Building Blog
Sunday October 22, 2017

HEADLINING: Club meetings on the last Thursday each month (Except Nov & Dec) at 8 PM in the Monroe First Aid Squad Building, 47 Monmouth Rd, Monroe Township, NJ. Directions

BREAKING NEWS
TCRC Facebook group: Click the Facebook icon to the right for access 

Part 1 of 2 parts (Stay tuned for the addition of photos)

Overview

It has been a while since I had the opportunity to do a write up so in this article rather than describing a build process. I’ll try to explain how to repair damage if one of those unfortunate “oops” moments happens. The article will focus on wing repair since that’s the most likely part that will need fixing if the aircraft is salvageable. Therefore this article builds on a previous article on wing repair. “Wing Repair, Easy as 1 2 3” article was published in our newsletter and the AMA Insider.

  • http://www.modelaircraft.org/insider/13_01/Wing%20Patching.htm
  • Foam – to repair the core of the wing
  • Balsa Sticks – to repair the leading edge of the wing
  • Balsa sheeting – to re-sheet the wing and rebuild the wing tip
  • Epoxy – to glue foam core repair, sheeting, leading edge and wing tip
  • Micro balloon Filler – to create a filler compound with epoxy to ensure proper fastening of sheeting to the foam core
  • Balsa Filler – to fill in glue joints and imperfections before covering
  • Monokote – to re-cover the repair
  • #11 Exacto – for cutting balsa and monokote
  • Saw – for cutting balsa and rough shaping foam
  • Miter box – for cutting leading edge
  • Painter’s tape – for marking, holding, and cutting monokote
  • Sharpie and a pen – for marking stuff up
  • Popsicle sticks – mixing epoxy
  • Cardboard – to make epoxy mixing pads
  • Sanding bars – to create and cut straight edges, shape sand, and final sand the wing core and sheeting
  • Butter knife – to separate old sheeting from foam core
  • Rasp - for shaping foam
  • Ruler, T-Square, and Protractor to make sure everything was straight and true
  • An old credit card or hotel key card to spread the epoxy and filler
  • Acetone – to clean stuff up like sharpie marks on monokote and to degrease the existing covering
  • Covering iron – to iron on covering

“Easy as 1 2 3” talked about repairing tears in iron on covering. This article will describe how to perform a wing repair on a foam core wing. It will provide an overview of step by step instruction of how to approach a repair of a damaged wing.

The reason the article focuses on foam core wings is because I recently had the opportunity to repair one for a good friend at the club. He’s notorious for spot landing his foamies nose first, but this time he took out a corn stalk or two with a giant scale Extra 330S 40%.

Not to discredit my friend, he’s as great a pilot as I am a procrastinator. The repair took about a week. The week included research, getting the repair materials like foam, thinking out how to approach the repair, and actually doing the job. The thing I have to mention is that my inordinate skill at procrastination caused the repair to spread over six months. But with encouragement from my friend and the quickly approaching season we got the job done. Here’s what was used and how.

Planning

I can’t stress enough that proper planning will make the job a lot easier. In this case I had to research how foam core wings are constructed and the best way to repair them. This can be done in one evening using the best tool ever, “Google”.

After completing all the research, finding and obtaining proper repair materials was the key. In this case, this included balsa sticks, balsa sheeting, foam, glues, and other items. I will list all of the items and why they were needed in the tools and materials section.

Tools and Materials

The following tools and materials were needed:

peter d 01

CA Glues – to quickly tack balsa in place, I used thin CA where needed but had medium on hand

peter d 02

Pins - to pin down the sheeting (I had a pin tool on hand as well but it’s not needed)

The Repair

Following are the steps that made the repair job simple. You can sit down in one weekend and get the job done, but breaking it up into small steps makes it simpler, fun, and you have time to assess why you’re doing this in the first place - dumb thumbs or just being helpful. I didn’t make the mistake so for me it was the learning experience.

Step 1

Assess the damage. This may require some dissecting, but you really don’t know what needs to be fixed until you look. Having a good wing on hand, a tracing of the wing tip was made since the damage also required a repair to that. This helped in shaping the wing later.

Using a Sharpie I’ve marked out the damaged areas and what repair I would be performing. This also helps in planning what materials will be used to perform the repair. I like to mark things up that will be cut away and / or replaced as shown in Figure 3.

Step 2

 peter d 03

This is where the fun begins. You get to cut away the damage. The first step I took is to mark the existing covering using a right angle ruler. I would cut away the monokote to expose the balsa sheeting, as shown in Figure 4 below.

peter d 04

 

Cutting away the MonoKote covering exposed the wing balsa sheeting. This allows for assessment of where to start cutting and what. You can see that there was damaged sheeting under the monokote that wasn’t previously visible.

After the MonoKote was removed and damage was re-assessed, I made cuts to eliminate any damaged sheeting and expose the foam core. After the core was exposed I saw how much of the foam core was crushed and needed to be replaced and made the appropriate cuts. To expose the foam core and remove the existing balsa sheeting. I used a butter knife to separate the two. This allowed me to create clean cuts in the sheeting and the foam core as shown in Figure 5 above.

peter d 05

 

 

 

Step 3

After all of the damage was assessed and removed, we are finally ready to start the repair. The first step is to glue in the foam core. I decided to glue in a block of foam and then rough shape it.

Note that I left part of the original wing tip in place when cutting away the damage as shown in Figure 5, 6. This would allow me to ensure that the foam core repair is shaped correctly. Here are the steps I took to shape the core:

  1. Using a straight edge I traced a line for the leading edge and cut away the excess.
  2. From the undamaged wing the contour of the wing tip was traced onto paper.
  3. I cut away the damaged part of the wing tip and laid up the paper tracing onto it. Then sketched a line where the wing tip was cut.
  4. Using the tracing I cut out the shape in 1/16 balsa and cut that out. Then I cut the part where the sketched line is. This was then lined up with the remaining wing tip on the damaged wing and epoxied onto the foam.
  5. After the epoxy dried I used a saw to rough cut the shape of the wing in the block.
  6. Using a rasp and a straight edge I shaped the wing core to its final shape.
 

peter d 06

After the core was shaped the wing was ready for the leading edge repair and sheeting.

Step 4

The wing is ready for sheeting. To the repair I cut 4 inch wide 1/16 sheeting to the right sizes. The sheeting is staggered and overlaps from the unrepaired core to the repaired core. After having all the pieces for one side of the wing I moved on to the leading edge.

To repair the leading edge I cut a three pieces of ¼” x ½” balsa stock to the length of the leading edge repair. I glued two pieces together to create a ¼” x 1” piece. The center line of the joint would allow for good centering between the existing leading edge and wing tip.

peter d 07

 

Once I had the pieces cut and fit, I used 30 minute epoxy mixed with micro balloons as filler. This would fill in any area in the unrepaired core and core repair where the foam was not completely flush against the balsa sheeting. After preparing the mixture I used an old hotel key to spread it on top of the wing and the leading edge. After a nice thin even coating, I placed and centered the leading edge piece in place and pinned it. To ensure it did not move when I was laying down the sheeting, I used fast CA to glue on end to the original leading edge and the other end to the wing tip I made from the 1/16 balsa sheet. Figure 7 below shows the leading edge in place, pinned, and the sheeting secured to the wing’s foam core.

I repeated the process for cutting the sheeting and lining it up and repaired the opposite side of the wing after the epoxy has cured as shown in Figure 8 below.

peter d 08

 

To be continued and completed next month.