Member Article

This Is Not a Build Article – It Is a Rebuild Article

{Editor’s note – This article was submitted by Mark Barnett, D5, back in February of 2017. Enjoy!}

A few K Factor readers have been critical of some of us district VPs for writing about our latest building project in order to have subject matter to meet the monthly deadline. They want wonderful, insightful and interesting articles about pattern aerobatics. Well let me invite them to write a monthly article about pattern in the frozen north in the winter. Building is just about all there is going on right now around here, but this is not a build article. You recall in late May that my second Lightning with Spark wings went down hard at the bottom of a figure M maneuver due to an unexplained loss of power and control. I described this to you in my July K Factor article. I resolved to rebuild the Lightning with Spark wings. Following the crash, my first Lightning served out the pattern season with honor and is still flying today with about 1500 total flights. However, the Spark of Lightning flew way better with no roll coupling in knife edge - it had to be rebuilt.

After the crash, an autopsy of the wreckage showed the fuselage was splintered to the back of the canopy, but the rudder had only minor damage. The canopy was destroyed, but the latches were reusable and I had the fiberglass canopy mold I had used to make it with. One stab had minor damage to the leading edge and the other was intact. One wing had leading edge damage in 3 spots and the other wing had sheeting and root rib damage including loss of both wing bolts and the adjuster pin. The wing tube, ailerons the majority of both wings and wing tips were undamaged. Therefore, if I built a new fuselage and canopy, the rest could be repaired and the Spark of Lightning could rise like a phoenix from the rubble and fly again. It could probably be ready before our trip to Arizona in February if I got my butt moving. This

became my quest.

Competition balsa was purchased at Sig Manufacturing in Montezuma, Iowa where I was allowed to hand weigh each piece to get the lightest weight competition balsa. This is one advantage of living within 2 hours of a balsa supplier. Build tables were cleared of old unfinished projects. The fuselage jig and build board were located and set up. The first jig support piece was modified for the front mount Pletty Advanced motor. A short kit for the Lightning fuselage was ordered from Eureka Hobbies. Some parts were modified or completely rebuilt to make them stronger or slightly different shape from the original design. For example, the ears on former #2 were modified for the Pletty motor. Some formers were laminated with carbon fiber cloth or tissue to strengthen them. The landing gear plate was remade from Dragon board and extended to the next former to help prevent rotation. I also planned to use fiber glass tapes as a sling around these landing gear extensions to bind them to the fuselage sides. Many of

these modifications have been developed since building the first Lightning, 3 years ago. The fuselage sides were made from sheeting, ply doublers and stringers and added to the formers on the jig. Stringers were made and added to the top. Turtle deck was made from 3/32” balsa sheeting based on poster board templates. The sheeting was bent over tubes after wetting until it dried, cut to fit exactly and then glued in place using a syringe filled with wood glue and a blunt tipped needle. The sheeting was held in place with external stringers and 1” Coban elastic bandage around the outside at the formers. The original canopy was built up balsa planks over a frame which took about a month to complete. The new canopy was made in the fiber glass mold. 3 layers of glass cloth totaling about 8 ounces were used with 40 grams of epoxy resin. The canopy build took less than a week to build. The fin was rebuilt and added to the fuselage. The fillet was made with strips of 1/8” balsa and balsa putty and sanded to shape. The fuselage was removed from the jig (this is always a great day in airplane construction). The bottom stringers and turtle deck were added followed by 4 cooling air outlet holes from 3/8” rings of covering tube. Some sanding and shaping of the nose area was required. The pin holes

and dents were filled and smoothed out. Fiberglass was applied to each side with 40 grams of epoxy per side. The primer was brushed on as described in my last month’s article. Painting was done with one step polyurethane auto body paint that was mixed to match the covering on the wings. Painting is a skill I have not perfected, but I got it done including my trade mark shark mouth with Oramask 810S mask film and a lot of masking tape. The fuselage weight came in at 897 grams which is 90 grams less than the first lightning which had a final weight of 4676 grams. Not too shabby. The canopy is 20 grams less too. I was happy

with this.

The wing with root rib and sheeting damage was brought out. The sheeting was removed from a small area on the bottom. The top sheeting was intact. The first 1/3 of the root rib was destroyed. Honey comb holes in the foam were exposed making recovering with sheeting difficult. I remembered a trick that Robert Green told me that he learned from Joe Dunnaway. Insulation foam in a can be used to replace the missing foam. I went to Lowes and got some of this stuff. The foam insulation expands over 2 times the initial volume, so don’t use too much. Luckily the open cell foam sands easily after it hardens. This trick really worked well for me and I was able to sheet this area the next day. The root rib was repaired. Remember the wing bolts don’t hold all that much. They just keep the wing from slipping off the wing tube in rolls. The old rudder was repaired and replaced. 3D printed parts made by Mark Woytassek were used for the clevis connection to the pull-pull cables due to the increased set back of the control horn from the crash damage. Now all that is left to do is to put in the motor, ESC, receiver, rudder servo, and battery tray. Set the CG, program the throws and I’m back in business. By the way, I will be using a receiver with multiple satellite receivers as in my first Lightning. I am worried that the carbon fiber tissue in the wings may have shielded the receiver long enough to cause the crash. Can’t

prove it, but….