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Fiberglass Repair Made Easy
Restoring Broken Airplanes To “As New” Condition
by
Gordon Dickens

On my last flight at the 2002 Superman event I embarked on an off road safari with my BVM F-16. I had landed a bit too fast when my right wheel locked up and the plane veered off of the runway into the grass.  The grass was about knee high and the ground was very soft from recent heavy rains.  The grass immediately grabbed the right wing causing the airplane to cartwheel.  The F-16’s nose sank into the ground about four inches in the middle of the cartwheel.  For an encore, upon completing the cartwheel, the nose remained stuck in the ground and broke completely off from the remainder of the fuselage leaving a ragged tear.  Ugh...

Nevertheless, I wasn’t too upset about my airplane’s damage.  I knew from past experience that this would be an easy repair.  Afterwards, several other modelers remarked that they may not have even attempted to repair the airplane.  They went on to say that the damage looked so severe that the repair appeared to be a daunting task. So, given how easy it is to repair this type of damage, I decided to put this article together so that other folks, when faced with an accident like this, wouldn’t worry and would quickly have their airplane back into “as new” condition.

I do not enjoy advertising my misfortunes.  However, in this hobby you need to just throw your ego out of the window because just about anything can happen to anybody’s airplane. After reading this article I hope that you will be able to confidently repair your airplane if this type of accident ever happens to you.

The five photographs to the right and below this caption were taken immediately upon my return home from Superman.  Not only had I snapped the nose off leaving severe jagged edges but I also had two large holes where I had failed to recover the fiberglass pieces.

It is very important that all of the broken pieces be recovered following an accident like this.  That will make the repair job much easier.  However, in this case, I was missing a .75” X 1.5” piece on the top left of the nose tip and a 1” X 2” piece on the bottom just aft of the main tear.

Repair Supplies

Many of the necessary repair supplies are depicted in the photo on the right. The Evercoat Metal Glaze is much lighter than most other automotive putties so I strongly recommend it.  Epoxy finishing resin may be substituted for the polyester resin, however, I prefer polyester resin for most applications.  The 3M Auto Body Repair Tape is an outstanding tool for repairing gaps in the fiberglass such as the two large holes in my F-16s nose that were missing. Six Ounce fiberglass cloth, milled fiber, micro- balloons and thin CA glue are also required although not depicted in the photograph.

Typically, I purchase my fiberglass cloth, milled fiber and CA glues from my local hobby store whereas I purchase the Evercoat Metal Glaze, Dynatron Polyester Fiberglass Resin and the 3M Auto Body Repair Tape at my local automotive paint store.  In the past I have had problems with other polyester resins that I purchased from hobby stores. Those other resins sometimes didn’t fully cure and remained tacky forever.  I have used the Dynatron Polyester Resin many times and it always cures completely hard in only a couple of hours.  This may be a result of the freshness of the polyester resin. Nevertheless, I have had outstanding results with the Dynatron resin and so I have continued to use it.  The Auto Body Repair Tape is heavy gauge aluminum tape.  A roll of this repair tape is shown atop its red box in the photograph.  This tape is applied to the outside fiberglass surfaces being repaired prior to laying up the cloth and resin on the inside surfaces.  The tape forms a surface that is very close to the original surface’s contours such that when the cloth and resin are applied they then take on the original surface’s contour and shape.

Repair Procedure

All of the surfaces should be cleaned inside and out with denatured alcohol or paint thinner.  Then, sand the inside surfaces where the glass cloth and resin will be applied with 80 grit paper.  Trim all of the ragged edges on the fiberglass pieces with an exacto knife.  As you do this you should constantly be checking the two main pieces for a good fit. Remove all of the shredded fiberglass edges and you will eventually attain a near perfect fit.
Once you have a good fit, place the two pieces together and choose a couple of spots to start wicking thin CA into the repair joint. The first two spots that you choose should be on the most visible part of the plane and should provide stability so that the pieces will stay after you release your hand hold.  In the case of my F-16’s nose, my first two CA glue spots were on either side of the top of the nose.  When I was through, I let go of the nose and the two CA glue spots held it on without a problem. Make sure the you align the pieces up perfectly so the outer surfaces are even on each side of each crack.  The reason that you start on the most visible part of the repair is because any problems with your fit generally will manifest itself as you finish fitting and gluing the last few places. Once the first two spot joints are glued then continue wicking the CA into the repair joint around the entire crack all the while making sure that the pieces are held in perfect alignment.

After you have spot glued the broken pieces all the way around the cracks then place some milled fiber within the cracks and wick in some more thin CA.  This should result in a fairly stable repair joint.  Then, resand the area inside of the fuselage around the cracks in preparation for laying up the fiberglass cloth.

Place the Auto Body Repair Tape on the outside of the fuselage over any gaps or holes.  You may elect to cover the entire crack areas with the tape.  Smooth the tape out over any larger holes so that the tape has taken on the contour and shape of the fuselage.

Place 2” to 4” wide strips of fiberglass cloth on the inside of the fuselage covering all cracks.  If you have problems with the cloth laying down with the contour of the fuselage then spray the repair area with 3M adhesive spray (available at most craft stores)  prior to laying the cloth inside the fuselage.  The adhesive spray will cause the fiberglass cloth to lay down nicely.  Then, mix up some resin and apply resin to the cloth.  Use just enough resin to wet the cloth.  Do not over apply the resin.
 
One layer of cloth is usually adequate, however, when you have an entire portion of the fuselage to break off, as was the case with my F-16 nose, I generally add a second layer of 6 oz cloth and resin.  When using polyester resin, I usually wait about 45 minutes to an hour and the resin will be 90% cured but still tacky.  I then repeat the process of laying the fiberglass cloth and I add more fresh resin.  Since the first coat remains tacky, the second coat of resin will chemically bond with the first coat.  Otherwise, especially if you are using epoxy resin, you should wait overnight and sand the first cloth/resin application prior to the second cloth/resin application.  Again, use just enough resin to wet the cloth and do not over apply the resin.

The repaired area is now structurally sound and probably stronger than any other part of the fuselage. 

The top three photographs show the front of my F-16 after the nose was reattached and reinforced with the fiberglass cloth and polyester resin.  I had applied the Auto Body Repair Tape over all of the gaps and holes prior to glassing. The glass cloth and resin then conformed to the tape’s shape such that there was very little deviation from the original contours and fuselage shape where the gaps and holes had existed. In the end, only minor sanding and glazing putty was required to finish these areas.

The next step in the process is to fill the remaining cracks and gaps.  First, mix up a batch of polyester resin, microballoons and milled fiber.  I add micro- balloons and milled fiber until the resin slurry has the viscosity of toothpaste.  The more micoballoons that you add, the lighter the slurry becomes and the easier that it is to sand once it is cured.  I then go over all of the cracks, gaps and any other visible imperfections with the resin slurry. I try to dribble the slurry on very lightly. 

The photograph at the right shows the slurry after being applied to all of the cracks and gaps. 

Notice where the large hole in the fiberglass had been. The glass cloth and resin filled in the hole perfectly as a result of the Auto Body Repair Tape which caused the cloth/resin to take on the original fuselage contour and shape. Very little sanding or filler was needed around where the hole had been since the cloth/resin filled in so nicely.

Next, all of the resin slurry was sanded off.  Then, all of the cracks, gaps and hole areas were coated with Evercoat Metal Glaze and then sanded yet again. The Evercoat Metal Glaze should fill any remaining pin holes and may also be used to level any uneven surfaces.

Now, lets talk about sanding technique.  First, it is very important that you use a sanding block. For repairs like this I typically use a small  hardwood block about 2” X 1” in size.  Secondly, use high quality wet/dry sandpaper such as the 3M paper that’s available at automotive paint stores.  Most of my sanding for my F-16 repair was performed wet.  The water lubricates the sandpaper so that it is much more effective. I use 80 grit paper for sanding the resin slurry.  Then, I use 220 grit paper for sanding the Evercoat Metal Glaze.   You should be careful not to sand to heavily.  Light pressure is best and while it may take a bit longer the results will more than reward the extra time. 

Sanding Chart

Resin and/or Resin Slurry - 80 grit
Automotive Glazing Putty - 220 grit
Primer Coats - 320/400 grit
Paint Coats - 600 grit

The above three photographs show the F-16 repair after the Evercoat Metal Glaze had been applied and sanded off.  Look closely and you will see that the panel lines are also etched into the repair areas.  This is  accomplished with a Dremmel engraving tool and a ruler.  Line the area up that needs a panel line with the ruler and then lightly go over it several times with the engraving tool. 

The repaired areas are now ready for primer.  First spray on a fairly heavy initial primer coat that only covers the repair areas and then sand it off almost completely with 320 grit paper.  Then, spray a light final primer coat and sand with 400 grit paper.  You are now ready for painting.

The following photographs show the F-16 at the conclusion of the repair job after being repainted.

The above photo shows the repair on the inside of the fuselage.  This area of the fuse is now actually much stronger than before the accident.

The crash damage is now invisible.  It is impossible to detect any of the cracks, gaps or holes and the canopy hatch mounts on with a perfect fit.   Upon completing the repair I went out to the field and put two more flights on the repaired F-16. Several other club members were also out flying that day and no one could detect any remnants of the accident. 

This airplane is now in “as new” condition.

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