxy is best mixed by weight rather than by volume.  Don has a scale for us to use.

Applying the Cloth with Epoxy

Using a foam brush, paint on a semi-thick layer of epoxy to the first half of the mold.

 

 

Before applying any cloth, mix a small slurry of epoxy and cab-o-sil into toothpaste consistency.  Apply the slurry to the mold with a stick in areas with sharp corners and radiuses such as the wing root area and around the canopy indentation line.
When complete, lay the first layer of 1.5 oz cloth in the mold.  Starting at one end, use the foam brush to push the cloth into the epoxy already on the mold.  Get more on the brush when needed.  Don will advise you on the amount of epoxy to use.  Just remember, epoxy is thicker than water and it takes more time for it to soak into the cloth.  Be patient on the wet-out.  Two small details to remember are 1) dob your brush on the cloth to force epoxy in, and 2) always brush in the same direction when smoothing puddles and cloth.
     Apply the subsequent layers of cloth in the same manner.  If air bubbles or voids appear and you cannot get them out with the brush, use your finger.

When the first half of the mold is finished, then repeat the same process with the other half.

Final Steps

When the epoxy on the first half of the mold starts getting green (stiff) the two halves of the mold will be joined together to make a single fuselage.  Sounds simple, but there are a few preparatory steps:
  1. On one side of the mold, dob epoxy onto the cloth on the topside of the fuselage to about ½ inch extending from the mold.
       
  2. On the other mold half, dob epoxy onto the cloth on the bottom-side of the fuselage to about ½ inch extending from the mold.
        
  3. With a pair of curved-tip scissors supplied by Don, trim the cloth as follows: On the side of the mold where the epoxy was applied to the cloth on the top-side, trim the cloth on the top-side to a length of 3/8 inch extending from the mold.  Trim the cloth on the bottom-side even with the mold.  Don will show you where to taper the cloth at the nose.  Trim the cloth on the fin LE even with the mold on both sides.
  1. On the other half of the mold where the epoxy was applied to the cloth on the bottom-side, trim the cloth on the bottom-side to a length of 3/8 inch extending from the mold.  Trim the cloth on the topside even with the mold.
       
  2. With a stick, place a bead of epoxy next to the cloth around the entire perimeter of both halves of the mold and make sure the cloth extending from the mold is perpendicular to the mold.

  1. Place one half of the mold on the workbench.  Then take the other mold half and, using a short sideslip motion, slide the two halves together.  Quickly look at the inside through the fin and through the canopy area to see if there are any bad folds at the seams.  If there are, straighten them up.  When satisfied, put the bolts through the holes and tighten the two halves together.
  1. Immediately, use the rollers-on-a-stick that Don provides to reach into the fuselage via the fin and canopy area and roll the extending cloth flat onto the cloth on the other half of the mold.  The 3/8-inch of cloth you left on the top and bottom sides are now layered onto the opposite half.  This is the magic step that bonds both halves together.
       
  2. Mix another slurry of epoxy and micro-balloons into a toothpaste consistency.  Liberally apply the slurry to the fin LE inside the mold.  Smooth it out with your finger or stick.

  1. Turn the fuselage nose down and drop a blob of slurry inside the nose.
        
  2. When satisfied, stand the assembled mold on its nose and let it setup about 24 hours.

Hatching and Cleaning

After 24 hours, remove the bolts from the mold and pull the halves apart.  To me it sounds like a ripe watermelon splitting open.  The beautiful, bright, gleaming fuselage jumps right out.  Even though there is epoxy flashing to be cleaned off the seam lines, the quality is readily apparent.  All that needs to be done is to carefully cut and scrape the flashing away from the seams and to smooth out the canopy area and fin area with razor blades, sandpaper and dremel tool.  Be very careful doing this, the cured epoxy and cloth can be like needles.  Avoid running your hand down the fuselage until the cleanup and smoothing has been done.  Wash off the PVA mold release with soap and water after you sand off all the flashing.  Do not use a solvent to remove the mold release.

Summary

The description outlined above highlights the things I learned in the process of making my own fiberglass sailplane fuselage with Don.  They represent the mechanical steps and a few insights.  There are many other things I observed that will only make sense to me and are now stored into my cumulative knowledge database of my favorite RC activity.  Before I started on this project, I had the book knowledge.  Now I have the experience.  Many thanks to Don Cleveland for offering his time, tools and experience for this club project.

Tommy Lamnek

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